Bergmann’s rule and Allen’s rule in two passerine birds in China

Abstract

Background Animals that live at higher latitudes/elevations would have a larger body size (Bergmann’s rule) and a smaller appendage size (Allen’s rule) for thermoregulatory reasons. According to the heat conservation hypothesis, large body size and small appendage size help animals retain heat in the cold, while small body size and large appendage size help them dissipate heat in the warm. For animals living in seasonal climates, the need for conserving heat in the winter may tradeoff with the need for dissipating heat in the summer. In this study, we tested Bergmann’s rule and Allen’s rule in two widely-distributed passerine birds, the Oriental Magpie (Pica serica) and the Oriental Tit (Parus minor), across geographic and climatic gradients in China. Methods We measured body size (body mass and wing length) and appendage size (bill length and tarsus length) of 165 Oriental Magpie and 410 Oriental Tit individuals collected from Chinese mainland. We used linear mixed-effect models to assess variation patterns of body size and appendage size along geographic and climatic gradients. Results Oriental Magpies have a larger appendage size and Oriental Tits have a smaller body size in warmer environments. Appendage size in Oriental Magpies and body size in Oriental Tits of both sexes were more closely related to the climates in winter than in summer. Minimum temperature of coldest month is the most important factor related to bill length and tarsus length of male Oriental Magpies, and wing length of male and female Oriental Tits. Bill length and tarsus length in female Oriental Magpies were related to the annual mean temperature and mean temperature of coldest quarter, respectively. Conclusions In this study, Oriental Magpies and Oriental Tits followed Allen’s rule and Bergmann’ rule respectively. Temperatures in the winter, rather than temperatures in the summer, drove morphological measurements in Oriental Magpies and Oriental Tits in Chinese mainland, demonstrating that the morphological measurements reflect selection for heat conservation rather than for heat dissipation.

A global test of Allen’s rule in rodents

“…This can be explained in terms of this association being adaptive for heat conservation in cold environments (by having relatively shorter tails) rather than heat dissipation in warmer environments (by having relatively longer tails). A similar interpretation was proposed in birds, where appendage size (bill and tarsus lengths) was found to be associated mainly with winter temperature (Danner & Greenberg, 2015;Fan et al, 2019;Friedman et al, 2017;Nudds & Oswald, 2007;Romano et al, 2020). Cold temperatures appear to be a greater evolutionary constraint than warm ones.…”

Generalized evidence for Bergmann’s rule: body size variation in a cosmopolitan owl genus

“…Ashton et al, 2002;Ashton, 2004;Blackburn et al, 2019;Blackburn & Ruggiero, 2001;Meiri, 2011;Meiri & Dayan, 2003;Olson et al, 2009) and at the within-species level on a continental geographical scale (e.g. Fan et al, 2019;Gibson et al, 2019;Graves, 1991;James, 1970;Jones et al, 2005). However, comprehensive intraspecific analyses on cosmopolitan taxa are almost null (but see Murphy, 1985).…”

“…In addition, however, variation in the body size and the size of different body parts have often been linked to the minimum or the maximum temperature recorded in a year, rather than to the mean annual temperature (e.g. Danner & Greenberg, 2015;Fan et al, 2019;Rodríguez et al, 2008). Therefore, we also extracted information on the minimum temperature of the coldest month and maximum temperature of the warmest month.…”

Comparative transcriptomic and metabolomic analysis reveals pectoralis highland adaptation across altitudinal songbirds

“…Great body mass and muscle weight in highland are concordance with Bergmann's rule [15,16]. Avian pectoralis is used to support the high metabolic costs through aerobic metabolism for flight or thermogenesis [4].…”