Novel host plant leads to the loss of sexual dimorphism in a sexually selected male weapon

Abstract

In this time of massive global change, species are now frequently interacting with novel players. Greater insight into the impact of these novel interactions on traits linked to fitness is essential, because effects on these traits can hinder population existence or promote rapid adaptation. Sexually selected weapons and ornaments frequently influence fitness and often have heightened condition-dependence in response to nutrition. Condition-dependence in response to different ecological conditions, a form of developmental plasticity, may be responsible for much of the intraspecific variation in sexually selected ornaments and weapons in wild populations. Here we examined the consequences of developing on a novel plant for the expression of size and shape in the leaf-footed cactus bug (Hemiptera: Coreidae). The males of this species possess enlarged, sexually dimorphic femurs on their hind legs. These legs are used as weapons in male-male contests. Females are typically larger in overall body size. Our study revealed that developing upon a novel host can lead to pronounced phenotypically plastic change in sexually dimorphic traits. Male hind femurs were greatly impacted by the novel diet to the extent that the sexual dimorphism in hind femurs was lost. Further, dimorphism in body size increased, as males became tiny adults while females better maintained their body size. These patterns underscore the complex effects that novel species interactions may have on sexual phenotypes.

On the Reciprocally Causal and Constructive Nature of Developmental Plasticity and Robustness

“…Intriguingly, inhibiting niche construction also altered scaling relationships in a number of traits, including eliminating or severely diminishing the expression of sexual dimorphism among male and female tibia in all species examined (Schwab et al, 2017). Although the presence and degree of sexual dimorphism is known to be environmentally contingent (as in Bonduriansky and Rowe, 2005; Bonduriansky, 2007; Allen and Miller, 2017), this finding extends earlier studies on the plasticity and condition-dependence of sexually dimorphic traits to the phenomenon of niche construction. Finally, Schwab et al implicated the dung beetle external rumen, established when larvae spread their feces and thus maternally inherited gut microbiota throughout the brood ball chamber, as a possible mechanism of niche construction.…”

Males that drop a sexually selected weapon grow larger testes

“…In escalated competitions, males kick and squeeze each other with their hind limbs until one male retreats (Nolen et al 2017). Hind limbs in this species appear to be costly and condition-dependent traits Allen and Miller 2017), and larger males are more successful in male-male contests (Procter et al 2012;Nolen et al 2017).…”

“…Hind limbs in this species appear to be costly and condition‐dependent traits (Miller et al. ; Allen and Miller ), and larger males are more successful in male–male contests (Procter et al. ; Nolen et al.…”

Sex differences in local adaptation: what can we learn from reciprocal transplant experiments?

“…Adopting an ontogenetic and developmental perspective on sex differences will increase our understanding of the role of genetic causes of sexual dimorphism between populations and the role of sex-specific phenotypic plasticity and environmentdependent growth rate differences between males and females [87,92,99,100]. It is common to find differences in the degree of sexual dimorphism between different habitats and environments, and sometimes such differences can be related to differences in sexual selection regimes and/or intensity of sexual conflict [47,73,87]. It would be interesting to know how, why and when those differences emerge and the role of sex-specific maternal effects [34,101], sex differences in growth rates [99] and early environmental effects [87].…”

“…It is common to find differences in the degree of sexual dimorphism between different habitats and environments, and sometimes such differences can be related to differences in sexual selection regimes and/or intensity of sexual conflict [47,73,87]. It would be interesting to know how, why and when those differences emerge and the role of sex-specific maternal effects [34,101], sex differences in growth rates [99] and early environmental effects [87]. Nowadays reciprocal transplant experiments are often combined with genomic approaches, creating new, powerful and integrative research opportunities for the study of local adaptation [1,[102][103][104][105].…”