Biology subjects

Davis, H. E.

Publications and source records attributed to Davis, H. E..

5 recordsLinked to original sources

bioRxiv2021

A lack of repeatability creates the illusion of a trade-off between basal and plastic cold tolerance.

The thermotolerance-plasticity trade-off hypothesis predicts that ectotherms with greater basal thermal tolerance have a lower acclimation capacity. This hypothesis has been tested at both high and low temperatures but the results often conflict. If basal tolerance constrains plasticity (e.g. through shared mechanisms that create physiological constraints), it should be evident at the level of the individual, provided the trait measured is repeatable. Here, we used chill-coma onset temperature and chill-coma recovery time (CCO and CCRT; non-lethal thermal limits) to quantify cold tolerance of Drosophila melanogaster across two trials (pre- and post-acclimation). Cold acclimation improved cold tolerance, as expected, but individual measurements of CCO and CCRT in non-acclimated flies were not (or only slightly) repeatable. Surprisingly, however, there was still a strong correlation between basal tolerance and plasticity in cold-acclimated flies. We argue that this relationship is a statistical artefact (specifically, a manifestation of regression to the mean; RTM) and does not reflect a true trade-off or physiological constraint. Thermal tolerance trade-off patterns in previous studies that used similar methodology are thus likely to be impacted by RTM. Moving forward, controlling and/or correcting for RTM effects is critical to determining whether such a trade-off or physiological constraint truly exists.

ecology↗

bioRxiv2020

Chill coma onset and recovery fail to reveal true variation in thermal performance among populations of Drosophila melanogaster

O_LISpecies from colder climates tend to be more chill tolerant regardless of the chill tolerance trait measured, but for Drosophila melanogaster, population-level differences in chill tolerance among populations are not always found when a single trait is measured in the laboratory. C_LIO_LIWe measured chill coma onset temperature, chill coma recovery time, and survival after chronic cold exposure in replicate lines derived from multiple paired African and European D. melanogaster populations. The populations in our study were previously found to differ in chronic cold survival ability, which is believed to have evolved independently in each population pair. C_LIO_LITo our surprise, the populations did not differ in chill coma onset temperature and chill coma recovery time in a manner that reflected their geographic origins, even though these traits are known to vary with origin latitude among Drosophila species and among the most common metrics of thermal tolerance in insects. The populations did, however, still differ in their ability to survive chronic cold exposure. C_LIO_LIWhile it is common practice to measure only one chill tolerance trait when comparing chill tolerance among insect populations, our results emphasise the importance of measuring more than one thermal tolerance trait to minimize the risk of missing real adaptive variation in insect thermal tolerance. C_LI

ecology↗

bioRxiv2020

Warm periods in repeated cold stresses protect Drosophila against ionoregulatory collapse, chilling injury, and reproductive deficits

In many insects, repeated cold stress, characterized by warm periods that interrupt cold periods, have been found to yield survival benefits over continuous cold stress, but at the cost of reproduction. During cold stress, chill susceptible insects like Drosophila melanogaster suffer from a loss of ion and water balance, and the current model of recovery from chilling posits that re-establishment of ion homeostasis begins upon return to a warm environment, but that it takes minutes to hours for an insect to fully restore homeostasis. Following this ionoregulatory model of chill coma recovery, we predicted that the longer the duration of the warm periods between cold stresses, the better a fly will recover from a subsequent chill coma event and the more likely they will be to survive, but at the cost of fewer offspring. Here, female D. melanogaster were treated to a long continuous cold stress (25 h at 0{degrees}C), or experienced the same total time in the cold with repeated short (15 min), or long (120 min) breaks at 23{degrees}C. We found that warm periods in general improved survival outcomes, and individuals that recovered for more time in between cold periods had significantly lower rates of injury, faster recovery from chill coma, and produced greater, rather than fewer, offspring. These improvements in chill tolerance were associated with mitigation of ionoregulatory collapse, as flies that experienced either short or long warm periods better maintained low hemolymph [K+]. Thus, warm periods that interrupt cold exposures improve cold tolerance and fertility in D. melanogaster females relative to a single sustained cold stress, potentially because this time allows for recovery of ion and water homeostasis.

zoology↗

bioRxiv2019

An impressive capacity for cold tolerance plasticity protects against ionoregulatory collapse in the disease vector, Aedes aegypti

O_LIThe mosquito Aedes aegypti is largely confined to tropical and subtropical regions but its range has recently been spreading to colder climates. As insect biogeography is closely tied to environmental temperature, understanding the limits of Ae. aegypti thermal tolerance and their capacity for phenotypic plasticity is important in predicting the spread of this species.\nC_LIO_LIIn this study we report on the chill coma onset and recovery, as well as low temperature survival phenotypes of larvae and adults of Aedes aegypti that developed or were acclimated to 15{degrees}C (cold) or 25{degrees}C (warm).\nC_LIO_LIDevelopmental cold acclimation did not affect chill coma onset of larvae but substantially reduced chill coma onset temperatures in adults. Chill coma recovery time was affected by both temperature and the duration of exposure, and developmental and adult acclimation both strongly mitigated these effects and increased rates of survival following prolonged chilling.\nC_LIO_LIFemale adults were far less likely to take a blood meal when cold acclimated and simply exposing females to blood (without feeding) attenuated some of the beneficial effects of cold acclimation on chill coma recovery time.\nC_LIO_LILastly, larvae suffered from hemolymph hyperkalemia when chilled, but development in the cold attenuated the imbalance, which suggests that acclimation can prevent cold-induced ionoregulatory collapse in this species.\nC_LIO_LIOur results demonstrate that Aedes aegypti larvae and adults have the capacity to acclimate to cold temperatures and do so at least in part by better maintaining ion balance in the cold. This ability for cold acclimation may facilitate the spread of this species to higher latitudes, particularly in an era of climate change.\nC_LI

physiology↗

bioRxiv2018

When to care and when to kill: termites shape their collective response based on stage of infection

Termites defend their colonies from disease using an array of social behaviours, including allogrooming, cannibalism, and burial. We tested how groups of eastern subterranean termites (Reticulitermes flavipes) deploy these behaviours when presented with a nestmate at different stages of infection with the entomopathogenic fungus Metarhizium anisopliae. As expected, the termites groomed pathogen-exposed individuals significantly more than mock-treated controls; however, grooming levels were significantly higher after spore germination than before. Cannibalism became prevalent only after exposed termites became visibly ill, and burial was rarely observed. These results demonstrate that termites employ different strategies depending on the stage of infection that they encounter. Grooming intensity is linked not only to pathogen presence, but also to germination status, and, given the temporal correlation between cannibalism and visible signs of illness, the host may play a role in triggering its own sacrifice.

animal behavior and cognition↗