Understanding the evolution of ecological sex differences: Integrating character displacement and the Darwin-Bateman paradigm

Abstract

Sex differences in selection arise for at least two possible reasons: (1) differences originating from anisogamy—the Darwin‐Bateman paradigm—and (2) competition‐driven ecological character displacement (ECD), agnostic of anisogamy. Despite mounting evidence of ECD and increasing focus on the ecological causes and consequences of sexual dimorphism, progress in understanding the evolution of ecological sex differences has likely been hindered because ecological dimorphisms are not exclusive to ECD. I argue that embracing nonexclusivity of causal models of sexual dimorphism itself may provide insight into evolution of sex differences. This integrated view of the evolution of sexual dimorphism leads to four predictions for how sex‐specific selection and phenotypic divergence between the sexes change over the course of the evolution of sexual dimorphism. First, dimorphism resulting directly from anisogamy likely precedes evolution of ecological dimorphism driven by ECD. Second, ecological sexual dimorphism driven by ECD may (initially) evolve in directions in trait space favored by other sources of sex‐specific selection. Third, we may expect correlated evolution of ecological dimorphism and other forms of sexual dimorphism. Finally, ecological optima may be sex specific even when competition plays a role in reaching them. Rather than simply a less‐parsimonious alternative explanation for ecological sex differences, ECD should be seen as one likely contributor to sex‐specific selection that could act at predictable times during the evolution of ecological sexual dimorphisms.

Intraspecific variability in the filter mesh size of suspension feeding organisms: the case of invasive Ponto-Caspian corophiids (Crustacea: Amphipoda)

“…However, in the light of the present results showing that sex-related differences vary among samples, it seems more likely that they indeed have a relevant biological background. Sexual dimorphism in niche-related traits can evolve as a result of the interplay between sexual selection and ecological character displacement (De Lisle, 2019). Remarkably, the sex effect was accompanied by body length dependency in almost all samples, indicating that it might also be related to the intensity of intraspecific competition.…”

Sexual dimorphism in an adaptive radiation: Does intersexual niche differentiation result in ecological character displacement?

“…Ecological competition is expectedly highest in populations of conspecifics (McGee et al, 2020). Divergent selection has been shown to play a key role in interspecific adaptive processes (Rundle & Nosil, 2005;Schluter, 2009) and might even be an important factor for divergence between sexes (De Lisle, 2019;De Lisle & Rowe, 2017;Roy et al, 2013). Divergent modes of resource use minimize intersexual competition for limited trophic resources, resulting in ecological character displacement between males and females (De Lisle, 2019;De Lisle & Rowe, 2017;Roy et al, 2013).…”

“…Although the role of intersexual variation in speciation processes has gained little attention so far (De Lisle, 2019;De Lisle & Rowe, 2017;Ronco et al, 2019), the few studies available suggest that intersexual niche differentiation is present in adaptive radiations (De Lisle & Rowe, 2017;Pfaender et al, 2011;Ronco et al, 2019). It has been demonstrated, for instance, in Anolis lizards, salamanders, and sticklebacks (Butler, 2007;De Lisle & Rowe, 2017;McGee & Wainwright, 2013).…”

“…Whether intersexual niche differentiation rather retards or promotes adaptive radiations is still an ongoing discussion (Bolnick & Doebeli, 2003;Butler, 2007;De Lisle & Rowe, 2015, but recent studies have shown that ecological speciation and ecological character displacement can occur simultaneously (De Lisle & Rowe, 2015. However, the actual role of intersexual niche differentiation in species flock formation remains largely unexplored (De Lisle, 2019;De Lisle & Rowe, 2017;Pfaender et al, 2011;Ronco et al, 2019).…”

“…Sexual dimorphism is widespread in adaptive radiations (Herler et al, 2010;McGee & Wainwright, 2013), most commonly as sexual size dimorphism or sexual color dimorphism (Herler et al, 2010;Tsuboi et al, 2012). It can either be induced by sexual selection, by intrinsic differences between males and females, or by intersexual competition (De Lisle, 2019;Hedrick & Temeles, 1989;Herler et al, 2010), whereby these drivers may interact in many cases of sexual dimorphism (Bolnick & Doebeli, 2003;Temeles et al, 2000). Sexual selection mechanisms provide plausible explanations for many of the spectacular cases, but cannot account for intersexual phenotypic variation in general (De Lisle, 2019;Hedrick & Temeles, 1989;Tsuboi et al, 2012).…”