Divergent sexual signals reflect costs of local parasites*

Abstract

Many closely related populations are distinguished by variation in sexual signals and this variation is hypothesized to play an important role in reproductive isolation and speciation. Within populations, there is considerable evidence that sexual signals provide information about the incidence and severity of parasite infections, but it remains unclear if variation in parasite communities across space could play a role in initiating or maintaining sexual trait divergence. To test for variation in parasite-associated selection, we compared three barn swallow subspecies with divergent sexual signals. We found that parasite community structure and host tolerance to ecologically similar parasites varied between subspecies. Across subspecies we also found that different parasites were costly in terms of male survival and reproductive success. For each subspecies, the preferred sexual signal(s) were associated with the most costly local parasite(s), indicating that divergent signals are providing relevant information to females about local parasite communities. Across subspecies, the same traits were often associated with different parasites, indicating that parasite-sexual signal links are quite flexible and may evolve relatively quickly. This study provides evidence for (1) variation in parasite communities and (2) different parasite-sexual signal links among three closely related subspecies with divergent sexual signal traits, suggesting that parasites may play an important role in initiating and/or maintaining the divergence of sexual signals among these closely related, yet geographically isolated populations.

Digest: Be honest with me: Do parasites play a role in divergence of sexual signals?*

“…In this issue, Hund et al. (2020) investigate if the divergence in relevant sexual signals among geographically isolated subspecies could be attributed to the costs of local parasite assemblages. They expected parasite assemblages to differ among subspecies and that sexual signals would reflect those local parasite assemblages, corresponding to a divergence among subspecies in which sexual signals are undergoing sexual selection (Fig.…”

“…Graphical representation of the pattern described by Hund et al. (2020) and the process by which it could initiate or maintain divergence among subspecies.…”

“…Associated parasites typically imposed a cost on their associated signal, with cost scaling with increasing parasite load (Hund et al. 2020). In barn swallows, divergent sexual signals thus communicate information about local parasites.…”

“…Most strikingly, they found that the sexually selected signals in each subspecies were associated with the most costly parasites. Associated parasites typically imposed a cost on their associated signal, with cost scaling with increasing parasite load (Hund et al 2020). In barn swallows, divergent sexual signals thus communicate information about local parasites.…”

Opposing dominance within a color gene block underpins hybrid plumage signal discordance

“…To be considered an 'honest' signal, plumage badges should be variable among counterparts of the same sex, correlate with quality or combat ability of the carrier (Rohwer 1975(Rohwer , 1982Rohwer and Rohwer 1978), and be a component of aggressive interactions among counterparts, either by dissuading combat among individuals of different status or triggering combats between individuals with similar badges (Rohwer 1975). Support for honest badges of status is often context dependent, but there is ample observational and experimental evidence to suggest that this mechanism of territorial signaling is widespread (e.g., (Studd and Robertson 1985;Møller 1987;Safran et al 2008;Hund et al 2020).…”