Male genitalia's evolutionary rate is higher than those of body traits: the case of two Liolaemus lizards' group

Abstract

Different studies suggest that reproductive characters evolve faster than non-reproductive characters. Males in the order Squamata have paired copulatory organs called hemipenes, with high morphological diversity, including differences in size, shape, and ornamentation. Some studies in the species-rich lizard genus, Anolis suggest that genital traits evolve faster than the rest of the body. However, these studies were made considering only a few traits, across a wide phylogeny, without considering species relatedness, which may inflate differences in evolutionary rates. Here, we study two phylogenetic distantly related lizard groups, which differ in the number of species, but have similar divergence times. We evaluate as follows: (1) evolutionary rate, models of evolution and phylogenetic signal among the different genital and non-genital traits; (2) which kind of traits (genital and non-genital) are divergent across sister species and (3) whether the species-rich group shows a faster rate of trait change. We studied 24 Liolaemus lizard species, belonging to two monophyletic groups that differ in species number: L. elongatus’ clade, which has more species than L. lineomaculatus’ clade. We studied 20 different traits (9 genital and 11 non-genital) and calculated their phylogenetic signal, evolutionary rate of change and models that best explain the evolutionary change. Our results show that: (1) in general, genital traits evolve faster than non-genital ones in both groups, and both phylogenetic signal and best evolutionary model vary depending on the trait. (2) Genital traits diverged more among sister species within the L. lineomaculatus group, but within the L. elongatus group, both sets of traits show similar degrees of divergence. Finally, (3) the species-rich group (L. elongatus), has the highest genital evolutionary rate but also the highest non-genital evolutionary rate.