Strategic Variation in Mobbing as a Front Line of Defense against Brood Parasitism (original) (raw)
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Cuckoos versus hosts in insects and birds: adaptations, counter-adaptations and outcomes
Biological Reviews
Avian parents and social insect colonies are victimized by interspecific brood parasites-cheats that procure costly care for their dependent offspring by leaving them in another species' nursery. Birds and insects defend themselves from attack by brood parasites; their defences in turn select counter-strategies in the parasite, thus setting in motion antagonistic co-evolution between the two parties. Despite their considerable taxonomic disparity, here we show striking parallels in the way that co-evolution between brood parasites and their hosts proceeds in insects and birds. First, we identify five types of co-evolutionary arms race from the empirical literature, which are common to both systems. These are: (a) directional co-evolution of weaponry and armoury; (b) furtiveness in the parasite countered by strategies in the host to expose the parasite; (c) specialist parasites mimicking hosts who escape by diversifying their genetic signatures; (d) generalist parasites mimicking...
Testing for correlations between behaviours in a cuckoo host: why do host defences not covary?
Animal Behaviour, 2014
Fitness costs associated with brood parasitism have led host species to evolve several lines of defence. The first two lines of defence, aggression against adult parasites and egg rejection, are present at varying levels in almost all hosts. However, it remains unclear how these two fundamental defences covary at host individual level, with previous studies suggesting both positive and negative correlations. A theoretically critical yet empirically untested scenario is that variation in host antiparasite behaviour may relate to individual variation in host behavioural types or personalities. Here we examined whether host aggression against adult brood parasites and egg rejection behaviour were correlated with host behaviours displayed outside the context of brood parasitism. We selected the great reed warbler, Acrocephalus arundinaceus, a favourite cuckoo, Cuculus canorus, host as a suitable model. Only females reject foreign eggs and show high individual repeatability of both aggression towards cuckoos and nest guarding. We found that female behaviours in different situations (nest guarding, nest defence, handling in the net) were strongly correlated with each other. This is the first empirical evidence on correlation between individually consistent antiparasite adaptation (female nest defence) and behaviours that are not directly related to brood parasitism. In contrast, egg rejection/acceptance responses and latency to these responses did not correlate with any of the female defence/guarding behaviours and behaviour during handling. Proximately, this may be because nest defence and egg recognition represent cognitively and behaviourally completely different tasks. These patterns were not affected by female mating status in this polygynous cuckoo host. We hypothesize that differences in host behavioural types, rather than host egg discrimination ability, may predict host nest defence behaviour against adult brood parasites in general. Ó
A parasite in wolf's clothing: hawk mimicry reduces mobbing of cuckoos by hosts
The reciprocal interactions between brood parasites and their hosts provide models for studying coevolution. For example, where hosts have evolved egg or chick discrimination, brood parasites have evolved mimicry of host eggs or chicks. Here, we suggest that there is another form of mimicry by cuckoos. A previous study has shown that naive small birds, with no evolutionary history of brood parasitism, are as afraid of adult common cuckoos Cuculus canorus as of sparrowhawks Accipiter nisus because of their physical resemblance. However, it has yet to be shown whether host species regard cuckoos as hawk like, or how hawk resemblance might benefit the cuckoo. We provide the first evidence that hawk resemblance involving barred underparts is an adaptive brood parasitic trait. We show by plumage manipulations of taxidermic models that reed warbler (Acrocephalus scirpaceus) hosts are more reluctant to approach and mob common cuckoos with barred rather than unbarred underparts. Our results indicate that reed warblers are more aggressive toward cuckoos that appear less hawk like and that hence, hawk resemblance facilitates access to host nests. Therefore, we suggest that cuckoos employ 2 forms of mimicry: To enhance parasitic laying, cuckoo adults are Batesian mimics of hawks, appearing dangerous to adult host survival, when in fact they could be safely attacked. At later stages, cuckoo eggs and chicks are aggressive mimics, appearing harmless but in fact dangerous to host reproduction. These strategies are each countered by host discrimination, providing the means for distinct coevolutionary arms races at successive stages of the host nesting cycle.
Social Transmission of a Host Defense Against Cuckoo Parasitism
Science
Coevolutionary arms races between brood parasites and hosts involve genetic adaptations and counter-adaptations. However, hosts sometimes acquire defenses too rapidly to reflect genetic change. Our field experiments show that observation of cuckoo (Cuculus canorus) mobbing by neighbors on adjacent territories induced reed warblers (Acrocephalus scirpaceus) to increase the mobbing of cuckoos but not of parrots (a harmless control) on their own territory. In contrast, observation of neighbors mobbing parrots had no effect on reed warblers’ responses to either cuckoos or parrots. These results indicate that social learning provides a mechanism by which hosts rapidly increase their nest defense against brood parasites. Such enemy-specific social transmission enables hosts to track fine-scale spatiotemporal variation in parasitism and may influence the coevolutionary trajectories and population dynamics of brood parasites and hosts.
Evicting cuckoo nestlings from the nest: a new anti-parasitism behaviour
Biology Letters, 2009
As avian brood parasitism usually reduces hosts' reproductive success, hosts often exhibit strong defence mechanisms. While such host defences at the egg stage (especially egg rejection) have been extensively studied, defence mechanisms at the nestling stage have been reported only recently. We found a previously unknown anti-parasitism behaviour in the large-billed Gerygone, which is a host species of the little bronze-cuckoo, a host-evicting brood parasite. The hosts forcibly pulled resisting nestlings out of their nests and dumped them. Although it has been suggested that defence mechanisms at the nestling stage may evolve when host defence at the egg stage is evaded by the parasite, the studied host seems to lack an anti-parasitism strategy at the egg stage. This suggests that the evolutionary pathway may be quite different from those of previously studied cuckoo–host systems. Future research on this unique system may give us new insights into the evolution of avian brood pa...
Frontiers in Zoology, 2014
Background: Why have birds evolved the ability to reject eggs? Typically, foreign egg discrimination is interpreted as evidence that interspecific brood parasitism (IP) has selected for the host's ability to recognize and eliminate foreign eggs. Fewer studies explore the alternative hypothesis that rejection of interspecific eggs is a by-product of host defenses, evolved against conspecific parasitism (CP). We performed a large scale study with replication across taxa (two congeneric Turdus thrushes), space (populations), time (breeding seasons), and treatments (three types of experimental eggs), using a consistent design of egg rejection experiments (n = 1057 nests; including controls), in areas with potential IP either present (Europe; native populations) or absent (New Zealand; introduced populations). These comparisons benefited from the known length of allopatry (one and a half centuries), with no gene flow between native and introduced populations, which is rarely available in host-parasite systems. Results: Hosts rejected CP at unusually high rates for passerines (up to 60%). CP rejection rates were higher in populations with higher conspecific breeding densities and no risks of IP, supporting the CP hypothesis. IP rejection rates did not covary geographically with IP risk, contradicting the IP hypothesis. High egg rejection rates were maintained in the relatively long-term isolation from IP despite non-trivial rejection costs and errors.
Experimental shift in hosts' acceptance threshold of inaccurate-mimic brood parasite eggs
Biology Letters, 2006
Hosts are expected to evolve resistance strategies that efficiently detect and resist exposure to virulent parasites and pathogens. When recognition is not error-proof, the acceptance threshold used by hosts to recognize parasites should be context dependent and become more restrictive with increasing predictability of parasitism. Here, we demonstrate that decisions of great reed warblers Acrocephalus arundinaceus to reject parasitism by the common cuckoo Cuculus canorus vary adaptively within a single egg-laying bout. Hosts typically accept one of their own eggs with experimentally added spots and the background colour left visible. In contrast, hosts reject such spotted eggs when individuals had been previously exposed to and rejected one of their own eggs whose background colour had been entirely masked. These results support patterns of adaptive modulation of antiparasitic strategies through shifts in the acceptance threshold of hosts and suggest a critical role for experience i...
The adaptiveness of defence strategies against cuckoo parasitism
2002
Host bird species of the Eurasian Cuckoo, Cuculus canorus, often display eggdiscrimination behaviour but chick-rejection behaviour has never been reported. In this paper, we analyse a host-cuckoo association in which both population dynamics and evolutionary dynamics are explored in a discrete-time model. We introduce four host types, each with their own defence behaviour, displaying either egg or chick rejection, neither or both, We also introduce fitness functions for each of these host types. Although we can characterize the long term behaviour in many cases by a simple heuristic argument which is in accordance with common views in ecology, there are a number of other phenomena that are not explained within this framework: we describe stable oscillatory behaviour and coexistence of two defensive host types. We analyse the scenarios in which chick rejection may establish itself and give a first explanation as to why this defence trait has never been recorded in nature. We find that chick rejectors generally are at an intrinsic disadvantage with respect to a host type that rejects eggs. Hosts benefit more from rejecting cuckoo eggs than cuckoo chicks, and our model suggests that this is chiefly responsible for the absence of chick rejection. Moreover, even though it seems that chick rejection must be useful as an extra defence, it is shown that hosts with both defence strategies are less likely to establish themselves in competition with egg-rejectors than