Microevolution and ecophysiology of Canary Island skinks (Chalcides)
Within-island geographic variation in three character systems (body dimensions, scalation, colour pattern) and in life history is described in the Gran Canarian skink (Chalcides sexlineatus). Numerical methods used to describe patterns of geographic variation include contouring, principal components analysis, multiple group principal components analysis and canonical variates analysis. The primary patterns of geographic variation are north-east/south-west clines, although altitudinal variation is also evident in some characters. Several hypothesized causes of the variation are erected and tested using Mantel Tests and partial correlation. This points to lush/arid ecotone adaptation as the cause. A suggestion by previous workers that there are two species on the island is rejected. Patterns of geographic variation in Chalcides viridanus on the neighbouring island of Tenerife are described and tested against hypotheses using similar methods. Tenerife shows similar lush/arid variation to that in Gran Canaria. Parallel patterns of geographic variation in morphology are found, most notably in colour pattern. This strongly suggests that adaptation to current ecological conditions, rather than ancient population vicariance, is the cause. Geographic variation in anti-predator strategy can explain the colour pattern microevolution. Ecological differences between populations of C. sexlineatus are investigated to elucidate the actual selection pressures acting on different aspects of the animals' morphology. Some thermoregulatory and also dietary and prey size differences are found among populations. Daily energy expenditure and water flux are compared among skinks from northern and southern populations in the field, using the doubly-labelled water technique. Between-population differences in energy expenditure can be attributed to body size differences.