QUANTITATIVE GENETICS OF LOCOMOTOR SPEED AND ENDURANCE IN THE LIZARD LACERTA-VIVIPARA

We used quantitative genetic analyses to test the hypothesis of a trad e-off between locomotor speed and endurance in a population of the Eur opean lizard Lacerta vivipara, which is the subject of long-term demog raphic studies. We estimated the heritability of maximal sprint speed treadmill endurance and tail length, a morphometric trait that may aff ect locomotor performance, as well as phenotypic, genetic, and environ mental correlations between these traits. Gravid females were captured in the field and held in the laboratory under standardized conditions until giving birth; traits were then measured on their offspring. Pri or to ge genetic analyses, we used multiple regressions to remove the effects of such covariates as body size (mass and snout-vent length), dam age, and length of time dams were held in captivity prior to partu rition. When we examined the residual characters, heritability was low and statistically nonsignificant for speed but relatively high for bo th endurance (0.46) and tail length (0.51). None of the phenotypic, ge netic, or environmental correlations between traits was statistically significant Thus, we found no evidence for a trade-off between speed a nd endurance; these results are consistent with those reported in two previous studies of squamate reptiles (the garter snake Thamnophis sir talis and the fence lizard Sceloporus occidentalis). The lack of a neg ative genetic correlation between speed and endurance suggests that th ese aspects of locomotor abilities are relatively free to evolve indep endently, such that natural selection could increase both speed and en durance. However, the species studied to date have low to moderate cap acities for speed and endurance, as compared with other squamates. Phy siologically based trade-offs-for example, those caused by the composi tion of muscle fiber types-should be more likely to exist in species t hat heave high capacities for speed and/or endurance.