Influence of incubation temperature on morphology, locomotor performance, and early growth of hatchling wall lizards (Podarcis muralis)

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Abstract
Eggs of wall lizards (Podarcis muralis) were incubated at three temperatures approaching the upper limit of viability for embryonic development in this species (26, 29, and 32°C) to assess the influence of temperature on various aspects of hatchling phenotype likely affecting fitness. The thermal environment affected size and several morphometric characteristics of hatchling lizards. Hatchlings from eggs incubated at 32°C were smaller (snout‐vent length, SVL) than those from 26 and 29°C and had smaller mass residuals (from the regression on SVL) as well as shorter tail, head, and femur relative to SVL. Variation in the level of fluctuating asymmetry in meristic and morphometric traits associated with incubation temperatures was quite high but not clearly consistent with the prediction that environmental stress associated with the highest incubation temperatures might produce the highest level of asymmetry. When tested for locomotor capacity in trials developed at body temperatures of 32 and 35°C, hatchlings from the 32°C incubation treatment exhibited the worst performance in any aspect considered (burst speed, maximal length, and number of stops in the complete run). Repeated measures ANCOVAs (with initial egg mass as covariate) of snout‐vent length and mass of lizards at days 0 and 20 revealed significant effects of incubation temperature only for mass, being again the hatchlings from eggs incubated at 32°C those exhibiting the smallest final size. All together, our results evidenced a pervasive effect of thermal regime during incubation (and hence of nest site selection) on hatchling phenotypes. However, incubation temperature does not affect hatchling phenotypes in a continuous way; for most of the analysed traits a critical threshold seems to exist between 29 and 32°C, so that hatchlings incubated at 32°C exhibited major detrimental effects. J. Exp. Zool. 286:422–433, 2000.