Biology subjects

Stevison, L. S.

Publications and source records attributed to Stevison, L. S..

6 recordsLinked to original sources

bioRxiv2026

Interaction of combined stressors and genetic background on recombination rate plasticity in Drosophila melanogaster

Recombination is an important source of genetic variation and plays a central role in adaptation and genome stability. Although environmental conditions such as temperature can alter recombination rates, much less is known about how multiple environmental stressors act together. Here, we tested the effects of low temperature and hypoxia, both independently and in combination, on recombination in Drosophila melanogaster across five genetic backgrounds. Using a quadruple X-linked marker stock, we measured recombination in 50,209 male backcross progeny from 194 backcrosses exposed to four conditions: control, hypoxia, low temperature, and combined hypoxia and low temperature. Low temperature significantly altered recombination across all three chromosome intervals examined and affected total map length with an average increase of 5 cM. Genetic background strongly influenced the magnitude of altered recombination rate. Hypoxia alone did not significantly change total map length, but its effects differed among genetic backgrounds with significant variation in both the magnitude and direction with an average decrease of 0.96 cM. The response to combined hypoxia and low temperature was not simply the sum of the responses to each stressor alone, with an average increase of 6.78 cM, that also varied across genetic backgrounds in magnitude and direction as well as over time. DGRP_57 and DGRP_508 showed some of the largest increases in recombination under combined stress, whereas DGRP_491 showed a decrease. DGRP_391 was robust across all treatments. Despite these changes in crossover frequency, crossover interference remained largely stable across treatments, with only the y-cv-v interval pair showing a significant treatment-by-genotype interaction. Together, these results show that recombination responses to environmental stress depend strongly on genetic background and on the combination of stressors experienced. Our findings highlight the importance of considering both genetic variation and interacting environmental conditions when predicting how populations may respond to increasingly complex environmental change.

genetics↗

bioRxiv2026

Effects of hypoxia and low temperature on female physiology and reproduction of Drosophila melanogaster

Because hypoxia and low temperature independently alter metabolism and reproductive investment, their interaction provides a tractable framework for testing whether combined stressors produce non-additive physiological and reproductive effects. Here, we investigated the single and combined effects of hypoxia and low temperature in Drosophila melanogaster across multiple genetic backgrounds. We quantified metabolic rate, thermal tolerance, body mass, fertility, oogenesis progression, and oocyte apoptosis to assess organismal responses to environmental stress. Hypoxia generally increased respiratory quotient and body mass, but its effects on thermal tolerance and fertility were highly genotype dependent. Across traits, combined stressors frequently produced responses that differed from those observed under single stressors, including reduced fertility, altered oogenesis, and changes in oocyte cell death. Importantly, these effects were not uniform: some genotypes exhibited increased oocyte production or reduced cell death under combined stress, highlighting pronounced genotype-dependent differences in stress sensitivity and reproductive allocation. Together, our results demonstrate that the interaction between hypoxia and temperature can modulate metabolic and reproductive responses in ways that are not predictable from single-stressor responses alone. These findings highlight the importance of incorporating genetic background and interacting environmental stressors when evaluating organismal tolerance and adaptive potential under ongoing environmental change.

physiology↗

bioRxiv2026

An extension of the Cx(Co)m model of crossover patterning to account for experimental mortality in Drosophila melanogaster

Classic recombination experiments designed to test genetic and environmental treatments do not directly measure crossing-over, instead rates and distribution of meiotic events in F1 meiocytes is inferred from genetic markers in F2 adults. In Drosophila melanogaster females this procedure introduces a substantial "missing data problem" because 75% of meiotic chromatids segregate to polar body nuclei and another 11% are transmitted to inviable F2 zygotes which cannot be scored for recombination. To address these sources of uncertainty and bias we extend the Cx(Co)m model of the data-generating process by assuming: 1) programmed double strand breaks occur as a Poisson point process, 2) crossover maturation is a stationary renewal process, 3) chromosome segregation is random one-half thinning of this process, 4) fertilization by X-versus Y-bearing sperm is mendelian, and 5) egg-to-adult survival is binomially distributed with a rate parameter determined by F2 marker alleles. To quantify experimental mortality, we performed egg counts in a 6-point X chromosome testcross and marker-free controls on identical genetic backgrounds under standard laboratory conditions. The 19,927 fly dataset reveals 44% F2 experimental mortality, and likelihood ratio tests support a model where 36 of the 44% is due to sex-specific, marker-associated viability defects. Variability in X chromosome genetic lengths with experimental mortality can be simulated and we provide case-control 80% power curves to guide experimental design. We propose that differential mortality should be the de facto null hypothesis when comparing F2 recombinant fractions and provide probabilistic models of the data-generating process to improve characterization of patterns in F1 meiotic events.

genetics↗

bioRxiv2022

Does it pay to pay? A comparison of the benefits of open-access publishing across various sub-fields in Biology

Authors are often faced with the decision of whether to maximize impact or minimize costs when publishing the results of their research. For example, to potentially improve impact via increased accessibility, many subscription-based journals now offer the option of paying a fee to publish open access (i.e., hybrid journals), but this solution excludes authors who lack the capacity to pay to make their research accessible. Here, we tested if paying to publish open access in a subscriptionbased journal benefited authors by conferring more citations relative to closed access articles. We identified 146,415 articles published in 152 hybrid journals in the field of biology from 2013-2018 to compare the number of citations between various types of open access and closed access articles. In a simple generalized linear model analysis of our full dataset, we found that publishing open access in hybrid journals that offer the option confers an average citation advantage to authors of 17.8 citations compared to closed access articles in similar journals. After taking into account the number of authors, journal impact, year of publication, and subject area, we still found that open access generated significantly more citations than closed access (p < 0.0001). However, results were complex, with exact differences in citation rates among access types impacted by these other variables. This citation advantage based on access type was even similar when comparing open and closed access articles published in the same issue of a journal (p < 0.0001). However, by examining articles where the authors paid an article processing charge, we found that cost itself was not predictive of citation rates (p = 0.14). Based on our findings of access type and other model parameters, we suggest that, in most cases, paying for access does confer a citation advantage. For authors with limited budgets, we recommend pursuing open access alternatives that do not require paying a fee as they still yielded more citations than closed access. For authors who are considering where to submit their next article, we offer additional suggestions on how to balance exposure via citations with publishing costs.

scientific communication and education↗

bioRxiv2020

High-altitude adaptation in rhesus macaques

When natural populations split and migrate to different environments, they may experience different selection pressures that can lead to local adaptation. To capture the genomic patterns of a local selective sweep, we develop XP-nSL, a genomic scan for local adaptation that compares haplotype patterns between two populations. We show that XP-nSL has power to detect ongoing and recently completed hard and soft sweeps, and we then apply this statistic to search for evidence of adaptation to high altitude in rhesus macaques. We analyze the whole genomes of 23 wild rhesus macaques captured at high altitude (mean altitude > 4000m above sea level) to 22 wild rhesus macaques captured at low altitude (mean altitude < 500m above sea level) and find evidence of local adaptation in the high-altitude population at or near 303 known genes and several unannotated regions. We find the strongest signal for adaptation at EGLN1, a classic target for convergent evolution in several species living in low oxygen environments. Furthermore, many of the 303 genes are involved in processes related to hypoxia, regulation of ROS, DNA damage repair, synaptic signaling, and metabolism. These results suggest that, beyond adapting via a beneficial mutation in one single gene, adaptation to high altitude in rhesus macaques is polygenic and spread across numerous important biological systems. Impact SummaryWhen positive selection is ongoing or a beneficial mutation has recently fixed in a population, genetic diversity is reduced in the vicinity of the adaptive allele, and we expect to observe long homozygous haplotypes at high frequency. Here we develop a statistic that summarizes these expected patterns and compares between two populations in order to search for evidence of adaptation that may have occurred in one but not the other. We implement this statistic in a popular and easy-to-use software package, and then apply it to study adaptation to high altitude in rhesus macaques. Extreme environments pose a challenge to life on multiple fronts. Very high-altitude environments are one such example, with low atmospheric oxygen, increased ultraviolet light exposure, harsh temperatures, and reduced nutrition availability. In spite of these challenges, many plants and animals, including humans, have genetically adapted to cope with these hardships. Here we study two populations of rhesus macaques, one living at high altitude and one living close to sea level. We apply our novel statistic to compare their haplotype patterns between them to search for evidence of genetic changes that are indicative of adaptation to their environment. We find evidence for adaptation at a critical gene that helps control physiological response to low-oxygen, one that has been the target of repeated convergent evolution across many species. We also find evidence for positive selection across a range of traits, including metabolic and neurological. This work helps to explain the evolutionary history of the rhesus macaque and furthers our understanding about the ways organisms genetically adapt to high-altitude environments.

evolutionary biology↗

bioRxiv2020

Refining the timing of recombination rate plasticity in response to temperature in 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.

genetics↗