Meeting Abstract

14.3  Wednesday, Jan. 4  Evolution and Development of Sexual Skull Dimorphism among Anolis lizards SANGER, Thomas J.*; SEAV , Susan M.; LOSOS, Jonathan B.; ABZHANOV, Arhat; Harvard University

Many species exhibit striking sexual dimorphisms in body size and shape. Sexual body size dimorphism is well studied in many biological contexts – ecological, evolutionary, and physiological - but few studies have examined sexual shape dimorphism in the same detail. We have explored patterns of sexual size and shape dimorphism in the skull of 30 Anolis lizard species using geometric morphometrics and found that species with relatively elongate skulls exhibit exceptional sexual shape dimorphism relative to other species. The greatest axis of sexual shape dimorphism is in the length of the rostrum, or snout. In species with relatively short skulls snout length is typically isometric with respect to body size. In contrast, in species with elongate skulls only females exhibit isometry, males consistently exhibit positive static allometry suggesting a fundamental difference in the regulation of skull growth between the sexes. To explore whether this difference is associated with the onset of sexual maturity or is developmentally regulated we studied snout growth and patterns of gene expression at three life history stages: in hatchlings, juveniles, and sub-adults. Gene expression was quantified for a panel of 15 genes involved with the hormonal regulation of growth using quantitative-rtPCR. Male and female skull shape is not sexually dimorphic as hatchlings or juveniles, though females do appear to grow more rapidly and show significant expression differences for several genes. Sexual shape dimorphism in snout length appears around sexual maturity and may be due to a localized down regulation of growth in females rather than a significant physiological change in males. Further molecular studies are needed to examine whether these differences are associated with physiological changes in circulating hormone levels associated with sexual maturity or are locally regulated changes.