Sib‐mating in the ant Plagiolepis pygmaea: adaptative inbreeding?

Multiple functional queens in a colony (polygyny) and multiple mating by queens (polyandry) in social insects challenge kin selection, because they dilute inclusive fitness benefits from helping. Colonies of the ant Plagiolepis pygmaea brash contain several hundreds of multiply mated queens. Yet, within‐colony relatedness remains unexpectedly high. This stems from low male dispersal, extensive mating among relatives and adoption of young queens in the natal colony. We investigated whether inbreeding results from workers expelling foreign males, and/or from preferential mating between related partners. Our data show that workers actively repel unrelated males entering their colony, and that queens preferentially mate with related males. These results are consistent with inclusive fitness being a driving force for inbreeding: by preventing outbreeding, workers reduce erosion of relatedness within colonies due to polygyny and polyandry. That virgin queens mate preferentially with related males could result from a long history of inbreeding, which is expected to reduce depression in species with regular sibmating.     

Has inbreeding depression led to avoidance of sib mating in the Glanville fritillary butterfly (Melitaea cinxia)?

Previous work on the Glanville fritillary butterfly (Melitaea cinxia) shows substantial inbreeding depression in both of our two study regions, Finland and southern France. The influence of inbreeding depression on population dynamics should depend on the strength of inbreeding avoidance. We conducted mate choice experiments to ascertain whether and to what extent butterflies avoid mating with their sibs. Experiments with similar design were done in the laboratory with Finnish butterflies and in the field with French butterflies. Each female was given a choice of mates with equal opportunity to mate with a sib or with a non-sib. In neither experiment was there a trend towards avoidance of sib mating. 95% confidence intervals for the proportion of non-sib matings were 12–62% in the laboratory experiment and 28–69% in the field experiment. Any preference for non-sibs must be slight, and can provisionally be ignored in modelling the dynamics of M. cinxia populations. This revised version was published online in August 2006 with corrections to the Cover Date.     

Are transcriptional responses to inbreeding a functional response to alleviate inbreeding depression?

Previous studies addressing the relationship between gene regulation and inbreeding depression did not allow for discerning the changes that alleviate the depression from those that generate it. We directly addressed this question by analyzing changes in gene expression, using Affymetrix 2.0 arrays in Drosophila melanogaster inbred sublines differing in their magnitudes of inbreeding depression relative to the expression in an outbred control. The total number of arrays analyzed was 27, with 9,133 probe sets showing a significant signal of expression. We found that for those genes differentially expressed between inbred and outbred sublines, most of them showed a pattern of expression consistent with a protective role against inbreeding effects. The observed increase in depression was presumably related to an inability of the genome to do the appropriate expression adjustments. Expression changes detected in our study showed a clear specificity of RNA-splicing and energy derivation functions. Thus, it appears that most of the observed changes in gene expression associated with inbreeding may occur predominantly to alleviate inbreeding depression, i.e., as a protection against the effects of inbreeding.     

Does inbreeding affect personality traits?

The question of why variation is maintained in personality traits is an evolutionary puzzle. According to the condition‐dependence hypothesis, such traits depend on condition, which limits the behavioral choices available to individuals. Because condition is affected by many genes, it can effectively be manipulated by inbreeding, which exposes the effects of deleterious recessive mutations. Here, I compared two personality traits, boldness and tendency to explore, of male guppies (Poecilia reticulata) from first‐generation inbred and outbred treatments. Boldness in guppies is associated with increased sexual attractiveness and is thus expected to affect fitness. Therefore, I hypothesized that the personality traits would be negatively affected by inbreeding. However, the results indicated that inbred guppies did not differ in either personality trait from their outbred counterparts. This finding suggests that mechanisms other than condition dependence are maintaining personality variation in the guppy.     

Structure-activity relationship of α hormones, the mating factors of phytopathogen Phytophthora

The mating hormones α1 and α2 induce sexual reproduction of the phytopathogenic genus Phytophthora. To demonstrate the structural elements responsible to hormonal activity, 17 derivatives of α1 and α2 were synthesized and their hormonal activity (oospore-inducing activity) was evaluated. The terminal ester derivatives of α1 (diacetate and dibenzoate) retained the hormonal activity, whereas a dicarbamate derivative completely suppressed the activity. Even monocarbamates showed weak activities; among them the 1-O-carbamate was less active than 16-O-carbamate, suggesting that the 1-OH group is a little more important than 16-OH. Dihydro, dehydro, and demethyl derivatives exhibited the minimum level of activity. Surviving activity of 15-epi-α1 suggested a less importance of this stereochemistry. Contrary to α1, not only the terminal diacetate derivative but also monoacetates of α2 exhibited no or little activity. Among the monoacetates, 1-O-acetyl-α2 exhibited little yet relatively better activity than the others. No activity was observed for mono- and dicarbamoyl derivatives of α2. Dihydro α2 with the saturated double bond lost most of the activity. These findings suggest that both the mating hormones α1 and α2 require most of the functional (hydroxyl, keto, and olefinic) groups they possess in their natural form for inducing the sexual reproduction of Phytophthora.     

Does heterozygosity estimate inbreeding in real populations?

Many recent studies report that individual heterozygosity at a handful of apparently neutral microsatellite markers is correlated with key components of fitness, with most studies invoking inbreeding depression as the likely underlying mechanism. The implicit assumption is that an individual's inbreeding coefficient can be estimated reliably using only 10 or so markers, but the validity of this assumption is unclear. Consequently, we have used individual-based simulations to examine the conditions under which heterozygosity and inbreeding are likely to be correlated. Our results indicate that the parameter space in which this occurs is surprisingly narrow, requiring that inbreeding events are both frequent and severe, for example, through selfing, strong population structure and/or high levels of polygyny. Even then, the correlations are strong only when large numbers of loci (~200) can be deployed to estimate heterozygosity. With the handful of markers used in most studies, correlations only become likely under the most extreme scenario we looked at, namely 20 demes of 20 individuals coupled with strong polygyny. This finding is supported by the observation that heterozygosity is only weakly correlated among markers within an individual, even in a dataset comprising 400 markers typed in diverse human populations, some of which favour consanguineous marriages. If heterozygosity and inbreeding coefficient are generally uncorrelated, then heterozygosity-fitness correlations probably have little to do with inbreeding depression. Instead, one would need to invoke chance linkage between the markers used and one or more gene(s) experiencing balancing selection. Unfortunately, both explanations sit somewhat uncomfortably with current understanding. If inbreeding is the dominant mechanism, then our simulations indicate that consanguineous mating would have to be vastly more common than is predicted for most realistic populations. Conversely, if heterosis provides the answer, there need to be many more polymorphisms with major fitness effects and higher levels of linkage disequilibrium than are generally assumed.     

Does inbreeding affect N-glycosylation of human plasma proteins?

Inbreeding depression and heterosis are the two ends of phenotypic changes defined by the genome-wide homozygosity. The aim of this study was to investigate the association of genetic marker-based homozygosity estimates with 46 N-glycan features measured in human plasma. The study was based on a total of 2,341 subjects, originating from three isolated island communities in Croatia (Vis and Korcula islands) and Scotland (Orkney Islands). Inbreeding estimates were associated with an increase in tetrantennary and tetrasialylated glycans, and a decrease in digalactosylated glycans (P?相似文献   

Does pollen competition reduce the cost of inbreeding?

We hypothesize that floral features promoting pollen competition in angiosperms may have evolved, in some cases, in response to selection generated by the negative effects of inbreeding, at least in plants with mixed-mating systems. Screening of haploid genotypes through pollen competition may purge recessive (or additive) deleterious alleles that are expressed in haploid pollen and hence may reduce the fitness cost of self-pollination, geitonogamy, or biparental inbreeding. We tested one prediction of this hypothesis, that offspring produced by more intense competition among self-pollen have higher fitness than offspring produced by less intense competition. Dalechampia scandens (Euphorbiaceae) flowers were pollinated with pollen from other flowers on the same plant (geitonogamous self-fertilization). Those flowers experiencing more intense pollen competition as a result of low pollen dispersion (positional variance) on the stigma produced heavier seeds and seedlings with faster-growing radicles than flowers experiencing less intense pollen competition (high pollen dispersion), as predicted by our hypothesis.     

Patterns of mating call preferences in túngara frogs, Physalaemus pustulosus

We examine acoustic mating preferences of a focal population at four different scales of divergence: within the population, between populations in the same genetic group, between populations in different genetic groups and between different species. At all scales there is substantial genetic divergence, variation in mating signals and preferences are influenced by signal variation. There is, however, no support for the hypothesis that mating preferences accumulate predictably with genetic distance. Females preferred the local conspecific call to the foreign conspecific call in about one-third of the experiments, and preferred the local call to all of the heterospecific calls tested. But there was no significant relationship between the variation in the strength of preference and genetic distance either among conspecific populations, or among heterospecific species. Thus, in this study macroevolutionary patterns are not apparent at the microevolutionary scale.     

Single mating type-specific genes and their 3′ UTRs control mating and fertility in Cochliobolus heterostrophus

To determine the number of proteins required for mating type (MAT) locus-regulated control of mating in Cochliobolus heterostrophus, MAT fragments of various sizes were expressed in MAT deletion strains. As little as 1.5?kb of MAT sequence, encoding a single unique protein in each mating type (MAT-1 and MAT-2), conferred mating ability, although an additional 160?bp of 3^′ UTR was needed for production of ascospores. No other mating type-specific genes involved in mating identity or fertility were found. Thus, although homologs of the C. heterostrophus MAT-1 and MAT-2 genes exist in the filamentous ascomycetes Neurospora crassa and Podospora anserina, C. heterostrophus does not appear to have mating type-specific homologs of two additional genes required by both N. crassa and P.?anserina for successful sexual reproduction. Three genes were identified in the common DNA flanking the MAT locus: a gene encoding a GTPase-activating protein and an ORF of unknown function lie 5^′ while a β-glucosidase encoding gene lies found 3^′. None of these genes appears to be involving in the mating process.     

Genetic diversity, mating system, and conservation of a Mexican subalpine relict, Picea mexicana Martínez

Mexican spruce (Picea mexicana Martínez), an endangered species of the highest sky islands in México's Sierra Madre Oriental and Sierra Madre Occidental, is threatened by fire, grazing, and global warming. Its conservation depends on whether it also is threatened by inbreeding and loss of genic diversity. We used 18 isozyme markers in 12 enzyme systems to assay genic diversity, characterize the mating system, and test for recent bottlenecks in three known populations. Unbiased, expected heterozygosity (H _e ) averaged 0.125. Despite a separation of 676 km between populations in the Sierra Madre Oriental and the Sierra Madre Occidental, Wright's F _ST , the proportion of total genic diversity among populations, was only 6.9%. Nei's genetic distance was 0.001 between the populations in the Sierra Madre Oriental and more than an order of magnitude greater, 0.019, between the Sierra Madre Oriental and Sierra Madre Occidental. However, both values point to relatively recent divergence. Mating systems were predominantly outcrossing, but with significant selfing. Multilocus estimates of selfing varied from 19% to 41%, and the means of single-locus estimates were higher, suggesting that additional inbreeding occurred by mating among relatives. Despite significant inbreeding, observed heterozygosity was as high as or higher than H _e ; Wright's fixation index, F _IS , was –0.107. Under the observed level of selfing, positive values of F _IS were expected. Therefore, selection against inbreds and homozygotes must be intense. Cornuet-Luikart tests indicate recent bottlenecks in at least two of the three populations. The results suggest that Mexican spruce is a genetically viable species, and threats are primarily environmental.     

Genetic variation,inbreeding and chemical exposure—combined effects in wildlife and critical considerations for ecotoxicology

Exposure to environmental chemicals can have negative consequences for wildlife and even cause localized population extinctions. Resistance to chemical stress, however, can evolve and the mechanisms include desensitized target sites, reduced chemical uptake and increased metabolic detoxification and sequestration. Chemical resistance in wildlife populations can also arise independently of exposure and may be spread by gene flow between populations. Inbreeding—matings between closely related individuals—can have negative fitness consequences for natural populations, and there is evidence of inbreeding depression in many wildlife populations. In some cases, reduced fitness in inbred populations has been shown to be exacerbated under chemical stress. In chemical testing, both inbred and outbred laboratory animals are used and for human safety assessments, iso-genic strains (virtual clones) of mice and rats are often employed that reduce response variation, the number of animals used and associated costs. In contrast, for environmental risk assessment, strains of animals are often used that have been selectively bred to maintain heterozygosity, with the assumption that they are better able to predict adverse effects in wild, genetically variable, animals. This may not necessarily be the case however, as one outbred strain may not be representative of another or of a wild population. In this paper, we critically discuss relationships between genetic variation, inbreeding and chemical effects with the intention of seeking to support more effective chemical testing for the protection of wildlife.     

Habitat fragmentation,genetic diversity,and inbreeding depression in a threatened grassland legume: is genetic rescue necessary?

Kincaid’s lupine (Lupinus oreganus), a threatened perennial legume of western Oregon grasslands, is composed of small, fragmented populations that have consistently low natural seed set, suggesting they may have accumulated high enough levels of genetic load to be candidates for genetic rescue. We used simple sequence repeat (SSR) loci, both nuclear DNA and chloroplast DNA, to screen populations throughout the species’ range for evidence of severe inbreeding and recent genetic bottlenecks due to habitat fragmentation. After genotyping about 40% of the known populations, only one of 24 populations had strong statistical evidence for a recent genetic bottleneck (H _e > H _eq). Both mean nSSR fixation coefficients and genetic diversity did not statistically differ between very small, small, medium, and large lupine population size classes. Within population chloroplast DNA haplotype number was high for an animal pollinated species, ≈4.2 haplotypes/population, and within population haplotype diversity was also relatively evenly distributed. Within population patterns of nSSR and cpSSR genetic diversity suggest that genetic diversity has not been lost over the last century of habitat fragmentation. With genet lifespan thought to exceed 100 years, overlap of several to many generations, and substantial reductions in seed set from inbreeding depression that shifts cohort composition towards those generated by outcrossing events, Kincaid’s lupine is likely maintain the currently high levels of within population genetic diversity. The case of Kincaid’s lupine provides an example of how the assumptions of severe inbreeding depression with small population size and habitat fragmentation can be inaccurate.     

Can varying inbreeding depression select for intermediary selfing rates?

We study the evolution of the self-fertilization of an annual hermaphroditic plant under varying inbreeding depression. While classical population genetic models treat inbreeding depression as a constant parameter, recent empirical research has shown that changing environmental conditions can make inbreeding depression vary. Here, we create a simple phenotypic model, assuming variable inbreeding depression. We investigate how different types of variability (spatial, temporal, and spatiotemporal variability) affect the evolution of selfing rates in three models. Two main results, which differ from the classical predictions, emerge from this study. First, we find that fluctuating environments, which influence the magnitude of inbreeding depression, are able to select for evolutionarily stable intermediary selfing rates. Second, we show that spatiotemporal variation of inbreeding depression can lead to the development and the maintenance of polymorphic selfing rates within a population.     

Single mating type-specific genes and their 3′ UTRs control mating and fertility in Cochliobolus heterostrophus

To determine the number of proteins required for mating type (MAT) locus-regulated control of mating in Cochliobolus heterostrophus, MAT fragments of various sizes were expressed in MAT deletion strains. As little as 1.5 kb of MAT sequence, encoding a single unique protein in each mating type (MAT-1 and MAT-2), conferred mating ability, although an additional 160 bp of 3^′ UTR was needed for production of ascospores. No other mating type-specific genes involved in mating identity or fertility were found. Thus, although homologs of the C. heterostrophus MAT-1 and MAT-2 genes exist in the filamentous ascomycetes Neurospora crassa and Podospora anserina, C. heterostrophus does not appear to have mating type-specific homologs of two additional genes required by both N. crassa and P.␣anserina for successful sexual reproduction. Three genes were identified in the common DNA flanking the MAT locus: a gene encoding a GTPase-activating protein and an ORF of unknown function lie 5^′ while a β-glucosidase encoding gene lies found 3^′. None of these genes appears to be involving in the mating process. Received: 21 November 1997 / Accepted: 28 April 1998     

Isolation and amino acid sequence of a mating pheromone produced by mating type α cells of Saccharomyces exiguus

A peptide, termed α^se pheromone, was isolated as a mating pheromone from culture filtrate of mating type a cells of Saccharomyces exiguus. The peptide showed both agglutinability-inducing activity to a cells of S. cerevisiae and shmoo-inducing action to a cells of S. cerevisiae, S. kluyveri and S. exiguus. The amino acid sequence of α^se pheromone was determined as H-Trp-His-Trp-Leu-Arg-Leu-Ser-Tyr-Gly-Gln-Pro-Ile-Tyr-OH by mass spectrometry, sequence analysis and enzymatic digestion.     

Rapid decrease in horn size of bighorn sheep: environmental decline, inbreeding depression, or evolutionary response to trophy hunting?

There are numerous examples demonstrating that selection has greatly influenced phenotypes in wild-harvested species. Here, a significant reduction in horn size in trophy desert bighorn sheep rams over 30 years in a reintroduced population in Aravaipa Canyon, Arizona is documented. After examining the potential effects of a detrimental change in the environment, inbreeding depression, and hunter-caused evolutionary change, it appears that environmental deterioration, apparently from the effects of drought, may be a major cause of the decline in horn size. In particular, the reduction in ram horn size is positively associated with reduced winter lifetime rainfall over the 3 decades. Over the same period, the demographic indicator lamb-to-ewe ratio has also declined in the Aravaipa population. On the other hand, lamb-to-ewe ratio has not declined statewide in Arizona, and the population size in Aravaipa appears to be increasing, suggesting local- and trait-specific effects. Using a theoretical context, neither inbreeding depression nor hunter selection by themselves appear to the sole causes of the lower horn size. However, some combination of environmental factors, inbreeding depression, and hunter selection may have caused the decrease in observed horn size. It is not clear what management actions might be successful in countering the environmental effects on horn size, but supplemental feeding and cattle removal are suggested while translocation is suggested to counter the effects of inbreeding depression and reduced hunting and translocation are suggested to counter the effects of hunter selection.