Presence Of Adult Males Research Articles

Social environment drives sex and age-specific variation in Drosophila melanogaster microbiome composition and predicted function.

Social environments influence multiple traits of individuals including immunity, stress and ageing, often in sex-specific ways. The composition of the microbiome (the assemblage of symbiotic microorganisms within a host) is determined by environmental factors and the host's immune, endocrine and neural systems. The social environment could alter host microbiomes extrinsically by affecting transmission between individuals, probably promoting homogeneity in the microbiome of social partners. Alternatively, intrinsic effects arising from interactions between the microbiome and host physiology (the microbiota-gut-brain axis) could translate social stress into dysbiotic microbiomes, with consequences for host health. We investigated how manipulating social environments during larval and adult life-stages altered the microbiome composition of Drosophila melanogaster fruit flies. We used social contexts that particularly alter the development and lifespan of males, predicting that any intrinsic social effects on the microbiome would therefore be sex-specific. The presence of adult males during the larval stage significantly altered the microbiome of pupae of both sexes. In adults, same-sex grouping increased bacterial diversity in both sexes. Importantly, the microbiome community structure of males was more sensitive to social contact at older ages, an effect partially mitigated by housing focal males with young rather than coaged groups. Functional analyses suggest that these microbiome changes impact ageing and immune responses. This is consistent with the hypothesis that the substantial effects of the social environment on individual health are mediated through intrinsic effects on the microbiome, and provides a model for understanding the mechanistic basis of the microbiota-gut-brain axis.

One in the Hand Worth Two in the Bush? Reproductive Effort of Young Males Is Not Affected by the Presence of Adult Males

Reproduction is a costly endeavor, and most large, long-lived, and iteroparous mammals exhibit conservative life-history tactics wherein an individual may forego or abandon a reproduction event for the sake of survival. Nevertheless, risks and benefits associated with reproduction are not equal across males and females, nor across their life. Whereas expenditure for females is associated with rearing young (e.g., lactation), expenditure for males occurs with securing mating opportunities. Young males may be more successful when dominant males are lacking, but it is less clear whether—and at what cost—young males will expend effort when those opportunities arise. We designed an experiment to quantify reproductive effort (e.g., food intake, somatic loss [body mass and fat]) of male white-tailed deer (Odocoileus virginianus) to better understand the reproductive ecology of male ungulates, with an emphasis on determining how adult males (≥4.5-years old) affect timing and extent of reproductive effort expended by yearling males (1.5-years old). Food intake, hormone levels, body mass, and somatic loss during rut were similar between yearling males that interacted with adult males and those that did not. Somatic loss by all males was greatest during peak estrus of females, but forage intake relative to metabolic body mass for yearling males was nearly twice that of adult males. Testosterone levels were lower for yearling than adult males early in rut and were related negatively to forage intake. Whereas adult males lost 20% (23.5kg) of body mass and 31% (5.3 percentage points [ppt]) of body fat during the rut, yearling males lost 12% (9.3kg) of body mass and 22% (4.7ppt) of body fat. Reproductive effort by young males was not influenced by the presence of adult males, though young males expended less reproductive effort than adults. Instead, reproductive allocation occurred in a state-dependent manner, where pre-season levels of somatic reserves dictated reproductive effort, regardless of age. Like female ungulates, male deer displayed risk-sensitive reproductive allocation wherein current reproductive allocation occurred as a function of resources garnered during the prior season and were expended in a way that should have avoided over-investing and creating a tradeoff between reproduction and survival.

Effect of social environment on sexual differentiation in the highly gregarious red cherry shrimp (Neocaridina davidi)

Studies on social control of functional sex in crustaceans are scarce and focused on hermaphroditic species. Hence, the objective of this study was to determine whether adult sex ratio affects juvenile sexual differentiation in the gonochoristic red cherry shrimp (Neocaridina davidi (Bouvier, 1904)) (Decapoda, Caridea). We tested two alternative hypotheses: (1) that undifferentiated juveniles become males when reared in the presence of adult females and vice versa; (2) that the presence of adult males affects juvenile sexual differentiation through androgenic gland secretions. Newly hatched juveniles were maintained with adult males or adult females during a 50-day period, after which they were sexed. In both treatments, juvenile sex ratios showed no deviations from the expected 1:1 relationship. This suggests that adult sex ratio is not a selective force determining juvenile phenotypic sex, even though mating opportunities may be null for juveniles differentiating into the sex of surrounding adults. The 1:1 sex ratio observed in broods reared with adult males and adult females also suggests that the potential chemical cues released by adults have neither masculinizing nor feminizing effects on undifferentiated juveniles. Present results reject our initial hypotheses and are consistent with a strong genetic basis of juvenile sexual differentiation in caridean shrimps.

No direct contact needed for drones to shorten workers lifespan in honey bee

The honey bee, Apis mellifera, has been extensively used as a model in gerontological research, although the presence of adult males has been a factor so far neglected in investigations of the social regulation of worker aging. In the honey bee, drones (males) are produced and maintained only in the swarming season, or if a colony loses its queen. Here, we report on the longevity cost incurred by queenless workers that provide care for adult drones under conditions of food resources limited to hydrocarbons only. We found that the presence of drones reduced the life expectancy of workers, even if the workers were prevented from direct contact with the drones (double-mesh-type test). At the same time, the survival rate of the drones was surprisingly high. This suggests that our results reveal the existence of a mechanism that drones use to increase their fitness. We hypothesize that drones are able to communicate their presence to workers without direct contact. Alternatively, queenless workers might try to recruit other individuals to take care of males. In both cases, queenless workers, which are not able to reproduce themselves when deprived of protein, dramatically respond to the presence of drones.

Social Cues of Future Sperm Competition Received during Development Affect Learning in Adult Male Fruit Flies, Drosophila melanogaster

The social environment provides males with information about the likelihood of reproductive competition. However, social context can be highly variable, and males must track their environment in order to alter reproductive investment appropriately. In addition to using information gained as adults to adjust reproductive strategies, males can use cues in early life to anticipate future mating competition and alter development of reproductive tissue. As responding to variable levels of competition may be cognitively challenging, and early life environments could influence neural development, cues of future competition during development could influence adult cognitive capacity. Male Drosophila melanogaster fruit flies reared with cues of future reproductive competition, high larval density or in the presence of adult males, develop larger accessory glands. We examined whether these early life conditions affect adult male learning ability. We assessed the learning ability of adults reared under different larval social conditions in a non-sexual and sexual context. We also measured gene expression in learning, memory and synapse-related genes previously found to respond to the adult social environment. The presence of adult males during development had no effect. Males from low larval densities, however, had better learning ability in the sexual-context assay and showed relatively higher gene expression compared to flies from high larval densities. This could suggest a trade-off between reproductive investment into accessory gland growth or an increased investment into neural plasticity at low density.

Multi-male groups positively linked to infant survival and growth in a cooperatively breeding primate

Cooperative breeding is a system where helper individuals care for breeding individuals’ offspring. As a result, social environment is likely to play a key role in regulating reproductive success. In primates, cooperative breeding is only found in the family Callitrichidae. Callitrichid males typically provide more infant care than non-breeding females, and in many callitrichid species, the presence of multiple males has been linked to infant survival. Leontopithecus chrysomelas (the golden-headed lion tamarin) is an endangered callitrichid found in the Atlantic Forest of Brazil. We used long-term data for wild L. chrysomelas to assess the influence of social group composition on reproductive success. Our survival model found that infant survival was negatively associated with group size, but this cost was mitigated by the presence of multiple adult males vs a single adult male. We also found that infants raised in groups with multiple adult males exhibited faster growth rates and higher adult weights than infants raised with a single adult male. This study adds novel evidence for the positive influence of adult males on callitrichid reproduction, demonstrating that adult males influence infant growth, as well as survival, in wild populations of cooperatively breeding primates. We suggest that social group composition, particularly the presence of adult males, be considered in future conservation strategies given its importance for reproductive success. In cooperatively breeding species, group members care for breeding individuals’ offspring. Due to this care, group composition may have a strong influence on infant success. In cooperatively breeding primates, males often provide more infant care than females. We investigated the influence of group composition on infant success in a cooperatively breeding primate, the golden-headed lion tamarin. Using long-term field data, we found that infant survival decreased as group size increased. However, this effect was reduced when multiple adult males were present in the group compared to a single male. We also found that infants grew faster and reached larger adult weights in the presence of multiple adult males compared to a single male. Our results demonstrate the importance of group composition for cooperative breeders and provide new evidence for the positive influence of adult males on cooperatively breeding primate infants.

Same-sex partner preference in adult male zebra finch offspring raised in the absence of maternal care

An important component of mate choice is the sex of the potential partner, yet little is known about the factors that cause an individual to pair with the opposite sex. In the current study, we addressed the role of exposure to adult females during development in adult mate choice using a socially monogamous and biparental avian species, the zebra finch, Taeniopygia guttata. In our experimental set-up, zebra finch offspring were either raised in the presence of adult males and females in their aviaries (control) or in the absence of all adult females including their mothers (female-deprived). The female-deprived subjects were raised successfully by the male parents and showed no growth deficits compared to controls. When we tested partner preference of control and female-deprived subjects as adults, 57% of males that had been raised without females paired with each other. In contrast, 76% of male offspring that were raised with adults of both sexes paired with females. The most likely interpretation of this dramatic effect on pairing outcome is imprinting on adult males in the aviary in the absence of all adult females. These results thus suggest that sexual imprinting or some other form of social learning is a key developmental process for sexual partner preference in addition to preference for species and individual characteristics.

Human-Carnivore Conflicts in Private Conservancy Lands of Elerai and Oltiyiani in Amboseli Area, Kenya

Human-carnivore conflicts represent the most common negative form of interactions between humans and wildlife. Most carnivores involved in such conflicts are: lion, hyena, leopard and cheetah. Three strategies are normally used in Kenya to mitigate such conflicts; consolation for lost livestock and human life to increase tolerance to them, use of predator proof homesteads especially among pastoralists, use flicking lights at night to discourage approach of carnivores near homesteads, and awareness creation among communities on the ecological role of carnivores. This study examined human-carnivore interactions in privately owned conservancies near Amboseli National Park, Kenya. The conservancies were found to have almost similar human and livestock demography. However, homesteads in Elerai had more fence broken parts and relatively higher levels of livestock predation by lion and hyena. The higher the number of each livestock type was, the higher the specific predation to that livestock type was, implying density dependent effects of predation by carnivores on livestock. It seemed that the fence structure and level of maintenance (including carnivore strategies on specializing on specific livestock size and age consistent with optimizing their foraging strategies) influenced predation incidences. However, the presence of adult males and Maasai warriors (morans) in bomas did not seem to be related with the number of livestock killed by carnivores, implying that they didn’t add vigilance as an additional strategy to prevent livestock depredation. It is recommended that attention be paid on maintenance of homestead and livestock fences as well as vigilance to deter predation. We further recommend strategies to prevent livestock predation such as, installation of chain link predator proof fences or carnivore lighting deterrents at night because woody plants fences are ineffective and deteriorate easily with time, and also lead to depletion of plant resources critical to households.

Individual variation in vigilance in female eastern grey kangaroos

For herbivores, vigilance usually involves a trade-off with foraging, and a further trade-off between antipredator and social vigilance. Thus individual variation in vigilance may result in significant fitness consequences. We used mixed-effects models to document individual variation in vigilance in wild adult female eastern grey kangaroos (Macropus giganteus) in Queensland, Australia. We tested the effects of group size, presence of adult males and wind on vigilance patterns and variation by analysing 399 five-minute samples on 31 individually identified females who were foraging on the periphery of groups. We determined the proportion of time that individuals spent vigilant, and the proportions of vigilance time spent in social versus antipredator vigilance and in low- versus high-intensity vigilance postures. The proportion of time females spent vigilant decreased with increasing group size but was not affected by wind speed or male presence, while the amount of their vigilance time spent in social vigilance was affected by interactions among the variables. After controlling for these effects, 13 females’ vigilance patterns were significantly different from the population mean. Individual variation was also found in vigilance postures used and the effect of male presence. Understanding individual variation in vigilance is important for understanding individuals’ antipredator and social strategies.

Ecological patterns, distribution and population structure of Prionace glauca (Chondrichthyes: Carcharhinidae) in the tropical-subtropical transition zone of the north-eastern Pacific

Regional ecological patterns, distribution and population structure of Prionace glauca were analyzed based on samples collected on-board two long-line fleets operating in oceanic waters (1994–96/2000–02) and in coastal oceanic waters (2003–2009) of the eastern tropical Pacific off México. Generalized additive models were applied to catch per unit of effort data to evaluate the effect of spatial, temporal and environmental factors on the horizontal distribution of the life stages (juvenile, adult) and the sexes at the estimated depth of catch. The presence of breeding areas was explored. The population structure was characterized by the presence of juveniles' aggregations and pregnant females towards coastal waters and the presence of adult males' aggregations towards oceanic waters. The species exhibited horizontal segregation by sex-size and vertical segregation by sex. Distribution of the sex-size groups at oceanic waters was seasonally affected by the latitude; however, at coastal oceanic waters mainly females were influenced by the longitude. Latitudinal changes on the horizontal distribution were coupled to the seasonal forward and backward of water masses through the study area. Adult males showed positive relationship with high temperatures and high-salinities waters (17.0°–20.0 °C; 34.2–34.4) although they were also detected in low-salinities waters. The distribution of juvenile males mainly occurred beyond low temperatures and low-salinities waters (14.0°–15.0 °C; 33.6–34.1), suggesting a wide tolerance of adult males to explore subartic and subtropical waters. At oceanic areas, adult females were aggregated towards latitudes <25.0°N, mainly associated to subtropical waters during summer. The distribution of juvenile females indicated its preference by lower temperatures and more saline waters. Presence of pregnant females suggests that the eastern tropical Pacific off México represents an ecological key region to the reproductive cycle of P. glauca.

Species-specific patterns in fecal glucocorticoid and androgen levels in zoo-living orangutans (Pongo spp.)

In contrast to most primate species, including the other great apes, orangutans maintain a fission–fusion social system in the wild without being part of a stable community. In zoos, however, they are kept in permanent groups, usually consisting of one adult male and several females. In zoo orangutans, we predict higher levels of glucocorticoids and androgens in the Bornean species compared to its congener from Sumatra, due to the much more solitary lifestyle of Bornean orangutans and the apparent higher frequency of male aggression directed towards females in this species in the wild. To compare hormone levels of the two orangutan species, we validated a fecal glucocorticoid and a fecal androgen assay. Subsequently, fecal samples from a total of 73 female and 38 male orangutans housed in 29 European zoos were analyzed to investigate the effect of species, social group size, age and (for female glucocorticoid levels) reproductive state and the presence of adult males on fecal hormone metabolite concentrations. The results of linear mixed effect models indicate that both male and female Bornean orangutans show a steeper increase in glucocorticoid levels with increasing group size than Sumatran orangutans. We therefore conclude that Sumatran zoo orangutans are better able to adjust to social housing conditions than their Bornean congeners. In addition, our analyses reveal higher glucocorticoid levels in lactating females of both species compared to non-lactating and juvenile females. Concerning androgen levels in males, our analyses revealed significantly higher concentrations in Bornean than Sumatran orangutans. These differences in both glucocorticoid and androgen output between the two species of orangutan are presumably linked to ecological and behavioral differences and could possibly be attributed to phenotypic plasticity. However, given that we found interspecific differences in hormone excretion in captivity, where both species live under very similar conditions, we conclude that this variation has a genetic basis.

First Record of the Indo-Pacific Swimming Crab, Charybdis Hellerii (A. Milne-Edwards, 1867) in the Gulf of Mexico

Charybdis hellerii (A. Milne-Edwards, 1867) is a native of the Indo-West Pacific faunal province, but the species has been introduced nearly worldwide. The species entered the Mediterranean Sea as a Lessepsian migrant after the opening of the Suez Canal in the late 1800s (Por, 1971). Shipping from eastern Mediterranean ports has been proposed as the method of introduction of the species into the western Atlantic Ocean in the late 1980s (Campos & T?rkay, 1989; Galil & Zenetos, 2002). Dineen et al. (2001) described the larval development of C. hellerii and concluded that development time is sufficiently long (44 days in the laboratory) to allow for trans-Atlantic transport of the larvae in ship ballast water. The western Atlantic introduction appears to have been widespread over a relatively short time period. Early reports of the locations of C. hellerii capture in the western Atlantic included the waters off South Carolina (captured in 1986, but not identified until 2001, per David Knott, pers. comm., as U.S. Geological Survey's (USGS) Nonindigenous Aquatic Species (NAS) Specimen ID # 164602), Cuba (1987; reported in G?mez & Mart?nez-Iglesias, 1990), Venezuela (1987; Hernandez & Bola?os, 1995), and Columbia (1987; Campos & T?rkay, 1989). By the midto late-1990s, established populations (defined by the presence of adult males and females, ovigerous females, and juveniles) had been observed in the Indian River Lagoon on the eastern Florida coast (Lemaitre, 1995) and as far south as Sao Paulo State, Brazil (Mantelatto & Garcia, 2001). The most recent reports extended the known range of C hellerii in the western Atlantic from approximately 35?N (North Carolina; USGS NAS Specimen ID # 164602) to nearly 28?S (Santa Catarina State, Brazil; Mantelatto & Dias, 1999). Coastal range expansions have been attributed to larval transport on southward-flowing coastal currents along the

BROOD SEX RATIO IN THE APPLE SNAIL POMACEA CANALICULATA (GASTROPODA: AMPULLARIIDAE) IS DETERMINED GENETICALLY AND NOT BY ENVIRONMENTAL FACTORS

Brood sex ratios of the apple snail Pomacea canaliculata vary greatly, but the cause of the variation remains unclear. This study investigated the effects of various environmental factors on brood sex ratios, rearing hatchlings from the same egg masses (or parents) under two different conditions for each environmental factor. The factors investigated were: (1) presence of adult males or females; (2) food availability; (3) position in the egg mass (upper or lower part); (4) temperature (20 or 25°C); (5) age of the parents; (6) size of the aquarium; and (7) indoor or outdoor conditions. None of these factors had a significant effect on the brood sex ratio. On the other hand, brood sex ratios were significantly different among different egg masses or parents in all experiments. These results suggest that environmental sex determination does not occur in this snail. Instead, both the sex determination and sex ratio variation are under genetic influence.

Production of Calanus chilensis in the upwelling area of Antofagasta, northern Chile

Salinities, temperatures, chlorophyll a (chl a), and quantitative samples of Calanus chilensis were obtained at -17 d intervals from June 1996 to June 1997 at 3 stations in the Bay of Mejillones, northern Chile, and from 53 stations in a broad-scale survey of surrounding waters from 17 to 21 December 1996. Temporal variability in cohort structure precluded direct estimates of production from samples. However, lack of relationship of eggs per female and stage-frequency distribution with chl a in the broad survey, the apparently continuous development (and presence of adult males) during the time series, and the seasonal correlation of female body size with temperature, but not chl a, all suggest that food supply did not determine production rates. Therefore, temperature-dependent production was estimated, from sample biomasses and from laboratory rearings of C. chilensis and other species, as 45 mg C m -3 yr -1 . This is substantially lower than comparable estimates for C. finmarchicus off eastern Canada and northeastern USA. However, broad-scale production in December 1996 was much higher than that at the 3 time-series stations. A production:biomass ratio of 45, compared with 8 for C. finmarchicus off eastern Canada, is compatible with the general view that the upwelling area off northern Chile is part of one of the world's most productive marine systems.

Social inhibition of territorial behaviour in yearling male collared lizards,Crotaphytus collaris

In central Oklahoma, collared lizard males display age-dependent differences in social behaviour, whereby sexually mature first-year (yearling) males adopt subordinate tactics, and males 2 years and older establish and defend all-purpose territories. We tested the hypothesis that the social activities of adult males inhibit the expression of territorial tactics in yearling males by recording the behaviour of yearlings in the presence of adult males, when all adult males were removed from study plots for 4 days, and then again when adult males were returned to their territories. The rates of yearling male patrol, display and intrasexual encounters increased during removals, especially during the last 2 days, following which the rates of these behaviour patterns declined when adult males were replaced. Yearling males also increased the frequency with which they interacted with females when adult males were removed. Moreover, the duration of intersexual encounters during the last 2 days of removal was over twice that during the first 2 days of removal, suggesting that females became more receptive to yearling males the longer adult males were absent. Our results suggest that the stable age-related behavioural differences in male collared lizards is governed by social feedback, where sexually mature yearling males are capable of displaying territorial behaviour patterns but are inhibited from doing so by the activities of adult males.

“PUSHY” BEHAVIOR IN A WILD DOLPHIN FEEDING PROGRAM AT TANGALOOMA, AUSTRALIA

AbstractA program where wild bottlenose dolphins (Tursiops truncatus) are fed by tourists in shallow water adjacent to a wharf has been established at Tangalooma, Queensland, Australia. Up to nine dolphins attend the nightly feedings, and between 60 and 80 resort guests are permitted to hand feed these dolphins each night. Since this program began in 1992, the dolphins have increased in confidence and have started, at times, to make forceful contact with guests who enter the water to feed them. This paper categorizes such behavior as “pushy” and reports on a study which quantifies the “pushiness” of the dolphins which feed at Tangalooma. The study examines ecological variables which may determine how pushy the dolphins are at different feeding sessions. The number of dolphins attending a particular feeding significantly increases the pushiness. In addition, the presence of adult males at a feeding is likely to increase pushing. Tidal state also influences how pushy the dolphins are. At low tide, when the dolphins’mobility is restricted by the water depth, they are less likely to be pushy. Given the problems experienced in a number of other situations where wild animals are fed by humans, it is important to monitor carefully the escalation of pushy behavior in this dolphin feeding program, as it may be a precursor to more aggressive actions on the part of the dolphins.

Potential for social interaction in a natural population of prairie voles (Microtus ochrogaster)

Many hypotheses on the role of social behavior in population regulation of microtine rodents assume that social interactions are more frequent at high density than at low density. We evaluated this assumption by measuring potential for social contact in a population of prairie voles (Microtus ochrogaster). Our livetrapping regime monitored presence of resident and nonresident animals at the periphery of home ranges of social groups. Resident adults and young of both sexes were captured at home range boundaries. Potential for social interaction with nonresidents was greater at the periphery of home ranges than at nests. Intruders tended to be male adults from neighboring social groups. Presence of adult males in the resident group played an important role in deterring visits by nonresident males. During the spring, summer, and autumn reproductive period, number of captures of nonresident males, but not females, showed a strong positive relationship with population density. Despite relatively high densities during the winter nonreproductive period, there were few captures of residents and nonresidents at the periphery of home ranges. We conclude that the relationship between potential for social interaction and population density varied as a function of sex and season.

Behavioural Changes At Adolescence in Chimpanzees

Male chimpanzees experience puberty (marked testicular growth and ejaculation) when they are about 9 years old and just over half adult weight. They reach adult weight at 14-15 years. Females start small sexual swellings at about 8 years, mate with adult males when they are about 10.5 years and have their first infants when they are about 12 years. Males reduce their constant association with their mothers when they reach puberty and associate more with adult males and cycling females. Some males form strong, long-lasting associations with particular adult males. Females remain with their mothers until first oestrus,and then associate with adult males either in their natal community or a new community during oestrus. The decline in association with the mother is more closely correlated with pubertal stage than with chronological age in both sexes. Immatures of all ages spend 3-13% of their time in social grooming, but grooming partners change during adolescence. Juveniles of both sexes groom their mothers and siblings most, but males groom individuals outside their maternal unit more than do females. Juveniles receive over 90% of their grooming from mothers and siblings. Adolescent males groom less with their mothers and more with cycling females and adult males. While early adolescent males start to be groomed by females only late adolescent males receive any grooming from adult males. Adolescent females without mothers groom little except with adult males when they are in oestrus. Social play is most frequent with individuals aged 2-9 years and individuals play most with others of their age. Time spent playing by both sexes declines markedly during adolescence. Juveniles and early adolescents of both sexes have friendly interactions with infants, but late adolescents rarely interact with infants. Males show frequent sexual behaviour with oestrous females from an early age. Males spend more time with oestrous females as they get older but frequency of copulation declines gradually through adolescence. Early adolescent males try to take females on consort, but only late adolescent males succeed. One female rejected the sexual advances of a male once he reached puberty. Rates of interference in copulations by males decline during adolescence and males become more cautious of copulating in the presence of adult males. Females show little sexual behaviour until they start getting large oestrus swellings. Males receive increased aggression from adult males during adolescence. They become tense in the presence of adult males and even late adolescents are peripheral to grooming clusters of adult males. Males start to challenge adult females in adolescence but are often attacked, and are not able to dominate them all until late adolescence. Male juveniles perform elements of charging displays without hair erection more frequently than females. The freqency of this declines in adolescence while the frequency of charging displays with hair erection by males increases in adolescence and displays become increasingly more adult-like in length and form. Males show the shoulder hunch for the first time in early adolescence. Males pant hoot more than females and rates of pant-hooting increase with age in both sexes.

Population structure and dynamics of wood mouse Apodemus sylvaticus in Iceland

Five‐year‐studies of two wood mouse populations (Apodemus sylvaticus L.) were carried out outside the village Vík. S. Iceland, and in a birch forest close to the lake Mývatn, N. Iceland. The population at Vík was studied on a 1.10 ha grid on a slope covered with Angelica archangelica L., the seeds of which constituted a major food resource for the mice. Altogether 948 individuals were caught, marked and followed during 1973–1978. No other free‐living small mammals occur in Iceland, and predator pressure is low and considered non‐existent on the Angelica slope. The population density was extremely high; highest autumn density recorded was 150 ind ha−1. Like other Apodemus populations, the one at Vík showed a typical seasonal pattern in numbers: a winter decrease, relatively stable numbers in late summer, and an autumn peak. Breeding started in late April or early May and ended in late September; no winter breeding was observed. Three or four litters were produced, and the last litter(s) of the season greatly contributed to the autumn increase. The output of young per reproductive female throughout the year was negatively correlated with spring density, and autumn peak density with the number of females in August. Also overwinter success and weight changes appeared to be associated with population density (and weather). Survival rates did not vary much between years and seasons and were consistently rather high. Autumn survival of juveniles was positively correlated with mean minimum temperatures. Juvenile survival was, at least at times, negatively affected by the presence of adult males. Trapping outside the main grid did not indicate any marked dispersal, though some immigration to the grid must have occurred, especially in spring and early summer. Among the factors governing the population density and dynamics of wood mouse at Vík we emphasize the absence of interspecific competition and predation, the rich and dependable food resources (mainly Angelica seeds), the mild (though moist and windy) climate, the shelter of dense Angelica stands, the abundance of crevices (e.g. nest‐sites), and the social interactions.The birch forest in northern Iceland was low productive and the wood mouse population differed from the Vík population by exhibiting low density, short breeding season, and high vagility; characteristics we consider to be representative for most Apodemus populations in Iceland.

Copulation of Adolescent Male Chimpanzees, with Special Reference to the Influence of Adult Males, in the Mahale National Park, Tanzania

The mating patterns of adolescent male chimpanzees (Pan troglodytes) of the Mahale National Park, Tanzania, were studied. Sequential events associated with their copulations were characterized as follows. (1) In encounter, the female tended to approach the male. (2) In precopulation stage, the male often gave courtship displays. (3) In postcopulation stage, the male often groomed the female. (4) In leaving, the female tended to leave first. In every stage, especially during copulation, adolescent males were sensitive to the presence of adult males. The presence of adult males seemed to be enough to prevent adolescent males from copulating with the female. Influences of adult males on copulation of adolescent males are discussed in relation to male-male bonding in chimpanzees.