GEOGRAPHIC-VARIATION IN THE LIFE-HISTORY OF THE LIZARD ANOLIS-CAROLINENSIS AND SUPPORT FOR THE PELVIC CONSTRAINT MODEL

The green anole (Anolis carolinensis) occurs throughout the southeaste rn United States and its distribution defines the northern limit of th e range of this genus of neotropical lizards. The variation in female, egg, and hatchling sizes is quantified for eight populations of the g reen anole that range from south Florida to the mountains of east Tenn essee. Six populations are composed of the typical red-throated (dewla p) morph of this species, one of the gray-throated morph, and one popu lation is representative of a variant of the red-throated morph. Among populations of the red-throated morph, female, egg, and hatchling siz es all increased significantly with increasing latitude. Additionally, females in the north had disproportionately larger eggs and offspring than did females to the south. We propose that increased selection pr essure for large hatchling body size associated with decreasing winter temperatures (i.e., increasing latitude) results in the observed lati tudinal diversification in the sizes of green anole eggs, juveniles, a nd adults. Whereas egg size was largely independent of female body siz e in southern populations, there was a significant positive relationsh ip between egg and female sizes in northern populations. The relations hips between egg width and pelvic aperture width, relative to female b ody size, were examined for lizards from three populations that varied in the degree to which egg size was related to female body size. The size of the pelvic girdle aperture appeared to constrain the egg size of northern females to a greater extent than it did in southern female s. Taken together, these data suggest that egg size may be optimized b y natural selection in southern populations, but not in northern popul ations. Optimization of egg size may not be possible for lizards in no rthern populations due to this apparent morphological constraint on eg g size, which is consistent with predictions of the pelvic constraint model. The environmental, physiological, and morphological factors tha t may combine to limit the continued northward range expansion of this successful colonizer are discussed.