Levels Of Extra-pair Paternity Research Articles

A Contrast in Extra‐Pair Paternity Levels on Mainland and Island Populations of Mediterranean Blue Tits

AbstractExtra‐pair copulation (EPC) is a widespread behaviour amongst birds, yet the rate of occurrence of extra‐pair offspring is highly variable both within and across species. Two populations of Mediterranean blue tits, Parus caeruleus, one on the mainland and the other on the island of Corsica, are characterized by high levels of extra‐pair paternity (EPP), with 14 and 25% of extra‐pair offspring (in 46 and 68% of the nests), respectively. The rate of EPP is significantly higher in the island population. Such high rates on Corsica contradict the predictions of higher mate fidelity and lower levels of EPP on islands. Despite expressing several traits that characterize an insular syndrome, blue tits of Corsica do not exhibit lower genetic variation which could be associated with low levels of EPP on islands. Furthermore, our results do not support any of the hypotheses that have been proposed so far to explain variation in EPP rates at the local level. We tentatively suggest that proximate Mediterranean constraints, especially consistent food shortage, prompt females to seek better breeding opportunities through a two‐step process including high rates of EPC and divorce.

Rare extra‐pair fertilizations in the semi‐colonially breeding linnet Carduelis cannabina

Microsatellite analysis was used to analyse the level of extra‐pair paternity (EPP) in the semi‐colonially breeding linnet Carduelis cannabina in Denmark. During the breeding seasons of 1998 and 1999 EPP accounted for only 3.8% of young (4/106, 95% CL=1–13%). These extra‐pair young were found in 9.1% of the broods (2/22, 95% CL=1–29%). We hypothesize that this low level of EPP is due to an efficient use of both mate guarding and frequent copulations as paternity guards. However, experimental tests with temporary detainment of males would be needed to establish whether there is a causal relationship between the low EPP level and the double paternity guard.

Extrapair paternity is influenced by breeding synchrony and density in the common yellowthroat

The effects of breeding synchrony and density on levels of extrapair paternity in birds are controversial. We used multilocus DNA fingerprinting and microsatellite analysis to examine the effects of breeding synchrony and density on levels of extrapair paternity in the common yellowthroat (Geothlypis trichas). As in many Neotropical migrants, breeding synchrony was greatest at the beginning of the breeding season. Levels of extrapair paternity were higher after the peak in synchrony, leading to an overall negative relationship between extrapair paternity and breeding synchrony. However, there was a significant interaction between breeding synchrony and density, as levels of extrapair paternity were higher only for males breeding when both synchrony and density were low. We discuss several possible explanations for this interaction, including lower quality males or territories in low density areas and greater demands on mate guarding among males with larger territories. Most studies have not considered simultaneously the effects of breeding synchrony and density on extrapair paternity. Our results suggest that ecological correlates of paternity may be revealed only after testing for interactions in multivariate analyses.

Mating systems, sperm competition, and the evolution of sexual dimorphism in birds.

Comparative analyses suggest that a variety of factors influence the evolution of sexual dimorphism in birds. We analyzed the relative importance of social mating system and sperm competition to sexual differences in plumage and body size (mass and tail and wing length) of more than 1,000 species of birds from throughout the world. In these analyses we controlled for phylogeny and a variety of ecological and life-history variables. We used testis size (corrected for total body mass) as an index of sperm competition in each species, because testis size is correlated with levels of extrapair paternity and is available for a large number of species. In contrast to recent studies, we found strong and consistent effects of social mating system on most forms of dimorphism. Social mating system strongly influenced dimorphism in plumage, body mass, and wing length and had some effect on dimorphism in tail length. Sexual dimorphism was relatively greater in species with polygynous or lekking than monogamous mating systems. This was true when we used both species and phylogenetically independent contrasts for analysis. Relative testis size was also related positively to dimorphism in tail and wing length, but in most analyses it was a poorer predictor of plumage dimorphism than social mating system. There was no association between relative testis size and mass dimorphism. Geographic region and life history were also associated with the four types of dimorphism, although their influence varied between the different types of dimorphism. Although there is much interest in the effects of sperm competition on sexual dimorphism, we suggest that traditional explanations based on social mating systems are better predictors of dimorphism in birds.

Offspring sex ratios in tree swallows: females in better condition produce more sons.

Organisms are expected to adjust the sex ratio of their offspring in relation to the relative fitness benefits of sons and daughters. We used a molecular sexing technique that amplifies an intron of the CHD1 gene in birds to examine the sex ratio at egg-laying in socially monogamous tree swallows (Tachycineta bicolor). We examined all individuals in 40 broods (210 young), including all unhatched eggs and nestlings. Thus, the sex ratio we measured was the same as the sex ratio at laying. Overall, the mean sex ratio per brood (+/- SD) was biased significantly towards males (57 +/- 2% male). Within broods, male-biased sex ratios were associated with females in better body condition, and these females were more likely to produce sons in better condition. Tree swallows have one of the highest known levels of extra-pair paternity in birds (38-76% extra-pair young), and, as a consequence, variance in male reproductive success is greater than that of females. Thus, in tree swallows, investment in sons has the potential for higher fitness returns than investment in daughters, assuming that sons in better condition have greater reproductive success.

Reproductive Anatomy and Indices of Quality in Male Tree Swallows: The Potential Reproductive Role of Floaters

AbstractAvian populations often consist of breeding residents and nonbreeding floaters. It is usually assumed that floaters are lower-quality individuals that do not reproduce, but floater tactics and potential reproductive success have rarely been examined carefully. To assess the potential reproductive role of male floaters in Tree Swallows (Tachycineta bicolor), we compared their reproductive organs and morphology with those of resident males. Tree Swallows show high levels of extrapair paternity, but two studies attempting to find the fathers of the extrapair offspring have been remarkably unsuccessful. Floater males that father extrapair young would face intense sperm competition. Theory predicts that under intense sperm competition, selection favors males that produce more sperm. Comparative studies in birds and other taxa provide evidence that the level of sperm competition influences relative testes size and sperm production. However, intraspecific adaptations to different levels of sperm competition have received far less attention. Floater Tree Swallows did not differ from resident males in any of the characters we measured, including testes size, but floaters had significantly larger cloacal protuberances. Thus, our results do not confirm the general assumption that floaters are lower-quality individuals that do not reproduce. Furthermore, floaters showed high variation in the volume of the cloacal protuberance (reflecting sperm numbers), which suggests that they engage in copulations. We conclude that floater male Tree Swallows invest heavily in sperm production (as do resident males) to exploit breeding opportunities through takeovers or extrapair copulations.

Male and female behaviour and extra-pair paternity in the wheatear

Behavioural observations and DNA fingerprinting were used to determine the relationship between male and female behaviours and levels of extra-pair paternity in the wheatear,Oenanthe oenanthe. Behavioural observations were consistent with the hypothesis that males attempted to ensure paternity by mate guarding, while pursuing extra-pair copulations (EPCs) primarily outside the fertile period of their pair female. The intensity of guarding varied with time of season and was greater at late nests. However, although males on territories with late nests also experienced high intrusion rates, the intensity of guarding was influenced more by the operational sex ratio (which was female skewed at early nests) than by intrusion rates per se. We suggest that early breeding males adopted a strategy of territorial defence to ensure paternity, as opposed to guarding their female directly (which late breeding males did), to capitalize on the increased opportunities to pursue EPCs in neighbouring territories. Females were less conspicuous than males in their pursuit of EPCs, were never seen off territory or observed to solicit extra-pair males directly, and rejected the majority of EPCs. The frequency of extra-pair paternity was 11% of 73 offspring, in 29% of 17 broods, and was not correlated with the intensity of guarding. Female cooperation appeared to be important for successful copulation, and extra-pair paternity is therefore likely to be a consequence of solicited, or at least accepted, EPCs. We discuss why females might have participated in EPCs.

Incomplete Female Knowledge of Male Quality May Explain Variation in Extra-Pair Paternity in Birds

Abstract We present and discuss an hypothesis to explain inter- and intraspecific variation in levels of extra-pair paternity (EPP) in birds. In species with biparental care, females may be willing to engage in extra-pair copulation (EPC) to improve the genetic quality of the offspring. However, it may be costly to sample males and difficult to assess their genetic quality. Hence, we suggest that variation occurs in the extent of such knowledge between females, causing variation in the extent to which they are willing to engage in EPC. From the hypothesis we present nine predictions on occurrence of EPP in birds, e.g. cuckolders should mainly be resident, close neighbours; rate of EPP should be positively related to breeding density, to rate of male intrusion, to female opportunity to assess male quality from competitive interactions between males, to early arrival time of females relative to time of egg laying, and to breeding synchrony. Finally, we discuss implications on male behaviour. We suggest a new function of male mate guarding, namely that mate guarding is a means to prevent the social mate from obtaining essential information about the quality of potential extra-pair mates.

Estimating Cuckoldry in Birds: The Heritability Method and DNA Fingerprinting Give Different Results

We compared two methods that have been used to assess cuckoldry in birds, i.e. DNA fingerprinting and comparison of heritability of morphological traits between the putative parents. DNA fingerprinting confirmed that the putative father had sired all young in 53 broods of great reed warblers Acrocephalus arundinaceus, from which 72 young became recruits in our study area in subsequent years. On the same data set, we found the heritability of both tarsus length and wing length between males and their offspring to be lower than between females and their offspring. In several studies, a lower heritability value between males and their putative offspring as compared to females and offspring has been interpreted as a result of cuckoldry. In the present study, heritability was estimated between offspring (measured as adults) and their genetic parents, as confirmed by DNA fingerprinting. This suggests that maternal effects may explain why tarsus length and wing length in the offspring are more similar to their mother than to their father. The present study then violates one of the basic assumptions of the heritability method, i.e. a similar contribution from the mother and the father to the expression of offspring traits. Whenever phenotypic traits (e.g. tarsus length and wing length) are under maternal influence, the method of comparing the heritability of such traits between the parents would over-estimate the frequency of cuckoldry. Because this kind of maternal effects are very difficult to control for, our study questions the heritability method as a reliable tool for revealing levels of extra-pair paternity

Extra-pair paternity in tree swallows: why do females mate with more than one male?

Recent studies of monogamous tree swallows (Tachycineta bicolor) suggest that females may receive some type of genetic benefit from extra-pair fertiliza- tions. In this study we attempted to determine what type of genetic benefits might be gained by females. We com- pared numerous morphological and behavioral traits (Table 1) of every male nesting on one grid of nest-boxes (n = 23) to determine what male traits were correlated with male success at gaining extra-pair fertilizations. DNA fingerprinting revealed an increase in the level of extra-pair paternity from the previous year (50% of broods contained extra-pair young in 1990 vs. 87% of broods in 1991), but no significant correlates of paterni- ty. We found six extra-pair fathers at seven nests (20 nests had extra-pair young). The traits of these extra- pair males did not differ from those of the males they cuckolded. We discuss several reasons for this lack of difference, but argue that our results are not inconsis- tent with females choosing extra-pair males to enhance the genotypic quality of their offspring. Despite a com- plete search of the nest-box grid for extra-pair fathers, we were able to explain the paternity of just 21% (13/63) of all extra-pair young. This suggests that extra-pair fa- thers were either residents off our study grid or non-ter- ritorial floaters. Tree swallows are quite mobile and spend only part of the day at their nest prior to laying. In addition, we rarely see swallows visiting other grids of nest-boxes. Therefore, we suggest that most extra- pair copulations occur at some unknown location, pos- sibly at a feeding or roosting area where females may be able to choose from many more potential extra-pair fa- thers than at their nest-site.