Behavioural ecologists investigate the evolutionary forces that select for one behavioural pattern over another (Krebs and Davies 1991, 1993. ) Why do lions hunt in prides while the tiger stalks its prey alone? Why are honey bee workers so industrious while the drones are so lazy? Why do koels lay their eggs in the nests of crows while the latter go through the trouble of building nests and caring for chicks, their own as well those of the koel? Why do Siberian cranes fly some 6400 kilometres from their breeding grounds in Siberia to over winter in Bharatpur in Rajasthan, India, only to return to Siberia in summer? Why are males in many species of birds monogamous, pairing for life and providing paternal care to the chicks, while the males of many mammals are polygynous, mating with many females and contributing little more than a sperm-full of genes to their offspring? Behavioural ecologists estimate, and wherever possible calculate, the relative costs and benefits of alternative behavioural strategies under the given ecological circumstances and attempt to predict the winning strategy. What are the relative advantages of cooperative hunting versus stalking in stealth, for the lion that lives in open savannas and the tiger that lives in dense jungle? What are the inclusive fitness benefits to the worker bee who rears sisters related to her by 0.75 instead of daughters related to her by 0.5, as compared to similar benefits for drones, of rearing sisters related to them by 0.5 instead of daughters related to them by 1.0? What are the benefits to the koel of saving the cost of nest building and brood care and to the crow of attempting to selectively destroy the koels' eggs without destroying her own? What are the costs for the Siberian crane of attempting to survive, let alone breed, in the severe winters of Siberia compared to the cost of risky and energy-consuming flights to Bharatpur and back? What are the costs to males of denying paternal care to their offspring when the mothers are up to the task by themselves and what are the costs to the females of abandoning their offspring? Difficult as it is to do, these costs and benefits are often measurable. The more risky gambit of the behavioural ecologists appears to be the assumption that alternative behavioural strategies are readily available or easily created by mutation so that natural selection can choose from among them (Grafen 1991). The source of uncertainty is our profound ignorance of the proximate physiological, genetic or epigenetic, neurobiological and developmental mechanisms that orchestrate these behaviours. This ignorance has to do, in part but only in part, with the formidable difficulty of unraveling the proximate mechanisms of complex behaviour patterns. The remaining part has undoubtedly to be attributed to the behavioural ecologists' obsession with ultimate factors and habitual neglect of proximate causation (Gadagkar 1997). But of course there are exceptions, and a particularly spectacular exception concerns our present understanding of the proximate factors involved in the presence and absence of affiliation, pair-bonding and paternal behaviour in voles. Voles are small mouse like rodents that can sometimes be serious pests. Of particular interest for this tale are two North American species, the prairie vole, Microtus ochrogaster, and the meadow vole, Microtus pennsylvanicus. These two species have contrasting mating systems. The prairie vole is very social, forms lasting pair bonds, males prefer the company of their mates and are aggressive to other individuals, and both parents provide extended parental care to offspring. In contrast, the meadow vole is rather asocial, mating is polygynous or promiscuous, mated pairs do not pair-bond and males do not provide parental care to offspring. There are also two other similarly contrasting species, the monogamous pine vole (Microtus pinetorum) and the promiscuous montane vole (Microtus montanus) which have been substituted for prairie voles and meadow voles, respectively, in some of the studies. Despite such contrasting social behaviour, prairie/pine voles and meadow/montane voles share more than 99% genome homology and look very similar. The obvious advantage of these vole species as model systems to investigate the evolution of social behaviour in general, and mat
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Jan 1, 2006
Hiroshi Momose + 2
Open Access
