Variation in body size and sexual size dimorphism in the most widely-ranging lizard: testing the effects of reproductive mode and climate

Reproductive mode, ancestry, and climate are hypothesized to determine
body-size variation in reptiles but their effects have rarely been
estimated simultaneously, especially at the intraspecific level. The
common lizard (Zootoca vivipara) occupies almost the entire Northern
Eurasia and includes viviparous and oviparous lineages, thus representing
an excellent model for such studies. Using body length data for
>10,000 individuals from 72 geographically distinct populations
over the species’ range we analysed how sex-specific adult body size and
sexual size dimorphism (SSD) is associated with reproductive mode, lineage
identity, and several climatic variables. Variation in male size was low
and poorly explained by our predictors. In contrast, female size and SSD
varied considerably, demonstrating significant effects of reproductive
mode and particularly seasonality. Populations of the western oviparous
lineage (northern Spain, south-western France) exhibited a smaller female
size and less female-biased SSD than those of the western viviparous
(France to Eastern Europe) and the eastern viviparous (Eastern Europe to
Far East) lineages; this pattern persisted even after controlling for
climatic effects. The phenotypic response to seasonality was complex:
across the lineages, as well as within the Eastern Viviparous lineage,
female size and SSD increase with increasing seasonality, whereas the
Western Viviparous lineage followed the opposing trends. Altogether,
viviparous populations seem to follow a saw-tooth geographic cline, which
might reflect the non-monotonic relationship of body size at maturity in
females with the length of activity season. This relationship is predicted
to arise in perennial ectotherms as a response to environmental
constraints caused by seasonality of growth and reproduction. 
The SSD allometry followed the converse of Rensch's rule, a rare
pattern for amniotes. Our results provide the first evidence of opposing
body-size—climate relationships in intraspecific units.