Process of comb division of reused nests in the Australian paper waspRopalidia plebeiana (Hymenoptera,Vespidae)

Summary InRopalidia plebeiana, combs made in the previous year are often reused by foundresses in the following spring and structurally divided into subnests by them. Close observations of the comb dividing process revealed that: 1) combs that had multiple brood areas (areas where cells had eggs) were frequently divided into subnests, while those with single brood areas were never divided; 2) groups of foundresses each occupied a particular brood area even before comb division started; and 3) frequency with which a foundress practiced comb cutting was independent of her social status or oviposition frequency. These observations suggest that the initial grouping of foundresses that colonize an old nest leads to subsequent comb division, rather than the major egg layers cutting combs to safeguard their oviposition territories from their rivals.     

Social behaviour of two primitively eusocial wasps,Ropalidia sp. nr.variegata andR. gregaria gregaria (Hymenoptera: Vespidae) in the Northern Territory,Australia, with special reference to task specialization and mating inhibition

Social behaviour of females of the Australian paper wasps,Ropalidia sp. nr.variegata (V) andR. gregaria gregaria (G) was observed near Darwin, the Northern Territory, Australia. Both species constructed multiple combs after the emergence of the first progeny. Frequency of intranidal dominance acts in speciesV on the post-emergence nests was significantly higher than that on the pre-emergence nests, while the frequency was constantly high in speciesG throughout the pre- and post- emergence periods. Some females ofG were specialized, at least on single days, to perform the particular task of water collection. In both species the dominant female tended to occupy the largest comb and subordinate females smaller combs. InG, not only the top-ranked female but also low-ranked ones oviposited, and a small proportion of eggs laid by the latter survived at least until the end of observation. InV, each colony had only 1 inseminated female which had highly developed ovaries, suggesting that subordinate females do not mate despite the presence of males. Such a limitation of mating to a single female in a colony has not been described previously in primitively eusocial wasps.     

Mate Choice and Mating Pattern in a Stream Goby of the Genus Rhinogobius

The mate choice and mating pattern of a benthic goby Rhinogobius sp. CB (cross band type) were investigated in the Kamo River, Shikoku, Japan. During the breeding season, gravid females assumed a nuptial color and either males or females initiated a courtship display. Males preferentially courted a female of similar size to lead her to his nest, whereas females courted more frequently when they encountered a large male. Eggs in any one nest were always at the same developmental stage. Sampling data of nesting males and females indicated that, in more than half the nests, males gathered more than one female before spawning. In some nests with eggs, two or three females had spent ovaries, indicating that the eggs were laid by multiple females within a short span of time. However, a comparison between the total number of eggs which females would spawn in one nest and the number of eggs actually deposited suggested that eggs were contributed by one female in most nests. This low level of polygyny in spite of multiple female availability is attributed to a limited available spawning area of the nest.     

Reconstruction ofRopalidia fasciata nests by progeny females after a typhoon and its significance in the social evolution of wasps

A strong typhoon, Typhoon 13, which swept through Okinawa on 2 and 3 September 1993, knocked down 57 to 61 of 97Ropalidia fasciata nests. Thirty-five colonies soon reconstructed their nests, and these nests produced 54±46 adults per nest during the remaining two and a half months before winter. The number of females involved in nest reconstruction was 21.3±15.7 per nest. The frequency of foraging activity was significantly higher in nests being reconstructed than in normal nests. As only one out of 205 foundresses marked in spring was found in early September, most cases of nest reconstruction were considered to be made exclusively by females that emerged during the spring and summer of 1993 (progeny females). All of the reconstructed nests but one produced adult females. Many females (31%) collected from the two reconstructed nests were inseminated. As all the reconstructed nests became vacant by early January, indicating completion of the colony cycle, and a large number of nests were established in the spring of 1994, females emerging from reconstructed nests in 1993 probably become foundresses in 1994.Ropalidia fasciata is considered to be, at least partially, bivoltine in Okinawa. The significance of these facts for the evolution of multi-queen social systems in the Polistinae is discussed.     

Water loss in desert ants: caste variation and the effect of cuticle abrasion

Water loss rates (WLRs) varied across castes (workers > alate males > alate females) for desert ants in the genera Aphaenogaster, Messor and Pogonomyrmex. Exposure to soil caused increased WLRs in workers and foundresses (mated, dealate females), apparently because of cuticular abrasion caused by nest excavation. Moreover, field‐collected workers and foundresses from incipient nests (those exposed to soil) had similar WLRs, as did unabraded workers and alate females (those unexposed to soil). These data call into question previous adaptive scenarios for differences in WLRs across ant species and castes. For live alate females, WLRs increased over two stages. The first increase occurred immediately after mating, and the second occurred for foundresses collected 2 days later from incipient nests. By contrast, WLRs of HCN‐killed females were unaffected by mating, but increased significantly for foundresses collected from 2‐day‐old nests.     

Colony development and social structure in a subtropical paper wasp,Ropalidia fasciata (F.) (Hymenoptera: Vespidae)

More than 50% of nests of Ropalidia fasciata were founded by association of foundresses (multifemale nests). The multifemale nests were generally initiated earlier and grew faster than the single-female nests. The survival rate of the multifemale nests was significantly higher than that of single-female nests, and the productivity as measured by the number of cells produced per foundress had a peak at a foundress-group size from 6 to 10. The number of marked foundresses which were seen on their original nest decreased as the colony cycle proceeded, but some of them continued to coexist on the original nests after emergency of many female progeny. Except in the case where a large number of foundresses attended a young nest so that some foundresses could not sit on the nest, the dominance interactions among cofoundresses were mild. More than twothirds (71.4%) of nests (including those at the post-emergence stage) had multiple egg-layers. The foundress association in this species is considered to be beneficial for every foundress because it raises ability to avoid predation or to reconstruct their nests when the nests are destroyed by typhoons.     

Virgin wasps develop ovaries on par with mated females, but lay fewer eggs

In the primitively eusocial wasp Ropalidia marginata, mating is not necessary for a female wasp to develop her ovaries, lay eggs, and even to become the sole egg layer of her colony despite the presence of other mated nestmates. Here, we show that virgin wasps do not differ from their mated counterparts in the extent and rapidity of their ovarian development, in the proportion of individuals that build a nest and laid eggs, and in the time taken to do so. However, a significantly larger proportion of virgin females showed resorbing oocytes, and laid fewer eggs as compared to mated individuals. Thus, virgin females have the ability to develop ovaries and lay eggs but also to refrain from necessarily laying all mature eggs produced, before mating opportunities arise. This dual ability would be adaptive in haplodiploid, tropical species with perennial nesting cycles and frequent opportunities for workers to become replacement queens or solitary nest foundresses throughout the year.     

Egg morphology fails to identify nests parasitized by conspecifics in common pochard: a test based on protein fingerprinting and including female relatedness

Conspecific brood parasites lay eggs in nests of other females of the same species. A variety of methods have been developed and used to detect conspecific brood parasitism (CBP). Traditional methods may be inaccurate in detecting CBP and in revealing its true frequency. On the other hand more accurate molecular methods are expensive and time consuming. Eadie developed a method for revealing CBP based on differences in egg morphology. That method is based on Euclidean distances calculated for pairs of eggs within a clutch using standardized egg measurements (length, width and weight). We tested the applicability of this method in the common pochard Aythya ferina using nests that were identified as parasitized (39 nests) or non‐parasitized (16 nests) based on protein fingerprinting of eggs. We also analyzed whether we can distinguish between parasitic and host eggs in the nest. We found that variation in MED can be explained by parasitism but there was a huge overlap in MED between parasitized and non‐parasitized nests. MED also increased with clutch size. Using discriminant function analysis (DFA) we found that only 76.4% of nests were correctly assigned as parasitized or non‐parasitized and only 68.3% of eggs as parasitic or host eggs. Moreover we found that MED in parasitized nests increased with relatedness of the females that laid eggs in the nest. This finding was supported by positive correlation between MED and estimated relatedness in female–female pairs. Although variation in egg morphology is associated with CBP, it does not provide a reliable clue for distinguishing parasitized nests from non‐parasitized nests in common pochard.     

Comparison of intraspecific nest usurpation between two haplometrotic paper wasp species (Hymenoptera: Vespidae:Polistes)

Intraspecific nest usurpation by foundresses was studied in 2 haplometrotic (solitary founding) species of different subgenera,Polistes (P.) riparius andP. (Polistella) snelleni, in areas where they cohabited. The overall probability for a nest to be usurped by a foreign foundress during the season was about twice as large inP. snelleni as inP. riparius. In both, however, probability of usurpation was largest on late pre-emergence nests, or in late June and early July. InP. riparius, all the usurpers of known origins were those foundresses that had lost their pre-emergence nests to destruction probably by some vertebrates; inP. snelleni, some usurpers had the same history as above, while the others had lost many of all larvae to predation by unknown agents before worker emergence. Usurpers of both species destroyed eggs and younger larvae to much greater extents than older larvae or pupae, and they produced fewer numbers of reproductives in comparison with non-usurping foundresses. We concluded that usurpation behavior has been maintained despite its relatively low productivity because renesting would lead to even lower or no reproductive production.     

Colony kin structure and breeding patterns in the social wasp, <Emphasis Type="Italic">Polistes biglumis</Emphasis>

We used DNA microsatellites to study colony kin structure and breeding patterns in the primitively eusocial wasp Polistes biglumis. P. biglumis inhabits cool areas at high altitudes and, as a consequence, has a reduced colony cycle compared to more temperate Polistes. P. biglumis colonies are always founded and controlled by a single foundress, but nest failure is common and foundresses losing their nests do not have time to start new ones due to the short season. Instead, nests are characterized by frequent female turnover, in the form of females taking over (usurpation) other con-specific nests. Our results showed that most nests had offspring from multiple unrelated females, including some where multiple females were not observed in monitoring. Reconstruction of behavioural events from the genetic data revealed three types of multiple matriline nests: (a) nests that were usurped by another female, where the original nest owner disappeared following the usurpation event, (b) nests that were joined by another female, where the original nest owner stayed following the joining event, (c) nests that were both usurped and joined by other females. We also found, for the first time, a clear indication of multiple mating by Polistes females. Moreover, males mating with the same female were related, which may be explained by the lek mating system of P. biglumis. Finally, we analysed the nest sex ratios and how it changed during the season and found that sexes were produced sequentially, males before females.     

Population consequences of huge nesting aggregations ofRopalidia plebeiana (Hymenoptera: Vespidae)

Nest survival rates and reproductive rates of females of the Australian paper wasp, Ropalidia plebeiana, in nest aggregations under a concrete bridge were studied. The annual colony cycle commenced in August with the reutilization of old nests and by the founding of new nests, mainly by associations of foundresses. Distribution patterns of the number of foundresses per nest was nearly random on new nests while contagious on old nests. About one-third of the increase in number of nest was achieved by dividing large, old nests and two-thirds by founding new nests. Nest survival rates for old nests (August to April) and new nests (November to April) were 89.6% and 88.8% respectively, far higher rates than those of other polistine wasps so far reported. The numbers of nests and reproductive females increased during a colony cycle by 2.30 and 10.98 times, respectively. Thus, huge aggregations of nests are probably beneficial for this species by enabling the realization of high reproductive rates. We could find no density-dependent effect in nest growth rate or production of female reproductives. Ratio of cells parasitized by ichneumonid wasps was low. Nests in the central part of an aggregation were prasitized at significantly lower rates than nests on the periphery or scattered nests outside a dense aggregation, suggesting a selfish herd effect.     

Nest Hydrocarbons as Cues for Philopatry in a Paper Wasp

Philopatric behavior has been demonstrated in a wide taxonomic spread of animals. In temperate environments, overwintered Polistes wasp foundresses often return to their natal nest prior to initiating colony construction. Previous research has shown that these spring foundresses can identify the natal nest in the absence of landmark and gross morphological cues. Hydrocarbons are essential recognition cues for Polistes nest and nestmate discrimination, but cuticular hydrocarbon profiles can become homogenized when foundresses overwinter in mixed colony groups. We examined the hydrocarbon profiles of Polistes dominulus foundresses and nests before and after an overwintering period, and found that the hydrocarbon profiles of nests remain unique over time and that this uniqueness is influenced by the original foundresses. Our data raise the possibility that in returning to the natal nest, foundresses reacquire their colony‐specific signature, which may play a role in the formation of cooperative associations.     

Egg Coloration and Recognition of Conspecific Brood Parasitism in Eastern Bluebirds

Individual eastern bluebird (Sialia sialis) females produce clutches of eggs with unique coloration and older females and females in better body condition lay more pigmented blue‐green eggs. Conspecific brood parasitism in this species is not uncommon and bluebirds occasionally reject what appear to be normal eggs by moving them to the periphery of the nest. I used UV‐visual reflectance spectrometry to objectively measure coloration of eggs and nest material. To estimate the conspicuousness of the trait, I calculated the contrast between eggs and background nest material. I found high achromatic and chromatic contrast between the coloration of eggs and of the nests, suggesting that bluebird eggs are highly conspicuous. To test the hypothesis that expression of blue‐green coloration eggs facilitates recognition of eggs laid by conspecific brood parasites, I cross‐fostered individual eggs into host nests during egg laying and monitored the fate of those eggs. I found no support, however, for the hypothesis that egg coloration facilitates discrimination of parasitic eggs from host eggs.     

Factors affecting egg predation in Black-tailed Gulls

In colonial seabirds, nesting density, egg-laying date and nest microhabitat affect the probability of eggs being taken by avian predators. Jungle Crows (Corvus macrorhynchos) are dominant predators of eggs of Black-tailed Gulls (Larus crassirostris). Factors affecting the probability of gulls allowing the crows to attack their nests or depredate their eggs and the probability of eggs being taken were studied by direct observation and egg census, respectively. The effect of vegetation heights, position in the colony, egg-laying date and neighbour nests on the probability of eggs being taken were examined at multiple spatial scales. Gull nests were depredated more easily by larger groups of crows. Nests in peripheral areas (<4 m from the edge of the colony) were also depredated more easily by the crows walking on the ground. Although the nests where eggs were laid early in the season were depredated more frequently, such nests highly synchronised in egg laying within a <2-m radius were less likely to be depredated than less-synchronised nests. The nests in tall vegetation were less likely to be depredated though those having neighbour nests in tall vegetation were not. The number of neighbour nests did not affect the probability of eggs being taken. Antipredation effects of nesting microhabitats vary with spatial scales at which the crows search and attack the nests of gulls.     

Characteristics, abundance and fertility of orphan eggs of the Lesser Rhea ( Pterocnemia-Rhea-pennata pennata ): implications for conservation

The Lesser Rhea (Pterocnemia-Rhea-pennata pennata) has a complex reproductive system that combines polygyny with sequential polyandry, in which males build the nest, fully incubate the eggs and care for the young. As occurs with the Greater Rhea (Rhea americana), Lesser Rhea females sporadically lay eggs outside the nest (‘orphan’ eggs), which are not incubated and thus fail to hatch. We have examined the orphan eggs of Lesser Rhea over two separate breeding seasons to determine their abundance and fertility status. During 2004 and 2005, weekly ground searches for orphan eggs were conducted in a wild population of Lesser Rhea in northwestern Patagonia, Argentina. During these searches the total number of nests, eggs in each nest and orphan eggs laid outside the nests was recorded. Orphan eggs represented approximately 7% of the total eggs laid in a breeding season. Six fresh orphan eggs were artificially incubated, four of them being fertile. Orphan eggs seemed to have two origins: some were laid near deserted nests in the early to mid-reproductive season; others were probably laid by first-time breeders and were found later in the reproductive season. Given the near-threatened status of the Lesser Rhea, harvesting and artificial incubation of orphan eggs, which otherwise would be unproductive, may contribute significantly to the conservation of this species, i.e., ‘recovered’ birds could be used for reintroduction or reinforcement of wild Lesser Rhea populations.     

Mate choice and cannibalism in a natural population of a stream goby,Rhinogobius sp.

Breeding ecology of the stream goby,Rhinogobius sp. LD (Large Dark), was investigated under natural conditions. Males selectively courted females of similar size to lead them to the nests, whereas females followed courting males preferentially when the relative male size was greater. Male-male competition for a female was relatively infrequent and not severe. Developmental stages of eggs and egg numbers in one nest indicated that males receive 1–3 clutches during one breeding cycle. Males guarding multiple clutches frequently ate some of the eggs, but those guarding single clutches rarely did so. Gravid females in the nest also frequently cannibalized eggs laid by a previous female, probably in order to extend the area available for egg deposition. Mate choice in this species is discussed in relation to paternal ability, limitation of available spawning area and the female-biased sex ratio.     

Colony Foundation and Nestmate Recognition in the Social Wasp,Belonogaster petiolata

Emergence from hibernation and synchronized nest foundation by foundresses of B. petiolata in the southern Transvaal, appeared to be stimulated largely by a rise in temperature during early and mid August of each season. Initial foundresses on newly built nests were joined by other foundresses during the first few weeks of the nesting season to form foundress associations. Although females were strongly philopatric and able to discriminate between nestmates (from their natal nests) and non-nestmates, former nestmates did not reassociate to a significant degree on new nests. Thus, associated foundresses were, on average, not closely related. Rather than facilitating the reassociation of former nestmates, the advantage of philopatric behaviour appears to lie in ensuring that foundresses return to an area of relatively high nesting density, where their chances of being involved in multiple-foundress groups (irrespective of intra-colonial relatedness) are high. Non-philopatric females which nest away from localities of high nesting density have a low probability of being involved in associations, and may therefore have to attempt colony foundation alone, with little or no chance of reproducing successfully.     

Social behaviour and social structure of Neotropical paper waspsMischocyttarus angulatus Richards andM. basimacula (Cameron)

Social behaviour and social structure of 2 Neotropical polistine wasps,Mischocyttrus angulatus andM. basimacula, were investigated in the Canal Area, Republic of Panama. About 80% ofM. angulatus colonies and a half ofM. basimacula colonies were founted by multiple females having mature eggs in their ovaries. All of single-female colonies examined failed before the emergence of the first progeny. During the pre-emergence period, neither biting nor chasing was observed among females coexisting on the multifemale nests of both species. Although one of the females tended to stay on her nest for most of the time (‘queen-like female’), she was often replaced by a different individual on differrent days. In the post-emergence period, however, frequent aggression among females (including the foundresses and the first brood adults) was observed. The roles of pleometrosis and dominance behaviour in social lives of the 2 species in the wet tropics are discussed.     

Inhibition of Host Queen Reproductive Capacity by the Obligate Social Parasite Polistes atrimandibularis (Hymenoptera,Vespidae)

Polistes atrimandibularis is the obligate and permanent parasite of the social paper wasp Polistes biglumis bimaculatus. This parasite lives together with the host foundress for a considerable period on the invaded nest. Ovarian development was measured in females of the host species (foundresses and, when present, workers) from 18 parasitized and 14 non-parasitized colonies. The reproductive capacity of foundresses from parasitized nests decreased faster than that of foundresses from non-parasitized nests. These results indicate that the presence of the parasite lowers reproductive capacity of the host queen. Simultaneously, the fertility of the host worker is inhibited.     

Comparison of investment in nest construction by the foundresses of consubgenericPolistes wasps,P. (polistes) riparius andP. (P.) chinensis (hymenoptera, vespidae)

Some metric characters of nests built during the founding phase by foundresses were compared between two consubgenericPolistes wasps,P. (Polistes) riparius andP. (P.) chinensis, the former of which inhabit higher latitudes. Volumes and dry weights ofP. riparius nests were strikingly larger than those ofP. chinensis, even when standardized by the foundress weight (2.5 times for volume and 2 times for weight), showing that foundresses ofP. riparius invest much more in the nest construction than those ofP. chinensis. However, percent weights of oral secretion used for nests to total nest weights were smaller inP. riparius than inP. chinensis (52.1% vs. 60.4%). The differences in the investment by foundresses of the two species in the construction and maintenance of nests were discussed in relation to climatic and other environmental factors.