An interspecific assessment of Bergmann's rule in 22 mammalian families.

Jostein Gohli,Kjetil L Voje

doi:10.1186/s12862-016-0778-x

Jostein Gohli, Kjetil L Voje

Open Access

https://doi.org/10.1186/s12862-016-0778-x

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Abstract

BackgroundBergmann’s rule proposes that animals in cold habitats will be larger than those in warm habitats. This prediction has been tested thoroughly at the intraspecific level, but few studies have investigated the hypothesis with interspecific data using phylogenetic comparative approaches. Many clades of mammals have representatives in numerous distinct biomes, making this order highly suitable for a large-scale interspecific assessment of Bergmann’s rule. Here, we evaluate Bergmann’s rule within 22 mammalian families—with a dataset that include ~35 % of all described species—using a phylogenetic comparative approach. The method is based on an Ornstein-Uhlenbeck model of evolution that allows for joint estimation of adaptation and constraints (phylogenetic inertia) in the evolution of a trait. We use this comparative method to investigate whether body mass evolves towards phenotypic optima that are functions of median latitude, maximum latitude or temperature. We also assess the closely related Allen’s rule in five families, by testing if relative forelimb length evolves as a function of temperature or latitude.ResultsAmong 22 mammalian families, there was weak support for Bergmann’s rule in one family: A decrease in temperature predicted increased body mass in Canidae (canids). We also found latitude and temperature to significantly predict body mass in Geomyidae (pocket gophers); however, the association went in the opposite direction of Bergmann’s predictions. Allen’s rule was supported in one of the five examined families (Pteropodidae; megabats), but only when forelimb length evolves towards an optimum that is a function of maximum latitude, not median latitude or temperature.ConclusionsBased on this exhaustive assessment of Bergmann’s rule, we conclude that factors other than latitude and temperature are the major drivers of body mass evolution at the family level in mammals.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0778-x) contains supplementary material, which is available to authorized users.

Highlights

Bergmann’s rule proposes that animals in cold habitats will be larger than those in warm habitats
We investigate whether log transformed body mass (Bergmann’s rule) and relative forelimb length have evolved towards optima that are influenced by latitude or temperature within different families of mammals
We found median latitude and temperature to be strongly negatively correlated in all 22 families, except for Nesomyidae (Table 1)

Summary

Introduction

Bergmann’s rule proposes that animals in cold habitats will be larger than those in warm habitats This prediction has been tested thoroughly at the intraspecific level, but few studies have investigated the hypothesis with interspecific data using phylogenetic comparative approaches. The method is based on an Ornstein-Uhlenbeck model of evolution that allows for joint estimation of adaptation and constraints (phylogenetic inertia) in the evolution of a trait We use this comparative method to investigate whether body mass evolves towards phenotypic optima that are functions of median latitude, maximum latitude or temperature. Bergmann’s hypothesis continues to receive a great deal of attention more than 150 years after it was originally proposed Bergmann proposed his rule as applying to closely related species within the same genus (see Blackburn et al [2] for a review of definitions of Bergmann’s rule), and it seems that Bergmann’s rule can operate at both the intraspecific and interspecific level [3, 4]. Temperature may describe a comparatively smaller amount of interspecific variation among species, since (many) species are different in their general biology, and will differ in important constraints or selective pressures on body mass

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