When David and Goliath share a home: Compound nesting of Pyramica and Platythyrea ants

We documented a commensal association between two phylogenetically distant ant subfamilies (Ponerinae and Myrmicinae). The host (Platythyrea conradti) and its tiny guest (Pyramica maynei) nest in the same hollow branches in West African forests. Brood chambers are adjacent but separate, and the guest scavenges on prey remains of the host, which may benefit from improved nest hygiene. Two mated dealate queens of Pyramica were collected in one small Platythyrea nest, suggesting that they can hunt (non-claustral foundation) in the safe environment provided. An experiment showed that the guest can survive alone and was able to hunt collembolans. Received 14 March 2006; revised 18 May 2006; accepted 24 May 2006.     

Shared parental care is costly for nestlings of common cuckoos and their great reed warbler hosts

Obligate avian brood parasitism typically involves one of 2strategies: parasite chicks are either 1) virulent and evictall other eggs and nest mates to be raised alone or 2) moretolerant and share foster parental care with host chicks forsome or the entirety of the nestling period. We studied theconsequences of experimentally forced mixed broods of age-matchedone common cuckoo (Cuculus canorus) and 2 great reed warbler(Acrocephalus arundinaceus) chicks. In these broods, both cuckooand host chicks grew slower than did either individual cuckoosor great reed warblers in broods of 1 parasite or 3 host chicks,respectively. Video records showed that in mixed broods, cuckoochicks received feedings less frequently than the 33% predictedby chance at 4 days of age but parental food allocations increasedto chance levels at 8 days of age. The consistent patterns oflower growth rates arose even though chicks in broods of 1 parasiteand 2 hosts received the largest prey items per feeding. Inaddition, several other measures of parental provisioning alsodid not predict species and brood-specific differences in nestlinggrowth rates across the different treatments. However, variationin begging displays and its specific costs on host and parasitechicks in the different nest treatments were not quantifiedin this study. We conclude that young of nest mate–evictorcommon cuckoos benefit from the sole occupancy of host nestsin part owing to an initial competitive disadvantage for parentalcare in broods with age-matched great reed warbler chicks.     

Competition with a host nestling for parental provisioning imposes recoverable costs on parasitic cuckoo chick's growth

Chicks of the brood parasitic common cuckoo (Cuculus canorus) typically monopolize host parental care by evicting all eggs and nestmates from the nest. To assess the benefits of parasitic eviction behaviour throughout the full nestling period, we generated mixed broods of one cuckoo and one great reed warbler (Acrocephalus arundinaceus) to study how hosts divide care between own and parasitic young. We also recorded parental provisioning behaviour at nests of singleton host nestlings or singleton cuckoo chicks. Host parents fed the three types of broods with similar-sized food items. The mass of the cuckoo chicks was significantly reduced in mixed broods relative to singleton cuckoos. Yet, after the host chick fledged from mixed broods, at about 10-12 days, cuckoo chicks in mixed broods grew faster and appeared to have compensated for the growth costs of prior cohabitation by fledging at similar weights and ages compared to singleton cuckoo chicks. These results are contrary to suggestions that chick competition in mixed broods of cuckoos and hosts causes an irrecoverable cost for the developing brood parasite. Flexibility in cuckoos' growth dynamics may provide a general benefit to ecological uncertainty regarding the realized successes, failures, and costs of nestmate eviction strategies of brood parasites.     

The reproductive phenology of an Amazonian ant species reflects the seasonal availability of its nest sites

In saturated tropical ant assemblages, reproductive success depends on queens locating and competing for scarce nest sites. Little is known about how this process shapes the life histories of tropical ants. Here I investigate the relationship between nest site availability and an important life history trait, reproductive phenology, in the common Amazonian ant species Allomerus octoarticulatus. A. octoarticulatus is a plant-ant that nests in the hollow, swollen stem domatia on Cordia nodosa. I provide evidence that nest sites are limiting for A. octoarticulatus. Most queens produced by A. octoarticulatus colonies died before locating suitable host plants, and most queens that located hosts died before founding colonies, probably from intraspecific competition among queens for control of host plants. I further show that the reproductive phenology of A. octoarticulatus closely matches the seasonal availability of its nest sites, domatia-bearing C. nodosa saplings. Both the production and flight of A. octoarticulatus reproductives, and the number of C. nodosa saplings available for colonization by ants, peaked from March to May. There was correlative evidence that A. octoarticulatus colonies use temperature as a cue to synchronize their reproduction to the availability of C. nodosa saplings: both the production of reproductives by ant colonies and the number of C. nodosa saplings available for colonization were correlated with temperature, and not with rainfall. All of these results suggest that nest site limitation constrains the reproductive phenology of A. octoarticulatus.     

Rediscovery of the workerless inquiline antPogonomyrmex colei and additional notes on natural history (Hymenoptera: Formicidae)

Summary Pogonomyrmex colei is a workerless inquiline ant known only from nests ofP. rugosus, its closest relative. Ten of 776 (1.3%) host nests were parasitized at a site in central Arizona, while none of 1499 potential host colonies were parasitized at two other locales. Colonies ofP. colei are perennial, and host alate females in 9 of 10 colonies demonstrates that host queens survive parasitism. Three of 10 colonies died over 19 colony years of observation, while only 1 of 601 colonies became newly parasitized. Mating occurs in morning for up to 2–3 days following summer and fall rains and in afternoon during cool fall days. Mating is intranidal just outside the nest entrance, with males returning to the natal nest. MaleP. colei may be flightless because their wing area is reduced compared to host males. Females fly from the nest and locate potential host colonies by following trunk trails. Workers are the largest barrier to nest establishment, as they removed over 90% ofP. colei females placed in trunk trails or that entered host nests. Males and females ofP. colei andP. anergismus, the only other congeneric inquiline species, are diminutive compared to their hosts, with females 30% lighter than host workers. Fat content is lower and water content is higher inP. colei andP. anergismus females than in their hosts.     

Host adaptation in the anther smut fungus Ustilago violacea (Microbotryum violaceum): infection success,spore production and alteration of floral traits on two host species and their F1-hybrid

It is often assumed that host specialization is promoted by trade-offs in the performance of parasites on different host species, but experimental evidence for such trade-offs is scant. We studied differences in performance among strains of the anther smut fungus Ustilago violacea from two closely related host plant species, Silene alba and S. dioica, on progeny of (1) the host species from which they originated, (2) the alternative host species, and (3) inter-specific hybrids. Significant intra-specific variation in the pathogen was found for both infection success on a range of host genotypes (virulence) and components of spore production per infected host (aggressiveness) (sensu Burdon 1987). Strains did not have overall higher virulence on conspecifics of their host of origin than on strains from the heterospecific host, but they did have a significantly (c. 3 times) higher spore production per infected male host. This finding suggests that host adaptation may have evolved with respect to aggressiveness rather than virulence. The higher aggressiveness of strains on conspecifics of their host of origin resulted both from higher spore production per infected flower (spores are produced in the anthers), and greater ability to stimulate flower production on infected hosts. The latter indicates the presence of adaptive intraspecific variation in the ability of host manipulation. As transmission of the fungus is mediated by insects that are both pollinators of the host and vectors of the disease, we also assessed the effect of strains on host floral traits. Infection resulted in a reduction of inflorescence height, flower size, and nectar production per flower. Strains did not differ in their effect on nectar production, but infection with strains from S. alba resulted in a stronger reduction of inflorescence height and petal size on both host species. Vectors may therefore in principle discriminate among hosts infected by different strains and affect their efficiency of transmission. Contrary to assumptions of recent hypotheses about the role of host hybrids in the evolution of parasites, hybrids were not generally more susceptible than parental hosts. It is therefore unlikely that the rate of evolution of the pathogen on the parental species is slowed down by selection for specialization on the hybrids.     

Field evidence that host selection by conopid parasitoids is related to host body size

Summary The body size of the host insect in which a parasitoid develops can have important effects on its development and life history. Large and small host body size have both been suggested to be advantageous to parasitoids, depending on the life-history of the species concerned. We test field data on the bumblebeeBombus terrestris and its conopid parasitoids for evidence of differences in size between parasitised and unparasitised worker bees. Bees acting as hosts for conopid parasitoids are on average larger-bodied than unparasitised bees. This result holds for bees collected in two different years, and whether bees are collected while foraging or from the nest. The results we present demonstrate differential parasitism of hosts of different body sizes, but do not necessarily indicate active host choice by conopids. However, they are in agreement with independent evidence that conopids develop more successfully in large-than in small-bodied hosts.     

Influence of host profitability and microenvironmental conditions on parasite specialization on a main and an alternative hosts

Parasite success depends on both host profitability and the microenvironment provided by the host, which together define host-parasite compatibility and can differ between hosts. We experimentally disentangled the effects of host profitability and microenvironmental conditions provided by nest material on the reproduction of a nest-based ectoparasite when exploiting its main and an alternative avian host species. Parasite reproductive performance was similar on both hosts when breeding in nests of their own species, suggesting no difference in host-parasite compatibility between hosts. The apparent parasite specialization could therefore result from differences in host-parasite encounter processes. However, when hosts were successful, the main host produced more young in infested nests, whereas the alternative host produced less; furthermore, host reproductive performance was higher in nests of the main host species, suggesting that this nest material alleviates parasitism cost. Therefore, our results suggest different evolutionary responses to parasites of the main and alternative hosts, with either higher tolerance or higher resistance, modulated by nest material.     

Parental care behavior in the monogamous,sexually dimorphic Madagascar paradise flycatcher: sex differences and the effect of brood size

I studied the parental care behavior of the Madagascar paradise flycatcher Terpsiphone mutata in northwestern Madagascar. I especially focused on feeding, brooding and vigilance behaviors. Feeding rate did not differ between males and females, but females spent more time at the nest than males. Females dedicated their time to brooding, while males perched on the nest and were vigilant. Both parents changed the feeding rate in relation to brood size, so the feeding rate per nestling was not different among nests of different brood size. Duration of brooding by females increased with decreasing brood size, suggesting that the Royama effect, the pattern of lower feeding rate per nestling in larger broods, did not apply in this study. Males spent more time on vigilance than females. Anti-predator vigilance by males should be important for nestling survival given the high predation pressure typical of this population. In conclusion, males provide considerable parental care probably to minimize nestling starvation and to avoid nest predation. My results are not consistent with the general pattern of less parental effort by males in monogamous, sexually dimorphic species.     

Polygynous great reed warblers Acrocephalus arundinaceus suffer more cuckoo Cuculus canorus parasitism than monogamous pairs

There is increasing evidence that hosts within a population may not be parasitized by common cuckoos Cuculus canorus with equal probability. Such non‐randomness has been documented, for example, for host nest sites and host quality. In this study we demonstrate association between successful cuckoo parasitism and host social mating system. We found that nests of socially polygynous great reed warblers Acrocephalus arundinaceus were more often successfully parasitized than the nests of their monogamous counterparts. We hypothesize that lack of parental assistance provided by polygynous males to their mates during egg laying period and higher nest activity in their territories could contribute to this discrepancy. These data imply that social mating system should be taken into account in future studies of brood parasitism.     

Effects of Common Origin and Common Rearing Environment on Variance in Ectoparasite Load and Phenotype of Nestling Alpine Swifts

Knowledge of the quantitative genetics of resistance to parasitism is key to appraise host evolutionary responses to parasite selection. Here, we studied effects of common origin (i.e. genetic and pre-hatching parental effects) and common rearing environment (i.e. post-hatching parental effects and other environment effects) on variance in ectoparasite load in nestling Alpine swifts (Apus melba). This colonial bird is intensely parasitized by blood sucking louse-flies that impair nestling development and survival. By cross-fostering half of the hatchlings between pairs of nests, we show strong significant effect of common rearing environment on variance (90.7% in 2002 and 90.9% in 2003) in the number of louse-flies per nestling and no significant effect of common origin on variance in the number of louse-flies per nestling. In contrast, significant effects of common origin were found for all the nestling morphological traits (i.e. body mass, wing length, tail length, fork length and sternum length) under investigation. Hence, our study suggests that genetic and pre-hatching parental effects play little role in the distribution of parasites among nestling Alpine swifts, and thus that nestlings have only limited scope for evolutionary responses against parasites. Our results highlight the need to take into consideration environmental factors, including the evolution of post-hatching parental effects such as nest sanitation, in our understanding of host-parasite relationships.     

The effect of environmental factors on the nesting and courtship behaviour ofTilapia zillii in Lake Kinneret (Israel)

Tilapia zillii is a polyphilic, guarding nest spawner which is widespread in west and north Africa and in the Middle East. A study of the nesting and courtship behaviour of this species in Lake Kinneret (Sea of Galilee), revealed that nesting and brood care differ according to the exposure of the nesting site to wave action and the nature of the substrate. The nests are simple and parental care is abbreviated in exposed, sandy sites whereas elaborate nests with brood chambers are excavated in sheltered areas with clayey substrates, and parental care is extensive. The implications of these findings to studies on cichlid breeding and the conservation ofT. zillii in Lake Kinneret are discussed.     

Breeding biology and provisioning of nestling snow buntings in the Canadian High Arctic

We examined basic breeding biology, as well as the effects of parental sex, brood size, nestling age, and nest habitat on foraging distances and parental food delivery rates of snow buntings (Plectrophenax nivalis) on Devon Island, NT, Canada, in the summers of 2003–2006. Clutch sizes and initiation dates were similar to those found in previous studies, although nest density was much higher. Feeding rates and foraging distances of buntings differed depending on the size and age of the brood, but were similar between nest habitats. Unlike in earlier studies, we found that male buntings made fewer feeding visits, but traveled longer distances to forage for food than females. Whether these differences between the sexes relate to reducing competition for prey, or to differing sex roles in parental care due to the poorly insulated nest cavities of this species, remains to be determined.     

Effect of host density on offspring sex ratios and behavioral interactions between females in the parasitoid waspNasonia vitripennis (Hymenoptera: Pteromalidae)

Pairs of females of the parasitoid waspNasonia vitripennis were videotaped with one or two hosts. The presence of an additional host decreased the number of interactions between females but had no measured effect on the nature of the interactions, i.e., on whether the interaction involved physical contact or occurred while one of the females was parasitizing a host. The number of hosts did not itself affect offspring sex ratios but did influence which other factors were correlated with sex ratio. When there was one host, the proportion of sons was more positively correlated with utilization of previously drilled holes than with female-female interactions, whereas when there were two hosts, the reverse was true. Parasitizing an already parasitized host appeared to affect a female's sex ratio beyond any effects of the physical presence of another female: When two hosts were present, the proportion of sons was greater from hosts parasitized by both females than from hosts parasitized by only one female. The observation that parasitizations in previously drilled holes and female-female interactions are correlated with sex ratios is consistent with previous studies; however, that these relationships are host density dependent is a new result and remains unexplained.     

Trade-offs between arbuscular mycorrhizal fungal competitive ability and host growth promotion in Plantago lanceolata

In this study we tested for trade-offs between the benefit arbuscular mycorrhizal (AM) fungi provide for hosts and their competitive ability in host roots, and whether this potential trade-off shifts in the presence of a plant stress (herbivory). We used three species of AM fungi previously determined to vary in host growth promotion and spore production in association with host plants. We found that these AM fungal species competed for root space, and the best competitor, Scutellospora calospora, was the worst mutualist. In addition, the worst competitor, Glomus white, was the best mutualist. Competition proved to have stronger effects on fungal infection patterns than herbivory, and competitive dominance was not altered by herbivory. We found a similar pattern in a previous test of competition among AM fungi, and we discuss the implications of these results for the persistence of the mutualism and feedbacks between AM fungi and their plant hosts.     

Benefits of self-superparasitism in a polyembryonic parasitoid

Macrocentrus grandii is a polyembryonic parasitoid, with embryos that divide asexually within the host (European corn borer, Ostrinia nubilalis) to produce broods of clonal offspring. From a biological control standpoint, polyembryony seems advantageous because each parasitized host yields multiple parasitoids with minimal time and egg investment. When we observed M. grandii in the field, however, we found that the parasitoid virtually always invested additional time and, if possible, stings into hosts that it had already stung, apparently reducing some of the advantages of polyembryony. We therefore investigated and found support for two potential benefits that can be gained by self-superparasitism in this system. First, multiple stings allowed production of mixed-sex broods: 27% of multiply-stung versus 0% of singly-stung hosts produced mixed-sex broods. Second, multiple stings increased mean parasitoid progeny produced per host, primarily by reducing the chance of complete brood failure. Our results indicate substantial benefit for a second sting, but little benefit for three or more stings, even though M. grandii was sometimes observed to invest more than two stings within a single host. However, we also found that within-host larval competition is prevalent, suggesting that supernumerary stings may pay off in competition against conspecific larvae. Such additional investment within a single host would be particularly beneficial when hosts, rather than eggs, are limiting, but would decrease the overall efficacy of M. grandii as a biological control agent.     

The distribution of <Emphasis Type="Italic">Symbiodinium</Emphasis> diversity within individual host foraminifera

While one-to-one specificity between reef-dwelling hosts and symbiotic dinoflagellates of the genus Symbiodinium may occur, detailed examination of some hosts reveals that they contain multiple symbiont types. Individuals of the foraminifer Amphisorus hemprichii living in Papua New Guinea contained mixed communities of Symbiodinium dominated by symbiont types in clades C and F. Moreover, the types showed a distinct pattern in their distribution across the radius of the foraminifer, with clade F Symbiodinium more prevalent in the center of the host cell. The mixed community of symbionts and their pattern of distribution within the foraminifer is likely the result of processes happening both inside the foraminifer and in its external environment. Persistent mixed symbiont communities in foraminifera may be stabilized through benefits conferred by maintaining multiple symbiont lineages for symbiont shuffling. Alternatively they may be stabilized through a heterogeneous internal host environment, partitioning of symbiont functional roles or limitation of symbiont reproduction by the host. Six factors generally determine the presence of any particular symbiont type within a foraminifer: mode of transmission, availability from the environment, recognition by the host, regulation by the host, competition between lineages, and fitness of the holobiont. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Density-dependent habitat selection by brown-headed cowbirds (<Emphasis Type="Italic">Molothrus ater</Emphasis>) in tallgrass prairie

Local distributions of avian brood parasites among their host habitats may depend upon conspecific parasite density. We used isodar analysis to test for density-dependent habitat selection in brown-headed cowbirds (Molothrus ater) among tallgrass prairie adjacent to wooded edges, and prairie interior habitat (>100 m from wooded edges) with and without experimental perches. Eight study sites containing these three habitat treatments were established along a geographical gradient in cowbird abundance within the Flint Hills region of Eastern Kansas and Oklahoma, USA. The focal host species of our study, the dickcissel (Spiza americana), is the most abundant and preferred cowbird host in the prairie of this region. Cowbird relative abundance and cowbird:host abundance ratios were used as estimates of female cowbird density, whereas cowbird egg density was measured as parasitism frequency (percent of dickcissel nests parasitized), and parasitism intensity (number of cowbird eggs per parasitized nest). Geographical variation in cowbird abundance was independent of host abundance. Within study sites, host abundance was highest in wooded edge plots, intermediate in the experimental perch plots, and lowest in prairie interior. Cowbirds exhibited a pattern of density-dependent selection of prairie edge versus experimental perch and interior habitats. On sites where measures of cowbird density were lowest, all cowbird density estimates (female cowbirds and their eggs) were highest near (100 m) wooded edges, where host and perch availability are highest. However, as overall cowbird density increased geographically, these density estimates increased more rapidly in experimental perch plots and prairie interiors. Variation in cowbird abundance and cowbird:host ratios suggested density-dependent cowbird selection of experimental perch over prairie interior habitat, but parasitism levels on dickcissel nests were similar among these two habitats at all levels of local cowbird parasitism. The density-dependent pattern of cowbird distribution among prairie edge and interior suggested that density effects on perceived cowbird fitness are greatest at wooded edges. A positive relationship between daily nest mortality rates of parasitized nests during the nestling period with parasitism intensity levels per nest suggested a density-dependent effect on cowbird reproductive success. However, this relationship was similar among habitats, such that all habitats should have been perceived as being equally suitable to cowbirds at all densities. Other unmeasured effects on cowbird habitat suitability (e.g., reduced cowbird success in edge-dwelling host nests, cowbird despotism at edges) might have affected cowbird habitat selection. Managers attempting to minimize cowbird parasitism on sensitive cowbird hosts should consider that hosts in otherwise less-preferred cowbird habitats (e.g., habitat interiors) are at greater risk of being parasitized where cowbirds become particularly abundant.     

Recognition of heterospecific parasitism: Competition between Aphidiid (Aphidius ervi) and Aphelinid (Aphelinus asychis) parasitoids of Aphids (Hymenoptera: Aphidiidae; Aphelinidae)

The solitary parasitoids Aphidius erviHaliday (Hymenoptera: Aphidiidae) and Aphelinus asychisWalker (Hymenoptera: Aphelinidae) attacked but generally did not oviposit in pea aphids parasitized by the other species. Wasps selectively oviposited in unparasitized hosts when given a choice. Host discrimination depended on the recognition of internal cues. Females of A. asychiseither could not recognize or ignored A. ervi'sexternal host marking pheromone. Under most conditions, A. ervisurvived in superparasitized hosts, killing competing A. asychislarvae by physical attack and possibly physiological suppression. The outcome of larval competition was not affected by oviposition sequence or age difference between larvae; A. asychissurvived only when it had substantially completed larval development before the host was superparasitized by A. ervi.It is suggested that competition for host resources incurs a cost, for the winner in terms of reduced size or increased development time and for the loser in terms of lost progeny and searching time. Consequently, heterospecific host discrimination can be functional. Internal, and probably general, cues enable wasps to recognize and avoid oviposition in hosts already parasitized by an unrelated species.     

Zombie fire ant workers: behavior controlled by decapitating fly parasitoids

Laboratory observations were conducted on four separate red imported fire ant, Solenopsis invicta, colonies that contained workers parasitized by the decapitating fly, Pseudacteon tricuspis. Parasitized S. invicta workers remained inside the nest during parasitoid larval development and left the nest approximately 8 – 10 hours before decapitation by the parasitoid. When parasitized ants left the nest, they were highly mobile, were responsive to tactile stimuli, and showed minimal defensive behavior. Ants ultimately entered into a grass thatch layer, where they were decapitated and the fly maggots pupariated. This study reveals that parasitized ants exhibit behaviors that are consistent with host manipulation to benefit survival of the parasitoid. Received 9 November 2006; revised 26 January 2007; accepted 7 February.