SFB-TRR 212

Temporal niche choice in Drosophila melanogaster

The majority of animals restrict their behavioural activity to defined times during the 24-hr day. This temporal niche is specified by an intricate interplay between the animal’s circadian clock and external factors like preferred temperature, light intensity, predators and food availability. Being active at the ‘wrong time’ can have severe impact on an organism’s fitness. Nevertheless, it is conceivable that ‘exploring’ or extending an individual’s temporal niche can have positive fitness effects. For example, extending individual activity outside of the original temporal niche may allow access to food sources not available to ‘conservative’ conspecifics. Also, changing environmental conditions likely change the conditions of temporal niches, which may activate niche conformance and/or choice mechanisms.

Here, we test the hypothesis that individuals can actively explore and choose temporal niches that support their own fitness. We designed a behavioural choice apparatus, allowing fruit flies (Drosophila melanogaster) to choose between temporal regimes. Using flies with altered circadian clock speed, we will first analyse if flies can actively seek an environment in which external and internal time match. This proof-of-principle experiment will then be modified to test if individual wild type flies differ in their choice for diverse natural environmental conditions.

By monitoring mating attempts and success, these assays may help to understand if individual variation in temporal niche choice leads to fitness gain in a changing environment (e.g. global warming).

To understand the cellular and molecular mechanisms underlying individual behavioural variation and temporal niche choice, and the potential role of cryptic genetic variation (CGV), we will investigate if the candidate evolutionary capacitator HSP90 contributes to behavioural variation among individuals. Previous studies indicate that Hsp90-mutant flies exhibit increased behavioural variation, including multiple transitions from rhythmic to arrhythmic behaviour. We will use transgenic RNAi and CRISPR/Cas9 technology to create cell type specific Hsp90 knock-outs. These mutants will be analysed behaviourally to see if Hsp90 contributes to individual differences in temporal niche choice, and to determine the cellular substrates and molecular targets of HSP90 protein function.

We are addressing three hypotheses:

1. Fruit flies can choose their preferred temporal niche, which has a positive effect on fitness
2. Individual differences of temporal niche choice are caused by variable release of cryptic genetic variation mediated by HSP90
3. Non-developmental HSP90 function is required in specific adult brain areas and cell types to mediate release of cryptic genetic variation

In summary, we aim to proof the existence of temporal niche choice for individual fitness gain. In addition, our novel approach will target the cellular and molecular mechanisms underlying temporal choice, which have not been described for any system.