The relative effects of pace of life‐history and habitat characteristics on the evolution of sexual ornaments: A comparative assessment

Abstract

Selection may favor greater investment into sexual ornaments when opportunities for future reproduction are limited, for example, under high adult mortality. However, predation, a key driver of mortality, typically selects against elaborate sexual ornaments. Here, we examine the evolution of sexual ornaments in killifishes, which have marked contrasts in life-history strategy among species and inhabit environments that differ in accessibility to aquatic predators. We first assessed if the size of sexual ornaments (unpaired fins) influenced swimming performance. Second, we investigated whether the evolution of larger ornamental fins is driven primarily by the pace of life-history (investment into current vs. future reproduction) or habitat type (a proxy for predation risk). We found that larger fins negatively affected swimming performance. Further, males from species inhabiting ephemeral habitats, with lower predation risk, had larger fins and greater sexual dimorphism in fin size, compared to males from more accessible permanent habitats. We show that enlarged ornamental fins, which impair locomotion, evolve more frequently in environments that are less accessible to predators, without clear associations to life-history strategy. Our results provide a rare link between the evolution of sexual ornaments, effects on locomotion performance, and natural selection on ornament size potentially through habitat differences in predation risk.

Sex dimorphism and evidence of sexually selected traits: A case study on the killifish Aphaniops stoliczkanus (Day, 1872)

“…Optimal habitats favour fitness of specimens, while more stressful environments will have negative effects on the physical condition of the fish, which can eventually suppress sex dimorphism in morphometric body traits due to metabolic constraints (see Bonduriansky, 2007). However, also predation pressures, reproductive cycles and life history may impact fitness in a killifish, with low predation pressure favouring increase of sexual dimorphism in fin sizes (Sowersby et al, 2021). Based on our field observations, a cichlid, the sailfin molly ( Poecilia latipinna ) and the Arabian goby ( Cryptocentroides arabicus ) co‐occur with A. stoliczkanus in Al Bahayez, but if any of these species is predating on A. stoliczkanus is not known.…”

“…Outliers include some large males with relatively short fin lengths (in % SL) similar to those of females, as well as some small males that had the relatively longest fins (in % SL) of all (Figure 4g,h). These exceptions may be related to differences in environmental conditions during growth or in the intensity of male–male competition, which can have an impact on the allocation of resources to body growth or sexual ornaments (dorsal‐ and anal‐fin size), the latter being a metabolically cheaper way to increase perceived size than increasing total body size (Rosenthal & Evans, 1998; Sowersby et al, 2021). Furthermore, a relatively slow growth rate of the anal fin resulting in negative allometry between body size and anal‐fin length has been noted in females of the killifish Nothobranchius orthonotus (suborder Aplocheiloidei; Vrtílek & Reichard, 2016).…”

“…It can be the result of sexual selection for specific traits having to do with mate choice (e.g. male courtship), and of ecological selection for dimorphic niches due to reproductive constraints or resource competition (Herler et al, 2010; Sowersby et al, 2021; Walker & McCormick, 2009). Moreover, sexually dimorphic traits can play an important role in population divergence and adaptive radiations because such traits can reinforce interspecific differences in behaviour, feeding and habitat use, thus adding to species diversification (Bolnick & Doebeli, 2003; Martínez‐Ruiz & Knell, 2017; Wasiljew et al, 2021).…”

Whole-genome comparisons identify repeated regulatory changes underlying convergent appendage evolution in diverse fish lineages

“…For example, changes in vertebral number, skeletal armor, teeth, scales, sensory modalities, locomotion, osmoregulation, temperature tolerance, and lifespan have evolved multiple times in independent lineages of fish (Norman, 1949;Nelson, Grande and Wilson, 2016;Kolora et al, 2021). Fin modificationsincluding extensive loss, dramatic expansion, and/or structural ornamentationare particularly interesting given the outsized effects of fins on mobility, defense/predation, and reproductive success, and how easily fins can be scored visually or by nondestructive methods (Norman, 1949;Davenport, 1994;Westneat et al, 2004;Yamanoue, Setiamarga and Matsuura, 2010;Price, Friedman and Wainwright, 2015;Nelson, Grande and Wilson, 2016;Goldberg et al, 2019;Giammona, 2021;Sowersby et al, 2022). Because fins are homologous to tetrapod limbs, 3 modification of these major body appendages in fish may also inform a variety of traits and diseases in other animals, including humans (Clack, 2009;Tanaka, 2016).…”

Concerted evolution of metabolic rate, economics of mating, ecology, and pace of life across seed beetles

“…The classic explanation for such differences is that ecology dictates the economics of reproduction, which, in turn, shapes mating systems and sexual selection ( 1 ). Sexual dimorphism indeed correlates with ecological factors in a wide range of taxa [e.g., ( 2 – 5 )]. To complicate matters, however, theory suggests that life histories and mating systems should be intimately linked ( 6 , 7 ), and several studies have documented covariation across species between life history traits, most commonly body size [e.g., ( 2 , 4 , 8 )], and mating systems or indices of sexual selection.…”