Proximate causes of intraspecific variation in locomotor performance in the lizard Gallotia galloti

To understand the evolution of biological traits, information on the degree and origins of intraspecific variation is essential. Because adaptation ca n take place only if the trait shows heritable variation, it is important t o know whether (at least) part of the trait variation is genetically based. We describe intra- and interindividual variation in three performance meas ures (sprint speed, climbing, and clambering speed) in juvenile Gallotia ga lloti lizards from three populations and examine how genetic, environmental (incubation temperature), and ontogenetic (age, size) effects interact to cause performance variation. Moreover, we test whether the three performanc e traits are intercorrelated phenotypically and genetically. Sprint speed i s highest in juveniles incubated at the lowest temperature (26 degreesC) ir respective of population. Climbing speed differs among populations, and the differences persist at least until the lizards are 30 wk old. This suggest s that the three populations experience different selective pressures. More over, mass, snout-vent length, and hindlimb length seem to affect climbing performance differently in the three populations. The variation in sprintin g and climbing ability appears to be genetically based. Moreover, the two p erformance traits are intercorrelated and thus will not evolve independentl y from each other. Clambering speed (i.e., capacity to climb up an inclined mesh) varies among individuals, but the origin of this variation remains o bscure.