Putative condition-dependent viability selection in wild type stocks of Drosophila pseudoobscura

Meiotic recombination rates vary in response to intrinsic and extrinsic factors. Recently, heat stress has been shown to reveal plasticity in recombination rates in Drosophila pseudoobscura. Here, a combination of molecular genotyping and X-linked recessive phenotypic markers were used to investigate differences in recombination rates due to either heat stress or advanced maternal age. However, haplotype frequencies deviated from equal proportions for crosses using phenotypic markers, indicating viability selection. Interestingly, skews in haplotype frequency were condition-dependent, consistent with the fixation of alleles in the wild type stocks used that are unfit at high temperature. Evidence of viability selection due to heat stress in the wild type haplotypes was most apparent on days 7-9 when more mutant non-crossover haplotypes were recovered in comparison to wild type (p=2.2e-4). Despite the condition-dependent mutational load in both wild type and mutant stocks, an analysis of recombination rate plasticity revealed days 7-9 (p=0.0085) and day 9 (p=0.037) to be significantly higher due to heat stress and days 1-3 as significantly higher due to maternal age (p=0.025). Still, to confirm these findings, SNP genotyping markers were used to further investigate recombination rate. This analysis supported days 9-10 as significantly different due to heat stress in two pairs of consecutive SNP markers (p=0.018; p=0.015), suggesting this time period as when recombination rate is most sensitive to heat stress. This peak timing for recombination plasticity is consistent with D. melanogaster based on comparison of similarly timed key meiotic events, enabling future mechanistic work of temperature stress on recombination rate.