From ornament to armament or loss of function? Breeding plumage acquisition in a genetically monogamous bird

Abstract

The evolution of conspicuous male traits is thought to be driven by female mate choice or male-male competition. These two mechanisms are often viewed as distinct processes, with most studies focusing on female choice. However, both mechanisms of sexual selection can act simultaneously on the same trait (i.e., dual function) and/or interact in a synergistic or conflicting way. Dual-function traits are commonly assumed to originate through male-male competition before being used in female choice; yet, most studies focusing on such traits could not determine the direction of change, lacking phylogenetic information. We investigated the role of conspicuous male seasonal plumage in male-male competitive interactions in the purple-crowned fairy-wren Malurus coronatus, a cooperatively breeding bird. Male breeding plumage in most Malurus species is selected by female choice through extra-pair mate choice, but unlike its congeners, M. coronatus is genetically monogamous, and females do not seem to choose males based on breeding plumage acquisition. Our study shows that, within groups, subordinate males that were older, and therefore higher-ranked in the queue for breeder position inheritance, produced a more complete breeding plumage. In line with this, subordinate males that were older and/or displayed a more complete breeding plumage were more successful in competitively acquiring a breeder position. A role as a signal of competitive ability was experimentally confirmed by presenting models of males: in breeding colours, these received more aggression from resident breeder males than in nonbreeding colours, but elicited limited response from females, consistent with competitors in breeding plumage being perceived as a bigger threat to the breeder male. The role of the conspicuous breeding plumage in mediating male-male interactions might account for its presence in this genetically monogamous species. As phylogenetic reconstructions suggest a past female choice function in M. coronatus, this could represent a sexual trait that shifted functions, or a dual-function trait that lost one function. These evolutionary scenarios imply that intra- and intersexual functions of ornaments may be gained or lost independently and offer new perspectives in understanding the complex dynamics of sexual selection.

Evolutionary drivers of seasonal plumage colours: colour change by moult correlates with sexual selection, predation risk and seasonality across passerines

“…An example for these processes is found in Malurus fairy‐wrens. Seasonal plumage colours have been lost in two species, the lovely and white‐shouldered fairy‐wrens ( M. amabilis and M. alboscapulatus; Fan et al ). Both species have high annual survival rates (Leitão et al ) and live in the tropics, where predation risk on fairy‐wrens appears to be relatively low (Cain et al ) and where reduced seasonality may favour less well‐defined breeding schedules (Leitão et al ).…”

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

“…Furthermore, the combination of behavioral observations with ancestral state reconstructions should help fill in the gaps for phylogenies in which some species are known to use dual‐utility traits, and in which other species may have lost the trait function for courtship, as in Malurus fairy wrens (Fan et al. ).…”

“…Dual-utility displays have been found in members of several species-rich groups, such as auks (Jones and Hunter 1999), widowbirds (Andersson et al 2002), Old World sparrows (Griggio et al 2007), antbirds (Tobias et al 2011), darter fish (Zhou and Fuller 2016), and deer (Morina et al 2018); and phylogenetic analyses of ornamentation in speciose clades (such as poeciliids) can provide a greater picture of the processes by which trait co-option has occurred. Furthermore, the combination of behavioral observations with ancestral state reconstructions should help fill in the gaps for phylogenies in which some species are known to use dual-utility traits, and in which other species may have lost the trait function for courtship, as in Malurus fairy wrens (Fan et al 2018).…”

Persistent low avian malaria in a tropical species despite high community prevalence

“…PCFWs were sampled at multiple time periods over their lives [ n = 105 nestlings 7 days old, free-flying birds ranging from age 1–139 months (1st year, n = 516; 2nd year, n = 134; 3rd year, n = 68; >4th year, n = 91)]. Sex was identified by plumage characteristics or molecular based techniques (Griffiths et al, 1998, Fan et al, 2018).

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