Discordancy or template-based recognition? Dissecting the cognitive basis of the rejection of foreign eggs in hosts of avian brood parasites

Abstract

SUMMARYMany avian hosts have evolved antiparasite defence mechanisms, including egg rejection, to reduce the costs of brood parasitism. The two main alternative cognitive mechanisms of egg discrimination are thought to be based on the perceived discordancy of eggs in a clutch or the use of recognition templates by hosts. Our experiments reveal that the great reed warbler (Acrocephalus arundinaceus), a host of the common cuckoo (Cuculus canorus), relies on both mechanisms. In support of the discordancy mechanism, hosts rejected their own eggs (13%) and manipulated ('parasitic') eggs (27%) above control levels in experiments when manipulated eggs were in the majority but when clutches also included a minority of own eggs. Hosts that had the chance to observe the manipulated eggs daily just after laying did not show stronger rejection of manipulated eggs than when the eggs were manipulated at clutch completion. When clutches contained only manipulated eggs, in 33% of the nests hosts showed rejection, also supporting a mechanism of template-based egg discrimination. Rejection using a recognition template might be more advantageous because discordancy-based egg discrimination is increasingly error prone with higher rates of multiple parasitism.

Pattern recognition algorithm reveals how birds evolve individual egg pattern signatures

“…It is interesting to note that the highly effective pattern signatures of the brambling, red-backed shrike and garden warbler are characterized by only low-to-moderate visual density. Perhaps recognition based on template learning, believed to be the rule among highly discriminating hosts like these 39 , works best if the signature is not overly complex or dense. Future experiments could test this idea by manipulating the visual complexity of egg pattern signatures and determining how this affects recognition and rejection behaviour in the field.…”

Brood parasites lay eggs matching the appearance of host clutches

“…A number of studies have been published on the mechanisms of own egg recognition in cuckoo hosts [76][77][78][79][80][81][82][83] and some of them suggest that birds possess an internal template of their own eggs [81][82][83]. So, one may expect that cuckoos may exhibit such abilities as well.…”

“…Owing to the elusive lifestyle of the cuckoo, however, the direct mechanism of how cuckoo females know the appearance of their own eggs remains enigmatic. Similar to the hosts, the memory template of their own eggs may comprise an inherited and a learned component acquired during the first egg laying [79]. The idea mentioned by Antonov et al [32] that the first cuckoo egg is laid somewhere in isolation seems highly unlikely [5].…”

Multiple mechanisms of egg recognition in a cuckoo host

“…Furthermore, an individual host also presents variable reactions toward alien eggs with different mimicry under different conditions (Avilés et al 2005;Holen and Johnstone 2006;Servedio and Hauber 2006). Therefore, consistency and flexibility coexist in the anti-parasite egg Communicated by N. Clayton * Wei Liang liangwei@hainnu.edu.cn * Xin Lu luxinwh@163.com rejection behavior of hosts, which implies that both genetic and learning mechanisms may be involved (Lotem et al 1995;Hauber and Sherman 2001;Martín-Gálvez et al 2006;Moskát et al 2010). So far, four kinds of mechanisms have been proposed to explain egg recognition behavior in hosts, including (1) direct comparison, (2) memory-based template, (3) onset of laying, and (4) phenotype distribution.…”