Polymorphic microsatellite loci for primitively eusocial wasp Ropalidia marginata

We report here development and characterization of 48 novel microsatellite markers for Ropalidia marginata, a tropical, primitively eusocial polistine wasp from peninsular India. Thirty-two microsatellites showed polymorphism in a wild population of R. marginata (N = 38) collected from Bangalore, India. These markers will facilitate answering some interesting questions in ecology and evolutionary biology of this wasp, such as population structure, serial polygyny, intra-colony genetic relatedness and the pattern of queen succession.

Middle aged wasps mate through most of the year, without regard to body size, ovarian development and nestmateship: a laboratory study of the primitively eusocial wasp Ropalidia marginata

We studied the mating behaviour of the primi-tively eusocial wasp Ropalidia marginata and the factors that may influence sperm transfer. By introducing a male and a female R. marginata into ventilated transparent plastic boxes, we were able to observe mating behaviour, and it involved mounting and short or long conjugation of the wasps. Dissection of female wasps after the observation indicated that long conjugation is a good behavioural predictor of sperm transfer. This finding makes it possible to obtain mated females without dissecting them every time. We tested the effect of age, season, relatedness, body size and female's ovarian status on mating. Under laboratory conditions, mating success declined rapidly below and above the ages 5-20 days. Within this age range mating success was significantly low in December compared to other months tested. There was no nestmate discrimination, and there was no influence of male and female body size or of the ovarian state of the female on the probability of sperm transfer.

Regulation of Reproduction in the Primitively Eusocial Wasp Ropalidia marginata: on the Trail of the Queen Pheromone

Queens and workers are not morphologically differentiated in the primitively eusocial wasp, Ropalidia marginata. Upon removal of the queen, one of the workers becomes extremely aggressive, but immediately drops her aggression if the queen is returned. If the queen is not returned, this hyper-aggressive individual, the potential queen (PQ), will develop her ovaries, lose her hyper-aggression, and become the next colony queen. Because of the non-aggressive nature of the queen, and because the PQ loses her aggression by the time she starts laying eggs, we hypothesized that regulation of worker reproduction in R marginata is mediated by pheromones rather than by physical aggression. Based on the immediate loss of aggression by the PQ upon return of the queen, we developed a bioassay to test whether the queen's Dufour's gland is, at least, one of the sources of the queen pheromone. Macerates of the queen's Dufour's gland, but not that of the worker's Dufour's gland, mimic the queen in making the PQ decrease her aggression. We also correctly distinguished queens and workers of R. marginata nests by a discriminant function analysis based on the chemical composition of their respective Dufour's glands.

Natural history and behaviour of the primitively eusocial wasp Ropalidia marginata (Hymenoptera: Vespidae): a comparison of the two sexes

We report the natural history and behaviour of the primitively eusocial wasp Ropalidia marginata with a special reference to the males. We found that just as nests of this species are found throughout the year, so are the males. Females spend all their life in their nests but males stay in their natal nests only for 1-12 days and leave to lead a nomadic life. Males maintained in the laboratory can live for up to 140 days. Like all eusocial hymenopteran males, R. marginata males also do not perform any colony maintenance activities. We found that males did not forage or feed larvae. Compared with females, males showed fewer dominance and subordinate behaviours and being solicited behaviour and more feeding self and soliciting behaviours. By comparing males with young females, we found similar differences, except that the males showed similar rates of feeding self and higher rates of subordinate behaviour.

Seasonal variation in the onset of egg laying in a primitively eusocial wasp: implications for the evolution of sociality

When freshly eclosed females of the primitively eusocial wasp, Rapalidia marginata are isolated into individual cages, only about half of them build nests and lay eggs and those that do so take a long and variable amount of time (Mean +/- SD = 66 +/- 37 days) before they lay their first egg. Part of the reason for this delay is because, when kept in isolation, no wasp begins to lay eggs during a period of approximately 82 days from mid - October to early January. Wasps maintained at a constant temperature of 26 +/- 1-degrees-C however initiate egg laying throughout the year, suggesting that the low temperatures during mid - October to early January may be at least one factor that makes this period unfavourable for wasps maintained at room temperature. Egg laying continues more or less normally throughout October-January however, in all natural and laboratory colonies studied. Natural colonies of R. marginata are initiated throughout the year and often by groups of females. Huddling together is a striking feature of the wasps especially on cold mornings. We therefore suggest that the isolated animals in our experiment are unable to lay eggs during the coldest part of the year because of their inability to huddle together, share metabolic heat and perform "co-operative thermoregulation". Such "co-operative thermoregulation" may thus be another factor that facilitates the evolution of socialitly.

The role of larval nutrition in pre-imaginal biasing of caste in the primitively eusocial wasp Ropalidia marginata (Hymenoptera: Vespidae)

1. When freshly eclosed females of the primitively eusocial wasp Ropalidia marginata (Lep.) are isolated, only about 50% of them build nests and lay eggs thereby suggesting a pre-imaginal biasing of caste. 2. Wasps that lay eggs take a very variable amount of time after eclosion to start doing so. 3. Females eclosing from nests where larvae are fed at a relatively higher rate are more likely to become egg-layers and are likely to take less time after eclosion to begin to lay eggs. 4. Thus, both forms of pre-imaginal biasing of caste, namely, differences in egg laying capacity and differences in the time taken to attain reproductive maturity, appear to be influenced by larval nutrition.

On reconfirming the evidence for pre-imaginal caste bias in a primitively eusocial wasp

Caste is usually thought to be determined entirely in the adult stage in most primitively eusocial wasps and bees. A pre-imaginal caste bias has however been recently discovered in the primitively eusocial waspRopalidia marginata. This study also suggested that reigning queens and possibly other adults may influence the production of new queens and implied at least partial support to the parental manipulation or sub-fertility hypothesis for the evolution of insect sociality. The interest of these results prompted an attempt at their reconfirmation. Complete reconfirmation has now been obtained using data from an independent experiment and two additional methods of data analysis. We therefore conclude that caste is at least partly determined prior to eclosion in the primitively eusocial waspRopalidia marginata which lacks morphological differentiation between egg-layers and non-egg-layers.

Can Dufour's gland compounds honestly signal fertility in the primitively eusocial wasp Ropalidia marginata?

Unlike queens of typical primitively eusocial species, Ropalidia marginata queens are docile and non-interactive, and hence cannot be using dominance to maintain their status. It appears that the queen maintains reproductive monopoly through a pheromone, of which the Dufour's gland is at least one source. Here, we reconfirm earlier results showing that queens and workers can be correctly classified on a discriminant function using the compositions of their respective Dufour's glands, and also demonstrate consistent queen-worker differences based on categories of compounds and on single compounds also in some cases. Since the queen pheromone is expected to be an honest signal of the fecundity of a queen, we investigate the correlation of Dufour's gland compounds with ovarian activation of queens. Our study shows that Dufour's gland compounds in R. marginata correlate with the state of ovarian activation of queens, suggesting that such compounds may portray the fecundity of a queen, and may indeed function as honest signals of fertility.

Science as a hobby: how and why I came to study the social life of an Indian primitively eusocial wasp

For the most part, my research career has involved prying into the life of the locally abundant primitively eusocial paper wasp, Ropalidia marginata, with the aim of understanding the origin and evolution of social life in insects. My interest in this wasp species began as a hobby, but I was privileged to soon convert my hobby into my profession. Here I describe how this conversion came about, what it meant to pursue my hobby as a full-time activity, describe some examples from my research and end with some reflections about the process of doing modern science, especially in India.

Males, but not females, mate with multiple partners: a laboratory study of a primitively eusocial wasp Ropalidia marginata

The intense interest in social Hymenoptera, on account of their elaborate sociality and the paradox of altruism, has often suffered from considerable gender imbalance. This is partly due to the fact that worker behaviour and altruism are restricted to the females and partly because males often live off the nest. Yet, understanding the males, especially in the context of mating biology is essential even for understanding the evolution of sociality. Mating patterns have a direct bearing on the levels of intra-colony genetic relatedness, which in turn, along with the associated costs and benefits of worker behaviour, are central to our understanding of the evolution of sociality. Although mating takes place away from the nest in natural colonies of the primitively eusocial wasp Ropalidia marginata, mating can be observed in the laboratory if a male and a female are placed in a transparent, aerated plastic container, and both wasps are in the range of 5-20 days of age. Here, we use this setup and show that males, but not females, mate serially with multiple partners. The multiple mating behaviour of the males is not surprising because in nature males have to mate with a number of females, only a few of whom will go on to lay eggs. The reluctance of R. marginata females to mate with multiple partners is consistent with the expectation of monogamy in primitively eusocial species with totipotent females, although the apparent discrepancy with a previous work with allozyme markers in natural colonies suggesting that females may sometimes mate with two or three different males remains to be resolved.

Road to Royalty - Transition of Potential Queen to Queen in the Primitively Eusocial Wasp Ropalidia marginata

Ropalidia marginata, a primitively eusocial wasp, is different from typical primitively eusocial species in having docile queens who cannot be using dominance to maintain reproductive monopoly and instead appear to use a pheromone from the Dufour's gland to do so. When a docile queen is removed from her colony, one of the workers (potential queen, PQ) becomes highly aggressive, and if the queen is not returned, gradually loses her aggression and becomes the new docile queen within a few days. We hypothesized that the decrease in aggression of the PQ with time since queen removal should be correlated with her change in ovaries and pheromone profile. Because the Dufour's gland hydrocarbon composition in R.marginata can be correlated with fertility, this also gave us an opportunity to test whether PQ is different from workers in her Dufour's gland hydrocarbons. In this study, we therefore trace the road to royalty in R.marginata, that is, the transition of the PQ during queen establishment, in terms of her ovaries, aggression, and Dufour's gland hydrocarbons. Our study focuses on queen establishment, which is important for understanding how reproductive conflict can be manifested and resolved.

Queens and Workers of the Primitively Eusocial Wasp Ropalidia marginata do not Differ in Their Dufour's Gland Morphology

Ropalidia marginata is a primitively eusocial paper wasp found in peninsular India, where recent work suggests the role of the Dufour's gland hydrocarbons in queen signaling. It appears that the queen signals her presence to workers by rubbing the tip of her abdomen on the nest surface, thereby presumably applying her Dufour's gland secretion to the nest. Since the queen alone produces pheromone from the Dufour's gland and also applies it on the nest surface, the activity level of queen gland should be higher than that of worker gland, as the gland contents would have to get replenished periodically for queens but not for workers. The difference in activity level can be manifested in difference in Dufour's gland morphology, larger glands implying higher activity levels and smaller glands implying lower activity levels, as positive correlation between gland size and gland activity has been reported in exocrine glands of various taxa (including Hymenopteran insects). Hence we investigated whether there is any size difference between Dufour's glands of queens and workers in R. marginata. We found that there was no difference between queens and workers in their Dufour's gland size, implying that Dufour's gland activity and Dufour's gland size are likely to be uncorrelated in this species.

Reproductive queue without overt conflict in the primitively eusocial wasp Ropalidia marginata

Colonies of the primitively eusocial wasp Ropalidia marginata consist of a single egg layer (queen) and a number of non-egg-laying workers. Although the queen is a docile individual, not at the top of the behavioral dominance hierarchy of the colony, she maintains complete reproductive monopoly. If the queen is lost or removed, one and only one of the workers potential queen (PQ)] becomes hyperaggressive and will become the next queen of the colony. The PQ is almost never challenged because she first becomes hyperaggressive and then gradually loses her aggression, develops her ovaries, and starts laying eggs. Although we are unable to identify the PQ when the queen is present, she appears to be a ``cryptic heir designate.'' Here, we show that there is not just one heir designate but a long reproductive queue and that PQs take over the role of egg-laying, successively, without overt conflict, as the queen or previous PQs are removed. The dominance rank of an individual is not a significant predictor of its position in the succession hierarchy. The age of an individual is a significant predictor, but it is not a perfect predictor because PQs often bypass older individuals to become successors. We suggest that such a predesignated reproductive queue that is implemented without overt conflict is adaptive in the tropics, where conspecific usurpers from outside the colony, which can take advantage of the anarchy prevailing in a queenless colony and invade it, are likely to be present throughout the year.

Ovarian developmental variation in the primitively eusocial wasp Ropalidia marginata suggests a gateway to worker ontogeny and the evolution of sociality

Social insects are characterized by reproductive caste differentiation of colony members into one or a small number of fertile queens and a large number of sterile workers. The evolutionary origin and maintenance of such sterile workers remains an enduring puzzle in insect sociobiology. Here, we studied ovarian development in over 600 freshly eclosed, isolated, virgin female Ropalidia marginata wasps, maintained in the laboratory. The wasps differed greatly both in the time taken to develop their ovaries and in the magnitude of ovarian development despite having similar access to resources. All females started with no ovarian development at day zero, and the percentage of individuals with at least one oocyte at any stage of development increased gradually across age, reached 100% at 100. days and decreased slightly thereafter. Approximately 40% of the females failed to develop ovaries within the average ecological lifespan of the species. Age, body size and adult feeding rate, when considered together, were the most important factors governing ovarian development. We suggest that such flexibility and variation in the potential and timing of reproductive development may physiologically predispose females to accept worker roles and thus provide a gateway to worker ontogeny and the evolution of sociality.

Ovarian development in a primitively eusocial wasp: Social interactions affect behaviorally dominant and subordinate wasps in opposite directions relative to solitary females

In many primitively eusocial wasp species new nests are founded either by a single female or by a small group of females. In the single foundress nests, the lone female develops her ovaries, lays eggs as well as tends her brood. In multiple foundress nests social interactions, especially dominance-subordinate interactions, result in only one `dominant' female developing her ovaries and laying eggs. Ovaries of the remaining `subordinate' cofoundresses remain suppressed and these individuals function as workers and tend the dominant's brood. Using the tropical, primitively eusocial polistine wasp Ropalidia marginata and by comparing wasps held in isolation and those kept as pairs in the laboratory, we demonstrate that social interactions affect ovarian development of dominant and subordinate wasps among the pairs in opposite directions, suppressing the ovaries of the subordinate member of the pair below that of solitary wasps and boosting the ovaries of dominant member of the pair above that of solitary females. In addition to being of physiological interest, such mirror image effects of aggression on the ovaries of the aggressors and their victims, suggest yet another mechanism by which subordinates can enhance their indirect fitness and facilitate the evolution of worker behavior by kin selection. (C) 2014 Elsevier B.V. All rights reserved.