Synergistic selection regimens drive the evolution of display complexity in birds of paradise

Abstract

Integrated visual displays that combine gesture with colour are nearly ubiquitous in the animal world, where they are shaped by sexual selection for their role in courtship and competition. However, few studies assess how multiple selection regimens operate on different components of these complex phenotypes on a macroevolutionary scale. Here, we study this issue by assessing how both sexual and ecological selection work together to influence visual display complexity in the birds of paradise. We first find that sexual dichromatism is highest in lekking species, which undergo more intense sexual selection by female choice, than non-lekking species. At the same time, species in which males directly compete with one another at communal display courts have more carotenoid-based ornaments and fewer melanin ornaments. Meanwhile, display habitat influences gestural complexity. Species that dance in the cluttered understorey have more complex dances than canopy-displaying species. Taken together, our results illustrate how distinct selection regimens each operate on individual elements comprising a complex display. This supports a modular model of display evolution, wherein the ultimate integrated display is the product of synergy between multiple factors that select for different types of phenotypic complexity.

Habitat structure drives the evolution of aerial displays in birds

“…Passerine birds (order Passeriformes) perform a particularly diverse set of sexual displays to attract mates or out‐compete same‐sex rivals for mates: from the simple, static ‘bill‐up' posture of the silver‐beaked tanager ( Ramphocelus carbo ; Isler & Isler, 1987 in Schulenberg, ) to the most complex, skilful dances performed by manakins (Prum, ) and birds‐of‐paradise (Miles & Fuxjager, ). Passerines also exhibit high variability in habitat preferences, having colonized environments as diverse as Arctic tundras, tropical rainforests and arid deserts (del Hoyo, Elliott, Sargatal, Christie, & de Juana, ).…”

“…While these case studies belong in the sensory drive realm (Cummings & Endler, 2018) and may be indicative of an evolutionary link between habitat and display, a phylogenetic comparative approach is the most appropriate way to uncover such a link (Harvey & Pagel, 1991). Phylogenetic comparative evidence accumulated to date suggests that (micro)habitat may influence aspects of avian and saurian displays such as repertoire size (Ligon et al, 2018;Miles & Fuxjager, 2018;Ord, Blumstein, & Evans, 2002) and repetition pattern (Ord & Martins, 2006; but see Perez et al, 2012). However, the role of habitat as a force that determines which elements of display repertoires should evolve -rather than how many elements -has yet to be demonstrated.…”

“…Passerine birds (order Passeriformes) perform a particularly diverse set of sexual displays to attract mates or out-compete samesex rivals for mates: from the simple, static 'bill-up' posture of the silver-beaked tanager (Ramphocelus carbo;Isler & Isler, 1987in Schulenberg, 2018 to the most complex, skilful dances performed by manakins (Prum, 1990) and birds-of-paradise (Miles & Fuxjager, 2018).…”

“…Recent phylogenetic comparative analyses have shed light on the evolution of passerine displays at the family level, with multiple factors influencing their evolution. For instance, latitude (Icteridae; Miles, Cheng, & Fuxjager, 2017), display height (Paradisaeidae; Ligon et al, 2018;Miles & Fuxjager, 2018), body size and brood parasitism (Estrildidae; Soma & Garamszegi, 2015) all have been found to influence some aspect of gestural displays in passerine families. Such diversity of clade-specific evolutionary forces might lead one to believe that the structure of passerine sexual displays is all but unpredictable.…”

Evolution and function of multimodal courtship displays

“…In the Montezuma oropendolas (Psarocolius montezuma), males synchronize the loudest note of their song with a specific visual courtship display (the bow and wing-spread), which could indicate the quality of an individual motor's skills (Miles & Fuxjager, 2018a, 2018b. Signal synchronization could itself indicate good neural control.…”