How a bird is an island

Abstract

Replicate adaptive radiations occur when lineages repeatedly radiate and fill new but similar niches and converge phenotypically. While this is commonly seen in traditional island systems, it may also be present in host-parasite relationships, where hosts serve as islands. In a recent article in BMC Biology, Johnson and colleagues have produced the most extensive phylogeny of the avian lice (Ischnocera) to date, and find evidence for this pattern. This study opens the door to exploring adaptive radiations from a novel host-parasite perspective.

Figure 1

Two types of species radiation in avian feather lice. (a) Convergent adaptive radiation. After colonizing a new host, feather lice diversify to exploit the same niche via similar morphotypes. In this example from Johnson et al. [4], body lice on Tinamous diversify into head and wing ecotypes and wing lice on Parrots diversify into head and body lice. (b) Non-adaptive radiation. In this example from Johnson et al., a head lice lineage appears to have colonized several orders of birds (Cuculiformes, yellow; Falcinoformes, blue; Piciformes, red). This could also represent an adaptive radiation as species would still be entering a novel environment - a new host.