Giant Steps From Small Thefts: Bypassing Constraint by Trait Co-option

Abstract

Species interactions can provide organisms with access to novel traits without having to evolve these traits themselves. Viewing such interactions as an alternative to trait evolution offers a new perspective to understanding species interactions—organisms can bypass evolutionary constraints and gain access to adaptive traits by co-opting them from other species. I explore the costs and benefits of trait co-option and generate 10 hypotheses for when and where selection might favor the co-option of traits as an alternative to typical trait evolution (Chapter 2). Next, I examine a possible case of trait co-option in nature, involving numerous species of birds that use aromatic seed-material from plants in the genus Eriocephalus to construct their nests (Chapter 3). I describe the bird-Eriocephalus interaction and focus on a single species of bird, the Karoo prinia (Prinia maculosa), which uses large amounts of Eriocephalus in their nests. Although previous work has suggested that both birds and plants benefit from their interaction, prinias gathered large quantities of E. racemosus seed fluff but avoided seeds, providing limited dispersal benefits to the plant. The time and effort invested into gathering fluff suggests that this material benefits prinias. I test two hypotheses for the fitness benefits of Eriocephalus material in bird nests—that chemical compounds reduced levels of nest ectoparasites (Chapter 4) and rates of nest predation by a specialist predator, the rhombic egg-eating snake (Dasypeltis scabra) (Chapter 5). Chemical compounds reduced levels of nest ectoparasites by functioning as either a deterrent to gravid female parasites, or as an ovicide. I found no evidence that chemical compounds reduced rates of nest predation from egg-eating snakes. Overall, these observations and experiments suggest that Karoo prinias benefit from co-opting Eriocephalus compounds for use in nest construction, likely at the expense of the plant. Overall, interactions similar to those involving prinias and Eriocephalus are widespread in nature, yet rarely are they viewed as an alternative to trait evolution. Viewing species interactions from the perspective of trait co-option and evolution has the potential to elucidate general patterns for when and which species should interact, broadening our understanding of nature and biodiversity.