Biology subjects

Lockwood, B. L.

Publications and source records attributed to Lockwood, B. L..

9 recordsLinked to original sources

bioRxiv2026

Heat stress drives opposing redox shifts in temperate versus tropical Drosophila melanogaster embryos

Redox balance is central to aerobic metabolism, yet acute heat stress can destabilize this balance by increasing metabolic rates and shifting the balance of critical electron carriers such as NADH. In early Drosophila melanogaster embryos, maintaining redox balance is particularly critical as embryos undergo a developmental redox shift and rely on oxidative phosphorylation to power nuclear divisions. Here, we assayed six isofemale D. melanogaster lines from temperate (Vermont, USA; France; Japan) and tropical (St. Kitts; Ghana; India) climates to assess metabolic responses to heat in heat-sensitive versus heat-tolerant embryos. We used untargeted LC-MS to measure 33 metabolites and the major redox couples (NADH/NAD+, NADPH/NADP+, and GSH/GSSG) at 25{degrees}C and after a 32{degrees}C heat shock. In all embryos, heat shock induced shared shifts in metabolic profiles, with increases in nucleotide monophosphates (e.g., AMP, CMP, and GMP) and amino acids (e.g., alanine, glutamic acid, serine). In contrast, redox metabolites diverged by region: heat-sensitive temperate embryos shifted toward a more oxidized state (46.6% decrease in NADH/NAD+ ratio and 4-fold increase in oxidized glutathione), while heat-tolerant tropical embryos maintained glutathione balance and increased the NADH/NAD+ ratio by 52.9%, indicating a more reduced state. These patterns are consistent with higher NADH oxidation and greater oxidative stress (inferred from oxidized glutathione) in the temperate embryos, versus better maintenance of redox balance in tropical embryos. Together, our results suggest that maintaining redox balance is a key determinant of acute heat tolerance, and healthy development overall, during early embryogenesis.

evolutionary biology↗

bioRxiv2026

Modes of natural selection on maternal and zygotic gene expression in Drosophila melanogaster embryos

Early embryonic development involves the coordination of gene expression from two distinct genomes, as mothers load eggs with gene products prior to the beginning of zygotic transcription. Because the maternal transcriptome is controlled by the mothers regulatory genotype rather than that of the embryo, these two sequential developmental programs may experience distinct evolutionary constraints and selection pressures despite both existing within the embryo. To infer modes of selection on gene expression at maternal and zygotic developmental stages, we used single-embryo RNA-sequencing and conducted variance tests of selection on transcriptomes of parents and F2 segregants of tropical and temperate Drosophila melanogaster embryos. We found that approximately 10% of maternal transcripts and 5% of zygotic transcripts showed signals of selection. Genome-wide, directional selection was more common than stabilizing selection. However, among core early developmental genes and transcription factors, maternal transcription showed patterns of both stabilizing and directional selection, whereas zygotic transcription was predominantly under stabilizing selection. Many heat shock genes showed patterns of directional selection between tropical and temperate embryos, consistent with local adaptation. Additionally, directional selection in piRNA-pathway genes suggests a role for germline defense during embryogenesis. Overall, while our data support the canonical view that core developmental networks are constrained by stabilizing selection, the genome-wide prevalence of directional selection highlights a substantial and previously underappreciated contribution of diversifying selection to the evolution of early development. Article SummaryThe evolution of embryonic gene expression remains poorly characterized on microevolutionary timescales. We conducted genetic crosses between tropical and temperate Drosophila melanogaster, combining single-embryo RNA sequencing with variance tests of selection, to infer patterns of adaptive evolution in gene expression. We found pervasive signals of selection. While core developmental genes were largely under stabilizing selection, directional selection was the predominant mode of selection genome-wide. These findings challenge the paradigm that early embryogenesis is evolutionarily inflexible, suggesting that diversifying selection and local adaptation play key roles in the evolution of development on short evolutionary timescales.

evolutionary biology↗

bioRxiv2025

Early life-stage thermal resilience is determined by climate-linked regulatory variation

Despite decades of research in environmental change, we know relatively little about the genetics of environmentally influenced traits across the life cycle of species with complex life histories. Previously, we reported that natural variation in heat tolerance is life-stage specific in Drosophila melanogaster, suggesting that thermal selection predominantly targets the early embryonic life stage. Here, we used advanced introgression and pooled whole-genome resequencing to map the genomic basis of enhanced embryonic heat tolerance in a neotropical line of D. melanogaster. We identified two loci on chromosomes 2R and X that were consistently targeted by 16 generations of thermal selection across six replicate introgressions. We compared alleles in these regions to published datasets of natural variation from North America and Europe using the DEST dataset. This analysis revealed that two SNPs associated with embryonic heat tolerance exhibited both clinal and seasonal patterns, with the seasonal variation significantly correlated with environmental variability in average precipitation and temperature variance across space and time. Further, tropical alleles at both loci exhibited enhanced embryonic heat tolerance in the Drosophila Genetics Reference Panel (DGRP), demonstrating the genotype-to-phenotype link in an independent set of diverse genetic backgrounds. The two SNPs lie in the putative regulatory regions of the genes SP70 and sog, where allelic differences in gene expression correlate with the heat tolerance phenotype. Overall, our results suggest that regulatory loci that influence embryonic heat tolerance are under selection in nature. Our study extends previous work in developmental genetics of Drosophila by characterizing the genomics of an ecologically relevant developmental trait in natural populations. Significance StatementBy comparing populations from distinct environments, we can determine the factors important for responses to environmental change. We used laboratory-based selection and whole-genome sequencing to uncover the genomic basis of embryonic heat tolerance in tropical and temperate fruit flies. We compared our results to published genomes of wild-collected flies from multiple continents and seasons. Strikingly, variants of two genes that influence embryonic heat tolerance are correlated with precipitation and temperature in natural populations. Further, different genetic variants produce distinct patterns of gene expression in response to heat stress. This is strong evidence that embryonic heat tolerance is under selection in nature and should be considered when forming predictions about responses to environmental change in species with complex life cycles.

evolutionary biology↗

bioRxiv2025

Single-nuclei multiome ATAC and RNA sequencing reveals the molecular basis of thermal plasticity in Drosophila melanogaster embryos

Embryogenesis is remarkably robust to temperature variability, yet the homeostatic mechanisms that offset thermal effects during early development remain poorly understood. We measured how acclimation shifts the upper thermal limit and profiled chromatin accessibility and gene expression in D. melanogaster embryos using single-nucleus multiome sequencing. Acclimation preserved shared primordial cell types yet rapidly shifted heat tolerance. Cool-acclimated embryos showed a homeostatic response characterized by increased accessibility at binding motifs for the transcriptional activator Zelda, along with enhanced activity of gene regulatory networks in a subset of primordial cell types including the gut, muscle, and nervous system. Cool-acclimated embryos also had higher expression of ribosomal and oxidative phosphorylation genes, reflecting a coordinated increase in translation and energy production to buffer slower biochemical kinetics in the cold. Our results indicate that maintaining developmental robustness across temperature requires homeostatic gene expression responses that may carry metabolic costs constraining upper thermal limits.

developmental biology↗

bioRxiv2024

Heat tolerance, oxidative stress response tuning, and robust gene activation in early-stage Drosophila melanogaster embryos

In organisms with complex life cycles, life stages that are most susceptible to environmental stress may determine species persistence in the face of climate change. Early embryos of Drosophila melanogaster are particularly sensitive to acute heat stress, yet tropical embryos have higher heat tolerance than temperate embryos, suggesting adaptive variation in embryonic heat tolerance. We compared transcriptomic responses to heat stress among tropical and temperate embryos to elucidate the gene regulatory basis of divergence in embryonic heat tolerance. The transcriptomes of tropical and temperate embryos were differentiated by the expression of relatively few genes, including genes involved in oxidative stress. But most of the transcriptomic response to heat stress was shared among all embryos. Further, embryos shifted the expression of thousands of genes and showed robust gene activation, demonstrating that, contrary to previous reports, early embryos are not transcriptionally silent. The involvement of oxidative stress genes in embryonic heat tolerance corroborates recent reports on the critical role of redox homeostasis in coordinating developmental transitions. By characterizing adaptive variation in the transcriptomic basis of embryonic heat tolerance, this study is a novel contribution to the literature on developmental physiology and genetics, which often lacks ecological and evolutionary context.

genetics↗

bioRxiv2020

Winter warming causes widespread shifts in the metabolome and hinders supercooling in Pieris rapae butterflies

Global climate change has the potential to negatively impact biological systems as organisms are exposed to novel temperature regimes. Increases in annual mean temperature have been accompanied by disproportionate rates of change in temperature across seasons, and winter is the season warming most rapidly. Yet, we know relatively little about how warming will alter the physiology of overwintering organisms. Here, we simulated future warming conditions by comparing diapausing Pieris rapae butterfly pupae collected from disparate thermal environments and by exposing P. rapae pupae to acute and chronic increases in temperature. First, we compared internal freezing temperatures (supercooling points) of diapausing pupae that were developed in common-garden conditions but whose parents were collected from northern Vermont, USA, or North Carolina, USA. Matching the warmer winter climate of North Carolina, North Carolina pupae had significantly higher supercooling points than Vermont pupae. Next, we measured the effects of acute and chronic warming exposure in Vermont pupae and found that warming induced higher supercooling points. We further characterized the effects of chronic warming by profiling the metabolomes of Vermont pupae via untargeted LC-MS metabolomics. Warming caused significant changes in abundance of hundreds of metabolites across the metabolome. Notably, there were warming-induced shifts in key biochemical pathways, such as pyruvate metabolism, fructose and mannose metabolism, and beta-alanine metabolism, suggesting shifts in energy metabolism and cryoprotection. These results suggest that warming affects various aspects of overwintering physiology in P. rapae and may be detrimental depending on the frequency and variation of winter warming events. Future research is needed to ascertain the extent to which the effects of warming are felt among a broader set of populations of P. rapae, and among other species, in order to better predict how insects may respond to changes in winter thermal environments.

evolutionary biology↗

bioRxiv2018

Aggression and discrimination among closely versus distantly related species of Drosophila

Fighting between different species is widespread in the animal kingdom, yet this phenomenon has been relatively understudied in the field of aggression research. Particularly lacking are studies that test the effect of genetic distance, or relatedness, on aggressive behavior between species. Here we characterized male-male aggression within and between species of fruit flies across the Drosophila phylogeny. We show that male Drosophila discriminate between conspecifics and heterospecifics and show a bias for the target of aggression that depends on the genetic relatedness of opponent males. Specifically, males of closely related species treated conspecifics and heterospecifics equally, whereas males of distantly related species were overwhelmingly aggressive toward conspecifics. To our knowledge, this is the first study to quantify aggression between Drosophila species and to establish a behavioral bias for aggression against conspecifics versus heterospecifics. Our results suggest that future study of heterospecific aggression behavior in Drosophila is warranted to investigate the degree to which these trends in aggression among species extend to broader behavioral, ecological, and evolutionary contexts.

animal behavior and cognition↗

bioRxiv2017

Maternal loading of a small heat shock protein increases embryo thermal tolerance in Drosophila melanogaster

Maternal investment is likely to have direct effects on offspring survival. In oviparous animals whose embryos are exposed to the external environment, maternal provisioning of molecular factors like mRNAs and proteins may help embryos cope with sudden changes in the environment. Here we sought to modify the maternal mRNA contribution to offspring embryos and test for maternal effects on acute thermal tolerance in early embryos of Drosophila melanogaster. We drove in vivo overexpression of a small heat shock protein gene (Hsp23) in female ovaries and measured the effects of acute thermal stress on offspring embryonic survival and larval development. We report that overexpression of the Hsp23 gene in female ovaries produced offspring embryos with increased thermal tolerance. We also found that brief heat stress in the early embryonic stage (0 to 1 hour-old) caused decreased larval performance later in life (5 to 10 days-old), as indexed by pupation height, as well as increased development time to pupation. Maternal overexpression of Hsp23 protected embryos against these heat-induced larval defects. Our data demonstrate that transient products of single genes have large and lasting effects on whole-organism environmental tolerance. Further, our results suggest that maternal effects have a profound impact on offspring survival in the context of thermal variability.\n\nSUMMARY STATEMENTA gene-specific maternal effect confers thermal tolerance to offspring embryos in the fruit fly Drosophila melanogaster.

evolutionary biology↗

bioRxiv2017

Disparate patterns of thermal adaptation between life stages in temperate vs. tropical populations of Drosophila melanogaster

Many terrestrial ectothermic species exhibit limited variation in upper thermal tolerance across latitude. However, these trends may not signify limited adaptive capacity to increase thermal tolerance in the face of climate change. Instead, thermal tolerance may be similar among populations because behavioral thermoregulation by mobile organisms or life stages may buffer natural selection for thermal tolerance. We compared thermal tolerance of adults and embryos among natural populations of Drosophila melanogaster from a broad range of thermal habitats around the globe to assess natural variation of thermal tolerance in mobile vs. immobile life stages. We found no variation among populations in adult thermal tolerance, but embryonic thermal tolerance was higher in tropical strains than in temperate strains. Average maximum temperature of the warmest month of the year predicted embryonic thermal tolerance in tropical but not temperate sites. We further report that embryos live closer to their upper thermal limits than adultso--i.e., thermal safety margins are smaller for embryos than adults. F1 hybrid embryos from crosses between temperate and tropical populations had thermal tolerance that matched that of tropical embryos, suggesting dominance of heat-tolerant alleles. Together our findings suggest that thermal selection has led to divergence in embryonic thermal tolerance but that selection for divergent thermal tolerance may be limited in adults. Further, our results suggest that thermal traits should be measured across life stages in order to better predict adaptive limits.\n\nImpact SummaryClimate change may threaten the extinction of many ectothermic species, unless populations can evolutionarily adapt to rising temperatures. Natural selection should favor individuals with higher heat tolerances in hotter environments. But recent studies have found that individuals from hot and cold places often have similar heat tolerances. This pattern may indicate that the evolution of heat tolerance is constrained. If this were true, then it would have dire consequences for species persistence under novel thermal conditions.\n\nAn alternative explanation for lack of variation in heat tolerance is that mobile organisms dont need higher heat tolerances to survive in hotter places. The majority of studies have focused on heat tolerance of the adult life stage. Yet, adults in many species are mobile organisms that can avoid extreme heat by seeking shelter in cooler microhabitats (e.g., shaded locations). In contrast, immobile life stages (e.g., insect eggs) cannot behaviorally avoid extreme heat. Thus, mobile and immobile life stages may face different thermal selection pressures that lead to disparate patterns of thermal adaptation across life stages.\n\nHere, we compared heat tolerances of fruit fly adults and eggs (Drosophila melanogaster) from populations in temperate North America and tropical locations around the globe. Consistent with previous studies, we found no differences among populations in adult heat tolerance. However, eggs from tropical flies were consistently more heat tolerant than eggs from North American flies. Further, eggs had lower heat tolerance than adults. Consequently, fly eggs in the hotter tropics may experience heat death more frequently than adult flies later in life. This may explain why patterns of divergence in heat tolerance were decoupled across life stages. These patterns indicate that thermal adaptation may be life-stage-specific and suggest that future work should characterize thermal traits across life stages to better understand the evolution of thermal limits.

evolutionary biology↗