Brood Parasitism of the Common Cuckoo

think up Parasitism of the Common CuckooBrood parasitism by the mutual hombre Cuculus smokeorus has excited wonder, interest and surmisal like few opposite bird bearings. Its a species which had been studied and dis foil well before Darwins time, generating a wealth of information that has provided a deeper discretion of interactions among species. However, recent studies atomic way bulge out 18 bringing up much details of the co maturationary family relationship in the midst of the bozo and its innkeepers. The aim of this paper is deuce-acefold to provide a concise review of the evolution of hatch parasitism in the putting green pussy, to abstraction the different strategies that innkeeper species welcome evolved to deter parasitism, and to identify some of the counter renderings the guy has developed against those strategies.IntroductionThe extraordinary plasticity in grooming expression of the family Cuculidae has no parallel among the worlds bird fami lies. Of the 136 species of zanys, 83 provide agnate cargon charm 53 species parasitize come ons, where testicle ar incubated and para come outs girlish are turn upd by a military species 1. Of those 53 parasitic species, the common slit Cuculus canorus (hereafter, puss) is the roughly widespread in Europe, inhabiting a different array of habitats and having at least 15 different boniface-specific races 2. Throughout report the cunt has attracted a wealth of attention and generated much fascination. In the fourth part century BC, Aristotle accurately described the parasitic habits of the hombre, noting that the cuddleling goose ejects the hosts testis or young, casting out of the nest those with whom it has so far lived 3. scorn these very early accounts of the cuckoos reproductive memory behavior, it was not until the 1700s that cuckoos biology regained attention by scientists. However, the cuckoo literature generated prior to the mid-twentieth century was a mix of ideational ceremonys and misc at onceptions. For instance, well into the 1750s it was thought that the feminine cuckoo upon freak laying the formal al pitiful for carry it with her beak to the hosts nest 3. such(prenominal) an idea was mistakenly fortify by observing cuckoo females carrying an egg, which later was proven to be the hosts eggs, scarcely assuming it was the cuckoos egg 3. This idea was later rejected by British physician Edward Jenner whose accurate observations direct to the current description of the cuckoos parasitism 3. Generally, cuckoos lay a gurglele egg in a host nest. Upon hatching, the young cuckoo pushes out the host nestlings, and any unhatched eggs. The cuckoo nestling thusly demands undivided care from its hosts with an extraordinary begging display, which consists of bright orange look and rapid calls to simulate several nestlings 4.Evolution of cuckoo parasitismIt was Charles Darwin who first mean attended to explain the evolution of predominate parasitism in European cuckoos. In The Origin of Species Darwin described an example of brood parasitism by an American cuckoo species. The cuckoo was reared by a Blue Jay Cyanocitta cristata until it fledged the nest. This observation led Darwin to suggest that brood parasitism has evolved through a repetitive cultivate in nature in which the young cuckoo inherits its mothers parasitic habits collectable to advantages gain in survival 3. Darwin proposed that cuckoo parasitism evolved from agnate cuckoos and phylogeny studies postulate supported his view. However, at that place is no consensus on how brood parasitism evolved. Taxonomists suggest that brood parasitism evolved as a separate event in 2 subfamilies of brood parasites, independently, the Old World Cuculinae and the New World Neomorphinae 1. On the other hand, a phylogeny study based on bone characteristics suggests that brood parasitism evolved as a single event in the family, placing Cuculinae and Neomorphinae together, while the genus Coccyzus put in the New World, re-evolved agnatic care from a parasitic forerunner 1. Yet another study on molecular phylogeny proposes three independent origins of brood parasitism, in genus Clamator, and other cuckoos of the Old World and cuckoos in the American continent 5.Avian brood parasitism between distinct species is presently thought to restrain evolved from an familial blood line with parental care breeding or as an indirect consequence of brood parasitism between conspecifics 3. However, while the argument still exists over which of the the two pathways pourboires to the parasitism of other species nests, there is large(p) support for the evolution of parasitism from a normal breeding behavior 1,3. It is considered that the ancestral form of modern day cuckoos probably was a parental care, non-migratory dweller of tropical forest, and that changes in habitat, migration patterns, range size and forage provoked the evolut ion of brood parasitism as a way to reduce order the bell of reproduction 1.3. When comparing energy expenditure on reproduction, it was estimated that a parasitic cuckoo buy the f implements of war half the amount of energy of a parental cuckoo in achieving comparable reproductive success1. In fact, within the Cuculidae family there are definitive dissimilarities between species with parental care and brood parasites. Cuckoos bring a lower consistency mass, lay tinyer eggs, and feed on prey of lesser size. 1. In the comparative analysis done by Krger and Davies (2002), it was concluded that the evolution of cuckoo parasitism was the result of changes in the environmental science of a parental ancestor and that once a parasitic behavior was adapted further specializations occurred.a. From raising your consume offspring to be a brood parasiteBefore brood parasitism evolved, there were key changes in the ecology and behavior of forest cuckoos. Initially, forest cuckoos expande d their range to include more open and seasonal habitats. This habitat expansion provoked a more migratory behavior, an extend in breeding-range size and the availability of newly food sources 1. These changes in ecology required a lessening in energy invested in reproduction. When comparing energy expenditure on reproduction, it was estimated that a parasitic cuckoo spends half the amount of energy of a parental cuckoo in achieving comparable reproductive success1. Therefore, divideion for brood parasitism became the emergent consequence of the ecological changes mentioned above.b. Brood parasitism caused the evolution of specialized parasitic translationsUpon the adaptation of obligated brood parasitism, cuckoo eggs became smaller. Kruger and Davies (2002) suggest two hypotheses for the reduction in egg size. First, parasitic cuckoos were able to increase clutch size which may have been possible upon the reduction of overall egg size. Since some hosts are smaller than the ir parasitic cuckoos, an adaptation to a decrease in egg size would have been selected in order to vacate host rejection while improving incubation efficiency. A preference for smaller hosts increases the military issue of egg-laying opportunities since there is a greater abundance of smaller species than adultr ones 1 .An adaptation to a parasitic behavior force have alike freed the cuckoo of the diet restraint when selecting breeding habitat. By relying on the host parental care, cuckoos are able to exploit a diversity of breeding habitats for breeding even those habitat where adult cuckoos cannot forage. Kruger and Davies (2002) note that some common cuckoos are required to travel large outgos when breeding in marshlands while foraging in woodland areas. This independence from breeding habitat restraints have enabled the common cuckoo to increase its range through Europe.Factors that affect brood parasitism by the Common CuckooThe size of the host and its abundance is an im portant forecaster of host parasitism 3. There is a greater diversity and abundance of small bird species which provides the cuckoo a larger pool of possible hosts. The absorption of the cuckoo at a assumption area in any reference plays a crucial role. It was ensnare that rejection rate increase as the rate of parasitism goes up in a given area 6. A greater stringency of female cuckoos at the breeding area of the selected hosts increases the endangerments that the hosts regulate a cuckoo female and proceed with egg rejection or nest desertion 6. This superpower be one of the multiple explanations for the fact that cuckoos are more widespread and their breeding-range is significantly larger than parental species of the same family. Additionally the choice of nesting site affects brood parasitism. Nests located nearby trees have a significant increase on the insecurity of being parasitized 7. Female cuckoos perch on trees to tack information on the hosts nest building ac tivity and therefore the availability of ocular points are crucial for the cuckoo to square hosts nest keisterment 7. Therefore, it is expected of the cuckoos hosts to show a high degree of plasticity in choice of nest site in order to decrease the distance to visual vantage point and to increase nest concealment 7. Interestingly, female cuckoos seem to gather cues from the host behavior not only to determine nest location but also to reveal the hosts parental capacities. Males that sing more actively during breeding season tend to attract females that reinforced larger nests. It was found that in great reed warblers Acrocephalus arundinaceous nestlings raise in larger nests receive more feeding than those in a small nest 8. It will be expected to see a larger rate of parasitism in hosts that are more plainspoken and active during nest construction. However, it was found that hosts with a high degree of steer expression nearby the nest are also more dullard to defend the ne st against intruders and to reject cuckoo eggs. Therefore, cuckoos may favor a host with a smaller nest and whose activity is less visually conspicuous 8. Polacikova et al. (2009) also found that great reed warblers affected by cuckoo parasitism have high body condition than individuals freed of parasitism. Additionally, females hosts had higher body mass and presented less uniformity in egg coloration 9 master of ceremonies antisubmarine strategies against cuckoos parasitismBrood parasitism by the cuckoo brings multiple be to the host 2. The primary cost is the loss of an egg once the female cuckoo lays hers. Additionally, rejection requires the expense of energy and time (for recognition) and it includes the risk of discriminating the hosts own eggs. By accepting the cuckoos egg the reproductive success of the host is then threaten since upon hatching the young cuckoo pushes out the hosts nestlings 4. Furthermore, the host parents must raise a much larger razzing which demand s more food than the hosts own nestlings. This costly is highly increased in the extraordinary case when the host and cuckoo nestlings grow up together like in the parasitism of the redstart Phoenicurus phoenicurus 2. Due to the multiple costs associated with brood parasitism, umteen host species have evolved adaptations to cope with parasitism such as egg rejection and nest desertion 10. However, these adaptations only partially offset the costs of parasitism since they take place once the nest has been already parasitized. Therefore, some host species have also evolved adaptations to eliminate laying opportunities for the cuckoo. Nesting in safe places, constructing well hidden nests, or an active protection of the nest from intrusions are example of adaptations that host species have evolved to avoid being parasitized 10,11.Mobbing behaviorThe reed warbler Acrocephalus scirpaceus is one of the species most quick selected by cuckoos as host for their eggs and therefore has evol ved adaptations that pose a coevolutionary arms race with the common cuckoo 12,13. Mobbing, the attacking or harassing of cuckoos by reed warblers has been determined to be an effective first line of refutal against parasitism 12. It has been well documented that reed warbler use audible and visual displays that in occasion leave behind to direct physical attacks to dissuade parasitism. Such antisubmarine behavior reduces the probability of parasitism and it is a direct cost to cuckoos which cogency lose feathers or stomach injuries during physical attacks by reed warblers 12. Additionally, mobbing attracts predators, and other brood parasites thus posing an indirect cost since the cuckoo or its eggs power be at risk of predation 12. The costs inflicted on the cuckoo can also be associated to the costs suffer by the reed warbler that mob brood parasites. First of all, there is a physical similarity between common cuckoos and sparrowhawks Accipiter nisus 10, a potential predato r of reed warblers. Therefore, reed warblers may need to spend time to identify the type of threat, parasitism or predation, before engaging in a mobbing display 12. In addition, the same indirect costs that mobbing brings to the cuckoo are also to the reed warbler which unknowingly might be attracting more parasites and predators to the nesting area 12. Therefore, the costs inflicted on the host select for a defensive behavior that discriminates between the type of threat and the degree of parasitism 12. Although some passeriform bird birds will mob a possible predators, nesting adult reed warbler have not been observed doing it. Welbergen and Davies (2008) note that adult reed warblers seek cover and remain silent in the presence of a sparrowhawk near the nest 10. Since sparrowhawks are a direct threat to the adults while cuckoos are to the nest, it makes sensory faculty that reed warblers mob the latter and not the former 12. Reed warblers also show plasticity in their mobbing behavior in terms of risk of nest parasitism. In areas where there is a higher probability that the cuckoos are able to find hosts nest, mobbing is the best strategy, while in areas with a low probability the best defensive method may be to avoid active and visible displays and remain hidden but alert 12. By presenting reed warblers with taxidermic mounts of cuckoos, Welbergen and Davies (2009) concluded that mobbing is an adapted, phenotypically trait with high plasticity in the defense against parasitism 12.Alarms Calls and Nest GuardingIt was previously noted that cuckoos and sparrowhawks share a resemblance that might pose a challenge for reed warblers in their nest defensive strategies. However, reed warblers have shown to vary their auditory displays accordingly to the kinds of danger and the succeeding response by conspecifics 10. Welbergen and Davies (2008) showed that reed warblers are able to identify cuckoos from sparrowhawks with consternation calls that attract not on ly mates but nearby neighbors. The shocks signals by reed warblers in the presence of a cuckoo are characterized by rasps and snaps. Rasps have a sharp commencement and a wide relative frequency range, which are important features that enable the location of the emitter 10. Alarms calls therefore are an important communal defensive mechanism against parasitism. Nest attendance and egg rejection by reed warblers might increase due to the information provided by the alarm calls emitted by neighbor conspecifics 10. Additionally, alerting on the presence of cuckoos might aerate the mobbing of the parasite by multiple reed warblers which could eject the cuckoo. Nest guarding has also been identified as a defensive strategy against parasitism. However, it is more passive and less conspicuous than mobbing and alarm displaying 11. An increase in nest guarding has been observed after laying has begun and is usually done by the male. This behavior might able the reed warblers to gain info rmation about cuckoos presence and chance of parasitism. Spotting a cuckoo before laying has begun might depart nest desertion whereas the sighting of a cuckoo once laying commences might increase the likelihood of rejection of the cuckoos egg 11.Egg rejectionHosts species have evolved two mechanisms in order to eject cuckoo eggs. In the case of hosts with large beaks, the eggs are stoveed and evicted out of the nest while species unable to grasp the egg, puncture and then eject the parasites egg 14. The reproductive success is stripped-down if a host accepts a cuckoo egg due to the inborn behavior of the cuckoo nestling of evicting hosts eggs and nestlings. Therefore, species parasitized by cuckoos should strongly select for an ejection adaptation to parasitism if the host is physically able of ejecting cuckoo eggs 14. For those species whose beak is too small to grasp the beak and that puncturing the egg would be too costly or impossible, nest desertion is the strategy selecte d once parasitism has been identified 14,15. The cost to the hosts when trying to puncture cuckoo eggs has been demo in marsh warblers Acrocephalus palustris which after unsuccessfully attempting to puncture the eggs have damaged their own eggs 15.Cuckoos Responses to Overcome Hosts AdaptationsCuckoo parasitism has led to the selection of defense mechanisms by the hosts. At the same time, in this coevolutionary arms race, more sophisticated trickeries are selected by the cucook 1,16. Egg caricature and vocal mimicry by the nestlings are of the most significant traits evolved in the cuckoo to cope with hosts defensive responses.Egg MimicryThe recognition and ejection of cuckoo eggs have selected for an increase in mimicry of the host egg by the cuckoo whose eggs display a high variant in color and/or spotting due to the diverse number of hosts it parasitizes 16. In a reed warbler study of parasitism by the common cuckoo, Avils et al. (2006) found the surprising speed in which egg similarity between the two species evolved in recently parasympatric poputions of reed warblers and cuckoos. Using museum egg collections, it was found that in 23 years, the degree of egg matching increase advantageously 16. Avils et al. note this rapid improvement egg matching a micro-evolutionary response to host removal of eggs differing in color or size and that egg mimicry has coevolved with this rejection behaviour 16. The importance of egg mimicry was exemplified by Antonov et al. (2008) on a study of cuckoo egg rejection by marsh warblers. On the study, unmanipulated cuckoo eggs were accepted more readily than painted cuckoo and great reed warbler eggs placed in marsh warbler nests 15. The aim of the Antnovo et al. was to determine the importance of egg shell strong point in deterring egg rejection. However, since painted cuckoo eggs suffered a higher rejection rate, it was indicated that egg mimicry is pivotal in determining the probability of rejection 15. call or Visual Mimicry by Parasite NestlingsBrood parasites can be differentiated into two categories Nonevictors which are parasites that grow up on board the hosts young and evictors in which the young parasite either kills the hosts nestlings or expels them out of the nest along with any unhatched eggs 17. Nonevictor species include the brown-headed cowbird, genus Molothrus ater, finches of the Vidua genus and great spotted cuckoo, Clamator glandarius. While the common cuckoo is a evictor brood parasite. Nonevictors showed certain mimicry of the host chicks as a counteradaptation against the host adult learning of the characteristics of the chicks during first brood. These imprinting of its own chicks characteristics will later permit the rejection of chicks that are different 17. For example, Vidua finch young show great resemblance of the mouth spot patterns of their hosts chicks 17. On the other hand, this adaptation has not been selected in hosts of evictor parasites. Since the cuckoo nest ling is raised alone, imprinting the characteristics of the parasite chick will be detrimental to future broods 17. Butchart et al. (2003) found that the begging calls produced by four different common cuckoo races did not differ which lead to the conclusion that in evictor species there is not selection for evolution of visual or vocal mimicry by the parasite chick 17. However, it should be advantageous for the cuckoo nestling to respond to the host alarm calls given in the presence of a predator 18. Davies et al. (2006) concluded that cuckoos that specialize on reed warblers have not only well-matched eggs but also chicks that are well-tuned to the hosts alarm calls 18.SummaryCoevolution relationship among species are significant in order to understand how species select for adaptations accordingly to the other species. In the case of brood parasitism by the common cuckoo, that relationship is truly an arms race. For instance, egg rejection lead to egg mimicry which in turn might lead to clutch variability in the host. However, before egg rejection is selected, hosts have evolved a first line of defense that includes direct confrontation against the parasite. The costs of parasitism are evident for the host species but also the parasite carries its own costs. As a relation observed well before Darwin and his theory of evolution, the cuckoo-host interaction was provided with a solid framework to be better study and soundless once Darwins work became public. However, necessity for further research remains. There is circumscribed work on the biology and ecology of cuckoo nestlings. Also there is still no detailed explanations on the failure of hosts to recognized cuckoos young as a different species 3. Furthermore, as anthropogenic actions change immanent ecosystems at a rapid scale, further research is needed in the relationship between cuckoos and hosts and the factors affected by habitat alterations. 7.