The Common Cuckoo (Cuculus canorus) is the only widely spread brood parasite in Europe. It is a successful species in the sense that it has already parasited most (perhaps all?) of the suitable host species all over Europe. On the other hand parasitised hosts during the contact with the Cuckoo developed antiparasite defence against this brood parasite, in which discrimination of the foreign egg seems to be the most important and effective way in reducing the negative consequences (“costs”) of parasitism on hosts’ reproduction. In egg discrimination the cognitive process of egg recognition is followed by egg rejection with any of the available methods (e.g. egg burial, nest desertion, egg ejection). However, each of these rejection methods cannot be restricted to brood parasitism, they seem to be more general behaviours than simple antiparasite adaptations. E.g. egg burial is the continuation of nest-building behaviour, nest desertion may occur from several reasons, and egg ejection shows high similarity with nest cleaning, but the usage of these behavioural elements in the rejection of Cuckoo eggs seems to be highly effective. In the present paper the relationship between the Cuckoo and its European hosts is reviewed, in the light of the coevolutionary arms race hypothesis and its variants. Generally, a metapopulation structure of the host gives the chance for a longstanding coevolutionary process between a host species and the Cuckoo, especially when there is immigration from unparasitised, highly reproductive host populations (“sources”) to parasitised host populations, where host’s reproduction rate is low (“sinks”). However, there is a little knowledge on how the arms race comes to an end.
Coevolutionary dynamics allow revealing ongoing microevolutionary processes and adaptations. Interactions between obligate avian brood parasites and their hosts are suitable systems for the study of coevolution. This fascinating subject has interested both scientists and the common man for decades, but there are still many unanswered questions. One of the main puzzles is the apparent imperfect rejection behaviour against parasite eggs among hosts of brood parasites leading to a situation where many hosts experience severe costs of parasitism, which dramatically reduce their fitness. In order to lower these costs, hosts are expected to evolve counteradaptations against parasitism. However, many host species show no rejection or only intermediate rejection rates against non-mimetic parasite eggs. In this review we consider several hypotheses set out to explain this phenomenon, and then we link these hypotheses with a consideration of various sources that can influence decision-making when hosts are faced with the possibility that a parasite egg is present in their nest.
The breeding behavior of Common Cuckoo Cuculus canorus females was studied in detail by individual marking, radio-tracking, and automatic recording of radio signals. A total of 132 female cuckoos was captured, and radio transmitters were attached to 44 of them. The female cuckoos parasitised three different types of hosts: Azure-winged Magpies Cynopica cyane, Great Reed Warbler Acrocephalus arundinaceus and Bull-headed Shrike Lanius bucephalus. Female cuckoos using magpie hosts were radio-tracked for a total of 131.1 hours, and females using warbler hosts were radio-tracked for a total of 142.1 hours. The total time for cuckoos using shrike hosts was 12.6 hours. Female cuckoos were found to have distinct breeding and feeding areas, which they commuted between every day. Dominant females maintained strict breeding site tenacity throughout the breeding season. Each female specialized on one host type, knew almost all of the host nests in their breeding areas, and laid eggs selectively among the nests. The reasons for commuting between breeding areas and feeding areas, and the existence of a dominance hierarchy among female cuckoos are discussed.
To clarify the influence of host aggression on the Common Cuckoo Cuculus canorus, the cuckoo's parasitic behaviour was compared between a new host, Azure-winged Magpie Cyanopica cyana, and an old host, Great Reed Warbler Acrocephalus arundinaceus. Magpies exhibited less aggression towards cuckoos than did the warblers, and hardly attacked cuckoos at the nest. Cuckoos spent longer in the vicinity of nests while parasitizing magpie nests than when parasitizing reed warbler nests; possibly because of the magpie's lower aggression. Cuckoos parasitized magpie nests later in the day than reed warblers, despite the lower aggression of the magpies. The effect of host aggression on cuckoo parasitic behaviour and the adaptive significance of parasitic behaviour are discussed.
Many studies revealed that parasitic young mostly emit signals that are used in parent-offspring communication of hosts, but sometimes not. The terms used to explain host manipulation signals are not unified, then presenting confusion. Here we propose a new categorization of signals used for parasitic manipulation. Host manipulative signals could roughly be divided into two patterns according whether a parasite exploits signals actually used in parent-offspring communication of hosts (signal exploitation) or not (sensory exploitation), in relation to particular selective pressures that parasites face, such as nestling discrimination by hosts or deficient stimulation by parasites to obtain sufficient food.
Avian brood parasites are virulent, both as adults and as nestlings, because they reduce the fecundity of their hosts. The extent of virulence varies widely, both within and between brood parasite species. Here I review previous explanations for variation in the harm that brood parasites inflict on their hosts, which focus largely on the benefits of virulence, and suggest that each hypothesis is in some way unsatisfactory. I then summarize the evidence that brood parasitic offspring experience costs when host young die. I argue that the virulent behaviours shown by brood parasites are exactly analogous to the virulence shown by pathogens. Both can experience benefits by damaging host fitness, but they come at a price. I suggest that the trade-off hypothesis, developed with some success for understanding the evolution of virulence in pathogens, ought to be adopted in future theoretical and empirical work on the evolution of virulence in brood parasites.
It has been suggested that parasitic interactions in general result in co-evolutionary arms races where parasites and hosts evolve adaptive behaviours and traits to maximize their fitness in a conflicting manner. Avian brood parasitism provides an ideal system for the study of such co-evolutionary interactions. In this paper I show and discuss possible consequences of the co-evolutionary arms race inherent in avian brood parasitism, especially focusing on egg appearance, a key factor for the reproduction of both hosts and parasites. In such an arms race, hosts evolve the ability to recognize and hence to reject dissimilar parasitic eggs, while parasites counter host defences by more closely mimicking their eggs. Egg mimicry by parasites might then be de-stabilized by hosts changing the appearance of their eggs, thus exposing the mimics. The evolutionary trajectory of the arms race varies depending on the specific detailed mode of interaction between parasite and host individuals. Mathematical modeling, as an important parallel approach to empirical study, helps point the way for further study of avian brood parasitism so as to better understand co-evolution in general.
The Malayan Night Heron Gorsachius melanolophus is a threatened species that inhabits the Yaeyama Island group in the extreme southwest of the Ryukyu Archipelago, southern Japan. The species' distribution in Japan, which has been poorly known, was surveyed on the basis of sound and sight records, and interviews. The species was confirmed to occur on Ishigaki, Iriomote, Kuroshima, Kohama, Taketomi, Hateruma, Yonaguni, Miyako, Kurima, and Tarama islands. This range is wider than expected and records were independent of the area of islands. The past underestimation of the species' range was likely to have been the result of a lack of research effort and the unremarkable ecology and morphology of the species. The population density was found to be higher on Iriomote Is., covered with abundant forest, than on Ishigaki Is. with more degraded forests. Despite the wider than previously thought range, its range is still not very extensive in Japan; furthermore, increasing predators and introduced competitors may well endanger the population in the near future.
Bombax ceiba is a deciduous tree that experiences leaf fall, flowering and fruiting events during the dry season and leaf flushing during the rainy season. It produces open, red, cup-shaped, hermaphrodite, nectar rich flowers, which are pollinated by bees, birds, and bats. Some bird species, squirrels and monkeys eat floral parts or whole flowers on a daily basis. Such florivory is detrimental to the reproductive success of B. ceiba as it is an obligate outcrosser for which only flower to flower visits between conspecific trees result in cross-pollination and subsequent fruit set. Very few fruits are produced per tree, but each fruit contains numerous seeds. Ripe, dry fruits dehisce and seed dispersal is by wind during the dry season.
Dominant-subordinate relationship among eight species was investigated at the individual level in mixed, winter flocks of birds in Hokkaido, Japan. In five pairs of species, some individuals of averagely smaller species always dominated those of averagely larger species on average, large species. The characteristics of individuals causing dominance reversal were examined for body size, sex and residency for each pair of individuals. Among individuals of Nuthatch Sitta eurpaea and Japanese Pygmy Woodpecker Dendrocopos kizuki, in which body size largely overlapped and both were residents, their dominance was perfectly related to body size. Between species for which body size did not overlap, i.e., Marsh Tit Parus palustris and Great Tit P. major, and Great-spotted Woodpecker D. major and two larger woodpecker species (White-backed Woodpecker D. leucotos and Grey headed Woodpecker Picus canus), resident males of small species often dominated immigrants of large species. This result can be due to site- or sex-related aggressiveness of individuals.
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