Eye development, structure and vision in the pest species Drosophila suzukii

The pest species Drosophila suzukii targets soft fruits and causes major economic damage. This species develops two distinct seasonal morphs depending on temperature. Summer morph adults are smaller and more lightly pigmented than the winter morph, which over-winters and undergoes reproductive diapause. Further characterising the morphology and behaviour of the winter and summer morphs is crucial to better understand and combat this pest species.

Insect eye size varies greatly reflecting environmental and behavioural adaptations. Eye size is specified by ommatidia number and size, which in combination determine visual acuity and contrast sensitivity. We have found that the eyes of the D. suzukii winter and summer morphs have the same surface area despite their body size difference.

However, the eyes of the winter morph have significantly more but narrower ommatidia than the summer morph. This indicates that these morphs differ in their vision and therefore this species likely has seasonal differences in visual behaviour. This project aims to characterise the differences in eye development and structure, and vision of these seasonal morphs of D. suzukii through the following complementary objectives.

Objective 1. Investigating the developmental basis of ommatidia differences.

Eye development will be compared between the two morphs by measuring cell division, morphogenetic furrow progression, cell death and ommatidia maturation, using live imaging and fixed tissues. This will reveal the developmental basis of differences in ommatidia number and size. Objective 2. Characterising the genetic regulation of ommatidia differences.

RNA-seq datasets will be generated from eye discs of the two morphs to identify differentially expressed genes during eye development. The student will then investigate the role of selected differentially expressed candidate genes in ommatidia size and number specification using CRISPR/Cas9. This will deliver new insights into genetic regulation of ommatidia differences between the morphs.

Objective 3. Modelling the impact of eye morphology differences on vision.

SEM and X-ray synchrotron tomography will be used to extract adult eye and ommatidia parameters of the two morphs to model predictions of their vision. The student will also explore if the morphs differ in colour vision by assaying their rhodopsin expression using immunohistochemistry. Objective 4. Testing the impact of differences in eye morphology variation between morphs.

Predictions from Objective 3 will be tested by assaying fly behaviour in psychophysics experiments to measure and compare their spatial acuity, temporal acuity and contrast sensitivity. We will also test differences in colour vision predicted by variation in rhodopsin expression.