Allometric analysis of sexual dimorphism and morphological variation in two chromosome races of the Sceloporus grammicus complex (Squamata: Phrynosomatidae) from Mexico

Sexual dimorphism is a widespread feature in the Animal Kingdom. In lizards of the Sceloporus grammicus complex, studies of sexual dimorphism that analyze the allometric trajectories of body traits remain unexplored. Here we investigate sexual dimorphism in key phenotypic traits, including body size (snout-vent length, SVL) as well as head length (HL), head width (HW), and forearm length (FL). We use an allometric approach to detect differences in scale relationships among body parts in the S. grammicus complex in Mexico. We focus on two chromosomal races within this complex, F5 (2n = 34) and FM2 (2n = 46). In the complex, we found that males are larger than females in all morphological variables, and this pattern was confirmed in both races. We determined negative allometric trajectories (SVLvs.HL and HW), isometry (SVLvs.FL) and intersexual differences in the slopes of the SVLvs.HL and HW; the males showed steeper slopes. Thus, the growth of the head is more pronounced in males than females. Additionally, we found between-race differences in these trajectories (SVLvs.FL) and in all morphological variables (F5 lizards are larger than those of the FM2 race), which correlate with their chromosomal divergence. We discuss biological implications of our findings in relation to sexual selection and natural selection.

Sexual dimorphism in the mountain dragon, Diploderma micangshanensis (Squamata: Lacertilia: Agamidae) from central China

Sexual dimorphism (SD) is a common phenomenon in the animal kingdom, especially in lizards. The mountain dragon (Diploderma micangshanensis) is a Chinese endemic that is widely distributed in montane regions of northern Sichuan, western Hubei Province, southern Gansu, Henan, and Shanxi Provinces. However, little is known about its morphology, ecology, behavior, physiology, and natural history. In this study, SD in size and shape in a population of D. micangshanensis from Henan Province, Central China was examined based on a sample of 35 males and 23 females. Sexual dimorphism was observed in a few body shape variables (e.g., head and trunk length) but not in body size (snout-vent length). Males had longer and wider heads and shorter trunks. Sexual dimorphism in these traits can be explained by the sexual selection, ecological divergence, and fecundity advantage hypotheses. Additional studies of the ecology, reproductive biology, natural history, and behavior of D. micangshanensis are needed to evaluate the relative contributions of these mechanisms to determining the patterns of SD observed in this population.