Abstract
BackgroundObligate brood parasites exert strong selective pressure on target hosts. In response, hosts typically evolve anti-parasitism strategies, of which egg recognition is one of the most efficient. Generally, host egg-recognition capacity is determined using model eggs. Previous studies have shown that some host species, which are capable of detecting parasite eggs, do not reject model eggs. However, it is unknown that whether the reaction to model eggs varies among distinct populations of the same host in relation to the degree of parasitism pressure.ResultsHere, we compared the rejection frequencies of model eggs and real eggs between mainland and island populations of the plain prinia (Prinia inornata), which are respectively sympatric and allopatric with their brood parasite, the common cuckoo (Cuculus canorus). Our results indicated that the mainland and island populations rejected real eggs at similar rates, but rejected model eggs, which were similar in size to real eggs but heavier, at significantly different rates: the island population rejected fewer model eggs, possibly because the rejection motivation of this population was lower due to absence of parasitism.ConclusionsOur results indicated that some factors affecting the decision to reject, such as rejection motivation, varied according to the degree of parasitism pressure, and thus influenced the frequency of egg rejection. Furthermore, our results suggested that model eggs should be used with caution in comparative studies of egg recognition abilities among species or populations subjected to different intensities of brood parasitism. That is, model eggs may fail to accurately detect egg recognition in host populations with little to no risk of parasitism.
Highlights
Obligate brood parasites exert strong selective pressure on target hosts
Egg recognition by brood-parasite hosts is typically assayed using model eggs, which are generally made of polymer clays; egg recognition behaviors are generally considered confirmed if the model egg is rejected by the host [1, 4, 5]
Two models were used because egg type and egg size represented two different methods of Results Both the mainland and the Taiwanese plain prinia populations accepted all conspecific eggs (n = 12 for both populations), and consistently rejected prinia eggs: 70.83% were rejected by the mainland population, and 71.43% were rejected by the island population
Summary
Obligate brood parasites exert strong selective pressure on target hosts. Hosts typically evolve anti-parasitism strategies, of which egg recognition is one of the most efficient. Previous studies have shown that some host species, which are capable of detecting parasite eggs, do not reject model eggs. Obligate brood parasites are birds that do not build nests, incubate eggs, or rear their own offspring; instead, these birds transfer such duties to other bird species, which are used as hosts [1, 2]. Natural selection favors hosts that have evolved anti-parasite adaptations, of which egg recognition is one of the most general and efficient [2]. Model eggs are difficult for small host species to reject, as the bills of these hosts are too small to grasp the model egg; such species must reject model eggs using
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