Age and growth in Lacerta agilis (ssp. L. a. boemica) and a closely related sympatric species L. strigata from the eastern North Caucasus, Russia were assessed by skeletochronology and back-calculation methods. We examined 320 specimens from one lowland, two submontane (both species), and two mountain (L. agilis) localities. Age structure, back-calculated snoutvent length (SVL) at hatching and subsequent hibernations, and asymptotic SVL were studied for sexual dimorphism, altitudinal variation and interspecific differences. Pattern of resorption of growth layers in bone and its possible effects on growth inferences from skeletochronological data were also considered. The back-calculated SVLs showed a good conformity to comparable field data. Mean and maximum SVL at the first hibernation clearly decreased with altitude. Within the same localities, these parameters were consistently higher in L. agilis than in L. strigata. Between the 1st and 2nd hibernations (the period of the highest increment in SVL in all study populations), L. strigata grew faster than the syntopic L. agilis. In the lowland locality, females of both species tended to grow slower than males between the 1st and 2nd hibernations, while at higher elevations they exhibited lower SVL increments than the males between the 2nd and 3d hibernations. This pattern, along with occurrence of gravid yearlings in the lowland locality (but not in the other sites), suggests an earlier onset of reproduction in the lowland populations compared to those from higher elevations. Asymptotic SVLs in the study populations tended to be larger in males than in females. In L. agilis these sexual size differences (SSD) varied among populations, being quite strong in the lowland site and negligible at the highest locality. The mountain populations (960 and 1900 m a.s.l.) of L. a. boemica exhibited higher mean age and longevity than the lowland and submontane populations (20-600 m a.s.l.) of both species; however, no clear altitudinal trend was found for adult SVL. Much of the variation revealed in this study, including the interlocality differences in SSD, can be related to the length of activity season, in line with recently published theoretical models and experimental studies stressing the role of proximate factors.
Key words: altitudinal variation, asymptotic size, life-history, lizards, sexual size dimorphism
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