Degree Of Inbreeding Depression Research Articles

Genetic Diversity of Asian Seabass (Lates calcarifer) in Captive Populations

This study examined the genetic diversity of Asian seabass (Lates calcarifer) captive populations using sequencing of the mitochondrial DNA cytochrome c oxidase I (COI) fragment. The phylogenetic analyses of the 609 base pair regions of the COI fragment from 146 samples identified 15 haplotypes and divided them into two clades with a genetic divergence of 10%. Thus, phylogenetic results supported two genetic groups (the Australia/Southeast Asia group and the India/Myanmar group) within the captive populations under study. Mixed levels of genetic diversity were observed among captive populations, which indicated a certain degree of inbreeding depression. The findings would be useful for future aquaculture management of captive Asian seabass in Malaysia.

Study on the Effect of Mass Selection and Hybridization on Growth Performance of Chinese Pearl Oyster Pinctada martensii

The pearl oyster Pinctada martensii is an important species for sea pearl production in China. To explore the influence of the combination of mass selection and hybridization on growth performance of P. martensii, we established four selected groups and four control groups (each with two within-family crosses and two reciprocal hybrid crosses) using 1-year-old offspring of two families (Family A and Family B) from Beihai, Guangxi Province, China. Generally, the growth of the selected group was greater than that of the control group for both within-family crosses and reciprocal hybrid crosses. Shell length and width were affected by genotype, environmental factors, and the interaction between the two on Days 210 and 360. The shell widths of the four reciprocal hybrid crosses all showed heterosis on Day 360. The four within-family crosses showed a certain degree of inbreeding depression during the growth period. On Day 360, the three genetic parameters for shell width of the selected group of ♀ Family B and ♂ Family A were the largest, with values of 0.70, 1.17, and 0.06 for realized heritability, standard response to selection, and current genetic gain, respectively. Overall, the growth performance of ♀ Family B × ♂ Family A in the selected group was the best. Therefore, the combination of mass selection and hybridization could be an effective way to improve the growth performance of P. martensii.

Invited review: Inbreeding in the genomics era: Inbreeding, inbreeding depression, and management of genomic variability.

Traditionally, pedigree-based relationship coefficients have been used to manage the inbreeding and degree of inbreeding depression that exists within a population. The widespread incorporation of genomic information in dairy cattle genetic evaluations allows for the opportunity to develop and implement methods to manage populations at the genomic level. As a result, the realized proportion of the genome that 2 individuals share can be more accurately estimated instead of using pedigree information to estimate the expected proportion of shared alleles. Furthermore, genomic information allows genome-wide relationship or inbreeding estimates to be augmented to characterize relationships for specific regions of the genome. Region-specific stretches can be used to more effectively manage areas of low genetic diversity or areas that, when homozygous, result in reduced performance across economically important traits. The use of region-specific metrics should allow breeders to more precisely manage the trade-off between the genetic value of the progeny and undesirable side effects associated with inbreeding. Methods tailored toward more effectively identifying regions affected by inbreeding and their associated use to manage the genome at the herd level, however, still need to be developed. We have reviewed topics related to inbreeding, measures of relatedness, genetic diversity and methods to manage populations at the genomic level, and we discuss future challenges related to managing populations through implementing genomic methods at the herd and population levels.

Interpopulation variability in Artemisia glauca Pall. ex Willd.- studies on three distinct cytotypes

Three wild populations of Artemisia glauca Pall. ex Willd. occurring in the Pir Panjal mountain ranges and in the Kishtwar Himalayas of Jammu and Kashmir State, India, have been analysed for their meiotic systems and reproductive output. Of the three, two namely Poonch and Rajouri populations have a chromosome count of 2n = 18, while the third population named as Kishtwar population has 2n = 36. These are in all probability diploid and tetraploid cytotypes. While the tetraploid Kishtwar population shows stunted growth, diploid ones show little variation at the morphological level but display prominent interpopulation differences in detail of chromosome size and chiasmata frequency. Meiotically Poonch population is more stable than Rajouri. The differences in ploidy level and chromosome constitution affect the reproductive output in these species. Although all of them show high degree of inbreeding depression (revealed by total absence of healthy seeds on forced selfing), seed and fruit set on open pollination also is extremely low. Of the three, Poonch population sets the highest percentage of healthy seeds.

Inbreeding depression in male gametic performance.

One key objective in evolutionary ecology is to understand the magnitude of inbreeding depression expressed across sex-specific components of fitness. One major component of male fitness is fertilization success, which depends on male gametic performance (sperm and pollen performance in animals and plants, respectively). Inbreeding depression in male gametic performance could create sex-specific inbreeding depression in fitness, increase the benefit of inbreeding avoidance and reduce the efficacy of artificial insemination and pollination. However, there has been no assessment of the degree to which inbreeding generally depresses male gametic performance and hence post-copulatory or post-pollination fertilization success. Because inbreeding depression is understood to be a property of diploid entities, it is not clear what degree of inbreeding depression in haploid gametic performance should be expected. Here, we first summarize how inbreeding depression in male gametic performance could potentially arise through gene expression in associated diploid cells and/or reduced genetic diversity among haploid gametes. We then review published studies that estimate the magnitude of inbreeding depression in traits measuring components of sperm or pollen quantity, quality and competitiveness. Across 51 published studies covering 183 study traits, the grand mean inbreeding load was approximately one haploid lethal equivalent, suggesting that inbreeding depresses male gametic performance across diverse systems and traits. However, there was an almost complete lack of explicit estimates from wild populations. Future studies should quantify inbreeding depression in systematic sets of gametic traits under naturally competitive and noncompetitive conditions and quantify the degree to which gamete phenotypes and performance reflect haploid vs. diploid gene expression.

Pollination biology in an endangered rocky mountain toadflax (Linaria cavanillesii)

Knowledge about the reproductive system of species inhabiting rocky habitats is scarce. The reproductive biology (floral biology, experimental pollination, insect visits, inbreeding depression, and seed predation) of the rupicolous Linaria cavanillesii was analyzed under field and experimental conditions. Self-compatibility was revealed by the high fruit set, seed set, and seed mass in the pollination experiment. Furthermore, results disclose that this species does not need insect visitors for seed production since fruit set after autonomous self-pollination was similar to that by hand cross-pollination. Self-offsprings were not affected by a strong degree of inbreeding depression in early life-cycle stages. Seed predation by Cucurlionidae is the main limiting factor of fruit and seed production in this species. Contrary to other perennial species of Linaria previously studied, L. cavanillesii represents the first clear report of self-fertility.

Comparative growth and survival of inbred and outbred Penaeus ( marsupenaeus) japonicus, reared under controlled environment conditions: indications of inbreeding depression

This study quantifies the effects of inbreeding on growth, survival (and associated yield), of domesticated Penaeus ( marsupenaeus) japonicus for inclusion in selective breeding programs of the future. To make this assessment, we systematically bred two generations of inbred ( F=28–31%) and outbred families with known parentage and inbreeding coefficients. During the 2 production years, we assessed growth, survival and yield. The estimated inbreeding depression coefficient (standard error) was −3.34±2.55% for growth and −3.43±3.59% for overall survival. The consistency in both size and direction of the inbreeding depression coefficients for two fully independent traits lends support to the hypothesis that inbreeding reduces growth and survival, even though the coefficients were not statistically significant due to high variability among animals and a relatively small effect. When growth and survival were combined, yield was depressed by an estimated −6.53±4.08%. Mortality was highest in the first growth stage (PL 30–PL 80), with 75.1% survival for inbred crosses compared with 82.5% survival for outbred crosses. In the second (PL 80–PL 124) and third (PL 124–PL 156) growth stages, survival ranged from 92.5% to 95.1% with little difference between inbred and outbred crosses. This study demonstrates that a level of inbreeding can be tolerated by penaeids but can cause a degree of inbreeding depression and reduced production. However, there was variation in inbreeding depression between families. The knowledge that inbreeding in penaeids can cause reduced production through inbreeding depression highlights the need to maximize the genetic diversity in founder stocks, and consider rate of inbreeding in selective improvement programs.

Inbreeding Depression and Genetic Rescue in a Plant Metapopulation.

While migration of individuals has been shown to increase the persistence of small isolated populations through a process known as the "rescue effect," the demographic effects that pollen-mediated gene flow may have in plant populations are not known empirically. This study investigates the role that inbreeding depression plays in newly colonized populations of a common, dioecious, weedy species, Silene alba. Experimental greenhouse studies presented here show that S. alba displays high levels of inbreeding depression (expressed as lowered germination success) in progeny produced with inbreeding coefficients of 0.125 (half-sib mated), 0.250 (full-sib mated), and 0.375 (second-generation sib mated). In addition, it is shown that the degree of inbreeding depression in 12 natural colonies varies with the degree of isolation from other established populations. Significantly, data from experimental populations showed that gene flow into patches comprised of full sibs was higher than those observed into patches comprised of unrelated individuals and may serve to mitigate the effects of inbreeding depression. It is suggested that population connectivity through pollen-mediated gene flow may have substantial effects on the persistence of isolated colonies and on the spatial structure of a metapopulation in general.

Inbreeding Depression and Genetic Rescue in a Plant Metapopulation

While migration of individuals has been shown to increase the persistence of small isolated populations through a process known as the “rescue effect,” the demographic effects that pollen‐mediated gene flow may have in plant populations are not known empirically. This study investigates the role that inbreeding depression plays in newly colonized populations of a common, dioecious, weedy species, Silene alba. Experimental greenhouse studies presented here show that S. alba displays high levels of inbreeding depression (expressed as lowered germination success) in progeny produced with inbreeding coefficients of 0.125 (half‐sib mated), 0.250 (full‐sib mated), and 0.375 (second‐generation sib mated). In addition, it is shown that the degree of inbreeding depression in 12 natural colonies varies with the degree of isolation from other established populations. Significantly, data from experimental populations showed that gene flow into patches comprised of full sibs was higher than those observed into patches comprised of unrelated individuals and may serve to mitigate the effects of inbreeding depression. It is suggested that population connectivity through pollen‐mediated gene flow may have substantial effects on the persistence of isolated colonies and on the spatial structure of a metapopulation in general.

Effects of inbreeding on mental-ability factors

The differential effects of inbreeding on 11 subtests of the WISC, in a Japanese (Hiroshima) population, are related to the factor structure of the tests. The degree of inbreeding depression on mental abilities is most strongly correlated with the subtests' loadings on the General factor, g, which is common to all of the subtests. Loadings on the Verbal factor are also positively correlated with inbreeding depression. The (non-verbal) Performance factor, however, is slightly enhanced by inbreeding. One possible inference from these findings is that at least the General factor shows genetic dominance, which is theoretically consistent with natural selection for g in the course of human evolution. It is also noted that the factor structure of the WISC in the Japanese population is highly similar to that of the U.S. standardization sample.

Studies on Variation and Selection in Italian Ryegrass Populations. : III. Response to Selection for Higher Dry Matter Weight

Within-population selection was carried out for three generations, and Japanese Italian ryegrass populations increased dry matter weight but no plateau in selection was reached. Degree of inbreeding depression in small populations and heterosis in a synthetic population were investigated. Possibility of further improvement in the growth from autumn to early spring in Italian ryegrass was discussed.