Male Migration in Barbary Macaques (Macaca sylvanus) at Affenberg Salem

We analyzed male migration during a 20-year period in the free-ranging Barbary macaque population of Affenberg Salem. Most natal migrations occurred around puberty, but only one third of all males left the natal group. Secondary group transfers were rare. All males immediately transferred to other bisexual groups. Migration rates were highest during periods with high adult female/male ratios within social groups. Immigrants highly preferred groups with fewer males of their own age than in the natal group, and many males immigrated into groups that had no male their own age. These groups originated from a skewed distribution of resident males during group fissions. A comparison of emigrants with their natal peers supports the inbreeding avoidance hypothesis as cause of emigration rather than the male competition avoidance hypothesis. Emigrants had no lower individual rank position and did not come from lower-ranking matrilines. Emigrants had more female maternal relatives, especially sisters. Males without female relatives almost never emigrated. Conversely, there is virtually no indication that emigrants were evicted from the natal group. Emigrants had no increased mortality. Paternity data revealed that the reproductive success of emigrants and natal males is similar, indicating that emigration had no reproductive cost. Many similarities between emigrants and natal males that separated from female maternal kin during group fissions suggest that inner migration during fissions is an alternative way to avoid maternal inbreeding. The mating system resulted in a genetic structure within social groups that largely diminished the chances for paternal inbreeding even without recognizing paternal kin.     

Social Influences on Group Membership in <Emphasis Type="Italic">Propithecus verreauxi verreauxi</Emphasis>

The size and composition of a social group can influence the reproductive success of its members. I examined the hypothesis that residents actively try to manipulate group size and composition in Verreaux’s sifaka (Propithecus verreauxi verreauxi). I collected behavioral data from 21 individuals in 5 social groups from November 2000 to March 2002 in the Kirindy Forest (C.F.P.F.) of western Madagascar. I investigated the affiliative and agonistic behaviors of resident males and females toward other group members to determine whether residents attempt to manipulate the costs and benefits of group membership. I also examined 3 cases of immigration attempts and 1 case of emigration. As expected, group members facilitated the residency of subordinate members of the opposite sex. For example, females sought out the subordinate males, responded to their calls, and even groomed them more. However, intrasexual relationships were also important for establishing or maintaining residency. The data, in conjunction with the observations of immigration and emigration events, suggest that resident individuals of both sexes attempt to influence group size and composition. I suggest that single–male groups are not the norm in Propithecus verreauxi verreauxi because females encourage, and males do not discourage, multiple males to reside in the group to increase group stability and to reduce the risk of infanticide.     

Patrilineal family values,family planning and variation in stature among Taiwanese six-year-olds

It has been argued that patrilineal joint family systems tend to bias family planning decisions in favour of sons. A simple model suggests that in such societies, any given son will be more highly valued by his parents (1) the fewer his brothers and (2) the earlier his birth is in the brother series. A daughter's value will be greater (1) the fewer brothers she has and (2) the earlier her birth is relative to other sisters. This study first addresses the extent of son preference as inferred from family composition data for 772 Taiwanese first-graders born in the mid-1970s in two socioeconomically distinct communities in Taipei, Taiwan. It then uses linear regression to consider whether the model criteria help account for statural variation among children in each study area when controlling for differences in measurement age, parental education and housing. With respect to family composition and gender preference, available evidence was consistent with previous surveys. While better-educated parents in the more affluent study area had significantly fewer children (p < 0.0005) and were more willing to stop without a son, girls there, as in the less affluent area, were still significantly more likely than boys to belong to large sibships (p < or = 0.005). Evidence from mean height of males and females partially accords with hypothetical predictions. In the less affluent area, the interaction effect of male birth order and the presence of younger siblings was significantly associated with mean stature (p = 0.002). Males without brothers were 2.0 cm taller than males with either an older or a younger brother (116.3 +/- 0.5 cm vs 114.3 +/- 0.4 cm). Males who had both younger and older brothers, but often no sisters, were about as tall, however, as those without brothers. A similar, but less pronounced, pattern was found among males in the more affluent area, but only among those who had sisters. These boys were also consistently shorter than boys without sisters (115.6 +/- 0.6 cm vs 117.7 +/- 0.6 cm; p = 0.001). Patterns of mean female stature did not clearly support the hypothesis. Girls in the more affluent area were relatively tall and did not show significant variation. Results among less affluent girls showed significant contrasts, but not necessarily in the predicted direction.     

Fraternal birth order and the maternal immune hypothesis of male homosexuality

In men, sexual orientation correlates with an individual's number of older brothers, each additional older brother increasing the odds of homosexuality by approximately 33%. It has been hypothesized that this fraternal birth order effect reflects the progressive immunization of some mothers to Y-linked minor histocompatibility antigens (H-Y antigens) by each succeeding male fetus and the concomitantly increasing effects of such maternal immunization on the future sexual orientation of each succeeding male fetus. According to this hypothesis, anti-H-Y antibodies produced by the mother pass through the placental barrier to the fetus and affect aspects of sexual differentiation in the fetal brain. This explanation is consistent with a variety of evidence, including the apparent irrelevance of older sisters to the sexual orientation of later born males, the probable involvement of H-Y antigen in the development of sex-typical traits, and the detrimental effects of immunization of female mice to H-Y antigen on the reproductive performance of subsequent male offspring. The maternal immune hypothesis might also explain the recent finding that heterosexual males with older brothers weigh less at birth than heterosexual males with older sisters and homosexual males with older brothers weigh even less than heterosexual males with older brothers.     

Gender,family configuration,and the effect of family background on educational attainment

Abstract

A comprehensive model of family influences on educational resemblance of siblings expands the traditional sibling pair model to a full sibship model in order to investigate how gender, gender composition of sibships, and a measure of ordinal position moderate the effect of social origins on educational attainments of siblings. One common family factor is sufficient to explain the variation of educational attainment among brothers and sisters. Although effects of social origin variables on brothers are larger than on sisters, the relative effects of measured social origins are virtually the same among sisters and brothers. The disparity between educational attainments of brothers and sisters persists across sex composition and family size. Ordinal position does not alter the effects of social origins on educational attainment nor does it directly affect educational attainment. Father's and mother's education are equally important for all siblings regardless of birth order, gender composition, and family size.     

Rank relations of juvenile and subadult natal males of Barbary macaques (Macaca sylvanus) at Affenberg Salem

Rank relations of more than 100 juvenile and subadult natal Barbary macaque males were analyzed. Hierarchical relations among individuals of the same age were established early during the first year of life. With few exceptions concerning infants from very high-ranking genealogies, males dominated female peers regardless of maternal rank. Males started to outrank females from older cohorts during the second year of life and completed the process of rank reversal with adult females at 5-6 years of age. An age-graded dominance pattern existed among males from different birth cohorts. Only 3 rank reversals between males from different cohorts were observed. Rank reversals among males of the same birth cohort occurred more frequently. Rank position of a male among his male peers was influenced by birth order, by maternal rank, and by the presence of juvenile brothers. Most males without juvenile brothers had low positions, regardless of maternal rank. Males born late in the birth season were also low-ranking, even when juvenile brothers were present. There was no cohort where ranking among males was determined by maternal rank alone, as is the case in rhesus monkeys and Japanese macaques. Adult/subadult male carriers had no noticeable effect on rank positions of 'their' infants. It is suggested that a weaker influence of Barbary macaque mothers on rank of their sons is related to very early integration of male infants in male social/play groups.     

Sex differences in the termination of social play in cats

Sixteen measures of social play between kittens were found to decrease significantly between 12 and 16 weeks of age. Behaviour was little influenced by the presence of the mother during this time. Although males' rates of behaviour did not differ from females' rates when the sexes were compared regardless of group composition, males from all-male groups played at higher rates than females from all-female groups. Females' rates of behaviour declined as the number of male companions decreased. Males' behaviour was little influenced by the number of females in the group. Females with male companions behaved more like males than did females with no male companions, but this was not because they directed behaviour to brothers at higher rates than to sisters.     

Unraveling the dispersal patterns and the social drivers of natal emigration of a cooperative breeding mammal,the golden lion tamarin

The study of the social drivers of animal dispersal is key to understanding the evolution of social systems. Among the social drivers of natal emigration, the conspecific attraction, aggressive eviction, and reduced social integration hypotheses predict that sexually mature individuals who receive more aggressive behavior and are engaged in less affiliative interactions are more likely to disperse. Few reports have explored these proximate factors affecting emigration in cooperatively breeding species, particularly of Neotropical primates. In this study, we investigated the dispersal patterns and tested the social drivers of natal emigration in the golden lion tamarin (Leontopithecus rosalia) — an endangered species inhabiting Atlantic rainforests fragments in Brazil. We used behavioral and demographic data collected during 7 years from 68 groups of tamarins inhabiting 20 forest fragments. Our analyses from the 160 dispersing individuals showed that dispersal success is higher for males and for those engaged in parallel dispersal, but that males and females use different strategies to enhance their dispersal success, males immigrate into established groups while females form new groups. We did not find high levels of agonistic behavior among group members before natal emigration. Instead we found that conspecific attraction drives natal emigration in both sexes, while additionally the low level of affiliative interactions within the natal group triggers male emigration. We discuss natal emigration in the broader perspective of the cooperative breeding system and the implications of these findings for the conservation of the species.     

Pairs and Harems in a Cichlid Fish,Lamprologus brichardi1

L. brichardi is a substrate brooding cichlid with facultative polygamy. The social organization was studied in the field for a 6-week period. The mating structure was examined in detail in the laboratory. Two types of social groupings are described:

• 1 Aggregations of sexually mature but nonterritorial fish, also frequently visited by territory holders in the vicinity.
• 2 Reproductive units (families) mainly consisting of the reproducing pair members and offspring from several broods. All family members defend a common territory around the shelter site. Occasionally a male has access to two females each with a separate territory (harem).

The factors influencing mating structure were investigated in the laboratory:

• 1 Females select breeding sites rather than partners.
• 2 Without competitors for breeding sites, and with an equal or nearly equal sex ratio, harems were established nearly as often as pairs.
• 3 Young males are physically able to mate and form a harem; but they are usually prevented from doing so by more competitive (larger) males.
• 4 Competition for breeding sites is not a prime influence on harem formation, although it is of great importance in determining the composition and size of the breeding population.
• 5 Just as many pairs as harems were formed with and without predators, even though, with predators, no young survived.
• 6 In L. brichardi the formation of harems is not predominantly determined by the distribution of suitable spawning sites. The monopolization of females is only slightly influenced by the distance between their territories.
• 7 In L. brichardi it is not necessary for harem formation that the male is bigger than the female.
• 8 Behavioural protocols and data on growth rates, as well as spawning intervals, did reveal any consistent difference between pairs and harmes.

Of the variables tested, male competition for females was therefore the sole determinant of who should mate.     

Dispersal mechanisms in a captive wild house mouse population (Mus domesticus Rutty)

The ecological implications of dispersal have been discussed in many studies of wild animals in the field but little is known about the social mechanisms leading to the emigration of certain members of a group. To study the social background of dispersal in wild house mice ( Mus domesticus Rutty) a population cage system was evaluated that allowed permanent observation of individually marked animals. It consisted of ten cages connected to a central cage by transparent plastic tubes. Two of these cages were defined as 'dispersal cages' and could be reached only by swimming through a water basin. Dispersal was defined as a permanent stay in one of these cages for at least 4 days. At the beginning of the experiment one pair of house mice with their litter was placed into the cage system. Each of six experiments lasted for 6 months during which data on spacing, social interactions, body condition, reproduction, mortality and dispersal were collected by daily observations. Results regarding this study could be summarized as follows: (1) dispersal in house mice is male-biased; (2) there are interfamiliar differences in dispersal age, dispersal rate, and in the development of the population structure; (3) after reaching sexual maturity subdominant males are evicted by the dominant one; (4) reproductive rate among females drops with increasing birth order, thus only the oldest females within a group reproduce; (5) females born under high population density conditions can only reproduce after dispersal.     

Do male house mice (Mus musculus) discriminate between females that differ in nutritional status?

Most studies of mate choice have focused on female preference for male traits because it is generally assumed that since males provide less parental investment they are not choosy. However, if males suffer missed opportunity costs by mating with lower quality females, selection should favor males with the ability to discriminate among females. We tested the hypothesis that male house mice (Mus musculus) discriminate between females that differ in nutritional status (non-food-deprived versus food-deprived). We recorded the time males spent investigating either type of female and used that to determine preference (spending ≥55% of their total investigation time with one female). We also examined the effects of female nutritional status and female preference status (preferred versus non-preferred) on the reproductive success of males. Males did not display a preference for non-food-deprived females nor did their reproductive success vary with nutritional status or preference status of females. Interestingly, males spent more time investigating females that were closest to the male's own weight. In addition, pairs that were closer in weight were more likely to produce a litter. These results suggest that male house mice are capable of discriminating among females and that such discrimination may influence their reproductive success.     

Aggression of breeding eastern bluebirds (Sialia sialis) toward their mates and models of intra-and interspecific intruders

Hypotheses regarding the evolution of aggressive patterns during the breeding season in eastern bluebirds (Sialia sialis) were tested by placing models of eastern bluebirds and house sparrows (Passer domesticus) into territories of experimentally naive breeding pairs of eastern bluebirds during three stages of the nesting cycle. The responses of the resident males to models of male bluebirds decreased from the egg-laying to the nestling stage, and this response pattern can be interpreted as support for the protection-of-parentage hypothesis or the nest-site-defence hypothesis. The aggression of resident males to resident females during trials with models of male bluebirds weakly conforms to the pattern predicted by the protection-of-parentage hypothesis. The aggressive response to models of house sparrows also decreased from the egg-laying to the nestling phase in a manner consistent with the nest-site-defence explanation. No aggression toward mates by males or females was observed during trials with house sparrow models, an observation consistent with the predictions of the protection-of-parentage hypothesis.     

Duration and benefits of biparental brood care in the dung beetle Onthophagus vacca (Coleoptera: Scarabaeidae)

Abstract.

• 1 Single males, single females or pairs of dung beetles, Onthophagus vacca, were released on artificial small (100 g) or large (1000 g) dung pats in the laboratory. Emigrating beetles were trapped at 12 h intervals, and the number and size of the brood chambers were recorded after each replicate.
• 2 Emigration of males was delayed if females were present in the same dung pats, whereas emigration times of females were independent of the presence or absence of males.
• 3 A residency of 60 h proved to be a threshold value. Females emigrating before this time did not breed, whereas those emigrating later had built at least two brood chambers.
• 4 Females paired with males built more brood chambers than single females.
• 5 The reproductive success of pairs was not influenced by the size of the dung pats.

     

Increased frequency of islet cell antibodies in unaffected brothers of children with type 1 diabetes

AIM: To assess the relation between islet cell antibody (ICA) positivity and demographic characteristics in an extensive series of first-degree relatives of children with type 1 diabetes (T1D). METHODS: Family members of children diagnosed with T1D before the age of 16 years and attending one of 27 participating paediatric units in Finland taking care of children with diabetes were invited to volunteer for an ICA screening program aimed at identifying individuals eligible for inclusion in the European Nicotinamide Diabetes Intervention Trial (ENDIT). The final series comprised 2,522 first-degree relatives (1,107 males) with a mean age of 20.4 (range 0.1-51.9) years, out of whom 390 were fathers, 622 mothers, 717 brothers, and 793 sisters of affected cases. RESULTS: Two hundred and four family members (8.1%) tested positive for ICA with levels ranging from 3 to 564 (median 18) Juvenile Diabetes Foundation (JDF) units. One hundred and five relatives (4.2%) had an ICA level of 18 JDF units or more. Males had detectable ICA more often than females (9.6 vs. 6.9%; p = 0.02). Antibody-positive family members under the age of 20 years had higher ICA levels than the older ones [median 18 (range 3-514) JDF units vs. 10 (range 3-564) JDF units; p = 0.008]. Among the adult relatives (>or=20 years of age) antibody-positive females had higher ICA levels than the males [median 10 (range 5-564) JDF units vs. 9 (range 3-130) JDF units; p = 0.04]. Siblings had an increased frequency of high-titre ICA (>or=18 JDF units) when compared to the parents (4.8 vs. 3.2%; p = 0.05). Among siblings, we found a higher frequency of ICA positivity in brothers than in sisters (10.8 vs. 6.9%; p = 0.01), and this was also true for high-titre ICA (6.0 vs. 3.8 %; p = 0.04). Geographically, the highest ICA prevalence was seen among relatives living in the middle of Finland (10.4 vs. 7.2% in the other parts of Finland; p = 0.01). CONCLUSIONS: These results imply that male gender and young age favour positive ICA reactivity among family members of children with T1D. Siblings test positive for high ICA titres (>or=18 JDF units) more frequently than parents. Accordingly, judged from demographic characteristics, the yield of ICA screening in first-degree relatives would be maximized by targeting young brothers of affected cases.     

Are flies kind to kin? The role of intra- and inter-sexual relatedness in mediating reproductive conflict

As individual success often comes at the expense of others, interactions between the members of a species are frequently antagonistic, especially in the context of reproduction. In theory, this conflict may be reduced in magnitude when kin interact, as cooperative behaviour between relatives can result in increased inclusive fitness. Recent tests of the potential role of cooperative behaviour between brothers in Drosophila melanogaster have proved to be both exciting and controversial. We set out to replicate these experiments, which have profound implications for the study of kin selection and sexual conflict, and to expand upon them by also examining the potential role of kinship between males and females in reproductive interactions. While we did observe reduced fighting and courtship effort between competing brothers, contrary to previous studies we did not detect any fitness benefit to females as a result of the modification of male antagonistic behaviours. Furthermore, we did not observe any differential treatment of females by their brothers, as would be expected if the intensity of sexual conflict was mediated by kin selection. In the light of these results, we propose an alternative explanation for observed differences in male–male conflict and provide preliminary empirical support for this hypothesis.     

Distribution of male yellow dungflies around ovipasition sites: the effect of body size

Abstract.

• 1 Spatial and temporal variation in body size of yellow dungflies, Scatophaga stercoraria, gathering on and around cow droppings was studied in an Icelandic population in order to elucidate the effect of male and female size on male mating tactics.
• 2 Males copulating on droppings were on average larger than males copulating in the grass, but of similar size to males guarding ovipositing females. Males searching on droppings were smaller than males copulating or guarding females on droppings but larger than males copulating in the grass. No such differences were found in female size.
• 3 Resource-holding power of males (RHP, i.e. male: female size ratio) differed between the three mating groups and was highest for males on the droppings. Size and RHP clearly affect the tactics of copulating males. Males with low RHP tend to copulate in the grass in spite of the cost of longer copulation duration. We argue that this is caused by risk of takeovers from large searching males.
• 4 There was no change in male size with the age of individual droppings. Contrary to what might be expected, large searching males are not predominantly found at fresh droppings when the probability of catching unpaired females is highest. We suggest instead that good prospects in taking females over from other males must make the strategy to search for females on older droppings profitable.
• 5 RHP did not change with age of dropping in the three mating groups. The size of ovipositing females increased with age of dropping, probably reflecting longer copulation and egg-laying times of large females.
• 6 We found an overall positive relationship between sizes of male and female partners. This correlation was highly significant for copulating pairs in the grass. This is probably a consequence of males with low RHP copulating in the grass and fights in which larger males take over females from smaller males. A weaker, but significant, correlation was found amongst ovipositing pairs. This must be due to take-over effects. No size correlation was found for pairs copulating on droppings.

     

Male morphology,performance and female mate choice of a swarming insect

1. Females of many species select mates based on important morphological and performance traits. This behaviour likely facilitates reproductive success thus exhibiting sexual selection. Most such studies have evaluated a single morphological variable, and only a minority of them studies the effects of behaviour and performance (functional capacity: Irschick et al., Evolutionary Ecology Research, 10 , 177–196, 2008) at all.
2. This study compares male morphological and performance traits differing in three variables that may correlate with fitness: condition index, flight ascent speed and resistance to torpor in relation to male mating success in the parasitoid wasp species Alabagrus texanus (Braconidae), a species where males swarm about emerging virgin females that display both choosy and non-choosy behavioural phenotypes.
3. Males that successfully mated with choosy females exhibited higher condition indices and somewhat stronger resistance to torpor than other males. Conversely, males that mated with non-choosy females did not differ in any trait from other males we measured. Early-arriving males did not have higher condition indices or greater mating success than other males.
4. Thus, both morphological and performance traits contributed to male success, which acted through female choice, indicating a role for sexual selection. Patterns of choice further differed among females, independent of male traits.

     

Ejaculate size varies with socio-sexual situation in an insect

Abstract.

• 1 Males operate within a finite energy budget and cannot produce limitless supplies of sperm. On the other hand, when a female mates with a second male while still containing fertile sperm from a rival male, selection should favour the male that inseminates more sperm. Optimal strategy should thus be for males to exercise discretion in the allocation of sperm to individual females. Assuming the outcome of sperm competition to be based on either the raffle or kamikaze principles, the sperm competition hypothesis predicts a positive association between the probability that the sperm will find themselves in competition with sperm from rival males and the number of sperm inseminated.
• 2 The beetle, Tenebrio molitor L., behaves in accordance with this hypothesis. Males accompanied by a rival male before and during mating inseminate more sperm per ejaculate than unaccompanied males. Accompanied males are also faster to initiate mating and more likely to show post-copulatory guarding. Adjustment of number of sperm inseminated was shown by males subjected to both long-term (5 days) and short-term (5 min) exposure to potential intrasexual competitors. Individual males exposed to both levels also demonstrated the ability to adjust their ejaculate according to socio-sexual situation.
• 3 We conclude that male T.molitor adjust the number of sperm they inseminate according to some perception of the risk of sperm competition.

     

Effect of Male Emigration on the Vigilance Behavior of Coresident Males in White-Faced Capuchins (Cebus capucinus)

I examined the vigilance behavior of male Cebus capucinus residing in four groups in Santa Rosa Park, Costa Rica. One male emigrated from each of three study groups, providing ideal experimental conditions for examining the effect of coresident males on male vigilance behavior (social and non-social). Following the predator and conspecific defense theories for the adaptive value of male vigilance behavior and the occurrence of multimale groups, I predicted that male nonsocial vigilance would increase after the emigration of a coresident male. My prediction was supported in only one of the three study groups. Males in two groups decreased their nonsocial vigilance after the emigration of a coresident male, which was probably influenced by seasonal changes and the peripherality of one group's coresident male before his emigration. The social vigilance hypothesis proposes that for species with rigid dominance hierarchies, social vigilance should increase with an increase in same sex competitors. Therefore, I predicted that male social vigilance would decrease after the emigration of a coresident male. The hypothesis is generally supported in my findings, as two of the three groups displayed a decrease in social vigilance after the emigration of a coresident male. Increased social vigilance in the third group is best explained by the change in the alpha male's social behavior after the emigration of his only coresident male.     

Differential dispersal and female-biased sex allocation in a parasitic wasp

1. Differential dispersal of males and females from a population is predicted to result in biased sex-allocation decisions, even in the absence of sibmating.
2. Mated Bracon hebetor Say (Hymenoptera: Braconidae) females produce distinctly female-biased sex ratios (≈ 30% male), yet sibmating is not a feature of the mating biology of this species. Therefore the dispersal behaviour of male and female B. hebetor from caged subpopulations was examined.
3. A higher proportion of females than males dispersed from the caged subpopulations. Furthermore, females dispersed earlier than males. This suggests that the level of competition for mates experienced by males is higher than the level of competition for hosts experienced by sisters.
4. Roughly half of the dispersing females left after they had mated. Females generally mate once in their lifetimes, suggesting that competition between brothers for mates may be high.