Assessing the role of family level variation and heat shock gene expression in the thermal stress response of the mosquito Aedes aegypti

Abstract

The geographical range of the mosquito vector for many human disease-causing viruses, Aedes aegypti , is expanding, in part owing to changing climate. The capacity of this species to adapt to thermal stress will affect its future distributions. It is unclear how much heritable genetic variation may affect the upper thermal limits of mosquito populations over the long term. Nor are the genetic pathways that confer thermal tolerance fully understood. In the short term, cells induce a plastic, protective response known as 'heat shock'. Using a physiological ‘knockdown’ assay, we investigated mosquito thermal tolerance to characterize the genetic architecture of the trait. While families representing the extreme ends of the distribution for knockdown time differed from one another, the trait exhibited low but non-zero broad-sense heritability. We then explored whether families representing thermal performance extremes differed in their heat shock response by measuring gene expression of heat shock protein-encoding genes Hsp 26, Hsp83 and Hsp70. Contrary to prediction, the families with higher thermal tolerance demonstrated less Hsp expression. This pattern may indicate that other mechanisms of heat tolerance, rather than heat shock, may underpin the stress response, and the costly production of HSPs may instead signal poor adaptation. This article is part of the theme issue ‘Infectious disease ecology and evolution in a changing world’.

Infectious disease ecology and evolution in a changing world

“…The final two papers in this theme address the evolutionary potential of hosts [ 23 ] and pathogens [ 24 ] in the face of rising temperatures. The geographical ranges of hosts, and the pathogens they carry, are expanding owing to changing climates [ 25 ].…”

“…Ware-Gilmore et al . [ 23 ] thoughtfully address this issue by studying how the heritable genetic variation and physiological responses in the mosquito Aedes aegypti may affect the upper thermal limits in populations over evolutionary time. In addition to driving vector evolution, will climate change select for more virulent pathogens?…”

“…Of particular concern is the future impact of climate change on the potential for mosquitoes-vectors for many human disease-causing viruses-to adapt to shifts in their thermal environment and move into new areas. Ware-Gilmore et al [23] thoughtfully address this issue by studying how the heritable genetic variation and physiological responses in the mosquito Aedes aegypti may affect the upper thermal limits in populations over evolutionary time. In addition to driving vector evolution, will climate change select for more virulent pathogens?…”

Mosquito thermal tolerance is remarkably constrained across a large climatic range

“…We note that prior studies of mosquito thermal tolerance have used a variety of methods to measure thermal tolerance including static and dynamic heat tolerance assays (e.g. 'thermal knockdowns') [12,26], reciprocal transplants Sample collection locations and experimental design used to measure mosquito thermal performance. Ten populations were collected as larvae from tree holes across the Western USA, reared in the laboratory under common conditions for one generation, then randomly designated into one of six temperature treatments.…”

“…We note that prior studies of mosquito thermal tolerance have used a variety of methods to measure thermal tolerance including static and dynamic heat tolerance assays (e.g. ‘thermal knockdowns’) [12,26], reciprocal transplants [13] and comparisons of niche-based distribution models [27]. These methods may each capture a slightly different component of thermal tolerance (e.g.…”