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PubMed2002

Extra pair paternity in birds: a review of interspecific variation and adaptive function.

The application of molecular genetic techniques has revolutionized our view of avian mating systems. Contrary to prior expectations, birds are only very rarely sexually monogamous, with 'extra-pair offspring' found in approximately 90% of species. Even among socially monogamous species, over 11% of offspring are, on average, the result of extra-pair paternity (EPP). Based on over 150 molecular genetic studies of EPP in birds, we review two topical areas: (i) ecological explanations for interspecific variation in the rate of EPP; and (ii) evidence bearing on the adaptive function of EPP. We highlight the remaining challenges of understanding the relative roles of genes and ecology in determining variation between taxa in the rate of extra paternity, and testing for differences between extra-pair offspring and those sired within-pair.

Adaptation, Physiological↗
PubMed2003

Paternity success and the direction of sexual selection in a field population of a semelparous marsupial, Antechinus agilis.

Antechinus agilis is a small sexually size dimorphic marsupial with a brief annual mating period of 2-3 weeks. All males die after this period, and females give birth to up to 10 young. Mating is thought to be promiscuous, however, there is no field data to confirm this. Using microsatellites, we investigated paternity patterns over two seasons in a wild population. Male weight was significantly positively related to the number of females fertilized and with the number of offspring sired, in both years. Furthermore, selection gradients indicated selection for larger males. Both results suggest that size dimorphism in A. agilis can be explained by sexual selection for larger males. The proportion of offspring sired within litters, did not relate to male size. Therefore, larger males are more successful through higher mating access, not through their sperm outcompeting that of smaller males. As expected from their known ranging behaviour, the number of offspring within litters left unassigned to a father did not depend on the grid location of the mother. Female size did not differ between successful reproducing and unsuccessful females. However, females that weaned offspring had larger heads than females that did not wean offspring. Males did not 'prefer' mating with larger females, nor did assortative mating occur. From our results, the mating system of A. agilis is clearly promiscuous. Selection for larger males occurred in both years, even though in one year the operational sex ratio was highly female biased, suggesting that the potential reproductive rate is a better predictor of the direction of sexual selection in A. agilis.

Animals↗
PubMed2003

Evidence for genetic monogamy and female-biased dispersal in the biparental mouthbrooding cichlid Eretmodus cyanostictus from Lake Tanganyika.

In this study, we investigate whether apparent social monogamy (where a species forms a pair bond but may participate in copulations outside the pair bond) corresponds with genetic monogamy (where individuals participate only in copulations within a pair bond) in a biparental mouthbrooding cichlid fish, Eretmodus cyanostictus, from Lake Tanganyika, Africa. Our findings suggest that E. cyanostictus is both socially and genetically monogamous and that monogamy may result from limited opportunities for polygyny, rather than from reproductive benefits of monogamy. Mating systems are believed to influence the relative rate of dispersal of the sexes, and our results suggest that E. cyanostictus displays female-biased dispersal, providing some support for the 'resource competition' hypothesis driving sex-biased dispersal.

Animals↗
PubMed2004

New insights from fine-scale spatial genetic structure analyses in plant populations.

Many empirical studies have assessed fine-scale spatial genetic structure (SGS), i.e. the nonrandom spatial distribution of genotypes, within plant populations using genetic markers and spatial autocorrelation techniques. These studies mostly provided qualitative descriptions of SGS, rendering quantitative comparisons among studies difficult. The theory of isolation by distance can predict the pattern of SGS under limited gene dispersal, suggesting new approaches, based on the relationship between pairwise relatedness coefficients and the spatial distance between individuals, to quantify SGS and infer gene dispersal parameters. Here we review the theory underlying such methods and discuss issues about their application to plant populations, such as the choice of the relatedness statistics, the sampling scheme to adopt, the procedure to test SGS, and the interpretation of spatial autocorrelograms. We propose to quantify SGS by an 'Sp' statistic primarily dependent upon the rate of decrease of pairwise kinship coefficients between individuals with the logarithm of the distance in two dimensions. Under certain conditions, this statistic estimates the reciprocal of the neighbourhood size. Reanalysing data from, mostly, published studies, the Sp statistic was assessed for 47 plant species. It was found to be significantly related to the mating system (higher in selfing species) and to the life form (higher in herbs than trees), as well as to the population density (higher under low density). We discuss the necessity for comparing SGS with direct estimates of gene dispersal distances, and show how the approach presented can be extended to assess (i) the level of biparental inbreeding, and (ii) the kurtosis of the gene dispersal distribution.

Demography↗
PubMed2003

Sexual size dimorphism and timing of spring migration in birds.

Sexually selected traits are limited by selection against those traits in other fitness components, such as survival. Thus, sexual selection favouring large size in males should be balanced by higher mortality of larger males. However, evidence from red-winged blackbirds (Agelaius phoeniceus) indicates that large males survive better than small males. A survival advantage to large size could result from males migrating north in early spring, when harsh weather favours large size for energetic reasons. From this hypothesis we predicted that, among species, sex differences in body size should be correlated with sex differences in timing of spring migration. The earlier males migrate relative to females, the larger they should be relative to females. We tested this prediction using a comparative analysis of data collected from 30 species of passerine birds captured on migration. After controlling for social mating system, we found that sexual size dimorphism and difference in arrival dates of males and females were significantly positively correlated. This result is consistent with the hypothesis that selection for survival ability promotes sexual size dimorphism (SSD), rather than opposes SSD as is the conventional view. If both natural selection and sexual selection favour large adult males, then limits to male size must be imposed before males become adults.

Animal Migration↗
PubMed2003

Constant relative age and size at sex change for sequentially hermaphroditic fish.

A general problem in evolutionary biology is that quantitative tests of theory usually require a detailed knowledge of the underlying trade-offs, which can be very hard to measure. Consequently, tests of theory are often constrained to be qualitative and not quantitative. A solution to this problem can arise when life histories are viewed in a dimensionless way. Recently, dimensionless theory has been developed to predict the size and age at which individuals should change sex. This theory predicts that the size at sex change/maximum size (L50/L(max)), and the age at sex change/age at first breeding (tau/alpha) should both be invariant. We found support for these two predictions across 52 species of fish. Fish change sex when they are 80% of their maximum body size, and 2.5 times their age at maturity. This invariant result holds despite a 60 and 25 fold difference across species in maximum size and age at sex change. These results suggest that, despite ignoring many biological complexities, relatively simple evolutionary theory is able to explain quantitatively at what point sex change occurs across fish species. Furthermore, our results suggest some very broad generalities in how male fitness varies with size and age across fish species with different mating systems.

Age Factors↗
PubMed2003

Environment-dependent inbreeding depression in a hermaphroditic freshwater snail.

Inbreeding depression was simultaneously studied under contrasted environments, laboratory and natural conditions, using individuals originating from 14 families of the freshwater snail Physa acuta. Both survival and growth of juveniles showed inbreeding depression under laboratory conditions. The same fitness components were monitored with mature snails either kept under laboratory conditions or released at a natural site and analysed using capture-mark-recapture models. Genetic composition of both samples was similar. Inbreeding depression on survival was highest in the laboratory while strong outbreeding depression was revealed in the field. Thus inbreeding depression may not be always higher under natural conditions, at the opposite of what is commonly assumed. We suggest that inbreeding depression is dependent on metabolic requirements imposed by the environment. Other evidences showing that inbreeding depression is environment-dependent are reviewed. We conclude that genetic models should include both genetic and environmental variance in inbreeding depression for studying mating system evolution.

Adaptation, Physiological↗
PubMed2004

Remating and sperm displacement in a natural population of Drosophila buzzatii inferred from mother-offspring analysis of microsatellite loci.

Prospects for estimation of parameters of models of sperm competition from field data have improved recently with the development of methods that employ multilocus genotype data from brood-structured samples. Sperm competition in Drosophila buzzatii is of special interest because it is possible to directly observe the breeding behaviour of this species in its natural habitat of rotting cactus. Previous laboratory experiments showed that this species exhibits an unusual pattern of frequent remating and sperm partitioning. This paper reports the first attempt to estimate the frequency of female remating and sperm competition in natural populations of D. buzzatii. For the Australian population studied, the mean remating frequency was lower (alpha = 2.12-2.20) than previously estimated in laboratory experiments with the same population, whereas mean sperm displacement (beta = 0.69-0.71) fell within the limits of previous laboratory results. The evolution of the D. buzzatii mating system is discussed.

Animals↗
PubMed2005

Pollination of Oncocyclus irises (Iris: Iridaceae) by night-sheltering male bees.

Irises in the section Oncocyclus (Siems.) Baker ( IRIS: Iridaceae) grow throughout the Middle East and have large and dark-coloured flowers but no nectar reward available to flower visitors. Consequently, no reward-collecting pollinators have been observed visiting the flowers during daytime. The only visitors are solitary male bees ( Eucera spp.: Apidae) that enter the flowers at dusk and stay there overnight. Here we describe the mating system of Oncocyclus irises, and the role of night-sheltering male bees in their pollination system. Pollen viability in I. haynei on Mt. Gilboa was very high (>90%) throughout all floral life stages. Stigmas were receptive in buds and in open flowers, but not in older ones. Self-pollination yielded no fruits in three species, confirming complete self-incompatibility in Oncocyclus irises. On average, 1.9 flowers were visited by each male bee before it settled for the night in the last one. Moreover, Iris pollen was present on the dorsal side of 38.8% of males caught sheltering in flower models mounted near an I. atrofusca population, indicating that pollen is transferred between flowers by night-sheltering solitary male bees. We have surveyed 13 flowering populations of six Oncocyclus species for the presence of night-sheltering male bees as well as for fruit set. We found a positive correlation, indicating that sexual reproduction in Oncocyclus irises is dependent on night-sheltering solitary male bees. Based on their complete self-incompatibility, the absence of nectar-collecting visitors during the day, and the transfer of pollen grains by the night-sheltering solitary male bees, we conclude that fertilization of Oncocyclus irises is totally dependent on pollination by night-sheltering solitary male bees.

Animals↗
PubMed1997

Immunocontraception in rodents: a review of the development of a sperm-based immunocontraceptive vaccine for the grey squirrel (Sciurus carolinensis).

The strategy for developing contraceptive vaccines for wild rodents will depend on the species. In rats and mice, high all-year birth rates, high levels of dispersal and promiscous mating systems suggest that, if immunocontraception was used alone, > 90% of the population would have to sterilized to achieve the desired control. In Britain, the grey squirrel (Sciurus carolinensis) may be a better candidate to investigate the feasibility of a contraceptive vaccine in rodents. This introduced species is a seasonal breeder with a much lower population turnover than rats or mice. As well as causing damage to woodland, it has ousted the native red squirrel (S. valgaris) from most of the UK. A human and selective method for the control of grey squirrels is therefore highly desirable. Numerous sperm-specific antigens have been identified on rodent spermatozoa. Monoclonal antibodies to particular components block sperm-egg interactions in laboratory animals and cross-react with grey squirrel spermatozoa. In vitro fertilization assays indicate that squirrel sperm-egg binding may be inhibited also. Currently, a cDNA library obtained from grey squirrel testis is being screened to identify genes encoding specific sperm antigens involved in fertilization. Methods of enhancing immunogenicity after oral immunization using microparticle carriers and immune-stimulating complexes are currently under investigation.

Administration, Oral↗
PubMed2003

Distribution of spermatozoa in the outer perivitelline layer from above the germinal disc of emu and ostrich eggs.

In the present study, we determined the distribution of spermatozoa in the perivitelline layer above the germinal disc (GD) of emu and ostrich eggs that had been laid at random intervals after mating. Eggs were opened, the perivitelline layer overlying the GD region was collected and sperm were visualized with 4',6'-diamidino-2-phenylindole under a fluorescence microscope. To map the distribution of sperm, the GD was divided into six areas (A-F), with A being the centre of the GD and F the area furthest from the centre. In both species, more spermatozoa were found in areas B, C and D than in areas A, E and F. More than half the GD spermatozoa were found in areas B, C and D. The pattern of distribution of spermatozoa across the GD depended on the total number of sperm in the GD. In the emu, the pattern was related to delay since last copulation and time of laying, whereas in the ostrich the pattern was related to the month of the season and the sex ratio of the mating system. When the total number of spermatozoa in the GD increased, the number of spermatozoa increased in every area of the GD, but the centre and the outer areas were the least affected. We conclude that sperm numbers are highest in a band immediately around the centre of the GD and then decline with increasing distance from the centre. The low numbers in the centre of the GD may be due to either low attractiveness of the centre for sperm or high attractiveness of the area immediately adjacent to the centre.

Animals↗
PubMed2006

Mammalian monogamy is not controlled by a single gene.

Complex social behavior in Microtus voles and other mammals has been postulated to be under the direct genetic control of a single locus: the arginine vasopressin 1a receptor (avpr1a) gene. Using a phylogenetic approach, we show that a repetitive element in the promoter region of avpr1a, which reportedly causes social monogamy, is actually widespread in nonmonogamous Microtus and other rodents. There was no evidence for intraspecific polymorphism in regard to the presence or absence of the repetitive element. Among 25 rodent species studied, the element was absent in only two closely related nonmonogamous species, indicating that this absence is certainly the result of an evolutionarily recent loss. Our analyses further demonstrate that the repetitive structures upstream of the avpr1a gene in humans and primates, which have been associated with social bonding, are evolutionarily distinct from those in rodents. Our evolutionary approach reveals that monogamy in rodents is not controlled by a single polymorphism in the promoter region of the avpr1a gene. We thus resolve the contradiction between the claims for an evolutionarily conserved genetic programming of social behavior in mammals and the vast evidence for highly complex and flexible mating systems.

Animals↗
PubMed2003

Distinct geographic patterns of genetic diversity are maintained in wild barley (Hordeum vulgare ssp. spontaneum) despite migration.

Mutations arise in a single individual and at a single point in time and space. The geographic distribution of mutations reflects both historical population size and frequency of migration. We employ coalescence-based methods to coestimate effective population size, frequency of migration, and level of recombination compatible with observed genealogical relationships in sequence data from nine nuclear genes in wild barley (Hordeum vulgare ssp. spontaneum), a highly self-fertilizing grass species. In self-fertilizing plants, gamete dispersal is severely limited; dissemination occurs primarily through seed dispersal. Also, heterozygosity is greatly reduced, which renders recombination less effective at randomizing genetic variation and causes larger portions of the genome to trace a similar history. Despite these predicted effects of this mating system, the majority of loci show evidence of recombination. Levels of nucleotide variation and the patterns of geographic distribution of mutations in wild barley are highly heterogeneous across loci. Two of the nine sampled loci maintain highly diverged, geographic region-specific suites of mutations. Two additional loci include region-specific haplotypes with a much shallower coalescence. Despite inbreeding, sessile growth habit, and the observation of geographic structure at almost half of sampled loci, parametric estimates of migration suggest that seed dispersal is sufficient for migration across the approximately 3,500-km range of the species. Recurrent migration is also evident based on the geographic distribution of mutational variation at some loci. At one locus a single haplotype has spread rapidly enough to occur, unmodified by mutation, across the range of the species.

Biological Evolution↗
PubMed2003

Synteny perturbations between wheat homoeologous chromosomes caused by locus duplications and deletions correlate with recombination rates.

Loci detected by Southern blot hybridization of 3,977 expressed sequence tag unigenes were mapped into 159 chromosome bins delineated by breakpoints of a series of overlapping deletions. These data were used to assess synteny levels along homoeologous chromosomes of the wheat A, B, and D genomes, in relation to both bin position on the centromere-telomere axis and the gradient of recombination rates along chromosome arms. Synteny level decreased with the distance of a chromosome region from the centromere. It also decreased with an increase in recombination rates along the average chromosome arm. There were twice as many unique loci in the B genome than in the A and D genomes, and synteny levels between the B genome chromosomes and the A and D genome homoeologues were lower than those between the A and D genome homoeologues. These differences among the wheat genomes were attributed to differences in the mating systems of wheat diploid ancestors. Synteny perturbations were characterized in 31 paralogous sets of loci with perturbed synteny. Both insertions and deletions of loci were detected and both preferentially occurred in high recombination regions of chromosomes.

Chromosomes, Plant↗
PubMed2002

Uncoupling direct and indirect components of female choice in the wild.

One of the most controversial debates in evolutionary biology concerns the fitness consequences of female choice in nature. Discriminating females may benefit from high-quality territories and/or sires with high-quality genes. Here we experimentally dissociate female preferences for high-quality territories and male body size in a wild population of side-blotched lizards, Uta stansburiana. Females preferred experimentally improved territories but still chose high-quality sires for their progeny. High-quality territories were associated with earlier egg-laying dates and larger eggs. These maternal effects, evidently stimulated by high-quality territories, have been shown to enhance competitive ability and therefore the likelihood that philopatric offspring will capitalize on the direct benefits of superior territories, previously shown to promote progeny growth rate and survival (most offspring do not disperse from their natal area). Paternity analysis within clutches co-sired by two males revealed that female preferences for large males were also adaptive in terms of indirect benefits. Females used sperm from large sires to produce sons and sperm from small sires to produce daughters. Differential allocation of resources and progeny sex was adaptive and demonstrates a high degree of female control in the mating system.

Animals↗
PubMed1977

Genetic mapping of Rhizobium meliloti.

The drug resistance factor RP4, originally isolated in Pseudomonas, was transferred to Rhizobium meliloti. In that strain, RP4 promotes conjugational transfer of chromosomal markers to form haploid recombinants. This mating system has been used to construct a linkage map of R. meliloti.

Chromosome Mapping↗
PubMed1987

Correlations, descent measures: drift with migration and mutation.

The analysis of gene frequencies for a nested structure of genes within individuals, individuals within subpopulations, and subpopulations within populations is considered. Alternative parameterizations are provided by measures of correlation and of identity by descent, but the latter parameters provide more flexibility. The effects of population size, mating system, mutation, and migration can be incorporated into transition equations for identity measures and the structure of equilibrium populations can be determined; the procedures are illustrated for a finite island model. With parameters defined before estimation procedures are developed, problems of estimates depending on the numbers of sampled subpopulations are avoided, while the descent measures also avoid the approximations found in other treatments.

Emigration and Immigration↗
PubMed1993

Randomly amplified polymorphic DNA markers are superior to somatic incompatibility tests for discriminating genotypes in natural populations of the ectomycorrhizal fungus Suillus granulatus.

Assessing genetic variation within populations and genetic exchange between populations requires an understanding of the distribution and abundance of individual genotypes within the population. Previous workers have used somatic incompatibility testing to distinguish clones or individuals in natural populations of ectomycorrhizal fungi. However, somatic incompatibility tests performed with isolates of Suillus granulatus from a natural population revealed a lack of transitiveness, which brought into question the validity of this method. Subsequent studies of genetic identity of these isolates, using randomly amplified polymorphic DNA (RAPD) markers, conclusively showed that somatically compatible isolates are not necessarily genetically identical. RAPD marker analysis is more reliable and provides higher resolution of genotype distribution in natural populations than does somatic incompatibility testing. This is of particular importance in populations of organisms such as ectomycorrhizal fungi in which the mating systems are incompletely known.

Journal Article↗