Comparative evidence supports a role for reproductive allocation in the evolution of female ornament diversity

Abstract

1. Sexually selected ornaments are highly variable, even among closely related species, and the ultimate causes of variation in ornament evolution are unclear, including in rare cases of female ornament expression. One hypothesis is that differences across species in female reproductive allocation may help to explain patterns of female ornament expression among insects with nuptial gifts.2. Dance flies (Diptera: Empididae: Empidinae) vary considerably among species in the presence and extravagance of female ornaments, which probably evolved through female contests for mates. In most dance flies, adult females appear to acquire all their dietary protein from nuptial gifts provided by males during mating. The importance of nuptial feeding on egg development is not yet known.3. To test the prediction that the presence of female ornaments reflects differences in the degree to which females rely on nuptial feeding for egg development, egg development was examined in wild females of two species, one ornamented and the other unornamented. An ageing technique based on cuticular bands was validated, which permitted a regression of egg size on adult age. 4. We found that egg development depended on mating status in the ornamented species alone, meaning the eggs of unmated females of the ornamented species did not develop. This contrast across species is consistent with expectations that females of different species vary in their dependence on nuptial gifts for egg development.5. These findings provide preliminary support for the hypothesis that differences in reproductive allocation mediate the intensity of female contests for nuptial gifts.

Competition for access to mates predicts female‐specific ornamentation and male investment in relative testis size

“…Therefore, the sometimes‐intense contests for mates we observe among females (Table 1, Fig. 4) are very likely associated with selection to obtain nutritious nuptial gifts to promote ovarian maturation (Hunter and Bussiere 2018). The skewed swarm sex ratios that arise due to these contests therefore reliably predict the degree of female‐specific ornamentation in most (but not all) species; for example R. longipes appears as a clear outlier in our dataset as an ornamented species with a strong male‐biased sex ratio (Table 1), that potentially represents a recent transition in mating system.…”

“…Male dance flies provide nutritious nuptial gifts to their mates at copulation (Collin 1961;Cumming 1994). Recently, Hunter and Bussière (Hunter and Bussiere 2018) showed that females of an ornamented dance fly species could only mature their eggs if they mated (and received a nuptial gift), while this was not the case for an unornamented species. Therefore, the sometimes-intense contests for mates we observe among females (Table 1, Figure 4) are very likely associated with selection to obtain nutritious nuptial gifts to promote ovarian maturation (Hunter and Bussiere 2018).…”

“…Recently, Hunter and Bussière (Hunter and Bussiere 2018) showed that females of an ornamented dance fly species could only mature their eggs if they mated (and received a nuptial gift), while this was not the case for an unornamented species. Therefore, the sometimes-intense contests for mates we observe among females (Table 1, Figure 4) are very likely associated with selection to obtain nutritious nuptial gifts to promote ovarian maturation (Hunter and Bussiere 2018). The skewed swarm sex ratios that arise due to these contests therefore reliably predict the degree of female-specific ornamentation in most (but not all) species; e.g.…”

The role of functional constraints in nonrandom mating patterns for a dance fly with female ornaments

“…belongs. In this subfamily (the Empidinae) not only is mating almost always accompanied by the presentation of nuptial gifts (Cumming, 1994), but adult females are not known to hunt, and must obtain their dietary protein from nuptial gifts (Hunter & Bussiere, 2018). Presumably as a consequence, females in many species compete intensely for the food gifts provided by males, and females have evolved a series of remarkable secondary sex characters that appear to improve their attractiveness to males (Collin, 1961;Cumming, 1994;Funk & Tallamy, 2000;LeBas, Hockham, & Ritchie, 2003;Murray, Wheeler, Gwynne, & Bussiere, 2018;Wheeler, Gwynne, & Bussière, 2012).…”

Competition for access to mates predicts female-specific ornamentation and polyandry

“…Recently, Hunter and Bussière (Hunter and Bussiere 467 2018) showed that females of an ornamented dance fly species could only mature their eggs if species. Therefore, the sometimes-intense contests for mates we observe among females 470 (Table 1, Figure 4) are very likely associated with selection to obtain nutritious nuptial gifts to 471 promote ovarian maturation (Hunter and Bussiere 2018). The skewed swarm sex ratios that 472 arise due to these contests therefore reliably predict the degree of female-specific 473 ornamentation in most (but not all) species; e.g.…”