Speciation is associated with changing ornamentation rather than stronger sexual selection

Abstract

Although sexual ornamentation mediates reproductive isolation, comparative evidence does not support the hypothesis that stronger sexual selection promotes speciation. Prior analyses have neglected the possibility that decreases in ornamentation may also promote speciation, such that both increases and decreases in the strength of sexual selection and associated changes in ornamentation promote speciation. To test this hypothesis, we studied color ornamentation in one of the largest and fastest avian radiations, the estrildid finches. We show that more ornamented lineages do not speciate more, even though they tend to have faster rates of ornamental evolution, whereas changes in ornamentation (i.e., increases or decreases) are associated with speciation. This indicates that divergence in sexually selected ornamentation, rather than stronger sexual selection, promotes or is otherwise associated with speciation. We also show that gregariousness and investment in reproduction are related to the elaboration of some ornamental traits, suggesting ecological influences on speciation mediated by ornamentation. We conclude that past work focusing specifically on the strength of sexual selection may have greatly underestimated the importance of sexual ornamentation for speciation.

Multimodal signalling in estrildid finches: song, dance and colour are associated with different ecological and life‐history traits

“…For detailed methods on these metrics, see Gomes et al . (). Data on male colour ornamentation were available for 132 species.…”

“…For this, we used body size data from Gomes et al . (), which comprises the first principal component of a principal component analysis on morphometric measures (tarsus length, bill length and depth, tail and wing lengths, all log 10 ‐transformed) from skins of estrildid species. These residual peak frequencies, in log 10 Hz, are henceforth referred to as sound frequency corrected for body size .…”

“…See Gomes et al . () for methods used to quantify these traits, and for the rationale for their potential relationships with sexual signals (see table in Gomes et al ., ). Unlike Gomes et al .…”

“…Unlike Gomes et al . (), we did not use the trait “diet” (extent of granivory), because this trait has a predicted relationship only with colour ornamentation, and not song or dance.…”

In love and war: The morphometric and phylogenetic basis of ornamentation, and the evolution of male display behavior, in the livebearer genus Poecilia

“…As increases in ornamentation are known to be associated with speciation (Gomes et al. ), co‐option of signals for courtship may lead to exaggeration of the signaling structure in speciose clades, although little empirical data exist on whether dual‐utility traits reach larger sizes than do pure ornaments or pure armaments (Outomuro et al. ).…”