Accumulation Of Deleterious Alleles Research Articles

Demography, genetic diversity and expansion load in the colonizing species Leontodon longirostris (Asteraceae) throughout its native range.

Unravelling the evolutionary processes underlying range expansions is fundamental to understand the distribution of organisms, as well as to predict their future responses to environmental change. Predictions for range expansions include a loss of genetic diversity and an accumulation of deleterious alleles along the expansion axis, which can decrease fitness at the range-front (expansion load). In plants, empirical studies supporting expansion load are scarce, and its effects remain to be tested outside a few model species. Leontodon longirostris is a colonizing Asteraceae with a widespread distribution in the Western Mediterranean, providing a particularly interesting system to gain insight into the factors that can enhance or mitigate expansion load. In this study, we produced a first genome draft for the species, covering 418Mbp (~53% of the genome). Although incomplete, this draft was suitable to design a targeted sequencing of ~1.5Mbp in 238 L.longirostris plants from 21 populations distributed along putative colonization routes in the Iberian Peninsula. Inferred demographic history supports a range expansion from southern Iberia around 40,000years ago, reaching northern Iberia around 25,000years ago. The expansion was accompanied by a loss of genetic diversity and a significant increase in the proportion of putatively deleterious mutations. However, levels of expansion load in L.longirostris were smaller than those found in other plant species, which can be explained, at least partially, by its high dispersal ability, the self-incompatible mating system, and the fact that the expansion occurred along a strong environmental cline.

Reintroducing Cuvier’s gazelle. Better than expected from captive-bred founders

The use of captive-bred animals as founder stock for reintroduction is sometimes discouraged due to their low genetic diversity and even accumulation of deleterious alleles. In October 2016, 43 Cuvier’s gazelles (12 males and 31 females), managed under a European Endangered Species Programme (EEP) and housed in captivity, formed the base of a reintroduction project in Tunisia. The project approach used soft-release techniques. Upon arrival, animals were released in acclimatisation pens, so they could adjust to the new conditions gradually before true release. This study reports on the three-year period gazelles were in the acclimatisation pens before release into the wild. To assess the suitability of captive-bred Cuvier’s gazelles as founder stock for reintroduction, the demographic parameters of the reintroduced population were studied for three reproductive seasons in Tunisia (2017–2019). The demographic parameters of the reintroduced population were also compared to those from the source captive population as a control during the first breeding season. If the animals used as founders were unsuited, a decrease in demographic parameters could be expected over time in the reintroduced population, as well as lower demographic variables compared to the source population. Contrary to expectations, during the three-year study period, all demographic variables increased in the population reintroduced in Tunisia, except juvenile mortality, which decreased. Moreover, none of the demographic values of the gazelles in Tunisia were significantly different from the source population. We hypothesize that in the extremely bottlenecked captive Cuvier’s gazelle population used as founder stock, genetic diversity was still high enough to surmount the presumably deleterious effects of inbreeding. This is probably due to very high heritability (h2), a parameter providing information on the quantitative genetic variation associated with multi-locus quantitative traits previously found in this population. Although reintroduction programs have traditionally been undertaken purely as management exercises, ours was designed to meet a research objective as well. We wanted to find out the adaptive variation in sex ratio in offspring of female Cuvier’s gazelles using the size of the enclosure as a proxy reflecting their body condition. As found in captivity using consanguinity level as a proxy of body condition, in the reintroduced population, mothers in large enclosures produced more daughters while those in the small ones produced more sons, which supports adaptive manipulation of the birth sex ratio favoured by natural selection in reintroduced Cuvier’s gazelles.

The mutation of a PECTATE LYASE-LIKE gene is responsible for the Yellow Margin phenotype in potato.

The yellow margin (ym) gene was mapped to a 30-kb genomic region in potato and the mutation of a pectate lyase gene led to this phenotype. The practice of clonally propagating potato (Solanum tuberosum L.), which has been lasted for thousands of years, has caused the accumulation of deleterious alleles. Despite yellow margin (ym) being a common cause of a detrimental weak-vigor phenotype and reduced yield in diploid potato, the underlying gene has eluded discovery to date. In this paper, we mapped the ym gene to a 30-kb region containing four annotated genes. Among them, PGSC0003DMG402023481 encodes a pectate lyase-like gene (StPLL) with lower expression in ym plants than in the wild-type plants. PCR amplification confirmed a 4.1-kb deletion in the mutant allele of StPLL. Knockout of StPLL in diploid potato resulted in a similar phenotype with the ym plants. This study not only characterizes the ym allele but also provides the molecular tools to select and purge it from populations, while also deepening our understanding of the morphogenesis in potato.

Preference for Outbreeding in Inbred Littledale’s Whistling Rats Parotomys littledalei

Inbreeding is sometimes tolerated in species occupying patchy, unpredictable habitats, when it becomes too costly to outbreed. Although traits leading to inbreeding depression may be selected against, the accumulation of deleterious alleles from constant inbreeding might promote outbreeding. Littledale’s whistling rat Parotomys littledalei occupies patchy habitats in arid western South Africa, and inbreeds in captivity without suffering inbreeding depression. We tested whether female whistling rats make different mate choice decisions based on their inbreeding status, by providing inbred and outbred females with male odours in four pairwise combinations: unrelated outbred (r = 0) versus either familiar littermate sibling (r = 0.5), half-sibling (r = 0.25), first cousin (r = 0.125), or unrelated inbred (r = 0). Inbred females generally preferred unrelated males, but did not show a preference between unrelated males and first cousins. In contrast, outbred females did not generally show a preference, but preferred first cousins to unrelated males. In breeding trials, reproductive success (output and viability of young) of outbred females paired with unrelated or related males was equally high, whereas inbred females suffered reduced reproductive success when paired with closely-related males. Our results indicate that the inbreeding status of female whistling rats influences their decision to outbreed or inbreed, which might influence their fitness. While outbred whistling rats do not suffer inbreeding depression, the costs of constant inbreeding could promote outbreeding by inbred females. We propose that the choice to inbreed or outbreed in female whistling rats depends on their inbreeding status and the genetic relatedness of available mates, with outbreeding more likely to occur unless unrelated mates are not available.

Ex Situ Conservation of Biodiversity with Particular Emphasis to Ethiopia

Biodiversity encompasses variety and variability of all forms of life on earth that play a great role in human existence. Its conservation embraces maintenance, sustainable utilization, and restoration, of the lost and degraded biodiversity through two basic and complementary strategies called in situ and ex situ. Ex situ conservation is the technique of conservation of all levels of biological diversity outside their natural habitats through different techniques like zoo, captive breeding, aquarium, botanical garden, and gene bank. It plays key roles in communicating the issues, raising awareness, and gaining widespread public and political support for conservation actions and for breeding endangered species in captivity for reintroduction. Limitations of ex situ conservation include maintenance of organisms in artificial habitats, deterioration of genetic diversity, inbreeding depression, adaptations to captivity, and accumulation of deleterious alleles. It has many constraints in terms of personnel, costs, and reliance on electric power sources. Ethiopia is considered to be one of the richest centers of genetic resources in the world. Currently, a number of stakeholders/actors are actively working on biodiversity conservation through ex situ conservation strategies by establishing gene banks, botanical garden, and zoo.

Consequences of metapopulation collapse: comparison of genetic attributes between two Allegheny woodrat metapopulations

Disruptions in metapopulation connectivity due to demographic pressure can leave genetically isolated subpopulations susceptible to genetic drift, accumulation of deleterious alleles, and inbreeding depression. Such a scenario may be playing out within Allegheny woodrat (Neotoma magister) metapopulations as a series of synergistic extrinsic pressures have contributed to the rangewide decline of the species over the last 40 years. Our goal was to elucidate the effects of demographic collapse on metapopulation function by using 11 microsatellites markers to quantify differences in patterns of connectivity and genetic diversity between a demographically stable metapopulation and one in severe demographic decline. The demographically diminished metapopulation had lower levels of genetic diversity than the stable metapopulation at all levels evaluated (metapopulation-, subpopulation-, and individual-scales). In contrast to patterns of connectivity observed within the stable metapopulation, peripheral subpopulations in the diminished metapopulation had become completely isolated and were drifting toward genetic fixation, likely as a result of the extirpation of stepping-stone subpopulations. The declining genetic parameters observed within these isolated peripheral subpopulations suggest that inbreeding depression may be contributing significantly to their demographic decline. Allegheny woodrats readily express the genetic consequences of metapopulation decline due to the low effective population sizes of subpopulations and the species’ limited dispersal capacity. Differences in genetic parameters observed between demographically stable and diminished Allegheny woodrat metapopulations emphasize the risks posed to metapopulation function and associated genetic processes introduced with demographic decline.

Low Genetic Diversity in Several Gopher Tortoise (Gopherus polyphemus) Populations in the Desoto National Forest, Mississippi

Gopherus polyphemus has experienced severe population declines, especially in the western portion of its range. As a consequence, G. polyphemus may have experienced population bottlenecks that resulted in a decrease in genetic diversity and an accumulation of deleterious alleles. The importance of genetic diversity has been well-documented for several fitness parameters (e.g., survival, disease resistance, growth and developmental rates, and developmental instability). Western populations of G. polyphemus in south Mississippi (USA) have lower hatching success (16.7–48%) than that found in eastern populations (67–97%). Even under laboratory conditions, approximately 40% of the eggs still failed to hatch, suggesting that intrinsic (egg quality) factors may be affecting development. Using nine microsatellite loci, we genotyped individuals from four populations in south Mississippi and one eastern population (Fort Benning, GA) and compared several genetic diversity indices (e.g., allelic richness, expected heterozygosity, and percent polymorphic loci) with published data from populations in the eastern portion of the range, such as populations east of the Mobile and Tombigbee rivers. We found significantly lower genetic diversity in the four Mississippi populations than in the eastern populations. However, these findings only demonstrate that these populations have low genetic diversity, and establishing any causal relationship between low genetic diversity (or other intrinsic factors; e.g., female condition) and reduced reproductive success should be further investigated.

A viable herd of genetically uniform cattle.

Inbreeding, which can lead to the loss of genetic variation or the accumulation of deleterious alleles, has been shown to reduce fitness in wild (1), zoo, laboratory (2) and farmed (3) animals. But it has been proposed that when combined with selection, inbreeding may purge deleterious alleles (4). Here we provide support for this hypothesis in a study of the Chillingham cattle, which shows that this viable herd is almost genetically uniform. The homozygosity of this herd far exceeds that of other cattle (5) and that found in wild populations of other mammalian species (6,7).

Biased sex ratios in laboratory strains of guppies, Poecilia reticulata

Older laboratory strains of guppies, Poecilia reticulata, exhibit female-biased sex ratios. The results of interstrain crosses and crosses involving exceptional Y Y males showed that the sex ratio phenomenon is determined primarily by Y-linked genes which result either in decreased production of Y-bearing sperm, or in lowered ability of Y-bearing sperm to compete with X-bearing sperm for ova. Inbreeding and local mate competition cannot account for the evolution of the sex ratio deviations. It is suggested that the sex ratio effect is caused either by pleiotropic effects of Y-linked genes increasing the ability of males to compete for females, or by a genetic deterioration of the Y-chromosomes through accumulation of deleterious alleles. The latter suggestion is supported by the theoretical models of Nei (1970) and Charlesworth (1978) on the evolution of inert Y-chromosomes.