Multiple reproductive strategies in a tropical hover wasp (original) (raw)
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Colony genetic structure in a facultatively eusocial hover wasp
Behavioral Ecology, 2006
The degree of genetic heterogeneity among the individuals in an animal society depends on the society's genetic structure. Genetic heterogeneity, in turn, means that group members will differ in their reproductive objectives and conflicts over reproduction may arise. The resolution of these conflicts may be reflected in the way that reproduction is partitioned between potential reproductives. We used 5 microsatellite loci to investigate genetic structure and reproductive skew in 17 nests of the Malaysian hover wasp, Parischnogaster alternata. Parischnogaster alternata colonies are small (1-10 females), and all adult colony members are capable of mating and producing offspring. We found that colonies tended to consist of closely related individuals and that at any one time the production of both female and male offspring was nearly always monopolized by a single dominant female, despite considerable variation between nests in parameters predicted to affect skew. Subordinate females that remained in their natal colonies obtained indirect fitness benefits by helping to raise offspring to which they were related. Subordinate females also appeared to be positioned within an age-based queue for inheritance of the dominant egg-laying position. We suggest that the high skew in P. alternata may result from strong ecological constraints on solitary nesting, high relatedness, and a relatively high probability that subordinates will eventually inherit the position of dominance. by guest on June 5, 2015 http://beheco.oxfordjournals.org/ Downloaded from 874 Behavioral Ecology by guest on June 5, 2015 http://beheco.oxfordjournals.org/ Downloaded from Means 6 standard errors and coefficients of variation are given for each category. Coefficients of variation were corrected for bias (Sokal and Rohlf 1995). Colonies are ranked according to their relatedness estimate. ND ¼ no data available. Bolton et al. • Hover wasps 877 by guest on June 5, 2015 http://beheco.oxfordjournals.org/ Downloaded from
Behavioral Ecology, 2002
Who reproduces in colonies of social insects is determined by some combination of direct competition and more peaceful convention. We studied these two alternatives in foundresses of the paper wasp, Polistes carolina, by examining two different contexts: what determines who becomes the dominant reproductive and what determines the amount of reproduction obtained by subordinates. The dominant queen on most nests was the foundress to arrive first, rather than the largest foundress, expected to be best at fighting. This suggests that dominance is initially determined by convention, although the persistence of some aggressive conflict throughout the foundress period suggests that this convention is not absolute. Attempts to explain the division of reproduction using several skew theories were generally unsuccessful. Skew was not correlated with relatedness, size differences, colony productivity, and challenges by the subordinate. P. carolina showed high constraints against solitary nesting, with a minority of females attempting to nest alone, and none succeeding. In this situation, most skew theories predict that group stability will be independent of relatedness, yet nearly all collected subordinates were full sisters to the queen. Reproductive partitioning in early P. carolina colonies may have more to do with enhancing worker production than with conflict over direct fitness.
Evolution of Reproductive Dominance in Animal Societies -Lessons From a Social Wasp
Proceedings of the Indian National Science Academy, 2018
Most insect societies can be classified as either primitively or highly eusocial. Primitively eusocial insect societies are usually led by queens who are morphologically indistinguishable from the workers and use aggression to control the workers, thereby typically holding top positions in the colony's dominance hierarchy. Highly eusocial species have morphologically large queens who regulate worker reproduction through pheromones and achieve larger colony sizes than their primitively eusocial counterparts. However, it is not clear whether this switch from aggression to pheromone took place in a single step in which a population as a whole evolved chemical regulation, or in two steps in which a queen used physical regulation when the colony size was small and switched to chemical regulation when the colony became larger. Ropalidia marginata is a primitively eusocial wasp, which also has some characteristics that are typically seen in highly eusocial species. The queens in this species do not usually lead the colony's dominance hierarchy and use pheromones to signal their presence to workers. Since new colonies are founded by one or a few individuals and grow through time, young colonies are small enough to permit suppression of worker reproduction through aggression. Queens in small colonies indeed sometimes occupy the top position in the colony's dominance hierarchy, thus providing a unique opportunity to test the above-mentioned hypotheses. We analysed data from 100 colonies of R. marginata to test these two competing hypotheses and found support for the former. Our findings are consistent with the hypothesis that the evolution of highly eusocial societies from primitively eusocial ones involved a one-step transition from physical control to chemical regulation of worker reproduction.
Colony life history and demography of a swarm-founding social wasp
Behavioral Ecology and Sociobiology, 1997
Colonies of social insects are sometimes viewed as superorganisms. The birth, reproduction, and death of colonies can be studied with demographic measures analogous to those normally applied to individuals, but two additional questions arise. First, how do adaptive colony demographies arise from individual behaviors? Second, since these superorganisms are made up of genetically distinct individuals, do conflicts within the colony sometimes modify and upset optima for colonies? The interplay between individual and superindividual or colony interests appears to be particularly complex in neotropical, swarm-founding, epiponine wasps such as Parachartergus colobopterus. In a long-term study of this species, we censused 286 nests to study colony-level reproduction and survivorship and evaluated individual-level factors by assessing genetic relatedness and queen production. Colony survivorship followed a negative exponential curve very closely, indicating type II survivorship. This pattern is defined by constant mortality across ages and is more characteristic of birds and other vertebrates than of insects. Individual colonies are long-lived, lasting an average of 347 days, with a maximum of over 4.5 years. The low and constant levels of colony mortality arise in part from colony initiation by swarming, nesting on protected substrates, and an unusual expandable nest structure. The ability to requeen rapidly was also important; relatedness data suggest that colonies requeen on average once every 9–12 months. We studied whether colony optima with respect to the timing of reproduction could be upset by individual worker interests. In this species, colonies are normally polygynous but new queens are produced only after a colony reaches the monogynous state, a result which is in accord with the genetic interests of workers. Therefore colony worker interests might drive colonies to reproduce whenever queen number happens to cycled down to one rather than at the season that is otherwise optimal. However, we found reproduction to be heavily concentrated in the rainy season. The number of new colonies peaked in this season as did the percentages of males and queens. Relatedness among workers reached a seasonal low of 0.21–0.27, reflecting the higher numbers of laying queens. This seasonality was achieved in part by a modest degree of synchrony in the queen reduction cycle. Worker relatedness reached peaks of around 0.4 in the dry season, reflecting a decrease to a harmonic mean queen number of about 2.5. Thus, a significant number of colonies must be approaching monogyny entering the rainy season. Coupled with polygynous colonies rearing only males (split sex ratios), this makes it possible for a colony cycle driven by selfish worker interests to be consistent with concentrating colony reproduction during a favorable season.
1998
Abstract Hamilton's kin selection theory predicts conflicts of interest among relatives, even within highly cooperative social insect societies. Because workers are the most numerous caste, collective worker interests may be an important force in determining the outcome of conflicts. In this study, we used genotypes from two DNA microsatellite loci to show that two kinds of collective worker interests are satisfied in Brachygastra mellifica, a member of the multiqueen epiponine wasps.
Molecular Ecology, 1998
Kin selection theory has received some of its strongest support from analyses of within-colony conflicts between workers and queens in social insects. One of these conflicts involves the timing of queen production. In neotropical wasps, new queens are only produced by colonies with just one queen while males are produced by colonies with more queens, a pattern favoured by worker interests. We now show that new colonies, or swarms, have few queens and variable within-colony relatednesses which means that their production is not tied to new queen production. The queens in these swarms are seldom the mothers of the workers in the swarm. Therefore, either colonies producing swarms have very many queens, or queens joining daughter swarms are reproductive losers on the original colonies. As new colony production is not linked to queen production, it can occur at the ecologically optimum time, i.e. the rainy season. This disassociation between queen production and new colony production allows worker interests in sex ratios to prevail without hampering new colony production at the most favourable season, an uncoupling that may contribute to the ecological success of the Epiponini.
Social and genetic structure in colonies of the social wasp Microstigmus nigrophthalmus
Insectes sociaux, 2010
Microstigmus (Hymenoptera: Crabronidae) is a genus of social apoid wasps which represents an origin of sociality independent from vespoids, but which has so far received little attention. Though group-nesting is widespread in Microstigmus, genetic relatedness has so far been studied in only one species, M. comes. We report on the social biology of M. nigrophthalmus, drawing from behavioural observations and molecular genetic analyses of relatedness and kinship. There was no evidence of distinctive behavioural suites that distinguished reproductive and non-reproductive individuals. Females could mate more than once, but mating frequency was low. Mean relatedness within nests was high, particularly between females (close to 0.5), but pairwise relatedness values were very variable, as nestmates displayed a wide range of relationships. Such high levels of relatedness should be a factor promoting social nesting and cooperative brood care in this species, as females gain only a slight genetic advantage through rearing their own offspring rather than those of nestmates. This study provides the finest analysis of genetic structure so far in an apoid wasp, and indicates that the form of sociality varies greatly between species of Microstigmus.
Caste in the swarming wasps:'queenless' societies in highly social insects
Biological Journal of the Linnean …, 2008
Morphometric data for 30 species of swarming wasps (Vespidae: Polistinae: Epiponini) are presented, representing all currently recognized genera. Data are coded according to whether females that were shown by dissection to be egglayers are larger, similar, or smaller for each dimension than non-egglayers. These data are analysed in a phylogenetic framework with primitively social Polistes and Mischocyttarus as outgroups. Representative measurements are illustrated to show that most genera of Epiponini appear to have ancestry in a lineage that has no queen caste comparable with either the primitively social outgroups, or the more derived species of the tribe. This analysis indicates that a conspiracy of workers that operates without a queen characterizes the societies of many Epiponini, or their recent ancestors.