Biology subjects

van Heerwaarden, B.

Publications and source records attributed to van Heerwaarden, B..

7 recordsLinked to original sources

bioRxiv2026

Mosquito fertility is (mostly) resilient to sublethal heat shocks

Insects can experience a loss of fertility under acute heat stress, but impacts vary among species and depend on life stage and sex. We examined the effects of sublethal heat shocks on the fertility of three mosquito species (Aedes aegypti, Aedes notoscriptus and Culex quinquefasciatus) when males or females were exposed at the pupal and adult stages. Reproductive performance was assessed through egg-laying success, fecundity, egg hatchability and viable offspring production. Female heat shock had limited effects on fertility in all three species, though exposure of adult females to 41 {degrees}C for 1 hr reduced viable offspring production in Ae. notoscriptus. Male heat shock reduced egg hatchability in Cx. quinquefasciatus and viable offspring production in Ae. aegypti depending on the life stage exposed. We investigated several other aspects of heat shock exposure on Ae. aegypti fertility. In this species, male fertility partially recovered within 24-48 hours following heat shock exposure, while effects of heat shocks on female fertility occurred regardless of whether heat exposure occurred pre- or post-mating. In addition, maternal heat shock exposure enhanced offspring fecundity and viable offspring production under subsequent sublethal heat stress. Overall, our findings demonstrate that mosquito fertility is largely robust to short-term heat shocks, but there are also complex trait, sex, stage, temporal and species-specific effects, with implications for predicting mosquito population persistence and species persistence under future climate extremes.

zoology↗

bioRxiv2025

Heat hardening enhances mosquito heat tolerance in a species-specific and trait-specific manner

Models predict that the distribution of ectotherms including mosquitoes will shift with climate change, but few incorporate adaptive capacity. Acclimation is one mechanism by which mosquitoes could adapt, allowing mosquitoes that have experienced sub-lethal stress previously to tolerate subsequent stressful environments. In this study we evaluated the heat tolerance of three vector mosquito species, Aedes aegypti, Ae. notoscriptus and Culex quinquefasciatus, after being previously exposed to heat hardening. Adult males and females were heat-hardened by exposure to 41{degrees}C for one hour and subsequently tested for heat survival and knockdown following one-hour heat shocks across a range of temperatures up to the lethal limit, ramping CTmax assays and static temperature knockdown time assays. The three species differed markedly in their heat tolerance across all assays, with Ae. aegypti being the most heat tolerant and Cx. quinquefasciatus being the least. Females from all three species were more heat tolerant than males in the one-hour heat shock assays, but effects of sex were absent or inconsistent for CTmax and heat knockdown time assays. A beneficial impact of heat hardening on subsequent heat shock knockdown was evident in both sexes of all three species. However, hardening effects differed substantially for survival 24 hr later, ranging from no effect of hardening in Cx. quinquefasciatus to a [~]1{degrees}C increase in LT50 in Ae. notoscriptus. In contrast, no effects of heat hardening were detected for CTmax or static knockdown time assays. An additional experiment in Ae. aegypti detected no benefits of heat shock exposure in female patents on the thermal tolerance of offspring. Our findings emphasize the need to consider effects of acclimation including heat hardening in models to predict the response of mosquitoes to climate warming. They also have implications for measuring thermal tolerance in mosquitoes more generally, given that both sex and hardening effects depend on the type of assay used and trait measured.

ecology↗

bioRxiv2025

Spiroplasma and heat hardening can buffer insect male fertility loss at high temperatures

Insects upper thermal limits for survival, activity, and fertility have been used to assess vulnerability to climate change, yet heritable endosymbionts - present in over 70% of insect species - are often overlooked. While emerging research suggests some endosymbionts can increase thermal tolerance, their effects on upper lethal and fertility thermal limits has rarely been investigated. Additionally, short-term exposure to sub-lethal high temperatures (heat hardening) can increase insect heat tolerance, but its impact on male fertility is unclear and potential interactions with endosymbionts has not been explored. Here, we investigate whether the endosymbiont Spiroplasma poulsonii and heat hardening influence upper survival and fertility thermal limits in a native widespread host of Spiroplasma (Drosophila hydei) and a novel host (Drosophila birchii), a rainforest-restricted species with low heat tolerance. Heat hardening generally improved survival and fertility following a heat shock. The presence of Spiroplasma increased survival and fertility of D. hydei males following heat-shock, while in D. birchii, it did not enhance survival but protected male fertility after heat-shock and modulated hardening responses at sub-lethal temperatures. While protective effects varied across species, sex, and trait, both Spiroplasma and hardening significantly buffered male fitness loss during heat shock in both host species and halved heat exposure risk under current and predicted climate change in the rainforest restricted D. birchii. These findings highlight that, beyond generating novel phenotypic variation, endosymbionts can interact with plastic responses to heat stress, emphasising the importance of accounting for endosymbiont-mediated effects on thermal tolerance when assessing insect vulnerability to climate change and exploring strategies to manipulate insect thermal tolerance.

evolutionary biology↗

bioRxiv2025

Variation in phenotypic plasticity in desiccation tolerance is driven by trade-offs, not climate, in Drosophila melanogaster

The capacity for species to respond to environmental variation via phenotypic plasticity has been proposed as a mechanism for buffering species against climate change. Two main theories are proposed to explain the evolution of phenotypic plasticity - the climate variability hypothesis and the trade-off hypothesis - but the evidence for these hypotheses remains mixed. In the current study, we examine phenotypic plasticity (hardening capacity) in desiccation resistance across populations of Drosophila melanogaster collected along a climatic gradient from eastern Australia. While climate was an important driver of innate desiccation tolerance, we found no evidence of climate shaping hardened desiccation tolerance or hardening capacity. Instead, we found that populations with high tolerance tended to have lower plasticity, indicative of a trade-off. Further analyses, accounting for statistical non-independence, showed a strong negative correlation between innate desiccation tolerance and hardening capacity, supporting the trade-off hypothesis. These results suggest that for species with high tolerance, phenotypic plasticity is unlikely to contribute to their response to climate change.

evolutionary biology↗

bioRxiv2024

Elevated developmental temperatures below the lethal limit reduce Aedes aegypti fertility

Aedes aegypti mosquitoes are the principal vectors of dengue and continue to pose a threat to human health, with ongoing urbanization, climate change, and trade all impacting the distribution and abundance of this species. Hot periods are becoming increasingly common and their impacts on insect mortality have been well established, but they may have even greater impacts on insect fertility. In this study, we investigated the impacts of high temperatures on Ae. aegypti fertility both within and across generations. Mosquitoes developing under elevated temperatures exhibited higher critical thermal maxima (CTmax) reflecting developmental acclimation, but their fertility declined with increasing developmental temperature. In females, elevated developmental temperatures decreased fecundity while in males it tended to decrease egg hatch proportions and the proportion of individuals producing viable offspring. Rearing both sexes at 35{degrees}C increased fecundity in the subsequent generation but effects of elevated temperatures persisted across gonotrophic cycles within the same generation. Moreover, exposure of adults to 35{degrees}C further decreased fertility beyond the effects of developmental temperature alone. These findings highlight sub-lethal impacts of elevated temperatures on Ae. aegypti fertility and plastic responses to thermal stress within and across generations. This has significant implications for mosquito populations thriving in increasingly warmer environments.

ecology↗

bioRxiv2024

Wolbachia strain wMelM disrupts egg retention by Aedes aegypti females prevented from ovipositing

Aedes aegypti mosquitoes are well adapted to dry climates and can retain their eggs for extended periods in the absence of suitable habitat. Wolbachia strains transferred from other insects to mosquitoes can be released to combat dengue transmission by blocking virus replication and spreading through populations, but host fitness costs imposed by Wolbachia, particularly under some environments, can impede spread. We therefore assessed the impact of two Wolbachia strains being released for dengue control (wAlbB and wMelM) on fecundity and egg viability following extended egg retention (12 or 18 d) under laboratory conditions. Egg viability decreased to a greater extent in females carrying wMelM compared to uninfected or wAlbB females. Fertility fully recovered in uninfected females following a second blood meal after laying retained eggs, while wMelM females experienced only partial recovery. Effects of wMelM on egg retention were similar regardless of whether females were crossed to uninfected or wMelM males, suggesting that fitness costs were triggered by Wolbachia presence in females. The fecundity and hatch proportions of eggs of wMelM females declined with age, regardless of whether females used stored sperm or were recently inseminated. Costs of some Wolbachia strains during egg retention may affect the invasion and persistence of Wolbachia in release sites where larval habitats are scarce and/or intermittent.

ecology↗

bioRxiv2023

Wolbachia infection negatively impacts Drosophila simulans heat tolerance in a strain- and trait-specific manner

The susceptibility of insects to rising temperatures has largely been measured by their ability to survive thermal extremes. However, until recently, the capacity for maternally inherited endosymbionts to influence insect heat tolerance has been overlooked. Further, the impact of heat on traits like fertility, which can decline at temperatures below the lethal thermal limit has largely been ignored. Here, we assess the impact of three Wolbachia strains (wRi, wAu, and wNo) on the survival and fertility of Drosophila simulans exposed to heat stress during development or as adults. The impact of Wolbachia infection on heat tolerance was generally small and trait/strain specific. Only the wNo infection significantly reduced survival and fertility of adult males after a heat shock. When exposed to a fluctuating heat stress during development, the wRi and wAu strains reduced egg-to-adult survival but only the wNo infection reduced male fertility. Wolbachia densities of all three strains decreased under developmental heat stress, but reductions occurred at temperatures above those that reduced fertility of the host. These findings reveal the complexity of endosymbiont-host-environment interactions and emphasise the necessity to account for endosymbionts and their effect on both survival and fertility when investigating the vulnerability of insects to climate change.

evolutionary biology↗