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      Geographic body size variation in ectotherms: effects of seasonality on an anuran from the southern temperate forest

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          Abstract

          Background

          Body size variation has played a central role in biogeographical research, however, most studies have aimed to describe trends rather than search for underlying mechanisms. In order to provide a more comprehensive understanding of the causes of intra-specific body size variation in ectotherms, we evaluated eight hypotheses proposed in the literature to account for geographical body size variation using the Darwin’s frog ( Rhinoderma darwinii), an anuran species widely distributed in the temperate forests of South America. Each of the evaluated hypotheses predicted a specific relationship between body size and environmental variables. The level of support for each of these hypotheses was assessed using an information-theoretic approach and based on data from 1015 adult frogs obtained from 14 sites across the entire distributional range of the species.

          Results

          There was strong evidence favouring a single model comprising temperature seasonality as the predictor variable. Larger body sizes were found in areas of greater seasonality, giving support to the “starvation resistance” hypothesis. Considering the known role of temperature on ectothermic metabolism, however, we formulated a new, non-exclusive hypothesis, termed “hibernation hypothesis”: greater seasonality is expected to drive larger body size, since metabolic rate is reduced further and longer during colder, longer winters, leading to decreased energy depletion during hibernation, improved survival and increased longevity (and hence growth). Supporting this, a higher post-hibernation body condition in animals from areas of greater seasonality was found.

          Conclusions

          Despite largely recognized effects of temperature on metabolic rate in ectotherms, its importance in determining body size in a gradient of seasonality has been largely overlooked so far. Based on our results, we present and discuss an alternative mechanism, the “hibernation hypothesis”, underlying geographical body size variation, which can be helpful to improve our understanding of biogeographical patterns in ectotherms.

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          Most cited references52

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          CONFRONTING MULTICOLLINEARITY IN ECOLOGICAL MULTIPLE REGRESSION

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            New perspectives for estimating body condition from mass/length data: the scaled mass index as an alternative method

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              Temperature and Organism Size—A Biological Law for Ectotherms?

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                Author and article information

                Contributors
                andresvalenzuela.zoo@gmail.com
                A.Cunningham@ioz.ac.uk
                csoto@unab.cl
                Journal
                Front Zool
                Front. Zool
                Frontiers in Zoology
                BioMed Central (London )
                1742-9994
                23 December 2015
                23 December 2015
                2015
                : 12
                : 37
                Affiliations
                [ ]Centro de Investigación para la Sustentabilidad, Facultad de Ecología y Recursos Naturales, Universidad Andres Bello, República 440, Santiago, Chile
                [ ]ONG Ranita de Darwin, Nataniel Cox 152, Santiago, Chile
                [ ]Institute of Zoology, Zoological Society of London, London, NW1 4RY United Kingdom
                Author information
                http://orcid.org/0000-0002-0445-9156
                Article
                132
                10.1186/s12983-015-0132-y
                4690379
                26705403
                a0e5b4a1-d9c3-46d2-b347-bee733a5ff8e
                © Valenzuela-Sánchez et al. 2015

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                History
                : 29 October 2015
                : 18 December 2015
                Funding
                Funded by: FundRef http://dx.doi.org/10.13039/100007463, Rufford Foundation;
                Award ID: 14460-1
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/501100002850, Fondo Nacional de Desarrollo Científico y Tecnológico;
                Award ID: 11140902
                Award Recipient :
                Categories
                Research
                Custom metadata
                © The Author(s) 2015

                Animal science & Zoology
                hibernation hypothesis,metabolic depression,rhinoderma darwinii,scaled mass index,starvation resistance

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