| The process of game adaptation between avian brood parasites and their hosts is one of the classic models for studying the co-evolution arms race.The adaptive evolution of this continuation of our species strategy that Strictly related to the host’s breeding trait depends upon the strength and adaptation of its host’s antiparasitic defenses.However,in view of the heterogeneity of the breeding life-history characteristics among hosts pupolation,this hence may cause different co-evolutionary adaptation status in different parasitic systems.In 2018 and 2019,the author initially explored the evolutionary status of parasitic adaptation and anti-adaptation of new nest parasitic system-Common cuckoo and thier host Grey Bush Chat system in Liuzhi,Guizhou,Southwestern China,from the aspects of parasitic nest site selection,host’s nest defense,egg rejection and recognition,and also egg retrieval.The findings are as follows:An analysis of the selection index of the parasitic nest characteristics(nest microhabitat,characteristics of nest and eggs)demonstrated that the Common cuckoo was biased towards selection the full clutches(4 or 5),the matched with host egg colors,close to the corn field,host nests with a distance of 10-20(m)from perch(even the average distance exceeds the non-parasitic nest),close to human and animal activity paths,medium edge distance,downhill positions,nesting under rock shelters,and nest heights of 0.5-1.5(m).Secondly,comparing and analyzing the characteristics of the nest sites for parasitic and non-parasitic nests,it was found that the former distance of corn field was significantly shorter than the latter.However,the difference between the mean distance of perch proximity of the parasitic nests is greater than that of the non-parasitic nests.Finally,the principal component analysis of the parasitic nest showed that habitat quality,host egg exposure,perch,and host activity factor may be the main influencing factors for the selection of parasitic nests of Common cuckoo.In addition,analysis of the host’s reproductive phenotypes in the three periods(0-25%-75%-100%)of breeding season found that their reproductive adaptation changed with the reproductive phenotype.The number of clutches decreased as the breeding season moved backwards,while the perch distance increased and then decreased with the breeding season.The above results show that in the research system,the Common cuckoo has a high parasitic adaptation in the selection of parasitic nests,while the grey bush chat may counteract the parasitic pressure of the parasites by adjusting the breeding phenology.In contradiction to the classical perch proximity hypothesis,in this system,the nest closest to the perch(<10 m)did not be parasited by Common cuckoo,but more often select the nest within the range of 10-20(m),so the author believes that the parasitic adaptation of the perch distance presented by the Common cuckoo in this system emphasizes the impact of host defense strength on parasitism,which further perfects the view of the perch proximity hypothesis that the perch closer the range of host’s effective defense is to the nest,the easier it is to be parasitic.The host’s frontline defense against parasites is considered to be the prerequisite for co-evolution of brood parasitism.The author’s experiments with different types of threats have shown that the grey bush chat can discrimination different types of intruders(parasites,predators)and act accordingly response.Under the predation risk,grey bush chat selects a trade-off to keep the parents to survive while sacrificing the fitness of the offspring.Besides strong attack behavior adaptation under parasitic risks,the author also found that some females choose to directly enter the nest and hatch eggs when occurs parasitic event.Thereby propose a possible explanation for this kind of nest defense: Host may attack or sit in the nest or even take both actions(by sexual division of labor)to prevent parasites when the parasite approaches the nest.The analysis of behavior between the two sexes showed that males were more aggressive than females,which may reflect the division of labour between the two sexes during the process of nest defense or reproductive life history.In addition,the author found that the common cuckoo evolved an effective parasitic strategy from the recorded natural parasitic events: it used the tree canopies as a shelter to prevent attack and change the direction of flight,and may be used humans as clues to locate the host nest or Waiting for opportunity to parasitic when artificially driving away parents from the nest.In conclusion,the recognition and behavioral adaptation of the grey bush chat to different types of specimen and the effective parasitic strategies of the Common cuckoo showed the co-evolutionary adaptation betwen the two species in the game confrontation of the nest defense period.Recognition and rejection to parasitic eggs and host egg simulation at the egg stage are considered to be one of the hotspots in the study of parasitic and antiparasitic evolution,and the differences in the adaptive ability shown in different systems can indirectly reflect the parasitic life history of the parasites and their host co-evolutionary status.In this study,artificial parasitic experiments(model eggs,parrot eggs)showed that grey bush chat has high ability to recognize and reject to foreign egg,and further proved that the performance characteristics of foreign eggs affect the host’s adaptation to egg rejection behavior.Acceptance of foreign eggs may not represent a rejection failure but an anti-parasitic strategy that prevent "retaliation" by the cuckoo.Through video analysis found the host had various ways of eggs rejection,and it was recorded for the first time that the host grasped the solid model eggs by their feet and flying away from the nest.This shows that the arasitic experiments(model eggs,parrot eggs)showed that grey bush chat in this parasitic system has a strong anti-parasitic adaptability in the process of egg recognition and rejection.In addition,it was found from the comparison of egg characterization that the arasitic experiments(model eggs,parrot eggs)showed that grey bush chat produced two kinds of eggs(pure blue and blunt end with red stripes),and the Common cuckoo be inclined to parasitic pure blue nest that matched it.However,it is necessary to further verify whether the appearance of the blunt end with red stripes is viewed as an anti-parasitic reproduction adaptation under parasitic pressure.The behavior of egg retrieval outside the nest is an effective life history breeding adaptation strategy for a few ground-nesting birds.For hosts suffering from specific brood parasitic stress,adaptation of egg retrieval behavior may have more complex cognitive processes and fitness implications.Response experiments of egg near the nest including parrot eggs and intra-species eggs showed that grey bush chat can recognize and retrieve its own eggs,but rid the parrot eggs.This further illustrate that grey bush chat has strong recognition ability to different eggs and makes corresponding behavioral decisions.In addition,the neglected behavior of extra-nest eggs(inter-and intra-species eggs)and a certain percentage of "wrong decisions" may reflect the important influence of nest parasitic pressure on the behavioral decision of grey bush chat.This research indicates that the emergence of host egg retrieving behavior in nest parasitic systems may have important adaptive significance for anti-parasitic and anti-predatory cognitive evolution. |
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