Unexpected Strong Polygyny in the Brown-Throated Three-Toed Sloth

Promiscuous mating strategies are much more common than previously appreciated. So much so, that several authors have proposed that promiscuity is the “rule” rather than the exception in vertebrate mating systems. Decreasing species mobility and increasing habitat fragmentation have both been suggested to reduce the “polygyny potential” of the environment and promote other mating strategies like promiscuity in females. We explored the social and genetic mating system for one of the most sedentary extant mammals, the brown-throated three-toed sloth (Bradypus variegatus), within a highly fragmented Neotropical habitat. Surprisingly, we found that three-toed sloths were strongly polygynous, with males excluding male competitors from their core ranges, and exhibiting strong reproductive skew. Indeed, only 25% of all resident adult males sired offspring and one individual sired half of all sampled juveniles. Paradoxically, a sedentary life-history strategy seems to facilitate polygyny in fragmented landscapes because multiple females can persist within small patches of habitat, and be monopolized by a single male. Our work demonstrates that strong polygyny can arise in systems in which the polygyny potential should be extremely low, and other strategies, including promiscuity, would be favoured. Mating systems can be influenced by a multitude of factor and are dynamic, varying among taxa, over time, and across habitats; consequently, mating systems remain difficult to predict based on general ecological principles.     

田鼠属动物婚配制度的研究范式

从社会组织的生态格局、熟悉性、社会等级和交配近况等择偶行为的影响因子,性二型和雄性射精能力等个体特征,配对关系的神经内分泌机制几方面综述了田鼠动物婚配制度的研究进展,同时从生态学、比较心理学、生理学、神经生物学等方面探讨择偶行类节式的特点。生态学方法,用鼠动物具有完整的婚配制度多样性格局,是婚配制度比较研究的哺乳动物类群。运用比较心理学方法,通过择偶行为实验可直接比较单配制与较研究的理想哺乳动物类     

Habitat, Niche, and Evolution of Sirenian Mating Systems

Lek polygyny, monogamy and scramble promiscuity have been reported in the two families and five species of Recent sirenians. Evidence for lek mating in the dugong or "sea pig" (Dugong dugon), monogamy in Steller's sea cow (Hydrodamalis gigas), and scramble promiscuity in the three manatees or "river cows" (Trichechus manatus, Trichechus senegalensis, and Trichechus inunguis), as well as in one dugong population, is reviewed. Sirenians are long-lived "K-strategists" with precocious young, few potential young per female lifetime, high female investment in a few young, little apparent opportunity for post-copulatory male investment, and "paenungulate" reproductive physiologies that appear to increase uncertainty as to female receptivity and assurance as to paternity. Common features notwithstanding, diverse habitats, climates, and niches may account for mating system diversity. Scenarios for evolution of diverse mating systems, based on our understanding of mating systems in terrestrial herbivores, are presented. The dugong retains the ancestral low latitude marine, seagrass dependent, bottom-feeding, niche characteristic of diverse, tusked, Oligocene and Miocene sirenian faunas. With a long breeding season and high polygyny potential, retention of tusks by male dugongs in the absence of any foraging function suggests that tusks may have always had social functions and lekking may be of ancient origin. The sea cow lineage, isolated on the shoreline of the northeastern Pacific as seagrasses declined, turned to surface foraging on chemically undefended kelps and lost both tusks and molar teeth. As it followed kelps northwards, adaptation to a cold-temperate climate compressed the breeding season, limited the polygyny potential, and, in conjunction with incentives for paternal investment, favored pair bonding and the monogamous mating system postulated by George Steller (1751). Manatees, evolving in botanically-rich fresh waters of the Amazon basin as an aberrant offshoot of the marine dugongid line, remained in the tropics and retained a high polygyny potential, but became generalist foragers in the upper few meters of the water column. Labyrinthine river systems provided little opportunity for male aggregation and display (or rhizome foraging) and tusks were lost as the uncertainty of female inseminability drove the mating system toward scramble promiscuity and sperm competition. An observation of manatee-like behavior in a dense and sedentary dugong population in eastern Australia suggests plasticity in sirenian mating, and the likelihood that a form of scramble promiscuity may exist where no suitable site for lekking is available, where large group size makes female defence impossible, or where vulnerability of territorial males to hunting has resulted in extirpation of a lekking tradition. Dugong and manatee life history characteristics conform to expectations based on observed differences in mating systems.     

Distribution patterns and chorological analysis of fish fauna of the Arctic Region

Chorological structure of ichthyofauna of the Arctic Region is described. Distribution patterns of 504 fish-like vertebrates and fish species are characterized. One hundred and eighty-nine range types are defined, which are combined into eight main categories: 1—Arctic; 2—Atlantic-Arctic; 3—transitional subarctic zone of Atlantic sector; 4—Pacific-Arctic; 5—transitional subarctic subarctic zone of Pacific sector, 6—Pacific-Atlantic (amphiboreal); 7—bipolar; 8—continental (fresh and brackish waters). Arctic and boreal regions are bordered by transitional (subarctic) zones, which are the areas of intermutual penetration of faunas. The distribution of most fish species that penetrate into to the Arctic Region from the southern areas is limited by these transitional zones. The benthic fish species prevail in the group of autochthonous Arctic species (which includes 64 species or 14% of marine fauna). The demersal fauna of the Arctic preudoabyssal is presented by endemic species. Ten variations of amphiboreal distribution patterns are revealed. Three areas may be defined within the Atlantic-subarctic zone in regard to the fish fauna and range types, i.e., Labrador-Greenland region, the Barents Sea region, and Icelandic (transitional) region.     

Sociobiological implications of unusual sexual behaviors of gulls: The genotype/behavioral phenotype problem

In all species of gulls studied thus far, pair-bonds are overwhelmingly heterosexual and monogamous, with a relatively high degree of mate fidelity. Other reproductive patterns are described: divorce, female—female and male—male pair-bonding, female promiscuity, polygyny, adults mating with subadults, and incubation of objects other than eggs. Unusual changes in the environmental or social contexts of the gulls are usually indicated. The evidence suggests that changes in social organization can occur within the lifetime of particular individuals, that behavioral flexibility in pair-bonding patterns exists in some individuals despite long periods of evolution favoring monogamy, female fidelity, and heterosexual pairing. It is argued that new or uncommon phenotypes should emerge or increase in times of rapid social or environmental change, and that the immediate direction of change can best be predicted using a “maximization-of-positive-reinforcement” hypothesis, rather than a maximization-of-inclusive-fitness hypothesis. Application of sociobiological theory to human behavior and social evolution is discussed, addressing the recurring problem of the relationship between genotype and behavioral phenotype.     

Mammalian mating systems

Male mammals show a diverse array of mating bonds, including obligate monogamy, unimale and group polygyny and promiscuity. These are associated with a wide variety of different forms of mate guarding, including the defence of feeding and mating territories, the defence of female groups and the defence of individual receptive females. Female mating bonds include long-term monogamy, serial monogamy, polyandry and promiscuity. Both male and female mating behaviour varies widely within species. Variation in male mating behaviour is related to the effect of male assistance in rearing young and to the defensibility of females by males. The latter is, in turn, related to female ranging behaviour and to the size and stability of female groups. Much of the variation in mammalian mating bonds and systems of mate guarding can be attributed to differences in these three variables.     

Trade up polygyny and breeding synchrony in avian populations

The advent of the molecular techniques used to assign paternity has focused attention on the differences between the social and the genetic mating systems of sexual species. In particular, the interrelations between breeding synchrony-the degree to which the fertility periods of individual females in a population overlap and the degree of extra pair paternity (EPP) in that population, has became a subject of a lively debate. Investigation of the subject can be facilitated by examining the criteria that females use in choosing extra pair partners. These preferences constitute a continuum ranging between two extremes. At one end, there are situations wherein all the females in a population exhibit a preference for males with particular phenotypic markers, and females mated to males lacking such "quality" markers seek extra pair fertilizations from males that do -trade up polygyny. At the other extreme, there are situations wherein females seek to maximize the total number of male partners, rather than secure fertilization by males of particular type -indiscriminate polygyny. Previously, we used game theoretical methods to model the interrelations between breeding synchrony and EPP in the context of indiscriminate polygyny. Here we present an analogous investigation in the context of trade up polygyny. Our results for the two cases, which delimit the range of the possible behavior, are similar. That is, we see that it is the pursuit of extra pair fertilizations opportunities that determines breeding synchrony of populations, rather than the vice versa as has been previously suggested.     

Promiscuity resolves constraints on social mate choice imposed by population viscosity

Population viscosity can have major consequences for adaptive evolution, in particular for phenotypes involved in social interactions. For example, population viscosity increases the probability of mating with close kin, resulting in selection for mechanisms that circumvent the potential negative consequences of inbreeding. Female promiscuity is often suggested to be one such mechanism. However, whether avoidance of genetically similar partners is a major selective force shaping patterns of promiscuity remains poorly supported by empirical data. Here, we show (i) that fine‐scale genetic structure constrains social mate choice in a pair‐bonding lizard, resulting in individuals pairing with genetically similar individuals, (ii) that these constraints are circumvented by multiple mating with less related individuals and (iii) that this results in increased heterozygosity of offspring. Despite this, we did not detect any significant effects of heterozygosity on offspring or adult fitness or a strong relationship between pair relatedness and female multiple mating. We discuss these results within the context of incorporating the genetic context dependence of mating strategies into a holistic understanding of mating system evolution.     

Local Competition, Inbreeding, and the Evolution of Sex-Biased Dispersal

Using game theory, we developed a kin-selection model to investigate the consequences of local competition and inbreeding depression on the evolution of natal dispersal. Mating systems have the potential to favor strong sex biases in dispersal because sex differences in potential reproductive success affect the balance between local resource competition and local mate competition. No bias is expected when local competition equally affects males and females, as happens in monogamous systems and also in polygynous or promiscuous ones as long as female fitness is limited by extrinsic factors (breeding resources). In contrast, a male-biased dispersal is predicted when local mate competition exceeds local resource competition, as happens under polygyny/promiscuity when female fitness is limited by intrinsic factors (maximal rate of processing resources rather than resources themselves). This bias is reinforced by among-sex interactions: female philopatry enhances breeding opportunities for related males, while male dispersal decreases the chances that related females will inbreed. These results meet empirical patterns in mammals: polygynous/promiscuous species usually display a male-biased dispersal, while both sexes disperse in monogamous species. A parallel is drawn with sex-ratio theory, which also predicts biases toward the sex that suffers less from local competition. Optimal sex ratios and optimal sex-specific dispersal show mutual dependence, which argues for the development of coevolution models.     

Habitat Patch Size,Facultative Monogamy and Sex Change in a Coral-dwelling Fish, <Emphasis Type="Italic">Caracanthus unipinna</Emphasis>

Synopsis We investigated the inter-relationships between coral colony size, social group size, mating system, and patterns of sex allocation in the pygmy coral croucher, Caracanthus unipinna (Caracanthidae), an obligate coral-dwelling fish. Histological examination of the gonads from all individuals in social groups revealed that the predominant mating system was harem polygyny. However, both group size and mating system co-varied with coral colony size, with pair forming and monogamy occurring on small corals and group forming and harem polygyny on large corals. This species therefore displays mating system plasticity in response to varying habitat patch size. Within-group sexual size dimorphism and individual gonad structure indicate that C. unipinna is also likely to be a protogynous hermaphrodite. These social and reproductive features of C. unipinna contrast with some other coral-dwelling fishes, which display a lack of social and mating system plasticity in response to habitat patch size, and either bi-directional or protandrous sex change. Possible reasons for this dichotomy include differences in spawning mode, parental care and levels of intrasexual aggression.     

Sexually transmitted diseases in polygynous mating systems: prevalence and impact on reproductive success

Studies of disease in relation to animal mating systems have focused on sexual selection and the evolution of sexual reproduction. Relatively little work has examined other aspects of ecological and evolutionary relationships between host social and sexual behaviour, and dynamics and prevalence of infectious diseases; this is particularly evident with respect to sexually transmitted diseases (STDs). Here, we use a simulation approach to investigate rates of STD spread in host mating systems ranging from permanent monogamy to serial polygyny or polyandry and complete promiscuity. The model assumes that one sex (female) is differentially attracted to the other, such that groups of varying size are formed within which mating and disease transmission occur. The results show that equilibrium disease levels are generally higher in females than males and are a function of variance in male mating success and the likelihood of a female switching groups between mating seasons. Moreover, initial rates of disease spread (determining whether an STD establishes in a population) depend on patterns of host movement between groups, variance in male mating success and host life history (e.g. mortality rates). Male reproductive success can be reduced substantially by a sterilizing STD and this reduction is greater in males that are more 'attractive' to females. In contrast, females that associate with more attractive males have lower absolute fitness than females associating with less attractive males. Thus, the potential for STDs to act as a constraint on directional selection processes leading to polygyny (or polyandry) is likely to depend on the details of mate choice and group dynamics.     

Monogamy and brood parasitism: an unlikely pair

Intensive observation of a population of brood parasitic brown-headed cowbirds (Molothrus ater), including 114 marked birds, demonstrated that monogamy is the prevalent mating system. Analysis of 1280 consort events and 73 copulations showed that nearly all copulations were between a female and the male most often seen with her, even though females had ample opportunities to mate with other males. Although monogamy prevails, some pair bonds do not endure throughout the breeding season. They are more unstable during the early season when resident cowbirds are establishing their social interrelations. This study provides strong evidence that the cowbird's mating system varies geographically, as the only previous study based on observed copulations demonstrated promiscuity. Current hypotheses for the evolution of avian mating systems, when considered in light of the field data presently available, do not fully explain the adaptive significance of monogamy in a parasitic bird.     

Breeding ecology of the Aquatic Warbler Acrocephalus paludicola on the Biebrza marshes, northeast Poland

Aquatic Warblers Acrocephalus paludicola were studied in a natural fen mire in the Biebrza River valley, the main breeding ground of the species in its entire distribution range. The number of males present and singing at the sample plot changed considerably during the breeding season. Individual identified colour-ringed males sang with unchanged intensity throughout the breeding season. The period of daily singing activity differed from other species of Acrocephalus ; males sang at dusk rather than at dawn. Males took no part in rearing nestlings but remained on territory and showed vigilance behaviour. The density of males in the breeding season ranged from 1.0 to 10.9 per 10 ha. The density of nesting females ranged from 1.3 to 15.7 per 10 ha. In the most suitable habitat females were more numerous than males. The distribution of females (nests) was clumped where potential food resources were higher. Nests were well hidden in places with deeper water between sedge tufts and an abundance of old dry sedge. Females feeding nestlings collected most food within a 5–60-m radius (mean 31.7 m). The return rate of males was higher than that of females. The results suggest a mating system that is intermediate between facultative polygyny and promiscuity.     

The role of genetic constraints and social environment in explaining female extra-pair mating

Why do females of socially monogamous species engage in extra-pair copulations? This long-standing question remains a puzzle, because the benefits of female promiscuous behavior often do not seem to outweigh the costs. Genetic constraint models offer an answer by proposing that female promiscuity emerges through selection favoring alleles that are either beneficial for male reproductive success (intersexual pleiotropy hypothesis) or beneficial for female fecundity (intrasexual pleiotropy hypothesis). A previous quantitative genetic study on captive zebra finches, Taeniopygia guttata, reported support for the first, but not for the second hypothesis. Here, we re-examine both hypotheses based on data from lines selected for high and low male courtship rate. In contrast to previous conclusions, our new analyses clearly reject the hypothesis that male and female promiscuity are genetically homologous traits. We find some support for a positive genetic correlation between female promiscuity and fecundity. This study also shows that the behavioral outcome of extra-pair courtships primarily depends on individual-specific female preferences and not on the “attractiveness” of the social mate. In contrast, patterns of paternity are strongly influenced by the social partner and the pair bond, presumably reflecting variation in copulation behavior, fertility, or sperm competitiveness.     

Factors promoting polygyny in European birds of prey—a hypothesis

Summary Polygyny is known in at least nine (out of 36) European raptor (Accipitriformes and Falconiformes) and seven (out of 13) owl (Strigiformes) species that hunt mobile prey. The hypothesis put forward here suggests that abundant food supply and nomadic tactics of breeding dispersal are crucial factors promoting polygyny in birds of prey. The hypothesis predicts that: (1) polygyny is more common in rodent-eating birds of prey than in bird-eating ones; (2) polygyny is more frequent in good vole years than in poor ones; (3) the frequency of polygyny in vole-eating species should increase northwards in Europe, as the densities of voles in the peak phase increase in that direction; (4) the frequency of polygyny and harem size should be increased by supplementary feeding; and (5) polygyny is more common in nomadic birds of prey with annual pair bonds and weak territoriality than in resident birds of prey with longerterm pair bonds and stronger territoriality. A majority of the available data is consistent with predictions 1–3 and 5, but data on prediction 4 are scanty. Further studies on ringed birds of prey are needed to test the validity of the hypothesis.     

Burrow architecture,family composition and habitat characteristics of the largest social African mole-rat: the giant mole-rat constructs really giant burrow systems

Among African mole-rats, the giant mole-rat Fukomys mechowii is the largest social species. Despite several attempts to study a free-living population, information on its biology from natural habitats is very scarce. We mapped two neighbouring burrow systems of the giant mole-rat in a miombo woodland in Zambia. We provide information on the size and kin structure of the respective mole-rat families, architecture of their burrow systems, and characteristics of the food supply and soil around the two mapped and additional ten burrow systems. Both uncovered burrow systems were very large (total lengths, 2,245 and 743 m), making them the largest burrow systems ever mapped. Food resources around the additional ten burrow systems had a clumped distribution (standardized Morisita index of dispersion = 0.526), but a relatively high biomass (298 ± 455 g m⁻²). This, together with favourable soil conditions even in the advanced dry season (cone resistance, 328 ± 50 N m⁻²; soil density, 1.36 ± 0.06 g cm⁻³) indicates relatively hospitable ecological conditions. Both food supply and soil conditions were comparable with the conditions found in a miombo habitat of the solitary silvery mole-rat in Malawi. This suggests that there are no ecological constraints which would preclude the solitary life of a subterranean herbivore from the examined habitat. Microsatellite analysis supported the assumption that giant mole-rats live in monogamous multigenerational families with only one breeding pair of non-related animals and their offspring. The mean family size is consistent with previous findings on this species and comparable to that found in other Fukomys species studied thus far.     

Pliocene and Pleistocene diatom datum levels related with paleoceanography in the northwest Pacific

Thick sections of Pliocene and Pleistocene biosiliceous clay and ooze were recovered by the Hydraulic Piston Corer (HPC) at three northwest Pacific sites (DSDP Sites 578, 579, and 580). They contain a well-preserved paleomagnetic record which made it possible to evaluate diatom events used in low and high latitudes in the transitional region of the northwest Pacific. Equatorial Pacific events are usually isochronous between the equatorial and subarctic regions. However, species which have short ranges in low latitudes tend to have diachronous first and last appearances in higher latitudes. All subarctic North Pacific datum species are present in the sediments at three sites which lie north and south across the subarctic front, but their ranges become shorter in southern regions. They do not penetrate into the equatorial region. Spatial distributions of these events are influenced by the paleo-position of the subarctic front. The migration of species from their home-area outwards, in the form of the first appearance, is related to the fluctuations of the subarctic front. The last appearance of species is a response to the change of the surface water temperature that is beyond the limit of tolerance of the species, or an unstable oceanic environment due to major change of climate.     

Origin and evolution of primate social organisation: a reconstruction

The evolution and origin of primate social organisation has attracted the attention of many researchers, and a solitary pattern, believed to be present in most nocturnal prosimians, has been generally considered as the most primitive system. Nocturnal prosimians are in fact mostly seen alone during their nightly activities and therefore termed 'solitary foragers', but that does not mean that they are not social. Moreover, designating their social organisation as 'solitary', implies that their way of life is uniform in all species. It has, however, emerged over the last decades that all of them exhibit not only some kind of social network but also that those networks differ among species. There is a need to classify these social networks in the same manner as with group-living (gregarious) animals if we wish to link up the different forms of primate social organisation with ecological, morphological or phylogenetic variables. In this review, we establish a basic classification based on spatial relations and sociality in order to describe and cope properly with the social organisation patterns of the different species of nocturnal prosimians and other mammals that do not forage in cohesive groups. In attempting to trace the ancestral pattern of primate social organisation, the Malagasy mouse and dwarf lemurs and the Afro-Asian bushbabies and lorises are of special interest because they are thought to approach the ancestral conditions most closely. These species have generally been believed to exhibit a dispersed harem system as their pattern of social organisation ('dispersed' means that individuals forage solitarily but exhibit a social network). Therefore, the ancestral pattern of primate social organisation was inferred to be a dispersed harem. In fact, new field data on cheirogaleids combined with a review of patterns of social organisation in strepsirhines (lemurs, bushbabies and lorises) revealed that they exhibit either dispersed multi-male systems or dispersed monogamy rather than a dispersed harem system. Therefore, the concept of a dispersed harem system as the ancestral condition of primate social organisation can no longer be supported. In combination with data on social organisation patterns in 'primitive' placentals and marsupials, and in monotremes, it is in fact most probable that promiscuity is the ancestral pattern for mammalian social organisation. Subsequently, a dispersed multi-male system derived from promiscuity should be regarded as the ancestral condition for primates. We further suggest that the gregarious patterns of social organisation in Aotus and Avahi, and the dispersed form in Tarsius evolved from the gregarious patterns of diurnal primates rather than from the dispersed nocturnal type. It is consequently proposed that, in addition to Aotus and Tarsius, Avahi is also secondarily nocturnal.     

Fish larvae assemblages in the Gulf of California

The distributional diversity and assemblages of fish larvae in the Gulf of California indicated two main seasonal stages and two transitional periods: in winter, the tropical water mass is confined to the south‐east portion of the mouth of the Gulf and larval fish assemblages are dominated by subtropical and temperate‐subarctic species; in summer; tropical water invades the Gulf and assemblages are dominated by tropical species. Both seasonal stages are separated by transitional periods coinciding with strong latitudinal temperature gradients. During the autumn and spring transitional periods, the Gulf of California splits into three regions: a northern region where temperate and subarctic species spawn from autumn to spring, a southern region dominated by tropical and subtropical species year round and a central region where tropical and temperate assemblages merge. Seasonal changes in the location of the regions, as well as the borders between them, show expansion and contraction of the northern and southern faunas related to the general oceanic circulation patterns during the year.     

Social mating systems and extrapair fertilizations in passerine birds

Two alternative hypotheses have been proposed to explain howsocial and genetic mating systems are interrelated in birds.According to the first (male trade-off) hypothesis, socialpolygyny should increase extrapair fertilizations because whenmales concentrate on attracting additional social mates, theycannot effectively protect females with whom they have already paired from being sexually assaulted. According to the second(female choice) hypothesis, social polygyny should decreaseextrapair fertilizations because a substantial proportion offemales can pair with the male of their choice, and males caneffectively guard each mate during her fertile period. To discriminatethese alternatives, we comprehensively reviewed informationon social mating systems and extrapair fertilizations in temperatezone passerine birds. We found significant inverse relationshipsbetween proportions of socially polygynous males and frequenciesof extrapair young, whether each species was considered asan independent data point (using parametric statistics) orphylogenetically related species were treated as nonindependent (using contrasts analyses). When social mating systems weredichotomized, extrapair chicks were twice as frequent in monogamousas in polygynous species (0.23 vs. 0.11). We hypothesize thatin socially polygynous species, (1) there is less incentivefor females and males to pursue extrapair matings and (2) femalesincur higher costs for sexual infidelity (e.g., due to physical retaliation or reduction of paternal efforts) than in sociallymonogamous species.