Correlated evolution of sex allocation and mating system in wrasses and parrotfishes

In accordance with predictions of the size-advantage model, comparative
evidence confirms that protogynous sex change is lost when mating behavior
is characterized by weak size advantage. However, we lack comparative
evidence supporting the adaptive significance of sex change. Specifically,
it remains unclear whether increasing male size advantage induces
transitions to protogynous sex change across species, as it can within
species. We show that in wrasses and parrotfishes (Labridae), the
evolution of protogynous sex change is correlated with polygynous mating,
and that the degree of male size advantage expressed by polygynous species
influences transitions between different types of protogynous sex change.
Phylogenetic reconstructions reveal strikingly similar patterns of sex
allocation and mating system evolution with comparable lability. Despite
the plasticity of sex determination mechanisms in labrids, transitions
trend towards monandry (all males derived from sex-changed females), with
all observed losses of protogyny accounted for by shifts in the timing of
sex change to prematuration. Likewise, transitions in mating system trend
from the ancestral condition of lek-like polygyny toward greater male size
advantage, characteristic of haremic polygyny. The results of our
comparative analyses are among the first to confirm the adaptive
significance of sex change as described by the size-advantage model.