Absence of strict monogamy in the Eurasian jackdaw, Coloeus monedula

The Eurasian Jackdaw is thought to be archetypically monogamous, but recent tagging research uncovered extra-pair copulations in the species. Here we examined extra-pair paternity (genetic monogamy) in Eurasian jackdaws breeding in the Judean Hills, Israel, at the global edge of the species range, using a set of highly polymorphic molecular microsatellites. We found roughly a sixth of nests sampled showed deviations from monogamy, more than previously found in DNA fingerprinting studies of jackdaws, suggesting a mixed mating strategy in this population. These findings support the trend of extra-pair paternity in avian species, even when social monogamy remains the rule, and highlight the importance of continued study of species throughout their geographical range.

Genetic monogamy and mate choice in a pair-living primate

In pair-living mammals, genetic monogamy is extremely rare. One possible reason is that in socially monogamous animals, mate choice can be severely constrained, increasing the risk of inbreeding or pairing with an incompatible or low-quality partner. To escape these constraints, individuals might engage in extra-pair copulations. Alternatively, inbreeding can be avoided by dispersal. However, little is known about the interactions between mating system, mate choice, and dispersal in pair-living mammals. Here we genotyped 41 wild individuals from 14 groups of coppery titi monkeys (Plecturocebus cupreus) in Peruvian Amazon using 18 microsatellite loci. Parentage analyses of 18 young revealed no cases of extra-pair paternity, indicating that the study population is mostly genetically monogamous. We did not find evidence for relatedness- or heterozygosity-based mate choice. Despite the lack of evidence for active inbreeding avoidance via mate choice, mating partners were on average not related. We further found that dispersal was not sex-biased, with both sexes dispersing opportunistically over varying distances. Our findings suggest that even opportunistic dispersal, as long as it is not constrained, can generate sufficient genetic diversity to prevent inbreeding. This, in turn, can render active inbreeding avoidance via mate choice and extra-pair copulations less necessary, helping to maintain genetic monogamy.

Genetic monogamy despite frequent extrapair copulations in “strictly monogamous” wild jackdaws

“Monogamy” refers to different components of pair exclusiveness: the social pair, sexual partners, and the genetic outcome of sexual encounters. Avian monogamy is usually defined socially or genetically, whereas quantifications of sexual behavior remain scarce. Jackdaws (Corvus monedula) are considered a rare example of strict monogamy in songbirds, with lifelong pair bonds and little genetic evidence for extrapair (EP) offspring. Yet jackdaw copulations, although accompanied by loud copulation calls, are rarely observed because they occur visually concealed inside nest cavities. Using full-day nest-box video surveillance and on-bird acoustic bio-logging, we directly observed jackdaw sexual behavior and compared it to the corresponding genetic outcome obtained via molecular parentage analysis. In the video-observed nests, we found genetic monogamy but frequently detected forced EP sexual behavior, accompanied by characteristic male copulation calls. We, thus, challenge the long-held notion of strict jackdaw monogamy at the sexual level. Our data suggest that male mate guarding and frequent intrapair copulations during the female fertile phase, as well as the forced nature of the copulations, could explain the absence of EP offspring. Because EP copulation behavior appeared to be costly for both sexes, we suggest that immediate fitness benefits are an unlikely explanation for its prevalence. Instead, sexual conflict and dominance effects could interact to shape the spatiotemporal pattern of EP sexual behavior in this species. Our results call for larger-scale investigations of jackdaw sexual behavior and parentage and highlight the importance of combining social, sexual, and genetic data sets for a more complete understanding of mating systems.

Almost faithful: SNP markers reveal low levels of extra-pair paternity in the Eurasian beavers

Mating systems largely affect individual reproductive strategies which further drives evolution. Monogamy, where males and females form exclusive pairs for more than one breeding season, is particularly intriguing in this context, as there are real and potential costs of genetic monogamy to both sexes. However, molecular studies in a variety of species have revealed that social monogamy does not necessarily imply genetic monogamy due to occurrence of extra-pair copulations resulting in extra-pair offspring. Although common in birds, <10% of mammals are monogamous. Here we use single nucleotide polymorphism (SNP) to investigate the genetic mating system of the Eurasian beaver (Castor fiber), a species traditionally considered to be not only socially but also genetically monogamous. We found evidence for low frequency of extra-pair paternity (EPP) and multiple paternity within litter. Only 5.4% young were produced by EPP and only 7% of litter contain at least one extra-pair young. Moreover, we found indications that only pairings of old individuals engaged in EPP. None of these pairs produced more than one litter as a result of EPP and none of the EPP events resulted in mate change. Our findings suggest that EPP in beavers might be the consequence of a lapse in mate guarding ability of old males.

Almost faithful: SNP markers reveal low levels of extra-pair paternity in the Eurasian beavers

Mating systems largely affect individual reproductive strategies which further drives evolution. Monogamy, where males and females form exclusive pairs for more than one breeding season, is particularly intriguing in this context, as there are real and potential costs of genetic monogamy to both sexes. However, molecular studies in a variety of species have revealed that social monogamy does not necessarily imply genetic monogamy due to occurrence of extra-pair copulations resulting in extra-pair offspring. Although common in birds, <10% of mammals are monogamous. Here we use single nucleotide polymorphism (SNP) to investigate the genetic mating system of the Eurasian beaver (Castor fiber), a species traditionally considered to be not only socially but also genetically monogamous. We found evidence for low frequency of extra-pair paternity (EPP) and multiple paternity within litter. Only 5.4% young were produced by EPP and only 7% of litter contain at least one extra-pair young. Moreover, we found indications that only pairings of old individuals engaged in EPP. None of these pairs produced more than one litter as a result of EPP and none of the EPP events resulted in mate change. Our findings suggest that EPP in beavers might be the consequence of a lapse in mate guarding ability of old males.

High Frequency of Multiple Paternity in Eastern Red Bats, Lasiurus borealis, Based on Microsatellite Analysis

Most species of bats give birth to only 1 pup each year, although Eastern red bats (Lasiurus borealis) can produce up to 5 pups per litter. Offspring in a single litter have been documented to be at different stages of development, suggesting that multiple paternity occurs. We tested the null hypothesis of genetic monogamy in red bats using 6 autosomal microsatellites and 1 X-linked microsatellite from 31 parent/offspring groups for a total of 128 bats. We sampled both pregnant females and mothers with pups that were obtained from bats submitted to departments of health in Oklahoma and Texas for rabies testing. Multiple paternity was assessed using a maximum-likelihood approach, hypothesis testing, and X-linked locus exclusion. The mean polymorphic information content of our markers was high (0.8819) and combined non-exclusion probability was low (0.00027). Results from the maximum-likelihood approach showed that 22 out of 31 (71%) parent/offspring groups consisted of half siblings, hypothesis testing rejected full sibship in 61% of parent/offspring groups, and X-linked locus exclusion suggested multiple paternity in at least 12 parent/offspring groups, rejecting our hypothesis of genetic monogamy. This frequency of multiple paternity is the highest reported thus far for any bat species. High levels of multiple paternity have the potential to impact interpretations of genetic estimates of effective population size in this species. Further, multiple paternity might be an adaptive strategy to allow for increased genetic variation and large litter size, which would be beneficial to a species threatened by population declines from wind turbines.