The mate guarding theory of conservative clothing posits that veiling reduces women's physical allure and sexual attractiveness, thereby diminishing men's attraction towards them and deterring potential rivals for a woman's partner. This theory argues that the importance of veiling is influenced by ecological factors in a way that it is of higher importance to control women's sexuality in harsher environments to secure paternal investment. A prediction of this theory is that the importance of veiling should be influenced by community size, where individuals’ reputations, specifically men's, might have different weightings, and their perceived sense of controlling a partner's activity may differ. Using pre-existing data from seven countries encompassing over 9000 individuals, the current study explored the association of town size and importance of veiling for women. Results showed a U-shaped relationship where in small towns and large cities, individuals, specifically men, give more importance to the veiling of women. This finding not only has multiple implications in terms of the effect of community size on male policing behaviours of women and sexual restrictions, but it also might point to a wider relationship regarding the association of community size and moral values.

According to the theory of evolved sex differences in jealousy, the challenge for women to ensure paternal investment increased their jealousy response to emotional infidelity, whereas paternal uncertainty exerted selective pressures that shaped men to become more distressed by sexual infidelity. Several studies have investigated whether the effect of these sexually dimorphic selection pressures can be detected in contemporary human populations, with conflicting results. To date, no genetically informed studies of sex differences in jealousy have been conducted. We used data from the Screening Across the Lifespan of Twins Younger (SALTY) sample, containing information concerning self-rated jealousy from 3,197 complete twin pairs collected by the Swedish Twin Registry. Intra-class correlations and structural equation models were used to assess the genetic influence on jealousy and to investigate sex differences at genetic level. We saw a highly significant sex effect on the relationship between infidelity types, indicating that men, relative to women, reported greater jealousy in response to sexual infidelity than in response to emotional infidelity. The twin models revealed significant heritabilities for both sexual (32%) and emotional (26%) jealousy. The heritabilities were of a similar magnitude in both sexes, and no qualitative sex differences could be detected. We show for the first time that variance in jealousy is to some extent explained by genetic factors. Even though our results from the mean value analyses are in line with the theory of evolved sex differences in jealousy, we could not identify any sex differences on a genetic level.

Throughout the latter part of the dry season (January-April) of 1985 and 1986, we studied the demography of mature adults in a small population of Argia chelata along a stream at Monteverde, Costa Rica. Males defended sunlit spots along the stream between 1030 h and 1400 h central standard time each day and females visiting these sunlit spots were soon mated. By individually marking all mature adults in the population we found that there was no significant difference between the sexes in daily survival rates (0.85 for males and 0.86 for females). Lifetime mating success was positively correlated with longevitiy in both males and females but the ability of males to obtain a mate appeared to be independent of age.

Although the sex ratio at emergence was 1:1, that of mature adults at the stream was strongly male-biased (87% male), perhaps as a result of a longer or more risky prereproductive period in females related to the costs of egg formation. We argue that the strongly male-biased sex ratio has important effects on the mating system of this species in that the male contact-guards the female for the entire oviposition period each day. Although this limits each male to mating with one female per day, it probably ensures that the male will fertilize most of the eggs laid by the female that day.

Despite being an exploited and economically important species, little is known about the reproductive behaviour of Loligo forbesi. During a captive trial performed in a closed seawater system in the Azores, three spawning events were directly witnessed. An account of their main behavioural aspects is given. A number of behavioural components are described for the first time in this species: ‘pair formation’, ‘mate guarding’, ‘egg holding’, ‘egg touching’, ‘white arms’, ‘red accessory nidamental glands’, ‘accentuated testis’, and ‘jockeying and parrying’. The chromatic, locomotor and postural components were very similar to other coastal loliginids observed on spawning grounds. From egg masses recovered on octopus traps, we show that in the Azores spawning activity occurs at least between 25 and 144 m, but greater depths might be expected. We suggest that this squid preferentially deposits egg masses on hard structures probably hiding them in cracks and crevices of volcanic substrata. The existence of spawning aggregations is supported by several factors: (i) these spawning grounds may coincide with the fishing spots, where the exploitation seasonally takes place, given that most individuals caught by fishermen are usually mature (more than 80%); and (ii) mate guarding and jockeying/parrying by males was observed, which is a common feature of spawning aggregation areas, where sperm competition occurs. Furthermore, our results, combined with available published and non-published data further confirm L. forbesi as an intermittent spawner. We estimate that throughout their short life cycle, females of L. forbesi are able to perform up to six spawning events, each composed of an average of ≈2300 eggs.

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.

Cerci are paired, sensory appendages extending from the terminal abdominal segment of crickets. While the cerci are acutely sensitive to air currents and thereby function in the detection of potential predators, they are also known to play a role in co-ordinating movements of males and females during copulation. The role of the male's cerci at four stages of the mating sequence (courtship, copulation, mate guarding and spermatophore removal) was examined by experimentally removing the cerci of male decorated crickets Gryllodes sigillatus and comparing their mating success with that of control males. The mating success of cercectomized males was significantly reduced relative to control males, primarily because of their greater inability to induce females to mount. Even when they succeeded in securing an initial mount, cercectomized males took significantly longer to transfer a spermatophore than did control males. Cercectomy had no influence on the efficacy of post-copulatory mate guarding by males, nor did females discriminate against cercectomized males by removing their spermatophores sooner than those of control males. We conclude that the primary function of the male's cerci in sexual interactions in G. sigillatus is to provide tactile stimuli to females that either elicit or guide their mounting response.

The Australian sleepy lizard Tiliqua rugosa forms socially monogamous pair bonds for 6 to 8 weeks each spring before mating occurs. This behaviour could not be explained by any hypothesis involving males helping to rear their young, because pairs split up soon after mating, and males seem to have no contact with the offspring of their partners. Short monogamous associations in other lizard species are often interpreted as mate guarding by the male to assure paternity. The mate guarding hypothesis was tested by experimental separation of pairs at various times during the pairing season. Data from 73 trials indicated that males were more likely to return to females than vice versa, and that the tendency of males to return to females increased as the time of mating approached. Also, reunion was more likely in pairs that had a greater tendency to remain together during the season. These results are consistent with predictions that the monogamous relationship is a form of mate guarding by males. However, the incidence of females re-uniting with males, and the long duration of pair bonds before mating occurs are not predicted by a mate guarding hypothesis. There may be additional explanations for monogamous pairing in the sleepy lizard.

Brants' whistling rat Parotomys brantsii is a gregarious rodent that undergoes marked population fluctuations every few years. Previous studies have variously described them as solitary or social. In this field study, based on direct observations, the social structure and breeding system of a population that almost quadrupled over 7 months was investigated. At the onset of the breeding season, the animals were solitary, each occupying a separate warren. By the end of the breeding season, there was multiple occupancy of some warrens. Each individual maintained a discrete territory within the warren, and exhibited no apparent social behaviour. Outside the breeding season the behaviour of males and females did not differ and both remained at their resident warrens. During the breeding season male P. brantsii visited more neighbouring warrens than did the females, and their visits were to unoccupied warrens or to those occupied by females. Females tended to remain within their own warren. Both sexes avoided warrens occupied by males and few male–male interactions were observed. Females were solicited at their warrens by males, who were frequently chased away. There was, however, evidence that reproductively receptive females were more tolerant of males, who may guard females following mating. This breeding system, based on competitive mate searching by males, and not overt aggression between males, parallels the scramble competition polygyny described for a number of other species, including North American ground squirrels.