Biology subjects

Dillon, M. E.

Publications and source records attributed to Dillon, M. E..

5 recordsLinked to original sources

bioRxiv2026

Mean temperature determines whether winter variability accelerates or buffers energy loss

Winter survival in dormant animals depends on conserving finite energy reserves, yet winter temperatures fluctuate around shifting means. In ectotherms, metabolic rate increases exponentially with temperature, so thermal variability is expected to accelerate energy loss, with important consequences for overwinter survival and population persistence under climate change. However, it remains unclear whether dormant ectotherms can compensate physiologically for thermal variability. We overwintered Bombus impatiens queens under constant (2, 3, 4{degrees}C) or variable (2 {+/-} 6{degrees}C or 4 {+/-} 6{degrees}C) regimes for six weeks, then measured metabolic rates across a range of temperatures. The temperature dependence of metabolic rate shifted in response to thermal experience, but the direction of compensation depended on mean temperature: variability centered on 2{degrees}C elevated metabolic rate and increased thermal sensitivity relative to all other conditions, whereas variability centered on 4{degrees}C reduced metabolic rate and dampened thermal sensitivity relative to constant 4{degrees}C. We used these metabolic responses to simulate rates of lipid depletion and found that survival trajectories echoed physiological shifts: experiencing variability around 2{degrees}C would reduce subsequent survival time, whereas experiencing variability around 4{degrees}C would preserve subsequent survival even under variable future conditions. Thus, identical thermal variance produced opposite energetic outcomes depending on the mean temperature around which fluctuations occurred. Integrating both temperature means and variability is, therefore, essential for predicting overwintering survival in a changing world.

physiology↗

bioRxiv2022

Phat queens emerge fashionably late: body size and condition predict timing of spring emergence for queen bumble bees

For insects, the timing of many life history events (phenology) depends on temperature cues. Body size is a critical mediator of insect responses to temperature, so may also influence phenology. The determinants of spring emergence of bumble bee queens are not well understood, but body size is likely important for several reasons. In fall, queens accumulate energy stores to fuel overwinter survival. Accumulation of fat stores prior to and depletion of fat stores during overwintering are likely size-dependent: larger queens can accumulate more lipids and have lower mass-specific metabolic rates. Therefore, larger queens and queens in relatively better condition may have delayed depletion of energy stores, allowing for later spring emergence. To test whether timing of spring emergence is associated with body size and condition, we captured 295 Bombus huntii queens in Laramie, WY, during the 2020 and 2021 growing seasons, weighed them, and measured intertegular width (a size metric unaffected by variation in feeding and hydration state). Early emerging queens were smaller than later emerging queens across years. Mass relative to intertegular width increased as the season progressed suggesting, as predicted, that body condition influences the timing of spring emergence for these crucial pollinators.

physiology↗

bioRxiv2021

Temperature-dependent use of daily torpor attenuates the energetic consequences of habitat selection for a widespread bat

Homeothermy requires increased metabolic rates as temperatures decline below the thermoneutral zone, so homeotherms typically select microhabitats within or near their thermoneutral zones during periods of inactivity. However, many mammals and birds are heterotherms that relax internal controls on body temperature when maintaining a high, stable body temperature is energetically costly. Such heterotherms should be less tied to microhabitats near their thermoneutral zones, and because heterotherms spend more time in torpor and expend less energy at colder temperatures, heterotherms may even select microhabitats in which temperatures are well below their thermoneutral zones. We studied how temperature and daily torpor influence selection of diurnal roosts by a heterothermic bat (Myotis thysanodes). We (1) quantified the relationship between ambient temperature and daily duration of torpor, (2) simulated daily energy expenditure over a range of microhabitat (roost) temperatures, and (3) quantified the influence of roost temperature on roost selection. While warm roosts substantially reduced energy expenditure of simulated homeothermic bats, heterothermic bats modulated their use of torpor to maintain a constant level of energy expenditure over the course of a day. Daily torpor expanded the range of energetically economical microhabitats, such that roost selection was independent of roost temperature. Our work adds to a growing literature documenting functions of torpor beyond its historical conceptualization as a last-resort measure to save energy during extended or acute energetic stress.

ecology↗

bioRxiv2020

Cold tolerance of mountain stoneflies (Plecoptera: Nemouridae) from the high Rocky Mountains

ABSTRACTHow aquatic insects cope with cold temperatures is poorly understood. This is particularly true for high-elevation species that often experience a seasonal risk of freezing. In the Rocky Mountains, nemourid stoneflies (Plecoptera: Nemouridae) are a major component of mountain stream biodiversity and are typically found in streams fed by glaciers and snowfields, which due to climate change, are rapidly receding. Predicting the effects of climate change on mountain stoneflies is difficult because their thermal physiology is largely unknown. We investigated cold tolerance of several alpine stoneflies (Lednia tumana, Lednia tetonica, and Zapada spp.) from the Rocky Mountains, USA. We measured the supercooling point (SCP) and tolerance to ice enclosure of late-instar nymphs collected from a range of thermal regimes. SCPs varied among species and populations, with the lowest SCP measured for nymphs from an alpine pond, which is much more likely to freeze solid in winter than flowing streams. We also show that L. tumana cannot survive being enclosed in ice, even for short periods of time (less than three hours) at relatively mild temperatures (−0.5 °C). Our results indicate that high-elevation stoneflies at greater risk of freezing may have correspondingly lower SCPs, and despite their common association with glacial meltwater, they appear to be living near their lower thermal limits.Competing Interest StatementThe authors have declared no competing interest.View Full Text

physiology↗

bioRxiv2019

Mountain stoneflies may tolerate warming streams: evidence from organismal physiology and gene expression

Rapid glacier recession is altering the physical conditions of headwater streams. Stream temperatures are predicted to rise and become increasingly variable, putting entire meltwater-associated biological communities at risk of extinction. Thus, there is a pressing need to understand how thermal stress affects mountain stream insects, particularly where glaciers are likely to vanish on contemporary timescales. In this study, we tested the critical thermal maximum (CTMAX) of stonefly nymphs representing multiple species and a range of thermal regimes in the high Rocky Mountains, USA. We then collected RNA-sequencing data to assess how organismal thermal stress translated to the cellular level. Our focal species included the meltwater stonefly, Lednia tumana, which was recently listed under the U.S. Endangered Species Act due to climate-induced habitat loss. For all study species, critical thermal maxima (CTMAX > 20{degrees}C) far exceeded the stream temperatures mountain stoneflies experience (< 10{degrees}C). Moreover, while evidence for a cellular stress response was present, we also observed constitutive expression of genes encoding proteins known to underlie thermal stress (i.e., heat shock proteins) even at low temperatures that reflected natural conditions. We show that high-elevation aquatic insects may not be physiologically threatened by short-term exposure to warm temperatures and that longer term physiological responses or biotic factors (e.g., competition) may better explain their extreme distributions.

physiology↗