Temperature (latitude) and nutrient (seabird guano) effects on limno-terrestrial Tardigrada (Testechiniscus spitsbergensis and Pilatobius recamieri) body size

ABSTRACT

Surveys of terrestrial microinvertebrate morphometry, especially spatial patterns of body size at wider geographical scales, including the polar regions, are very scarce. In this study, we focused on Tardigrada, common limno-terrestrial microinvertebrates. Considering Bergmann’s rule, originally formulated for endothermic animals, we tested the hypothesis that body length of limno-terrestrial tardigrades augments with increasing latitude and decreasing temperature. Since some of our sampling areas adjoined seabird colonies, we also explored the effects of nutrients from seabird guano deposits. Individual body length of Testechiniscus spitsbergensis was measured in populations obtained from seven localities distributed along a latitudinal gradient extending from 45°N (northern Italy) to 80°N (northern Svalbard), and for Pilatobius recamieri from three localities in Svalbard (77°N-80°N). Considering both latitude and proximity to a seabird colony there were significant effects of locality on the body length of T. spitsbergensis; however, no clear pattern of increasing individual body size with increasing latitude could be detected. Immense differences in body size may be a signal for cryptic species diversity within this genus. No effect of latitude, or proximity to a seabird colony, on the body length of Arctic populations of P. recamieri was documented. Evidently, there is no tendency towards body size increase along the latitudinal gradient in either T. spitsbergensis or P. recamieri. Our study, and recent literature, indicates that larger body size in polar regions reported for several groups of micro-fauna may be a taxon-dependent response, and cannot be taken as a universally applicable rule for limno-terrestrial animals.

KEYWORDS:

• Arctic
• Bergmann’s rule
• body length
• ectotherms
• latitudinal patterns
• temperature gradient

ABBREVIATIONS:

• ANOVA: analysis of variance
• DIC: differential interference contrast
• NI: Graian Alps, Italy
• PCM: phase contrast microscopy
• Sco: Aberdeenshire, Scotland, UK; SvB: Bjørnøya, Svalbard, Norway
• SvF: Fuglesangen, Svalbard, Norway
• SvH: Hornsund, Svalbard, Norway
• SvN: Nordaustlandet, Svalbard, Norway
• SvP: Phippsøya, Svalbard, Norway
• Tat: Tatra Mountains, Poland; Tro: Tromsø, Norway

Acknowledgements

The remarks and suggestions of two anonymous reviewers greatly improved the paper, and we are gratefully indebted to them. We thank Professor Stephen J. Coulson (University Centre in Svalbard, ArtDatabanken, The Swedish Species Information Centre, Swedish University of Agricultural Sciences) and Brian Blagden (The Scottish Environment Protection Agency) for collecting samples in Nordaustlandet (Svalbard) and Aberdeenshire, respectively. Brian Blgaden also critically read the manuscript and made necessary linguistic corrections, as did Katherine Short (British Antarctic Survey). Special thanks go also to Professor Łukasz Kaczmarek (Adam Mickiewicz University) and Jerzy Smykla (Polish Academy of Sciences) for sharing material collected in 2010 from Hornsund. KZ thanks Daniel Stec (Jagiellonian University) for comments on the Results section and Lidia Szymkowiak for help with part of the measurements. KJ thanks to the Czech Arctic Research Infrastructure Josef Svoboda Station.

Disclosure statement

No potential conflict of interest was reported by the authors.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

Studies were conducted as part of the Polish–Norwegian Research Programme, operated by the National Centre for Research and Development under the Norwegian Financial Mechanism 2009-2014 in the framework of project contract no. Pol-Nor/201992/93/2014 (DWARF). The study was supported by the Polish Ministry of Science and Higher Education via the Diamond Grant programme (grant no. DIA 2011035241, to KZ) and by the project EXCELLENCE (grant no. CZ.02.1.01/0.0/0.0/15_003/0000460 OP RDE to KJ and KZ). During this study, KZ was a beneficiary of a National Science Centre scholarship to support doctoral research (no. 2015/16/T/NZ8/00017). KJ is supported by project CzechPolar2 and project ECOPOLARIS no. CZ.02.1.01/0.0/0.0/16_013/0001708.