Host and brood parasite coevolutionary interactions covary with comparative patterns of the avian visual system

Abstract

In coevolutionary arms-races, reciprocal ecological interactions and their fitness impacts shape the course of phenotypic evolution. The classic example of avian host–brood parasite interactions selects for host recognition and rejection of increasingly mimetic foreign eggs. An essential component of perceptual mimicry is that parasitic eggs escape detection by host sensory systems, yet there is no direct evidence that the avian visual system covaries with parasitic egg recognition or mimicry. Here, we used eye size measurements collected from preserved museum specimens as a metric of the avian visual system for species involved in host–brood parasite interactions. We discovered that (i) hosts had smaller eyes compared with non-hosts, (ii) parasites had larger eyes compared with hosts before but not after phylogenetic corrections, perhaps owing to the limited number of independent evolutionary origins of obligate brood parasitism, (iii) egg rejection in hosts with non-mimetic parasitic eggs positively correlated with eye size, and (iv) eye size was positively associated with increased avian-perceived host–parasite eggshell similarity. These results imply that both host-use by parasites and anti-parasitic responses by hosts covary with a metric of the visual system across relevant bird species, providing comparative evidence for coevolutionary patterns of host and brood parasite sensory systems.

Nest architecture influences host use by avian brood parasites and is shaped by coevolutionary dynamics

“…Obligate brood parasitic bird species appear to target those species that build open cup nests. Targeting host species with open cup nests is akin to brood parasites targeting species with poorer visual acuity, whereby hosts have relatively smaller eyes than non-hosts; this may mean that hosts are less able to spot foreign eggs in their nests [72]. Although parasites may target host species with open cup nests because those nests are relatively accessible to egg-laying females, it follows that open-nesting host species should be expected to employ other tactics to reduce their chances of being parasitized.…”

Host learning selects for the coevolution of greater egg mimicry and narrower antiparasitic egg-rejection thresholds

“…Accordingly, increasing avian-perceptual mimicry by brood parasites is positively related to the experimental rejection of model egg colors from the nests by the respective host species ( Stoddard & Stevens, 2010 , 2011 ). Such behavioral defenses are also paralleled by the evolution of greater sensitivity of the avian visual system (e.g., greater relative eye sizes) in some of these more-rejecting host species ( Ausprey & Hauber, 2021 ). However, it has remained empirically unclear whether learning is involved in the antiparasitic defenses of host species since we are faced with mixed evidence for a role of learning in the experimental literature for the ontogenetic shifts in hosts’ egg rejection behaviors (e.g., no: Amundsen et al, 2003 ; yes: Lotem et al, 1995 ; Molina-Morales et al, 2014 ; Moskat et al, 2014 ).…”