Context-sensitive dance–vocal displays affect song patterns and partner responses in a socially monogamous songbird

Multimodal signaling contributes to efficient communication by improving signal efficacy and increasing signal information. Songbirds often combine dance displays with songs according to the socio-sexual context; therefore, the song is assumed to function differently depending on dance displays. In this study, we tested how dance displays affect song patterns and the responses of paired partners using male and female blue-capped cordon-bleus (Uraeginthus cyanocephalus). Blue-capped cordon-bleus are a socially monogamous estrildid finch, and both males and females perform songs and distinct “tap dance”-like displays. Songs with dance displays were longer and more stereotyped than songs without dance displays in both males and females. Furthermore, both male and female paired partners showed more gestural responses to songs with dance displays than those without dance displays. Songs without dance displays were performed under both isolated and paired conditions, whereas songs with dance displays were only performed when the focal bird was housed with a paired partner. These results suggest that songs had different functions depending on dance displays and social contexts. The multimodal display of blue-capped cordon-bleus seems to draw the attention of paired partners to the physical abilities of the performer.     

A comparative study on the evolution of reversed size dimorphism in monogamous waders

Sexual dimorphism in size is common in birds. Males are usually larger than females, although in some taxa reversed size dimorphism (RSD) predominates. Whilst direct dimorphism is attributed to sexual selection in males giving greater reproductive access to females, the evolutionary causes of RSD are still unclear. Four different hypotheses could explain the evolution of RSD in monogamous birds: (1) The ‘energy storing’ hypothesis suggests that larger females could accumulate more reserves at wintering or refuelling areas to enable an earlier start to egg laying. (2) According to the ‘incubation ability’ hypothesis, RSD has evolved because large females can incubate more efficiently than small ones. (3) The ‘parental role division’ hypothesis suggests that RSD in monogamous waders has evolved in species with parental role division and uniparental male care of the chicks. It is based on the assumption that small male size facilitates food acquisition in terrestrial habitats where chick rearing takes place and that larger females can accumulate more reserves for egg laying in coastal sites. (3) The ‘display agility’ hypothesis suggests that small males perform better in acrobatic displays presumably involved in mate choice and so RSD may have evolved due to female preference for agile males. I tested these hypotheses in monogamous waders using several comparative methods. Given the current knowledge of the phylogeny of this group, the evolutionary history of waders seems only compatible with the hypothesis that RSD has evolved as an adaptation for increasing display performance in males. In addition, the analysis of wing shape showed that males of species with acrobatic flight displays had wings with higher aspect ratio (wing span/²wing area) than non-acrobatic species, which probably increases flight manoeuvrability during acrobatic displays. In species with acrobatic displays males also had a higher aspect ratio than females although no sexual difference was found in non-acrobatic species. These results suggest that acrobatic flight displays could have produced changes in the morphology of some species and suggest the existence of selection favouring higher manoeuvrability in species with acrobatic flight displays. This supports the validity of the mechanisms proposed by the ‘display agility’ hypothesis to explain the evolution of RSD in waders.     

Intraspecific Variation in the Mating System of Spectral Tarsiers

Historically, a species’ social system was perceived to be a fixed attribute and deviations were usually treated as aberrant or maladaptive. Over the last few decades, socioecologists have started to recognize that variation in social systems is normal and adaptive. Here I explore how ecological variation affects the mating system of a nocturnal primate, the spectral tarsier, Tarsius spectrum. Several studies of the spectral tarsier have illustrated variation in this species’ mating system. Although most groups exhibit a monogamous mating system, a small proportion of the population consistently exhibits a polygynous mating system. I conducted this study at Tangkoko Nature Reserve in Sulawesi, Indonesia during 2007. I found that group size was highly variable, ranging from 2 individuals to as many as 8 individuals per sleeping site. Although most groups (21 of 26) were composed of a single adult male and a single adult female, ca. 19% of the groups contained 2 adult females. Three of the 5 groups with 2 adult females contained 2 young infants. As might be expected, polygynous groups were larger than were monogamous groups. The mean group size of monogamous groups was 2.9, whereas the mean group size of polygynous groups was 6.0. Polygynous groups were also more likely to use Ficus caulocarpa trees than were the monogamous groups. Polygynous groups consistently used more sleeping sites as well as larger diameter sleeping trees, than did monogamous groups. The large-diameter fig trees are ideal homes for the spectral tarsiers in that they offer multiple entrances and exits as well as protection from the elements. Polygynous and monogamous groups exhibited no differences in insect biomass available, home range size, or height of sleeping tree. These results support the hypothesis that ecological variation is an important determinant of mating system within spectral tarsiers.     

Variations in group composition and population density of the two sympatric Mentawaian leaf-monkeys

The Mentawai snub-nosed langur (Simias concolor) and the Mentawai langur (Presbytis potenziani) were observed on Siberut Island, off the west coast of Sumatra, for about 20 months during 1974–1978. The Mentawai snub-nosed langur was organized into monogamous groups in the major study area, but formed larger polygamous groups in some limited areas. Where larger polygamous groups were observed, the snub-nosed langur was found at an extremely high density. On the other hand, in the area where monogamous groups were observed, they occurred at a low density. Such differences in social organization are discussed in relation to excessive hunting by the natives. Mentawai langurs were found in small monogamous groups throughout the island, a condition never observed in any other known Old World monkeys.     

杂色山雀的婚外父权与配偶间的遗传相容性无关

婚配制度作为一种进化稳定对策是动物对某一环境包括种群内部环境适应的结果。据统计,约92%的鸟类为社会性单配制,但单配制鸟类中很多都存在婚外父权现象,表现出社会性婚配制度与遗传性婚配制度的不一致性。杂色山雀(Parus varius)是一种社会性单配制的小型森林洞巢鸟,其是否存在婚外父权现象至今尚未见报道。通过对杂色山雀进行亲权鉴定以确定其有无婚外父权现象及婚外父权的比例,结果显示:45.45%(20/44)的巢存在婚外父权,14.39%(38/264)的后代为婚外子代,说明杂色山雀具有较高的婚外父权水平。进一步探究其婚外父权的发生原因,结果如下:(1)有、无婚外父权巢的社会性亲本之间的遗传相似性无显著差异(P=0.504);(2)有婚外父权巢中婚内子代和无婚外父权巢中子代的杂合度(P=0.118)以及有婚外父权巢中婚外子代与婚内子代的杂合度(P=0.206)均无显著差异。(3)有婚外父权巢中的婚内子代与婚外子代间8项体征指标比较,差异均不显著(Ps0.05)。综上,社会性单配制杂色山雀婚外父权的发生与配偶间的遗传相容性无关,还有待从其他角度进行探究。     

Uncertainty in partner recognition and the tail-up display in a monogamous butterflyfish

Many monogamous birds and fish perform displays towards mates that are either identical or very similar to threat displays. Uncertainty in partner recognition may be a key to explaining this behaviour in the monogamous butterflyfishChaetodon lunulatus . From a causal perspective, when partner recognition is uncertain, the butterflyfish may follow the same decision rules as in territorial interactions with nonpartners. From this hypothesis, I derived three predictions of the frequencies of social behaviours, that is, solo displays, mutual displays, attacks and rejoinings. If the frequencies areS , M, A and R, respectively, the predictions are that (1) M/ (M+A) andM/ (M+S) should be higher in rejoining situations than in a pair-swimming situation; (2) (M+S)/R and (M+A) /R should increase with the duration of separation; and (3) M/ (M+A) should be larger than M/ (M+S). To test the predictions, I made field observations. The results supported all of these predictions. Therefore, I suggest that uncertainty of partner recognition causes the butterflyfish to perform the tail-up display, which is usually used in territorial interactions, towards the partner. From a functional perspective, this hypothesis implies that the display serves to reduce the risk of failure to recognize a partner, which could result in an attack. The display causes the conspecific to hesitate before attacking, providing sufficient time for partner recognition. Field data indicated that more than 70% of dangerous attacks were prevented by a tail-up display.     

Male parental behavior in black howler monkeys (Alouatta palliata pigra) in Belize and Guatemala

Male parental behavior was observed in black howler monkeys (Alouatta palliata pigra) in Belize and Guatemala from December 1978 to March 1979, with the objective of relating parental behavior to the prevailing monogamous group structure. The results revealed that male parental behavior inAlouatta palliata pigra agrees in some respects with reports from the literature on polygamous and polygynous species ofAlouatta, while in other respects the situation more closely resembles that in monogamous species of non-human primates. Considerable inter-individual variability in male-infant interactions prevailed among the study groups. Male parental behavior in the Belize groups became more prominent with increasing age of an infant.     

Female-to-male shift of mouthbrooding in a cichlid fish,Tanganicodus irsacae,with notes on breeding habits of two related species in Lake Tanganyika

Synopsis Parental-care patterns and mating systems of three goby-like cichlids in Lake Tanganyika were investigated. In Tanganicodus irsacae females mouthbrooded eggs and small young for about two weeks and then males took over the role for about one week. Field observations of tagged fish suggest that this species is monogamous: a male's home range largely overlapped with that of its mate, while their home ranges were segregated from those of similar-sized consexual adults. Eretmodus cyanostictus also performed female-to-male shift of mouthbrooding and appeared to be monogamous. The third species, Spathodus marlieri, however, exhibited exclusively maternal mouthbrooding. The differences in parental care and mating system among the three species are discussed in relation to their feeding habits, and the pattern of monogamy in the goby-like cichlids is compared with those of other fishes.     

Evolution of mating systems in coral reef gobies and constraints on mating system plasticity

Social and mating systems can be influenced by the distribution, abundance, and economic defendability of breeding partners and essential resources. Polygyny is predicted where males can economically defend multiple females or essential resources used by females. In contrast, monogamy is predicted where neither sex can monopolise multiple partners, either directly or through resource control, but where one mate is economically defendable. The mating system and reproductive behaviour of five species of coral reef goby were investigated and contrasted with population density and individual mobility. The two most abundant species (Asterropteryx semipunctatus and Istigobius goldmanni) were polygynous. In contrast, the less populous and more widely dispersed epibenthic species (Amblygobius bynoensis, Amblygobius phalaena and Valenciennea muralis) were pair forming and monogamous. All five species had low mobility, mostly remaining within metres (3 epibenthic species) or centimetres (2 cryptobenthic species) of a permanent shelter site. Interspecific differences in the mating system may have been shaped by differences in population density and the ability of reproductive individuals to economically defend breeding partners/sites. However, in a test of mating system plasticity, males of the three monogamous species did not mate polygynously when given the opportunity to do so in experimental manipulations of density and sex ratio. Mate guarding and complex spawning characteristics, which have likely co-evolved with the monogamous mating system, could contribute to mating system inflexibility by making polygynous mating unprofitable for individuals of the pair forming species, even when presented with current-day ecological conditions that usually favour polygyny.     

Dispersal Patterns in <Emphasis Type="Italic">Tarsius spectrum</Emphasis>

One of the most widely accepted explanations for the difference in the sex bias between mammals and birds is that male-biased dispersal in mammals is due to the preponderance of polygynous mating systems exhibited by this class, whereas birds are predominantly monogamous. Spectral tarsiers (Tarsius spectrum) are unusual in that they exhibit variation in its mating system. Although the majority of spectral tarsier groups are monogamous, ca. 15% are polygynous. If mating system influences dispersal, then I predicted that the polygynous groups would exhibit male biased dispersal whereas I predicted that the dispersal patterns of the monogamous groups would be analogous to that exhibited by birds, specifically female biased. Alternatively, I hypothesized that ecological variation may influence dispersal habits in this species. Specifically, I predicted that polygynous groups would exhibit greater habitat quality than monogamous groups. The 2 hypotheses are not mutually exclusive. On the basis of 14 individuals birdbanded between 1994 and 1999, I determined that individuals of both sexes were equally likely to disperse (males, n = 5; females, n = 9). Males dispersed twice as far as females did. The mean dispersal distance for males was 660 m, and for females it was 266 m. Females (77%) were more likely to form a territory adjacent to the parental territory than were males (20%). Individuals exhibited relatively high amounts of site fidelity (86%) that were related to physical characteristics of the sleeping site. Adults that dispersed a second time (n = 4) initially resided in trees that were shorter and had a smaller diameter-at-breast height than the trees of individuals that exhibited site fidelity. The results of my study partly support the parental mating system hypothesis and also support the habitat quality hypothesis.     

Mathematical formulation and studies of the risk parameters involved in HIV transmission

The probability of becoming infected with HIV is formulated in terms of the total number of sexual contacts (N), the probability that a sexual act is infectious (r) and the prevalence (p). Using the appropriate equations we studied the effect of reducing each of the risk factors on lowering the probability of infection. We show that for many realistic situations the probability of becoming infected by multiple partners is equal to the probability of becoming infected by one partner in a monogamous relationship given that the prevalence is the same in both cases; however if the multiple partners are chosen over time from a pool of a growing prevalence, then one is better off in a monogamous relationship where that partner is chosen early in the epidemic.     

Social structure,habitat use and breeding biology of hedgerow Dunnocks Prunella modularis

A population of Dunnocks Prunella modularis inhabiting hedgerows was studied over a period of four years in order to examine the habitat structure of breeding territories and to attempt to determine how the constraints imposed by the linear structure of hedgerows might influence the mating combinations and breeding success. Eleven monogamous and 14 polyandrous territories were observed. No examples of polygyny or polygynandry were recorded. Polyandrous territories were significantly larger than monogamous territories but contained significantly more grassland, which is of little value for Dunnock foraging. Overgrown hedgerows formed the largest component of territories, and young and overgrazed hedgerow types constituted only a small area. All territories supported large patches of Nettle Urtica dioica and Bramble Rubus fruticosus/Dog Rose Rosa canina, the latter supporting most Dunnock nests. Clutch sizes, nestling weights and numbers of young fledged did not differ significantly between monogamous and polyandrous systems, but sample sizes were small. It is suggested that the restricted availability of mature overgrown hedgerows, the relatively low breeding density and the linear shape of hedgerows contributed towards the less complex mating system. The preference for overgrown hedgerows with basal outgrowths of Nettle and Bramble/Rose is discussed in the light of the recent decline of the Dunnock on farmland.     

Facultative monogamy in obligate coral-dwelling hawkfishes (Cirrh tidae)

Synopsis Obligate coral-dwelling hawkfishes have been hypothesized to be monogamous. This hypothesized mating system is at odds with what is known of those of other cirrhitids. Neocirrhites armatus, which inhabits Pocillopora spp. corals, and Oxycirrhites typus, which inhabits gorgonians and antipatharian corals, were examined for evidence of a monogamous mating system. Life history criteria that favor monogamy in reef fishes (Barlow 1986) were examined for these two species. Facultative monogamy was found in both. In this mating system, males are limited in their ability to acquire and maintain females, and thus have only a single mate, but may acquire additional females if conditions for doing so are favorable.     

Chick growth and survival in northern lapwings Vanellus vanellus indicate that secondary females do the best of a bad job

The polygyny threshold model predicts that monogamous and secondary females on average settle at the same time and have similar reproductive success. This is not generally found. Incorporating varying female competitive strength into the model, changes the predictions to state that secondary females should breed later and show a reduced success compared to that of monogamous and primary females. We examined if this was the case by investigating growth and survival in chicks of northern lapwings Vanellus vanellus from mothers of monogamous, primary and secondary mating status. Chicks where monitored from hatching to the age of 15–18 d. Growth and survival in secondary chicks was lower than in monogamous and primary chicks. Primary chicks survived significantly better than secondary chicks. Survival of monogamous chicks was comparable to primary chicks and close to significantly higher than in secondary chicks (p = 0.086). Among surviving chicks, daily weight gain in monogamous chicks was significantly higher than in secondary chicks. Growth rates of primary chicks were comparable to monogamous chicks and tended to be higher than in secondary chicks (p = 0.11). Monogamous and primary females both bred significantly earlier than secondary females, and chick survival and body‐mass growth decreased significantly with hatching date. Given the premium on early breeding in lapwings, secondary females appeared to do the best of a bad job, and their later onset of breeding could have been caused by poorer condition and/or lower breeding experience. Additional costs might also have accrued from sharing breeding resources with primary females that presumably were stronger competitors.     

Patterns of paternal care in primates

An interspecific comparison was carried out to understand better the relationships among paternal care, paternal certainty, and reproductive burden in primates. Although monogamy is generally rare among mammals, a number of primate species are monogamous. Extensive paternal care is a related issue but is one that is not necessarily associated with monogamy or with paternal certainty. For example, despite paternal certainty, primate mothers in monogamous species with body weights over 2 kg still remain the primary infant caretakers, while males in the communally breeding tamarins carry infants more frequently than mothers do, even in the absence of paternal certainty. Several different tactics are used by small-bodied primates to cope with the energetic burden of raising proportionately large infants in an arboreal environment: (1) infant carrying by subadult and/or related nulliparous females (Saimiri, Lemur monogoz); (2) infant carrying by fathers and offspring (Aotus, Callicebus, Saguinus, Cebuella, Leontopithecus); (3) parking infants while family members forage (Tarsius, Galago, Microcebus, Cheirogaleus, Varecia); or (4) some combination of the above (Callithrix, Hapalemur, Loris). Lactation length and infant growth patterns appear to influence which of these tactics is employed by a given species. Moreover, although most small-bodied, mated, monogamous female primates spend no more than 9 months annually in gestation and lactation,Aotus andCallicebus mated females are either pregnant or lactating on a year-round basis. It is this heavy female reproductive burden that may be an important factor in selection for extensive paternal care in these monogamous cebids.     

Variation in testosterone levels and male reproductive effort: Insight from a polygynous human population

Recent evidence suggests that, in humans, variations in testosterone (T) levels between men reflect their differential allocation in mating versus parenting efforts. However, most studies have been conducted in urbanized, monogamous populations, making generalizations from them questionable. This study addresses the question of whether indicators of male reproductive effort are associated with variations in salivary T levels in a polygynous population of agriculturists in rural Senegal. We first show that pair-bonding and/or transition to fatherhood is associated with T profiles: married fathers (N = 53) have lower morning and afternoon T levels than unmarried non-fathers (N = 28). Second, among fathers, individual differences in parenting effort, as well as variations in mating effort, predict morning T levels. Indeed, men highly investing in parental care show lower morning T levels. Moreover, among men under 50, polygynous men show higher morning T levels than monogamous men. Taken together with previous results in monogamous settings, these findings suggest that the endocrine regulation of reproductive effort is probably a general feature of human populations.     

Male sexual attractiveness and aggressiveness in rodents having different mating systems

Male aggressiveness can affect male reproductive success both directly by increasing competitiveness and indirectly through female preference. Assuming that significance of male aggressiveness in species having different mating systems can be different, we studied how male aggressiveness relates to sexual attractiveness in polygynous rodents, the water vole (Arvicola terrestris) and the house mouse (Mus musculus), and in a monogamous species, the steppe lemming (Lagurus lagurus). Our analysis revealed that the relation between odor attractiveness and aggressiveness is nonlinear. In polygynous species, males are more aggressive, so females opt for aggressive, albeit not too aggressive, males. In the monogamous steppe lemming, males show low level of intermale aggressiveness, and the most attractive are slightly aggressive males who have greater reproductive potential.     

Genetic monogamy in the Common Crossbill ( Loxia curvirostra )

Extrapair paternity seems to be common in socially monogamous passerines, but the genetic mating system of most species is currently unknown. Here, we report the first study of paternity in the socially monogamous Common Crossbill (Loxia curvirostra). We found no evidence of extrapair paternity among 96 offspring in 34 examined broods. An upper 95% confidence limit of 3.1% suggests that extrapair fertilizations were truly infrequent in our study population. Common Crossbills thus seem to represent an exception to the rule of extrapair mating among socially monogamous passerine bird species. A potentially important selective pressure preventing promiscuity in Common Crossbills is the harsh environmental conditions experienced during breeding at wintertime, which may increase the importance of paternal care and limit the time available for seeking extrapair copulations.     

The relative influence of prey abundance and co-breeders on the reproductive performance of polyandrous Pale Chanting-goshawks

This study investigates if the reproductive performance of polyandrous Pale Chanting-goshawks, Melierax canorus, is governed by the abundance of dominant rodent-prey species or a co-breeding male participating fully in prey being delivered to the female and young. Polyandrous trios in prey-rich habitat, the only habitat where these trios occurred, failed to produce more offspring than monogamous pairs, but attempted more second broods in years of high prey abundance. The higher the prey-delivering rates at the nesting sites by either one monogamous male or two polyandrous males (combined effort), the higher the proportion of time their females spent in close proximity to the nest. Since there were no significant differences between the body masses of nestlings fledged by polyandrous and monogamous groups, higher delivery rates relieved females from away-from-the-nest hunting duties and permitted them to feed on prey not fed to offspring. Although breeding in polyandrous trios held fitness benefits for females, e.g. to accumulate the necessary body reserves for laying a second clutch in years of high prey abundance, it is still not clear how males benefited. The reproductive performance of each group was strongly linked to the abundance of the dominant, otomyine rodent prey (Otomys unisulcatus and Parotomys brantsii) and it was therefore prey abundance, and not the number of males delivering prey to the female and nestlings at each nesting site, that controlled the reproductive performance of cooperative-breeding Pale Chanting-goshawks.