Comparative population genomics reveals convergent adaptation across independent origins of avian obligate brood parasitism.

Parental care evolved as a strategy to enhance offspring survival at the cost of reduced adult survival and fecundity. While 99% of bird species provide parental care, obligate brood parasites circumvent this trade-off by exploiting the parental behaviours of other species. This radical life-history shift occurred independently seven times in birds, offering an outstanding opportunity to test for convergent adaptation. To investigate genomic adaptations underlying this transition, we analyse population resequencing data from five brood-parasitic species across three independent origins of brood parasitism-three parasitic finches, a honeyguide and a cowbird-alongside related non-parasitic outgroups. Using the McDonald-Kreitman framework, we find evidence for adaptation in genes involved in sperm function in multiple parasitic clades, but not in the matched, non-parasitic outgroups, consistent with evidence for increased male-male competition in parasitic lineages following the loss of parental care. We also detect selective sweeps near genes associated with nervous system development in parasitic lineages, perhaps associated with improved spatial cognition that aids brood parasites in locating and monitoring host nests. Finally, we detect more selective sweeps in the genomes of host specialist brood parasites as compared to non-parasitic outgroups, perhaps reflecting ongoing host-parasite coevolutionary arms races.