Are lemurs' low basal metabolic rates an adaptation to Madagascar's unpredictable climate?

It has been argued for nearly two decades that lemurs' low basal metabolic rate (BMR) by comparison to other primates is an adaptation to Madagascar's unpredictable climate. However, data from two recently published studies show that it is not just lemurs, but all strepsirrhines (the Suborder to which lemurs belong), that have low metabolic rates by comparison to other primates. Therefore, the better comparison to substantiate the argument is one with other strepsirrhines, not with all other primates. Data from the two studies do not allow the conclusion that lemurs' BMR is lower than that of other strepsirrhines.

Primate evolution: a biology of holocene extinction and survival on the southeast Asian Sunda Shelf islands.

What biological traits distinguish taxa susceptible to extinction from less susceptible taxa? Substantiated island biogeographic theory suggests that after insularization, small islands lose more species than do large islands. Thus, susceptible taxa are those now found on only large islands. The traits of susceptible taxa can thus be found by comparing the biology of species found only on large islands with those also found on small islands. The islands examined here are those of the Sunda Shelf, created as a result of the Holocene rise in sea levels of 120 m. We use four statistical comparisons: comparative analysis by (phylogenetically) independent contrasts (N = 8 contrasts at the subgeneric or deeper level), Spearman correlations, stepwise regression, and principle components analysis (N = 9 subgenera/genera). The genera and one subgenus considered are: Hylobates, Macaca, Nasalis, Nycticebus, Pongo, Presbytis, Symphalangus, Tarsius, and Trachypithecus. Traits of risk appear to be large body mass, low density, large annual home range, and low maximum latitude. Expected traits that did not correlate with susceptibility were low interbirth interval, high percent frugivory, high group mass, low altitudinal range, and small geographic range. The risky traits also apply to just the anthropoids (i.e., prosimians excluded). The risky traits are explained if susceptibility is induced by requirements for a large extent of habitat, a small population size, and specialization. These findings, which indicate that efficiency and plasticity of use of the environment separate susceptible from successful primate taxa, might be relevant to an understanding of hominoid evolution.

An encyclopaedia of sexuality.

Primate Sexuality. Comparative Studies of the Prosimians, Monkeys, Apes and Human Beings by Alan F. Dixson, Oxford University Press, 1998. £75.00 hbk, £32.50 pbk (656 pages) ISBN 0 19 850183 8/0 19 850182 X.

Sexual selection and genital anatomy of male primates.

Correlations between mating system and various aspects of genital anatomy suggest a strong influence of sexual selection on genital morphology. We test the generality of the influence by examining whether primate taxa in which there might be enhanced sexual selection (those with multi-male mating systems) possess, as expected, relatively more spinous penises than do taxa with other mating systems. As most prosimians, but few anthropoids (monkeys and apes), possess penile spines, and because the predominant mating systems of the two taxa differ, taxonomic constraints are taken into account. Sexual selection apparently does not act on penile spines in the same manner as on other aspects of genital anatomy: spinosity is not greatest in multi-male taxa of either prosimians or anthropoids. In some taxa, spines might stimulate reproductive readiness and synchrony in situations in which the sexes live apart and do not have other means of communicating reproductive state (dispersed social systems and 'stolen' extra-pair copulations), but problems exist with the hypothesis, as they do with the idea that spines are involved with scent marking. It seems that either penile spines have several functions, or penile spinosity in primates, and other orders, remains to be explained.

SPERM COMPETITION AND THE EVOLUTION OF NONFERTILIZING SPERM IN MAMMALS.

Nonfertilizing sperm with special morphologies have long been known to exist in invertebrates. Until recently, abnormal sperm in mammals were considered errors in production. Now, however, Baker and Bellis (1988, 1989) have proposed that mammalian sperm, like some invertebrate sperm, are polymorphic and adapted to a variety of nonfertilizing roles in sperm competition, including prevention of passage of sperm inseminated by another male. More specifically, their "kamikaze" sperm hypothesis proposes that deformed mammalian sperm are adapted to facilitate the formation and functioning of copulatory plugs (Baker and Bellis, 1988). Here I argue that most, maybe all, mammals are unlikely to produce nonfertilizing sperm. First, mammals might not be able to afford to evolve nonfertilizing sperm, given that a) fertilization is often unlikely despite the huge numbers of sperm produced; b) production of larger numbers of sperm is constrained, presumably because of metabolic costs, evidence for which includes the fact that in species in which sperm morphology and anatomy of the female reproductive tract increase the probability of fertilization, the numbers of sperm produced is lower than in others; and c) selection appears to act against the production of deformed sperm. Second, some of the evidence advanced for the existence of nonfertilizing sperm does not in fact support the idea. Third, accessory gland secretions are sufficient on their own to coagulate semen and produce fully functioning plugs; thus the male that used accessory gland secretions would be at a clear advantage over the male that diluted his fertilizing sperm with "kamikaze" sperm; and indeed, current evidence indicates selection on accessory glands, not sperm morphology, to enhance coagulation of semen. Fourth, predictions made on the basis of the "kamikaze" sperm hypothesis are not supported by quantitative comparisons of data from polyandrous and monandrous primates (i.e., those in which several males mate with a fertile female, and therefore in which sperm competition should be operating, and those in which only one male mates). Although sperm competition is almost certainly more intense in polyandrous genera than in monandrous genera (as indicated by, e.g., more frequent copulations and the production of more sperm per ejaculate from larger spermatogenic organs), polyandrous genera do not produce a greater proportion of deformed (i.e., nonfertilizing) sperm than do monandrous genera, or even necessarily a greater number of deformed sperm; nor a greater variety of sperm sizes-indeed they might produce fewer; nor fewer motile sperm (as might be expected if sperm are selected to stay behind and compete with sperm from subsequent males); and nor larger sperm (as might be expected if sperm are produced for functions other than to reach the egg). In sum, currently available evidence suggests that the function of all mammalian sperm is to fertilize, and that sperm competition in mammals occurs through scramble competition, not contest competition.

Environment, competition and reproductive performance of female monkeys.

In most wild and captive monkey groups, some females are clearly dominant over others. Dominant animals have priority of access to resources, and well fed animals generally outreproduce poorly fed ones. So why is it that only in some social groups are dominant female monkeys more fecund than subordinate ones? The distribution of food influences the intensity of competition between group members, and it appears that dominants do better only when interference competition is intense. In addition, dominance influences reproductive performance via reproductive parameters other than simple fecundity. Analysis of the different components of reproductive success, and of the environmental conditions under which dominants outreproduce subordinates, should help our understanding of the biological processes by which differential reproductive performance arises.

Reproduction in wild gorillas and some comparisons with chimpanzees.

Information was collected over a period of almost 12 years on the gorillas of the Virunga Volcanoes region of Rwanda and Zaire, most of it collected since September 1972. Comparisons were made with the Gombe Stream chimpanzee population (values in parentheses). Gorilla females matured at about 8 years (compared with 9-10 years for the chimpanzee) and first bred at 10-11 years (11-12 years). Males started to breed later, possibly at 15 years (about 13 years). Oestrous periods of female gorillas lasted for about 2 days (10 days) and oestrous cycles for about 30 days (36 days). Gestation in the gorilla lasts 255 days (228 days). Intervals between surviving offspring in the Virunga study groups was about 4 1/2 (5 1/2 years) but in the whole Virunga population was nearer 8 years. Lactational amenorrhoea lasted about 2 1/2 years (3 1/2 years). In gorillas and chimpanzees there were about 3 cycles to conception after parturition and females probably produce in their lifetime about 3 offspring that survive to adulthood. A successful male's productivity is greater. Mortality of immature gorillas was about 40% (50%). Initiation of courtship is generally by the female in gorillas but the male in chimpanzees. Copulation in gorillas lasts for about 1 1/2 min (7 sec) and occurs at a rate of once every 3 h when a female is in oestrus (once in 2 h). Interference in copulation is more common in the chimpanzee than the gorilla, but competition between individual males is more intense in gorilla populations. Females of both species can clearly exercise their preferences for particular males. The observed differences between the species in courtship and mating behaviour can be related to differences in the number of males available to and competing for oestrous females: in the loose multi-male chimpanzee community there is more advantage to males in initiating copulation and mating frequently and efficiently, and to females in advertising oestrus, than in the relatively stable one-male mating system of the gorilla.

Strategies of emigration and transfer by primates, with particular reference to gorillas.

In many primate species, more males than females leave their natal group and transfer to another. In man, chimpanzee and the gorilla, however, the reverse is the case. This paper presents detailed data for the gorilla on individuals' movements into and out of breeding units. Comparisons are made with other primates, and with data on two non-primate species in which females rather than males move between breeding units. Proximate causes and functions of emigration and transfer are considered, and the reasons (proximate and evolutionary) for the observed sex differences in frequency of movement are discussed.