Small Effective Population Size Research Articles

Analysis of genetic variability and population structure of the Mangalica pig breed using pedigree data

The maintenance of genetic diversity (GD) and low rate of inbreeding are two main goals for any conservation programs, especially in a small, closed population which is likely to violate these conservation targets in a long run. Among the conservation programs in Hungary probably the most characterizing is that of the Mangalica pigs, which is an autochthonous Hungarian pig breed group that has been preserved for biological diversity since 1973. The current study aimed to expose the evolution of population structure, GD and inbreeding coefficient with different approaches by analysing the pedigree of these breeds in the context of the conservation program. Genealogy analysis used the data of 12,808, 2393 and 3963 Blonde, Swallow-Belly and Red breeding animals born between 1980 and 2021, respectively. The reference populations (REF2021) were defined as breeding animals born between 2016 and 2021. Pedigree completeness was more than 90% in the fifth generation and the complete generation equivalent ranged from 4.29 to 7.08 and from 6.87 to 9.73 for the whole and the reference populations (REF2021), respectively. Generation interval on average was vary from 3.06 to 3.45 years with the longer pathways to the son. Most of different estimated inbreeding coefficient showed increased trends through pedigrees except for the Kalinowski new inbreeding coefficient (FNew) which decreased in all breeds in the last decade. The mean Wright inbreeding coefficient (Fw) was low, being 5.50%, 4.30% and 7.54% for the Blonde, Swallow-Belly, and Red reference populations (REF2021), respectively. Fw showed strong correlation with FNew but low correlation with FBal while the two types of ancestral inbreeding coefficients (FBal and FKal) were ranging from moderate strong to strong correlation in every breed. Effective population size of the reference populations (REF2021) was 85.57, 76.91, and 57.56, respectively. Based on the predicted future inbreeding for the next 25 years only the Red Mangalica breed was predicted to be “Transitional” in the endangerment categories. The GD loss in these three breeds was 5.6%, 5.7% and 8.7%, respectively, in which the loss due to genetic drift was decisive compared to the unequal founder contributions. In conclusion, the three populations at the present and in the next few generations are having optimistic perspective in terms of GD. These populations should be focused on reducing new inbreeding in mating plans and the Red population need to be monitored more carefully because of its current highest GD loss, smallest effective population size and highest inbreeding coefficient.

Association between anti-Müllerian hormone levels and reproductive parameters in Wagyu cattle raised in Brazil.

The production of in vitro embryos has sped up the dissemination of superior genetic material. However, the variation among the cattle response to oocyte and embryo production is a challenging factor. This variation is even higher in the Wagyu cattle as the breed has a small effective population size. The identification of an effective marker related to reproductive efficiency would allow the selection of more responsive females to reproductive protocols. The objective of this study was to evaluate the blood levels of anti-Müllerian hormone and associate it with oocyte recovery and blastocyst rate of embryos produced in vitro in Wagyu cows, as well as observe the hormone circulating levels in males. Serum samples from 29 females with seven follicular aspirations and four bulls were used. AMH measurements were performed using the bovine AMH ELISA kit. A positive correlation was identified between oocyte production and blastocyst rate (r = 0.84, P = 9 × 10-9), and AMH levels with oocyte (r = 0.49, P = 0.006) and embryo (r = 0.39, P = 0.03) production. The mean levels of AMH were different between animals with low (11.06 ± 3.01) and high (20.75 ± 4.46) oocyte production (P = 0.01). Males showed high serological levels of AMH (3829 ± 2328 pg/ml) compared with other breeds. It is possible to use the serological measurement of AMH as a method to select Wagyu females with greater capacity for oocyte and embryo production. Further studies correlating AMH serological levels with Sertoli cell function in bulls are needed.

Uncovering inbreeding, small populations, and strong genetic isolation in an Australian threatened frog, Litoria littlejohni

AbstractThe status of many amphibian populations remains unclear due to undetected declines driven by disease and difficulties in obtaining accurate population estimates. Here, we used genome complexity reduction-based sequencing technology to study the poorly understood Littlejohn’s treefrog, Litoria littlejohni across its fragmented distribution in eastern Australia. We detected five identifiable genetic clusters, with moderate to strong genetic isolation. At a regional scale, population isolation was likely driven by population crashes, resulting in small populations impacted by founder effects. Moderate genetic isolation was detected among populations on the Woronora Plateau despite short distances between population clusters. Evidence of recent declines was apparent in three populations that had very small effective population size, reduced genetic diversity and high inbreeding values. The rates of inbreeding detected in these populations combined with their small size leave these populations at elevated risk of extinction. The Cordeaux Cluster was identified as the most robust population as it was the largest and most genetically diverse. This study exemplifies the value of employing genetic methods to study rare, cryptic species. Despite low recapture rates using traditional capture-recapture demographic methods, we were able to derive population estimates, describe patterns of gene flow, and demonstrate the need for urgent conservation management.

Using conservation genetics to prioritise management options for an endangered songbird

Genetic data can be highly informative for answering questions relevant to practical conservation efforts, but remain one of the most neglected aspects of species recovery plans. Framing genetic questions with reference to practical and tractable conservation objectives can help bypass this limitation of the application of genetics in conservation. Using a single-nucleotide polymorphism dataset from reduced-representation sequencing (DArTSeq), we conducted a genetic assessment of remnant populations of the endangered forty-spotted pardalote (Pardalotus quadragintus), a songbird endemic to Tasmania, Australia. Our objectives were to inform strategies for the conservation of genetic diversity in the species and estimate effective population sizes and patterns of inter-population movement to identify management units relevant to population conservation and habitat restoration. We show population genetic structure and identify two small populations on mainland Tasmania as ‘satellites’ of larger Bruny Island populations connected by migration. Our data identify management units for conservation objectives relating to genetic diversity and habitat restoration. Although our results do not indicate the immediate need to genetically manage populations, the small effective population sizes we estimated for some populations indicate that they are vulnerable to genetic drift, highlighting the urgent need to implement habitat restoration to increase population size and to conduct genetic monitoring. We discuss how our genetic assessment can be used to inform management interventions for the forty-spotted pardalote and show that by assessing contemporary genetic aspects, valuable information for conservation planning and decision-making can be produced to guide actions that account for genetic diversity and increase chances of recovery in species of conservation concern.

Drivers of strong isolation and small effective population size at a leading range edge of a widespread plant

Climate change has influenced species distributions worldwide with upward elevational shifts observed in many systems. Leading range edge populations, like those at upper elevation limits, are crucial for climate change responses but can exhibit low genetic diversity due to founder effects, isolation, or limited outbreeding. These factors can hamper local adaptation at range limits. Using the widespread herb, Argentina anserina, we measured ecological attributes (population density on the landscape, area of population occupancy, and plant and flower density) spanning a 1000 m elevation gradient, with high elevation populations at the range limit. We measured vegetative clonal potential in the greenhouse for populations spanning the gradient. We combined these data with a ddRAD-seq dataset to test the hypotheses that high elevation populations would exhibit ecological and genomic signatures of leading range edge populations. We found that population density on the landscape declined towards the high elevation limit, as is expected towards range edges. However, plant density was elevated within edge populations. In the greenhouse, high elevation plants exhibited stronger clonal potential than low elevation plants, likely explaining increased plant density in the field. Phylogeographic analysis supported more recent colonization of high elevation populations which were also more genetically isolated, had more extreme heterozygote excess and had smaller effective population size than low. Results support that colonization of high elevations was likely accompanied by increased asexuality, contributing to a decline in effective population size. Despite high plant density in leading edge populations, their small effective size, isolation and clonality could constrain adaptive potential.

GENETIC DIVERSITY AND STRUCTURE OF THE WHITE-FRONTED PARROT (AMAZONA ALBIFRONS) IN MEXICO

In this study we assessed the genetic diversity and differentiation, and genealogical relationships in a group of individuals of A. albifrons distributed on the Pacific slope and in the Yucatan Peninsula, Mexico using mitochondrial DNA markers.Both range regions the species showed a high genetic diversity, suggesting population expansion from a small effective population size. Genealogical relationships revealed the presence of two genetic groups that have gone through different demographic events, one in the Yucatan Peninsula and the other in the Pacific slope. Considering that the individuals of the Yucatan Peninsula formed a genetic group exclusive to the region due to isolation events and a unique evolutionary history, we suggest its recognition as an evolutionarily significant unit (ESU). In addition, considering the presence of unique haplotypes in the localities of Sinaloa and Michoacan, we recommended that conservation plans focus on these regions.

Conservation initiatives of Syngnathiformes species in the southern Philippines: What does the mitochondrial DNA signature tell us?

Abstract Mitochondrial DNA signatures based on the control region and 12S rRNA gene were used to assess the impact of conservation measures on the effective management of vulnerable Syngnathiformes (seahorses, pipefishes, and allies) species. Results from phylogenetic inference, polymorphism, neutrality indices, haplotype networks and microhabitat information may justify the establishment of distinct management units for different species. For smooth seahorses, Hippocampus kuda was identified as a species complex that formed three clusters with 20 haplotypes. Based on molecular data, these are the first records of Hippocampus capensis and Hippocampus casscsio in the Philippines. High haplotype diversity (h = 28; Hd = 0.943), yet low nucleotide diversity (Pi:0.18095) for polymorphism, suggests minor differences among haplotypes. Neutrality indices calculated using Tajima's D (−2.00774), with P < 0.05 and Fu's Fs (−11.645), were significant. However, both tests were negative, a signature of rapid population expansion from a small effective population size, which could be attributed to past heavy harvests and habitat destruction, as supported by local data. For pipefishes and their allies, there was high haplotype diversity (h = 22; Hd = 0.875) and low nucleotide diversity of Pi: 0.16671. However, neutrality indices calculated using Tajima's D (−1.68518) and Fu's Fs (11.549) were not significant, with P > 0.05, indicating a balancing selection for this population. Results reveal that the recent population expansion of seahorses proves that current conservation measures are effectively safeguarding populations, while balancing selection is maintaining genetic polymorphism in pipefishes and their relatives, making them resilient to changing environments. Moreover, as revealed by haplotype networks, intraspecific variation suggests distinct management for different species. In addition, underwater surveys show an essential association between microhabitats and species' survival, thus encouraging future initiatives regarding habitat protection, especially coral reefs, seagrass beds, sponge gardens, mangrove areas and estuaries.

Jaguar density in the most threatened ecoregion of the Amazon

Abstract Population parameters provide essential information for conservation efforts aimed at target species. We used the spatially explicit capture-recapture method to estimate the jaguar density and population size in the Gurupi Jaguar Conservation Unit (JCU), located in the most threatened ecoregion of the Amazon. The estimated density of 2.62 individuals/100 km2 in a continuous forest of over 10,000 km2 implies a small effective population size, underscoring the threat to the long-term viability of the Gurupi JCU’s jaguar population. We recommend urgent forest restoration actions to reduce fragmentation and improve connectivity between Gurupi JCU and other forest fragments to facilitate jaguar gene flow.

Small population of the largest water strider after the late Pleistocene and the implications for its conservation

Climate oscillation and its synergistic impacts on habitat fragmentation have been identified as threatening the survival of some extant species. However, the mechanisms by which semi-aquatic insects impacted by such events remain poorly understood. Herein, we studied the largest water strider in the world, Gigantometra gigas, to explore the effect of these two factors on its evolutionary history. The sequences of mitogenomic and nrDNA cluster were utilized to reconstruct phylogenetic relationship among G. gigas populations and its demographic history. Mitochondrial genes were separately reconstructed topologies of that populations and detected remarkable differences. We found that G. gigas populations conform to the isolation-by-distance model, and decline occurred at about 120 ka, which was probably influenced by the climate change during the late Pleistocene and eventually maintained a small effective population size (Ne) around 85,717. The populations in Guangdong Province of China are worthy of note in that they exhibit low genetic diversity, a small Ne around 18,899 individuals, and occupy an area with little suitable future habitat for G. gigas. This work recommends that conservation efforts are implemented to ensure the long-term survival of small G. gigas populations, and notes that further evaluation of their extinction risk under the impacts of human activities is required.

Genetic structure and relatedness of juvenile sicklefin lemon shark (Negaprion acutidens) at Dongsha Island

Negaprion acutidens (sicklefin lemon shark) is distributed in the Indo-Pacific and in close association with coral reefs. Under the protection of the Dongsha Atoll National Park, a small but well-established juvenile population of N. acutidens inhabiting coastal areas of Dongsha Island was recently observed to display site fidelity by using acoustic telemetry. This study was designed to reveal the fine scale genetic structure and relatedness within and among 5 juvenile shark cohorts inhabiting 3 sampling sites at Dongsha Island. A total 188 juveniles were caught and sampled between 2016 and 2017, and genotyped with twelve loci. They were assigned to 5 year cohorts (2013–2017) based on the body length and date they were caught, also assigned to 3 sites based on where they were caught. Among five cohorts, the percentage of unrelated pairs within a cohort is more than 62% in average, suggesting a potential high mortality during their early life stage. The results of Fst and assignment testing showed that there was no significant genetic structure between sites and cohorts indicating that there was no fine scale genetic structure, even though the juveniles possessed strong site fidelity. A small effective population size (Ne) was detected (Ne = 86.7) which indicates the presence of a potentially isolated and vulnerable population at Dongsha. These results provide the genetic diversity as a baseline for future management and conservation of N. acutidens in the South China Sea.

Genome-wide data suggest a revision in management of the Caspian Sea trout Salmo caspius.

Salmo caspius Kessler, 1877 is one of the most commercially important species of Salmonidae in the southern basin of the Caspian Sea. The occurrence of its wild populations has undergone sever reduction during the last years. In spite of the yearly restocking activity, still no progress on the recovery of its wild population has been observed. Hence, the present study was done in order to assess the efficiency of the current restocking activity in the southern Caspian basin in term of genetic diversity. DNA extracts of 32 S. caspius from four different groups were screened using 62621 genome-wide single nucleotide polymorphisms (SNP). The overal genetic diversity and Fst values were 0.18 and 0.08, respectively. Considering the observed admixture pattern and the positive values for inbreeding coeficient it seems that S. caspius suffers from its small effective population size. In order to obtain the maximum performance, alonside with expanding the size of brood stocks, rehabilitation of the habitats and spawning rivers of this nationally endangered species is of great importance.

Kontrola uzgoja u srodstvu u populaciji banijske šare svinja pomoću optimizacijskih metoda

The aim of the study was to estimate genetic diversity parameters for Banija spotted pig population and to apply optimisation methods to control the inbreeding in the population in three different scenarios. The first scenario consisted of minimizing inbreeding by minimizing the average kinship without considering breeding values. The second scenario was to minimize inbreeding by minimizing the average kinship accounting for breeding values. The third scenario was to apply traditional optimal contribution selection by maximizing the breeding value of the offspring. A total of 5 boars and 49 sows were selected to create mating plan minimise inbreeding in the next generation. The average inbreeding coefficient in the population was 6.97, while effective population size was 8.47. In the first scenario, different kinship constrains between candidates resulted in a change in the number of selected animals and a change in the average breeding values, such that the number of selected candidates increased when the constraint on kinship was stronger, with a simultaneous decrease in breeding values. The second scenario resulted in increased inbreeding when additional weight was placed on genetic gain. The Maximisation of breeding values resulted with drastically increased average inbreeding coefficient in the next generation. Due the small total and effective population size, the application of optimisation methods demonstrated that genetic improvement is possible at a high cost of loss of the genetic variability and preservation of diversity remains the first objective in the breeding programme for Banija spotted pig.

Genetic diversity and structure of a recent fish invasion: Tench (Tinca tinca) in eastern North America.

Introduced and geographically expanding populations experience similar eco-evolutionary challenges, including founder events, genetic bottlenecks, and novel environments. Theory predicts that reduced genetic diversity resulting from such phenomena limits the success of introduced populations. Using 1900 SNPs obtained from restriction-site-associated DNA sequencing, we evaluated hypotheses related to the invasion history and connectivity of an invasive population of Tench (Tinca tinca), a Eurasian freshwater fish that has been expanding geographically in eastern North America for three decades. Consistent with the reported history of a single introduction event, our findings suggest that multiple introductions from distinct genetic sources are unlikely as Tench had a small effective population size (~114 [95% CI=106-123] individuals), no strong population subdivision across time and space, and evidence of a recent genetic bottleneck. The large genetic neighbourhood size (220 km) and weak within-population genetic substructure suggested high connectivity across the invaded range, despite the relatively large area occupied. There was some evidence for a small decay in genetic diversity as the species expanded northward, but not southward, into new habitats. As eradicating the species within a ~112 km radius would be necessary to prevent recolonization, eradicating Tench is likely not feasible at watershed-and possibly local-scales. Management should instead focus on reducing abundance in priority conservation areas to mitigate adverse impacts. Our study indicates that introduced populations can thrive and exhibit relatively high levels of genetic diversity despite severe bottlenecks (<1.5% of the ancestral effective population size) and suggests that landscape heterogeneity and population demographics can generate variability in spatial patterns of genetic diversity within a single range expansion.

Severe inbreeding, increased mutation load and gene loss-of-function in the critically endangered Devils Hole pupfish.

Small populations with limited range are often threatened by inbreeding and reduced genetic diversity, which can reduce fitness and exacerbate population decline. One of the most extreme natural examples is the Devils Hole pupfish (Cyprinodon diabolis), an iconic and critically endangered species with the smallest known range of any vertebrate. This species has experienced severe declines in population size over the last 30 years and suffered major bottlenecks in 2007 and 2013, when the population shrunk to 38 and 35 individuals, respectively. Here, we analysed 30 resequenced genomes of desert pupfishes from Death Valley, Ash Meadows and surrounding areas to examine the genomic consequences of small population size. We found extremely high levels of inbreeding (FROH = 0.34-0.81) and an increased amount of potentially deleterious genetic variation in the Devils Hole pupfish as compared to other species, including unique, fixed loss-of-function alleles and deletions in genes associated with sperm motility and hypoxia. Additionally, we successfully resequenced a formalin-fixed museum specimen from 1980 and found that the population was already highly inbred prior to recent known bottlenecks. We thus document severe inbreeding and increased mutation load in the Devils Hole pupfish and identify candidate deleterious variants to inform management of this conservation icon.

Differential response to climate change and human activities in three lineages of Sichuan snub‐nosed monkeys (Rhinopithecus roxellana)

AbstractAimDetermining the mechanisms by which climate change and human activities affect patterns of ecological specialization in different genetic units of the same species is crucial for developing local or regionally‐based conservation solutions. This study uses species distribution models and genetic analysis to (1) identify the evidence of intraspecific differences in the population size and distribution of the three extant lineages (Sichuan/Gansu (SG), Qinling (QL) and Shennongjia (SNJ)) of Sichuan snub‐nosed monkeys and (2) determine why some lineages have lower population numbers, a smaller geographical distribution, and are more threatened with extinction.LocationChina.MethodsWe used n‐dimensional hypervolume modelling and genotype‐environment association (GEA) models to compare the climatic niches of three snub‐nosed monkey lineages, SDMs to reconstruct the historical, current and future distributions of each lineage and SMC++ to calculate their effective population sizes.ResultsWe found evidence of: (1) climatic niche differentiation among the SG, QL and SNJ lineages of Sichuan snub‐nosed monkeys; (2) geographical isolation combined with a decrease in population size during the LGM resulted in ecological specialization among these three lineages; and (3) a decline in climatic suitability and anthropogenically driven land conversion, combined with small population size and a narrow distributional range, indicates that the SNJ lineage is at a greater risk of extinction than the SG and QL lineages.Main conclusionsWe demonstrate that during the LGM a reduction in habitat suitability driven by climate change, in concert with decreasing population size, resulted in the geographical isolation of the three Sichuan snub‐nosed monkey subpopulations, leading to lineage differences in ecological specialization. GEA models and hypervolume models demonstrated that the three lineages occupy different ecological niches. Based on lineage‐level models, the SNJ and QL lineages should be the immediate focus of conservation efforts due to their small effective population size and expected future reductions in available suitable habitats. The modelling approach used here is robust and can be applied effectively to examine the biogeography, recent evolutionary history and effective population size of other endangered animal taxa.

Genomic Assessment of Cancer Susceptibility in the Threatened Catalina Island Fox (Urocyon littoralis catalinae).

Small effective population sizes raise the probability of extinction by increasing the frequency of potentially deleterious alleles and reducing fitness. However, the extent to which cancers play a role in the fitness reduction of genetically depauperate wildlife populations is unknown. Santa Catalina island foxes (Urocyon littoralis catalinae) sampled in 2007–2008 have a high prevalence of ceruminous gland tumors, which was not detected in the population prior to a recent bottleneck caused by a canine distemper epidemic. The disease appears to be associated with inflammation from chronic ear mite (Otodectes) infections and secondary elevated levels of Staphyloccus pseudointermedius bacterial infections. However, no other environmental factors to date have been found to be associated with elevated cancer risk in this population. Here, we used whole genome sequencing of the case and control individuals from two islands to identify candidate loci associated with cancer based on genetic divergence, nucleotide diversity, allele frequency spectrum, and runs of homozygosity. We identified several candidate loci based on genomic signatures and putative gene functions, suggesting that cancer susceptibility in this population may be polygenic. Due to the efforts of a recovery program and weak fitness effects of late-onset disease, the population size has increased, which may allow selection to be more effective in removing these presumably slightly deleterious alleles. Long-term monitoring of the disease alleles, as well as overall genetic diversity, will provide crucial information for the long-term persistence of this threatened population.

Patterns of genetic diversity of brown trout in a northern Spanish catchment linked to structural connectivity

The alteration of structural connectivity in fluvial networks is important for the genetic dynamics of aquatic species. Exploring the effects of network fragmentation through genetic analysis is crucial to assess the conservation status of riverine species. In this study, we investigated the genetic consequences of the altered connectivity of brown trout in the Deva–Cares catchment (northern Spain). We investigated (1) genetic diversity, (2) genetic differentiation and genetic structure, (3) migration rates and effective population size and (4) genetic differentiation and riverscape characteristics. Analysis of the genetic variation among 197 individuals from the 13 study sites revealed a high degree of genetic differentiation (FST = 0.181). Below-barrier study sites had higher genetic diversity and lower FST values, while headwater and above-barrier study sites had lower genetic diversity and higher FST values. Most of the genetic groups identified were separated by one or more impermeable barriers. We reported an abrupt decrease in genetic diversity and effective population size in upper course tributaries and isolated reaches. Likewise, a downstream-biased gene flow was found, and it was most likely related to the fragmentation caused by barriers, since the results from migration indicated that gene flow between groups without impermeable barriers was higher bidirectionally. Isolation by impermeable barriers played a more important role than hydrological distance in determining the genetic structure. Most of the genetic groups showed small effective population sizes. Genetic analysis at the river network scale provides evidence for the role of barriers in determining genetic diversity patterns, highlighting the importance of maintaining and restoring river longitudinal connectivity.

Reduced representation sequencing to understand the evolutionary history of Torrey pine (Pinus torreyana parry) with implications for rare species conservation.

Understanding the contribution of neutral and adaptive evolutionary processes to population differentiation is often necessary for better informed management and conservation of rare species. In this study, we focused on Pinus torreyana Parry (Torrey pine), one of the world's rarest pines, endemic to one island and one mainland population in California. Small population size, low genetic diversity, and susceptibility to abiotic and biotic stresses suggest Torrey pine may benefit from interpopulation genetic rescue to preserve the species' evolutionary potential. We leveraged reduced representation sequencing to tease apart the respective contributions of stochastic and deterministic evolutionary processes to population differentiation. We applied these data to model spatial and temporal demographic changes in effective population sizes and genetic connectivity, to identify loci possibly under selection, and evaluate genetic rescue as a potential conservation strategy. Overall, we observed exceedingly low standing variation within both Torrey pine populations, reflecting consistently low effective population sizes across time, and limited genetic differentiation, suggesting maintenance of gene flow between populations following divergence. However, genome scans identified more than 2000 candidate SNPs potentially under divergent selection. Combined with previous observations indicating population phenotypic differentiation, this indicates natural selection has probably contributed to the evolution of population genetic differences. Thus, while reduced genetic diversity, small effective population size, and genetic connectivity between populations suggest genetic rescue could mitigate the adverse effects of rarity, evidence for adaptive differentiation suggests genetic mixing could disrupt adaptation. Further work evaluating the fitness consequences of inter-population admixture is necessary to empirically evaluate the trade-offs associated with genetic rescue in Torrey pine.

Inbreeding depression and the probability of racing in the Thoroughbred horse.

Small effective population sizes and active inbreeding can lead to inbreeding depression due to deleterious recessive mutations exposed in the homozygous state. The Thoroughbred racehorse has low levels of population genetic diversity, but the effects of genomic inbreeding in the population are unknown. Here, we quantified inbreeding based on runs of homozygosity (ROH) using 297 K SNP genotypes from 6128 horses born in Europe and Australia, of which 13.2% were unraced. We show that a 10% increase in inbreeding (FROH) is associated with a 7% lower probability of ever racing. Moreover, a ROH-based genome-wide association study identified a haplotype on ECA14 which, in its homozygous state, is linked to a 32.1% lower predicted probability of ever racing, independent of FROH. The haplotype overlaps a candidate gene, EFNA5, that is highly expressed in cartilage tissue, which when damaged is one of the most common causes of catastrophic musculoskeletal injury in racehorses. Genomics-informed breeding aiming to reduce inbreeding depression and avoid damaging haplotype carrier matings will improve population health and racehorse welfare.

Globally Relaxed Selection and Local Adaptation in Boechera stricta.

The strength of selection varies among populations and across the genome, but the determinants of efficacy of selection remain unclear. In this study, we used whole-genome sequencing data from 467 Boechera stricta accessions to quantify the strength of selection and characterize the pattern of local adaptation. We found low genetic diversity on 0-fold degenerate sites and conserved non-coding sites, indicating functional constraints on these regions. The estimated distribution of fitness effects and the proportion of fixed substitutions suggest relaxed negative and positive selection in B. stricta. Among the four population groups, the NOR and WES groups have smaller effective population size (Ne), higher proportions of effectively neutral sites, and lower rates of adaptive evolution compared with UTA and COL groups, reflecting the effect of Ne on the efficacy of natural selection. We also found weaker selection on GC-biased sites compared with GC-conservative (unbiased) sites, suggested that GC-biased gene conversion has affected the strength of selection in B. stricta. We found mixed evidence for the role of the recombination rate on the efficacy of selection. The positive and negative selection was stronger in high-recombination regions compared with low-recombination regions in COL but not in other groups. By scanning the genome, we found different subsets of selected genes suggesting differential adaptation among B. stricta groups. These results show that differences in effective population size, nucleotide composition, and recombination rate are important determinants of the efficacy of selection. This study enriches our understanding of the roles of natural selection and local adaptation in shaping genomic variation.