Infanticide in male laboratory mice: Effects of social status,prior sexual experience,and basis for discrimination between related and unrelated young

Several aspects of infanticide, including effects of social status, prior sexual experience, and the basis for discrimination between related and unrelated young, were examined in Swiss-Webster laboratory mice (Mus musculus). Strange males introduced into the female's cage for 24 h on day 1 postpartum significantly reduced pup survival whereas the introduction of sires did not. Direct observations of infanticide were frequent, and the motor patterns used by males to kill pups are described. Males killed their own offspring when those young were in the nest of a strange female, whereas most males did not kill unrelated young in the nest of a familiar female. Thus, past association with the mother appears to be the single most important factor mediating male discrimination of young. Prior contact with a specific female's urine reduced a male's propensity for subsequently killing her young. The act of copulation itself also reduced infanticide. Infanticidal behaviour was correlated with the male's social status: most dominant males killed unrelated pups, whereas none of the subordinates engaged in infanticide. These results are discussed in terms of the population biology of this species.     

Group mating among Norway rats II. The social dynamics of copulation: Competition,cooperation, and mate choice

The social interactions within groups of Norway rats (Rattus norvegicus) had a strong impact on the individual pattern of copulation which, in turn, affects sperm precedence and the probability of implantation in this species. Males alternated uninterrupted ejaculatory series, augmenting each others' copulatory investment. Females took turns mating after receiving an intromission, collectively potentiating the males' copulatory behaviour; increasing the number of oestrous females increased the number of intromissions and ejaculations achieved by each male but did not affect the amount of copulation experienced by each female. These turn-taking patterns within each sex provided the opportunity to change partners and permitted the emergence of different sex-typical patterns of copulation. Furthermore, the dominant male contributed more intromissions and tended to give each female more ejaculations than the subordinates did. Dominant males were also more likely to inhibit the subordinates' sperm transport. Females competed among themselves for the opportunity to mate with a male as he approached ejaculation and were likely to protect more of the dominant male's sperm transport than the subordinate male's.     

To breathe or not to breathe; the newt's problem

In a number of experiments designed to investigate the interaction between sexual behaviour and breathing, male newts were presented with females whose behaviour was controlled by the experimenter. In some experiments the male received sufficient positive feedback from the female to enable him to complete his sexual sequence; in others he did not. The results are interpreted in terms of McFarland's (1969) hypothesis that the transitions from one activity of another may occur either by competition or by disinhibition. It is suggested that in the absence of sufficient positive stimulation to enable the male to complete his sexual sequence, breathing occurs by competition with sexual behaviour. When the male has sufficient stimulation the temporal patterning of his behaviour becomes more under his control and breathing occurs by disinhibition.     

Linyphid spider courtship: Releaser and attractant functions of a contact sex pheromone

Experiments with male bowl-and-doily spiders (Frontinella communis) on methanol-washed and unwashed female webs indicate that the courtship of males is chemically released. Parallel experiments on the webs of females of another linyphiid species and on immature F. communis webs indicate that the releaser pheromone is species specific and that it is produced only by mature females. The pheromone that releases male courtship also functions as an attractant, changing the male's orientation from negatively to positively geotactic. The presence or absence of a female on the test web has only a slight effect on the male's behaviour.     

Social correlates of fecal testosterone in male ursine colobus monkeys (Colobus vellerosus): the effect of male reproductive competition in aseasonal breeders

Male testosterone (T) levels are thought to be linked with the mating system, degree of parental care, and male–male aggression in reproductive contexts (The ‘challenge hypothesis’; Wingfield et al., 1990). In many species though, T increases associated with mating behavior cannot be separated from those associated with male–male aggression. We tested the challenge hypothesis on aseasonally breeding ursine colobus (Colobus vellerosus), where male–male competition is intense outside of mating contexts. Fecal samples (N = 109) were collected from > 27 subadult and adult males in seven groups during 13-months of research in Ghana in 2004–2005. Fecal T (fT) levels were determined by enzyme immunosorbant assays. Behavioral data was collected using focal-animal and ad libitum sampling. The number of receptive females in each group did not positively correlate with male fT. There was a trend for adult males to have higher fT than subadult males; however there was no effect of rank on fT. The level of male–male aggression experienced was positively correlated with fT and individual males showed higher mean fT during ‘challenge’ than during ‘non-challenge’ periods. The number of male incursions experienced positively correlated with fT whereas the number of between-group encounters did not. Males attempt to gain reproductive opportunities during incursions, thus these results support the ‘challenge hypothesis’ in C. vellerosus. Outside of mating contexts, higher male fT levels are associated with increased aggression. Male parental investment in the form of infant defense was associated with increased fT, rather than the decline expected from other forms of paternal care.     

Behaviour of one-year-old rhesus monkeys in a strange situation

When one-year old rhesus monkeys and their mothers were removed from the colony to a strange situation, infants' activity was initially low compared with behaviour six days later. Although absolute values did not differ between males and females, correlations did. That is, three days after return to the colony, correlations with baseline colony behaviour were significantly positive for females, while males had one significantly negative correlation. On the other hand, males had more significant correlations than females when behaviour in the strange situation was correlated with colony scores. Of the six individuals that had adverse early experience, five showed extreme behaviour. The exception was CT, son of a female with a very low ‘excitable’ score. In fact for all males, mothers' colony scores were significantly correlated with sons' behaviour in the strange situation.     

Effects of long-acting testosterone treatment on freeliving pied flycatchers, Ficedula hypoleuca, during the breeding period

Breeding behaviour and spermatogenesis of all males in a population of pied flycatchers, Ficedula hypoleuca, were experimentally prolonged by long-acting testosterone. The behaviour of these birds was compared with that of birds from an untreated population and a population where the males were given the vehicle only. The testosterone treatment prolonged territorial behaviour, and a higher percentage of nests without a feeding male during the nestling period was found in the experimental area. The proportion of polygamous males did not however differ between the experimental and control areas. The feeding activity of those testosterone-treated males returning to their home territories was markedly depressed. The female of such a pair did not compensate for the male's low feeding activity, but fed the nestlings as she would have done with a normal untreated male at the nest. On the other hand, females without a male present during the nestling period compensated for their mates' absence by increasing their own feeding frequency. It was also shown that the song of the male pied flycatcher is dependent upon androgens. The testosterone-treated males produced fewer fledglings than the control males.     

Interactions Between Swarming Chironomus annularius (Diptera: Chironomidae) Males: Role of Acoustic Behavior

Males of swarming species of chironomids use their auditory system (Johnston's organs) to recognize a female within swarm and do not respond to male flight tones. However, in some cases the male–male interactions were observed at a high frequency. The role of acoustic behavior in this phenomenon in C. annularius was studied. The results showed that male Johnston's organs were sensitive to male flight tones from a distance of about 1–1.5 cm. The carrier frequencies of these sounds negatively correlated with male body size. Thus we would expect that male–male interactions will occur mainly between large males. Nonetheless, the analysis of caught pairs revealed that in both male–male and female–male interactions small males had an advantage. The ability of males to perceive the male flight tones is discussed with respect to swarming behavior and mating success.     

Postpartum copulatory and maternal behaviour in Norway rats under seminatural conditions

Virgin female rats were mated at a freely cycling oestrus, and then again with the same males at the subsequent postpartum oestrus. Copulatory behaviour at each mating was compared and the temporal patterning of the female's mating and maternal behaviour was analysed. Postpartum females were found to conserve the number of ejaculatory series received, yet the series were shorter, resulting in a shorter time being occupied, by this mating. During mating, females spent little time with their litters, and then mainly in the post-ejaculatory intervals. Ejaculatory series were rarely disrupted by nesting. The postpartum female rat seems to engage in behavioural time-sharing.     

It takes two to tango: reproductive skew and social correlates of male mating success in a lek-breeding bird

Variance in reproductive success among individuals is a defining characteristic of many social vertebrates. Yet, our understanding of which male attributes contribute to reproductive success is still fragmentary in most cases. Male–male reproductive coalitions, where males jointly display to attract females, are of particular interest to evolutionary biologists because one male appears to forego reproduction to assist the social partner. By examining the relationship between social behaviour and reproductive success, we can elucidate the proximate function of coalitions in the context of mate choice. Here, we use data from a 4-year study of wire-tailed manakins (Pipra filicauda) to provide molecular estimates of reproductive skew and to test the hypothesis that male–male social interactions, in the context of coordinated displays, positively influence a male''s reproductive success. More specifically, we quantify male–male social interactions using network metrics and predict that greater connectivity will result in higher relative reproductive success. Our data show that four out of six leks studied had significant reproductive skew, with success apportioned to very few individuals in each lek. Metrics of male social affiliations derived from our network analysis, especially male connectivity, measured as the number of males with whom the focal male has extended interactions, were strong predictors of the number of offspring sired. Thus, network connectivity is associated with male fitness in wire-tailed manakins. This pattern may be the result of shared cues used by both sexes to assess male quality, or the result of strict female choice for coordinated display behaviour.     

Visual signals in the courtship of Drosophila melanogaster: Mutant analysis

Visual cues are necessary for optimal mating success in Drosophila melanogaster. The male's most important visually guided behaviour is tracking. It is shown here that tracking requires intact visual receptor cells R1–6 and the presence of screening pigments in the eye. Thus flies carrying the mutation ebony as well as wild type flies affected in receptor cell R1–6 are unable to use visual cues when they track females. A similar defect was obseved in white-eyed flies lacking screening pigments. Female receptivity depends on visual signals provided by the male flies. Most important cues are the light reflection from and the shape of the male's eyes. No influence of the light reflected from the thorax could be seen. Absence of eyes in the male, however, does not depress female receptivity as much as white eyes. Some evidence is provided that male courtship behaviour is evaluated visually by the female.     

Bayesian mating decisions in an amphipod, Gammarus lawrencianus Bousfield

In G. lawrencianus, females of a given fecundity and proximity to copulation day are assessed by males to be more valuable as mates, the longer the males have amplexed with the females (i.e. the greater their past investment in the act of amplexus). This behaviour is consistent with the hypotheses that (1) males are uncertain of the true reproductive state of a female on first contacting her; (2) the prior distribution of unamplexed females likely to be encountered by the males affects their initial estimates of a female's state; and (3) the time spent amplexing with a female allows information to be gathered which reduces a male's uncertainty of the female's state.     

Sexual conflict over mating in Gnatocerus cornutus? Females prefer lovers not fighters

Female mate choice and male–male competition are the typical mechanisms of sexual selection. However, these two mechanisms do not always favour the same males. Furthermore, it has recently become clear that female choice can sometimes benefit males that reduce female fitness. So whether male–male competition and female choice favour the same or different males, and whether or not females benefit from mate choice, remain open questions. In the horned beetle, Gnatocerus cornutus, males have enlarged mandibles used to fight rivals, and larger mandibles provide a mating advantage when there is direct male–male competition for mates. However, it is not clear whether females prefer these highly competitive males. Here, we show that female choice targets male courtship rather than mandible size, and these two characters are not phenotypically or genetically correlated. Mating with attractive, highly courting males provided indirect benefits to females but only via the heritability of male attractiveness. However, mating with attractive males avoids the indirect costs to daughters that are generated by mating with competitive males. Our results suggest that male–male competition may constrain female mate choice, possibly reducing female fitness and generating sexual conflict over mating.     

Body size as a factor determining dominance in staged agonistic encounters between male brown anoles (Anolis sagrei)

The results of staged agonistic encounters between males indicate that body size is an important determinant of dominance in male brown anoles (Anolis sagrei). Larger males defended their perch sites more successfully than did smaller males, perched higher than smaller males, and were most often the first male to enter the other male's territory. Larger males also exhibited more challenge displays than did smaller males. Head-nods, a display given by subordinate individuals, were observed only in smaller males.     

Female choice, male interference, and sperm precedence in the red-spotted newt

Darwin first identified female choice and male—male competitionas forms of sexual selection resulting in the evolution of conspicuoussexual dimorphism, but it has proven challenging to separatetheir effects. Their effects on sexual selection become evenmore complicated when sperm competition occurs because spermprecedence may be either a form of cryptic female choice ora form of male—male competition. We examined the effectsof tail height on male—male competition and female choiceusing the sexually dimorphic red-spotted newt (Notophthalmusviridescens viridescens). Experiment 1 examined whether maletail height influenced male mating success. Males with deeptails were more successful at mating with females than thosewith shallow tails. Successful, deep-tailed males also were bigger(snout-vent length; SVL) than unsuccessful, shallow-tailed males,but they did not vary in tail length or body condition. Of these,only tail height and tail length are sexually dimorphic traits.Experiment 2 tested the hypothesis that the differential successof males with deeper tails was due to female choice by examiningboth simultaneous female preference for association and sequentialfemale choice. We found no evidence of female choice. When maleswere not competing to mate with females, tail height did notinfluence male mating success. Successful males did not havedifferent SVL and tail lengths than unsuccessful males. Thus,tail height in male red-spotted newts appears to be an intrasexuallyselected secondary sexual characteristic. Experiment 3 usedpaternity exclusion analyses based on molecular genetic markersto examine the effect of sperm precedence on sperm competitionin doubly-mated females. Sperm precedence likely does not havea pervasive and consistent effect on fertilization success becausewe found evidence of first, last, and mixed sperm usage.     

Sex differences in the termination of social play in cats

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

Pairing strategies and mate choice in female robins Erithacus rubecula

Female European robins (Erithacus rubecula) adopted three different pairing strategies. These were, in order of frequency: moving on to a male's territory; fusing her territory with that of a neighbouring male; and being joined by a male on her territory. Although females were not free to choose between strategies during a particular season, individuals frequently changed strategy between different years. Their behaviour suggested that they were exercising mate choice, although the scope for such choice was limited by a strong tendency for a female to pair in areas where she had lived previously (her ‘Familiar Areas’). Males with large territories were more likely to pair and tended to pair earlier than those defending small territories. Female pairing strategy was also correlated with the area of their own territory. Although it is considered likely that some unidentified confounding variable was responsible for at least part of these relationships, possible causal explanations involving territory size are discussed. These include mate choice and a random settlement model. However the simplest explanation for the advantage enjoyed by males on large territories is that their territories were more likely to overlap with females' Familiar Areas.     

Comparative courtship behaviour in two species of the parasitic chalcid wasp Melittobia (Hymenoptera: Eulophidae)

Timing and form of courtship behaviour elements constitute a major isolating mechanism for two morphologically and ecologically similar parasitic wasps. Because males are blind, the complex courtship of Melittobia chalybii and a new as yet undescribed species previously confused with it, designated as M. sp. A, depends upon tactile and chemical cues. In both species, after the female orients to the male's abdomen, the male turns in the direction of contact and mounts. However, chalybii males antennate females continuously, lifting mesothoracic legs at regular intervals, while in sp. A male antennation alternates with metathoracic leg pumping. Courtship and copulation duration are greater in Chalybii than in sp. A.     

Determinants of mating success in the golden hamster (Mesocricetus auratus): Social dominance and mating tactics under seminatural conditions

We tested the hypothesis that high social status leads to high levels of copulatory behaviour and increased number of offspring in hamsters. When paired with albino female golden hamsters, males of three genotypic strains showed differences in the frequency and temporal patterning of some measures of copulatory behaviour but did not differ in general fertilization success. The results of two-male, one-female tests in which mating order and ejaculation frequencies were controlled indicated only relatively small differences in differential fertilizing capacity among these genotypes. Males of the genotypic strains displayed an equal probability of achieving alpha status in three-male, one-female competitive mating tests in which animals were habituated to semi-natural enclosures. Alpha males often slept in the female's nest box the night before she became receptive, were the first to mate on the following morning, achieved higher scores for all measures of sexual behaviour including ejaculation frequency and subsequently sired more young than did lower ranking males. However, the differential reproductive success of alpha males was not simply a function of higher ejaculation scores since they obtained more than twice as many young per ejaculation as subordinate males. Alpha males continued to copulate with long intromissions after exhausting their supply of ejaculates. Although females mated with several males, mating preferences were evidenced by their flank-gland and vaginal marking patterns on the day before receptivity and in their initial choice of mates during tethered male tests. The behaviour of alpha males is consistent with previous findings regarding the effects of mating order and prolonged copulation on sperm competition and suggests that sperm utilization patterns and mating tactics have coevolved.     

Dominance is not always an honest signal of male quality,but females may be able to detect the dishonesty

Females prefer dominant males as mating partners in numerous species. Male dominance rank is considered as an honest signal of male quality, because only healthy males in good condition are thought to be able to win fights with other males. Here, we tested whether activation of the immune system influences the success of males in male–male competition and mating in the field cricket, Gryllus integer. We activated the immune system of males with a nylon monofilament (to mimic a parasitoid larva), and arranged fights between male pairs to assess male dominance and associated mating success. Activation of the immune system with nylon monofilament substantially enhanced the fighting success of males during male–male competition but had no effect on mating success. However, sham-manipulation (a wound only) did not have any effect on fighting success although females mated more often with dominant males. Our study suggests that when male crickets meet an apparent survival threat they may behave more dominantly, probably owing to terminal investment. Male success during male–male competition is not always an honest signal of males’ quality, but females may be able to detect this dishonesty.