High Frequency Of Extra-pair Paternity Research Articles

Spatial patterns of extra‐pair paternity for spotted towhees Pipilo maculatus in urban parks

The extra‐pair (EP) mating system of birds may be influenced by food resources, such that nutritionally stressed females are unable to pursue EP fertilizations (constrained female hypothesis; CFH), or that females on poor territories acquire EP fertilizations during extra‐territorial forays in search of food (mating opportunity hypothesis; MOH). Edges of urban habitat fragments are sites of apparent high food abundance for spotted towhees Pipilo maculatus, and we used distance to habitat edge in four urban parks in Portland, OR, USA (2004–2006), to test the CFH and MOH. EP paternity was independent of park identity and year; 44% of nests contained EP young and 26% of all young were EP. As predicted by the CFH, EP paternity was more common in nests of long‐tailed (presumably) high quality females. However, independently of tail length, younger females had more EP young than older females, a finding consistent with the MOH. Contrary to predictions of both hypotheses, the probability that a nest contained EP young was highest both at the habitat edge and habitat interior while the proportion of young in nests of EP origin (for nests with EP young) was highest at intermediate distances from habitat edge. We propose that high frequency of EP paternity among females in the interior occurred because, as predicted by the MOH, they ranged more widely in search of food and often encountered EP males. High probability of EP paternity near edges was likely unrelated to female quality. Instead, anthropogenic food sources may have attracted individuals to edges and increased encounters between potential EP mates. Simple opportunity seems likely to account for patterns of EP paternity in spotted towhees, suggesting that human altered environments have the potential to substantially affect EP mating behavior.

High frequency of extra-pair paternity in an urban population of Cooper's Hawks

Raptors exhibit some of the highest rates of intra-pair copulations among birds, perhaps in an attempt by males to reduce the risk of being cuckolded. Indeed, the frequency of extra-pair fertilizations reported in studies of raptors to date is relatively low (0–11.2%). Socially monogamous Cooper's Hawks (Accipiter cooperii) exhibit one of the highest copulation rates among birds, yet there are no published accounts of extra-pair copulations (or paternity). We studied a population of Cooper's Hawks in Milwaukee, Wisconsin, during three breeding seasons (2003, 2004, and 2007), examining the possible effects of age (1 yr old vs. ≥ 2 yr old), adult mass, and brood size on the frequency of extra-pair paternity (EPP). We found that 19.3% of nestlings (N = 27/140) were extra-pair young (EPY), and 34% of all broods (N = 15/44) had at least one EPY. The sires of the EPY in our study were identified for only two broods, suggesting that floater males may have engaged in extra-pair copulations with territorial females. We found that brood size was a good predictor of the occurrence of EPP (EPP) in nests, but adult mass and female age were not. To our knowledge, these possible correlates of the occurrence of EPP in raptors had not previously been investigated. Male Cooper's Hawks provide food for females during the pre-nesting period, and delivery of food is, in contrast to other raptor species, typically followed by copulation. Thus, one possible explanation of the relatively high rates of EPP in our study is that females might accept or even solicit extra-pair copulations from males other than their mates as a means of maximizing energy intake for egg production. Such behavior might be particularly likely in our study area, i.e., a food-rich urban setting with a high breeding density of Cooper's Hawks. RESUMEN Alta frecuencia de paternidad con mas de una hembra en una poblacion urbana de los halcones de Cooper Entre las aves, los rapaces machos presentan algunas de las tasas mas altas de copulacion con mas de una hembra, tal vez en un intento de los machos para reducir el riesgo de ser enganado. De hecho, la frecuencia de fertilizaciones con mas de una hembra reportado en estudios de rapaces hasta hoy en dia es relativamente baja (0 – 11.2%). Halcones de Cooper (Accipiter cooperii) son socialmente monogamos y presentan una de las tasas mas altas de copulacion entre las aves, sin embargo, no hay cuentas publicadas de copulas fuera de la pareja (o paternidad). Se estudio una poblacion de halcones de cooper en Milwaukee, Wisconsin, durante tres temporadas de cria (2003, 2004, y 2007). Examinamos los efectos posibles de la edad (un ano de edad hasta dos anos de edad), la masa corporal de adultos, y el numero de pollos en el nido contra la frecuencia de paternidad con mas de una hembra. Se encontro que el 19.3% de los polluelos (N = 27/140) eran de una pareja en que el macho copulo con mas de una hembra (EPY), y el 34% de todos los nidos (N = 15/44) tuvieron al menos una EPY. Se identificaron los padres de la EPY en nuestro estudio para solo dos crias, lo que sugiere que los machos flotantes (aparean con mas de un individuo) pudieron haber participado en copulaciones con mas de una hembra territorial. Se encontro que el tamano de la nidada fue un buen factor predictivo de la incidencia de la EPP en los nidos, pero la masa corporal de los adultos y la edad de la hembra no fueron factores importantes. A nuestro entender, no han hecho investigaciones de estos correlatos en la ocurrencia de EPP en rapaces. Los machos de los halcones de Cooper proporcionan alimento para las hembras durante el periodo previo a la anidacion, y la entrega de alimentos es normalmente seguida por la copulacion, lo cual es en contraste de otras especies de rapaces. Por lo tanto en nuestro estudio, una posible explicacion de relativamente altas tasas de paternidad con mas de una hembra, es que las hembras pueden aceptar o incluso solicitar EPCs de machos que no son sus companeros como un medio para maximizar el consumo de energia para la produccion de huevos. Tal comportamiento puede ser particularmente probable en nuestra area de estudio, es decir, un entorno urbano rico en alimentos con una alta densidad de cria de halcones de Cooper.

Sperm dimensions differ between two Coal Tit Periparus ater populations

The evolutionary forces that shape and maintain variation in sperm traits across species in birds have recently attracted increased attention. Much less is known about the patterns, the causes and the consequences of variation in sperm traits within and, in particular, between populations of the same species. We here analyse intraspecific variation in sperm dimensions within and between two populations of the Coal Tit Periparus ater, a socially monogamous passerine with a high frequency of extra-pair paternity. Spermatozoa from a Norwegian population had a greater mean total length compared to those from a German population, mainly as a result of longer sperm heads. Sperm head length in the Norwegian population also accounted for a larger percentage of sperm total length suggesting differences in sperm proportions between populations. Furthermore, spermatozoa from the Norwegian population showed lower mean within-male variation in sperm length and there was significant between-male variation in sperm total length within each of the two populations. We discuss these results in the light of recent comparative evidence suggesting relationships between sperm length, and variation in sperm length, and the frequency of extra-pair paternity across passerine birds.

The genetic similarity between pair members influences the frequency of extrapair paternity in alpine marmots

Extrapair paternity is widespread in birds and mammals. In particular, the alpine marmot, Marmota marmota, has a high frequency of extrapair paternity that seems to be explained by the genetic compatibility hypothesis. We investigated whether the number and proportion of extrapair young depend on the heterozygosity (individual genetic diversity) of the social male, or on the genetic similarity between the social male and his mate (relatedness). Both the number and the proportion of extrapair young increased with both high similarity and dissimilarity between the social pair. In combination with previous results, our study suggests that patterns of extrapair paternity in alpine marmots can best be explained by the genetic compatibility hypothesis, and more precisely its optimal outbreeding variant. Our results indeed suggest that extrapair paternity is a mechanism to avoid both in- and outbreeding depression. We discuss which proximal mechanisms may be involved in extrapair paternity in this species.

Editorial and Retrospective 2007

Editorial and Retrospective 2007

High frequency of extra-pair fertilisations in the moustached warbler, a songbird with a variable breeding system

Summary We examined the genetic mating system of the moustached warbler Acrocephalus melanopogon, a multi-brooded songbird that sometimes breeds in trios (one female and two males). The second male, which appears relatively late in the breeding cycle, participates in all forms of parental care but provides less care than the pair male. DNA fingerprinting revealed a high frequency of extra-pair paternity: 39% (7/18) of the broods contained extra-pair young, comprising 27% (12/44) of the chicks. An additional 7 broods contained at least 9 chicks (out of 20) that were not sired by the resident male. We were able to assign paternity for 11 (52%) of the extra-pair young. Of these, 7 (64%) were sired by secondary males and 4 (36%) by close neighbours (nesting within 50 m). Consistently, pairs with extra-pair young had more close neighbours, and they also tended to have a secondary male at the nest. Caring for nestlings that they might have sired through extra-pair copulations may be a way for secondary males to salvage their reproductive effort. They may also provide parental care because of the possibility of pairing with the female in future breeding attempts. Our results suggest that female moustached warblers obtain direct benefits (i.e., help with brood care) from extra-pair copulations. However, a skewed fertilisation pattern implies that genetic compatibility between mates and copulation partners may also influence female extra-pair behaviour in this species.

Ecological constraints on extra-pair paternity in the bluethroat.

The mating system of the bluethroat (Luscinia s. svecica) involves a high level of sperm competition, and consequently a high frequency of extra-pair paternity (EPP). There is considerable variation in the frequency of EPP. Over the course of ten study years in a population in Norway, the frequency has fluctuated between 7% and 33% of young, and 8% and 76% of broods. In this paper, we address the issue of whether ecological factors can explain some of the variation in EPP between years and broods. Factors include breeding density, breeding synchrony and two meteorological variables (ambient temperature and precipitation) during the period of peak female fertility. There were no significant relationships between annual averages of the four variables and the annual level of EPP, but the statistical power of these tests was low, due to a restricted sample (n=10 years). Focussing on individual broods, none of the factors had significant effects when including all broods in the analyses (including those with zero EPP). When limiting the analyses to broods with one or more extra-pair offspring, morning temperature had a significant effect on the frequency of EPP. When the temperature was low during the peak of the fertile period, EPP occurred less frequently. Male extra-pair behaviour was not generally constrained by synchrony between the fertile periods of the social mate and the extra-pair mate, but for a subgroup of males ("unattractive males") there appeared to be a trade-off between mate guarding and pursuing extra-pair copulations. Our results indicate that ecological conditions have no influence on whether or not a brood will contain extra-pair offspring, but when EPP does occur, its frequency is influenced by air temperature. Possibly, there is a causal relationship between weather conditions and the frequency of extra-pair encounters in this species. The breeding season is initiated at a phenologically early stage, when large parts of the territories are still covered with snow, and cold weather conditions may force the birds to devote most of their time to maintenance and thereby constrain sexual activities.

High Frequency of Extra-Pair Paternity in Eastern Kingbirds

Abstract Genetic parentage in the socially monogamous and territorial Eastern Kingbird (Tyrannus tyrannus) was examined in a central New York population by multilocus DNA fingerprinting. Extra-pair young were identified in 60% (12 of 20) of nests. Of the 64 nestlings profiled, 42% were sired by extra-pair males, but no cases of conspecific brood parasitism were detected. These results are markedly different from a previous electrophoretic study of the same species in a Michigan population, which reported 39% of nestlings were unrelated to one (typically the mother, quasiparasitism) or both (conspecific brood parasitism) of the putative parents. In the New York population, extra-pair paternity was most common among females that returned to breed on a former territory. Among females that were new to a breeding territory, extra-pair paternity increased directly with breeding density. Although the power of the tests was low, neither breeding synchrony nor male experience with a breeding territory appeared to ...

Male parental care, female reproductive success, and extrapair paternity

Birds differ considerably in the degree of male parental care, and it has been suggested that interspecific variation in extrapair paternity is determined by the relative importance of benefits to females from male parental care and good genes from extrapair sires. I estimated the relationship between extrapair paternity and the importance of male parental care for female reproductive success mainly based on male removal studies, using a comparative approach. The reduction in female reproductive success caused by the absence of a male mate was positively correlated with the male contribution to feeding offspring. The frequency of extrapair paternity was negatively related to the reduction in female reproductive success caused by the absence of a mate. This was also the case when potentially confounding variables such as developmental mode of offspring and sexual dichromatism were considered. A high frequency of extrapair paternity occurs particularly in bird species in which males play a minor role in offspring provisioning and in which attractive males provide relatively little parental care. Bird species with frequent extrapair paternity thus appear to be those in which direct fitness benefits from male care are small, females can readily compensate for the absence of male care, and indirect fitness benefits from extrapair sires are important.

High Frequency of Extra-Pair Paternity in the Coal Tit

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High Frequency of Extra-Pair Paternity in a Dense and Synchronous Population of Willow Warblers Phylloscopus trochilus

Genetic parentage was studied in a Norwegian, sub-alpine population of Willow Warblers Phylloscopus trochilus by means of multilocus DNA fingerprinting. We found that 33% (36/109) of the offspring were unrelated to the putative father, and that one additional offspring was unrelated to both putative parents. Altogether 50% (10/20) of the broods contained illegitimate young. The distribution of extra-pair paternity was bimodal, with several broods containing many extra-pair offspring. These results contrast markedly with a previous study of the same species, reporting no cases of mismatched parentage in a Swedish lowland population. Potentially, the high frequency of extra-pair paternity could be attributed to a higher breeding density and/or synchrony in our study population. Cuckolded males had a lower body mass, but no shorter tarsi or wings, than non-cuckolded males. This suggests that a male's loss of paternity is somehow related to his body condition. The data set includes five broods in which the pair male was permanently removed on the day the first egg was laid. There was no tendency that the manipulation increased the

The high frequency of extra-pair paternity in tree swallows is not an artifact of nestboxes

A common criticism of nestbox studies is one of creating artificial nesting conditions and breeding behavior different from what would be seen under natural conditions. We assessed the frequency of extra-pair paternity (percentage of broods with at least one extra-pair young) in 25 families of tree swallows (Tachycineta bicolor) nesting in natural cavities and compared it to that in a nestbox population. We found that 84% of females nesting in natural cavities obtained fertilizations from extra-pair males. These extra-pair males fathered 69% of all nestlings. Studies of tree swallows breeding in nestboxes have shown that 50–87% of broods contained extra-pair young, with extra-pair males fathering 38–53% of all the young. In broods with extra-pair paternity, natural cavities contained a significantly greater proportion of extra-pair young than did nestboxes. Despite differences in nesting habitat and female age structure, the frequency of extra-pair paternity did not differ significantly between the natural-cavity and nestbox populations. Therefore, the presence of extra-pair paternity in tree swallows is not an artifact of nestboxes or of artificial nesting conditions.

High frequency of extra-pair paternity in Swedish pied flycatchers revealed by allozyme electrophoresis and DNA fingerprinting

We used two genetic techniques to study multiple parentage in the pied flycatcher (Ficedula hypoleuca). Allozyme electrophoresis of 131 nestlings from 22 clutches sampled in 1982 and 1987 showed that one nestling had a mismatched allele compared with its putative parents. In one additional nest the devitation from Mendelian inheritance of parental genotypes suggested extra-pair paternity. The calculated probability of detecting multiple paternity from the genetic variation at four loci was 0.115. The estimated population frequency of extra-pair fertilization (EPF) was 13%, based on two mismatches and the probability of detecting multiple paternity. The seven families (n = 38 nestlings) in the 1987 sample were also analyzed by DNA fingerprinting using the M13 and Jeffrey's 33.15 probes. Overall, 24% (n = 9) of the nestlings analyzed were genetically inconsistent with their putative father, with EPF occurring in three (43%) of the seven clutches. One nestling originated by intraspecific brood parasitism. Comparison of the two techniques using the same samples showed that allozyme electrophoresis has a resolution only 11% of that of DNA fingerprinting, close to the calculated probability of detecting multiple paternity (0.115). Both techniques suggest that extra-pair fertilization is relatively common in the Swedish populations investigated compared to the low frequency reported from a Norwegian population.