Bergmann’s rule in amphibians: combining demographic and ecological parameters to explain body size variation among populations in the common toadBufo bufo

Abstract

Large-scale patterns of body size variation are described by well-known generalizations such as BergmannÕs rule; the generality and underlying causes of these patterns have been much debated. Intraspecific extension of this rule was tested in various ectotherms, and evidence was found for both Bergmann and converse Bergmann clines. In this study, we explored spatial patterns of variation in a widespread amphibian, the Common toad (Bufo bufo), along a 2240 km latitudinal gradient across Europe. We tested for covariation of adult body size, age and growth parameters with latitude, altitude, length of activity period and mean temperature during this period using both original and literature data. We selected 13 European populations, representing a latitudinal range from 43 to 63°N and altitudinal range from 15 to 1850 m a.s.l. The length of activity period (12-33 weeks) and T mean (6.6-15.6°C) significantly decreased as latitude and altitude of these populations increased. Mean body size decreased as latitude increased (not with altitude), and increased with T mean (not with length of activity period). Mean and minimal adult age increased with latitude and altitude, longevity increased with altitude only. Age increased as length of activity period decreased (not with T mean ). The growth coefficient (0.32-0.92 in males, 0.18-0.74 in females, available for six populations) decreased as altitude increased, and increased as both length of activity period and T mean increased; latitudinal trend was non-significant. Our analysis shows that B. bufo clearly exhibited a converse Bergmann cline along latitudinal gradient, but not along altitudinal gradient; the main effect of elevation was on age. The effects of ecological conditions also differed: body size increased with T mean , while age parameters were related to the length of activity period. This study highlights that, to identify causal factors underlying general ecogeographical rules, we have to take into account different phases of the life cycle, co-variation among life history traits and ecological factors acting on each of these traits. In amphibians with complex life cycles, lack of appropriate demographical or ecological data may affect our understanding of the variety of observed body size patterns.

Altitudinal variation in body size and age structure of the Sauter’s frog Rana sauteri in Taiwan

“…However, N. parkeri showed a steeper altitudinal decrease in female size, whereas no clear altitudinal relationship was detected for males . In this study, the different trends of body size in relation to altitudes between the two sexes of R. sauteri suggested that the temperature gradient was not only the factor affecting the body size variation in amphibians (Cvetković et al 2009). Various life history traits and environmental factors may also affect the variation.…”

“…During the breeding season when calling males aggregated, we visited 630-, 1,380-, and 2,320-m sites weekly and recorded the numbers of frogs, freshly deposited egg masses, and larval developmental stages to determine the period of breeding activities (Morrison et al 2004;Cvetković et al 2009). A total of 1,405 males and 145 females of R. sauteri were caught during the study period.…”

“…For this, we used the mean SVL 13.46 ± 0.72 mm (n = 37) of the tadpoles at Gosner stages 42 to 45 captured at the 630-m site. Annual growth rates (R) were calculated as R = dSVL / dt = k × (SVL max − SVL t ) (Cvetković et al 2009;Ma et al 2009a;Iturra-Cid et al 2010). …”

“…Environmental factors determine body size often through their influences on life history traits related with body size (Berven 1982;Miaud et al 1999;Cvetković et al 2009). Adult body size of frogs may be affected by many factors such as age at sexual maturity, growth rate, length of activity period, longevity, food availability, and predation (Iturra-Cid et al 2010;Oromi et al 2012;Manyak-Davis et al 2013).…”

Phenotypic divergence of the common toad (Bufo bufo) along an altitudinal gradient: evidence for local adaptation

“…Delayed age at maturity at high altitude is common in most species (for example, Oromi et al, 2012) and often associated with a subsequent increase in longevity (for example, Miaud et al, 1999). The intraspecific variation of body size along altitudinal gradients seems to differ among species (Morrison and Hero, 2003;Cvetković et al, 2009). Growth and development rates seem to follow a countergradient pattern (that is, individuals from colder environments grow or develop more slowly in situ, but are able to grow or develop more rapidly than conspecifics from warmer parts of the range when compared in a common garden setting; Conover and Schultz, 1995, Ficetola and De Bernardi, 2005, 2006Marquis and Miaud, 2008) but exceptions exist (for example, Sommer and Pearman, 2003) and explicit tests of local adaptation are lacking ( (Berven, 1982a,b) but see Muir et al, 2014).…”