Mismatch between calf paternity and observed copulations between male and female reindeer:Multiple mating in a polygynous ungulate?

In polygynous systems,such as that exhibited by reindeer Rangifer tarandus,mate choice can be difficult to disentangle from male intrasexual competition because male behavior may constrain female choice.Multiple mating may provide an avenue for female mate choice,though it is difficult to identify using behavioral estimators alone.Molecular techniques address this issue by affording ecologists an opportunity to reassess mating systems from a genetic perspective.We assessed the frequency and possible explanations for multiple mating in reindeer using a genetic approach to determine the success of observed copulations in a semi-domesticated herd in Kaamanen,Finland.Behavioral and genetic data were synthesized with population characteristics over a 7-year period to test the hypothesis that,if present,polyandry in reindeer is driven by sexual harassment from sub-dominant males.We observed multiple mating in 42%of females,with as many as 60%exhibiting multiple mating in certain years.We found no evidence that multiple mating resulted from sexual harassment by sub-dominant males,suggesting that it is likely a deliberate strategy among females.Conversion rate of copulations into paternities varied with male size,with smaller males more likely to experience mismatch than larger males.Female preference for larger males persisted despite the occurrence of multiple mating,possibly suggesting a mechanism for cryptic post-copulatory selection.We suggest further research to delineate the possible influence of cryptic post-copulatory selection and multiple mating to defend against infertility in exhausted males.

Novel insights into the reproductive strategies of wild Chinese sturgeon(Acipenser sinensis)populations based on the kinship analysis

Understanding the reproductive strategy of an organism is important in conservation ecology as it directly affects the population performance under changing environmental conditions.Chinese sturgeon(Acipenser sinensis)are the largest anadromous fish in the Yangtze River,China.Currently,the species has only one spawning ground and has failed to spawn in recent years,leading it to the brink of extinction.To develop effective conservation measures,a further understanding of its reproductive strategy is needed.In our study,we conducted kinship analyses by using mitochondrial and microsatellite DNA data from 216 wild juveniles collected over nine years(2006
2013,2015)to understand the mating system,breeding interval,effective number of breeding adults,and reproductive success.The results from these analyses suggested polygynandry,with some parents contributing up to eight half-sibling juvenile genotypes.Although the spawning ground was restricted to a limited area,genetic diversity was maintained at a relatively high level(observed heterozygosity from 0.698 to 0.787 and expected heterozygosity from 0.763 to 0.787)and inbreeding coefficients in each year-class ranged from
1% to 9%(low to modest detrimental effects on offspring).A parental inference analysis revealed that Chinese sturgeon have a breeding interval of 2-6 years,indicating that it has the potential to feed,accumulate nutrition in the ocean,and then migrate back to the Yangtze River for iteroparous reproduction.The annual effective number of breeders in the Yangtze River ranged from 14 to 161 during the study period,and it decreased by 62.1%from the 2011
2014 year-classes.This sharp population decline likely contributes to the reproduction failure.However,the ratios of effective to census population size(Ne/Nc)were all larger than 0.20 after the 2010 year-class,indicating relatively even reproductive success.Based on these results,a suggested approach to protect this species is to restock parent fish to increase the reproductive stock size and optimize the discharge of the Three Gorges Dam to reduce the unsuitable hydrological conditions and rehabilitate spawning ground habitats.

Social biology of rodents

Herein, I summarize some basic components of rodent social biology. The material in this paper is summarized andcondensed from a recent book “Rodent Societies: An Ecological and Evolutionary Perspective” edited by J. O.Wolff and P. W. Sherman (2007). I describe the four basic spacing patterns and illustrate how female territoriality isa function of offspring defense and male mating tactics are a function of female defensibility. The vulnerability ofyoung to infanticide shapes female spacing and mating behavior. Food does not appear to be a defensible resourcefor rodents, except for those species that larder hoard nonperishable items such as seeds. Philopatry and theformation of kin groups result in genetic sub-structuring of the population, which in turn affects effectivepopulation size and genetic diversity. Dispersal is male biased and typically involves emigration from the maternalsite to avoid female relatives and to seek unrelated mates. Scent marking is a major form of communication and isused in reproductive competition and to assess prospective mates, but it is also eavesdropped by predators to locateprey. Females do not appear to alter the sex ratio of litters in response to maternal condition but among arvicolinerodents daughters appear to be favored in spring and sons in autumn. Rodents are relatively monomorphic;however, females tend to be larger than males in the smallest species and smaller in the larger species. Predationrisk results from an interaction among foraging time and vulnerability and in turn affects behavioral and life historycharacteristics.

Sexual selection in cane toads Rhinella marina： A male＇s body size affects his success and his tactics

Abstract Male body size can play an important role in the mating systems of anuran amphibians. We conducted labora- tory-based trials with cane toads Rhinella （Bufo） marina from an invasive population in the wet-dry tropics of northern Australia, to clarify the effects of a male＇s body size on his reproductive success and behavior （mate choice）. Males were stimulated with a synthetic hormone to induce reproductive readiness. Larger body size enhanced a male toad＇s ability to displace a smaller rival from amplexus, apparently because of physical strength： more force was required to dislodge a larger than a smaller amplectant male. A male＇s body size also affected his mate-choice criteria. Males of all body sizes were as likely to attempt amplexus with another male as with a female of the same size, and preferred larger rather than smaller sexual targets. However, this size prefe- rence was stronger in larger males and hence, amplexus was size-assortative. This pattern broke down when males were given access to already-amplectant male-female pairs： males of all body sizes readily attempted amplexus with the pair, with no size discrimination. An amplectant pair provides a larger visual stimulus, and prolonged amplexus provides a strong cue for sex iden- tification （one of the individuals involved is almost certainly a female）. Thus, a male cane toad＇s body size affects both his ability to defeat rivals in physical struggles over females, and the criteria he uses when selecting potential mates, but the impacts of that selectivity depend upon the context in which mating occurs