Limited scope for plasticity to increase upper thermal limits

Authors: Belinda van Heerwaarden, Vanessa Kellermann and Carla M Sgrò

Published in: Functional Ecology (early view)

Summary

Increases in average temperature and the frequency of extreme temperature events are likely to pose a major risk to species already close to their upper physiological thermal limits. The extent to which thermal phenotypic plasticity can buffer these changes and whether plasticity is constrained by basal tolerance levels remains unknown.

We examined the effect of developmental temperature under both constant and fluctuating thermal regimes (developmental acclimation), as well as short-term heat hardening, on upper thermal limits (CTmax) in a tropical and temperate population of Drosophila melanogaster.

We found evidence for thermal plasticity in response to both developmental acclimation and hardening treatments; CTmax increased at warmer developmental temperatures and with a prior heat hardening treatment. However, hardening and acclimation responses were small, improving CTmax by a maximum of 1·01 °C. These results imply that overheating risk will only be minimally reduced by plasticity.

We observed significant associations between developmental temperature and both basal CTmax and hardening capacity (a measure of the extent of the plastic response). Basal CTmax increased, while hardening capacity decreased, with increasing developmental acclimation temperature. This indicates that increases in basal heat resistance at warmer temperatures may come at the cost of a reduced capacity to harden.

While plasticity in CTmax is evident in both populations of D. melanogaster we studied, plastic increases in upper thermal limits, particularly at warmer temperatures, may not be sufficient to keep pace with temperature increases predicted under climate change.

Citation

van Heerwaarden B, Kellerman V, Sgrò CM (2016) Limited scope for plasticity to increase upper thermal limits. Functional Ecology PDF DOI

 

Thermal plasticity in Drosophila melanogaster populations from eastern Australia: quantitative traits to transcripts

Authors: Allannah S Clemson, Carla M Sgrò, and Marina Telonis-Scott

Published in: Journal of Evolutionary Biology, volume 29, issue 12 (December 2016)

Abstract

The flexibility afforded to genotypes in different environments by phenotypic plasticity is of interest to biologists studying thermal adaptation because of the thermal lability of many traits. Differences in thermal performance and reaction norms can provide insight into the evolution of thermal adaptation to explore broader questions such as species distributions and persistence under climate change.

One approach is to study the effects of temperature on fitness, morphological and more recently gene expression traits in populations from different climatic origins. The diverse climatic conditions experienced by Drosophila melanogaster along the eastern Australian temperate-tropical gradient are ideal given the high degree of continuous trait differentiation, but reaction norm variation has not been well studied in this system.

Here, we reared a tropical and temperate population from the ends of the gradient over six developmental temperatures and examined reaction norm variation for five quantitative traits including thermal performance for fecundity, and reaction norms for thermotolerance, body size, viability and 23 transcript-level traits.

Despite genetic variation for some quantitative traits, we found no differentiation between the populations for fecundity thermal optima and breadth, and the reaction norms for the other traits were largely parallel, supporting previous work suggesting that thermal evolution occurs by changes in trait means rather than by reaction norm shifts.

We examined reaction norm variation in our expanded thermal regime for a gene set shown to previously exhibit G×E for expression plasticity in east Australian flies, as well as key heat-shock genes.

Although there were differences in curvature between the populations suggesting a higher degree of thermal plasticity in expression patterns than for the quantitative traits, we found little evidence to support a role for genetic variation in maintaining expression plasticity.

Citation

Clemson AS, Sgrò CM, Telonis-Scott M (2016) Thermal plasticity in Drosophila melanogaster populations from eastern Australia: quantitative traits to transcripts. Journal of Evolutionary Biology, PDF DOI

PhD scholarships ×2: Evolutionary responses to environmental change

Two fully-funded PhD stipends are available for a suitably qualified student interested in working on the evolutionary responses to environmental change in my lab.

The project will be supervised by Associate Professor Carla Sgrò, School of Biological Sciences, Monash University, Melbourne, Australia.

The key questions that drive our research program are:

  1. How does the environment influence the expression of genetic variation that underpins adaptation?
  2. How important is sex-specific adaptation to evolutionary responses to environmental change? (in collaboration with Dr Tim Connallon)

Successful candidates will be fully funded for 3.5 years (the length of a PhD in Australia), for full-time research, and with no teaching requirements. The annual stipend is approximately $25,000 AUD tax-free (equivalent to approximately $33,000 before tax) with additional expenses for research, coursework, and conference attendance (once per year) also covered.

To apply, please send a CV and academic transcript to carla.sgro@monash.edu.

Applicants must hold a Bachelor’s degree with first-class honours, or a master’s degree.

Review of applications will begin immediately, and short-listed candidates will be contacted to set up interviews.

The effect of temperature on Wolbachia-mediated dengue virus blocking in Aedes aegypti

Authors: Yixin H Ye, Alison M Carrasco, Yi Dong, Carla M Sgrò and Elizabeth A McGraw

Published in: The American Society of Tropical Medicine and Hygiene, volume 94 issue 4 (April 2016)

Abstract

Dengue fever, caused by dengue virus (DENV), is endemic in more than 100 countries. The lack of effective treatment of patients and the suboptimal efficacies of the tetravalent vaccine in trials highlight the urgent need to develop alternative strategies to lessen the burden of dengue fever.

Wolbachia pipientis, an obligate intracellular bacterium, is being developed as a biocontrol strategy against dengue because it limits the replication of the DENV in the mosquito vector, Aedes aegypti. However, several recent studies have demonstrated the sensitivity of pathogens, vectors, and their symbionts to temperature.

To understand how the tripartite interactions between the mosquito, DENV, and Wolbachia may change under different temperature regimes, we assessed the vector competence and transmission potential of DENV-infected mosquitoes reared at a common laboratory setting of a constant 25°C and at two diurnal temperature settings with mean of 25°C and 28°C and a fluctuating range of 8°C (±4°C).

Temperature significantly affected DENV infection rate in the mosquitoes. Furthermore, temperature significantly influenced the proportion of mosquitoes that achieved transmission potential as measured by the presence of virus in the saliva. Regardless of the temperature regimes, Wolbachia significantly and efficiently reduced the proportion of mosquitoes achieving infection and transmission potential across all the temperature regimes studied.

This work reinforces the robustness of the Wolbachia biocontrol strategy to field conditions in Cairns, Australia, and suggests that similar studies are required for local mosquito genotypes and field relevant temperatures for emerging field release sites globally.

Citation

Ye YH, Carrasco AM, Dong Y, Sgrò CM, McGraw EM (2016) The effect of temperature on Wolbachia-mediated dengue virus blocking in Aedes aegypti. American Journal of Tropical Medicine and Hygiene, 94(4) 812‒819 PDF DOI

Drosophila as models to understand the adaptive process during invasion

Authors: Patricia Gibert , Matthew Hill, Marta Pascual, Christophe Plantamp, John S Terblanche, Amir Yassin and Carla M Sgrò

Published in: Biological Invasions, volume 18, issue 4 (April 2016)

Abstract

The last few decades have seen a growing number of species invasions globally, including many insect species.

In drosophilids, there are several examples of successful invasions, i.e. Zaprionus indianus and Drosophila subobscura some decades ago, but the most recent and prominent example is the invasion of Europe and North America by the pest species, Drosophila suzukii.

During the invasive process, species often encounter diverse environmental conditions that they must respond to, either through rapid genetic adaptive shifts or phenotypic plasticity, or by some combination of both. Consequently, invasive species constitute powerful models for investigating various questions related to the adaptive processes that underpin successful invasions.

In this paper, we highlight how Drosophila have been and remain a valuable model group for understanding these underlying adaptive processes, and how they enable insight into key questions in invasion biology, including how quickly adaptive responses can occur when species are faced with new environmental conditions.

Citation

Gibert P, Hill M, Pascual M, Plantamp C, Terblanche JS, Yassin A, Sgrò, CM (2016) Drosophila as models to understand the adaptive process during invasion. Biological Invasions, 18:1089–1103 PDF DOI

PhD project: The role of nutrition in mediating evolutionary responses to rapid environmental change

Update: this position is now filled.

A fully-funded PhD stipend is available for a suitably qualified student interested in working on the evolutionary responses to environmental change, with particular reference to the genetic and physiological pathways that mediate the role of nutrition in adaptation to change.

The project will be supervised by Associate Professor Carla Sgrò, School of Biological Sciences, Monash University, Melbourne, Australia.

Studies attempting to understand organismal responses to climate change have focussed on climatic stressors. However food limitation is one of the most common environmental challenges faced by organisms. How energy intake is balanced to optimise fitness under changing climates, and how this affects the capacity of organisms to respond to climate change, is unknown.

This project will combine genomics, developmental genetics and experimental evolution, within the geometric framework for nutrition, to understand how nutrition mediates evolutionary responses to environmental change. It will do so by identifying the genetic and physiological pathways that mediate the role of nutrition in adaptation to environmental change.

Successful candidates will be fully funded for 3.5 years (the length of a PhD in Australia), for full-time research, and with no teaching requirements. The annual stipend is approximately $25,000 AUD tax-free (equivalent to approximately $33,000 before tax) with additional expenses for research, coursework, and conference attendance (once per year) also covered.

To apply, please send a CV and academic transcript to carla.sgro@monash.edu.

Applicants must hold a Bachelor’s degree with first-class honours, or a master’s degree.

Review of applications will begin immediately, and short-listed candidates will be contacted to set up interviews via phone or Skype.

Cross-study comparison reveals common genomic, network, and functional signatures of desiccation resistance in Drosophila melanogaster

Authors: Marina Telonis-Scott, Carla M Sgrò, Ary A Hoffmann and Philippa C Griffin

Published in: Molecular Biology and Evolution (early view)

Abstract

Repeated attempts to map the genomic basis of complex traits often yield different outcomes because of the influence of genetic background, gene-by-environment interactions, and/or statistical limitations. However, where repeatability is low at the level of individual genes, overlap often occurs in gene ontology categories, genetic pathways, and interaction networks.

Here we report on the genomic overlap for natural desiccation resistance from a Pool-genome-wide association study experiment and a selection experiment in flies collected from the same region in southeastern Australia in different years.

We identified over 600 single nucleotide polymorphisms associated with desiccation resistance in flies derived from almost 1,000 wild-caught genotypes, a similar number of loci to that observed in our previous genomic study of selected lines, demonstrating the genetic complexity of this ecologically important trait.

By harnessing the power of cross-study comparison, we narrowed the candidates from almost 400 genes in each study to a core set of 45 genes, enriched for stimulus, stress, and defense responses.

In addition to gene-level overlap, there was higher order congruence at the network and functional levels, suggesting genetic redundancy in key stress sensing, stress response, immunity, signaling, and gene expression pathways. We also identified variants linked to different molecular aspects of desiccation physiology previously verified from functional experiments.

Our approach provides insight into the genomic basis of a complex and ecologically important trait and predicts candidate genetic pathways to explore in multiple genetic backgrounds and related species within a functional framework.

Citation

Telonis-Scott M, Sgrò CM, Hoffmann AA, Griffin PC (2016) Cross-study comparison reveals common genomic, network and functional signatures of desiccation resistance in Drosophila melanogasterMolecular Biology and Evolution PDF DOI