Meeting Abstract
A host which has been targeted by an avian brood parasite can recover most of its potential fitness loss by ejecting the foreign egg(s) or offspring from its nest. The propensity for some hosts to engage in this behavior has put selective pressure on their parasites to evolve mimetic eggshells of the host’s color and maculation. In turn, hosts have counter-evolved increasingly more sophisticated detection methods such as narrowing visual discrimination thresholds or even using non egg-specific cues. However, multiple sensory and cognitive mechanisms acting simultaneously could theoretically interfere with one another and ultimately decrease egg rejection accuracy. Through an artificial parasitism protocol, we tested a host of the common cuckoo Cuculus canorus, the great reed warbler Acrocephalus arundinaceus’s response to 1, 3, or 5 simulated foreign eggs of varying color and uniformity. Using reflectance spectra of egg background coloration and avian perceptual modeling, we then estimated the sensory thresholds of this host. Rejection rates were positively related to the perceptual distance between own and foreign eggs in the nests in all treatments, but rejection thresholds were more permissive (error prone) both with greater proportions of foreign eggs and when the suite of foreign eggs were perceptually more variable within the nest. These results suggest that the evolution of host recognition of parasite mimicry has multiple trajectories regarding both the specific sensory and cognitive defense mechanisms underlying their recognition thresholds, and their vulnerability to parasitic counterstrategies.
