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PubMed1979

Female transference and mate choice among Tana River red colobus.

Red colobus are one of a small number of primate species in which females have been reported to transfer between breeding groups more commonly than males. Several authors have hypothesised that in such species transference may serve to reduce the risk to females of producing offspring of lower fitness through inbreeding. The hypothesis offers no explanation of why females rather than males are responsible for outbreeding in these species, but remains plausible so long as male membership of breeding groups is relatively stable; for once members of one sex have evolved dispersal mechanisms reducing the risk of inbreeding, pressures on the other sex to do likewise will be lowered. Hence, if both sexes commonly migrate, the hypothesis is weakened. I describe here the membership dynamics of a group of Tana River red colobus, Colobus badius rufomitratus, which provide the first evidence of high rates of membership turnover by both sexes in primates, and speculate that the function of female transference in this case may be related to mate choice and the avoidance of infanticide.

Animals↗
PubMed2001

Female sticklebacks count alleles in a strategy of sexual selection explaining MHC polymorphism.

The origin and maintenance of polymorphism in major histocompatibility complex (MHC) genes in natural populations is still unresolved. Sexual selection, frequency-dependent selection by parasites and pathogens, and heterozygote advantage have been suggested to explain the maintenance of high allele diversity at MHC genes. Here we argue that there are two (non-exclusive) strategies for MHC-related sexual selection, representing solutions to two different problems: inbreeding avoidance and parasite resistance. In species prone to inadvertent inbreeding, partners should prefer dissimilar MHC genotypes to similar ones. But if the goal is to maximize the resistance of offspring towards potential infections, the choosing sex should prefer mates with a higher diversity of MHC alleles. This latter strategy should apply when there are several MHC loci, as is the case in most vertebrates. We tested the relative importance of an 'allele counting' strategy compared to a disassortative mating strategy using wild-caught three-spined sticklebacks (Gasterosteus aculeatus) from an interconnected system of lakes. Here we show that gravid female fish preferred the odour of males with a large number of MHC class-IIB alleles to that of males with fewer alleles. Females did not prefer male genotypes dissimilar to their own.

Alleles↗
PubMed1992

Parents suppress reproduction and stimulate dispersal in opposite-sex juvenile white-footed mice.

Juvenile dispersal is sex-biased in many mammals and birds: one sex often disperses more often or farther than the other. Two hypotheses are generally presented for sex-biased dispersal. The first holds that juvenile dispersal reduces reproductive and/or resource competition between parents and same-sexed offspring. If so, presence of a parent on the natal home range should both promote dispersal of same-sex offspring and suppress reproduction of those that remain. The second is that juvenile dispersal reduces matings between parents and offspring, thus decreasing the likelihood of inbreeding depression. If so, presence of a parent should favour dispersal and reproductive suppression of offspring of the opposite sex. Here I present evidence that juvenile dispersal in white-footed mice, Peromyscus leucopus, is due to inbreeding avoidance. When population density was high, experimental removal of one parent delayed dispersal of opposite-sexed offspring and only the presence of the parents of opposite sex suppressed juvenile reproduction.

Animals↗
PubMed2002

Genetic cost of reproductive assurance in a self-fertilizing plant.

The transition from outcrossing to self-fertilization is one of the most common evolutionary trends in plants. Reproductive assurance, where self-fertilization ensures seed production when pollinators and/or potential mates are scarce, is the most long-standing and most widely accepted explanation for the evolution of selfing, but there have been few experimental tests of this hypothesis. Moreover, many apparently adaptive floral mechanisms that ensure the autonomous production of selfed seed might use ovules that would have otherwise been outcrossed. This seed discounting is costly if selfed offspring are less viable than their outcrossed counterparts, as often happens. The fertility benefit of reproductive assurance has never been examined in the light of seed discounting. Here we combine experimental measures of reproductive assurance with marker-gene estimates of self-fertilization, seed discounting and inbreeding depression to show that, during 2 years in 10 Ontario populations of Aquilegia canadensis (Ranunculaceae), reproductive assurance through self-fertilization increases seed production, but this benefit is greatly outweighed by severe seed discounting and inbreeding depression.

Fertility↗
PubMed1980

An inbred strain of rats with a high incidence of squamous-cell carcinomas of the mouth.

Intra-oral squamous-cell carcinomas occurred in over 50% of the HMT inbred strain of rats. In the outbred stock from which it was derived the incidence was 5% or less, both when inbreeding was begun and after the inbred strain was fully established. Various factors in food and husbandry which might have irritated the oral mucosa were investigated, but there was no signficiant evidence that they played any part in the high incidence of mouth tumours. It is concluded that there must have been an accidental selection during inbreeding in favour of rats which had an inherited tendency to develop squamous-cell carcinoma of the mouth. There are a number of similarities between the rat tumour and intra-oral squamous-cell carcinoma in man and it is suggested that the rat tumour could be used as a model of the human disease.

Animals↗
PubMed1977

The evolution of dominance: Haldane v Fisher revisited.

Fisher's model for the evolution of dominance indicates that the accumulation of dominance modifiers will be accelerated by (1) an increased frequency of the mutant heterozygote, (2) increased selection for the phenotype of the normal homozygote. The model has been criticised by Haldane on the grounds that point (1) is not fulfilled, that is dominance appears to be more common in populations with a low frequency of mutant heterozygotes (populations of inbreeders). In support of Fisher's model it is argued that intense selection for the wild type phenotype is more common in inbreeders than outbreeders. This situation should promote the accumulation of dominance modifiers (point (2) above).

Biological Evolution↗
PubMed1994

Mitochondrial DNA sequence divergence among some west European brown bear (Ursus arctos L.) populations. Lessons for conservation.

We used the polymerase chain reaction and nucleotide sequencing to study mitochondrial DNA (mtDNA) genetic variability of brown bears (Ursus arctos) belonging to some western European populations. Demographic decline and isolation have apparently shaped genetic variability within and between populations. Small relict bear populations were apparently monomorphic and fixed for different mtDNA haplotypes. Genetic relationships among mtDNA haplotypes suggested the existence of a phylogeographic structure. We discuss the possible roles of historical and demographic factors in determining the observed genetic patterns. The low genetically effective size of the studied brown bear populations points to risks of continuing future loss of gene diversity and increase in inbreeding. Artificial gene flow through restocking could alleviate inbreeding depression in small isolated brown bear populations, and mtDNA phylogeographic relationships may provide a framework for their genetic management.

Animals↗
PubMed2003

Females increase offspring heterozygosity and fitness through extra-pair matings.

Females in a variety of species commonly mate with multiple males, and there is evidence that they benefit by producing offspring of higher genetic quality; however, the nature of these genetic benefits is debated. Enhanced offspring survival or quality can result from intrinsic effects of paternal genes---'good genes'--or from interactions between the maternal and paternal genomes--'compatible genes'. Evidence for the latter process is accumulating: matings between relatives lead to decreased reproductive success, and the individual level of inbreeding--measured as average heterozygosity--is a strong fitness predictor. Females should thus benefit from mating with genetically dissimilar males. In many birds, social monogamy restricts mate choice, but females may circumvent this by pursuing extra-pair copulations. Here we show that female blue tits, Parus caeruleus, increase the heterozygosity of their progeny through extra-pair matings. Females thereby produce offspring of higher reproductive value, because less inbred individuals have increased survival chances, a more elaborate male secondary sexual trait (crown colour) and higher reproductive success. The cost of inbreeding may therefore be an important factor driving the evolution of female extra-pair mating.

Animals↗
PubMed2005

Mate fidelity and intra-lineage polygyny in greater horseshoe bats.

Mating strategies that lead to increased kinship within socially cooperative groups may offer inclusive fitness benefits to individuals, but can also result in higher levels of inbreeding. Here we show in a sexually segregated bat species that females avoid this conflict through two mating behaviours. First, most females revisit and breed with specific, individual males across years, so that their single offspring born in different years are full siblings. Second, relatives in the maternal line, including mothers and daughters, share breeding partners (intra-lineage polygyny) more often than expected by chance. Although these behaviours increased levels of co-ancestry among colony members, there was no concomitant rise in inbreeding. We suggest that when females engage in mate fidelity and intra-lineage polygyny, kin ties among female roost mates will be strengthened, thereby potentially contributing to social group cohesiveness. Our findings reveal the hidden complexity that can underlie polygynous breeding, and highlight a new potential route by which female mate choice could influence social evolution.

Animals↗
PubMed2005

Complex haplotypes, copy number polymorphisms and coding variation in two recently divergent mouse strains.

Inbred mouse strains provide the foundation for mouse genetics. By selecting for phenotypic features of interest, inbreeding drives genomic evolution and eliminates individual variation, while fixing certain sets of alleles that are responsible for the trait characteristics of the strain. Mouse strains 129Sv (129S5) and C57BL/6J, two of the most widely used inbred lines, diverged from common ancestors within the last century, yet very little is known about the genomic differences between them. By comparative genomic hybridization and sequence analysis of 129S5 short insert libraries, we identified substantial structural variation, a complex fine-scale haplotype pattern with a continuous distribution of diversity blocks, and extensive nucleotide variation, including nonsynonymous coding SNPs and stop codons. Collectively, these genomic changes denote the level and direction of allele fixation that has occurred during inbreeding and provide a basis for defining what makes these mouse strains unique.

Animals↗
PubMed2000

A robust test for assortative mating.

Testing for random mating in human populations is difficult due to confounding factors such as ethnic preference and population stratification. With HLA, the high level of polymorphism is an additional problem since it is rare for couples to share the same haplotype. Focus on an ethnically homogeneous population, where levels of polymorphism at HLA loci are more limited, may provide the best situation in which to detect non-random mating. However, such populations are often genetic isolates where there may be inbreeding to an extent that is difficult to quantify and account for. We have developed a test for random mating at a multiallelic locus that is robust to stratification and inbreeding. This test relies on the availability of genotypic information from the parents of both spouses. The focus of the test is on families where there is allele sharing between the parents of both spouses, so that potential spouses could share an allele. Denoting the shared allele at the locus of interest by A, then under the assumption of random mating, heterozygous parents AX should transmit allele A equally as frequently as allele X to their offspring. When there is positive (negative) assortative mating, A will be transmitted more (less) often than X. The power of the test has been computed in a number of situations. Data on high resolution HLA haplotypes from the Hutterite population were reinvestigated by the proposed test. The test detects significant negative assortative mating when the parental origin of the shared haplotype is taken into account.

Alleles↗
PubMed2003

Population structure, mating system, and sex-determining allele diversity of the parasitoid wasp Habrobracon hebetor.

Besides haplo-diploid sex determination, where females develop from fertilized diploid eggs and males from unfertilized haploid eggs, some Hymenoptera have a secondary system called complementary sex determination (CSD). This depends on genotypes of a 'sex locus' with numerous sex-determining alleles. Diploid heterozygotes develop as females, but diploid homozygotes become sterile or nonviable diploid males. Thus, when females share sex-determining alleles with their mates and produce low fitness diploid males, CSD creates a genetic load. The parasitoid wasp Habrobracon hebetor has CSD and displays mating behaviours that lessen CSD load, including mating at aggregations of males and inbreeding avoidance by females. To examine the influence of population structure and the mating system on CSD load, we conducted genetic analyses of an H. hebetor population in Wisconsin. Given the frequency of diploid males, we estimated that the population harboured 10-16 sex-determining alleles. Overall, marker allele frequencies did not differ between subpopulations, but frequencies changed dramatically between years. This reduced estimates of effective size of subpopulations to only N3 approximately 20-50, which probably reflected annual fluctuations of abundance of H. hebetor. We also determined that the mating system is effectively monogamous. Models relating sex-determining allele diversity and the mating system to female productivity showed that inbreeding avoidance always decreased CSD loads, but multiple mating only reduced loads in populations with fewer than five sex-determining alleles. Populations with N3 less than 100 should have fewer sex-determining alleles than we found, but high diversity could be maintained by a combination of frequency-dependent selection and gene flow between populations.

Alleles↗
PubMed2004

Invasion dynamics of two alien Carpobrotus (Aizoaceae) taxa on a Mediterranean island: II. Reproductive strategies.

This study compares sexually and asexually produced fruit set, seed production, biomass, germination, and seedling size in Carpobrotus acinaciformis and C. edulis following controlled pollination experiments in order to evaluate the potential role of reproductive traits with respect to the invasive potential of these taxa. C. edulis is slightly agamospermic, completely self-fertile, slightly preferentially self-compatible, experiences no inbreeding depression, and has low hybrid vigour. In contrast, C. acinaciformis does not have reliable agamospermy, is only slightly self-fertile and self-compatible, experiences a slight inbreeding depression, and has a strong hybrid vigour. Both taxa have relatively low, although significantly different germination frequencies, and insignificantly different seedling sizes. Owing to the high performance in hybridisation as compared to all other controlled pollinations in C. acinaciformis, as well as a large amount of previously demonstrated introgression, we refer to the population studied on the island of Bagaud (France) as C. affine acinaciformis. We conclude that both C. edulis and C. affine acinaciformis should be considered as harmful invasive plants in the Mediterranean Basin, the former because of the flexibility of its mating system and high seed production, and the latter because of its strong clonality, high hybrid vigour, and potential for continued introgression from C. edulis genes. These differences require different control strategies, while the avoidance of sympatry is a distinct priority.

Aizoaceae↗
PubMed2005

Ontogenetic change in relative performance of allozyme genotypes influences detection of heterosis in the earthworm Eisenia andrei.

The effect of ontogeny on relationships between allozyme genotypes and fresh weight was measured weekly throughout the life history of the earthworm Eisenia andrei to test the hypothesis that there is an ontogenetic component to variation in such relationships. Two of six allozyme loci showed a significant increase in apparent heterosis with ontogeny, while one locus showed a significant decrease in apparent heterosis. Three loci showed a significant decrease in the performance of common homozygotes with ontogeny. Patterns of relative genotypic performance varied among loci, but the cumulative effect was an increase in apparent allozyme heterosis later in ontogeny coinciding with a series of positive relationships between multilocus heterozygosity and fresh weight. The results could not be used to determine whether these patterns were caused by selection acting on the loci directly or on loci tightly linked to allozyme loci. However, because the same individuals were used throughout this study and thus allele frequencies and heterozygote deficiency were constant, the presence of both ontogenetic effects and differences in such patterns among loci is not compatible with a general inbreeding effect. Examining relative genotypic performance repetitively using the same individuals through ontogeny or in different environments is a very powerful experimental design for testing the effects of inbreeding or other populational factors.

Animals↗
PubMed2005

Single-locus complementary sex determination absent in Heterospilus prosopidis (Hymenoptera: Braconidae).

In the haplodiploid Hymenoptera, haploid males arise from unfertilized eggs, receiving a single set of maternal chromosomes while diploid females arise from fertilized eggs and receive both maternal and paternal chromosomes. Under single-locus complementary sex determination (sl-CSD), sex is determined by multiple alleles at a single locus. Sex locus heterozygotes develop as females, while hemizygous and homozygous eggs develop as haploid and diploid males, respectively. Diploid males, which are inviable or sterile in almost all cases studied, are therefore produced in high frequency under inbreeding or in populations with low sex allele diversity. CSD is considered to be the ancestral form of sex determination within the Hymenoptera because members of the most basal taxa have CSD while some of the more derived groups have other mechanisms of sex determination that produce the haplo-diploid pattern without penalizing inbreeding. In this study, we investigated sex determination in Heterospilus prosopidis Viereck, a parasitoid from a relatively primitive subfamily of the Braconidae, a hymenopteran family having species with and without CSD. By comparing sex ratio and mortality patterns produced by inbred and outbred females, we were able to rule out sl-CSD as a sex determination mechanism in this species. The absence of sl-CSD in H. prosopidis was unexpected given its basal phylogenetic position in the Braconidae. This and other recent studies suggest that sex determination systems in the Hymenoptera may be evolutionary labile.

Animals↗
PubMed2006

Effect of variation in herkogamy on outcrossing within a population of Gilia achilleifolia.

The diverse features of floral morphology are often thought to be well-designed mechanisms to manipulate plant mating systems. We evaluated the effectiveness of one such mechanism, anther-stigma separation (herkogamy), in controlling variation in the level of outcrossing among plants in a population of Gilia achilleifolia. Variation in outcrossing rates within populations has the potential to influence the coevolution between inbreeding depression and mating system. Using four polymorphic allozymes, we compared the outcrossing-rate estimates of two groups of individuals under natural conditions: one group with low herkogamy and another with high herkogamy. The high herkogamy group had a higher outcrossing rate (0.572) than the low herkogamy group (0.335). This suggests that the within-population variation in outcrossing rate could potentially cause the previously observed association between herkogamy and inbreeding depression (Takebayashi and Delph, 2000). A previous study of floral traits among G. achilleifolia populations failed to detect a relationship between herkogamy and outcrossing rate, demonstrating that the functionality of traits may be obscured in among-population studies as a consequence of uncontrolled environmental variation. Additionally, the effect of herkogamy on outcrossing rate in delayed selfers such as G. achilleifolia may be particularly prominent when pollinator availability is low. Our population-level estimate of outcrossing rate (0.444) was somewhat lower than an estimate from the same population, 15 years prior to our study (0.75), suggesting that pollinator availability may fluctuate among years. Both within-year and among-year variation in the outcrossing rate may have a strong influence on mating-system evolution.

Analysis of Variance↗
PubMed1999

Effect of population size on the mating system in a self-compatible, autogamous plant, aquilegia canadensis (Ranunculaceae)

In self-compatible plants, small populations may experience reduced outcrossing owing to decreased pollinator visitation and mate availability. We examined the relation between outcrossing and population size in eastern Ontario populations of Aquilegia canadensis. Experimental pollinations showed that the species is highly self-compatible, and can achieve full seed-set in the absence of pollinators via automatic self-pollination. We estimated levels of outcrossing (t) and parental inbreeding coefficients (F) from allozyme variation in naturally pollinated seed families for 10 populations ranging in size from 32 to 750 reproductive individuals. The proportion of seeds produced through outcrossing was generally low (mean = 0.29 +/- 0.02 SE) and varied widely among populations (range = 0.00-0.83). Accordingly, estimates of F were large (mean = 0.26 +/- 0.05) and significantly greater than zero in seven populations. As expected, four small populations (N < 40) outcrossed less (0.17 +/- 0.03) than six large populations (N > 90; 0.38 +/- 0. 03). However, parental plants were not significantly more inbred in small than large populations (P = 0.18). There was no difference in the germination of seeds from hand self- and cross-pollinations. However, population genetic estimates of inbreeding depression for survival expressed from seed to reproductive maturity were very high (mean delta = 1 - relative fitness of selfed seed = 0.88 +/- 0.14). The combination of self-compatibility and automatic self-pollination makes the mating system of A. canadensis sensitive to variation in ecological factors that affect the likelihood of cross-pollination.

Journal Article↗
PubMed2003

Evaluation of the present breeding programme against copper toxicosis in Danish Bedlington terriers.

A breeding programme to eradicate copper toxicosis in Danish Bedlington terriers has been established based on a DNA marker test. Genotyping of both parents is compulsory and after 1 January 2000, only homozygous non-carriers are used for breeding. In this study, two groups of Bedlington terriers were genotyped at 18 microsatellite loci. One group represented the original population of Bedlington terriers before introducing the breeding programme (n = 23); the other represented a group of homozygous non-carriers (n = 24) available for breeding after year 2000. Allele numbers, allele frequencies, observed heterozygosities (Ho), expected heterozygosities (He), locus-specific coefficients of inbreeding (Fl) and Nei's genetic distance (D) was calculated. Individual coefficients of inbreeding (Fi) were calculated from the pedigrees and an assignment test was performed. Four rare alleles were lost in the group of homozygous non-carriers. No significant differences were observed between the mean values of allele numbers, Ho, He, Fl and Fi of the two populations of dogs. Nei's genetic distance between the two populations was 0.06 and 88% of the homozygous non-carriers were assigned correctly in the assignment test. The overall diversity of the breed was low (Ho = 0.41) and the breeders were advised to include the heterozygous carriers again.

Alleles↗