Female dewlap ornaments are evolutionarily labile and associated with increased influence diversification rates in Anolis lizards

The evolution of costly signaling traits has largely focused on male
ornaments. However, our understanding of the ornament evolution is
necessarily incomplete without investigating the causes and consequences
of variation in female ornamentation. Here, we study the Anolis lizard
dewlap, a trait extensively studied as a male secondary sexual
characteristic but present in females of several species. We characterized
female dewlaps for 339 species to test hypotheses about their evolution.
Our results did not support the hypothesis that female dewlaps are
selected against throughout the anole phylogeny. Rather, we found that
female dewlaps were evolutionary labile. We also did not find support for
the adaptive hypothesis that interspecific competition drove the evolution
of female dewlaps. However, we did find support for the non-adaptive
pleiotropy hypothesis as species with larger females and reduced sexual
size dimorphism were more likely to possess female dewlaps. Lastly, we
found that female dewlap presence influenced diversification rates in
anoles, but only secondarily to a hidden state. Our results demonstrate
that female ornamentation is widespread in anoles and the traditional
hypothesis of divergent selection between the sexes does not fully explain
their evolution. Instead, female ornamentation is likely subject to
complex adaptive and non-adaptive evolutionary forces.