Ecology and mating competition influence sexual dimorphism in Tanganyikan cichlids

Abstract

Sexual selection contributes strongly to the evolution of sexual dimorphism among animal taxa. However, recent comparative analyses have shown that evolution of sexual dimorphism can be influenced by extrinsic factors like mating system and environment, and also that different types of sexual dimorphism may present distinct evolutionary pathways. Investigating the co-variation among different types of sexual dimorphism and their association with environmental factors can therefore provide important information about the mechanisms generating variation in sexual dimorphism among contemporary species. Using phylogenetic comparative analyses comparing 49 species of Tanganyikan cichlid fishes, we first investigated the pairwise relationship between three types of sexual dimorphism [size dimorphism (SSD), colour dimorphism (COD) and shape dimorphism (SHD)] and how they were related to the strength of pre-and post-copulatory sexual selection. We then investigated the influence of ecological features on sexual dimorphism. Our results showed that although SSD was associated with the overall strength of sexual selection it was not related to other types of sexual dimorphism. Also, SSD co-varied with female size and spawning habitat, suggesting a role for female adaptations to spawn in small crevices and shells influencing SSD in this group. Further, COD and SHD were positively associated and both show positive relationships with the strength of sexual selection. Finally, the level of COD and SHD was related to habitat complexity. Our results thus highlight distinct evolutionary pathways for different types of sexual dimorphism and further that ecological factors have influenced the evolution of sexual dimorphism in Tanganyikan cichlid fishes.

Diet is correlated with otolith shape in marine fish

“…Likewise, sexual dimorphism in otolith shape is generally attributed to physiological differences between sexes. However, sexual dimorphism in diet composition, especially at the time of mating, has been documented in several fish species (Casselman & Schulte-Hostedde 2004, Tsuboi et al 2011 and could thus also explain otolith shape dimorphism. Finally, environmental abiotic factors, such as temperature and salinity, are also known to influence otolith shape variation (Lombarte & Lleonart 1993) and spatial variation in otolith shape are often interpreted as resulting from habitat differentiation (Morat et al 2012).…”

Sexual dimorphism in a trophically polymorphic cichlid fish?

“…Given the degree of craniofacial sexual dimorphism in other cichlids (Kajiura et al, 2005;Sch€ utz et al, 2006;Herler et al, 2010;Parnell et al, 2012;Tsuboi et al, 2012Tsuboi et al, , 2015 the lack of association of these phenotypes with sex in H. minckleyi is somewhat surprising. Future studies should determine if there is a genetic basis to the highly variable trophic phenotypes found in H. minckleyi as well as if they show any genetic linkage among themselves or to sex.…”

“…Sex could often be tightly linked with intraspecific differences in ecologically relevant traits and a large number of fishes exhibit this type of sexual dimorphism (Shine, 1989;Pyron, 1996;Kajiura et al, 2005;Sch€ utz et al, 2006;Herler et al, 2010;Tsuboi et al, 2012;McGee and Wainwright, 2013;Tsuboi et al, 2015). For instance, divergence in male and female body size could lead indirectly to resource partitioning if, for example, the larger sex can consume larger prey (Shine, 1989;Katsikaros and Shine, 1997).…”

Diet disparity among sympatric herbivorous cichlids in the same ecomorphs in Lake Tanganyika: amplicon pyrosequences on algal farms and stomach contents

“…Tanganyikan cichlids are unique because of the species richness of each of the ecomorphs [7,8] that have evolved convergently and coexist in similar habitats, not only among different lakes but also within Lake Tanganyika [4]. Additionally, only six of the fourteen tribes present in Lake Tanganyika show sexual dichromatism; the others are monochromatic lineages [5,9], in contrast to other African lakes in which the degree of cichlids' adaptive radiation correlates highly with the presence of sexual dichromatism [5].…”