The structure of dominance hierarchies in the primitively eusocial wasp Ropalidia marginata

In queenright colonies of the old world tropical primitively eusocial polistine wasp, Ropalidia marginata, queens are behaviourally docile and subordinate individuals. Yet, they are completely successful in suppressing reproduction by all nestmates. Here we show that dominance hierarchies in queenright colonies are never significantly linear but, in the queen determination stage, when new queens use overt physical aggression to establish their status, dominance hierarchies among the same individuals are significantly linear. This striking difference in the structure of dominance hierarchies in queenright colonies as compared to the queen determination stage, is consistent with the previously postulated hypothesis that, while dominance behaviour functions to regulate worker reproduction in the queen determination stage, the same behaviours are used by the workers to regulate each others' foraging in queenright colonies

Division of labor among a cohort of young individuals in a primitively eusocial wasp

Age polyethism has recently been demonstrated in the primitively eusocial wasp Ropalidia marginata, and it has been shown that workers allocate tasks based more on their relative age rather than on their absolute age, thus providing flexibility to division of labor. The flexibility of division of labor and the respective roles of absolute and relative ages is further evaluated here by creating colonies of only young individuals (young-cohort colonies). The results show that workers in young-cohort colonies can forage at an earlier age, in larger numbers and with a higher probability and frequency. This confirms that division of labor in the colony can indeed be independent of absolute age. The results also show that relative age governs the probability of task performance while absolute age governs the frequency of task performance. The constraints posed by absolute age in the organization of work in an insect colony and the flexibility lent to it by relative age are discussed

Kin recognition in a semi-natural context: behaviour towards foreign conspecifics in the social wasp Ropalidia marginata (Lep.) (Hymenoptera: Vespidae)

Female wasps of the tropical primitively eusocial species Ropalidia marginata are known to discriminate unfamiliar nestmates from unfamiliar non-nestmates outside the context of their nests. Here, we show that when foreign conspecifics are introduced in the context of a nest in laboratory cages, genetic relatives among them are treated by nest inhabitants more tolerantly than non-relatives, but that no foreign conspecifics are accepted into the nests. However, some wasps may leave their nest and join the foreign relatives and non-relatives to found new colonies cooperatively. Very few of the introduced animals are severely attacked or killed; most are allowed to remain in parts of the cage away from the nest. These results suggest that factors other than genetic relatedness may be involved in regulating tolerance and acceptance of foreign conspecifics on a nest and its vicinity. Our results are different from those of similar experiments with ants, which have demonstrated that former nestmates that are removed as pupae and later introduced as adults are either accepted into the nest or attacked and killed. We attribute this difference to the fact that in a primitively eusocial species such as R. marginata, the rules governing tolerance and acceptance of foreign conspecifics must be quite different from those in highly eusocial species. We also attempt to test some predictions of the conspecific acceptance threshold models of Reeve (Am. Nat. 133:407-435, 1989). Our results uphold the predictions of his fitness consequence submodel but do not support those of his "interaction frequency sub-model"

Do social wasps choose nesting strategies based on their brood rearing abilities?

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Unmated queens in the primitively eusocial wasp Ropalidia marginata (Lep.) (Hymenoptera: Vespidae)

In the primitively eusocial tropical wasp Ropalidia marginata, five out of eleven colonies studied had an unmated female as their queen. In two colonies this was the case despite the presence of another mated individual in the colony. We found no detectable differences between colonies with unmated queens and those with mated queens. We argue that in species such as R. marginata, where intracolony relatedness is expected to be low and where sociality is likely to be maintained because several individuals have opportunities for direct reproduction in the future, individual selection is likely to override "the good of the colony" and lead to such phenomena as that of unmated queens

Phylogenetic inference under varying proportions of indel-induced alignment gaps

<p>Abstract</p> <p>Background</p> <p>The effect of alignment gaps on phylogenetic accuracy has been the subject of numerous studies. In this study, we investigated the relationship between the total number of gapped sites and phylogenetic accuracy, when the gaps were introduced (by means of computer simulation) to reflect indel (insertion/deletion) events during the evolution of DNA sequences. The resulting (true) alignments were subjected to commonly used gap treatment and phylogenetic inference methods.</p> <p>Results</p> <p>(1) In general, there was a strong – almost deterministic – relationship between the amount of gap in the data and the level of phylogenetic accuracy when the alignments were very "gappy", (2) gaps resulting from deletions (as opposed to insertions) contributed more to the inaccuracy of phylogenetic inference, (3) the probabilistic methods (Bayesian, PhyML & "ML<it>ε</it>, " a method implemented in DNAML in PHYLIP) performed better at most levels of gap percentage when compared to parsimony (MP) and distance (NJ) methods, with Bayesian analysis being clearly the best, (4) methods that treat gapped sites as missing data yielded less accurate trees when compared to those that attribute phylogenetic signal to the gapped sites (by coding them as binary character data – presence/absence, or as in the ML<it>ε </it>method), and (5) in general, the accuracy of phylogenetic inference depended upon the amount of available data when the gaps resulted from mainly deletion events, and the amount of missing data when insertion events were equally likely to have caused the alignment gaps.</p> <p>Conclusion</p> <p>When gaps in an alignment are a consequence of indel events in the evolution of the sequences, the accuracy of phylogenetic analysis is likely to improve if: (1) alignment gaps are categorized as arising from insertion events or deletion events and then treated separately in the analysis, (2) the evolutionary signal provided by indels is harnessed in the phylogenetic analysis, and (3) methods that utilize the phylogenetic signal in indels are developed for distance methods too. When the true homology is known and the amount of gaps is 20 percent of the alignment length or less, the methods used in this study are likely to yield trees with 90–100 percent accuracy.</p

Social organization in experimentally assembled colonies of Ropalidia marginata: comparison of introduced and natal wasps

In the primitively eusocial wasp, Ropalidia marginata worker behaviour cannot be explained satisfactorily by the haplodiploidy hypothesis due to the existence of polyandry, serial polygyny and movement of wasps between nests, which reduce intra-colony genetic relatedness to levels lower than the value expected between a solitary foundress and her offspring. We introduced wasps eclosing from one set of colonies into other colonies separated by a distance of 10 km or more, to examine the possibility of kin recognition and task specialization under conditions of low intracolony relatedness. Introduced wasps were readily accepted into unrelated foster colonies, where they performed most of the behaviours and tasks shown by the natal wasps. We found no evidence of kin recognition or task specialization among natal and introduced wasps. Introduced wasps sometimes became replacement queens in spite of the presence of natal wasps. Taken together with previous observations, these results lend support to the idea that factors other than genetic relatedness must play a prominent role in the evolution of worker behaviour in Ropalidia marginata

Identification of polymorphic microsatellite loci in the queenless, ponerine ant Diacamma ceylonense

Diacamma ceylonenseis a queenless, ponerine ant whose colonies are headed by a single, mated, egg-laying worker referred to as the gamergate. Thus, new colonies are a result of dispersal by wingless gamergates. This is expected to influence patterns of colony dispersal and spatial distribution of genetic variablity. In order to facilitate the study of population genetic structure we have identified six unique, polymorphic, microsatellite loci. We have used fluorescence tagged primers to detect polymorphism at these loci

Queen success is correlated with worker-brood genetic relatedness in a primitively eusocial wasp (Ropalidia marginata)

Ropalidia marginata is a primitively eusocial polistine wasp in which, although there is only one queen at any given time, frequent queen replacements lead to a system of serial polygyny. One of the most striking features of this system is the enormous variation in the success of different queens. Measuring queen success as queen tenure, total number of offspring produced, number of offspring produced per day of tenure, and proportion of eggs laid that develop into adults, we show here that each measure of queen success is correlated with worker-brood genetic relatedness and not correlated with worker:brood ratio or the age of the queen at takeover. We interpret these results as meaning that queens are better able to obtain the cooperation of workers when worker-brood genetic relatedness is high

Ropalidia rufoplagiata: a polistine wasp society probably lacking permanent reproductive division of labour

Ropalidia rufoplagiata Cameron (Hymenoptera: Vespidae), a polistine species from penisular India, appears to be unique among all known primitively eusocial wasps. A total of 33 out of 46 identified females from an observed colony were found to oviposit on 1-17 occasions. No single predominant egg-layer could be identified during the 45-day period. Of the 17 dissected egg-layers, 12 were mated. All egg-layers showed several oviposition-related behavioural patterns including systematic, but indiscriminate, cannibalism of eggs and larvae, cleaning of empty cells, and guarding of freshly-laid eggs. There was no correlation between the egg-laying activity of the females (whether mated or not), oophagy, and their position in the dominance hierarchy. All nest-maintenance activities were performed exclusively by the egg-layers, while the non-egg-layers were mainly involved in the extranidal task offoraging. No significant morphometric differences between egg-layers and foragers could be discerned. Almost all the older individuals in the colony were egg-layers, while foragers were mainly younger animals. Such a temporal differentiation in reproductive labour suggests the absence of a permanent reproductive caste in this species