Journal of Heredity最新文献

Mountain lions, Puma concolor, are widespread and adaptable carnivores. However, due to their large home ranges and long distance dispersals, they are strongly impacted by habitat fragmentation, which results in small and isolated populations. Genomic analyses play an important role in understanding and predicting the impacts of increased isolation of populations, such as decreased genetic diversity and increased levels of inbreeding. Here we report a high-quality, chromosome-level reference genome of P. concolor that was generated as part of the California Conservation Genomics Project. The primary assembly has a total length of 2.5 Gb contained in 258 scaffolds, a contig N50 of 42.3 Mb, a scaffold N50 of 149.8 Mb, and a BUSCO completeness score of 95%. This P. concolor genome assembly will provide an important resource for genomic analyses that aid decision makers in managing the species in fragmented landscapes.

Calasterella californica belongs to a monotypic genus of liverworts endemic to the west coast of North America, primarily distributed in California. This dioicous species occurs in a variety of ecosystems from deserts to redwood forest; little is known about how this species is adapted to live in those seemingly contrasting environments. In this paper, we report the assembly of the nuclear genome of Calasterella californica. As part of the California Conservation Genomics Project (CCGP), we used Pacific Biosciences HiFi long-read sequencing data to produce a de novo assembly that consists of 772 contigs, with a total length of 517 Mbp and a BUSCO complete score of 95%. C. californica is only the sixth species of liverworts - a group with more than 7200 described species - to have a nuclear reference genome. The availability of this reference genome will facilitate the study of the unique features of C. californica and other liverworts, pave the road towards a comparative understanding of liverwort genomes, and add an important starting point for studies of the geographic variation of this species within the CCGP project.

The allelic diversity of exon 2 (DQB gene) and exon 3 (DRB gene) of major histocompatibility complex class II was studied for the first time in two species of the landlocked pinnipeds, Baikal (N = 79) and Caspian (N = 32) seals, and these were in compared with the widespread Arctic species, the ringed seal (N = 13). The analysis of the second exon comprising the antigen-binding region revealed high allelic diversity in all three species but the pattern of the diversity was the most specific for the Baikal seal. This species differs from the other two by the smallest number of alleles in the population, yet they have the largest number of alleles per individual and by the maximum similarity of individual genotypes. Presumably, this specificity is a consequence of the spatial and temporal homogeneity of the Lake Baikal environment. Analysis of the third exon encoding the conserved β2-domain showed that the Baikal seal differs by the greatest number of amino acid sequences per individual, while the Caspian seal has the lowest number of variants. A single variant of the β2-domain, the same as in the ringed seal, predominates in the Caspian seal, whereas in the Baikal seal the two other variants predominate. At the same time, three species-specific amino acid sequences were observed among minor variants in the Caspian seal, while only one was found in the Baikal seal. This fact may suggest a longer period of independent evolution in the Caspian seal compared to the Baikal seal.

Hybridization produces a range of outcomes from advantageous to disadvantageous, and a goal of genetic research is to understand the gene interactions that generate these outcomes. Interactions between cytoplasmic elements, such as mitochondria, and the nucleus may be particularly vulnerable to accruing disadvantageous combinations as a result of their different rates of evolution. However, mitonuclear incompatibilities often do not have an observable effect until the F2 and later generations. We used Tigriopus californicus, a model system for mitonuclear incompatibilities that is also known for exhibiting heterosis in the F1 generation, to test whether hypoxia was more stressful for mitonuclear interactions than other environmental stressors. We generated 284 parental and 436 F1 hybrids from four population crosses (720 total) and compared parental and F1 populations for hypoxia tolerance. We observed that, on average, F1 hybrids were less likely to survive a hypoxia stress test than parental populations (Parental:F1 coefficients ranged from -0.04 to 0.14 with none significantly different from 0). This suggests that hypoxia may be a particularly intense stressor for mitonuclear coordination, and that hybridization outcomes vary by trait.

The penstemons are ornamental annual flowering plants native to the Intermountain West and Rocky Mountains and commonly used for urban landscaping. Elite commercial penstemons are generally susceptible to abiotic stresses, including drought, root rot, cold, and high salinity. Firecracker penstemon (Penstemon eatonii), however, is much more tolerant to these stresses than most elite cultivars. Importantly, firecracker penstemon has been reported to hybridize with many other penstemons and therefore provides the opportunity to develop more tolerant elite cultivars through strategic crossing. To facilitate the study and utilization of firecracker penstemon, we sequenced and annotated the genome of a P. eatonii accession collected from Utah, USA. We also performed low-coverage, whole-genome sequencing of 26 additional accessions from three different varieties of P. eatonii. This chromosome-scale genome assembly is the most contiguous and complete Penstemon genome sequenced to date.

Male mice who are heterozygous for distorting and non-distorting alleles at the t-haplotype transmit the driving t-haplotype around 90% of the time-a drastic departure from Mendelian expectations. This selfish act comes at a cost. The mechanism underlying transmission distortion in this system causes severe sterility in males homozygous for the drive alleles, ultimately preventing its fixation. Curiously, many driving t-haplotypes also induce embryonic lethality in both sexes when homozygous; however, this is neither universal nor a necessity for this distortion mechanism. Charlesworth provided an adaptive explanation for the evolution of lethal t-haplotypes in a population segregating for distorting and non-distorting t alleles-if mothers compensate by replacing dead embryos with new offspring (or by transferring energy to surviving offspring), a recessive lethal can be favored because it effectively allows mothers the opportunity to trade in infertile males for potentially fertile offspring. This model, however, requires near complete reproductive compensation for the invasion of the lethal t-haplotype and produces an equilibrium frequency of lethal drivers well below what is observed in nature. We show that low levels of systemic inbreeding, which we model as brother-sister mating, allow lethal t-haplotypes to invade with much lower levels of reproductive compensation. Furthermore, inbreeding allows these lethal haplotypes to largely displace the ancestral male-sterile haplotypes. Our results show that together inbreeding and reproductive compensation move expected equilibria closer to observed haplotype frequencies in natural populations and occur under lower, potentially more reasonable, parameters.

Multicopy sequences evolve adaptations for increasing their copy number within nuclei. The activities of multicopy sequences under constraints imposed by cellular and organismal selection result in a rich intranuclear ecology in germline cells. Mitochondrial and ribosomal DNA are managed as domestic herds subject to selective breeding by the genes of the single-copy genome. Transposable elements lead a peripatetic existence in which they must continually move to new sites to keep ahead of inactivating mutations at old sites and undergo exponential outbreaks when the production of new copies exceeds the rate of inactivation of old copies. Centromeres become populated by repeats that do little harm. Organisms with late sequestration of germ cells tend to evolve more "junk" in their genomes than organisms with early sequestration of germ cells.

Sex-ratio meiotic drivers are selfish genes or gene complexes that bias the transmission of sex chromosomes resulting in skewed sex ratios. Existing theoretical models have suggested the maintenance of a four-chromosome equilibrium (with driving and standard X and suppressing and susceptible Y) in a cyclic dynamic, but studies of natural populations have failed to capture this pattern. Although there are several plausible explanations for this lack of cycling, interference from autosomal suppressors has not been studied using a theoretical population genetic framework even though autosomal suppressors and Y-linked suppressors coexist in natural populations of some species. In this study, we use a simulation-based approach to investigate the influence of autosomal suppressors on the cycling of sex chromosomes. Our findings demonstrate that the presence of an autosomal suppressor can hinder the invasion of a Y-linked suppressor under some parameter space, thereby impeding the cyclic dynamics, or even the invasion of Y-linked suppression. Even when a Y-linked suppressor invades, the presence of an autosomal suppressor can prevent cycling. Our study demonstrates the potential role of autosomal suppressors in preventing sex chromosome cycling and provides insights into the conditions and consequences of maintaining both Y-linked and autosomal suppressors.

The XX/XY sex chromosome system is deeply conserved in therian mammals, as is the role of Sry in testis determination, giving the impression of stasis relative to other taxa. However, the long tradition of cytogenetic studies in mammals documents sex chromosome karyotypes that break this norm in myriad ways, ranging from fusions between sex chromosomes and autosomes to Y chromosome loss. Evolutionary conflict, in the form of sexual antagonism or meiotic drive, is the primary predicted driver of sex chromosome transformation and turnover. Yet conflict-based hypotheses are less considered in mammals, perhaps because of the perceived stability of the sex chromosome system. To address this gap, we catalog and characterize all described sex chromosome variants in mammals, test for family-specific rates of accumulation, and consider the role of conflict between the sexes or within the genome in the evolution of these systems. We identify 152 species with sex chromosomes that differ from the ancestral state and find evidence for different rates of ancestral to derived transitions among families. Sex chromosome-autosome fusions account for 79% of all variants whereas documented sex chromosome fissions are limited to three species. We propose that meiotic drive and drive suppression provide viable explanations for the evolution of many of these variant systems, particularly those involving autosomal fusions. We highlight taxa particularly worthy of further study and provide experimental predictions for testing the role of conflict and its alternatives in generating observed sex chromosome diversity.