Preliminary assessment of metabolic costs of the nematode Myrmeconema neotropicum on its host, the tropical ant Cephalotes atratus

The parasitic nematode Myrmeconema neotropicum infects workers of the neotropical arboreal ant Cephalotes atratus. Infected ants exhibit altered behavior, e.g., reduced aggression and slower tempo, as well as physical traits, e.g., gaster changes from shiny black to bright red. These changes are thought to induce fruit mimicry and attract frugivorous birds, which are the presumed paratenic hosts for the nematodes. We used respirometry to measure the energetic costs of nematode infection, testing the prediction of higher metabolic rates for infected workers maintaining both ant and nematode biomass. Contrary to this prediction, infected workers had lower mass-specific metabolic rates than uninfected workers. Parasites are limited to the gasters (abdomens) of adult ants, and infected gasters had 57% more mass, but 37% lower metabolic rates, compared to uninfected gasters. These results use a metabolic currency to measure, in vivo, the energetic costs of parasitism, and they shed light on the complex co-evolutionary relationship between host and parasite.     

Animal Models for Echinostoma malayanum Infection: Worm Recovery and Some Pathology

Echinostomes are intestinal trematodes that infect a wide range of vertebrate hosts, including humans, in their adult stage and also parasitize numerous invertebrate and cold-blooded vertebrate hosts in their larval stages. The purpose of this study was to compare Echinostoma malayanum parasite growth, including worm recovery, body size of adult worms, eggs per worm, eggs per gram of feces, and pathological changes in the small intestine of experimental animals. In this study, 6-8-week-old male hamsters, rats, mice, and gerbils were infected with echinostome metacercariae and then sacrificed at day 60 post-infection. The small intestine and feces of each infected animal were collected and then processed for analysis. The results showed that worm recovery, eggs per worm, and eggs per gram of feces from all infected hamsters were higher compared with infected rats and mice. However, in infected gerbils, no parasites were observed in the small intestine, and there were no parasite eggs in the feces. The volume of eggs per gram of feces and eggs per worm were related to parasite size. The results of histopathological changes in the small intestine of infected groups showed abnormal villi and goblet cells, as evidenced by short villi and an increase in the number and size of goblet cells compared with the normal control group.     

FIRST EVIDENCE FOR SLAVE REBELLION: ENSLAVED ANT WORKERS SYSTEMATICALLY KILL THE BROOD OF THEIR SOCIAL PARASITE PROTOMOGNATHUS AMERICANUS

During the process of coevolution, social parasites have evolved sophisticated strategies to exploit the brood care behavior of their social hosts. Slave-making ant queens invade host colonies and kill or eject all adult host ants. Host workers, which eclose from the remaining brood, are tricked into caring for the parasite brood. Due to their high prevalence and frequent raids, following which stolen host broods are similarly enslaved, slave-making ants exert substantial selection upon their hosts, leading to the evolution of antiparasite adaptations. However, all host defenses shown to date are active before host workers are parasitized, whereas selection was thought to be unable to act on traits of already enslaved hosts. Yet, here we demonstrate the rebellion of enslaved Temnothorax workers, which kill two-thirds of the female pupae of the slave-making ant Protomognathus americanus . Thereby, slaves decrease the long-term parasite impact on surrounding related host colonies. This novel antiparasite strategy of enslaved workers constitutes a new level in the coevolutionary battle after host colony defense has failed. Our discovery is analogous to recent findings in hosts of avian brood parasites where perfect mimicry of parasite eggs leads to the evolution of chick recognition as a second line of defense.     

Evidence for aggressive mimicry in an adult brood parasitic bird,and generalized defences in its host

Mimicry of a harmless model (aggressive mimicry) is used by egg, chick and fledgling brood parasites that resemble the host''s own eggs, chicks and fledglings. However, aggressive mimicry may also evolve in adult brood parasites, to avoid attack from hosts and/or manipulate their perception of parasitism risk. We tested the hypothesis that female cuckoo finches (Anomalospiza imberbis) are aggressive mimics of female Euplectes weavers, such as the harmless, abundant and sympatric southern red bishop (Euplectes orix). We show that female cuckoo finch plumage colour and pattern more closely resembled those of Euplectes weavers (putative models) than Vidua finches (closest relatives); that their tawny-flanked prinia (Prinia subflava) hosts were equally aggressive towards female cuckoo finches and southern red bishops, and more aggressive to both than to their male counterparts; and that prinias were equally likely to reject an egg after seeing a female cuckoo finch or bishop, and more likely to do so than after seeing a male bishop near their nest. This is, to our knowledge, the first quantitative evidence for aggressive mimicry in an adult bird, and suggests that host–parasite coevolution can select for aggressive mimicry by avian brood parasites, and counter-defences by hosts, at all stages of the reproductive cycle.     

Imperfect mimicry of host begging calls by a brood parasitic cuckoo: a cue for nestling rejection by hosts?

Coevolutionary interactions between avian brood parasites and their hosts often lead to the evolution of discrimination and rejection of parasite eggs or chicks by hosts based on visual cues, and the evolution of visual mimicry of host eggs or chicks by brood parasites. Hosts may also base rejection of brood parasite nestlings on vocal cues, which would in turn select for mimicry of host begging calls in brood parasite chicks. In cuckoos that exploit multiple hosts with different begging calls, call structure may be plastic, allowing nestlings to modify their calls to match those of their various hosts, or fixed, in which case we would predict either imperfect mimicry or divergence of the species into host-specific lineages. In our study of the little bronze-cuckoo (LBC) Chalcites minutillus and its primary host, the large-billed gerygone Gerygone magnirostris, we tested whether: (1) hosts use nestling vocalizations as a cue to discriminate cuckoo chicks; (2) cuckoo nestlings mimic the host begging calls throughout the nestling period; and (3) the cuckoo begging calls are plastic, thereby facilitating mimicry of the calls of different hosts. We found that the begging calls of LBCs are most similar to their gerygone hosts shortly after hatching (when rejection by hosts typically occurs) but become less similar as cuckoo chicks get older. Begging call structure may be used as a cue for rejection by hosts, and these results are consistent with gerygone defenses selecting for age-specific vocal mimicry in cuckoo chicks. We found no evidence that LBC begging calls were plastic.     

AVIAN BROOD PARASITISM: INFORMATION USE AND VARIATION IN EGG‐REJECTION BEHAVIOR

Hosts of avian brood parasites often vary in their response to parasitized clutches: they may eject one or several eggs, desert the nest, or accept all the eggs. Focusing on hosts exposed to single‐egg parasitism by an evicting brood parasite, we construct an optimality model that includes all these behavioral options and use it to explore variation in rejection behavior. We particularly consider the influence of egg mimicry and external cues (observations of adult parasites near the nest) on optimal choice of rejection behavior. We find that several rejection responses will be present in a host population under a wide range of conditions. Ejection of multiple eggs tends to be adaptive when egg mimicry is fairly accurate, external cues provide reliable information of the risk of parasitism, and the expected success of renesting is low. If the perceived risk of parasitism is high, ejection of one or a few eggs may be the optimal rejection response even in cases in which hosts cannot discriminate between eggs. This may have consequences for the long‐term outcome of the coevolutionary chase between hosts and parasites. We propose an alternative evolutionary pathway by which egg ejection may first arise as a defense against brood parasitism.     

The population biology of parasite-induced changes in host behavior

The ability of parasites to change the behavior of infected hosts has been documented and reviewed by a number of different authors (Holmes and Bethel, 1972; Moore, 1984a). This review attempts to quantify the population dynamic consequences of this behavior by developing simple mathematical models for the most frequently recorded of such parasite life cycles. Although changes in the behavior of infected hosts do occur for pathogens with direct life cycles, they are most commonly recorded in the intermediate hosts of parasites with complex life cycles. All the changes in host behavior serve to increase rates of transmission of the parasites between hosts. In the simplest case the changes in behavior increase rates of contact between infected and susceptible conspecific hosts, whereas in the more complex cases fairly sophisticated manipulations of the host's behavioral repertory are achieved. Three topics are dealt with in some detail: (1) the behavior of the insect vectors of such diseases as malaria and trypanosomiasis; (2) the intermediate hosts of helminths whose behavior is affected in such a way as to make them more susceptible to predation by the definitive host in the life cycle; and (3) the behavior and fecundity of molluscs infected with asexually reproducing parasitic flatworms. In each case an expression is derived for R0, the basic reproductive rate of the parasite when first introduced into the population. This is used to determine the threshold numbers of definitive and intermediate hosts needed to maintain a population of the pathogen. In all cases, parasite-induced changes in host behavior tend to increase R0 and reduce the threshold number of hosts required to sustain the infection. The population dynamics of the interaction between parasites and their hosts are then explored using phase plane analyses. This suggests that both the parasite and intermediate host populations may show oscillatory patterns of abundance. When the density of the latter is low, parasite-induced changes in host behavior increase this tendency to oscillate. When intermediate host population densities are high, parasite population density is determined principally by interactions between the parasites and their definitive hosts, and changes in the behavior of intermediate hosts are less important in determining parasite density. Analysis of these models also suggests that both asexual reproduction of the parasite within a host and parasite-induced reduction in host fecundity may be stabilizing mechanisms when they occur in the intermediate hosts of parasite species with indirect life cycles.(ABSTRACT TRUNCATED AT 400 WORDS)     

Egg mimicry by the Pacific koel: mimicry of one host facilitates exploitation of other hosts with similar egg types

When brood parasites exploit multiple host species, egg rejection by hosts may select for the evolution of host‐specific races, where each race mimics a particular host's egg type. However, some brood parasites that exploit multiple hosts with the ability to reject foreign eggs appear to have only a single egg type. In these cases, it is unclear how the parasite egg escapes detection by its hosts. Three possible explanations are: 1) host‐specific races are present, but differences in egg morphology are difficult for the human eye to detect; 2) the brood parasite evolves a single egg type that is intermediate in appearance between the eggs of its hosts; 3) or the parasite evolves mimicry of one of its hosts, which subsequently allows it to exploit other species with similar egg morphology. Here we test these possibilities by quantifying parameters of egg appearance of the brood‐parasitic Pacific koel Eudynamys orientalis and seven of its hosts. Koel eggs laid in the nests of different hosts did not show significant differences in colour or pattern, suggesting that koels have not evolved host‐specific races. Koel eggs were similar in colour, luminance and pattern to the majority of hosts, but were significantly more similar in colour and luminance to one of the major hosts than to two other major hosts, supporting hypothesis 3. Our findings suggest that mimicry of one host can allow a brood parasite to exploit new hosts with similar egg morphologies, which could inhibit the evolution of host defences in naïve hosts.     

Chemical deterrent enables a socially parasitic ant to invade multiple hosts

Social parasites are involved in a coevolutionary arms race, which drives increasing specialization resulting in a very narrow host range. The Formicoxenus ants are a small group of social parasites with a xenobiotic lifestyle. Formicoxenus quebecensis and Formicoxenus provancheri are highly specialized ants using chemical mimicry to blend into their respective Myrmica ant host colonies. However, Formicoxenus nitidulus is unique in being able to survive in over 11 different ant host species. We observed that when live or dead F. nitidulus adults are seized by their host they are immediately dropped undamaged, despite possessing a cuticular hydrocarbon profile that differs markedly from its host. Hexane extracts of the F. nitidulus cuticle made previously acceptable prey items unattractive to their Formica host, indicating a chemical deterrent effect. This is the first time that a social parasite has been shown to exploit the generalized deterrence strategy to avoid host aggression over long periods of time. This supports the idea that coevolved and generalist diseases or parasites require fundamentally different defence mechanisms. We suggest that F. nitidulus uses its cuticular chemistry, possible alkadienes, as a novel deterrent mechanism to allow it to switch hosts easily and so become a widespread and abundant social parasite.     

Cleptoparasites, social parasites and a common host: Chemical insignificance for visiting host nests, chemical mimicry for living in

Social insect colonies contain attractive resources for many organisms. Cleptoparasites sneak into their nests and steal food resources. Social parasites sneak into their social organisations and exploit them for reproduction. Both cleptoparasites and social parasites overcome the ability of social insects to detect intruders, which is mainly based on chemoreception. Here we compared the chemical strategies of social parasites and cleptoparasites that target the same host and analyse the implication of the results for the understanding of nestmate recognition mechanisms. The social parasitic wasp Polistes atrimandibularis (Hymenoptera: Vespidae), and the cleptoparasitic velvet ant Mutilla europaea (Hymenoptera: Mutillidae), both target the colonies of the paper wasp Polistes biglumis (Hymenoptera: Vespidae). There is no chemical mimicry with hosts in the cuticular chemical profiles of velvet ants and pre-invasion social parasites, but both have lower concentrations of recognition cues (chemical insignificance) and lower proportions of branched alkanes than their hosts. Additionally, they both have larger proportions of alkenes than their hosts. In contrast, post-invasion obligate social parasites have proportions of branched hydrocarbons as large as those of their hosts and their overall cuticular profiles resemble those of their hosts. These results suggest that the chemical strategies for evading host detection vary according to the lifestyles of the parasites. Cleptoparasites and pre-invasion social parasites that sneak into host colonies limit host overaggression by having few recognition cues, whereas post-invasion social parasites that sneak into their host social structure facilitate social integration by chemical mimicry with colony members.     

Getting rid of the cuckoo Cuculus canorus egg: why do hosts delay rejection?

Egg discrimination is well documented in many hosts of avianbrood parasites, but the proximate mechanisms of egg recognitionand rejection decisions are poorly understood. Relevant in thisrespect is the observation that rejectors of parasite eggs oftendelay their response. This delay has implications for understandingmechanisms important for egg recognition and is the main focusof the present study. We investigated experimentally the relativeeffects of egg mimicry and eggshell strength of common cuckooCuculus canorus eggs on the delay in rejection in marsh warblersAcrocephalus palustris. In addition, by video recording hostresponses, we elucidate the proximate mechanisms behind thedelayed rejections. Host nests were experimentally parasitizedwith 3 types of real eggs differing in mimicry and/or eggshellstrength. Both egg mimicry and eggshell strength significantlyaffected the time to rejection, but the effect of mimicry wasdominant. The delayed rejection of mimetic eggs was explainedby the existence of latency to the release of rejection behaviorbecause of recognition problems. Second, when rejection responsetowards mimetic eggs was initiated, it was less intense comparedwith hosts experiencing nonmimetic eggs. Our results are consistentwith the hypothesis that host motivation when confronted withmimetic eggs needs to increase above a certain threshold beforerejection behavior is released, which likely minimizes the riskof recognition errors. An additional component of the delayin rejection as shown by hosts facing nonmimetic eggs was theseemingly inefficient host rejection behavior, probably reflectinglack of previous experience.     

Seasonal dynamics of Skrjabinoptera phrynosoma (Nematoda) infection in horned lizards from the Alvord Basin: temporal components of a unique life cycle

The nematode Skrjabinoptera phrynosoma is a stomach parasite of horned lizards in the genus Phrynosoma. This nematode demonstrates a distinctive life cycle wherein entire gravid females harboring infective eggs exit with lizard feces. Pogonomyrmex spp. harvester ants collect these females and feed them to their larvae, which are the only stages of the intermediate host that can become infected. We hypothesized that the seasonal dynamics of nematode abundance within lizard hosts would be correlated with the seasonal availability of suitable intermediate hosts. To describe seasonal variation of nematode population variables and elucidate the timing of critical events in the parasite life cycle, nematodes were collected from both hosts across three collection periods in the ant-and-lizard activity season of 2008 in the Alvord Basin of southeastern Oregon. Among 3 collection periods, and across the activity season, nematodes were harvested from individual Phrynosoma platyrhinos , and the distribution of developmental categories and body lengths of nematodes was analyzed to determine the seasonal change in nematode population composition. Pogonomyrmex spp. ants were collected in pit-fall traps and dissected to determine infection prevalence. The abundance of non-gravid female and juvenile nematodes collected from lizards' stomachs decreased significantly between the early and late collection period, which was likely a consequence of the sequential conversion of these developmental categories to gravid females. The presence of gravid female nematodes peaked in cloacal and fecal collections during mid-season. The body lengths of male nematodes increased as the activity season progressed, perhaps due to growth, but their abundance remained the same. Smaller juvenile nematodes were present in late-season collections from lizards, possibly indicating new acquisitions from infected ants. We propose that once a set population of male nematodes establishes in lizards' stomachs, newly acquired juvenile nematodes develop into non-gravid females that mate, become gravid females, and exit the lizard mid-season. We additionally suggest that the exit of females may be timed with the peak foraging activity of ant intermediate hosts and access to larval ants in the nests. Infection prevalence in the intermediate host was low, with only 1 of 6,000 dissected harvester ants containing a single larval nematode. The temporal dynamics of S. phrynosoma populations within P. platyrhinos at this northern locale is most likely driven by the seasonal availability of harvester ant intermediate hosts.     

Interplay between the parasite Amoebophrya sp. (Alveolata) and the cyst formation of the red tide dinoflagellate Scrippsiella trochoidea

Syndiniales (Alveolata) are marine parasites of a wide range of hosts, from unicellular organisms to Metazoa. Many Syndiniales obligatorily kill their hosts to accomplish their life cycle. This is the case for Amoebophrya spp. infecting dinoflagellates. However, several dinoflagellate species known to be infected by these parasites produce diploid resting cysts as part of their life history. These resting cysts may survive several seasons in the sediment before germinating. How these parasites survive during the dormancy of their host remained an open question. We successfully established infections by Amoebophrya sp. in the red tide dinoflagellate Scrippsiella trochoidea. This host strain was homothallic and able to continuously produce typical calcified cysts covered by calcareous spines. Presence of the parasite significantly speeded up the host cyst production, and cysts produced were the only cells to resist infections. However, some of them were clearly infected, probably earlier in their formation. After 10 months, cysts produced in presence of the parasite were able to germinate and new infective cycles of the parasite were rapidly observed. Thus, a very novel relationship for protists is demonstrated, one in which parasite and host simultaneously enter dormancy, emerging months later to propagate both species.     

Behavioural resistance against a protozoan parasite in the monarch butterfly

1. As parasites can dramatically reduce the fitness of their hosts, there should be strong selection for hosts to evolve and maintain defence mechanisms against their parasites. One way in which hosts may protect themselves against parasitism is through altered behaviours, but such defences have been much less studied than other forms of parasite resistance. 2. We studied whether monarch butterflies (Danaus plexippus L.) use altered behaviours to protect themselves and their offspring against the protozoan parasite Ophryocystis elektroscirrha (McLaughlin & Myers (1970), Journal of Protozoology, 17, p. 300). In particular, we studied whether (i) monarch larvae can avoid contact with infectious parasite spores; (ii) infected larvae preferentially consume therapeutic food plants when given a choice or increase the intake of such plants in the absence of choice; and (iii) infected female butterflies preferentially lay their eggs on medicinal plants that make their offspring less sick. 3. We found that monarch larvae were unable to avoid infectious parasite spores. Larvae were also not able to preferentially feed on therapeutic food plants or increase the ingestion of such plants. However, infected female butterflies preferentially laid their eggs on food plants that reduce parasite growth in their offspring. 4. Our results suggest that animals may use altered behaviours as a protection against parasites and that such behaviours may be limited to a single stage in the host-parasite life cycle. Our results also suggest that animals may use altered behaviours to protect their offspring instead of themselves. Thus, our study indicates that an inclusive fitness approach should be adopted to study behavioural defences against parasites.     

Easier detection of invertebrate "identification-key characters" with light of different wavelengths

Evolutionary arms-races between avian brood parasites and their hosts have typically resulted in some spectacular adaptations, namely remarkable host ability to recognize and reject alien eggs and, in turn, sophisticated parasite egg mimicry. In a striking contrast to hosts sometimes rejecting even highly mimetic eggs, the same species typically fail to discriminate against highly dissimilar parasite chicks. Understanding of this enigma is still hampered by the rarity of empirical tests - and consequently evidence - for chick discrimination. Recent work on Australian host-parasite systems (Gerygone hosts vs. Chalcites parasites), increased not only the diversity of hosts showing chick discrimination, but also discovered an entirely novel host behavioural adaptation. The hosts do not desert parasite chicks (as in all previously reported empirical work) but physically remove living parasites from their nests. Here, I briefly discuss these exciting findings and put them in the context of recent empirical and theoretical work on parasite chick discrimination. Finally, I review factors responsible for a relatively slow progress in this research area and suggest most promising avenues for future research.     

Host and brood parasite coevolutionary interactions covary with comparative patterns of the avian visual system

In coevolutionary arms-races, reciprocal ecological interactions and their fitness impacts shape the course of phenotypic evolution. The classic example of avian host–brood parasite interactions selects for host recognition and rejection of increasingly mimetic foreign eggs. An essential component of perceptual mimicry is that parasitic eggs escape detection by host sensory systems, yet there is no direct evidence that the avian visual system covaries with parasitic egg recognition or mimicry. Here, we used eye size measurements collected from preserved museum specimens as a metric of the avian visual system for species involved in host–brood parasite interactions. We discovered that (i) hosts had smaller eyes compared with non-hosts, (ii) parasites had larger eyes compared with hosts before but not after phylogenetic corrections, perhaps owing to the limited number of independent evolutionary origins of obligate brood parasitism, (iii) egg rejection in hosts with non-mimetic parasitic eggs positively correlated with eye size, and (iv) eye size was positively associated with increased avian-perceived host–parasite eggshell similarity. These results imply that both host-use by parasites and anti-parasitic responses by hosts covary with a metric of the visual system across relevant bird species, providing comparative evidence for coevolutionary patterns of host and brood parasite sensory systems.     

Gnathostoma binucleatum: Pathological and parasitological aspects in experimentally infected dogs

Lesions and antibody kinetics produced by inoculation of Gnathostoma binucleatum larvae into dogs are described, as well as the morphology of the recovered parasites. In four out of five infected bitches parasite phases were found in the stomach. Only one bitch eliminated eggs and adult parasite phases in feces. In this bitch, the prepatency period lasted 22 weeks and the patency period 14 weeks. Necropsy results showed a copiously vascularized 8-cm diameter fibrous nodule lodged in the greater curvature of the stomach. Two bitches that eliminated no eggs showed 1- to 2-cm diameter nodules on the gastric wall, with five juvenile phases in each. One bitch that eliminated no eggs and exhibited no gastric nodules showed juvenile parasites on the gastric wall. Results confirm dogs as definitive hosts of this parasite. New data on the pathological and parasitological aspects of canine gnathostomosis are presented.     

Exoskeletal thinning in Cephalotes atratus ants (Hymenoptera: Formicidae) parasitized by Myrmeconema neotropicum (Nematoda: Tetradonematidae)

Some parasites modify the color of their arthropod hosts, presumably to facilitate transmission to a new host. Mechanisms for such changes often are unknown, but altered exoskeletal color in adult insects typically occurs via structural modifications or redistribution of pigments. Here, we examine the cuticle structure of workers of the Neotropical canopy ant Cephalotes atratus infected with the nematode Myrmeconema neotropicum. We hypothesized that the conspicuous red color of the gaster (the globular posterior body region) of infected ants results from structural changes, specifically localized exoskeletal thinning. We used scanning electron microscopy to quantify the thickness of gaster cuticle in healthy and infected ants. For comparison, we also measured the cuticle thickness of the head of each ant, which is black in both infected and healthy individuals. The gaster cuticle was 23% thinner in infected ants (average ±SE: 14.8 ± 1.02 μm) versus healthy ants (19.2 ± 0.65 μm) after correcting for body size. In contrast, the thickness of the head exoskeleton was similar among groups. We conclude that parasite-induced thinning of the exoskeleton is associated with the red color of the gaster. Other mechanisms, including translocation or leaching of melanin (by the ant or the parasite, respectively) may operate in concert with thinning to effect the color change, and would be an appropriate extension of this research.     

Mimicry vs. similarity: which resemblances between brood parasites and their hosts are mimetic and which are not?

Mimicry is one of the most conspicuous and puzzling phenomena in nature. The best-known examples come from insects and brood parasitic birds. Unfortunately, the term 'mimicry' is used indiscriminately and inconsistently in the brood parasitic literature despite the obvious fact that similarities of eggs, nestlings and adults of brood parasites to their hosts could result from many different processes (phylogenetic constraint, predation, intraspecific arms-races, vocal imitation, exploitation of pre-existing preferences, etc.). In this note I wish to plead for a more careful use of the term. I review various processes leading to a similarity between propagules (both eggs and nestlings) of brood parasites and their hosts and stress that: (1) mimetic and non-mimetic similarities should be differentiated, (2) a mere similarity of host and parasite propagules provides no evidence for mimicry, (3) mimicry is more usefully understood as a (coevolutionary) process rather than an appearance, and (4) mimicry terminology should reflect the process which led to mimetic similarity. Accepting the mimicry hypothesis requires both the experimental approach and rejection of alternative hypotheses explaining similarities of host and parasite propagules.  © 2005 The Linnean Society of London, Biological Journal of the Linnean Society , 2005, 84 , 69–78.     

Evolution of host egg mimicry in a brood parasite, the great spotted cuckoo

Brood parasitism in birds is one of the best examples of coevolutionary interactions in vertebrates. Coevolution between hosts and parasites is assumed to occur because the parasite imposes strong selection pressures on its hosts, reducing their fitness and thereby favouring counter-adaptations (e.g. egg rejection) which, in turn, select for parasite resistance (e.g. egg mimicry). Great spotted cuckoos ( Clamator glandarius ) are usually considered a brood parasite with eggs almost perfectly mimicking those of their host, the magpie ( Pica pica ). However, Cl. glandarius also exploits South African hosts with very different eggs, both in colour and size, while the Cl. glandarius eggs are similar to those laid in nests of European hosts. Here, we used spectrophotometric techniques for the first time to quantify mimicry of parasitic eggs for eight different host species. We found: (1) non-significant differences in appearance of Cl. glandarius eggs laid in nests of different host species, although eggs laid in South Africa and Europe differed significantly; (2) contrary to the general assumption that Cl. glandarius eggs better mimic those of the main host in Europe ( P. pica ), Cl. glandarius eggs more closely resembled those of the azure-winged magpie ( Cyanopica cyana ), a potential host in which there is no evidence of recent parasitism; (3) the appearance of Cl. glandarius eggs was not significantly related to the appearance of host eggs. We discuss three possible reasons why Cl. glandarius eggs resemble eggs of some of their hosts. We suggest that colouration of Cl. glandarius eggs is an apomorphic trait, and that variation between eggs laid in South African and European host nests is due to genetic isolation among these populations and not due to variation in colouration of host eggs.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 79 , 551–563.