Small Harem Research Articles

Evidence of resource-defense polygyny in an endangered subtropical bat, Eumops floridanus

Understanding sociality and animal behavior is critical for developing effective conservation strategies. Many tropical bat species form harems, where dominant males play key social roles by defending groups of females directly (female-defense polygyny) and/or the resources that females need (resource-defense polygyny). The Florida bonneted bat (Eumops floridanus) is an endangered subtropical species suspected to form harems, but our understanding of its social structure, reproduction, and behavior is rudimentary. In this study, we evaluated demographic variation in morphological and behavioral characteristics of Florida bonneted bats to test the hypothesis that this species forms harem groups and exhibits resource-defense polygyny at roost sites. We used a 4-year dataset of 341 individuals uniquely marked with passive integrated transponders (PIT tags), coupled with tri-annual capture records, to track activity patterns of bats at five roosts fitted with PIT tag readers. We identified the likely dominant males and other demographic groups in each roost using morphometric characteristics and reproductive status. We assessed differences between sexes and among status categories in three primary metrics: amount of activity at the roost, time of emergence, and initial foray duration per night. Dominant males consistently were the most active individuals at roosts and spent the least amount of time away from roosts during forays, relative to females and other males. Females spent more time away from roosts than males and shared similar foraging activity patterns regardless of status. Our findings suggest that Florida bonneted bats form small harem groups that are active year round. Male bats exhibit characteristics of resource-defense polygyny at roost sites and a size-biased hierarchy, with the largest reproductively active males appearing to defend the roost at the expense of time spent foraging. We suggest that the roost site represents a critical, limited and defendable resource for male Florida bonneted bats to gain access to females, which has important implications for the conservation and enhancement of roost sites. Our study highlights the importance of accounting for differences in behavior across demographic groups and social roles when considering resource needs for imperiled species.

Seasonal dynamics of agonistic behavior and hormones in an ex situ all-male colony of large flying foxes.

Large flying foxes (Pteropus vampyrus) are a socially complex species. In situ colonies typically comprise thousands of individuals in small harems of one male to many females. In ex situ environments, all-male colonies are becoming more common due to a surplus of males in the population. There is limited information describing the hormonal and behavioral patterns of all-male colonies during the breeding season. We assessed seasonal changes in hormones and behavior in an all-male colony of 12 large flying foxes at Disney's Animal Kingdom® . We validated hormone assays using morning urine and fecal samples to assess seasonal changes in excreted immunoreactive testosterone and glucocorticoid metabolites. We collected behavior data using an all-occurrence method, recording agonistic behaviors related to territorial defense (hooking, biting, wing flexing, vocalizing, and wrestling), and sexual behavior (mounting and frontal grabbing). Results indicated that (i) we could reliably measure testosterone and glucocorticoid metabolites concentrations from fecal and urine samples collected from individual bats; (ii) there were distinct relationships between changes in levels of agonism and hormone concentrations throughout the year; and (iii) three agonistic behaviors (chasing, wrestling, and open-mouth threat) peaked prior to the increase in testosterone and glucocorticoid hormones measured during the breeding season. These three behaviors could potentially be used as early indicators to signal the onset of the breeding season and allow time to implement ex situ management changes to reduce the incidence of agonism between individuals.

Males and females differentially adjust vigilance levels as group size increases: effect on optimal group size

A strong motivation for one individual to aggregate with others is to reduce their vigilance because other group members provide coverage and warning of approaching predators. This collective vigilance means that a focal individual is usually less susceptible to predation than when alone. However, individuals differ in their vigilance levels depending on status and context. They may also differ in how they adjust their vigilance levels as group size changes. This flexibility in response means that the collective vigilance of a group, and hence its optimal size, is not intuitive. We demonstrate, in both natural and experimental systems, that male and female pheasants, Phasianus colchicus, in harems differentially adjusted their vigilance levels as harem size changed. Females became less vigilant as harems became larger, and benefited by increasing their foraging time. Conversely, males became more vigilant as harems became larger. We calculated the collective probability that a harem would detect a predator. Within natural harem sizes, a male and two females exhibited the highest probability of collective detection, with decreases as more females joined. This optimal harem size matched the average harem size observed at our study site. Females may join harems for benefits of collective vigilance. Despite both sexes having a shared interest in larger harems for mating benefits, optimal harem size is influenced by trade-offs in a nonsexual behaviour, vigilance. This results in males with relatively small harems, females associating with less preferred males and each male being surrounded by fewer females than he could mate with.

Decadal den fidelity of a highly mobile reef lobster

Palinurid (spiny) lobsters are a group of highly mobile decapod crustaceans (Childress and Jury 2006). An understanding of lobster behaviour and habitat use is valuable for fisheries management and conservation, especially since palinurids are among the world’s most sought-after seafood. The painted spiny lobster (Panulirus versicolor) exclusively inhabits coral reefs of the Indian and Pacific Oceans, including the Great Barrier Reef (GBR; Australia). Although some lobster species show fidelity to small reef areas, none are known to remain in the same place for periods up to a decade (Childress and Jury 2006). Here we report an observation of long-term (decadal) site fidelity of P. versicolor from Northwest Island (23°18’S, 151°43’E) in the GBR. On 3 May 2013, we captured a male P. versicolor (144 mm carapace length) that was initially captured on 28 December 2003 (114 mm carapace length). Identity was confirmed via elastomer implant and unique body markings (Fig. 1). Initial capture and final capture occurred at the same coral shelter or den (confirmed by GPS), although it was known occasionally to use other nearby dens (within 200 m). It shared a den with a small (two to three) harem of females, which changed through time. Despite being periodically harassed (i.e. captured and handled on at least five occasions between 2004 and 2006) and occasionally injured (i.e. limb loss due to autotomy), this individual maintained a long-term association with a particular den. Previous work has shown that individual spiny lobsters, including those of Jasus edwardsii and P. versicolor, are capable of moving 0.5–6 km (Kelly and MacDiarmid 2003; Frisch 2007). A high degree of site fidelity in marine species is often associated with a tendency towards over-exploitation and/or vulnerability to extinction (Cheung et al. 2007). Given the importance of the den for protection against potential predators and for providing mating opportunities, it is likely that protection of high quality dens (in marine reserves, for example) may provide excellent conservation outcomes for this species.

Reversed Sex Change in The Haremic Protogynous Hawkfish Cirrhitichthys falco in Natural Conditions

AbstractBi‐directional sex change has recently been reported in a range of reef fishes, including haremic species that were earlier thought to be protogynous (female to male). However, the occurrence of this phenomenon and the social conditions driving the reversion of males to females (reversed sex change) have been poorly documented under natural conditions. Reversed sex change is predicted to occur in low‐density populations where facultative monogamy is common. However, few studies have evaluated this over a long period in such populations. We documented the occurrence of bi‐directional sex change during a 3‐yr demographic survey of a population characterised by small harem sizes in haremic hawkfish Cirrhitichthys falco. New males were derived following a change in sex of functional females (secondary males; n = 3) and juveniles always matured first as females (n = 3). Thus, C. falco exhibited a typical protogynous sexual pattern, consistent with a range of haremic fish species. We observed reversed sex change in two males. In both cases, all the females disappeared from their harems and the neighbouring males expanded their territories to encompass the territories of the sex changers. However, bachelor males did not always revert to females. A dominant male experienced bachelor status twice but regained mating opportunities following the immigration of a female into his territory or by taking a female from a neighbouring harem. Thus, we conclude that bachelor males use reversed sex change as a facultative tactic to regain reproductive status in a haremic mating system. In addition, we discuss the influence of harem size upon occurrence of reversed sex change.

Matrisibs, Patrisibs, and the Evolution of Imprinting on Autosomes and Sex Chromosomes

The conflict theory of genomic imprinting argues that parent-of-origin effects on allelic expression evolve as a consequence of conflict between maternally and paternally derived genomes. I derive explicit population-genetic models of this theory when individuals in a cohort with an arbitrary and variable number of sires and dams interact. I show that the evolution of imprinting is governed by the reciprocal of the harmonic mean number of fathers but the reciprocal of the arithmetic mean number of mothers per cohort. Thus, a few monandrous females in a polyandrous population decrease the strength of the genetic conflict and the opportunity for conflict-driven paternal imprinting. In contrast, in populations in which few males control large harems, rare males with small harems do not have such a disproportionate effect on genetic conflicts and maternal imprinting. Additionally, I demonstrate that under the conflict theory, selection for imprinted expression on paternally derived X chromosomes is much weaker than it is on maternally derived X chromosomes or autosomes.

A bald encounter: hairless southern sea lion at the Falkland Islands

A hairless adult male southern sea lion (Otaria flavescens) was sighted at Sea Lion Island, Falkland Islands, on the 14th of August 2009. The sea lion was observed on several further occasions and was defending a small harem consisting of four females. To our knowledge, this is the first report of an apparently healthy sea lion being entirely hairless with the exception of vibrissae on the muzzle.

Large males dominate: ecology, social organization, and mating system of wild cavies, the ancestors of the guinea pig

Ecological factors differently affect male and female animals and thereby importantly influence their life history and reproductive strategies. Caviomorph rodents are found in a wide range of habitats in South America and different social and mating systems have evolved in closely related species. This permits to study the impact of ecological factors on social evolution. In this study, we investigated the social organization and the mating system of the wild cavy (Cavia aperea), the ancestor of the domestic guinea pig, in its natural habitat in Uruguay. Based on our laboratory investigations, we expected a polygynous system with large males controlling access to females. Results from radiotelemetry and direct observations showed that females occupied small stable home ranges which were largely overlapped by that of one large male, resulting in a social organization of small harems. In some cases, small satellite males were associated with harems and intermediate-sized roaming males were occasionally observed on the study site. However, microsatellite analyses revealed that offspring were exclusively sired by large males of the same or neighboring harems, with a moderate degree of multiple paternity (13–27%). Thus, the mating system of C. aperea can be described as polygynous and contrasts with the promiscuous organization described for other species of cavies (Cavia magna, Galea musteloides and Microcavia australis) living under different ecological conditions. Our findings stress the strong impact of environmental factors on social evolution in Caviomorphs as resource distribution determines female space use and, thereby, the ability of males to monopolize females.

Social buffering of the cortisol response of adult female guinea pigs

When housed in spacious, mixed age/sex colonies, male guinea pigs form small harems of females with which attachment-like social bonds are established. A previous study indicated that the bonded male, but not an unfamiliar male from the same colony, could reduce the plasma cortisol response of a female when exposed to a novel environment. We examined the effect of several classes of social partners on the cortisol response of females maintained under standard laboratory housing conditions. Eight “artificial harems” comprised of one adult male and two adult females were formed in standard group-housing cages 2 weeks prior to the study. Behavior observed in these home cages indicated that interactions between males and females of the triads were overwhelmingly positive in nature. When exposed to a novel environment for 2 h, the presence of either the male or female cage mate reduced the subject female's plasma cortisol response, whereas the presence of an unfamiliar adult male did not. Changes in plasma cortisol levels were not predicted by the frequency of various social behaviors observed in the novel environment. These findings: (1) demonstrate that the buffering effect of male partners on the cortisol response of adult females can be observed in guinea pigs maintained in conventional laboratory housing; (2) indicate that unfamiliar adult males are ineffective at reducing cortisol responses of females under these conditions; and, (3) appear to be the first to show buffering effects by adult female guinea pigs on the cortisol responses of other adult females.

Variation in harem size of red deer (Cervus elaphus L.): the effects of adult sex ratio and age‐structure

AbstractThe relationships among harem size, adult sex ratio (proportion of males > 5 years in the adult population, i.e. males > 5 years plus females > 2 years) and male age‐structure of red deer Cervus elaphus were investigated in La Petite Pierre National Reserve (PPNR) in France. We tested whether: (1) increasing adult sex ratio leads to a decrease in harem size along with an increase in the number of harems within a given rut period; (2) whether participation of sub‐adult males in mating activities increases with decreasing adult sex ratio, and as the proportion of adult males decreases. Harem size did not vary over the mating period, suggesting a high turnover of harem‐holders leading to an increase in the costs of mating for males. Harem size averaged 1.43 ± 0.91 and was lower than harem sizes typically reported for red deer (e.g. > 2.5 in Scotland and Norway). In support of the first prediction, a decrease in harem size and an increase in the total number of harems seen with an increasing sex ratio was observed (harem size = 2.08 – 1.26 [±0.43] ± (sex ratio); r2= 0.25, F1,18= 6.19, P= 0.02). Both the uniform distribution of females among harem stags and the small harem sizes observed in PPNR might concur to a smaller variance in male reproductive success than previously reported in red deer. Lastly, in partial support of the second prediction, the proportion of sub‐adult males observed during the mating season decreased with increasing adult sex ratio and with increasing proportions of adult males. Whether or not the lower proportion of sub‐adults seen when competition among mature males increases means that fewer young males mate cannot be assessed from our study.

Roosting ecology and social organization of the spotted-winged fruit bat, Balionycteris maculata (Chiroptera: Pteropodidae), in a Malaysian lowland dipterocarp forest

The aims of this study were to investigate the roosting ecology and social organization of the spotted-winged fruit bat, Balionycteris maculata (Megachiroptera), within an old-growth Malaysian dipterocarp forest, and test the hypothesis that males spend a significantly greater proportion of the night in the immediate vicinity of their day roosts than females. Balionycteris maculata roosted in cavities and formed small harem groups that consisted of one adult male accompanied by up to nine adult females and their dependent young. Both male and female bats foraged locally, within approximately 1 km of their roost sites. However, in contrast to females, which remained away from the roost site throughout the night, both harem and solitary adult males divided their nightly activity between foraging and returning to their roost sites. Individual females were also found roosting sequentially with up to three different males. Hence, these results suggest that B. maculata has a resource-defence polygynous mating system, in which the roost cavity may represent a critical and defendable resource by which males recruit and gain improved reproductive access to females. Roost cavities occupied by B. maculata were found within a number of different forest structures, including ant nests, termite nests and the root masses of epiphytes. The consistent shape and position of the cavities, along with a single observation of cavity enlargement, provide the first evidence of roost-cavity excavation, by a megachiropteran bat, within the nests of social insects. Although the cues by which females select their roost sites are unclear, some aspect of roost cavity size, or condition, may provide a possible means by which females can assess the reproducÍtive fitness of potential mates.

Ecological, Behavioral, and Life‐History Correlates of Mammal Extinctions in West Africa

Abstract: Identifying the biological traits of species that predispose them to extinction is a focus of research in evolutionary ecology and conservation biology. This research has traditionally been divided between studies of extinction or decline in undisturbed habitat islands and studies of the persistence of species affected adversely by human influence. I combined these approaches to test for correlations between nine ecological, behavioral, and life‐history traits and vulnerability to local extinction for 41 species of carnivores, primates, and ungulates in fragmented and exploited habitats in Ghana, West Africa, while accounting statistically for phylogeny. Species distributed in isolated populations were most prone to local extinction, and monogamous species and those wherein males defended small harems were also prone to extinction. Body size, fecundity, abundance, habitat specialization, trophic group, and the degree to which hunters and consumers preferred a species generally were unrelated to species persistence. Although population isolation and mating system were the only traits that explained a significant amount of the observed variation in persistence of all species, analyses of carnivores, primates, and ungulates as groups yielded varied results. Mammals most prone to local extinction in my study reserves were also those listed by the World Conservation Union as being at greatest risk of global extinction. Thus, my results suggest that the relative isolation of populations and the mating system displayed by mammals may be good general predictors of their persistence.

Queuing for harem access in colonies of the greater sac-winged bat

Colonies of the greater sac-winged bat, Saccopteryx bilineata, consist of nonterritorial males and males that defend harem territories in which females roost. The traits of nonterritorial males that define their success in harem take-overs are so far unknown. We predicted that the time nonterritorial males spent in the colony and their proximity to harems would be important factors. We temporarily removed harem holders from a colony of 60 greater sac-winged bats on consecutive days and observed which of the nonterritorial males took over the harem. To test for consistency of results, we repeated the experiments in some of the territories. In a second set of experiments, we removed both the harem holder and the corresponding usurper from the first experiment. On average, usurping males preferred territories with a large harem over territories with a small harem and they belonged to groups of males who spent the daytime near the corresponding harems. Usurpers in the second experiment were present in the colony for a shorter time than usurpers in the first experiment. Overall, the results support the hypothesis that nonterritorial males form overlapping peripheral groups for harems and that they live in a hierarchy according to their tenure in the group. Group membership and hierarchy seemed to be the factors that determined whether a male occupied a vacant harem. Hence, instead of floating, the pattern of harem succession in greater sac-winged bats is best described by queuing of nonterritorial males for access to a harem. Copyright 2003 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Individual variation in perfume blending in male greater sac-winged bats

Male greater sac-winged bats, Saccopteryx bilineata, use hovering flights to court females in their harem territory. While hovering, males fan a fragrant perfume from sac-like organs in the wing membrane towards the females. Each afternoon, males renew the perfumes of their wing sacs during a stereotypical and time-consuming behavioural sequence, which includes blending secretions from genital and gular glands. I investigated whether male perfume-blending behaviour varies between the mating and the nonmating season, and whether successful males, those with large harems, have different patterns of perfume blending than less successful males. I measured variation in perfume-blending behaviour in 21 adult males. The pattern of perfume blending was not significantly different between the mating and the nonmating season. However, the time at which perfume blending began and terminated differed between seasons. During the mating season, males spent about the same time cleaning their wing sacs during phase I of perfume blending, irrespective of the number of females in their harem. During phase II, males with large harems spent significantly less time refilling and blending perfume than males with small harems. In addition, males with large harems took up fewer droplets of secretion from the genital region. Overall, male–male interactions were rare during perfume blending, and the decrease in duration in phase II was not attributable to more disturbance in large harems. There was also no evidence that males prevented each other from transferring secretions into their wing sacs. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Pup mortality in southern elephant seals at Marion Island

Pre- and early post-weaning pup mortality of southern elephant seals (Mirounga leonina) at Marion Island from 1990 through 1999 ranged from 1.6% to 7.3% and averaged 3.8%. Mortality of pups after weaning before their first trip to sea accounted for only 12% of the total mortality. We found no relationship between population size and percentage pup mortality, indicating that pup survival is independent of seal density, at least at the densities of breeding seals that prevailed. Indeed, pup mortality was greatest in the smallest harems, apparently owing to a greater number of younger, less experienced mothers. Small harems were generally also found on less suitable beaches than larger harems and this could have contributed to pup injury as a cause of pup mortality on these beaches. Mother–pup separation and injury caused by beachmasters is likely to be responsible for pup mortality in the larger harems. The low rates of pup mortality observed in this study obviate it being a major population regulating agent at Marion Island.

Social effects of space availability on the breeding behaviour of elephant seals in Patagonia

The Patagonian breeding colony of southern elephant seals, Mirounga leonina, of Penı́nsula Valdés, Argentina is characterized by long, continuous, homogeneous and spacious beaches. Reproduction in this colony occurs at the lowest group densities reported for the species. The availability of ample space resulted in the dispersion of reproductive females along 160 km of coastline, with a range of 0–300 reproductive individuals per km. Females grouped together in small harems (median=11 females, range 2–122, N=432), and individual distance between females was one to two female body lengths. Body contact within the harem was rare. Consequently, agonistic interactions (AIs) between females and female aggression (Ag) towards alien pups occurred infrequently (median rate=4 AIs/female per 100 h and 1 Ag/pup per 100 h, respectively). Pup mortality rate was low for an elephant seal rookery (3.5% for 3487 pups). Most dead pups were stillborn, and only three of 38 pups whose cause of mortality could be determined died from trauma or starvation following mother–pup separation. Female dispersal allowed many males to have access to females. About 45% of all males of reproductive size in the colony (about 1000 individuals) had a harem. Most adult males mated with receptive females. Low-density breeding conditions benefited female reproductive success through an increase in pup survival. Female dispersal resulted in small harem size, however, and limited the potential for polygyny. 1996 The Association for the Study of Animal Behaviour

Group Sizes of Oribis in Different Habitats

Data collected on group sizes of the oribi Ourebia ourebi at midland elevations in Natal, South Africa, were compared with available data from montane (Drakensberg) and tropical (East Africa) grasslands. Mean group sizes were lowest in montane grassland and highest in tropical grassland. In the montane areas adults occurred mainly in pairs or as single animals, whereas small harem herds predominated in tropical grassland, while the organization at midland areas was intermediate. It is suggested that the social organization of the oribi is influenced by habitat suitability, and availability and quality of food during winter. This hypothesis is discussed in relation to the three areas considered.

Male reproductive success in harem troops of hanuman langurs (Presbytis entellus)

Based on cross-sectional and longitudinal data collected in 1967–1988 by various observers, male reproductive success was studied in the Hanuman langurs of Jodhpur, India. The harem-structured social organization ensures a high degree of paternity certainty. Births occur throughout the year, with significant peaks and minima in March and November, respectively (n =398).The interbirth interval averages 16.7 months (n = 114).The duration of harem residencies varies between 3 days and ≥ 74.0 months, with a mean of 26.5 (n = 64). Harem holder replacements occur during all months of the year. No male achieves residency in more than one troop, suggesting that residency is associated with a distinct peak in the resource holding potential of a given male. Reproductive success among males varies considerably. Male mortality is high due to migration and intrasexual competition, leading to an adult sex ratio of 1:4.9. It is estimated that one-quarter of all adult males will never gain harem residency. Conceptions achieved outside harem residencies are so rare (4.7%) that a viable low-risk strategy, opting for longevity instead of harem residency, is unlikely. Tenure length has a stronger influence on male reproductive success than harem size because interbirth intervals are significantly shorter in small harems than in larger ones. It is assumed that females in one-male breeding structures compete for sperm and that such competition is more intense in larger harems.

The status and ecology of the dama gazelle in the aïr and ténéré national nature reserve, Niger

As part of the biological survey of the recently proposed Aïr and Ténéré National Nature Reserve in Niger, information was gathered on the status and ecology of the dama gazelle Gazella dama. The population of the reserve was estimated at 150–250. Dama gazelle were most often in small harems or mixed groups, or singly. Average group size was 1·92±1·20. Dama gazelles were primarily browsers, with the leaves of Balanites aegyptiaca and Acacia tortilis forming the bulk of their diet. They were most often observed in temporary watercourses. The primary threats to dama gazelle in the reserve were hunting and habitat degradation, and conservation measures are proposed.

Harem Social Organization in Cave Roosting Artibeus jamaicensis (Chiroptera: Phyllostomidae)

Harem Social Organization in Cave Roosting Artibeus jamaicensis (Chiroptera: Phyllostomidae)