Patterns and determinants of geographic variation in adult body size and sexual size dimorphism in two widespread lizard species
Final Report Abstract
Intraspecific variation is an important issue because it links macroevolutionary patterns to microevolutionary processes which lead to the phenotypic diversity we wish to understand. Wide-ranging species present promising models for simultaneously evaluating the role of different factors shaping the phenotypic diversity, because the variation of target traits can be documented from numerous localities exhibiting diverse combinations of putative predictors. However, comprehensive range-wide studies of geographic variation in widespread species are rare, even for fundamentally important traits such as adult body size, offspring size and fecundity. During the first project phase I documented patterns of geographic variation in body size, sexual size dimorphism (SSD), and female reproductive output for the two most widespread terrestrial reptiles in the world, the lacertid lizards Lacerta agilis and Zootoca vivipara. Under careful consideration of potential confounding factors I investigated relationships of these patterns with the environment (climate), with evolutionary lineage, and among each other. Specifically, I tested several predictions of Darwin's fecundity-advantage hypothesis (FAH). I also confronted the revealed patterns of reproductive divergence to other prominent models of lifehistory evolution. In Z. vivipara, I also examined body size clines and the SSD allometry to address two currently debated patterns of body size variation, Bergmann’s rule and Rensch’s rule. In overall, geographic SSD variation within the intraspecific lineages provides no consistent support for FAH. At the same time, the pattern of reproductive divergence between the lineages is straight in line with the FAH predictions: the subspecies with consistently female-biased SSD (L. a. agilis) exhibits a higher clutch size relative to female size, and a steeper increase of clutch size with maternal SVL than the subspecies with a weak and variable SSD (L. a. exigua). L. a. agilis also shows clearly lower egg and hatchling sizes, but higher relative clutch mass than L. a. exigua. A comparable association of reproductive divergence with SSD was found between the studied lineages of Z. vivipara: the lower SSD of the oviparous clade, as compared to the two viviparous clades, is also consistent with FAH. In both species, the lineage which exhibits smaller offspring size also shows a higher clutch mass relative to post-oviposition female mass. This pattern is consistent with Winkler & Wallin's model predicting a negative evolutionary link between the total reproductive investment and allocation to individual offspring (classical models of life-history evolution treat the two variables as independent). Only little empirical evidence for this model has been thus far reported. Across the range of Z. vivipara, sex-specific adult body size (snout-vent length, SVL) tends to increase in more continental climates (lower mean annual temperatures). As the female SVL responds to this gradient more rapidly than the male size, SSD shows a similar cline. Female SVL also varies in overall stronger than male SVL resulting in a converse-Rensch allometry of SSD. The latter pattern has rarely been reported within a vertebrate species, and its interaction with a Bergmann's cline appears to be the first detailed evidence of this kind. Although each of the studied intraspecific lineages inhabits an apparently wide range of climates, the sets of study samples for the western and eastern forms within a species naturally differ in terms of continentality rate. Further data and analyses are therefore required to more reliably disentangle the effects of environment and ancestry on the geographic variation for body size and reproductive variation in the two species.
Publications
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2011. Inter-observer and intra-observer differences in measuring body length: a test in the common lizard, Zootoca vivipara. Amphibia-Reptilia 32: 477-484
Bulakhova, Nina A.; Böhme, Wolfgang; Clasen, Astrid; Orlova, Valentina F.; Carretero, Miguel A.; Kuranova, Valentina N.; Ljubisavljevic, Katarina; Roitberg, Evgeny S.; Shamgunova, Regina R.; Zinenko, Oleksandr I. & Fokt, Michael
