Number and size of clutch in Ptomascopus morio (Coleoptera: Silphidae: Nicrophorinae), with comparisons to Nicrophorus

Ptomascopus morio displays simpler parental care than Nicrophorus species. The effects of carcass size and clutch number on clutch size in P. morio were examined. Clutch size was related to carcass size. There was a negative correlation between number of clutch and clutch size for most sizes of carcass. Longevity of females was shorter when the carcass size was larger, such that total lifetime fecundity did not differ among carcasses of different sizes. The clutch size of P. morio was larger than that of Nicrophorus quadripunctatus. The clutch size of P. morio declined rapidly with repeated clutch production, but that of N. quadripunctatus was rather constant. This indicates that N. quadripunctatus maintains a more constant clutch size than P. morio over several reproductive attempts, although the former displays more complex parental care.     

Brood size reduction in Nicrophorus vespilloides after usurpation of carrion from Nicrophorus quadripunctatus (Coleoptera: Silphidae)

Burying beetles bury small vertebrate carcasses, which become food for their larvae. They sometimes usurp carcasses occupied and buried by other beetles. Brood sizes of intraspecific and interspecific intruders were examined using Nicrophorus quadripunctatus as the resident. The brood sizes of usurpers were not reduced relative to control brood sizes when the usurper was conspecific, but were reduced when the usurper was heterospecific (N. vespilloides).     

Changing dominant–subordinate relationships during carcass preparation between burying beetle species (Nicrophorus: Silphidae: Coleoptera)

I studied the influence of carrion burial on the interaction between Nicrophorus quadripunctatus and Nicrophorus vespilloides. In the preburial phase, N. quadripunctatus, the smaller species, occupied more carcasses than N. vespilloides, the larger species, when both species were allowed to compete for mouse carcasses. However, after carcasses were buried, N. vespilloides was more successful in protecting those it had buried, and more successful in intruding on carcasses buried by N. quadripunctatus. Direct observation supported these findings. These results may suggest that N. vespilloides is cleptoparasitic on N. quadripunctatus for carrion burial. Received: March 25, 1999 / Accepted: August 31, 1999     

Intrasexual Competition and Mating Behavior in <Emphasis Type="Italic">Ptomascopus morio</Emphasis> (Coleoptera: Silphidae Nicrophorinae)

In nicrophorine beetles, genus Nicrophorus care their larva using small vertebrate carrion, whereas genus Ptomaucopusreproduce with small vertebrate carrion but show no parental care. Aggression and sexual behavior were examined in Ptomascopus morio and Nicrophorus quadripunctatus. Nicrophorus quadripunctatus had intense female–female as well as male–male contests. In Ptomascopus morio, by contrast, female–female aggression was rarely observed. Male–male aggression (pushing, biting, male–male mounting) in Ptomascopus morio was observed when a resource for breeding was present, whether or not a female was present. The lack of female–female aggression, and male–male aggression when resources but not females are present, suggest that the mating system of Ptomascopus morio is resource defense polygyny. Large males of Ptomascopus morio were also found to exhibit mate choice, preferring large females over small females.     

Effects of carcass size and male presence on clutch size in Nicrophorus quadripunctatus (Coleoptera: Silphidae)

The effects of carcass size and male presence on clutch size in Nicrophorus quadripunctatus were examined. Male presence increased clutch size and improved the female's ability to produce replacement clutches. Clutch size was also related to carcass size. There was a negative correlation between number of clutches and clutch size for most carcass sizes. We conclude that N. quadripunctatus is potentially iteroparous and hypothesize that reproductive energy is reserved for brood failure.     

Polyrhachis lama, a parasitic ant with an exceptional mode of social integration

Social parasitism is a common phenomenon amongst ants that occurs in manifold variations with differing levels of parasite–host integration. Particularly, high levels of social integration occur amongst closely related species (Emery’s rule), which form mixed colonies with their hosts and comprise the vast majority of social parasites. Considerable lower levels of integration are typically found amongst unrelated species that live in clearly separated colonies. The formicine ant Polyrhachis lama, however, parasitises a phylogenetically distant host species, Diacamma sp. of the subfamily Ponerinae, but lives spatially mixed with the host colonies. Studies on integration and communication have indicated that P. lama shows a high degree of host integration. However, the allocation of brood care behaviour, a central aspect of parasite integration, has not been studied. Because all known ant social parasites that are fully mixed with their host colonies are also true brood parasites, we investigated the integration of P. lama brood. Our results demonstrate that the parasite brood has a high degree of spatial integration, although it remains functionally separated regarding nutritive brood care. This can be attributed to behavioural and morphological differences between the phylogenetically distant species. The observed spatial confinement of parasite brood, however, is most likely due to an unusual method of chemical host integration. The parasite brood remains accepted in the Diacamma colonies only under the presence of adult parasites. Altogether, this suggests an active mechanism of chemical integration based on the acceptance allomones originating from P. lama workers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

The evolution of acceptance and tolerance in hosts of avian brood parasites

Avian brood parasites lay their eggs in the nests of their hosts, which rear the parasite's progeny. The costs of parasitism have selected for the evolution of defence strategies in many host species. Most research has focused on resistance strategies, where hosts minimize the number of successful parasitism events using defences such as mobbing of adult brood parasites or rejection of parasite eggs. However, many hosts do not exhibit resistance. Here we explore why some hosts accept parasite eggs in their nests and how this is related to the virulence of the parasite. We also explore the extent to which acceptance of parasites can be explained by the evolution of tolerance; a strategy in which the host accepts the parasite but adjusts its life history or other traits to minimize the costs of parasitism. We review examples of tolerance in hosts of brood parasites (such as modifications to clutch size and multi‐broodedness), and utilize the literature on host–pathogen interactions and plant herbivory to analyse the prevalence of each type of defence (tolerance or resistance) and their evolution. We conclude that (i) the interactions between brood parasites and their hosts provide a highly tractable system for studying the evolution of tolerance, (ii) studies of host defences against brood parasites should investigate both resistance and tolerance, and (iii) tolerance and resistance can lead to contrasting evolutionary scenarios.     

Long‐term coevolution between avian brood parasites and their hosts

Coevolutionary theory predicts that the most common long‐term outcome of the relationships between brood parasites and their hosts should be coevolutionary cycles based on a dynamic change selecting the currently least‐defended host species, given that when well‐defended hosts are abandoned, hosts will be selected to decrease their defences as these are usually assumed to be costly. This is assumed to be the case also in brood parasite‐host systems. Here I examine the frequency of the three potential long‐term outcomes of brood parasite–host coevolution (coevolutionary cycles, lack of rejection, and successful resistance) in 182 host species. The results of simple exploratory comparisons show that coevolutionary cycles are very scarce while the lack of rejection and successful resistance, which are considered evolutionary enigmas, are much more frequent. I discuss these results considering (i) the importance of different host defences at all stages of the breeding cycle, (ii) the role of phenotypic plasticity in long‐term coevolution, and (iii) the evolutionary history of host selection. I suggest that in purely antagonistic coevolutionary interactions, such as those involving brood parasites and their hosts, that although cycles will exist during an intermediate phase of the interactions, the arms race will end with the extinction of the host or with the host acquiring successful resistance. As evolutionary time passes, this resistance will force brood parasites to use previously less suitable host species. Furthermore, I present a model that represents the long‐term trajectories and outcomes of coevolutionary interactions between brood parasites and their hosts with respect to the evolution of egg‐rejection defence. This model suggests that as an increasing number of species acquire successful resistance, other unparasitized host species become more profitable and their parasitism rate and the costs imposed by brood parasitism at the population level will increase, selecting for the evolution of host defences. This means that although acceptance is adaptive when the parasitism rate and the costs of parasitism are very low, this cannot be considered to represent an evolutionary equilibrium, as conventional theory has done to date, because it is not stable.     

To eject or to abandon? Life history traits of hosts and parasites interact to influence the fitness payoffs of alternative anti‐parasite strategies

Hosts either tolerate avian brood parasitism or reject it by ejecting parasitic eggs, as seen in most rejecter hosts of common cuckoos, Cuculus canorus, or by abandoning parasitized clutches, as seen in most rejecter hosts of brown‐headed cowbirds, Molothrus ater. What explains consistent variation between alternative rejection behaviours of hosts within the same species and across species when exposed to different types of parasites? Life history theory predicts that when parasites decrease the fitness of host offspring, but not the future reproductive success of host adults, optimal clutch size should decrease. Consistent with this prediction, evolutionarily old cowbird hosts, but not cuckoo hosts, have lower clutch sizes than related rarely‐ or newly parasitized species. We constructed a mathematical model to calculate the fitness payoffs of egg ejector vs. nest abandoner hosts to determine if various aspects of host life history traits and brood parasites’ virulence on adult and young host fitness differentially influence the payoffs of alternative host defences. These calculations showed that in general egg ejection was a superior anti‐parasite strategy to nest abandonment. Yet, increasing parasitism rates and increasing fitness values of hosts’ eggs in both currently parasitized and future replacement nests led to switch points in fitness payoffs in favour of nest abandonment. Nonetheless, nest abandonment became selectively more favourable only at lower clutch sizes and only when hosts faced parasitism by a cowbird‐ rather than a cuckoo‐type brood parasite. We suggest that, in addition to evolutionary lag and gape‐size limitation, our estimated fitness differences based on life history trait variation provide new insights for the consistent differences observed in the anti‐parasite rejection strategies between many cuckoo‐ and cowbird‐hosts.     

The ghosts of parasitism past: lingering frontline anti-brood parasite defenses in a former host

Coevolutionary arms races between brood parasites and hosts provide tractable systems for understanding antagonistic coevolution in nature; however, little is known about the fate of frontline antiparasite defenses when the host “wins” the coevolutionary arms race. By recreating bygone species interactions, using artificial parasitism experiments, lingering defensive behaviors that evolved in the context of parasitism can be understood and may even be used to identify the unknown agent of parasitism past. Here we present the first study of this type by evaluating lingering “frontline” nest defenses that have evolved to prevent egg laying in a former brood parasite host. The Australian reed warbler Acrocephalus australis is currently not parasitized but is known to exhibit fine-tuned egg discrimination—a defensive behavior indicative of a past brood parasite–host arms race and common in closely related parasitized species. Here, using 3D-printed models of adult brood parasites, we examined whether the Australian reed warbler also exhibits frontline defenses to adult brood parasites, and whether we could use these defenses to identify the warbler’s “ghost of parasitism past.” Our findings provide evidence that the Australian reed warbler readily engages in frontline defenses that are considered adaptive specifically in the context of brood parasitism. However, individuals were unable to discriminate between adults of different brood parasite species at their nest. Overall, our results demonstrate that despite a relaxation in selection, defenses against brood parasitism can be maintained across multiple stages of the host’s nesting cycle, and further suggest that, in accordance with previous findings, that learning may be important for fine-tuning frontline defense.     

Relationship Between Nest Predation Suffered by Hosts and Brown-Headed Cowbird Parasitism: A Comparative Study

There are at least four main hypotheses that may explain how the evolution of host selection by avian brood parasites could be linked to nest predation among their potential hosts. First, selection may have favoured parasite phenotypes discriminating among hosts on the basis of expected nest failure. Second, parasitized nests may be more easily detected by predators and extra costs of parasitism may accelerate the evolution of host defences. Third, selection may have favoured predator phenotypes avoiding parasitized nests because parasitism enhances nest defence. Fourth, female brood parasites may directly or indirectly induce host nesting failures in order to enhance future laying opportunities. We collected data on brood parasitism and nest failure due to predation to test these hypotheses in a comparative approach using North American passerines and their brood parasite, the brown-headed cowbird Molothrus ater. Under the hypotheses 1 or 3 we predicted brood parasitism to be negatively associated with nest predation across species, whereas this relation is expected to be positive if hypotheses 2 or 4 are true. We demonstrate that independent of host suitability, nest location, habitat type, length of the nestling period, body mass and similarity among species due to common ancestry, species experiencing relatively high levels of nest predation suffered lower levels of cowbird parasitism. Our results suggest a previously ignored role for nest predation suffered by hosts on the dynamics of the coevolutionary relationships between hosts and avian brood parasites. Co-ordinating editor: Dr. F. Stuefer     

Molecular tracking of individual host use in the Shiny Cowbird – a generalist brood parasite

Generalist parasites exploit multiple host species at the population level, but the individual parasite's strategy may be either itself a generalist or a specialist pattern of host species use. Here, we studied the relationship between host availability and host use in the individual parasitism patterns of the Shiny Cowbird Molothrus bonariensis, a generalist avian obligate brood parasite that parasitizes an extreme range of hosts. Using five microsatellite markers and an 1120‐bp fragment of the mtDNA control region, we reconstructed full‐sibling groups from 359 cowbird eggs and chicks found in nests of the two most frequent hosts in our study area, the Chalk‐browed Mockingbird Mimus saturninus and the House Wren Troglodytes aedon. We were able to infer the laying behavior of 17 different females a posteriori and found that they were mostly faithful to a particular laying area and host species along the entire reproductive season and did not avoid using previously parasitized nests (multiple parasitism) even when other nests were available for parasitism. Moreover, we found females using the same host nest more than once (repeated parasitism), which had not been previously reported for this species. We also found few females parasitizing more than one host species. The use of an alternative host was not related to the main hosts' nest availability. Overall, female shiny cowbirds use a spatially structured and host species specific approach for parasitism, but they do so nonexclusively, resulting in both detectable levels of multiple parasitism and generalism at the level of individual parasites.     

Parental care influences social immunity in burying beetle larvae

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Effect of temperature on circadian rhythm controlling the crepuscular activity of the burying beetle Nicrophorus quadripunctatus Kraatz (Coleoptera: Silphidae)

Locomotor activity rhythm was examined at various temperatures under a 16 h light : 8 h dark photoperiod (LD 16:8) or LD 12:12 using adults of the burying beetle Nicrophorus quadripunctatus. At 20°C, the locomotor activity of the beetles showed a bimodal daily pattern with two peaks around lights on and lights off under both photoperiods. This bimodal activity rhythm persisted under constant darkness; therefore, the activity of adult N. quadripunctatus is controlled by a circadian clock. Adults showed a bimodal activity pattern for temperatures ranging from 15 to 25°C. The evening peak of the daily activity was earlier at lower temperatures. These findings suggest that in the field, N. quadripunctatus shows crepuscular activity, and is active earlier in the afternoon in cooler seasons. In this species, therefore, temperature appears to play an important role in the determination of daily activity patterns.     

Does Brood Parasitism Induce Paternal Care in a Polygynous Host?

Red‐winged blackbirds (Agelaius phoeniceus) are a polygynous songbird with facultative biparental care, and a common host for brown‐headed cowbirds (Molothrus ater), an obligate brood parasite. We examined brood parasitism and paternal care in a long‐term study of parental care in red‐winged blackbirds. The presence of a cowbird nestling was associated with a higher likelihood of paternal care by the host male redwing in both naturally and experimentally parasitized nests. This result indicates that it was the presence of the brood parasite that was important and not simply that brood parasites chose hosts where paternal care was more likely. Both male and particularly female redwings increased provisioning to parasitized broods. Our work suggests that brood parasites raise the cost of parental care and push a polygynous host species toward monogamy.     

Timing of Spawning and Host-nest Choice for Brood Parasitism by the Japanese Minnow,Pungtungia herzi,on the Japanese Aucha Perch,Siniperca kawamebari

A field study of the breeding ecology of the Japanese aucha perch, Siniperca kawamebari, and brood parasitism by the Japanese minnow, Pungtungia herzi, on nests of the perch was carried out from 1989 to 1991. Observations of perch nests under natural conditions in 1990 showed that brood parasitism by the minnow was concentrated on host nests in which nest owners had just begun their nesting cycle. When spawned in a perch nest with recently spawned perch eggs, parasite eggs always hatched earlier than host eggs. An experiment with imitation perch eggs in 1991 confirmed that changing colour of host eggs was the cue for the parasites to distinguish between different developmental stages of host eggs. Parasite eggs rapidly disappeared without guarding by a host male (Baba et al. 1990). This loss was caused by predation by fishes. Parasite fry left the nest immediately after hatching, so parasite eggs spawned in a host nest in an early stage should be well guarded until they hatch. In the field, minnows deposited their eggs in perch nests which had larger numbers of newly spawned perch eggs. Since the perch males always deserted their nests when their own eggs disappeared, the parasite's choice of host nests with larger numbers of host eggs may ensure survival of the parasite eggs. The timing of egg deposition and choice of host nest by the minnow appear to be adaptive in terms of brood parasitism on nests of the perch.     

Prevalence of the parasite Strepsiptera in <Emphasis Type="Italic">Polistes</Emphasis> as detected by dissection of immatures

Summary. hough the paper wasp genus, Polistes, is well studied, we know little of the incidence of parasitism in this group. Here we present details of 45 nest dissections for 4 species: P. dominulus (Christ), P. gallicus (L.), P. stabilinus Richards and P. carnifex (F.) to detail levels of parasitism of colony members by the obligate parasitic group of insects, the Strepsiptera. All 4 species showed evidence of parasitism among immature members. For 3 species, more than 50% of inspected nests were parasitized and the levels of parasitism among brood (larvae and pupae) was very high and did not differ significantly between parasitized nests. One species, P. stabilinus, suffered very low levels of parasitism, which may be related to its habitat choice. The number of parasites per host was positively related to the proportion of infected brood (parasite prevalence) and in some cases reached phenomenally high levels, which casts doubt on previ ously assumed mechanisms of infection for nest-making Hymenoptera, i.e. phoresy. We also document cases of egg parasitism and encapsulation in Polistes nests. Our data show that parasitism levels greatly varied among areas. Finally, the recent debate on the competitive advantage of P. dominulus in its introduced range, USA, has credited an absence of strepsipteran parasites of this species in facilitating its spread. For the first time, we document levels of parasitism for this species in its nature P range and this would appear to corroborate previous claims. We place our work in the context of other studies of parasitism of social insects and posit that the genus Polistes may have much to offer to this field.     

Brood parasitism by brown-headed cowbirds and the expression of sexual characters in their hosts

Interspecific brood parasites may use the secondary sexual characters of the hosts to decide which species to parasitize. Hence, species with conspicuous and well-recognisable traits may have higher chances of becoming parasitised. Using North American birds and their frequent brood parasite, the brown-headed cowbird Molothrus ater, we tested the relationship between features of song and plumage coloration of hosts and the frequency of brood parasitism while controlling for several potentially confounding factors. Relying on two sets of analysis, we focused separately on the evolutionary view of the parasite and the host. From the cowbirds perspective, we found that males of heavily parasitized species posit songs with low syllable repertoire size, shorter inter-song interval and have brighter plumage. From the hosts perspective, a phylogenetic analysis revealed similar associations for features of song, but not for plumage characteristics that were unrelated to brood parasitism. These comparative findings may imply that brood parasites choose novel hosts based on heterospecific signals; and/or host species working against sexual selection escape from brood parasitism by evolving inconspicuous sexual signals. Although our data do not allow us to distinguish between these two evolutionary scenarios, our results suggest that selection factors mediating cowbird parasitism via host recognition by heterospecific signals may have an important role in the evolutionary relationship between brood parasites and their hosts.Electronic Supplementary Material Supplementary material is available for this article at     

Facultative social parasitism in the allodapine bee Macrogalea berentyensis

Previous research on social parasitism has largely ignored allodapine social parasites, which is surprising given the huge potential of these bees to provide a better understanding of social parasitism. Macrogalea berentyensis, a species that was previously suggested to be a social parasite, was collected in nests of M. ellioti, and also in nests consisting of only M. berentyensis. These f＇mdings, along with morphological and phylogenetic evidence, show that this species is a facultative social parasite. In the independently living M. berentyensis nests, brood were present that had been reared to an advanced stage, suggesting that： （i） these parasites may be effective at foraging and caring for their brood; or （ii） these nests may be colonies where all the hosts had died, and these parasites had yet to disperse. Macrogalea berentyensis is the closest relative of the facultative social parasite, M. antanosy, and both these species represent the most recent evolutionary origin of social parasitism within the allodapines. Further behavioral research on both these parasitic species would therefore have important implications for the understanding of the evolution of social parasitism.     

Evolution of social parasitism in ants: size of sexuals,sex ratio and mechanisms of caste determination

Social parasitism, one of the most intriguing phenomena in ants, has evolved to various levels, the most extreme form being parasites that have lost the worker caste and rely completely on the host''s worker force to raise their brood. A remarkable feature of workerless social parasites is the small size of sexuals. It has been suggested that reduced size evolved as a means to take advantage of the host''s caste-determination system, so that parasite larvae develop into sexuals with less food than is required to produce host workers. An important consequence of size reduction is that it might restrict the host workers'' ability to discriminate between the brood of the social parasite and their own brood and might protect parasite sexuals from elimination. We found that sexuals of the workerless inquiline ant Plagiolepis xene were significantly smaller than the sexuals of their host Plagiolepis pygmaea, but remarkably similar to the host workers. The size variance of parasite sexuals was much lower than that of their host; this result possibly suggests that there is very stabilizing selection acting on size of the parasite sexuals. Comparison of the primary (egg) and secondary (adult) sex ratios of the parasite and host showed that miniaturization of P. xene sexuals has been accompanied by their ability to develop into sexuals even when the host P. pygmaea actively prevents production of its own sexuals. These results suggest that the inquiline''s size and caste threshold have been reduced such that all individuals in a parasite brood will develop into sexuals. We also found that the adult sex ratio of P. xene was heavily female-biased. This bias probably stems from local mate competition that arises from sexuals mating within the nest. There was no significant difference between the proportion of haploid eggs and adult males produced; this observation indicates that a female-biased sex ratio is achieved by queens producing a higher proportion of diploid eggs rather than by a higher mortality of haploid males.