Why do Anatolian ground squirrels exhibit a Bergmannian size pattern? A phylogenetic comparative analysis of geographic variation in body size

Abstract

A phylogenetic comparative analysis of geographic variation in body size of an obligately hibernating marmotine species (Anatolian ground squirrels, Spermophilus xanthoprymnus) is presented in relation to environmental variables that pertain to four principal hypotheses (heat conservation, heat dissipation, primary productivity, and seasonality hypotheses). Adult Anatolian ground squirrels (78 males and 90 females) were collected from ten geographic localities in Anatolia for use in morphometric analyses. First, the study tested whether significant variation in body size occurs over the geographic range of S. xanthoprymnus. Then, to understand the possible cause(s) of the observed pattern of geographic variation in body size of Anatolian ground squirrels, four hypotheses were tested, separately and simultaneously, using a phylogenetic comparative method. Overall, food availability (primary productivity hypothesis) and, especially in males, over-winter fasting endurance (seasonality hypothesis) are likely the primary underlying mechanisms generating the observed pattern of increasing body size towards colder, more seasonal environments, with higher summer precipitation and productivity (or a Bergmannian size pattern).

Sexual size dimorphism in ground squirrels (Rodentia: Sciuridae: Marmotini) does not correlate with body size and sociality

“…Adults were identified according to the degree of teeth abrasion or stage (adult/juvenile) was obtained directly from specimen tags. Our dataset can be biased by geographic intraspecific variability in body size documented in ground squirrels [54]. Nevertheless, taking into account the large variability in body size across species of the studied group, we expect that intraspecific variability does not largely influence the interspecific pattern.…”

“…Nevertheless, body mass is not a good expression of body size in ground squirrels [54], because many species considerably fluctuate in body mass throughout the year. For instance, data on body mass before and after hibernation are highly different e.g.…”

“…[58]) and most body measurements use to be highly intercorrelated in morphometric analyses. For example, skull measurements are highly correlated with each other in ground squirrels [54]. To avoid this problem, we selected CBL and HFL, because they reflect size of very different body parts, although due to large variability in body size among ground squirrels, we can a priori expect that these measures will be highly correlated across all species included (we tested the correlation by Pearson test for males and females separately).…”

No inbreeding effects on body size in two captive endangered gazelles

“…The first principal component (PC1) can be interpreted as a measure of body size if the measurements load strongly and evenly on PC1 (Pimentel, 1979;Rising and Somers, 1989). PC1 has been widely used as an indicator of overall body size in previous morphometric studies in many species (Wiklund, 1996;Schulte-Hostedde et al, 2004;Gür, 2010). In our study we used cranium PC1 (PC1cr) and postcranium PC1 (PC1pstcr) as descriptors of overall cranium and postcranium size, respectively.…”

Spermophilus xanthoprymnus (Rodentia: Sciuridae)

“…Food availability and, especially in males, overwinter fasting endurance are likely the primary underlying mechanisms generating the observed pattern of geographic variation in body size. As expected, sexual size dimorphism, too, varies geographically and appears to increase toward northeastern highland Anatolia (Gü r 2007(Gü r , 2010.…”