Multiply Mating Males in Gnamptogenys striatula Mayr (Hymenoptera, Formicidae)

Multiply mating ant males are rare, because in most ant species, multiple mating opportunities for males are scarce. Gnamptogenys striatula is an exception to this rule, as intranidal mating offers protection and a local female-biased sex ratio. In a behavioral experiment, we confirm the males’ ability to inseminate several receptive workers, with four females being the observed maximum. D. Allard is a Research Assistant for the Fund of Scientific Research—Flanders.     

Estimating the proportion of offspring attributable to candidate adults

Statistical methods for estimating genetic parentage are increasingly applied to accommodate limited marker polymorphism and the incomplete sampling of individuals. Neff et al. (2000a, Mol. Ecol. 9, 515–528; 2000b, Mol. Ecol. 9, 529–539) published a method (Pat) that estimates the proportion of next-generation individuals sired by a focal male, taking into account that the male may be genetically compatible, by random chance, with offspring that are not his own. Here we employ this method to reestimate paternity of 68 nest-guarding males from several fish species. The difference between the conventional exclusion-based estimate and Pat was >0.05 in only four of the 68 (5.9%) fish nests analyzed. An analytical formula shows that the difference between the two estimates is expected to be negligible if the focal male is consistent with a large proportion of the genotyped offspring, or if marker polymorphism is high. In addition, computer simulations illustrate how numbers of marker loci and their levels of genetic polymorphism, as well as the mating system of the organism under study, can influence estimates of paternity derived from exclusion-based estimates and Pat. Finally, we discuss various applications of these estimators including cases where additional biological information is present in the form of behavioral observations on parental care.     

Opening Pandora's box: comparative studies of genetic mating systems reveal reproductive complexity

Genetic analyses of realized reproductive success have fundamentally changed our understanding of mating behaviour in natural systems. While behavioural ecologists have long been interested in what factors influence mating behaviour, early studies were limited to direct observations of matings and thus provided an incomplete picture of reproductive activity. Genetic assessments of parentage have revolutionized the study of reproductive behaviour, revealing that many individuals engage in extra‐pair copulations ( Griffith et al. 2002 ) and that social mating partners frequently invest substantial resources into raising offspring that are unrelated to one or both of them ( Avise et al. 2002 ). While these findings have changed the way we think about reproductive behaviour, most investigations of genetic parentage have been restricted to single populations at a single point in time, obscuring spatial and/or temporal variation in mating behaviour and limiting our ability to determine how environmental changes can lead to shifts in mating strategies. In this issue of Molecular Ecology, Mobley & Jones (2009) compare genetic mating behaviour across five populations of Syngnathus floridae ( Fig. 1 ), a widespread species of pipefish distributed along the Gulf‐ and Atlantic Coasts of North America. The authors document how genetic mating behaviour varies across space in S. floridae and identify correlations between reproductive variation and particular ecological characteristics. Mobley & Jones’ paper is one of an increasing number of studies which address the question of how ecological variables influence mating behaviour, and highlights how our understanding of mating system variation and evolution is likely to expand through the wider application of high‐throughput parentage assessment in a comparative context.

Figure 1 Open in figure viewer PowerPoint A pregnant male dusky pipefish (Syngnathus floridae) in its natural habitat. Photo credit: Joe O’Hop.     

The genetic structure and mating system of Acrocomia aculeata (Arecaceae)

Acrocomia aculeata is a perennial, fruit-producing palm tree, native to tropical forests. Its fruits have spurred interest because of their significant potential for use in the cosmetic industry and as feedstock for biofuel. In the present study, the genetic structure and mating system in Acrocomia aculeata were analyzed, using eight nuclear micro-satellite loci and samples from São Paulo and Minas Gerais states, Brazil. By means of Bayesian analysis, these populations were clustered into two or three groups. A high multilocus outcrossing rate suggests that outcrosses were predominant, although a certain degree of biparental inbreeding also occurred. Thus, although monoecious and self-compatible, there is every indication that A. aculeata bears a mixed reproductive system, with a predominance of outcrossing. Given the genetic structure revealed hereby, future conservation strategies and germplasm collecting should be focussed on sampling and preserving individuals from different clusters.     

Multiple paternity in a philopatric rodent: the interaction of competition and choice

Paternity confusion is often suggested as the benefit that femalemammals accrue by mating with multiple males, but genetic advantagesare also possible. Microsatellite-based parentage analyses demonstratethat female banner-tailed kangaroo rats (Dipodomys spectabilis)commonly mate with more than one male; we asked how male andfemale behaviors interact to influence the characteristics ofmales that sire offspring. Specifically, we compared attributes(age, weight, mobility, relatedness, proximity) of the fathersof 229 known-maternity offspring with those of the other malesaccessible to the mothers. Adult males living adjacent to eachfemale attempt to monopolize access to her, and the nearestmale sires a plurality of offspring, but most mothers' youngare fathered by more than one male and littermates are usuallyhalf-sibs. Male proximity and mobility, but not size, influencethe probability of paternity, suggesting a role for competitivemate searching. Females significantly reduce the inbreedingcoefficient of their offspring by mating with males other than(or in addition to) the nearest male. Fathers are less closelyrelated to the mother in years of high density when unrelatedmales are more accessible to the female. Our results favor thegenetic "bet-hedging" hypothesis, whereby females actively butunselectively seek matings with additional males when the malemost likely to win in mate competition is costly to her (inthis case, genetically less compatible). We anticipate thatgenetic bet hedging will be common in species whose femalesare defendable, especially if they are also philopatric.     

The Social System of Lariang Tarsiers <Emphasis Type="Italic">(Tarsius lariang)</Emphasis> as Revealed by Genetic Analyses

Previous sociobiological studies of tarsiers were invariably based on field observations. Sulawesi tarsiers are known for monogamous or facultative polygynous social mating systems, but, to date, no data exist to describe the genetic mating system. We here bring together behavioral studies and molecular tools for the first time to elucidate mating behavior and kinship within a tarsier population. We investigated the social system of the recently described Tarsius lariang, which researchers have never studied before. Between September and November 2005, we conducted field observations and sampling in central Sulawesi, Indonesia, where this species is endemic. Ten of 11 social groups of the focal population were composed of 1 adult male, 1 adult female, and putative offspring. To enlighten genetic relationships, we used 12 microsatellite loci and mitochondrial DNA sequences of 26 captured and sampled Lariang tarsiers for parentage and relatedness analyses. A significant number of young were the offspring of the sampled group adults, suggesting a predominantly monogamous social and genetic mating system. There is evidence for extrapair young in groups in which adult pairs exhibit close relationships, leading to the assumption that extrapair mating is solicited to avoid inbreeding. Ten of 11 social groups lived in monogamous social systems, indicating monogamy to be the rule in Tarsius lariang.     

Twenty-one novel microsatellite DNA loci isolated from the Puget Sound white-crowned sparrow, Zonotrichia leucophrys pugetensis

The white‐crowned sparrow, Zonotrichia leucophrys, has served as a model species for studies of song and reproductive physiology. Here, we describe primers for 21 novel microsatellite loci isolated from the Puget Sound subspecies, Zonotrichia leucophrys pugetensis, which will be useful for parentage and population genetic analyses. Based on genotypes from seven to 22 adult birds from one population, the average number of alleles per locus was 10.9 (four to 21 alleles) and observed heterozygosity varied from 0.50 to 1.00. All loci also amplified products in at least one of three other passerine species tested.