Avoidance of post-coital cannibalism in the brachyurid paddle crab Ovalipes catharus

Sexual cannibalism was examined experimentally in the New Zealand paddle crab Ovalipes catharus, where it is the female that risks cannibalism during and after sexual activity. In this species copulation only occurs when the female is soft-shelled after moulting and she is most vulnerable to cannibalism. Male paddle crabs protect and copulate with the females until the females are no longer sexually receptive. Males appear able to identify a female with whom they have recently copulated. After a brief separation, significantly fewer females were cannibalized in cases where a female was returned to her original sexual partner than in those that had exchanged partners. The asymmetry, where females gain some protection during moulting but males receive no such advantage, may, at least partially, explain the skewed sex ratios which are sometimes found in samples of O. catharus from nature.     

Nonconceptive Sexual Behavior in Bonobos and Capuchins

Sexual behavior by infecundable females, and by same-sex and adult-immature dyads, occurs in wild and captive bonobos (Pan paniscus). Proposed functions of these behaviors, in social primates generally, include practice, paternity confusion, exchange, and communication as well as appeasement. We used this framework to interpret and to compare observations of sexual behavior in a captive bonobo group and a wild white-faced capuchin (Cebus capucinus) group. In both species, (a) sexual behavior was no more frequent in cycling females than in pregnant or lactating females and (b) same-sex and adult-immature dyads engaged in as much mounting or genitogenital contact as adult heterosexual dyads did. The species differed in that (a) bonobos engaged in sexual behavior 65 times as frequently as capuchins, (b) only bonobos engaged in sexual contact other than ventrodorsal mounting during focal observation, and (c) bonobo sexual contact was concentrated most heavily in socially tense situations in adult female–female dyads, whereas capuchin sexual contact was concentrated most heavily in socially tense situations in adult male–male dyads. These data and published literature indicate that (a) practice sex occurs in both species, (b) paternity confusion may be a current function of C. capucinus nonconceptive sex, (c) exchange sex remains undemonstrated in capuchins, and (d) communication sex is more important to members of the transferring sex—female bonobos and male capuchins—than to members of the philopatric sex.     

Context and Development of Sexual Behavior of Wild Bonobos (Pan paniscus) at Wamba, Zaire

I studied sexual behavior of immature bonobos (Pan paniscus) in a wild group living at Wamba, Zaire, with special reference to its development. Even immature individuals under 1 year old performed sexual behavior. Sexual behavior occurred in almost all age–sex combinations, except between immature and mature females. Based on analyses of behavioral pattern and context, I classified sexual behavior involving immature individuals into three categories. (1) Genital contact between immature individuals was observed during play, and was performed by males more frequently than by females. This sexual behavior shared many traits with that of other great apes. (2) Copulation-like genital contact was observed between immature males and mature females. Its frequency increased with the immature male's age; it developed into copulation in adulthood. (3) Genital contact used to regulate interindividual relationships. This behavior, which is unique to bonobos, was absent among infants. It developed between late juvenile and early adolescent periods in association with changes in social circumstances.     

Female menstrual cyclicity and sexual behavior in stumptail Macaques (Macaca arctoides)

The sexual behavior and female reproductive cycles of a captive group of stumptail macaques (Macaca arctoides)were monitored during a 12-month period. The data, consisting of 303 ad libitummounts and copulations and 125 hr of focal-female testing, were analyzed by their frequency of occurrence during the three hormonal phases of the female menstrual cycle. Regularly cycling females exhibited statistically higher frequencies of all sexual behaviors compared to the amenorrheal controls. Contrary to previous reports which indicate no variation in sexual behavior throughout the reproductive cycle in this species, our data show marked increases in copulations during the periovulatory phase. Male dominance rank is associated with sexual behavior only at midcycle.     

Sexual Isolation Between Drosophila Melanogaster, D. Simulans and D. Mauritiana: Sex and Species Specific Discrimination

The sexual isolation among the related species Drosophila melanogaster, D. simulans and D. mauritiana is asymmetrical. While D. mauritiana males mate well with both D. melanogaster and D. simulans females, females of D. mauritiana discriminate strongly against males of these two species. Similarly, D. simulans males mate with D. melanogaster females but the reciprocal cross is difficult. Interspecific crosses between several populations of the three species were performed to determine if (i) males and females of the same species share a common sexual isolation genetic system, and (ii) males (or females) use the same genetic system to discriminate against females (or males) of the other two species. Results indicate that although differences in male and female isolation depend on the populations tested, the isolation behaviour between a pair of species is highly correlated despite the variations. However, the rank order of the isolation level along the populations was not correlated in both sexes, which suggests that different genes act in male and female sexual isolation. Neither for males nor for females, the isolation behaviour of one species was paralleled in the other two species, which indicates that the genetic systems involved in this trait are species-pair specific. The implications of these results are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Seasonal aspects of sexual cannibalism in the praying mantis (<Emphasis Type="Italic">Mantis religiosa</Emphasis>)

According to the adaptive foraging hypothesis of sexual cannibalism, females face a trade-off between mating and consuming a courting male. Because male and prey availability can change seasonally, sexual cannibalism may change with season. However, we are not aware of any work examining how sexual cannibalism in insects relates to the time of season. Here, we examined the seasonal pattern of sexual cannibalism and reproductive behaviour in the sexually cannibalistic praying mantis (Mantis religiosa). We repeatedly collected the last instars of praying mantises from the field and brought them up under natural weather and photoperiod, but standardised feeding and socioecological conditions. After the females reached sexual maturity, we allowed all of the females to mate during two mating trials. In comparison to female praying mantises maturing later in the season, early-maturing females were larger but of poorer body condition on the day of a mating trial (20 days after the adult moult). During the first round of mating trials, early-maturing virgin females cannibalised males more frequently than their late-maturing counterparts. In contrast, late-maturing females that mated in the first round of mating trials were more likely than early-maturing, nonvirgin females to be cannibalistic in the second round of mating trials. The latency time until copulation was correlated with a risk of sexual cannibalism and was longer in early-maturing females. Our study suggests that the date of the last (adult) moult plays an important role in the occurrence of sexual cannibalism.     

Sexual and vegetative reproduction in the aboveground part of a dioecious clonal plant, <Emphasis Type="Italic">Dioscorea japonica</Emphasis> (Dioscoreaceae)

In dioecious clonal plants, the reproductive effort required to set seeds will be responsible for the larger investment in sexual reproduction by females. If there will be a trade-off in resource allocation between sexual and clonal reproduction, this differential sexual reproduction will lead to sexual differentiation in the relative amount of clonal reproduction. To test this prediction, we studied differences between the sexes in their phenologies and investments in sexual and vegetative reproduction (clonal reproduction by means of bulbils) with respect to ramet size in a dioecious clonal plant, Dioscorea japonica Thunb. The period of bulbil production overlapped the period during which infructescences developed. Females flowered later, produced heavier inflorescences, and fewer flowers per inflorescence than did males. Regression analysis using the size of the individual plants demonstrated that large females made smaller investments in inflorescences and larger investments in sexual reproduction than did large males. In contrast, females invested fewer resources in vegetative reproduction than did males. However, the total investments in sexual and vegetative reproduction did not differ between the sexes. These results supported our hypothesis on the sexual differentiation in sexual and clonal reproduction.     

Life-history characteristics of a wild population of vervets (Cercopithecus aethiops sabaeus) in Barbados,West Indies

Life history data are presented for a population of vervets, Cercopithecusaethiops sabaeus, in Barbados, West Indies. The data were obtained from two habituated troops and from vervets captured during a large-scale trapping program. Individuals of known age from one troop were weighed periodically, and separate growth curves generated for males and females. The mean weight of captured adult females was 3.3 kg; that of adult males, 5.3 kg. The average age at sexual maturity is estimated at 34 months for females and 60 months for males. Vervets give birth throughout the year, but most infants are born between April and July. The average interbirth interval following a surviving infant is 11.8 months. The mortality of juveniles is heaviest between birth and 2 years of age and decreases thereafter. Males emigrate from their natal troops at sexual maturity and one incident of a juvenile female emigrating is reported.     

Sexual behavior in brown capuchins ( Cebus apella )

We observed sexual behavior patterns in two captive groups of Cebus apella.We obtained data on intersexual solicitations and intersexual competition. The length of proceptivity cycles by females averaged 18.8 ± 1.2 days; this corresponds with published reports of physiological measures of ovulatory cycles. Females initiated sexual interactions with males significantly more than males initiated interactions with females, and female solicitations increased in frequency over the duration of displayed periods of proceptivity. In contrast, male solicitations of females were infrequent and did not change significantly throughout female proceptive phases. Each female solicited the same male throughout a given proceptive phase. We observed no evidence of male-male or female-female competition. Males seem to respond to female sexual behavior directed toward them, rather than initiating sexual interactions themselves. Even so, male sexual interactions with females followed only a small proportion of solicitations.     

The effect of feeding status on sexual attractiveness of Ixodes ricinus (Acari: Ixodidae) females

Sexual attractiveness of unengorged, semiengorged and fully engorged females of both field and laboratory populations of Ixodes ricinus was studied under laboratory conditions by means of a computerised video tracking system. A male and a female were allowed to walk freely in a glass arena during 1 h and their behavioural interactions were observed. Obtained results revealed that the feeding status of I. ricinus females affects their sexual attractiveness. The highest attractiveness was observed in engorged females, the lowest in unengorged females of the field population. Copulation occurred in all experimental groups with the highest frequency observed in the unengorged virgin laboratory females. Despite engorged females being highly attractive for males on distance, the frequency of copulation was low. Differences between field and laboratory populations were found in both behavioural parameters and frequency of copulation. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth,mortality and reproduction of Sargochromis codringtonii in Lake Kariba,Zimbabwe

Age determination of Sargochromis codringtonii was undertaken using scalimetry. Marginal scale analysis, used for age validation, indicated that annulus formation occurred in October and November. The possible reasons for this are discussed. S. codringtonii is relatively long-lived, surviving up to 8 years. It is sexually dimorphic with males growing at a faster rate and attaining a larger size than females. It is suggested that the mouth brooding habits of the female fish is one possible reason for sexual dimorphism. A higher total mortality rate (Z) was recorded for females as compared to males. S. codringtonii reproduces throughout the year, but with a peak during the hot wet months. The right ovary is atrophied and the possible significance of this is discussed.     

Sexual size dimorphism,growth, and maturity of the fluvial eight-barbel loach in the Kako River,Japan

The maturation and growth pattern of the fluvial eight-barbel loach Lefua sp. (Japanese name: nagare-hotoke-dojo), an endangered species, was investigated using an individual identification-recapture method from 1995 to 1998 in an upper reach of a headwater tributary of the Kako River, Hyogo Prefecture, Japan. Based on observations of the gonads through the abdominal skin, the loach was estimated to breed mostly from May to July. All the males matured by age 1⁺, and all the females matured by age 2⁺. Gamete release in all individuals of both males and females was predicted from recaptured loaches during each breeding season. The standard length of mature females was significantly larger than that of males, showing sexual size dimorphism (SSD). The maximum sizes recorded were 75.4 mm SL for females and 61.2 mm SL for males. Both males and females of immature specimens grew mainly from May to November, including the breeding season, with no significant differences in growth rates between them. After sexual maturity, both males and females grew mainly from July to October (or November), after the breeding season, and the females exhibited higher growth rates than males. Therefore, SSD of the species seems to be attributable to the different growth rates after maturity. The longevity of the loach was estimated to exceed ten years based on individual growth patterns of various sizes during the survey period. It is likely that the loach has an iteroparous life history, breeding every year, and moderate growth rates after maturity.     

Differential effects of kinship,dominance, and the mating season on female allogrooming in a captive group ofMacaca fuscata

An analysis of allogrooming (total times spent grooming individual partners) of 8 sexually mature females (3–12 years of age) in a captive group of 17 Japanese macaques, shows that during the nonmating season, grooming distributions were characterized by high proportions of grooming given to family members and/or higher ranking nonkin. During the mating season, all eight females showed significant shifts in their grooming distributions, and four females showed significant shifts in grooming between their nonestrous and estrous periods (defined behaviorally). Fox six of eight females, mating season grooming was characterized by either high proportions of grooming given to family members and/or heterosexual and homosexual partners. It was found that within dyadic sexual relationships, dominants gave more grooming to subordinates than the former received, in contrast to a reversal of this pattern in the majority of these same dyads during the nonmating season. This is interpreted as one short-term function of grooming: a dominant asymmetrically grooms a subordinate sexual partner to maintain proximity with (or reduce tension in) the latter. The two remaining focal females (middle ranking, nulliparous) differed from the other females in that they shifted their mating season grooming to subordinate nonkin, despite the lack of evidence that this was a result of sexual interactions, patterns of partner availability, competition, patterns of grooming reciprocity, or agonistic alliance support. From these results, it is suggested that in some contexts, grooming of subordinate nonkin may function to reduce tension in thegroomer. In the Japanese macaque, this latter possibility and the asymmetric grooming of subordinate homosexual partners may prove to be exceptions to the general rule that female cercopithecine grooming of nonkin flows up the dominance hierarchy.     

Initiation of early breeding in a population of Microtus townsendii (Rodentia) with the secondary plant compound 6-MBOA

Summary Feeding the secondary plant compound 6-Methoxybenzoxazolinone (6-MBOA) during winter to a free living population of Microtus townsendii accelerated breeding in females. Both the recruitment of young and sexual maturation of these young were advanced by four weeks in comparison with a control population. Overwintered females supplied with 6-MBOA matured at a lower body weight than control females. But there was no such weightat-maturity difference between the grids for males. During April and May 72% of all juveniles captured came from the experimental population. Winter reproduction and early recruitment of young stimulated by 6-MBOA could have important population consequences for these voles.     

Mating behavior of male deer ticksIxodes dammini (Acari: Ixodidae)

To analyze the sexual behavior of male black-legged deer ticks Ixodes dammini,we collected ticks infesting 202 white-tailed deer. On average, 17.7 males and 8.8 females infested each deer. Field-collected males copulated with a mean of 2.25 females, and virgin males mated with 2.4 females. On experimental hosts, males established sexual contact with feeding females and repelled other males, and about half remained paired after their mate detached. Engorged females continue to be receptive, and males mate more readily with them than with nonfed females. We conclude that male I. damminiare endowed with a repertoire of behaviors which favor an opportunistic mating before seeking a host and a preference for mating with feeding females on the host accompanied by tenacious mate guarding.     

Size-related sexual selection and yeast diet inDrosophila buzzatii (Diptera: Drosophilidae)

Size-related sexual selection (SRSS) was examined on four traits (thorax and wing length and head and face width) inDrosophila buzzatii, by scoring male copulatory status in two mass-mating experiments. Using axenic females, experiment 1 was carried out with axenic males, and experiment 2 with yeast-supplemented males. While there was no indication of SRSS in experiment 1, such selection was substantial in yeast-supplemented males, which transmitted yeasts to mating females. Multivariate analyses of selection indicated that face width is the measured trait on which directional SRSS essentially acted in yeast-supplemented males, resulting in indirect selection on body size. Because this selection was affected by yeast diet in males, its possible interaction with the yeast transmission from males to females during the courtship is discussed.     

Sexual harassment in a live-bearing fish (<Emphasis Type="Italic">Poecilia mexicana</Emphasis>): influence of population-specific male mating behaviour

We investigated male sexual behaviour and the cost of sexual harassment, as measured by the reduction of female feeding time in the presence of a male, in a cave-dwelling population of Poecilia mexicana, in which sexual harassment does not occur naturally. We asked whether the lack of sexual harassment in this population is due to low sexual activity of the males, or low feeding motivation of the females. We experimentally increased the sexual activity of males or the females feeding motivation, or we used a combination of both treatments. Female feeding time was not lower in the presence of a male than in the presence of a female after sexual deprivation of the males or food deprivation of the females. Only in the combined experiment was female feeding time lower in the presence of a large male than in the presence of a small male, indicating a weak effect of sexual harassment by large males. Virgin females did not suffer a cost of sexual harassment, indicating that sexual experience does not cause the lack of sexual harassment in cave mollies. Males from a surface population, where sexual harassment occurs, significantly reduced the feeding time of cave-dwelling females even though these males exhibited surprisingly little sexual behaviour. The sexual activity of cave mollies did not correlate with male body size in any experiment, indicating that even after sexual deprivation, small cave molly males do not switch to the alternative mating behaviour known in surface-dwelling P. mexicana, where sexual activity is correlated negatively with male body size.     

Non-reproductive copulation behavior among Tibetan macaques (<Emphasis Type="Italic">Macaca thibetana</Emphasis>) at Huangshan,China

Non-reproductive copulation, which takes place outside of the mating season and does not result in conception and birth, was studied in a free-ranging group of Tibetan monkeys (Macaca thibetana) at Mt. Huangshan, China, in the birth seasons of 1992 and 1997. We employed all occurrence and focal animal samplings to record sexual and related behaviors and affiliation interactions, respectively. Compared with sexual behavior in mating season, non-reproductive copulation occurred at a lower frequency, with less frequent ejaculation, less harassment, shorter mount duration, and an absence of pause with vocalization. It often took place in a situation in which non-lactating females were involved in social conflict or approached males for mating. Neither pregnant nor lactating females were observed to mate in the birth seasons. Copulation during the birth season did not increase a sexually receptive female’s delivery the next year, nor was it associated with increased proximity, grooming, or agonistic aid for the mating pair. However, copulated pairs spent more time co-feeding, presumably reflecting an increased tolerance on the part of the male. Adolescent males, who rarely copulated in the mating season, engaged in mating activity in birth seasons as well. Therefore, though birth-season copulation had no reproductive functions, it may have fulfilled social functions for females, such as post-aggression appeasing by males or gaining access to resources. This also offered good opportunities for adolescent males and females to develop their sexual skills for later competition.     

Antibiotic curing of parthenogenesis in Eretmocerus mundus (Australian parthenogenic form)

The thelytokous parasitoid, Eretmocerus mundus (Australian parthenogenetic form) was infected with a species of Group B Wolbachia. Antibiotic treatment of the parasitoid cured parthenogenesis and lead to male production and reduced egg hatching by virgin females. For each generation infected females produced more progeny than cured females. The descendants of individuals treated with antibiotic were in most cases free of a detectable infection. Both treated females and descendant females mated and received sperm, but these were not used as mated and unmated cured females produced offspring with a similar sex ratio. Males produced as a result of the antibiotic treatment were at least partially functional as they produced sperm and copulated with and inseminated females. However, no sexual line could be established.     

Winter Host Plant Specialization in a Host-Alternating Aphid

The host alternating aphid, Rhopalosiphum padi (L.), feeds in summer on several different species of grasses but is monophagous on its winter host, Prunus padus L. The monophagy on P. padus could be a result of the restricted host range of the several different generations colonizing, or feeding, on this host during autumn–winter–spring. This study shows that the winter host plant specificity of R. padi is controlled mainly by the preference of the females remigrating (gynoparae) to the winter host, P. padus, in autumn. The other generations living on the winter host, i.e., sexual females, males, and spring generations, all accept a broader range of winter hosts. One alternative host plant, Prunus spinosa L., could be utilized by all generations associated with the winter host, except for the females remigrating at autumn.