Macroevolutionary Patterns of Sexual Size Dimorphism Among African Tree Frogs (Family: Hyperoliidae)

Sexual size dimorphism (SSD) is shaped by multiple selective forces that drive the evolution of sex-specific body size, resulting in male or female-biased SSD. Stronger selection on one sex can result in an allometric body size scaling relationship consistent with Rensch’s rule or its converse. Anurans (frogs and toads) generally display female-biased SSD, but there is variation across clades and the mechanisms driving the evolution of SSD remain poorly understood. We investigated these topics in a diverse family of African treefrogs (Hyperoliidae). Hyperoliids display traits considered rare among amphibians, including sexual dichromatism and protogynous sex change. Using phylogenetic comparative methods, we tested if adult ecology, sexual dichromatism, and sex change were predictors of body size or SSD. We also tested whether hyperoliids displayed allometric interspecific body size scaling relationships. We found a majority of hyperoliid taxa display female-biased SSD, but that adult ecology and sexual dichromatism are poor predictors of sex-specific body size and SSD. Regardless of the groupings analyzed (partitioned by clades or traits), we found support for isometric body size scaling. However, we found that sex change is a significant predictor of SSD variation. Species in the Hyperolius viridiflavus complex, which putatively display this trait, show a significant reduction in SSD and are frequently sexually monomorphic in size. Although protogynous sex change needs to be validated for several of these species, we tentatively propose this trait is a novel mechanism influencing anuran body size evolution. Beyond this association, additional factors that shape the evolution of anuran body size and SSD remain elusive.

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.

Rediscovering hermaphroditism in Grammatidae with the description of the testicular gland in Brazilian Basslet Gramma brasiliensis

Many aspects of sex change in reef fishes have been studied, including behavior and social organization. However, gonad histology remains the most robust way to identify sexual patterns in fishes. Some uncommon tissues remain poorly described, such as the accessory gonadal structures found in species from the Gobiidae family, which are rare in other bony fishes. This is the first report of the testicular gland in Gramma brasiliensis and for the Grammatidae family. Between April 2011 and February 2012 eighty specimens were collected during four dive campaigns on the Taipus de Fora reef (13°56’20”S 38°55’32”W), Bahia, Northeast Brazil, and their sex was determined. Thirteen per cent of the active-females and 90% of the active-males had testicular gland tissue in their ovotestis. This discovery led to additional research into the characteristics of the gland tissue and its relationship with gonadal maturation. Three patterns of testicular gland development were found in Brazilian basslet ovotestis. Both ova and sperm-producing gonad contained testicular gland tissue, and the appearance of this tissue seems to be the first modification of ovotestis tissue marking the beginning of the protogynous sex-change process in G. brasiliensis.