Identifying the genes that confer evolutionary adaptation to environmental temperature in an ectotherm

Lead Research Organisation: University College London
Department Name: Genetics Evolution and Environment

Abstract

Many animals grow to be larger under cold conditions. For instance, warm-blooded animals such as species of birds and mammals often have larger body size in the colder parts of their geographical range. This pattern makes sense because it is easier for a large animal to keep warm, since it has a larger volume of heat-producing tissue in relation to the area of the body surface over which heat is lost to the environment. However, it has become apparent that cold-blooded creatures too become large in the cold, and the aim of this project is to find out why. This is an important topic, because global climate change will expose animals to changing temperature and we need to understand how they will respond. Food animals such as fish are cold-blooded and our work will be directly relevant to understanding how their growth efficiency is altered by temperature. To do this, we shall focus on a small animal, the fruit fly Drosophila, which has a wide geographic range. Fruit flies evolve to be larger at higher latitudes; experiments where flies from different populations are grown in the same environment shows that they differ genetically in size. Temperature seems to be a critical variable in the evolution of larger body size at higher latitudes, because experiments where flies are allowed to evolve for several years at different temperatures in the laboratory also result in genetically larger body size at lower culture temperatures. In addition, flies from the same population that grow up to adulthood at different temperatures produce larger adults with growth at lower temperatures, showing that there is a direct, environmental effect of temperature on size. We shall discover the reasons for larger size in the cold. First, we shall identify the genes that produce larger body size at higher latitudes in nature. We shall do this by mapping their location in the genetic material and by looking for altered patterns of gene expression. Critically, we shall then confirm our identification by experimentally inducing the genetic variants that we think are critical and checking their effects on body size. We shall test the importance of temperature in the evolution of body size, by measuring the performance of flies with the 'hot' and 'cold' genetic variants at different temperatures. We shall also find out which genes show altered expression during growth at different temperatures. By identifying the genes and pathways that control changes in body size in response to temperature, we shall start to understand the reasons why cold-blooded animals become larger in the cold.
 
Description The research aimed to determine the genetic basis of natural clinal variation in body size in Drosophila melanogaster. The broader aim of this work was to understand the molecular basis of Our main achievements are as follows:

-Successfully identify candidate genes producing clinal body size variation in Drosophila using gene expression data. We undertook a comprehensive analysis of gene expression variation of multiple populations from cline ends to identify candidate genes for traits that are involved in clinal adaptation. These genes help us to understand how evolutionary adaptation occurs along a temperate-tropical climate gradient.

-Carried out functional and sequence analyses of the Dca gene to identified molecular basis of adaptive shift in body size in Drosophila melanogaster. The Dca gene has previously been identified as being involved in climate adaptation. We have found that it underlies body size variation, affecting particularly wing size. We clarified the evolutionary history of the three most common Dca promoter alleles and provide strong support that Dca is an ideal candidate for climatic adaptation in D. melanogaster.

-We showed that polymorphism in the neurofibromin gene, Nf1, is associated with antagonistic selection on body size and development time in Drosophila melanogaster. Antagonistic selection occurs when one form of selection occurs on a trait in one direction but this is counteracted by selection on the same trait in a different direction. The genes underlying this type of selection are mostly unknown but here we have a putative example. We identified two major Nf1 haplotypes in natural populations that show a significant cline. We found that, despite its negative association with body size, the latitudinal cline of Nf1-insertion-A in Australia might be explained by its positive association with rapid larval development. These results suggest that polymorphisms in neuronal genes (such as Nf1) can shape climatic adaptation through subtle, sex-dependent compromises.
Exploitation Route This information is relevant to environmental managers dealing with climate change, given that shifts in body size can contribute to adaptability under climate change. The research provides information on the molecular basis of adaptation, which contributes to our overall understanding of evolutionary processes in populations.
Sectors Environment

Pharmaceuticals and Medical Biotechnology

 
Description Clinal variation in Drosophila; a signature of climatic adaptation and a resource for adaptive gene discovery
Amount £600,000 (GBP)
Funding ID DP120100916 
Organisation University of Massachusetts 
Department University of Massachusetts Medical School
Sector Academic/University
Country United States
Start 01/2012 
End 12/2014
 
Description Clinal variation in Drosophila; a signature of climatic adaptation and a resource for adaptive gene discovery
Amount £600,000 (GBP)
Funding ID DP120100916 
Organisation University of Massachusetts 
Department University of Massachusetts Medical School
Sector Academic/University
Country United States
Start 01/2012 
End 12/2014
 
Description Identifying genes causing thermal evolution of ectotherm body size
Amount £572,513 (GBP)
Organisation University of Massachusetts 
Department University of Massachusetts Medical School
Sector Academic/University
Country United States
Start 01/2007 
End 12/2011
 
Description Identifying genes causing thermal evolution of ectotherm body size
Amount £572,513 (GBP)
Organisation University of Massachusetts 
Department University of Massachusetts Medical School
Sector Academic/University
Country United States
Start 01/2007 
End 12/2011
 
Title Whole genome tiling array data of clinal end populations of Australian Drosophila 
Description Whole genome tiling array data of clinal end populations of Australian Drosophila 
Type Of Material Database/Collection of data 
Year Produced 2012 
Provided To Others? No  
 
Description CSIRO Ecosystems 
Organisation Commonwealth Scientific and Industrial Research Organisation
Country Australia 
Sector Public 
PI Contribution The research has contributed to a new collaboration with CSIRO Ecosystems in Australia on the genomics of climate change adaptation.
Start Year 2012
 
Description Public lectures by Prof Ary Hoffmann on climate change adaptation. 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Primary Audience Public/other audiences
Results and Impact Three public lectures by Prof Ary Hoffmann on climate change adaptation.
Year(s) Of Engagement Activity 2008