Chimpanzee fathers bias their behaviour towards their offspring

Promiscuous mating was traditionally thought to curtail paternal investment owing to the potential costs of providing care to unrelated infants. However, mounting evidence suggests that males in some promiscuous species can recognize offspring. In primates, evidence for paternal care exists in promiscuous Cercopithecines, but less is known about these patterns in other taxa. Here, we examine two hypotheses for paternal associations with lactating mothers in eastern chimpanzees ( Pan troglodytes schweinfurthii ): paternal effort, whereby males associate and interact more with their own infants, and mating effort, whereby males invest in mothers and offspring for mating privileges. We found that fathers associated more with their offspring than they did with non-kin infants, particularly early in life when infanticide risk is highest. Additionally, fathers and their infant offspring interacted more than expected. Notably, association between fathers and mother–infant pairs did not predict the probability of siring the mother's next offspring. Our results support the paternal effort, but not the mating effort hypothesis in this species. Chimpanzees are one of the most salient models for the last common ancestor between Pan and Homo , thus our results suggest that a capacity for paternal care, possibly independent of long-term mother–father bonds, existed early in hominin evolution.

Paternal behaviour in a socially monogamous but sexually promiscuous passerine bird

We documented parental behaviour and paternity of eastern kingbirds (Tyrannus tyrannus) to test the predictions that paternal care would decline with increasing loss of paternity, increasing nesting density (a proxy for probability of paternity loss), male quality, and number of fertile females available in the population. Extra-pair young were found in 58% of 45 nests for which behaviour was recorded and a higher proportion of young were extra-pair as nesting density increased. Male feeding rate declined with increasing nesting density and male quality, but neither feeding rate nor a composite measure of paternal behaviour varied with number of fertile females or paternity. Although alternative explanations exist, one interpretation of the reduced paternal care at high nesting density was that it was a response to perceived threats of paternity loss. The ultimate basis for the lower paternal effort of higher quality males is unclear but we discuss several possible explanations.

Plasma testosterone levels of male European starlings (Sturnus vulgaris) during the breeding cycle and in relation to song and paternal care

In temperate-zone birds, seasonal testosterone (T) profiles often vary among species with different mating systems. The trade-off hypothesis suggests that T levels in male birds represent a trade-off between additional mating effort, stimulated by high T, and paternal effort, inhibited by high T. To study the role of T in mediating the trade-off between paternal and mating effort in the facultatively polygynous European starling ( Sturnus vulgaris ), we monitored seasonal fluctuations in T levels and song activity, which functions mainly in mate attraction, and we investigated natural covariation between plasma T levels and male parental and song behaviour during the parental phase. T concentrations peaked during nest building, remained high during the fertile period, and then decreased gradually during the period of paternal care. This resembles the profile typically found in polygynous species with biparental care. Seasonal variation in song activity paralleled seasonal changes in T. The proportion of time spent incubating was significantly negatively correlated with T levels in individual males. There was a positive, but non-significant, correlation between song activity at an additional nest box and T levels during incubation. We suggest that this negative correlation between T and incubation behaviour may be partly explained by T increases in males responding to the presence of prospecting females with additional nestbox occupation and mate attraction song, rather than that high T levels stimulate mate attraction song. During the feeding period, characterized by a very low availability of unmated females, variation in T levels was low and there was no covariation between T and feeding. T levels during the parental phase reflect, but do not seem to directly regulate, the trade-off between parental and additional mating effort and other factors such as opportunities for additional matings may influence the resolution of this reproductive trade-off.

PARENTAL CARE AND PARENTAGE IN MONOGAMOUS GREAT SPOTTED WOODPECKERS (PICOIDES MAJOR) AND MIDDLE SPOTTED WOODPECKERS (PICOIDES MEDIUS)

Paternal effort is high in some monogamous mating systems. Trivers' (1972) model predicts that high male investment in brood care should evolve only when males have a high certainty of paternity. For this study, we chose two woodpecker species: the great spotted woodpecker (Picoides major) and the middle spotted woodpecker (Picoides medius). Both species were socially monogamous despite a very high breeding density in the study area. We used DNA fingerprinting to determine whether these two species were also genetically monogamous. We found that in great spotted and middle spotted woodpeckers paternal effort was high. Multi-locus DNA-fingerprinting showed that its actual paternity was also very high. In P. major all 161 young from 36 broods and in P. medius all 61 young from 13 broods were sired by the male feeding at the nest hole. There were also no cases of intraspecific brood parasitism or quasi parasitism (P. major: 114 chicks from 24 broods; P.medius: 33 chicks from 8 broods). We further found no case of mate switching during the fertile period of the female. Great spotted and middle spotted woodpeckers are typical of a group of monogamous nonpasserine birds with high male investment in brood care having low frequencies of EPP. We did not find efficient paternity guards. High certainty of paternity may be explained by paternal care being essential for female reproductive success, as in many seabirds and birds of prey. Females rarely engage in extra-pair copulations probably because they are constrained by male care. Males in both species spend little effort in acquiring mates as well as in extrapair copulations. They expend their reproductive effort in defending territories and in parental care. Females compete intensely with members of their own sex for pair formation before the time of frequent copulation. Choosing and securing a high quality partner is the only possibility to achieve high reproductive success for both sexes.