Global patterns of body size evolution in squamate reptiles are not driven by climate

Abstract

Aim Variation in body size across animal species underlies most ecological and evolutionary processes shaping local‐ and large‐scale patterns of biodiversity. For well over a century, climatic factors have been regarded as primary sources of natural selection on animal body size, and hypotheses such as Bergmann's rule (the increase of body size with decreasing temperature) have dominated discussions. However, evidence for consistent climatic effects, especially among ectotherms, remains equivocal. Here, we test a range of key hypotheses on climate‐driven size evolution in squamate reptiles across several spatial and phylogenetic scales. Location Global. Time period Extant. Major taxa studied Squamates (lizards and snakes). Methods We quantified the role of temperature, precipitation, seasonality and net primary productivity as drivers of body mass across ca. 95% of extant squamate species (9,733 spp.). We ran spatial autoregressive models of phylogenetically corrected median mass per equal‐area grid cell. We ran models globally, across separate continents and for major squamate clades independently. We also performed species‐level analyses using phylogenetic generalized least square models and linear regressions of independent contrasts of sister species. Results Our analyses failed to identify consistent spatial patterns in body size as a function of our climatic predictors. Nearly all continent‐ and family‐level models differed from one another, and species‐level models had low explanatory power. Main conclusions The global distribution of body mass among living squamates varies independently from the variation in multiple components of climate. Our study, the largest in spatial and taxonomic scale conducted to date, reveals that there is little support for a universal, consistent mechanism of climate‐driven size evolution within squamates.

No evidence for the ‘rate‐of‐living’ theory across the tetrapod tree of life

“…In our study, we found a similar and significant role for high environmental temperatures in driving shorter life span (although the temperature-size rule is unlikely to be the driver, as amphibians and reptiles show no size-temperature clines either within or between species; Adams & Church, 2008;Slavenko et al, 2019;. Our findings align with recent predictions emerging from the mathematical integration between neutral, metabolic and niche theories (Worm & Tittensor, 2018) that evolutionary processes on a global scale are dominated by environmental temperatures.…”

Global patterns of body size evolution are driven by precipitation in legless amphibians

“…The leading rule, Bergmann's rule -increases in body sizes toward colder climates as greater body mass, relative to surface area, reduces heat loss (Bergmann 1847) -has set the theoretical benchmark for research on large-scale patterns of animal size (James 1970, Blackburn et al 1999, Meiri and Dayan 2003. However, evidence from across the animal kingdom reveals that Bergmann's rule tends to hold in endotherms (Freckleton et al 2003, Meiri and Dayan 2003, de Queiroz and Ashton 2004, Olson et al 2009, but see Riemer et al 2018), while its validity is inconsistent in ectotherms (Ashton and Feldman 2003, Olalla-Tarraga et al 2006, Olalla-Tarraga and Rodriguez 2007, Pincheira-Donoso et al 2007, Adams and Church 2008, Pincheira-Donoso and Meiri 2013, Feldman and Meiri 2014, Moreno-Azocar et al 2015, Amado et al 2019, Slavenko et al 2019). These discrepancies have discredited temperature as a primary driver of body size clines (Pincheira-Donoso 2010, Meiri 2011, Olalla-Tarraga 2011.…”

Macroecology and macroevolution of body size inAnolislizards

“…Macroecological studies have usually asked whether geographical body size gradients (e.g. mean body sizes across assemblages) are associated with spatial environmental variation (Terribile et al , Olalla‐Tárraga et al , Slavenko et al ). These studies typically use an assemblage‐based approach wherein body size is averaged for each set of species occurring in a single grid cell or latitudinal band (Olalla‐Tárraga et al ).…”

“…These approaches often uses phylogenetic comparative methods (PCMs) to evaluate the contribution of phylogenetic effects from the resulting geographical body size gradients but they do not explicitly address questions about macroevolutionary processes. That is, PCMs in macroecology have been commonly used for ‘correction for phylogeny’ in statistical analyses and not necessarily to infer evolutionary processes through deep temporal scales (Slavenko et al ). Conversely, macroevolutionary approaches based on PCMs allow identifying changes in tempo (i.e.…”

“…The integration of macroecological and macroevolutionary perspectives has been a challenging for researchers attempting to evaluate how biodiversity patterns emerge across spatial and temporal scales (Bromham and Cardillo , McGill et al ). Most studies have usually explored each dimension, spatial or temporal, separately (Smith and Lyons , Amado et al 2019, Slavenko et al ). Few studies have attempted to integrate both spatial and temporal dimensions simultaneously to evaluate geographical and evolutionary body size patterns (Carotenuto et al , Villalobos et al ).…”