Division of labour and organization of work in the primitively eusocial wasp Ropalidia marginata

Ropalidia marginata is a primitively eusocial polistine wasp with the expected lack of morphological caste differentiation between queens and workers. The lack of morphological caste differentiation appears to be compensated by a system of behavioural caste differentiation. The wasps in a colony may be classified into three behavioural castes which we have called Sitters, Fighters and Foragers and the queens are almost always in the Sitters caste. Consistent with this and unlike in most other primitively eusocial species studied, R. marginata queens are relatively inactive, behaviourally subordinate individuals. There is no evidence that they regulate activities of their workers. The workers continue to remain active, bring food and feed the larvae, even if the queen is removed. Worker activity appears to be regulated by the workers themselves through the use of dominance behaviours' which are hypothesized to have come to represent larval and adult hunger signals, to the foragers. In undisturbed colonies, intranidal workers who also unload food and pulp bearing foragers, appear to regulate foraging rates. In the absence of unloaders, the foragers themselves feed the larvae and apparently obtain first-hand information about larval hunger levels. In spite of its primitively eusocial status, R. marginata has a well developed age polyethism. Workers show strong preferencest o feed larvae, build the nest, bring pulp and bring food, in that order, as they age. However, the relative position of a wasp in the age distribution of the colony, rather than her absolute age, is a stronger predictor of her task performance. Soliciting behaviour (a form of trophallaxis) provides a plausible mechanism for the wasps to assess their relative ages. A computer simulation model, adapting the verbal activator-inhibitor model proposed for honey bees, demonstrates that a relative-age based rule for division of labour provides the necessaryfl exibility for coloniest o respond adaptivelyt o changing colony demography or varying demands for food. Thus, morphologically identical individuals, and in spite of retaining some reproductive options,h ave accessto a variety of mechanismsto efficiently divide labour and organize work

Some reflections on the pursuit and evaluation of science

Practising scientists are usually very busy practising their craft and most of us also devote a significant amount of time to evaluate what our peers do. However we seldom find the time or have the inclination to reflect on how we pursue our craft and here by craft I mean, both the craft of doing science as well as the craft of evaluating science

Kin recognition in social insects and other animals- a review of recent findings and a consideration of their relevance for the theory of kin selection

Kin selection is a widely invoked mechanism to explain the origin; evolution of social behaviour in animals. Proponents of the theory of kin selection place great emphasis on the correlation between asymmetries in genetic relatedness created by haplodiploidy; the multiple origins of eusociality in the order Hymenoptera. The fact that a female is more closely related genetically to her full sister than to her daughters makes it more profitable for a Hymenopteran female; in terms of inclusive fitness to raise full sisters rather than daughters or full siblings with a female biased sex ratio rather than offspring. This is sometimes referred to as the haplodiploidy hypothesis. In reality however, genetic relatedness between workers in social insect colonies, the reproductive brood they rear is far below 0.75, the value expected for full sisters, often below 0.5 the value expected between mother and daughter and not uncommonly approaching zero. Such values are on account of queen turnover multiple mating by queens or polygyny. This situation raises doubts regarding the haplodiploidy hypothesis unless workers can discriminate between full half sisters preferentially direct their altruism towards their full sisters only. This would still mean an effective coefficient of genetic relatedness of 0.75 between altruist and recipient. For this to be possible however, workers should be able to recognise their full sisters inspite of growing up with being habituated to an assortment of full sisters half sisters and perhaps other even less related individuals. Even outside the Hymenoptera, social animals may find themselvesg rowing up together in the company of individuals of varying degrees of relatedness. An ability to tell apart the more; less related individuals under such circumstances should favour kin selection. Much effort is now going into assessingth e abilities of animals to discriminate betweenk in; non kin. In every case studied carefully so far and animals appear to be capable of recognising their kin. Ants, wasps, sweat bees, honey bees, frogs, toads, mice, rats, voles, squirrels, monkeys and even humans appear to be able to recognise their kin in one circumstance or another. An ability to recognize true genetic relatedness requires genetically specified recognition labels; these must therefore be present. Recent findings of the role of the histocompatibility system provides some clues to the possible nature of recognition labels. An ability to recognise full sisters for example; inspite of being habituated to full; half sisters requires not merely genetically specified labels but also recognition templates which are based on the characteristics of the individual animals making the recognition; not templates based on all animals one grows up with. Some animals such as honey bees; tadpoles; ground squirrels appear to have such templates but others such as sweat bees; some mice appear not to. It is entirely possible that our inability to devise natural enough assays for recognition prevents us from understandingt he full potential of the kin recognition abilities of many animals peciesI.n any case; genetically specified labels; self based templates should greatly facilitate the evolution of social behaviour by kin selection

Social biology of Ropalidia: investigations into the origins of eusociality

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Subterranean farmers: Ants invented agriculture some 50 million years before the humans

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A test of the role of haplodiploidy in the evolution of Hymenopteran eusociality

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Genetically engineered monogamy in voles lends credence to the modus operandi of behavioural ecology

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Next time we hear a frog croak, let's say thank you!

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How to gain the benefits of sexual reproduction without paying the cost: a worm shows the way

Sexual reproduction is perhaps the greatest of all evolutionary puzzles. It's a puzzle because sexually reproducing species pay the cost of spending half their resources (over and above what is needed for vegetative growth) in producing males, whereas parthenogenetic species utilize all their resources meant for reproduction in producing only females (or hermaphrodites) like themselves. This twofold cost of sexual reproduction [1,2] is sometimes referred to as the twofold cost of producing males. Three advantages of sexual reproduction that might offset this cost have been proposed. Genetic recombination and cross fertilization permit sexually reproducing species to (1) bring together, in the same individual, mutations arising in different individuals [3,4]; (2) generate genetic variability and thus adapt to changing environments[2, 5, 6]; and (3) shuffle their genes in every generation and thus keep parasites at bay [7,8,9]. While evolutionary biologists are busy testing their favourite ideas for offsetting the twofold cost of producing males, recent work by Craig LaMunyon and Samuel Ward[10] shows that a nematode, Caenorhabditis briggsae, appears to have found a way of gaining the benefits of sexual reproduction without paying the cost of producing males

Genetic diversity and evolution

Estimation of the amount of genetic variability in natural populations of living organisms is of such great interest that sharply divided opinion on the outcome of such estimation existed even before any reliable method of estimation was available. The biochemical technique of enzyme electrophoresis has revealed an unexpectedly high level of genetic variability in a variety of organisms. This technique suggests that organisms may be heterozygous for 6 to 15% of their loci and 15 to 50% of the loci may be polymorphic in any population. The more recent technique of DNA restriction fragment length polymorphism (RFLP) has confirmed such high levels of genetic variability. The debate now concerns, how such a high level of genetic variability is maintained. The nature of this debate is bound to have profound implications, both for evolution and for conservation. Besides, recent discoveries in eukaryote genetics are likely to upset many of our traditional views about the genetics of evolution, and hence about its relevance for conservation