Model eggs fail to detect egg recognition in host populations after brood parasitism is relaxed

Abstract

Background: Obligate 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. Results: Here, 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. Conclusions: Our 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.

Egg rejection and egg recognition mechanisms in Oriental Reed Warblers

“…Successful nest parasitism results in significant reproductive losses to the host, prompting the host to evolve a range of antiparasitic strategies (Davies 2000;Soler 2014). Egg recognition and egg rejection are among the most common antiparasitic strategies and are important indicators of host adaptation to nest parasitism (Davies and Brooke 1989a;Moksnes et al 1991b;Soler et al 2017;Yang et al 2020Yang et al , 2021. For example, in cuckoo parasitic systems, bird species lacking a history of cuckoo parasitism has low or no egg recognition ability, whereas cuckoo hosts often have varied egg recognition abilities (Davies and Brooke 1989a, b;Moksnes et al 1991a, b).…”

Egg Rejection and Nest Sanitation in an Island Population of Barn Swallows (Hirundo rustica): Probability, Response Latency, and Sex Effects

“…The population of Hainan Island in this study was exposed to higher species diversity of parasitic cuckoo than the northern population [ 31 ], and no cases of natural parasitism were observed in either of these two populations. However, this does not indicate that the intensity of selection pressure from parasitism is similar between these populations because historical contact between parasites and hosts is responsible for the long-term maintenance of egg recognition in hosts [ 29 , 32 , 33 ]. Therefore, the level of egg recognition may be regarded as a more suitable way to evaluate host response to selection pressure.…”

Beyond genes-for-behaviour: the potential for genomics to resolve questions in avian brood parasitism

“…Behavioural experiments have revealed spatial correlations between host and parasite traits (e.g. reed warblers vs. common cuckoo: [133][134][135][136]; magpies vs. great spotted cuckoo: [137]; prinias and parrotbills vs. common cuckoo: [138,139], providing evidence for hot spots as well as cold spots where parasitism is absent and defences vary, but we lack quantitative estimates of the strength of selection and trait remixing at the genomic level. These estimates are essential [140,141] to explain how coevolutionary interactions persist in time [142] There have been some attempts to quantify gene flow and local allele frequencies of a putative candidate marker for egg rejection in magpies [47], but this is where studies on brood parasitism, and tests of GMT for behavioural coevolution more broadly, have hit a stumbling block.…”