Volume 94, Issue 6
December 1985, pages 575-665
pp 575-586 December 1985
The form that any communicatory exchange takes would depend on the extent to which the interests of the signaller and the recipient are at variance. Where such interests coincide, i.e. in cases of mutualism, the signals may be conspicuous when an immediate response is favoured, but rather subtle and variable otherwise. Over 80 % of the events of tactile communication that we have noted in our study of the social behaviour of free ranging groups of tame elephants appear to belong to this latter category. On Smith’s standard classification, they can only be classified as ‘associative’, related to remaining in the company of another individual. However, such signals are commoner by a factor of 20–100 amongst elephant calves and their mothers and allomothers when compared to exchanges between adult cows. We suggest that the function of these signals is mutual monitoring of the state of well being amongst related individuals. The considerable degree of altruistic behaviour displayed in social groups, such as those of elephants is now believed to subserve the function of enhancing the inclusive fitness of the individuals concerned. We explore a mathematical model of exchange of social aid which suggests that animals in social groups may enhance their inclusive fitness further by adjusting the amount of social aid exchanged in relation to the state of well being of the donor as well as the recipient. Our model further suggests that optimal social aid depends on the state of well being in a complex fashion making it difficult for the recipient to deceive the donor so as to extract more aid. We therefore expect that by and large honest communication of the state of well being would be characteristic of the higher social animals. Such communication would be based on normal physiological changes consequent on a change in well being. Thus animals with a superior degree of well being would take postures conducive to greater activity, would be more receptive to sensory inputs and may also shift the balance of production of various metabolites. This monitoring of the well being has greatly advanced in the human species and may be at the base of the elaborate health care amongst human societies.
pp 587-621 December 1985
Kin selection is a widely invoked mechanism to explain the origin and 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 and 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 and 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 and half sisters and 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 and 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 themselves growing up together in the company of individuals of varying degrees of relatedness. An ability to tell apart the more and less related individuals under such circumstances should favour kin selection.
Much effort is now going into assessing the abilities of animals to discriminate between kin and non kin. In every case studied carefully so far, 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 and 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 and 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 and not templates based on all animals one grows up with. Some animals such as honey bees, tadpoles and ground squirrels appear to have such templates but others such as sweat bees and some mice appear not to. It is entirely possible that our inability to devise natural enough assays for recognition prevents us from understanding the full potential of the kin recognition abilities of many animal species. In any case, genetically specified labels and self based templates should greatly facilitate the evolution of social behaviour by kin selection.
pp 623-637 December 1985
All biological characteristics are subject to conflicting selection pressures. This is particularly true of those characteristics that are subject to sexual selection. The classic example is the peacock’s tail. Others are the calls used by male frogs and toads to attract their mates. The forces which have acted in the evolution of these calls are varied and the calls that we hear made by these animals are diverse.
Two kinds of factors can be recognized: constraints and forces. Constraints on the kind of a call that a frog might evolve include its phylogeny, the energy required to produce different kinds of calls, the risks incurred from attracting predators. Also important is the morphology of the frog: both the structures used by the males to make the calls and the apparatus with which the females hear the calls. For example, frog size has an important influence both on the frequencies of the sounds that a frog produces and the acuity with which they are heard. Both passive and active selective forces can be identified. Passive forces include the distances that environments transmit sounds of different frequencies and the interference from other sounds that calls encounter. Active forces include the reactions of conspecific males and females to the calls. Males interact acoustically in a variety of ways to organize their choruses in both space and time. They position themselves, and time their calls so that they minimize the interference from other males while maximizing their chances of securing a mate. Female choice has been studied in test arenas. Females choose louder calls, calls that are most easily located, and the calls of their own rather than other species. In choosing among males of their own species, females have been shown to pick the males controlling the best resources, sometimes using calls to do so. They should also be expected to choose those males who can contribute the best genes to their offspring. The extent to which they do this and the role of calls in choosing is actively being argued.
Sexual selection, both interactions between males and female choice, have undoubtedly been important in the evolution of frog calls but only within the constraints imposed by a variety of other factors.
pp 639-653 December 1985
Exceptionally for a developing system, the pathways of intercellular communication are fairly well characterised in the cellular slime molds. This paper attempts to provide adaptive explanations for the origin of the following features and consequences of communication between cellular slime mold cells: the tendency to congregate, chemotaxis to a released signal, signal relay from cell to cell, oscillatory signal release and an invariant ratio of the terminally differentiated cell types. For the sake of specificity attention is directed at the speciesDictyostelium discoideum. Central to the entire analysis is the assumption that contiguous groups of feeding cells are, and in the past were, genetically identical. It is suggested that, in respect of most of the features listed above, the critical event which started things off must have been the acquisition by the cell membrane of permeability for a substance normally produced intracellularly as a response to the stress of starvation. An argument is presented for treating social behaviour in these organisms, and in particular the suicide by cells which differentiate into stalk, as an example of group selection.
pp 655-665 December 1985
There is communication and social synchronization of the circadian rhythm in the flight activity of the microchiropteran cave-dwelling batHipposideros speoris. Thus captive bats surrounded by free-flying conspecifics synchronize their activity to the colony activity. The circadian rhythm of a solitary bat in a solitary cave freeruns. Even the rhythm of an ‘alien’ bat (Taphozous nudiventris kachhensis) held captive in the hipposiderid bat cave freeruns. But the rhythms of a closely-related species,Hipposideros fulvus partially entrain to social cues fromHipposideros speoris. Social synchronization of circadian rhythms in bats may be species-specific. This synchronization is abolished when continuous light of 10–20 lux is shone inside the natural cave.