Sexual Size Dimorphism of Two Species of the Sceloporus Pyrocephalus Species Group from Mexico

Sexual size dimorphism (SSD) in body size and head size can vary among species in the lizard genus Sceloporus. We studied the SSD in body and head size of two closely related species, Sceloporus nelsoni from Chihuahua and two populations of S. pyrocephalus, one from Michoacán and the other from Guerrero. Males had larger bodies than females in both species. However, SSD in head size was only found in the two populations of S. pyrocephalus, with males having relatively longer and wider heads than females. Our results suggest that these two species share SSD in body size, but vary in SSD in head size. This species pair might therefore be an interesting system in which to further explore the underlying causes of SSD in body and head size.