Search for: All records

Abstract Climatic and soil features influence resources and mate availability for plants. Because of different resource/mating demands of the male and female reproductive pathways, environmental variation can drive geographic patterns of sex‐specific factors in sexually polymorphic species. Yet, the relationship between environment and sex, sexual dimorphism or sex chromosomes at the range‐wide scale is underexamined.Using ~7000 herbarium and iNaturalist specimens we generate a landscape‐scale understanding of how sex ratio and sexual dimorphism vary with geographic, climatic and soil gradients in the sexually polymorphic wild strawberry (Fragaria virginiana) and test whether these conform to predictions from theory. Then, for ~300 specimens we use genotyping of the sex‐determining region (SDR haplotypes) to reveal geographic and phenotypic patterns in sex chromosome types.Across North America, the sex ratio was hermaphrodite/male‐biased and was associated more with soil attributes than climate. Sex ratio‐environment associations matched predictions for subdioecy in the West but for gynodioecy in the East. Climatic factors correlated with sexual dimorphism in traits related to carbon acquisition (leaf size and runnering while flowering) but not mate access (petal size, flowering time). Variation in sexual dimorphism was due to one sex being more responsive to the environmental variation than the other. Specifically, leaf length in females was more responsive to variation in precipitation than in hermaphrodite/males, but the probability of runnering while flowering in hermaphrodite/males was more responsive to variation in temperature than in females. The ancestral sex chromosome type was most common overall. But the frequency of the more derived sex chromosomes varied with environmental factors that differed between East–West regions.Synthesis. A landscape‐level perspective revealed that variation in soil and climate factors can explain geospatial variation in sex ratio and sexual dimorphism in a wild strawberry. Variation in sex ratio was associated more with soil resources than climate, while variation in sexual dimorphism was the result of sex‐differential responses to climate for vegetative traits but a similar response to abiotic factors in mate access traits. Finally, sex chromosome types were associated with soil moisture and precipitation in ways that could contribute to the evolution of sex determination. 

Future adaptation to snow cover depends on standing genetic variation for winter camouflage in white-tailed jackrabbits. 

Abstract The X chromosome of therian mammals shows strong conservation among distantly related species, limiting insights into the distinct selective processes that have shaped sex chromosome evolution. We constructed a chromosome-scale de novo genome assembly for the Siberian dwarf hamster (Phodopus sungorus), a species reported to show extensive recombination suppression across an entire arm of the X chromosome. Combining a physical genome assembly based on shotgun and long-range proximity ligation sequencing with a dense genetic map, we detected widespread suppression of female recombination across ∼65% of the Phodopus X chromosome. This region of suppressed recombination likely corresponds to the Xp arm, which has previously been shown to be highly heterochromatic. Using additional sequencing data from two closely related species (P. campbelli and P. roborovskii), we show that recombination suppression on Xp appears to be independent of major structural rearrangements. The suppressed Xp arm was enriched for several transposable element families and de-enriched for genes primarily expressed in placenta, but otherwise showed similar gene densities, expression patterns, and rates of molecular evolution when compared to the recombinant Xq arm. Phodopus Xp gene content and order was also broadly conserved relative to the more distantly related rat X chromosome. These data suggest that widespread suppression of recombination has likely evolved through the transient induction of facultative heterochromatin on the Phodopus Xp arm without major changes in chromosome structure or genetic content. Thus, substantial changes in the recombination landscape have so far had relatively subtle influences on patterns of X-linked molecular evolution in these species. 

Abstract When sex chromosomes stop recombining, they start to accumulate differences. The sex-limited chromosome (Y or W) especially is expected to degenerate via the loss of nucleotide sequence and the accumulation of repetitive sequences. However, how early signs of degeneration can be detected in a new sex chromosome is still unclear. The sex-determining region of the octoploid strawberries is young, small, and dynamic. Using PacBio HiFi reads, we obtained a chromosome-scale assembly of a female (ZW) Fragaria chiloensis plant carrying the youngest and largest of the known sex-determining region on the W in strawberries. We fully characterized the previously incomplete sex-determining region, confirming its gene content, genomic location, and evolutionary history. Resolution of gaps in the previous characterization of the sex-determining region added 10 kb of sequence including a noncanonical long terminal repeat-retrotransposon; whereas the Z sequence revealed a Harbinger transposable element adjoining the sex-determining region insertion site. Limited genetic differentiation of the sex chromosomes coupled with structural variation may indicate an early stage of W degeneration. The sex chromosomes have a similar percentage of repeats but differ in their repeat distribution. Differences in the pattern of repeats (transposable element polymorphism) apparently precede sex chromosome differentiation, thus potentially contributing to recombination cessation as opposed to being a consequence of it.