Abstract

Like other meiofaunal organisms, tardigrades suffer from a significant knowledge gap concerning many aspects of their biodiversity. The lack of an up-to-date digital collection with all species and details of limnoterrestrial and freshwater tardigrades in South and Central America is one of the most critical gaps to be filled. Therefore, the present work aims to develop a database containing all valid species of limnoterrestrial and freshwater tardigrades from South and Central America found until 2023 and provide open access to the results. Data for each species were obtained directly from the literature using Google Scholar and the website tardigrada.net. This compiled data resulted in the creation of a database with the species name, author and year of species description, genus, family, class, type country, type location, coordinates (longitude and latitude), if it is aquatic and/or limnoterrestrial, substrate where it was found, the country and location of collection, and manuscript containing the species identification. Furthermore, the coordinates of each occurrence were plotted on maps with political-administrative boundaries and Neotropical and Andean biogeographic regions. In addition, statistical analysis was performed related to the geographic distribution of the sampling effort. From the literature, 2157 records of valid non-marine Tardigrada species, endemic or not, were computed. From these records, 271 species of tardigrades have been identified in the two regions combined, with 223 species in South America and 129 species in Central America. We were able to show that there are still many biases in the sampling of tardigrades in the Neotropical and Andean regions and that further studies are needed on the biogeography of these meiofaunal organisms in these biogeographic regions. We expect this database to help better understand the richness and distribution patterns of limnoterrestrial and aquatic tardigrade species in Central and South America.

Keywords
meiofauna; tardigrades; biogeography; Neotropical; sampling effort

Resumo

Tardígrados, assim como outros organismos meiofaunais, possuem uma lacuna de conhecimento significativa acerca de muitos aspectos da sua biodiversidade. A inexistência de um acervo digital, e atualizado, com todas as espécies e detalhes de tardígrados limnoterrestres e aquáticos na América Central e Sul é uma das lacunas mais importantes a serem preenchidas. Dessa maneira, o presente trabalho tem como objetivo elaborar e disponibilizar, de maneira gratuita, um banco de dados contendo todas as espécies válidas de tardígrados limnoterrestres e aquáticos das América do Sul e América Central encontradas até 2023. Os dados de cada espécie foram obtidos diretamente na literatura, utilizando o Google Scholar e o site tardigrada.net. Com todos esses dados compilados, foi elaborado um banco de dados com nome da espécie, autor e ano de descrição da espécie, gênero, família, classe, país tipo, local tipo, coordenadas (longitude e latitude), se é aquático e/ou limnoterrestre, substrato onde foi encontrado, país coletado, local de coleta e manuscrito com a identificação da espécie. Ademais, as coordenadas obtidas de cada ocorrência foram plotadas em mapas das fronteiras político-administrativas e das regiões biogeográficas Neotropical e Andina. Além disso, uma análise estatística quanto à distribuição geográfica do esforço amostral foi feita. Da literatura, foram computados 2157 registros de espécies válidas de tardígrados limnoterrestre, endêmicas ou não. Desses registros, foram descobertas, até hoje, 271 espécies de tardígrados entre as duas regiões, com 223 espécies na América do Sul e 129 espécies na América Central. Foi possível demonstrar que ainda há muito viés na amostragem de tardígrados nas regiões Neotropical e Andina, e mais estudos acerca da biogeografia desses organismos meiofaunais nessas regiões biogeográficas são necessários. A partir desse banco de dados, espera-se contribuir para um maior entendimento da riqueza e dos padrões de distribuição de espécies de tardígrados limnoterrestres e aquáticos nas América Central e Sul.

Palavras-chave
meiofauna; tardígrados; biogeografia; Neotropical; esforço amostral

Introduction

Water bears are free-living, microscopic animals (about 50-1200 μm in size) that belong to the phylum Tardigrada and are divided into the classes Heterotardigrada and Eutardigrada (Nelson et al. 2020NELSON, D.R., GUIDETTI, R., REBECCHI, L., KACZMAREK, Ł. & MCINNES, S. 2020. Phylum Tardigrada. In Thorp and Covich’s Freshwater Invertebrates Elsevier, p.505–522.). They have segmented bodies with four pairs of legs and inhabit terrestrial, aquatic, and marine environments (Peluffo et al. 2007PELUFFO, J.R., ROCHA, A.M & MOLLY DE PELUFFO, M.C. 2007. Species diversity and morphometrics of tardigrades in a medium–sized city in the Neotropical region: santa Rosa (La Pampa, Argentina). Animal Biodiversity and Conservation 30(1)43-51. https://doi.org/10.32800/abc.2007.30.0043
https://doi.org/10.32800/abc.2007.30.004... , Vicente & Bertolani 2013VICENTE, F. & BERTOLANI, R. 2013. Considerations on the taxonomy of the phylum Tardigrada. Zootaxa 3626(2):245–248. https://doi.org/10.11646/zootaxa.3626.2.2
https://doi.org/10.11646/zootaxa.3626.2.... , Schill 2018, Bartels et al. 2020BARTELS, P.J., FONTANETO, D., ROSZKOWSKA, M., NELSON, D.R. & KACZMAREK, Ł. 2020. Latitudinal gradients in body size in marine tardigrades. Zoological Journal of the Linnean Society 188(3):820–838. https://doi.org/10.1093/zoolinnean/zlz080
https://doi.org/10.1093/zoolinnean/zlz08... , Nelson et al. 2020NELSON, D.R., GUIDETTI, R., REBECCHI, L., KACZMAREK, Ł. & MCINNES, S. 2020. Phylum Tardigrada. In Thorp and Covich’s Freshwater Invertebrates Elsevier, p.505–522.). Most tardigrade species are limnoterrestrial, inhabiting mosses, lichens, leaf litter, and soil; however, some are aquatic, living in sediments or roots of aquatic plants in inland waters or marine sediments from the intertidal zone to abyssal depths (Guil & Cabrero-Sañudo 2007GUIL, N. & CABRERO-SAÑUDO, F. 2007. Analysis of the species description process for a little known invertebrate group: The limnoterrestrial tardigrades (Bilateria, Tardigrada). Biodiversity and Conservation 16:1063-1086. https://doi.org/10.1007/s10531-006-9069-y
https://doi.org/10.1007/s10531-006-9069-... , Schill 2018, Bartels et al., 2020BARTELS, P.J., FONTANETO, D., ROSZKOWSKA, M., NELSON, D.R. & KACZMAREK, Ł. 2020. Latitudinal gradients in body size in marine tardigrades. Zoological Journal of the Linnean Society 188(3):820–838. https://doi.org/10.1093/zoolinnean/zlz080
https://doi.org/10.1093/zoolinnean/zlz08... , Nelson et al. 2020GARRAFFONI, A., SØRENSEN, M.V., WORSAAE, K., DI DOMENICO, M., SALES, L.P., SANTOS, J. & LOURENÇO, A. 2021. Geographical sampling bias on the assessment of endemism areas for marine meiobenthic fauna. Cladistics 37(5):571–585. https://doi.org/10.1111/cla.12453
https://doi.org/10.1111/cla.12453... ).

Like other meiofaunal organisms, tardigrades suffer from the “meiofauna paradox”. They are animals believed to have a cosmopolitan distribution but without dispersal capabilities (Giere, 2008GIERE, O. (2009) Meiobenthology. The Microscopic Motile Fauna of Aquatic Sediments. Springer, Berlin.). At the same time, the “Everything is everywhere, but environment selects’’ (EiE) hypothesis (Finlay et al. 1996FINLAY, B.J., ESTEBAN, G.F. & FENCHEL, T. 1996. Global diversity and body size. Nature 383(6596):132–133. https://doi.org/10.1038/383132a0
https://doi.org/10.1038/383132a0... , Fenchel et al. 1997FENCHEL, T., ESTEBAN, G.F. & FINLAY, B.J. 1997. Local versus global diversity of microorganisms: cryptic diversity of ciliated Protozoa. Oikos 80(2):220–225. https://doi.org/10.2307/3546589
https://doi.org/10.2307/3546589... , Fenchel & Finlay 2004FENCHEL, T. & FINLAY, B.J. 2004. The ubiquity of small species: patterns of local and global diversity. BioScience 54(8):777–784. https://doi.org/10.1641/0006-3568(2004)054[0777:TUOSSP]2.0.CO;2
https://doi.org/10.1641/0006-3568(2004)0... ) was widely accepted for small metazoans, implying the absence of any discernible biogeographic pattern (Cerca et al. 2018CERCA, J., PURSCHKE, G. & STRUCK, T.H. 2018. Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox. Marine Biology 165(8):123. https://doi.org/10.1007/s00227-018-3383-2
https://doi.org/10.1007/s00227-018-3383-... , Morek et al. 2021MOREK, W., SURMACZ, B., LÓPEZ-LÓPEZ, A. & MICHALCZYK, Ł. 2021. “Everything is not everywhere”: time-calibrated phylogeography of the genus Milnesium (Tardigrada). Molecular Ecology 30(14):3590–3609. https://doi.org/10.1111/mec.15951
https://doi.org/10.1111/mec.15951... ). Most available data on tardigrade species distribution has barely any records which were identified utilizing an integrative taxonomic approach; this hinders the delimitation of species and the understanding of their distribution patterns (Morek et al. 2019MOREK, W., STEC, D., GĄSIOREK, P., SURMACZ, B. & MICHALCZYK, Ł. 2019. Milnesium tardigradum Doyère, 1840: the first integrative study of interpopulation variability in a tardigrade species. Journal of Zoological Systematics and Evolutionary Research 57(1):1–23. https://doi.org/10.1111/jzs.12233
https://doi.org/10.1111/jzs.12233... , Gąsiorek et al. 2019aGĄSIOREK, P., JACKSON, K.J., MEYER, H.A., ZAJĄC, K., NELSON, D.R., KRISTENSEN, R.M. & MICHALCZYK, Ł. 2019a. Echiniscus virginicus complex: the first case of pseudocryptic allopatry and pantropical distribution in tardigrades. Biological Journal of the Linnean Society 128(4):789–805. https://doi.org/10.1093/biolinnean/blz147
https://doi.org/10.1093/biolinnean/blz14... ). Thus, it is essential to utilize both molecular and observational data to better comprehend tardigrade species distribution patterns (Gąsiorek et al. 2019aGĄSIOREK, P., JACKSON, K.J., MEYER, H.A., ZAJĄC, K., NELSON, D.R., KRISTENSEN, R.M. & MICHALCZYK, Ł. 2019a. Echiniscus virginicus complex: the first case of pseudocryptic allopatry and pantropical distribution in tardigrades. Biological Journal of the Linnean Society 128(4):789–805. https://doi.org/10.1093/biolinnean/blz147
https://doi.org/10.1093/biolinnean/blz14... ).

The presence of a geographic sampling bias and the fact that only a few species have been studied make it difficult to understand the limits of dispersal and, consequently, the distribution patterns and richness of tardigrades, especially in the Southern Hemisphere (Bini et al. 2006BINI, L.M., DINIZ-FILHO, J.A.F., RANGEL, T.F.L.V.B., BASTOS, R.P. & PINTO, M.P. 2006. Challenging Wallacean and Linnean shortfalls: knowledge gradients and conservation planning in a biodiversity hotspot. Diversity and Distributions 12(5):475–482. https://doi.org/10.1111/j.1366-9516.2006.00286.x
https://doi.org/10.1111/j.1366-9516.2006... , Guil et al. 2009GUIL, N., SÁNCHEZ‐MORENO, S. & MACHORDOM, A. 2009. Local biodiversity patterns in micrometazoans: are tardigrades everywhere? Systematics and Biodiversity 7(3):259–268. https://doi.org/10.1017/S1477200009003016
https://doi.org/10.1017/S147720000900301... , Yang et al. 2013YANG, W., MA, K. & KREFT, H. 2013. Geographical sampling bias in a large distributional database and its effects on species richness-environment models. Journal of Biogeography 40(8):1415–1426. https://doi.org/10.1111/jbi.12108
https://doi.org/10.1111/jbi.12108... , Cerca et al. 2018CERCA, J., PURSCHKE, G. & STRUCK, T.H. 2018. Marine connectivity dynamics: clarifying cosmopolitan distributions of marine interstitial invertebrates and the meiofauna paradox. Marine Biology 165(8):123. https://doi.org/10.1007/s00227-018-3383-2
https://doi.org/10.1007/s00227-018-3383-... , Azovsky et al. 2020AZOVSKY, A.I., CHERTOPRUD, E.S., GARLITSKA, L.A., MAZEI, Y.A. & TIKHONENKOV, D.V. 2020. Does size really matter in iogeography? Patterns and drivers of global distribution of marine micro- and meiofauna. Journal of Biogeography 47(5):1180–1192. https://doi.org/10.1111/jbi.13771
https://doi.org/10.1111/jbi.13771... , Garraffoni et al. 2021GARRAFFONI, A., SØRENSEN, M.V., WORSAAE, K., DI DOMENICO, M., SALES, L.P., SANTOS, J. & LOURENÇO, A. 2021. Geographical sampling bias on the assessment of endemism areas for marine meiobenthic fauna. Cladistics 37(5):571–585. https://doi.org/10.1111/cla.12453
https://doi.org/10.1111/cla.12453... ). In the Neotropical region, the number of recorded limnoterrestrial tardigrade species is much lower compared to other regions, mainly due to the scarce number of specialized researchers, which in turn reduces the number of studies conducted there (Guil & Cabrero Sañudo 2007GUIL, N. & CABRERO-SAÑUDO, F. 2007. Analysis of the species description process for a little known invertebrate group: The limnoterrestrial tardigrades (Bilateria, Tardigrada). Biodiversity and Conservation 16:1063-1086. https://doi.org/10.1007/s10531-006-9069-y
https://doi.org/10.1007/s10531-006-9069-... , Fontaneto et al. 2012FONTANETO, D., BARBOSA, A.M., SEGERS, H. & PAUTASSO, M. 2012. The ‘rotiferologist’ effect and other global correlates of species richness in monogonont rotifers. Ecography 35(2):174–182. https://doi.org/10.1111/j.1600-0587.2011.06850.x
https://doi.org/10.1111/j.1600-0587.2011... , Nelson et al. 2020NELSON, D.R., GUIDETTI, R., REBECCHI, L., KACZMAREK, Ł. & MCINNES, S. 2020. Phylum Tardigrada. In Thorp and Covich’s Freshwater Invertebrates Elsevier, p.505–522., Garraffoni et al. 2021GARRAFFONI, A., SØRENSEN, M.V., WORSAAE, K., DI DOMENICO, M., SALES, L.P., SANTOS, J. & LOURENÇO, A. 2021. Geographical sampling bias on the assessment of endemism areas for marine meiobenthic fauna. Cladistics 37(5):571–585. https://doi.org/10.1111/cla.12453
https://doi.org/10.1111/cla.12453... ).

Kaczmarek et al. (2014KACZMAREK, Ł., MICHALCZYK, Ł. & MCINNES, S.J. 2014. Annotated zoogeography of non-marine Tardigrada. Part I: Central America. Zootaxa 3763(1):1-62. https://doi.org/10.11646/zootaxa.3763.1.1
https://doi.org/10.11646/zootaxa.3763.1.... , 2015KACZMAREK, Ł., MICHALCZYK, Ł. & MCINNES, S.J. 2015. Annotated zoogeography of non-marine Tardigrada. Part II: South America. Zootaxa 3923(1):1-107. https://doi.org/10.11646/zootaxa.3923.1.1
https://doi.org/10.11646/zootaxa.3923.1.... ) compiled the records of non-marine tardigrades in Central and South America up to the respective years of their publication. However, updating the data, and facilitating access and use is necessary. Therefore, this study presents a georeferenced database created through an extensive literature search of all limnoterrestrial and freshwater tardigrades in Central and South America, along with statistical analyses and maps to represent their distribution graphically. This digital and updated collection of the occurrence data of limnoterrestrial and freshwater tardigrades in Central and South America will undoubtedly benefit future biology studies or large-scale analyses and interpretations of biodiversity and distribution data of tardigrades in the Neotropics.

Material and Methods

Distribution data for limnoterrestrial and freshwater tardigrades was mainly obtained from Kaczmarek et al. (2014)KACZMAREK, Ł., MICHALCZYK, Ł. & MCINNES, S.J. 2014. Annotated zoogeography of non-marine Tardigrada. Part I: Central America. Zootaxa 3763(1):1-62. https://doi.org/10.11646/zootaxa.3763.1.1
https://doi.org/10.11646/zootaxa.3763.1.... , who listed all non-marine tardigrades from Central America, and Kaczmarek et al. (2015)KACZMAREK, Ł., MICHALCZYK, Ł. & MCINNES, S.J. 2015. Annotated zoogeography of non-marine Tardigrada. Part II: South America. Zootaxa 3923(1):1-107. https://doi.org/10.11646/zootaxa.3923.1.1
https://doi.org/10.11646/zootaxa.3923.1.... from South America. In addition, a literature search was conducted from 2014 to 2023 using Google Scholar and the “Recent papers’’ section of tardigrada.net. A set of terms was used to try to locate all possible publications that had limnoterrestrial tardigrade species as the central topic: “south american limnoterrestrial tardigrade OR central american limnoterrestrial tardigrade OR new south american tardigrade species OR new central american tardigrade species OR limnoterrestrial tardigrade south america OR limnoterrestrial tardigrade central america OR new species limnoterrestrial tardigrade south america OR new species limnoterrestrial tardigrade central america’’.

For our final dataset, we removed all records from species that present any kind of taxonomical problem (e.g. unknown type material, dubious name, dubious species and/or descriptions with insufficient morphological data) cited in Kaczmarek et al. (2014KACZMAREK, Ł., MICHALCZYK, Ł. & MCINNES, S.J. 2014. Annotated zoogeography of non-marine Tardigrada. Part I: Central America. Zootaxa 3763(1):1-62. https://doi.org/10.11646/zootaxa.3763.1.1
https://doi.org/10.11646/zootaxa.3763.1.... , 2015KACZMAREK, Ł., MICHALCZYK, Ł. & MCINNES, S.J. 2015. Annotated zoogeography of non-marine Tardigrada. Part II: South America. Zootaxa 3923(1):1-107. https://doi.org/10.11646/zootaxa.3923.1.1
https://doi.org/10.11646/zootaxa.3923.1.... ) or in the most updated checklist of Tardigrada species organized by Degma & Guidetti (2023)DEGMA, P. & GUIDETTI, R. 2023. Actual checklist of Tardigrada species. DOI: https://doi.org/10.25431/11380_1178608 (Accessed date 29/04/2023).
https://doi.org/10.25431/11380_1178608... (Table S2). Species records that contained names with c.f. were also not used. Furthermore, we grouped the species sampled in both regions into endemic (i.e. locus typicus is in Central or South Americas) and traditionally treated as allegedly cosmopolitan (i.e. locus typicus is outside of Central and South America; usually records of those species are scattered across the globe and unreliable in the light of modern tardigrade systematics) since many recent studies showed that records of species are prone to contain misidentifications (e.g. Michalczyk et al. 2012MICHALCZYK, Ł., WEŁNICZ, W., FROHME, M., & KACZMAREK, Ł. 2012. Redescriptions of three Milnesium Doyère, 1840 taxa (Tardigrada: Eutardigrada: Milnesiidae), including the nominal species for the genus. Zootaxa 3154(1):1–20. https://doi.org/10.11646/zootaxa.3154.1.1
https://doi.org/10.11646/zootaxa.3154.1.... , Morek et al. 2019MOREK, W., STEC, D., GĄSIOREK, P., SURMACZ, B. & MICHALCZYK, Ł. 2019. Milnesium tardigradum Doyère, 1840: the first integrative study of interpopulation variability in a tardigrade species. Journal of Zoological Systematics and Evolutionary Research 57(1):1–23. https://doi.org/10.1111/jzs.12233
https://doi.org/10.1111/jzs.12233... , Morek et al. 2021MOREK, W., SURMACZ, B., LÓPEZ-LÓPEZ, A. & MICHALCZYK, Ł. 2021. “Everything is not everywhere”: time-calibrated phylogeography of the genus Milnesium (Tardigrada). Molecular Ecology 30(14):3590–3609. https://doi.org/10.1111/mec.15951
https://doi.org/10.1111/mec.15951... ).

To visualize the reported locations of all species, we plotted geographic coordinates on two maps, one shows reported localities from both sections, and the other contains the number of records in each area. Maps were elaborated for both geopolitical boundaries and biogeographic regions in Central and South America. For the latter maps, we used the Andean and Neotropical provinces proposed by Morrone (2015a)MORRONE, J.J. 2015a. Biogeographical regionalisation of the Andean region. Zootaxa 3936(2):207–236. https://doi.org/10.11646/zootaxa.3936.2.3
https://doi.org/10.11646/zootaxa.3936.2.... and Morrone et al. (2022)MORRONE, J.J., ESCALANTE, T., RODRÍGUEZ-TAPIA, G., CARMONA, A., ARANA, M. & MERCADO-GÓMEZ, J.D. 2022. Biogeographic regionalization of the Neotropical region: new map and shapefile. Anais da Academia Brasileira de Ciência. 94(1):e20211167. https://doi.org/10.1590/0001-3765202220211167
https://doi.org/10.1590/0001-37652022202... , respectively. The data on the biogeographic regions map had to be adjusted (removal of 27 records and four species) because northern Mexico is not fully represented in the Neotropical region. In addition, an interactive and free-to-use online map was created, where each point represents a sampling site of a single species. For this map, sampling sites were flagged in three ways: putatively cosmopolitan, endemic or taxonomic problems. Additionally, we created charts of observed species richness from published articles for countries and biogeographic provinces to illustrate the relationship between observed species richness and sampling effort.

We merged shapefiles from the Andean and Neotropical biogeographic regions produced by Löwenberg-Neto (2015)LÖWENBERG-NETO, P. 2015. Andean region: a shapefile of Morrone’s (2015) biogeographical regionalization. Zootaxa 3985(4):600. https://doi.org/10.11646/zootaxa.3985.4.9
https://doi.org/10.11646/zootaxa.3985.4.... and Morrone et al. (2022)MORRONE, J.J., ESCALANTE, T., RODRÍGUEZ-TAPIA, G., CARMONA, A., ARANA, M. & MERCADO-GÓMEZ, J.D. 2022. Biogeographic regionalization of the Neotropical region: new map and shapefile. Anais da Academia Brasileira de Ciência. 94(1):e20211167. https://doi.org/10.1590/0001-3765202220211167
https://doi.org/10.1590/0001-37652022202... . This procedure yields duplicate provinces that overlap (transition zone). The Neotropical South American transition zone (Atacama, Comechigones, Cuyan High Andean, Desert, Monte, Paramo and Puna provinces) was kept to solve this, while the same Andean unit was removed (Atacama, Desert, Monte, Paramo, Prepuna, and Puna provinces).

For the elaboration of the maps and charts in this article, we used R v4.3.0 (R Core Team 2023R CORE TEAM (2023). R: a language and environment for statistical computing. R Foundation for Statistical Computing, Vienna, Austria. https://www.R-project.org/. (Accessed date 25/05/2023).SCHILL, R.O. 2018. Water bears: The biology of tardigrades. Springer International Publishing, Cham.
https://www.R-project.org/... ), Rstudio v2023.3.1.446 (Posit Team 2023POSIT TEAM (2023). RStudio: integrated development environment for R. Posit Software, PBC, Boston, MA.URL http://www.posit.co/. (Accessed date 25/05/2023).
http://www.posit.co/... ), and the packages ggpubr v0.6.0 (Kassambara 2023KASSAMBARA A. 2023. ggpubr: ‘ggplot2’ based publication ready plots. R package version 0.6.0, https://rpkgs.datanovia.com/ggpubr/. (Accessed date 25/05/2023).
https://rpkgs.datanovia.com/ggpubr/... ), tmap v3.3-3 (Tennekes 2018TENNEKES, M. 2018. tmap: thematic maps in R. Journal of Statistical Software 84(6):1–39. https://doi.org/10.18637/jss.v084.i06
https://doi.org/10.18637/jss.v084.i06... ), sf v1.0-13 (Pebesma 2018PEBESMA, E. 2018. Simple features for R: standardized support for spatial vector data. The R Journal 10(1):439.), rnaturalearth v0.3.2.9000 (South 2017SOUTH A. 2017. rnaturalearth: World map data from Natural Earth. R package version 0.1.0, https://CRAN.R-project.org/package=rnaturalearth (Accessed date 10/02/2023).
https://CRAN.R-project.org/package=rnatu... ), rnaturalearthdata v0.2.1 (South 2022SOUTH A. 2022. rnaturalearthdata: World vector map data from Natural Earth used in ‘rnaturalearth. https://docs.ropensci.org/rnaturalearthdata, https://github.com/ropensci/rnaturalearthdata (Accessed date 10/02/2023).
https://docs.ropensci.org/rnaturalearthd... ), and tidyverse v1.3.0 (Wickham et al. 2019WICKHAM, H., AVERICK M, BRYAN J, CHANG W, MCGOWAN LD, FRANÇOIS R, GROLEMUND G, HAYES A, HENRY L, HESTER J, KUHN M, PEDERSEN TL, MILLER E, BACHE SM, MÜLLER K, OOMS J, ROBINSON D, SEIDEL DP, SPINU V, TAKAHASHI K, VAUGHAN D, WILKE C, WOO K, YUTANI H. 2019. Welcome to the tidyverse. Journal of Open Source Software 4(43):1686. https://doi.org/10.21105/joss.01686
https://doi.org/10.21105/joss.01686... ). We also used ArcGIS online (2023)ARCGIS ONLINE. 2023. http://www.arcgis.com. Accessed 27 February 2023.
http://www.arcgis.com... for the interactive map.

Results

Between 2014 to 2023, we found nine published papers regarding descriptions of new species and new records in Central America, while in South America, there were 27 (Table S1).

With all this data compiled, the database is a comma-separated value (.csv) file consisting of a single table with 19 columns:

• – Species: taxon of the collected species;

• – Author and year of species’ description: name(s) of the author(s) and year of species description;

• – Genus: taxon of the species’ genus;

• – Family: taxon of the species’ family;

• – Class: taxon of the species’ class;

• – Type country: country of the collected specimen that gave the species its name;

• – Type location: geographic location of the collected specimen that gave the species its name;

• – Longitude (Lon): longitude of the species’ occurrence;

• – Latitude (Lat): latitude of the species’ occurrence;

• – Aquatic or limnoterrestrial: defines whether the species is limnoterrestrial or aquatic;

• – Substrate where it was found: divided into six columns, there are three primary substrates (moss, lichen, and others) with a column for each, followed by another column describing the location of the collected substrate;

• – Country of collection: the country where the occurrence of the species was documented;

• – Place of collection: geographic location where the occurrence of the species was documented;

• – Manuscript containing the species’ identification: work in the literature that recorded the occurrence of the species.

Valid species records of non-marine Tardigrada from South and Central America, endemic or not, totalized 271 species, of which 129 were found in Central America (33 endemic) and 223 in South America (110 endemic), amounting to 2157 sampling sites (Figure 1A). A total of 141 endemic species corresponded with 732 sites (Figure 1C), while 130 were “cosmopolitan” ones that were recorded at 1425 sites (Figure 1E). The occurrence of substantial sampling effort for endemic species was noticed in Costa Rica (212 records), Argentina (176 records), and Colombia (77 records) (Figure 1D). “Cosmopolitan” species were amply registered in Argentina (353 records), Costa Rica (341 records) and Chile (161 records) (Figure 1F). The highest observed endemic richness was recorded in Argentina (51 species), Mexico (25 species), and Costa Rica (23 species), and the highest number of “cosmopolitan” species was also recorded in these same countries (66 spp., 39 spp. and 35 spp., respectively). Belize, El Salvador, Guatemala, Guyana, Haiti, Honduras, Jamaica and Panama had no registers for limnoterrestrial and freshwater tardigrades (Figure 1B). The most abundant “cosmopolitan” species were Macrobiotus hufelandi, Milnesium tardigradum, and Paramacrobiotus ritchersi, with 196, 150, and 84 sampling sites, respectively, while Barbaria bigranulata, Mesobiotus coronatus and Minibiotus continuus, with 79, 63 and 62, respectively, were the most frequent endemic ones. Species observed only at their type locality amounted to 66.

Figure 1.
A Central and South America map showing the recorded sampling sites (red circles) of limnoterrestrial and freshwater valid tardigrades‘ species. B Documented localities of limnoterrestrial and freshwater valid tardigrades‘ species in each Central and South American country. C Central and South America map showing the recorded sampling sites (red circles) of limnoterrestrial and freshwater valid endemic tardigrades‘ species. D Documented localities of limnoterrestrial and freshwater valid endemic tardigrades‘ species in each Central and South American country. E Central and South America map showing the recorded sampling sites (red circles) of limnoterrestrial and freshwater valid “cosmopolitan” tardigrades‘ species. F Documented localities of limnoterrestrial and freshwater valid “cosmopolitan” tardigrades‘ species in each Central and South American country.

Valid species records of non-marine Tardigrada from Andean and Neotropical biogeographic regions, endemic or not, totalized 267 species, of which 186 were found in the Neotropical region (96 endemic and 90 “cosmopolitan”), 105 in the Andean region (43 endemic and 62 “cosmopolitan”) and 90 in the Transition Zone (36 endemic and 54 “cosmopolitan”), amounting to 2130 sampling sites (Figure 2A). A total of 139 endemic species corresponded with 715 sites (Figure 2C), while 128 “cosmopolitan” ones were recorded at 1415 sites (Figure 2E). The occurrence of substantial sampling effort for endemic species was noticed in the Guatuso-Talamanca province (112 records), the Puntarenas-Chiriqui province (100 records), and the Guajira province (61 records) (Figure 2D). “cosmopolitan” species were amply registered in the Puntarenas-Chiriqui province (167), the Guatuso-Talamanca province (155) and the Valdivian Forest province (141) (Figure 2F). The highest observed endemic richness was recorded in the Guajira province (21 species), the Valdivian Forest province (19 species), the Puntarenas-Chiriqui, Guatuso-Talamanca and Magellanic Forest provinces (all three with 18 species), and the highest number of “cosmopolitan” species was recorded in the Valdivian Forest province (40 species), the Magellanic Forest (35 species), Atlantic and Puna provinces (both with 30 species). Bahama, Chapada Diamantina, Choco Darien, Comechigones, Ecuadorian, Falkland Islands, Guianan, Imeri, Jamaica, Juan Fernandez, Pará, Roraima, Southern Espinhaço, Trinidad, and Ucayali had no registers for limnoterrestrial and freshwater tardigrades (Figure 2B). Provinces such as Guatuso-Talamanca, Puntarenas-Chiqui, Valdivian Forest, Magellanic Forest, Pampean, and Puna have more sampling sites than all the other 60 provinces. This discrepancy results from the fact that five of these six provinces overlap with countries where most tardigrades were sampled. The most abundant “cosmopolitan” and endemic species in the biogeographical regions were the same as seen for Central and South America.

Figure 2.
A Neotropical and Andean biogeographic regions‘ map with the recorded sampling sites (red circles) of limnoterrestrial and freshwater valid tardigrades‘ species. B Documented localities of limnoterrestrial and freshwater valid tardigrades‘ species in each biogeographic province of the Andes and Neotropical regions. C Neotropical and Andean biogeographic regions‘ map with the recorded sampling sites (red circles) of limnoterrestrial and freshwater valid endemic tardigrades‘ species. D Documented localities of limnoterrestrial and freshwater valid endemic tardigrades‘ species in each biogeographic province of the Andes and Neotropical regions. E Neotropical and Andean biogeographic regions‘ map with the recorded sampling sites (red circles) of limnoterrestrial and freshwater valid “cosmopolitan” tardigrades‘ species. F Documented localities of limnoterrestrial and freshwater valid “cosmopolitan” tardigrades‘ species in each biogeographic province of the Andes and Neotropical regions.

Figure 3 shows screenshots from the ArcGis online platform of Limnoterrestrial and Freshwater Tardigrada of Central and South America. Four views are depicted here: A map view showing all sampling sites included in our dataset, B map view showing selected valid endemic species records (blue triangles), C map view showing selected valid “cosmopolitan” species records (orange squares), D map view showing selected invalid species records due to taxonomical problems (green circles). Each occurrence on the map can be clicked, after which a window with information about the record appears (Fig. 3D). The map can be accessed at https://arcg.is/1jjO84.

Figure 3.
A All available sampling sites. B Selected record of Barbaria bigranulata Ritchers, 1907 (valid endemic species). C Selected records of Macrobiotus hufelandi C.A.S. Schultze, 1834 (valid “cosmopolitan” species). D Selected records of Diaforobiotus islandicus nicaraguensis Seméria, 1985 (taxonomically invalid) and associated information is shown when a record is clicked on.

When analyzing the influence of sampling bias on tardigrade records, we see a positive correlation (R = 0.78 and p < 0.0001 for countries and R = 0.77 and p < 0.0001 for biogeographic provinces) between sampling effort and higher observed species richness (Figure 4). Since Argentina is an outlier compared to all other countries and stands out (Figure 4A), it could affect the correlation between variables (Goodwin & Leech 2006GOODWIN, L.D. & LEECH, N.L. 2006. Understanding correlation: factors that affect the size of r. The Journal of Experimental Education 74(3):249–266. https://doi.org/10.3200/JEXE.74.3.249-266
https://doi.org/10.3200/JEXE.74.3.249-26... ). The model was run without Argentina, and the positive correlation was not only maintained, but we obtained a higher value with an even smaller p-value (Figure S1), confirming a consistent pattern in sampling bias.

Figure 4.
A Correlation between the number of published articles and known valid species richness for each country. Orange squares represent Central American countries, while purple diamonds represent South American ones. There are overlapping data represented in the chart. Countries with zero published papers (Belize, El Salvador, Guatemala, Guyana, Haiti, Honduras and Panama) were excluded. Kendall Rank‘s Rvalue correlation and p-value are shown in the upper left corner. B Correlation between the number of published papers and known valid species richness for each biogeographic province. Pink triangles represent Neotropical biogeographic provinces, while blue circles represent Andean and green squares Transition zone provinces. There are overlapping data in the chart. Provinces with zero published papers (Bahama, Chapada Diamantina, Choco Darien, Comechigones, Ecuadorian, Falkland Islands, Guianan, Imeri, Jamaica, Juan Fernandez, Pará, Roraima, Southern Espinhaço, Trinidad, and Ucayali provinces) were excluded. Kendall Rank‘s R correlation and p-value are shown in the upper left corner.

Discussion

In this study, we demonstrate that general taxonomic literature (e.g., descriptions of new species, checklists, or faunal lists) can be used to create databases that summarize knowledge about species distributions, despite biases caused by predominant taxonomic approaches in each historical period or by the singular view of each researcher (Lewis 1990LEWIS, J.E. 1990. Evaluating taxonomic databases for biogeographic use. Bulletin of Marine Science 47(1):115–123.). These databases contain highly curated registers that are an essential source of information to gain insights into species distributions and diversity patterns (Griffiths et al. 2003GRIFFITHS, H.J., LINSE, K. & CRAME, J.A. 2003. SOMBASE – Southern Ocean Mollusc Database: a tool for biogeographic analysis in diversity and ecology. Organisms Diversity & Evolution 3(3):207–213. https://doi.org/10.1078/1439-6092-00079
https://doi.org/10.1078/1439-6092-00079... , Guénard et al. 2017GUÉNARD, B., WEISER, M., GÓMEZ, K., NARULA, N. & ECONOMO, E. 2017. The Global Ant Biodiversity Informatics (GABI) database: synthesizing data on the geographic distribution of ant species (Hymenoptera: Formicidae). Myrmecological News 24:83–89. http://id.nii.ac.jp/1394/00000179/
http://id.nii.ac.jp/1394/00000179/... ). Decades or centuries of taxonomic information can be summarized in just one file or website, and records of species occurrences can become publicly available to the scientific community at no cost (Zizka et al. 2019ZIZKA, A., SILVESTRO, D., ANDERMANN, T., AZEVEDO, J., DUARTE RITTER, C., EDLER, D., FAROOQ, H., HERDEAN, A., ARIZA, M., SCHARN, R., SVANTESSON, S., WENGSTRÖM, N., ZIZKA, V. & ANTONELLI, A. 2019. CoordinateCleaner: standardized cleaning of occurrence records from biological collection databases. Methods in Ecology and Evolution 10(5):744–751.https://doi.org/10.1111/2041-210X.13152
https://doi.org/10.1111/2041-210X.13152... ). Furthermore, according to Griffiths et al. (2003)GRIFFITHS, H.J., LINSE, K. & CRAME, J.A. 2003. SOMBASE – Southern Ocean Mollusc Database: a tool for biogeographic analysis in diversity and ecology. Organisms Diversity & Evolution 3(3):207–213. https://doi.org/10.1078/1439-6092-00079
https://doi.org/10.1078/1439-6092-00079... , “...when relational databases are linked to a Geographical Information System (GIS), they become an even more powerful tool for taking on large-scale biogeographical patterns”.

Critical evaluation of the historical and contemporary tardigrade records is of utmost importance to understand this taxon’s phylogenetic diversity and distribution patterns around the globe (Morek et al. 2019MOREK, W., STEC, D., GĄSIOREK, P., SURMACZ, B. & MICHALCZYK, Ł. 2019. Milnesium tardigradum Doyère, 1840: the first integrative study of interpopulation variability in a tardigrade species. Journal of Zoological Systematics and Evolutionary Research 57(1):1–23. https://doi.org/10.1111/jzs.12233
https://doi.org/10.1111/jzs.12233... ). Most of the records in our dataset (1425 out of 2157) are from so-called “cosmopolitan” species and date to a period (early and middle 20^th century) when the widespread distribution of many tardigrades was broadly accepted. One emblematic case regarding this thought is Milnesium tardigradum Doyerè, 1840, which was considered ubiquitous for decades (Morek et al. 2021MOREK, W., SURMACZ, B., LÓPEZ-LÓPEZ, A. & MICHALCZYK, Ł. 2021. “Everything is not everywhere”: time-calibrated phylogeography of the genus Milnesium (Tardigrada). Molecular Ecology 30(14):3590–3609. https://doi.org/10.1111/mec.15951
https://doi.org/10.1111/mec.15951... ). In our study it was the second species with the highest number of records among all 271 species and was found in 15 countries in both regions. This view changed only recently when Michalczyk et al. (2012)MICHALCZYK, Ł., WEŁNICZ, W., FROHME, M., & KACZMAREK, Ł. 2012. Redescriptions of three Milnesium Doyère, 1840 taxa (Tardigrada: Eutardigrada: Milnesiidae), including the nominal species for the genus. Zootaxa 3154(1):1–20. https://doi.org/10.11646/zootaxa.3154.1.1
https://doi.org/10.11646/zootaxa.3154.1.... and Morek et al. (2019)MOREK, W., STEC, D., GĄSIOREK, P., SURMACZ, B. & MICHALCZYK, Ł. 2019. Milnesium tardigradum Doyère, 1840: the first integrative study of interpopulation variability in a tardigrade species. Journal of Zoological Systematics and Evolutionary Research 57(1):1–23. https://doi.org/10.1111/jzs.12233
https://doi.org/10.1111/jzs.12233... applied an integrative approach to redescribe and better understand the intraspecific variability in M. tardigradum and when Tumanov et al. (2022)TUMANOV, D.V., ANDROSOVA, E.D., AVDEEVA, G.S. & LEONTEV, A.A. 2022. First faunistic investigation of semiterrestrial tardigrade fauna of North-West Russia using the method of DNA barcoding. Invertzool 19(4):452–474. https://doi.org/10.15298/invertzool.19.4.08
https://doi.org/10.15298/invertzool.19.4... found that the distribution of this species is restricted to the Paleartic region. Together with M. tardigradum, many other widespread species (e.g., Macrobiotus hufelandi, Paramacrobiotus ritchersi, Minibiotus intermedius, Pseudechiniscus (Pseudechiniscus) suillus) were described in the late 19^th or early 20^th centuries, which means that taxonomic problems may arise due to incomplete descriptions, lack of type series deposited in zoological Museums and/or the non-use of modern techniques for morphological analyses. Thus, most species identification and records should be considered dubious or invalid (Michalczyk et al. 2012MICHALCZYK, Ł., WEŁNICZ, W., FROHME, M., & KACZMAREK, Ł. 2012. Redescriptions of three Milnesium Doyère, 1840 taxa (Tardigrada: Eutardigrada: Milnesiidae), including the nominal species for the genus. Zootaxa 3154(1):1–20. https://doi.org/10.11646/zootaxa.3154.1.1
https://doi.org/10.11646/zootaxa.3154.1.... , Morek et al. 2019MOREK, W., STEC, D., GĄSIOREK, P., SURMACZ, B. & MICHALCZYK, Ł. 2019. Milnesium tardigradum Doyère, 1840: the first integrative study of interpopulation variability in a tardigrade species. Journal of Zoological Systematics and Evolutionary Research 57(1):1–23. https://doi.org/10.1111/jzs.12233
https://doi.org/10.1111/jzs.12233... , Gąsiorek et al. 2021GĄSIOREK, P., VONČINA, K., NELSON, D.R. & MICHALCZYK, Ł. 2021. The importance of being integrative: a remarkable case of synonymy in the genus Viridiscus (Heterotardigrada: Echiniscidae). Zoological Letters 7(1):13.https://doi.org/10.1186/s40851-021-00181-
https://doi.org/10.1186/s40851-021-00181... ). Despite that, many tardigrade species’ definitive distribution range is far from known, the “EiE” hypothesis does not explain the wide geographic distribution of many of them. However, although it is not simple to distinguish natural and human-mediated dispersal, Gąsiorek et al. (2019aGĄSIOREK, P., JACKSON, K.J., MEYER, H.A., ZAJĄC, K., NELSON, D.R., KRISTENSEN, R.M. & MICHALCZYK, Ł. 2019a. Echiniscus virginicus complex: the first case of pseudocryptic allopatry and pantropical distribution in tardigrades. Biological Journal of the Linnean Society 128(4):789–805. https://doi.org/10.1093/biolinnean/blz147
https://doi.org/10.1093/biolinnean/blz14... , bGĄSIOREK, P., VONČINA, K. & MICHALCZYK, Ł. 2019b. Echiniscus testudo (Doyère, 1840) in New Zealand: anthropogenic dispersal or evidence for the ‘Everything is Everywhere’ hypothesis? New Zealand Journal of Zoology 46(2):174–181. https://doi.org/10.1080/03014223.2018.1503607
https://doi.org/10.1080/03014223.2018.15... ) extend the discussion regarding the latter, proposing human’s pivotal role in the dispersal of some tardigrade species worldwide.

We plotted records on countries’ geopolitical/administrative boundaries as well as biogeographical regions, mapping geographical areas categorized according to their climatic, geological, and biota (including endemic taxa) criteria (Escalante et al. 2009ESCALANTE, T., SZUMIK, C. & MORRONE, J.J. 2009. Areas of endemism of mexican mammals: reanalysis applying the optimality criterion. Biological Journal of the Linnean Society 98(2):468–478. https://doi.org/10.1111/j.1095-8312.2009.01293.x
https://doi.org/10.1111/j.1095-8312.2009... , Morrone 2015aMORRONE, J.J. 2015a. Biogeographical regionalisation of the Andean region. Zootaxa 3936(2):207–236. https://doi.org/10.11646/zootaxa.3936.2.3
https://doi.org/10.11646/zootaxa.3936.2.... , Morrone 2015bMORRONE, J.J. 2015b. Biogeographical regionalisation of the world: a reappraisal. Australian Systematic Botany 28(3):81-90. https://doi.org/10.1071/SB14042
https://doi.org/10.1071/SB14042... , Morrone 2017MORRONE, J.J. 2017. Neotropical biogeography: regionalization and evolution. 1 ed. CRC Press, Boca Raton : Taylor & Francis, 2017. | Series: CRC biogeography series., Morrone et al. 2017MORRONE, J., TANIA, E. & RODRÍGUEZ-TAPIA, G. 2017. Mexican biogeographic provinces: map and shapefiles. Zootaxa 4277(2):277-279. https://doi.org/10.11646/zootaxa.4277.2.8
https://doi.org/10.11646/zootaxa.4277.2.... , Morrone 2018MORRONE, J.J. 2018. Evolutionary biogeography of the Andean region. 1 ed. CRC Press, Boca Raton : Taylor & Francis, 2018. | Series: CRC biogeography series., Morrone et al. 2022MORRONE, J.J., ESCALANTE, T., RODRÍGUEZ-TAPIA, G., CARMONA, A., ARANA, M. & MERCADO-GÓMEZ, J.D. 2022. Biogeographic regionalization of the Neotropical region: new map and shapefile. Anais da Academia Brasileira de Ciência. 94(1):e20211167. https://doi.org/10.1590/0001-3765202220211167
https://doi.org/10.1590/0001-37652022202... ), in Central and South America (Andean and Neotropical regions). When studying species distribution and diversity patterns, a widely used method considers geopolitical/administrative boundaries valid units (Murphy 2021MURPHY, S.J. 2021. Sampling units derived from geopolitical boundaries bias biodiversity analyses. Global Ecology and Biogeography 30(9):1876–1888. https://doi.org/10.1111/geb.13352
https://doi.org/10.1111/geb.13352... ), however they rarely concur with ecological boundaries, as they are constantly subject to changes (Wilson & Donnan 2012WILSON, T.M. & DONNAN, H. 2012. A companion to border studies. 1 ed. John Wiley & Sons, Ltd.). Murphy (2021)MORRONE, J.J., ESCALANTE, T., RODRÍGUEZ-TAPIA, G., CARMONA, A., ARANA, M. & MERCADO-GÓMEZ, J.D. 2022. Biogeographic regionalization of the Neotropical region: new map and shapefile. Anais da Academia Brasileira de Ciência. 94(1):e20211167. https://doi.org/10.1590/0001-3765202220211167
https://doi.org/10.1590/0001-37652022202... demonstrated several critical issues of this practice, which include overestimating endemism, underestimating biodiversity metrics (particularly endemism estimates), hindering understanding of biodiversity discontinuity across the world (especially true for measures containing species range size), and identifying hotspots. Thus, biogeographic regionalization is essential to comprehend ecological and evolutionary aspects of life (Crisp et al. 2009CRISP, M.D., ARROYO, M.T.K., COOK, L.G., GANDOLFO, M.A., JORDAN, G.J., MCGLONE, M.S., WESTON, P.H., WESTOBY, M., WILF, P. & LINDER, H.P. 2009. Phylogenetic biome conservatism on a global scale. Nature 458(7239):754–756. https://doi.org/10.1038/nature07764
https://doi.org/10.1038/nature07764... , Holt et al. 2013HOLT, B.G., LESSARD, J.-P., BORREGAARD, M.K., FRITZ, S.A., ARAÚJO, M.B., DIMITROV, D., FABRE, P.-H., GRAHAM, C.H., GRAVES, G.R., JØNSSON, K.A., NOGUÉS-BRAVO, D., WANG, Z., WHITTAKER, R.J., FJELDSÅ, J. & RAHBEK, C. 2013. An update of Wallace’s zoogeographic regions of the world. Science 339(6115):74–78. https://doi.org/10.1126/science.1228282
https://doi.org/10.1126/science.1228282... , Flores-Tolentino et al. 2021FLORES-TOLENTINO, M., BELTRÁN-RODRÍGUEZ, L., MORALES-LINARES, J., RODRÍGUEZ, J.R.R., IBARRA-MANRÍQUEZ, G., DORADO, Ó. & VILLASEÑOR, J.L. 2021. Biogeographic regionalization by spatial and environmental components: numerical proposal. PLOS ONE 16(6):e0253152. https://doi.org/10.1371/journal.pone.0253152
https://doi.org/10.1371/journal.pone.025... ).

The Andean and Neotropical regions are hierarchically arranged in five levels: kingdoms, regions, dominions, provinces, and districts (Morrone 2015bMORRONE, J.J. 2015b. Biogeographical regionalisation of the world: a reappraisal. Australian Systematic Botany 28(3):81-90. https://doi.org/10.1071/SB14042
https://doi.org/10.1071/SB14042... ), meaning they do not represent countries’ political boundaries. However, countries with considerable sampling effort and intensity will translate to provinces with more sampling sites and higher observed richness (Figure 4), as seen in this study. Due to a sampling bias, this phenomenon is known as the “specialist” effect, where distribution data explains who is researching these organisms instead of their actual distribution (Fontaneto et al. 2012FONTANETO, D., BARBOSA, A.M., SEGERS, H. & PAUTASSO, M. 2012. The ‘rotiferologist’ effect and other global correlates of species richness in monogonont rotifers. Ecography 35(2):174–182. https://doi.org/10.1111/j.1600-0587.2011.06850.x
https://doi.org/10.1111/j.1600-0587.2011... ). Argentina is a clear example of this statement, as it was ranked second in the total number of records and first in observed richness. The substantial sampling effort in this country was enough to consider it an outlier in our analysis and removing it from the statistical analysis yields a higher positive correlation (Figure S1). Thus, Argentina outperforms all other countries in Central and South America regarding the relationship between observed richness and published articles. Another case would be Costa Rica. The country already had studies of tardigrade ecology conducted there (Mehlen 1969MEHLEN, R.H. 1969. Tardigrada: Taxonomy and distribution in Costa Rica. Transactions of the American Microscopical Society 88(4):498–505. https://doi.org/10.2307/3224244
https://doi.org/10.2307/3224244... , Kaczmarek et al. 2011KACZMAREK, Ł., GOŁDYN, B., WEŁNICZ, W. & MICHALCZYK, Ł. 2011. Ecological factors determining Tardigrada distribution in Costa Rica. Journal of Zoological Systematics and Evolutionary Research 49(s1):78–83. https://doi.org/0.1111/j.1439-0469.2010.00603.x
https://doi.org/10.1111/j.1439-0469.2010... , Stander 2016STANDER, L. 2016. Comparing tardigrade abundance and diversity on rock, log, live tree, and canopy in Monteverde, Costa Rica. Tropical Ecology and Conservation [Monteverde Institute]. ), justifying why it is the first and third country in overall sampling sites and observed richness. Consequently, overlapping biogeographical provinces with both countries will have higher observed richness due to substantial localized sampling effort (e.g., Guatuso-Talamanca and Puntarenas-Chiriqui provinces with Costa Rica).

Finally, studying species’ large-scale distribution patterns is not a simple task for meiofaunal organisms, especially in the Southern Hemisphere (Fontaneto et al., 2012FONTANETO, D., BARBOSA, A.M., SEGERS, H. & PAUTASSO, M. 2012. The ‘rotiferologist’ effect and other global correlates of species richness in monogonont rotifers. Ecography 35(2):174–182. https://doi.org/10.1111/j.1600-0587.2011.06850.x
https://doi.org/10.1111/j.1600-0587.2011... , Garraffoni et al., 2021GARRAFFONI, A., SØRENSEN, M.V., WORSAAE, K., DI DOMENICO, M., SALES, L.P., SANTOS, J. & LOURENÇO, A. 2021. Geographical sampling bias on the assessment of endemism areas for marine meiobenthic fauna. Cladistics 37(5):571–585. https://doi.org/10.1111/cla.12453
https://doi.org/10.1111/cla.12453... ), because of significant sample bias and predominantly Eurocentric sampling (Guil & Cabrero Sañudo 2007GUIL, N. & CABRERO-SAÑUDO, F. 2007. Analysis of the species description process for a little known invertebrate group: The limnoterrestrial tardigrades (Bilateria, Tardigrada). Biodiversity and Conservation 16:1063-1086. https://doi.org/10.1007/s10531-006-9069-y
https://doi.org/10.1007/s10531-006-9069-... , Schill 2018). The “meiofaunal paradox” (Giere 2008), while supposedly adhering to the “EiE” hypothesis (Finlay et al. 1996FINLAY, B.J., ESTEBAN, G.F. & FENCHEL, T. 1996. Global diversity and body size. Nature 383(6596):132–133. https://doi.org/10.1038/383132a0
https://doi.org/10.1038/383132a0... , Fenchel et al. 1997FENCHEL, T., ESTEBAN, G.F. & FINLAY, B.J. 1997. Local versus global diversity of microorganisms: cryptic diversity of ciliated Protozoa. Oikos 80(2):220–225. https://doi.org/10.2307/3546589
https://doi.org/10.2307/3546589... , Fenchel & Finlay 2004FENCHEL, T. & FINLAY, B.J. 2004. The ubiquity of small species: patterns of local and global diversity. BioScience 54(8):777–784. https://doi.org/10.1641/0006-3568(2004)054[0777:TUOSSP]2.0.CO;2
https://doi.org/10.1641/0006-3568(2004)0... ), does not help with the current shortfalls (Linnean and Wallacean) to explain how these organisms were able to colonize multiple habitats. Moreover, consolidating historical non-marine tardigrade records without a thorough taxonomical analysis, especially with an integrative approach, only hinders advancements in comprehending the diversity, biogeography, and evolution of limnoterrestrial tardigrades (Morek et al. 2019MOREK, W., STEC, D., GĄSIOREK, P., SURMACZ, B. & MICHALCZYK, Ł. 2019. Milnesium tardigradum Doyère, 1840: the first integrative study of interpopulation variability in a tardigrade species. Journal of Zoological Systematics and Evolutionary Research 57(1):1–23. https://doi.org/10.1111/jzs.12233
https://doi.org/10.1111/jzs.12233... , Gąsiorek et al. 2019aGĄSIOREK, P., JACKSON, K.J., MEYER, H.A., ZAJĄC, K., NELSON, D.R., KRISTENSEN, R.M. & MICHALCZYK, Ł. 2019a. Echiniscus virginicus complex: the first case of pseudocryptic allopatry and pantropical distribution in tardigrades. Biological Journal of the Linnean Society 128(4):789–805. https://doi.org/10.1093/biolinnean/blz147
https://doi.org/10.1093/biolinnean/blz14... , Gąsiorek et al. 2021GĄSIOREK, P., VONČINA, K., NELSON, D.R. & MICHALCZYK, Ł. 2021. The importance of being integrative: a remarkable case of synonymy in the genus Viridiscus (Heterotardigrada: Echiniscidae). Zoological Letters 7(1):13.https://doi.org/10.1186/s40851-021-00181-
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This database and the online interactive map will significantly help future studies on limnoterrestrial and freshwater tardigrades’ biogeography and ecology in Central and South America. Although we have provided valuable insights into certain areas of knowledge of these organisms, their study continues to face obstacles due to numerous critical deficiencies that remain unresolved. We believe that implementing a more homogenous and widespread sampling across both regions and performing analyses of all specimens utilizing an integrative taxonomic approach will greatly benefit the understanding of the diversity and distribution patterns of limnoterrestrial and freshwater tardigrades.

Supplementary Material

The following online material is available for this article:

Table S1 - List of publications from 2014 to 2023 on limnoterrestrial and freshwater Tardigrada from Central and South America.

Table S2 - List of species with their respective taxonomical issue(s) and reference(s) for species of non-marine tardigrades from Central and South America according to Degma & Guidetti (2023)DEGMA, P. & GUIDETTI, R. 2023. Actual checklist of Tardigrada species. DOI: https://doi.org/10.25431/11380_1178608 (Accessed date 29/04/2023).
https://doi.org/10.25431/11380_1178608... .

Figure S1 - Correlation between the number of published articles and known species richness for each country (excluding Argentina). Orange squares represent Central American countries, while purple diamonds represent South American ones. There are overlapping data represented in the chart. Countries with zero published papers (Belize, El Salvador, Guatemala, Guyana, Haiti, Honduras and Panama) were excluded. Pearson’s R-value correlation and p-value are shown in the upper left corner.

Acknowledgments

P.D.S.U. and A.R.S.G. are grateful to Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP), via Process 2018/10313-0, 2021/05612-0 and 2022/14458-8, for the concession of grants that enabled this study. We also acknowledge Yasmina Shah Esmaeili for the English revision of the manuscript and two anonymous reviewers for offering suggestions that significantly improved the paper.

Data Availability

The dataset generated during the current study is available at: https://doi.org/10.48331/scielodata.JQJBE9.

References

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