1. Considerable within-population variability of locomotor performance
traits has been shown to exist in several species of
squamate reptiles. In general, high values for speed and endurance are thought to have positive effects on the ability to capture prey, escape from predators, compete with conspecifics and acquire mates. On the other hand, variation in performance might trade-off with other components of fitness such that the net effect on Darwinian fitness is unpredictable.
2. Gravid females of the common lizard (Lacerta vivipara) were captured and several phenotypic traits of their offspring measured immediately following birth. These were endurance, body length and body mass. Offspring were marked for individual identification, released into the field, and correlations between the phenotypic traits and their subsequent growth, activity and survival rate over the next months were then tested for. Parasitism by hematozoa was monitored and predation risk by tail losses estimated.
3. It was found that individuals with a low endurance at birth
tended to have reduced activity and growth rate, and higher
parasite load; on the positive side, however, they experienced lower predation risk as assessed by tail losses. Conversely,
individuals with a high endurance at birth had high activity and growth rates, low parasite load, but higher incidence of broken
tails. Finally, endurance at birth was not correlated with survivorship up to the age of sexual maturity. Thus, individuals with
varying locomotor endurance seem to exhibit behaviours that may result in the same level of Darwinian fitness.
4. The possibility that our results reveal a trade-off between
the risk of becoming infected with parasites when lizards are less
active (which is related to having lower endurance) vs the risk of being predated when the lizards are more active (higher endurance) is discussed.
Copyright 2000 British Ecological Society