Cousin marriage, a spousal union between close kin, occurs at high frequencies in many parts of the world. The rates of cousin marriage in humans are concordant with empirical studies that challenge the traditionally held view that reproduction with kin is generally avoided in animals. Similarly, some theoretical models in animal behaviour show that inbreeding avoidance is more constrained than previously thought. Such studies highlight the importance of quantifying the costs and benefits of reproduction among close kin over the whole life-course. Here, we use genealogical data from two human populations with high frequencies of cousin marriage (the Dogon from Mali, and the Ancien Régime nobility from Europe) to estimate these potential costs and benefits. We compare age-specific fertility and survival curves, as well as the projected growth rates, of subpopulations of each marriage type. Fitness costs of cousin marriage are present in terms of reduced child survival (in both populations), while benefits exist as increased fertility for men (in the Dogon) and for women (in the Ancien Régime nobility). We also find some differences in the projected growth rates of lineages as a function of marriage type. Finally, we discuss the trade-offs that might shape marriage decisions in different ecological conditions.

When every individual has an equal chance of mating with other individuals, the population is classified as panmictic. Amongst metazoan parasites of animals, local-scale panmixia can be disrupted due to not only non-random mating, but also non-random transmission among individual hosts of a single host population or non-random transmission among sympatric host species. Population genetics theory and analyses can be used to test the null hypothesis of panmixia and thus, allow one to draw inferences about parasite population dynamics that are difficult to observe directly. We provide an outline that addresses 3 tiered questions when testing parasite panmixia on local scales: is there greater than 1 parasite population/species, is there genetic subdivision amongst infrapopulations within a host population, and is there asexual reproduction or a non-random mating system? In this review, we highlight the evolutionary significance of non-panmixia on local scales and the genetic patterns that have been used to identify the different factors that may cause or explain deviations from panmixia on a local scale. We also discuss how tests of local-scale panmixia can provide a means to infer parasite population dynamics and epidemiology of medically relevant parasites.

Spatial organization within animal populations is often thought to reflect the outcome of strategies implemented by each individual to enhance its reproductive success and survival (Clutton-Brock 1989). Thus, while females usually focus on the acquisition of food and breeding sites, male dispersion is more often determined by the distribution and availability of females (Clutton-Brock 1989). Due to these factors, intraspecific competition for space could lead to the adoption of a territorial strategy, whenever the benefits of territorial defence are higher than the costs (Brown & Orians 1970). Among small mammals, two main hypotheses have been proposed to explain the occurrence of territoriality in females. Ostfeld (1990) proposed that females should defend food resources, so the distribution and availability of food items should determine the cost–benefit relationship of adopting a territorial strategy. However, Wolff (1993) developed a hypothesis, based on small rodents, that females should defend nest sites in order to avoid infanticide, the so-called pup-defence hypothesis.

The present study describes the reproductive biology, population structure and life history traits of the abundant intertidal crab Xantho poressa. Between March 2007 and April 2008, a total of 1918 individuals were collected in Corrales de Rota (south-western Spain), a human-modified intertidal habitat characterized by an artificial high complexity. Suitable refuges for crabs (cobbles and boulders) are very abundant in this area and density (maximum of 50 ind*m−2) was directly related with the area covered by these stones. In spring and summer, size–frequency distributions showed a polymodal pattern with seasonal variations related to the incorporation of juveniles to the adult population. Newly settled juveniles were not found in the Corrales suggesting an ontogenetic migration from a distant recruitment habitat. The annual reproductive cycle was seasonal and successive peaks in the abundance of ovigerous females were observed in late spring and summer. Females probably produced multiple broods during a long intermoult period. The gonadosomatic index had a cyclic pattern of variation with peaks two weeks prior to those of ovigerous females; it was lower during the non-reproductive season. The hepatosomatic index was high during spring, decreased during summer and increased gradually at the end of the reproductive season. There was a monthly cycle of larval release resulting from a combination of a cyclic and synchronic ovarian maturity, oviposition and incubation; hatching took place during neap tides when the moon was at last quarter. The adaptive significance of the rhythmic reproduction and hatching observed may not be explained by the predator avoidance hypotheses. The overall sex-ratio did not differ from 1:1 but one male and several females coexist under a stone, indicating a female biased operative sex-ratio. The combination of a complex habitat, its use, and a strong sexual dimorphism suggest a refuge–defence polygenic mating system. The survival and fitness of X. poressa in the Corrales de Rota are probably enhanced by the availability of shelter, a consequence of a highly complex habitat, and probably, of human activity.

Sperm competition occurs when the gametes of two, or more, males compete for opportunities to fertilize a given set of ova. This study examined whether mammalian sperm morphology could be affected by sexual selection. Comparisons were made of linear and volumetric measurements of the sperm head, midpiece and flagellum for 123 species representing 71 genera of mammals having either single partner mating systems or multiple partner mating systems. Sperm midpiece volume was found to be significantly larger in those species were females mate with more than one male during a single peri-ovulatory period. A positive correlation was also found between relative testes sizes and sperm midpiece volumes, while no relationship was found with any other sperm measure. These results indicate that, within mammals, the evolution of sperm midpiece volume has been affected by selection pressures resulting from sperm competition. The significance of these findings may relate to the density of mitochondria within the sperm midpiece. The mitochondria provide the energy required for sperm motility, in the absence of glycolytic support. A higher mitochondrial loading may therefore be associated with enhanced sperm motility.

The formation of long-term pair bonds in marine fish has elicited much empirical study. However, the evolutionary mechanisms involved remain contested and previous theoretical frameworks developed to explain monogamy in birds and mammals are not applicable to many cases of monogamy in marine fish. In this review, we summarise all reported occurrences of social monogamy in marine fish, which has so far been observed in 18 fish families. We test quantitatively the role of ecological and behavioural traits previously suggested to be important for the evolution of monogamy and show that monogamous species occur primarily in the tropics and are associated with coral reef environments in which territory defence and site attachment is facilitated. However, there is little evidence that obligately monogamous species are smaller in body size than species that can adopt a polygynous mating system. We review the evidence pertaining to six hypotheses suggested for the evolution of monogamous pair bonds: (1) biparental care, (2) habitat limitation, (3) low population density/low mate availability/low mobility, (4) increased reproductive efficiency, (5) territory defence, and (6) net benefit of single mate sequestration. We outline predictions and associated empirical tests that can distinguish between these hypotheses, and assess how generally each hypothesis explains monogamy within and between breeding periods for species with different types of territories (i.e. feeding only or feeding and breeding). Hypotheses (1) and (2) have limited applicability to marine fishes, while hypotheses (3)–(5) have little empirical support beyond the species for which they were designed. However, the role of paternal care in promoting monogamous pair bonds is not explicit in these hypotheses, yet paternal care has been reported in more than 70 monogamous marine fish. We show that paternal care may act to increase the likelihood of monogamy in combination with each of the proposed hypotheses through decreased benefits to males from searching for additional mates or increased advantages to females from sequestering a single high-quality mate. Among species defending breeding and feeding territories, the benefits, both within and between reproductive periods, of sequestering a single high-quality mate (hypothesis 6) appear to be the best explanation for socially monogamous pairs. For species without parental care (i.e. holding only feeding territories), territory defence (hypothesis 5) in combination with the benefits of guarding a large mate (hypothesis 6) could potentially explain most instances of monogamy. Empirical studies of marine fishes over the past two decades are therefore slowly changing the view of monogamy from a mating system imposed upon species by environmental constraints to one with direct benefits to both sexes.

Studies of the grey seal Halichoerus grypus mating system, using focal animal sampling constrained by study site location and size, limit the measurement of variation in male mating tactics and success. Using this method, the mating tactics of grey seal males have been classified as either ‘tenured’ or ‘transient’. Preliminary evidence is presented of wider variation in male mating tactics and success using mobile focal-animal techniques that are not constrained by site, and of the effects of age on behaviour when accounting for body mass. The study was conducted during the breeding seasons of 1997 and 1998 at Sable Island, Nova Scotia. Six young (11–12 years) and five old (20–25 years) males were captured at the beginning of the breeding season, weighed and fitted with a VHF transmitter and time-depth recorder. Each male was located daily, and a count of late-lactating females within a 10 m radius recorded as a measure of mating potential. Female guarding and observed copulatory attempts were used as a measure of mating success. Mean initial body mass of young males and old males was similar, 291 ± 13 kg and 298 ± 14 kg, respectively. All males changed location during the study period. Young males changed sites more often and moved shorter distances between sites than old males. Estimated mating success varied from probably no matings to a minimum of seven; there were no differences between young and old males. Maximum duration of stay at a site and the number of late-lactating females at a site significantly influenced mating success. All the males except for two young males departed on diving excursions during the breeding season and engaged in deep diving behaviour. Diving behaviour did not differ between the age classes. Our results indicate that the current classification of mating tactics in grey seal males is an oversimplification. Preliminary data show that age may account for some of the variation in male behaviour on land and mating success, but not for behaviour at sea.

Whilst the use of molecular genetic techniques is widespread in the fields of population and evolutionary biology, their application within the mammalian order Chiroptera neither reflects the species richness nor the ecological and behavioural diversity of the order. This is despite the fact that the Chiroptera are problematic to study using more direct observational techniques. Here, we standardize and synthesise the current data, assess the contribution of molecular research to the study of bat species and highlight the importance of its continued and expanded use. At an inter-population level, molecular studies have demonstrated a great diversity of population genetic structure within the order. Among populations of migratory species, genetic structure appears universally low, and hence seasonal movement is likely to be the prevailing influence. However, for sedentary species an array of factors including dispersal ability, extrinsic barriers to gene flow and historical events may determine the extent of genetic partitioning among populations. Intrinsic factors such as wing morphology or roost requirements may also influence population genetic structure in sedentary bat species, a proposal which requires further research. Molecular studies have also made important contributions towards an understanding of social organisation in bats. Evidence indicates that in many polygynous species male mating success does not translate directly into reproductive success, perhaps as a result of multiple mating by females. Estimates of relatedness within and genetic structure among colonies are, in general, very low; a finding which has important implications regarding theories concerning the formation and persistence of bat social groups. Molecular studies have provided new and important insights into the ecology of bats, and have opened up exciting and previously unexplored avenues of research. The data from these studies suggest not only a predictive framework for future studies, but also the use of genetic data in the management and conservation of bat species.

Stochastic simulation is used to compare different systems of mating to reduce rates of inbreeding in selection programmes with phenotypic or animal model best linear unbiased prediction (BLUP) evaluation. Compensatory mating (the mating between individuals from the largest selected families to individuals from the smallest) turns out to be proportionately about 0-30 more effective than minimum coancestry matings for situations with low rates of inbreeding, such as phenotypic selection or high population size, although the advantage is less apparent if common environmental effects are important. A modification of this system of mating is proposed which can be applied for overlapping generations, and this is shown to reduce rates of inbreeding proportionately by about 0-50 more than for discrete generations. Under high inbreeding, however, such as for BLUP selection and small population size, minimum coancestry matings, or even avoidance of sib matings are more effective. A procedure combining compensatory and minimum coancestry matings is also simulated and gives the largest reductions in the rate of inbreeding. The effects of these and other systems of mating on the rate of inbreeding are shown to occur through a reduction in the cumulative effect of selection and a deviation from Hardy-Weinberg proportions.

The value of a parameter such as heritability (h2) or intra-dass correlation in best linear unbiased prediction (BLUP) with the animal model or a family selection index affects both the rate of response achieved and the rate of inbreeding. If in BLUP an estimate of h2 is used which is biased upwards above its actual value, the rate of inbreeding can be substantially reduced with little reduction in the rate of response. Further, by mating individuals from families in which many are selected to others from families with few selected (compensatory mating), rates of inbreeding can be further reduced without substantial effect on response.

Simulation results of closed MOET schemes have evidenced several problems issuing from selection in small populations using family information and diverse modifications of the original schemes have been proposed. Mate selection, based on linear programming techniques, includes most of the desirable properties of other methods and offers additional advantages. Some applications of this technique to improve the results of dairy cattle MOET schemes with hierarchical and factorial mating systems have been analysed in this note by computer simulation. Other applications of the method are also discussed.