A New Round of Arms Race

The advance in breadth and depth of international arms control and disarma- ment has its great significance in eliminating the threat of a nuclear war and pro-pelling the world situation onward in the direction of relaxation of tension. At thesame time, a negative trend also claims our attention. The strong military powerslike the United States are contending among themselves for retaining their militarysuperiority and seizing military sci-tech commanding heights while using

Reviewing 30 years of studies on the Common Cuckoo:accumulated knowledge and future perspectives

In Europe, eggs of the Common Cuckoo (Cuculus canorus) have been found in more than 125 different host species. However, very few species are frequently parasitized. The Cuckoo is divided into several distinct races termed gentes. Females of each gens specialize in parasitizing a particular host species. More than 20 such gentes are recognized in Europe. Each female Cuckoo lays eggs of constant appearance. Most gentes can be separated based on their distinct egg types, which in many cases mimic those of their hosts. Different gentes may occur in sympatry or may be separated geographically. Some gentes may occur in restricted parts of the host’s distribution area. These patterns raise some fundamental questions like: Why are some passerine species preferred as hosts while others are not? Why does a host population consist of individuals either accepting or rejecting Cuckoo eggs? Why is there marked variation in egg rejection behavior between various host populations? How distinct and host-specialized are Cuckoo gentes? These questions are discussed in relation to existing knowledge and future perspectives.

Cuckoo parasitism on two closely-related Acrocephalus warblers in distant areas:a case of parallel coevolution?

Common Cuckoos(Cuculus canorus) parasitize nests of small passerines.e Cuckoo chicks cause the death of their nest-mates when evicting eggs or nestlings from the nests;consequently,hosts su er from a high loss of reproduction.Host adaptations against parasitism,e.g.,by egg discrimination behavior,and cuckoo counter-adaptations to hosts,e.g.,by mimetic eggs,are often regarded as a result of the arms race between the two interacting species.In Hungary Great Reed Warblers(Acrocephalus arundinaceus) are the main hosts of cuckoos,su ering from heavy parasitism(ca.40-65%).e Oriental Reed Warbler(A.orientalis),formerly a subspecies of the Great Reed Warbler(A.a.orientalis),is also a highly parasitized host in Japan(25-40%).We compared main characteristics of Cuckoo parasitism in these two distant areas from the Western and Eastern Palearctic by comparing cuckoo egg mimicry.We measured color characteristics of host and parasitic eggs by spectrophotometer.Visual modeling revealed lower chromatic distances between Cuckoo and host eggs in Hungary than in Japan,but high variation both in host and Cuckoo eggs may cause matching problems in Hungary.Achromatic(brightness) di erence between host and Cuckoo eggs were lower in Japan than in Hungary,and it proved to be the most important factor a ecting egg rejection.Hosts rejected Cuckoo eggs at similar frequencies(37% and 35% in Hungary and Japan,respectively).Host adaptation,i.e.,egg rejection behavior,seems to be preceding Cuckoo counter-adaptations to hosts in Japan.We suggest that the Cuckoo-Great/Oriental Reed Warbler relationships developed in alternative ways in Japan and Hungary,and they represent di erent stages of their arms race.

Intra-clutch variation in egg appearance assessed by human vision does not relate to rejection of parasite eggs in Iberian Azure-winged Magpies

e coevolutionary arms race between cuckoos and their hosts predicts that low variation in egg features within a host clutch would facilitate discrimination of mimetic parasite eggs.Here,we experimentally examine this prediction by using arti cial and natural parasite eggs showing contrasting level of matching with host eggs.We quanti ed,based on human assessment,intra-clutch variation in egg appearance and egg discrimination in the Iberian Azure-winged Magpie(Cyanopica cyanus),a presumed former host of the Great Spotted Cuckoo(Clamator glandarius).Azure-winged Magpies rejected parasitic eggs in relation to their degree of dissimilarity with own eggs:Great Spotted Cuckoo model eggs were relatively more o en rejected(73.7%) than real Great Spotted Cuckoo eggs(44.4%) and the less contrasting conspeci c eggs(35.5%).Contrary to our predictions,we found that,irrespective of mimicry level of parasitic eggs,intra-clutch variation in host egg appearance did not di er signi cantly between rejecters and acceptors.We found,however,that individuals with higher variation in egg-size were almost signi cantly more prone to be rejecters than individuals showing lower variation in egg size.Our results do not support the hypothesis that the extent of intraclutch variation in egg discrimination varied with parasite egg mimicry in this particular system,and add to previous ndings suggesting that perhaps an increase in intra-clutch variation in egg appearance,rather than a decrease,might be advantageous when discriminating against non-mimetic Great Spotted Cuckoo eggs.

Sexual deception： Coevolution or inescapable exploitation？

Sexual deception involves the mimicry of another species＇ sexual signals in order to exploit behavioural routines linked to those signals. Known sexually deceptive systems use visual, acoustic or olfactory mimicry to exploit insects for preda- tion, cleptoparasitism and pollination. It is predicted that where sexual deception inflicts a cost on the receiver, a coevolutionary arms race could result in the evolution of discriminating receivers and increasingly refined mimicry. We constructed a conceptual model to understand the importance of trade-offs in the coevolution of sexually deceptive mimic and receiver. Four components examined were： the cost of mimicry, the cost to receiver for being fooled, the density of mimics and the relative magnitude of a mimicry-independent component of fitness. The model predicts that the exploitation of non-discriminating receivers by accurate signal mimicry will evolve as an evolutionary stable strategy under a wide range of the parameter space explored. This is due to the difficulty in minimising the costs of being fooled without incurring the cost of falsely rejecting real mating opportunities. In the model, the evolution of deception is impeded when mimicry imposes substantial costs for both sides of the arms race. Olfac- tory signals that are potentially cheap to produce are therefore likely to be more vulnerable to exploitation than expensive visual ornaments

Discrimination and ejection of eggs and nestlings by the fan-tailed gerygone from New Caledonia

Nestling rejection is a rare type of host defense against brood parasitism compared with egg rejection.Theoretically,host defenses at both egg and nestling stages could be based on similar underlying discrimination mechanisms but,due to the rarity of nestling rejector hosts,few studies have actually tested this hypothesis.We investigated egg and nestling discrimination by the fan-tailed gerygone Gerygone flavolateralis,a host that seemingly accepts nonmimetic eggs of its parasite,the shining bronze-cuckoo Chalcites lucidus,but ejects mimetic parasite nestlings.We introduced artificial eggs or nestlings and foreign gerygone nestlings in gerygone nests and compared begging calls of parasite and host nestlings.We found that the gerygone ejected artificial eggs only if their size was smaller than the parasite or host eggs.Ejection of artificial nestlings did not depend on whether their color matched that of the brood.The frequency of ejection increased during the course of the breeding season mirroring the increase in ejection frequency of parasite nestlings by the host.Cross-fostered gerygone nestlings were frequently ejected when lacking natal down and when introduced in the nest before hatching of the foster brood,but only occasionally when they did not match the color of the foster brood.Begging calls differed significantly between parasite and host nestlings throughout the nestling period.Our results suggest that the fan-tailed gerygone accepts eggs within the size range of gerygone and cuckoo eggs and that nestling discrimination is based on auditory and visual cues other than skin color.This highlights the importance of using a combined approach to study discrimination mechanisms of hosts.