Occurrence Of Inbreeding Depression Research Articles

Fine-Scale Analysis of Runs of Homozygosity Islands Affecting Fertility in Mares.

The loss of genetic variability in livestock populations bred under strict selection processes is a growing concern, as it may lead to increased inbreeding values and lower fertility, as a consequence of the “inbreeding depression” effect. This is particularly important in horses, where inbreeding levels tend to rise as individuals become more and more closely related. In this study, we evaluated the effect of increased inbreeding levels on mare fertility by combining an SNP-based genomic approach using runs of homozygosity and the estimation of genetic breeding values for reproductive traits in a large population of Pura Raza Española mares. Our results showed a negative correlation between whole-genome homozygosity and fertility estimated breeding values (EBVs) at the genome level (ρ = −0.144). However, the analysis at chromosome level revealed a wide variability, with some chromosomes showing higher correlations than others. Interestingly, the correlation was stronger (−0.241) when we repeated the analysis in a reduced dataset including the 10% most and least fertile individuals, where the latter showed an increase in average inbreeding values (FROH) of around 30%. We also found 41 genomic regions (ROHi, runs of homozygosity islands) where homozygosity increased 100-fold, 13 of which were significantly associated with fertility after cross-validation. These regions encompassed 17 candidate genes previously related to oocyte and embryo development in several species. Overall, we demonstrated the relationship between increased homozygosis at the genomic level and fertility in mares. Our findings may help to deal with the occurrence of inbreeding depression, as well as further our understanding of the mechanisms underlying fertility in mares.

Reproductive barriers and genetic differentiation between continental and island populations of Epidendrum fulgens (Orchidaceae)

Studies on insular organisms provide an important framework for investigating patterns of genetic differentiation and reproductive isolation. By focusing on populations of the same species, we have the opportunity to study the mechanisms operating during the earliest stages of speciation, as reproductive barriers can be examined among divergent lineages in a geographic context. We investigated the genetic differentiation and the evolution of early stages of intrinsic postmating reproductive isolation between continental and insular populations of Epidendrum fulgens, a neotropical orchid distributed in southeastern Brazil. Genetic diversity and structure were estimated for both nuclear and plastid markers by using genetic differentiation measures and model-based assignment test. Furthermore, two components of reproductive isolation were examined by analyzing fruit set and seed viability in interpopulation crosses. Strong plastid genetic structure (FST = 0.679) was found between insular and remaining populations, indicating that E. fulgens reduced gene flow via seed dispersal, although significant nuclear genetic structure was lower (DST = 0.179), likely due to the smaller effective population size of the plastid genome. Significant differences in seed viability between self- and cross-pollinated plants were found, indicating the occurrence of inbreeding depression in all populations. Seed viability was significantly lower in crosses between insular and remaining populations, suggesting a late postzygotic reproductive barrier due to low migration associated with genetic drift (i.e., bottleneck) and its consequences. Our results confirm the importance of islands as drivers for populational differentiation and suggest a central role for outbreeding depression during the early stages of lineage diversification.

Inbreeding depression for severity caused by leaf diseases in cassava

The use of inbred populations in cassava has been little exploited by breeding programs. Therefore, the objective of this study was to evaluate the effects of inbreeding depression (ID) in S1 families for resistance to leaf diseases and to select transgressive individuals. Five cassava varieties (Cascuda, BRS Formosa, Fecula Branca, Mani-Branca and BRS Mulatinha) were selfed, and the families S0 and S1 were evaluated for severity caused by cassava white leaf spot (CWLS), cassava brown leaf spot (CBRLS) and cassava blight leaf spot (CBLS) under field conditions. Differences among S1 families and between generations (S0 × S1) were identified for all diseases. The wide variation of CWLS (2.16–93.38%), CBRLS (15.31–69.39%) and CBLS (15.70–53.64%) severity highlighted the occurrence of ID in S1 families, in which the average was 12.61% (CWLS), 13.72% (CBRLS) and 15.92% (CBLS). Mean estimates of homozygous loci contribution (µ + α) were of higher magnitude compared with heterozygous loci contribution (δ) for all diseases and families. Even in the occurrence of ID, it was possible to select resistant S1 individuals, in a way that the reduction in the severity of diseases based on the selection of the five most resistant individuals was 75.80% (S1-BRS Formosa) for CWLS, 38.64% (S1-Cascuda) for CBRLS and 33.51% (S1-Cascuda) for CBLS. These results demonstrate the predominance of additive genetic effects and the possibility to select transgressive individuals in S1 families for increasing the resistance to cassava leaf diseases.

Dwindling Numbers of Eremostachys superba Royle ex Benth. in its Type Locality: Mohand (Dehradun)

An assessment of Eremostachys superba (Lamiaceae) was done in the type locality of Mohand (Dehradun) for its gradual decrease in the number from 100 to 25 in the last decades and only 7-9 plants at present. A regular visit has revealed that no flowering has been observed in the area from past two years and due to this no breeding has taken place which could result in further decrease in the number of the plants. The plant mainly breeds through cross pollination and no other population exists in the nearby area. But as no flowering has been observed in the area, the chances of self fertilization is also nil and it means that no propagation is taking place in the area. Further trampling of the plant by cattle grazing in the area has caused deterioration of the existing plants. The experiments carried out in the laboratory indicate that the seeds produced by the selfing have very poor germination percentage. As there is no other nearby population in the area, all the seeds that were produced in the earlier decades might have been the result of selfing and hence could not germinate under natural conditions. This strongly indicated occurrence of inbreeding depression and loss of fitness of the offspring right from the stage of germination, which is harmful for the perpetuation of the species and thereby leading to its rarity and making its conservation a challenge.

Comparative reproductive biology and pollinator specificity among sympatricGomesa(Orchidaceae: Oncidiinae)

The incredible pollination mechanisms displayed by orchid flowers has inspired biologists over the centuries. Based on the intriguing flower structures, the relationship among orchid species and their pollinators has been frequently regarded as very specialised. Given that visits on flowers pollinated by oil-collecting bees are regularly rare, and in Oncidiinae the flowers frequently attractexclusively species that act as effective pollinators, the comparative reproductive biology and pollinator specificity of two sympatric Gomesa (G.varicosa and G.montana; Oncidiinae) were analysedbased on records of floral morphology, production of floral rewards, pollinators and pollination mechanisms. Furthermore, experimental pollinations were carried out in order to examine the breeding systems. The results have show that in the studied population, both Gomesa are visited by several bee species, but these orchids present a specific pollination system.Pollinaria are deposited on the head of Centridini (G.varicosa and G.montana) and Epicharitini (G.varicosa) bees when landed on the central callus of the labellumto collect lipoidal substances produced by glandular elaiophores on lateral lobes of the labellum. Both species are dependent on a biotic pollen vector to set fruits. Gomesamontana is completely self-incompatible, while G.varicosa is partially self-compatible. Our results indicate that although the occurrence of self-sterile species seems to be common in Oncidiinae, in partially self-incompatible species, as is the case of G.varicosa, self-compatibility has been considered as an important factor favouring reproductive assurance in populations with low visitation frequencies, despite occurrence of inbreeding depression.

Inbreeding depression in crambe1

ABSTRACT Inbreeding depression in plants, caused by selfing or crossing among plants with a high degree of relatedness, is a genetic phenomenon that affects quantitative traits. This study aimed at verifying the occurrence of inbreeding depression in crambe progenies originated from selfing, in comparison with open pollination progenies. A randomized blocks design, with three replications, in a 32 x 2 factorial arrangement, with 32 crambe progenies and two reproduction systems (artificial selfing and open pollination), was used. Grain yield, 1,000-grain weight, plant height and final stand were evaluated. A significant interaction was observed between progenies and reproduction systems in all traits evaluated. A reduction in grain yield, 1,000-grain weight and plant height occurred in the majority of the selfing progenies, when compared to open pollination progenies. Inbreeding depression was observed in all traits, especially for grain yield. The heritability coefficients of selfed progenies were higher than the open pollinated ones, except for 1,000-grain weight.

Influence of spatial distribution and size of clones on the realized outcrossing rate of the marsh cinquefoil (Comarum palustre)

Clonal growth is a common feature in flowering plants. As clone size increases, the selfing rate in self-compatible species is likely to increase due to more frequent geitono-pollination events (i.e. pollination among flowers within the same genet). This study investigated the breeding system of the marsh cinquefoil (Comarum palustre) and assessed spatial distribution of clones, clone size and architecture, and their effects on realized outcrossing rates. In addition, pollen dispersal was investigated in two patchy populations. The species' breeding system was investigated under controlled conditions through hand pollinations (self- vs. cross-pollination). Using microsatellite markers, an assessment was made of the realized outcrossing rates and the genetic diversity in four natural populations, the clonal structure in two populations within five 15 × 15 m sampling plots following 0.5 × 0.5 m grids, and the pollen dispersal through paternity assignment tests in those two populations. Comarum palustre is a self-compatible species but only presents a low rate of spontaneous self-pollination. The occurrence of inbreeding depression was not detected at the seed set stage (δ(SS) = 0.04). Clones were spatially clumped (A(C) = 0.60-0.80), with intermediate to no intermingling of the ramets (D(C) = 0.40-1.00). Genet size ranged from one to 171 ramets. Patchy populations had low outcrossing rates (t(m) = 0.33-0.46). Large clones showed lower outcrossing rates than small clones. Pollen dispersal mainly occurred within patches as only 1-7 % of the pollination events occurred between patches of >25 m separation. Seedling recruitment events were detected. Genet size together with distances between patches, through increasing geitono-pollination events, appeared to be important factors influencing realized outcrossing rates. The study also revealed seed flow allowing seedling recruitment, which may contribute to increasing the number of new patches, and potentially further enhance gene flow within populations.

Biologia reprodutiva de Melocactus glaucescens Buining & Brederoo e M. paucispinus G. Heimen & R. Paul (Cactaceae), na Chapada Diamantina, Nordeste do Brasil

Foi estudada a biologia reprodutiva de Melocactus glaucescens e M. paucispinus (Cactaceae) no Municipio de Morro do Chapeu, Chapada Diamantina, Bahia, sendo abordados aspectos da fenologia, biologia floral, polinizacao e sistema reprodutivo. Foram registrados os periodos de floracao e frutificacao, visitantes florais, frequencia e tipo de visitas, alem de estrategia e comportamento dos visitantes as flores. Foram realizadas polinizacoes experimentais para verificar o sistema reprodutivo das especies. As duas especies de Melocactus estudadas apresentaram sobreposicao de floracao ao longo do periodo de estudo. Os atributos florais de ambas as especies sao tipicos da sindrome da ornitofilia: cores atrativas, estrutura tubulosa e producao de nectar com baixa concentracao de solutos, entre 20% e 30%. O beija-flor Chlorostilbon aureoventris Boucier & Mulsant (1948) foi o visitante mais frequente, com 82% e 89% do total de visitas para M. paucispinus e M. glaucescens, respectivamente. Outras especies de beija-flores e borboletas tambem visitaram as flores das especies. A sobreposicao no periodo de floracao e a similaridade na composicao da guilda de polinizadores destas e demais especies simpatricas de Melocactus favorece a hibridacao no genero, como foi observado na regiao. Melocactus glaucescens apresentou auto-incompatibilidade e alogamia, enquanto M. paucispinus e auto-compativel e autogâmica, porem com menor frutificacao em autopolinizacao do que em polinizacao cruzada, possivelmente devido a ocorrencia de depressao endogâmica. Polinizacoes interespecificas indicam a ocorrencia de inter-compatibilidade entre M. paucispinus e M. concinnus Buining & Brederoo, sustentando hipoteses correntes de hibridacao entre estas especies.

Genetic diversity and reproductive success in mandrills (Mandrillus sphinx).

Recent studies of wild animal populations have shown that estimators of neutral genetic diversity, such as mean heterozygosity, are often correlated with various fitness traits, such as survival, disease susceptibility, or reproductive success. We used two estimators of genetic diversity to explore the relationship between heterozygosity and reproductive success in male and female mandrills (Mandrillus sphinx) living in a semifree ranging setting in Gabon. Because social rank is known to influence reproductive success in both sexes, we also examined the correlation between genetic diversity and social rank in females, and acquisition of alpha status in males, as well as length of alpha male tenure. We found that heterozygous individuals showed greater reproductive success, with both females and males producing more offspring. However, heterozygosity influenced reproductive success only in dominant males, not in subordinates. Neither the acquisition of alpha status in males, nor social rank in females, was significantly correlated with heterozygosity, although more heterozygous alpha males showed longer tenure than homozygous ones. We also tested whether the benefits of greater genetic diversity were due mainly to a genome-wide effect of inbreeding depression or to heterosis at one or a few loci. Multilocus effects best explained the correlation between heterozygosity and reproductive success and tenure, indicating the occurrence of inbreeding depression in this mandrill colony.

Restricted dispersal in a long-distance migrant bird with patchy distribution, the great reed warbler.

In patchily distributed species dispersal connects local populations into metapopulations. Reliable quantifications of dispersal are therefore crucial to understanding the population dynamics and genetic structure of such metapopulation systems. The great reed warbler (Acrocephalus arundinaceus) inhabits eutrophic lakes and has a patchy breeding distribution. In this study we investigated the dispersal pattern of the great reed warbler based on an extensive capture-recapture effort covering a large census area (22,500km2). At two adjacent breeding sites (10km apart) in southern Central Sweden, the "main study area", we ringed the majority of adult and nestling great reed warblers between 1992 and 1999. In 1998 and 1999, we opportunistically searched for territorial males at the majority of the Swedish breeding sites, and were able to examine about 56% of all males in the region. Analyses of recaptured males demonstrated that philopatry predominated. Sixty-nine percent of the recruiting nestlings returned to breed in the main study area (their natal area), and 92% of the resighted adults were found at the same breeding locality in both study years. Breeding dispersal was significantly more restricted than natal dispersal. Additional data on natal and breeding dispersal within the main study area in 1992-1999 suggested that females were as philopatric as males. The overall high level of philopatry, with only occasional longer dispersal distances documented, yielded a root-mean-square dispersal distance of 33km per generation. High philopatry, short dispersal distances and similar dispersal patterns of male and female great reed warblers contrast the findings among birds in general, but conform to data of species having patchy breeding habitat and isolated populations. Restricted dispersal suggests limited gene flow even among several Swedish populations, which is in line with some previous findings of the population ecology of the great reed warbler: (1) structured mtDNA lineages among European populations; (2) small-scale population differences in song patterns; and (3) low genetic variation and occurrence of inbreeding depression in our main study population.

In vitro propagation of cauliflower, Brassica oleracea var. botrytis for hybrid seed production

Methods for obtaining heterotic F1 and maintaining purebred lines for breeding of Brassica oleracea are limited by absence of male sterile lines and occurrence of inbreeding depression, respectively. The use of vegetative (stem, petiole, leaf, leaf rib) and floral (peduncle, pedicel, flower bud, curd) explants of cauliflower to regenerate purebred lines for crossing were examined. Of four growth regulator treatments and explant types used, best results were obtained with curd explants on MS medium with 6-benzyladenine (cytokinin) and gibberellic acid. Although 6-benzyladenine alone promoted formation of shoots in floral explants, both 6-benzyladenine and α-napthaleneacetic acid were required for vegetative explants. Use of α-napthaleneacetic acid, however, often increased callus formation. These culture techniques to maintain purebred regenerated plants will complement newly-derived nuclear-based male sterile lines obtained by the introduction of antisense copies of the gene BcpI, which is required for pollen fertility.

INBREEDING DEPRESSION AND ITS EVOLUTIONARY CONSEQUENCES

The harmful effects of close inbreeding have been noticed for many centuries (34, 35, 165). With the rise of Mendelian genetics, it was realized that the main genetic consequence of inbreeding is homozygosis (165, Ch. 2). Two main theories were early proposed to account for inbreeding depression and its converse, heterosis (the increase in vigor observed in an F1 between two inbred lines). These are the overdominance and partial dominance hypotheses, discussed in more detail below. Research into this question has continued up to the present, and this is one of the topics that we discuss. Darwin (35, 36) was the first to point out that the evident adaptations of many plants for ensuring outcrossing could be understood in terms of the selective advantage of avoiding inbreeding depression. We review the evidence that the evolution of breeding systems of animals and plants has been significantly influenced by the occurrence of inbreeding depression. In order to do this, we consider the contemporary genetic theory of inbreeding depression and heterosis, and the experimental data concerning the strength of inbreeding depression. We emphasize data and theory relevant to natural, rather than domesticated, populations as we are chiefly concerned to evaluate the evolutionary significance of inbreeding depression. We do not attempt to give a complete bibliography of this very extensive field but try to concentrate on what seem to be the most significant findings in relation to this aim.