Inbreeding effects on lifetime in David's deer (Elaphurus davidianus,Milne Edwards 1866) population

The current population of David's deer is derived from 18 individuals kept in Woburn Abbey Park (England). The aim of this study is to evaluate the inbreeding rate as well as inbreeding depression in longevity. The recorded data have been extracted from the International Species Information System (ISIS). Complete records of 2042 individuals (born in 1947-2000) from zoological gardens were studied. The following four subsets of data were formed: all individuals, individuals over 31 days of life, sexually mature individuals (above 450 days old) and individuals with identified sex. Two models (including inbreeding coefficient as linear and quadratic covariables, respectively) have been employed. These computations were performed by the use of the DFREML package programs. This study has shown that average levels of inbreeding in the David's deer are relatively low (no exceed 0.028). The highest level of inbreeding was registered for mature individuals. In general, the average inbreeding on length of life was small for the above mentioned the inbreeding level (from 24 days to 77 days). However, on the basis estimated regression coefficients it can be suggested that an increase of inbreeding could lead to a drastic reduction of longevity. Relationships between inbreeding level and longevity are usually better described by quadratic partial regression (except for the oldest individuals). On the other hand, from a statistical point of view, a relatively low inbreeding level of the population studied is not suitable to derive the slope of the dependencies.     

Inbreeding depression and male survivorship in Drosophila: implications for senescence theory

The extent to which inbreeding depression affects longevity and patterns of survivorship is an important issue from several research perspectives, including evolutionary biology, conservation biology, and the genetic analysis of quantitative traits. However, few previous inbreeding depression studies have considered longevity as a focal life-history trait. We maintained laboratory populations of Drosophila melanogaster at census population sizes of 2 and 10 male-female pairs for up to 66 generations and performed repeated assays of male survivorship throughout this time period. On average, significant levels of inbreeding depression were observed for median life span and age-specific mortality. For age-specific mortality, the severity of inbreeding depression increased over the life span. We found that a baseline inbreeding load of 0.307 lethal equivalents per gamete affected age-specific mortality, and that this value increased at a rate of 0.046 per day of the life span. With respect to some survivorship parameters, the differentiation of lineages was nonlinear with respect to the inbreeding coefficient, which suggested that nonadditive genetic variation contributed to variation among lineages. These findings provide insights into the genetic basis of longevity as a quantitative trait and have implications regarding the mutation-accumulation evolutionary explanation of senescence.     

Inbreeding depression and purging in a haplodiploid: gender-related effects

Compared with diploid species, haplodiploids suffer less inbreeding depression because male haploidy imposes purifying selection on recessive deleterious alleles. However, alleles of genes only expressed in the diploid females are protected in heterozygous individuals. This leads to the prediction that haplodiploids suffer more from inbreeding effects on life-history traits controlled by genes with female-limited expression. To test this, we used a wild population of the haplodiploid mite Tetranychus urticae. First, negative effects of inbreeding were investigated by comparing maturation rate, juvenile survival, oviposition rate and longevity between lines created by three generations of either outbreeding or mother–son inbreeding. Second, purging through inbreeding was investigated by comparing the intensity of inbreeding depression between outbred families with known inbreeding/outbreeding mating histories. Negative effects of inbreeding and evidence for purging were found for the female trait oviposition rate, but not for juvenile survival and longevity. Both male and female maturation rate were negatively affected by inbreeding, most likely due to maternal effects because inbred offspring of outbred mothers was not affected. These results support the hypothesis that, in haplodiploids inbreeding effects and genetic variation due to deleterious recessive alleles may depend on gender.     

Possible negative effects of inbreeding on semen quality in Shetland pony stallions

Inbreeding is widely believed to negatively affect reproductive performance. Indeed, in some species, high levels of inbreeding are thought to be the major cause of poor semen quality. It is, however, not clear whether inbreeding affects fertility in horses. In this study, the relationship between inbreeding and semen quality was examined in 285 immature Shetland pony stallions submitted for breeding soundness examination in March-April of the years 1992-1997. The majority of stallions examined were 3 years old (85%) and their coefficients of inbreeding ranged from 0 to 25% (mean+/-S.D.: 3+/-4.6%). For the purpose of analysis, stallions were divided into six inbreeding classes (0-1, 1-2, 2-5, 5-8, 8-12 and >12%) containing 132, 40, 42, 27, 25 and 19 animals, respectively. The degree of inbreeding significantly affected many aspects of sperm production and quality, based on a standard examination of two ejaculates collected at a 1.5-3h interval. In particular, coefficients of inbreeding above 2% were associated with lower percentages of motile (p<0.01) and morphologically normal sperm (p<0.001). When the data set was used to estimate heritability of semen characteristics, the high values calculated for sperm progressive motility (0.46) and concentration (0.24) suggested that these traits could be improved by phenotypic selection. These findings support the hypothesis that inbreeding has a detrimental effect on semen quality in Shetland ponies, although examination of multiple ejaculates after repeated semen collection to bring the animals to daily sperm output is needed to confirm this conclusion. Nevertheless, the results support previous suggestions that inbreeding is an important cause of reduced semen quality.     

Inbreeding depression in development,survival, and reproduction in the adzuki bean beetle (<Emphasis Type="Italic">Callosobruchus chinensis</Emphasis>)

Inbreeding depression of an aspect of fitness is observed in many insects, but the traits that are of importance for inbreeding depression of fitness remain poorly understood. Here the magnitude of inbreeding depression of fitness-related traits in the development and adult stages was measured in a captive population of the adzuki bean beetle, Callosobruchus chinensis (Coleoptera: Bruchidae). Beetles produced by full-sib matings had 8% lower survival in the development stage than did beetles produced by unrelated matings. Although inbred and outbred offspring did not differ in body size after emergence, inbred offspring took 2–3% longer to develop to emergence. This indicates inbreeding depression of growth rate. At the adult stage, inbreeding had no significant effect on longevity, however lifetime offspring production was reduced by 11%. Thus, the magnitude of inbreeding depression was relatively large for offspring production. This suggests inbreeding depression of fitness manifests, to a particularly significant extent, in reduced productivity. This study shows the C. chinensis population, which has been in captivity for more than 100 generations, harbors genetic loads.     

Inbreeding depression and genetic load in laboratory metapopulations of the butterfly Bicyclus anynana

Abstract.— We investigated the effects of inbreeding on various fitness components and their genetic load in laboratory metapopulations of the butterfly Bicyclus anynana . Six metapopulations each consisted of four subpopulations with breeding population sizes of N = 6 or N = 12 and migration rate of m = 0 or m = 0.33. Metapopulations were maintained for seven generations during which coancestries and pedigrees were established. Individual inbreeding coefficients at the F₇ were calculated and ranged between 0.01 and 0.51. Even though considerable purging had occurred during inbreeding, the genetic load remained higher than that of many outbreeding species: approximately two lethal equivalents were detected for egg sterility, one for zygote survival, one for juvenile survival, and one for longevity. Severe inbreeding depression occurred after seven generations of inbreeding, which jeopardized the metapopulation survival. This finding suggests that the purging of genetic load by intentional inbreeding cannot be recommended for the genetic conservation of species with a high number of lethal.     

Breakdown in correlations during laboratory evolution. II. Selection on stress resistance in Drosophila populations

We trace the evolutionary correlation between stress resistance and longevity in populations of Drosophila melanogaster selected for stress resistance over many generations. Females selected for desiccation resistance and both females and males selected for increasing starvation resistance initially show concurrent increases in longevity, but then begin to decrease in longevity, even as stress resistance continues to increase. We demonstrate that the correlation between two fitness traits can change and that this change is due to sustained selection rather than a genotype-by-environment interaction or inbreeding depression. The breakdown in evolutionary correlation we report underscores the difficulty of extrapolating the results from short-term selection experiments to predictions of long-term evolution.     

Male inbreeding status affects female fitness in a seed-feeding beetle

Inbreeding generally reduces male mating activity such that inbred males are less successful in male-male competition. Inbred males can also have smaller accessory glands, transfer less sperm and produce sperm that are less motile, less viable or have a greater frequency of abnormalities, all of which can reduce the fertilization success and fitness of inbred males relative to outbred males. However, few studies have examined how male inbreeding status affects the fitness of females with whom they mate. In this study, we examine the effect of male inbreeding status (inbreeding coefficient f = 0.25 vs. f = 0) on the fecundity, adult longevity and the fate of eggs produced by outbred females in the seed-feeding beetle, Callosobruchus maculatus. Females mated to inbred males were less likely to lay eggs. Of those that laid eggs, females mated to inbred males laid 6-12% fewer eggs. Females mated to inbred males lived on average 5.4% longer than did females mated to outbred males, but this effect disappeared when lifetime fecundity was used as a covariate in the analysis. There was no effect of male inbreeding status on the proportion of a female's eggs that developed or hatched, and no evidence that inbred males produced smaller nuptial gifts. However, ejaculates of inbred males contained 17-33% fewer sperm, on average, than did ejaculates of outbred males. Our study demonstrates that mating with inbred males has significant direct consequences for the fitness of female C. maculatus, likely mediated by effects of inbreeding status on the number of sperm in male ejaculates. Direct effects of male inbreeding status on female fitness should be more widely considered in theoretical models and empirical studies of mate choice.     

Breakdown in correlations during laboratory evolution. I. Comparative analyses of Drosophila populations

We provide evidence from comparisons of populations of Drosophila that evolutionary correlations between longevity and stress resistance break down over the course of laboratory evolution. Using 15 distinct evolutionary regimes, we created 75 populations that were differentiated for early fecundity, longevity, starvation resistance, desiccation resistance, and developmental time. In earlier experiments, selection for postponed aging produced increases in stress resistance, whereas selection for increased stress resistance produced increases in longevity. Direct estimates of correlations also indicated an antagonistic relationship between early fecundity on one hand and longevity or stress resistance on the other. Laboratory evolution of extreme values of stress resistance, however, led to a breakdown in these evolutionary relationships. There was no evidence that these significant changes in correlation resulted from genotype-by-environment interactions or inbreeding. These findings suggest that correlations between functional characters are not necessarily durable features of a species, and that short-term evolutionary responses cannot be extrapolated reliably to longer-term evolutionary patterns.     

Female reproductive success in captive Ammotragus lervia (Bovidae, Artiodactyla). Study of its components and effects of hierarchy and inbreeding

Four components of female reproductive success in captive Saharan arrui (Barbary sheep), Ammotragus lervia sahariensis (Rothschild, 1913), have been analysed: longevity, fecundity, offspring one-month survival rate and the age at first birth. Longevity accounts for 69.9% of the variance of reproductive success, fecundity for 54.2%, offspring one-month survival rate for 29.8%, and the age at first birth for 10.4%. A detailed study of these components leads to the following conclusions: (a) longevity is higher in those individuals in better physical condition; (b) fecundity is related to age and social rank; (c) heavier offspring at birth have a higher probability of surviving during their first month of life; and (d) the age at first birth is delayed by high levels of population density, inbreeding coefficients, and birth weights. On the other hand, highranking females are characterized by shorter inter-birth intervals and give birth to a higher proportion of twins.     

Longevity differences among lines artificially selected for developmental time and wing length in Drosophila buzzatii

We assessed the indirect response of longevity in lines selected for wing length (WL) and developmental time (DT). Longevity in selection lines was compared to laboratory control lines and the offspring of recently collected females. Wild flies (W lines), flies from lines selected for fast development (F lines), and for fast development and large wing length (L lines) outlived control laboratory lines (C lines) and lines selected for fast development and short wing (S lines). The decline in longevity in S lines is in line with the idea that body size and longevity are correlated and may be the result of the fixation of alleles at loci affecting pleiotropically the two traits under selection and longevity. In addition, inbreeding and artificial selection affected the correlation between wing length and longevity that occurs in natural populations of Drosophila buzzatii, suggesting that correlations between traits are not a perdurable feature in a population.     

Life span of queens in the antFormica exsecta

Summary The antFormica exsecta commonly has two types of colonies: either polygynous and polydomous or monogynous and monodomous. The longevity of queens was studied in monogynous colonies in southern Finland by indirect methods using genetic markers; these data were also used to estimate the number of matings and queen replacement. The average genetic relatedness among worker nest mates was 0.72. Taking inbreeding into account (the inbreeding coefficient wasF=0.16), this value agrees with the assumption that 40% of the queens mated with one male and 60% with two males. The distribution of genotypes within colonies remained stable in successive years, indicating that queen replacement did not occur or was extremely rare. This means that the life span of nests reflects directly the life span of the queens. Eleven of the 16 nests found in 1979 were still alive ten years later. This corresponds to an annual mortality of 3.7% and a mean life span of 27 years. A total of 57 colonies were mapped in the population over a period of ten years. Averaging over the years, the annual mortality was estimated to be 4.9%. This represents a mean life span of 20 years if mortality was independent of age.     

No evidence of inbreeding depression in sperm performance traits in wild song sparrows

Inbreeding is widely hypothesized to shape mating systems and population persistence, but such effects will depend on which traits show inbreeding depression. Population and evolutionary consequences could be substantial if inbreeding decreases sperm performance and hence decreases male fertilization success and female fertility. However, the magnitude of inbreeding depression in sperm performance traits has rarely been estimated in wild populations experiencing natural variation in inbreeding. Further, the hypothesis that inbreeding could increase within‐ejaculate variation in sperm traits and thereby further affect male fertilization success has not been explicitly tested. We used a wild pedigreed song sparrow (Melospiza melodia) population, where frequent extrapair copulations likely create strong postcopulatory competition for fertilization success, to quantify effects of male coefficient of inbreeding (f) on key sperm performance traits. We found no evidence of inbreeding depression in sperm motility, longevity, or velocity, and the within‐ejaculate variance in sperm velocity did not increase with male f. Contrary to inferences from highly inbred captive and experimental populations, our results imply that moderate inbreeding will not necessarily constrain sperm performance in wild populations. Consequently, the widely observed individual‐level and population‐level inbreeding depression in male and female fitness may not stem from reduced sperm performance in inbred males.     

Inbreeding depression on beef cattle traits: Estimates,linearity of effects and heterogeneity among sire-families

Records from up to 19054 registered cows and 10297 calves in 155 herds of the Alentejana cattle breed were used to study the effects of individual (F_i) and maternal (F_m) inbreeding on reproductive, growth and carcass traits, as well as assessing the importance of non-linear associations between inbreeding and performance, and evaluating the differences among sire-families in the effect of F_i and F_m on calf weight at 7 months of age (W7M). Overall, regression coefficients of performance traits on inbreeding were small, indicating a minor but still detrimental effect of both F_i and F_m on most traits. The traits with the highest percentage impact of F_i were total number of calvings through life and calf weight at 3 months of age (W3M), followed by longevity and number of calves produced up to 7 years, while the highest effect of F_m was on W3M. Inbreeding depression on feed efficiency and carcass traits was extremely small and not significant. No evidence was found of a non-linear association between inbreeding and performance for the traits analyzed. Large differences were detected among sire-families in inbreeding depression on W7M, for both F_i and F_m, encouraging the possibility of incorporating sire effects on inbreeding depression into selection decisions.     

Life history correlates of inbreeding depression in mandrills (Mandrillus sphinx)

Inbreeding depression reflects the negative consequences of increased homozygosity at genes that affect fitness. We investigate inbreeding depression in a semi-free-ranging colony of mandrills (Mandrillus sphinx), using high-quality pedigree data, comprising five maternal generations and 20 years of morphological and demographic data. We examine the relationship between inbreeding coefficients and four fitness correlates: two growth parameters (mass and height for age) and longevity in both sexes, and age at first conception in females. Inbreeding was correlated with both growth parameters, but only in females, with inbred females being smaller than noninbred females. Inbreeding was also correlated significantly with age at first conception, with inbred females giving birth earlier in life than noninbred females. We suggest that sex-biased maternal investment may explain this sex-differential response to inbreeding, although the lack of a significant association between inbreeding and growth in males may also be due to the provisioned nature of the colony. The surprising relationship between age at first conception and inbreeding may be related to smaller adult size in inbred females, or to their being less able to escape from male sexual coercion.     

Effects of inbreeding and temperature stress on life history and immune function in a butterfly

Theory predicts that inbreeding depression should be more pronounced under environmental stress due to an increase in the expression of recessive deleterious alleles. If so, inbred populations may be especially vulnerable to environmental change. Against this background, we here investigate effects of inbreeding, temperature stress and its interactions with inbreeding in the tropical butterfly Bicyclus anynana. We use a full‐factorial design with three levels of inbreeding (F = 0/0.25/0.38) and three temperature treatments (2 h exposure to 1, 27 or 39 °C). Despite using relatively low levels of inbreeding significant inbreeding depression was found in pupal mass, pupal time, thorax mass, abdomen fat content, egg hatching success and fecundity. However, stress resistance traits (heat tolerance, immune function) were not affected by inbreeding and interactions with temperature treatments were virtually absent. We thus found no support for an increased sensitivity of inbred individuals to environmental stress, and suspect that such patterns are restricted to harsher conditions. Our temperature treatments evidently imposed stress, significantly reducing longevity, fecundity, egg hatching success and haemocyte numbers, while fat content, protein content and lysozyme activity remained unaffected. Males and females differed in all traits measured except pupal time, protein content and phenoloxidase (PO) activity. Correlation analyses revealed, among others, a trade‐off between PO and lysozyme activity, and negative correlations between fat content and several other traits. We stress that more data are needed on the effects of inbreeding, temperature variation and sexual differences on insect immune function before more general conclusions can be drawn.     

Life-history plasticity and inbreeding depression under mate limitation and predation risk: cumulative lifetime fitness dissected with a life table response experiment

Environmental effects on the evolution of mating systems are increasingly discussed, but we lack many examples of how environmental conditions affect the expression and consequences of alternative mating systems. Variation in mate availability sets up a trade-off between reproductive assurance and inbreeding depression, but the consequences of both mate limitation and inbreeding may depend on other environmental conditions. Predation risk is common under natural conditions, and known to affect allocation to reproduction, but we know little about the effects of isolation and inbreeding under predation risk. We reared selfed and outcrossed hermaphroditic freshwater snails (Physa acuta) in four environments (predator cues present or absent crossed with mating partners available or not) and quantified life-history traits and cumulative lifetime fitness. Our results confirm that isolation from mates can increase longevity and growth, resulting in higher lifetime fecundity. Thus, we observed no evidence for mate limitation of reproduction. However, reproduction under isolation (i.e., selfing) resulted in inbreeding depression, which should counteract the benefits of selfing. Inbreeding depression in fitness occurred in both predator and no-predator environments, but there was no overall change in inbreeding depression with predator cues. This represents, to our knowledge, the first empirical estimate of the effect of predation risk on inbreeding depression in an animal. Cumulative fitness was most influenced by early survival and especially early fecundity. As predation risk and inbreeding (both ancestral and due to a lack of mates) reduced early fecundity, these effect are predicted to have important contributions to population growth under natural conditions. Therefore life-history plasticity (e.g., delayed reproduction) is likely to be very important to overall fitness.     

Inbreeding avoidance in an isolated indigenous Zapotec community in the valley of Oaxaca, southern Mexico

We analyzed inbreeding using surname isonymy in an indigenous genetic isolate. The subjects were residents of a rural Zapotec-speaking community in the valley of Oaxaca, southern Mexico. The community can be classified as a genetic isolate with an average gene flow of < or = 3% per generation. Surnames were collected for individuals in each household in pedigree form using the culturally traditional patronym-matronym naming. Estimation of inbreeding from surname isonymy is facilitated by the traditional patronym-matronym name assignment among indigenous Mexican populations. A total of 2,149 individuals had valid surname patronym-matronym pairings, including 484 deceased ancestors. Surname isonymy analysis methods were used to estimate total inbreeding and to segregate it into random and nonrandom components. The surname isonymy coefficient computed from 119 isonymous surname pairings (119/2,149) was 0.0554. The estimated inbreeding coefficient from surname isonymy was 0.0138 (0.0554/4). The random and nonrandom components of inbreeding were F(r) = 0.0221 and F(n) = -0.0091, respectively. The results suggest that consanguinity is culturally avoided. Nonrandom inbreeding decreased total inbreeding by about 41%. Total estimated inbreeding by surname isonymy was 0.0138, which is similar to inbreeding estimated from a sample of pedigrees, 0.01. Socially prescribed inbreeding avoidance substantially lowered total F through negative nonrandom inbreeding. Even in the situation of genetic isolation and small effective population size (N(e)), estimated inbreeding is lower than may have otherwise occurred if inbreeding were only random. However, among the poorest individuals, socially prescribed jural rules for inbreeding avoidance failed to operate. Thus the preponderance of inbreeding appears to occur among the poor, economically disadvantaged in the community.     

Sorting out the effects of Wolbachia, genotype and inbreeding on life-history traits of a spider mite

Wolbachia bacteria manipulate host reproduction by inducing cytoplasmic incompatibility (CI) and sex ratio distortion. Wolbachia are transmitted from mother to offspring through the cytoplasm of the egg. Therefore, reproduction of Wolbachia is tightly coupled to reproduction of its host. Mathematical analysis predicts that in the course of evolution, traits that reduce the physiological costs of the infection will be selectively favored. For a Wolbachia-host system to evolve, traits under selection must have some genetic component and variation must be present in the population. We have previously established that highly inbred isofemale lines of the two-spotted spider mite Tetranychus urticae may differ regarding the effects of infection by Wolbachia, and that at least some of the traits affected had a genetic component. However, the effects measured could have been affected by the fact that the lines were severely inbred prior to the experiments. In this paper we attempt to distinguish between the effects of Wolbachia, isofemale line, and inbreeding. We show that Wolbachia did not affect longevity but infected females produced smaller clutch sizes, more daughter-biased sex ratios and had decreased F1 mortality; between-line variation was found for clutch size, F1 mortality and sex ratio; finally, inbreeding resulted in an overall reduction of clutch sizes, and a change in survival curves and mean longevity. This revised version was published online in July 2006 with corrections to the Cover Date.     

Inbreeding Effects upon Growth and Maternal Ability in Laboratory Mice

The effects of systematically increasing levels of inbreeding upon growth and postnatal maternal ability were determined in laboratory mice by utilizing the reciprocal crossfostering technique. Two experiments were conducted. The first included postnatal dams which were inbred 0, 12, 25 and 38% while corresponding levels in the litter were 0, 22, 38 and 50%, respectively. The second experiment included 0, 25, 50 and 73% inbred dams with litters inbred 0, 38, 59 and 79%, respectively. Increasing the level of inbreeding was found to linearly depress postnatal maternal performance. Young which had been suckled by the more inbred dams were smaller at 12 and 21 days of age than those which had been nursed by the more outbred dams. In the second experiment, these effects were carried over into the postweaning period. Increasing levels of inbreeding in the litter significantly depressed birth weight and weight at 12, 21, 42 and 56 days. The depressing effects of inbreeding in the litter were primarily linear for both males and females under the conditions of the more moderate levels of inbreeding included in the first experiment, but were curvilinear for females and linear for males in the second experiment. The curvilinearity in females was due to the general lack of depression until inbreeding had reached 50 to 60%, after which significant inbreeding depression developed.