Adaptáció, koevolúció és stabilitás a gazda-költésparazita kapcsolatokban = Adaptation, coevolution and stability in host-brood parasite relationships

A madarak költésparazitizmusa a gazdafaj és a költésparazita közötti koevolúció példái. A közismert kakukk (Cuculus canorus) Magyarországon szokatlanul nagymértékben (41-68%) parazitálja a nádirigót (Acrocephalus arundinaceus), lecsökkentve annak reprodukciós sikerét. A jelen OTKA pályázatban a két faj koevolúciós adaptációit kutattuk, így pl. a gazda tojásdiszkriminációs viselkedését (tojáseltemetés, tojáskidobás és fészekelhagyás). Kimutattuk, hogy a nádirigó fejlett tojásfelismeréssel rendelkezik, s a tojások alapszíne és nem a foltozottság játszik elsődleges szerepet az idegen tojások felsimerésében. Ugyancsak kimutattuk és egy modellel érzékeltettük, hogy a gazdák felismerik saját tojásaikat és memória-sablonnal rendelkeznek róla, s ennek szűk tartományában fogadnak el mimikris kakukktojásokat. A fészekaljon belüli tojások foltozottságnak viszont együttesen van szerepe, azok kis változatossága elősegíti az idegen tojás felismerését, míg azok nagy változatossága gyengíti. Többszörös parazitizmusban a nádirigók kisebb mértékben tudják elutasítani a kakukktojásokat, s így nagyobb lesz a költésparazita reprodukciós sikere. Többek között vizsgáltuk még a kakukkfióka kihordási ösztönének az okát, azaz a tojásból kikelő fióka minden tojást és fiókát kidob a fészekből 3 napon belül. Kísérleteink szerint ennek oka, hogy jobban ki tudja sajátítani a forrásokat ha egyedül van a fészekben, s a gazdákat nagyobb méretű táplálék gyűjtésére ösztönzi. | Cases of avian brood parasitism are examples for coevolution between hosts and brood parasites. In Hungary, the well-known common cuckoos (Cuculus canorus) parasitize great reed warblers (Acrocephalus arundinaceus) at an unusually high rate (41-68%), reducing their reproductive success. We studied coevolutionary adaptations between hosts and brood parasites within the framework of the present OTKA grant, e.g. egg discrimination ability of hosts (egg burial, egg ejection and nest desertion). We showed the well-developed egg discrimination ability of great reed warblers, and the importance of background colour of eggs in respect to spottedness in egg recognition. We also revealed and showed by a model that hosts know their own eggs and have a memory-template of these eggs. They accept mimetic cuckoo eggs if their characteristics fall below the acceptance threshold. We showed that intraclucth variation of eggshell spottedness facilitates foreign egg recognition if intraclucth variation is low, but it was found an opposite effect if it was high. In multiple parasitism hosts showed high tolerance toward cuckoo eggs, resulted in a higher fledging success of the brood parasite. We also revealed that the cuckoo chicks grow up alone in host nests to utilize parental provisioning ability of hosts better than in mixed broods of hosts and cuckoos

Ancient origin and maternal inheritance of blue cuckoo eggs

Maternal inheritance via the female-specific W chromosome was long ago proposed as a potential solution to the evolutionary enigma of co-existing host-specific races (or 'gentes') in avian brood parasites. Here we report the first unambiguous evidence for maternal inheritance of egg colouration in the brood-parasitic common cuckoo Cuculus canorus. Females laying blue eggs belong to an ancient (∼2.6 Myr) maternal lineage, as evidenced by both mitochondrial and W-linked DNA, but are indistinguishable at nuclear DNA from other common cuckoos. Hence, cuckoo host races with blue eggs are distinguished only by maternally inherited components of the genome, which maintain host-specific adaptation despite interbreeding among males and females reared by different hosts. A mitochondrial phylogeny suggests that blue eggs originated in Asia and then expanded westwards as female cuckoos laying blue eggs interbred with the existing European population, introducing an adaptive trait that expanded the range of potential hosts

Disappearance of eggs from nonparasitized nests of brood parasite hosts: the evolutionary equilibrium hypothesis revisited

The evolutionary equilibrium hypothesis was proposed to explain variation in egg rejection rates among individual hosts (intra- and interspecific) of avian brood parasites. Hosts may sometimes mistakenly reject own eggs when they are not parasitized (i.e. make recognition errors). Such errors would incur fitness costs and could counter the evolution of host defences driven by costs of parasitism (i.e. creating equilibrium between acceptors and rejecters within particular host populations). In the present study, we report the disappearance of host eggs from nonparasitized nests in populations of seven actual and potential hosts of the common cuckoo Cuculus canorus. Based on these data, we calculate the magnitude of the balancing parasitism rate provided that all eggs lost are a result of recognition errors. Importantly, because eggs are known to disappear from nests for reasons other than erroneous host rejection, our data represent the maximum estimates of such costs. Nonetheless, the disappearance of eggs was a rare event and therefore incurred low costs compared to the high costs of parasitism. Hence, costs as a result of recognition errors are probably of minor importance with respect to opposing selective pressure for the evolution of egg rejection in these hosts. We cannot exclude the possibility that low or intermediate egg rejection rates in some host populations may be caused by spatiotemporal variation in the occurrence of parasitism and gene flow, creating a variable influence of opposing costs as a result of recognition errors and the costs of parasitism

Coevolution in Action: Disruptive Selection on Egg Colour in an Avian Brood Parasite and Its Host

Trait polymorphism can evolve as a consequence of frequency-dependent selection. Coevolutionary interactions between hosts and parasites may lead to selection on both to evolve extreme phenotypes deviating from the norm, through disruptive selection.Here, we show through detailed field studies and experimental procedures that the ashy-throated parrotbill (Paradoxornis alphonsianus) and its avian brood parasite, the common cuckoo (Cuculus canorus), have both evolved egg polymorphism manifested in discrete immaculate white, pale blue, and blue egg phenotypes within a single population. In this host-parasite system the most common egg colours were white and blue, with no significant difference in parasitism rates between hosts laying eggs of either colour. Furthermore, selection on parasites for countering the evolution of host egg types appears to be strong, since ashy-throated parrotbills have evolved rejection abilities for even partially mimetic eggs.The parrotbill-cuckoo system constitutes a clear outcome of disruptive selection on both host and parasite egg phenotypes driven by coevolution, due to the cost of parasitism in the host and by host defences in the parasite. The present study is to our knowledge the first to report the influence of disruptive selection on evolution of discrete phenotypes in both parasite and host traits in an avian brood parasitism system

Dynamic Regulation of Myosin Light Chain Phosphorylation by Rho-kinase

Myosin light chain (MLC) phosphorylation plays important roles in various cellular functions such as cellular morphogenesis, motility, and smooth muscle contraction. MLC phosphorylation is determined by the balance between activities of Rho-associated kinase (Rho-kinase) and myosin phosphatase. An impaired balance between Rho-kinase and myosin phosphatase activities induces the abnormal sustained phosphorylation of MLC, which contributes to the pathogenesis of certain vascular diseases, such as vasospasm and hypertension. However, the dynamic principle of the system underlying the regulation of MLC phosphorylation remains to be clarified. Here, to elucidate this dynamic principle whereby Rho-kinase regulates MLC phosphorylation, we developed a mathematical model based on the behavior of thrombin-dependent MLC phosphorylation, which is regulated by the Rho-kinase signaling network. Through analyzing our mathematical model, we predict that MLC phosphorylation and myosin phosphatase activity exhibit bistability, and that a novel signaling pathway leading to the auto-activation of myosin phosphatase is required for the regulatory system of MLC phosphorylation. In addition, on the basis of experimental data, we propose that the auto-activation pathway of myosin phosphatase occurs in vivo. These results indicate that bistability of myosin phosphatase activity is responsible for the bistability of MLC phosphorylation, and the sustained phosphorylation of MLC is attributed to this feature of bistability