Evolution of Eye Morphology and Rhodopsin Expression in the Drosophila melanogaster Species Subgroup

Abstract

A striking diversity of compound eye size and shape has evolved among insects. The number of ommatidia and their size are major determinants of the visual sensitivity and acuity of the compound eye. Each ommatidium is composed of eight photoreceptor cells that facilitate the discrimination of different colours via the expression of various light sensitive Rhodopsin proteins. It follows that variation in eye size, shape, and opsin composition is likely to directly influence vision. We analyzed variation in these three traits in D. melanogaster, D. simulans and D. mauritiana. We show that D. mauritiana generally has larger eyes than its sibling species, which is due to a combination of larger ommatidia and more ommatidia. In addition, intra- and inter-specific differences in eye size among D. simulans and D. melanogaster strains are mainly caused by variation in ommatidia number. By applying a geometric morphometrics approach to assess whether the formation of larger eyes influences other parts of the head capsule, we found that an increase in eye size is associated with a reduction in the adjacent face cuticle. Our shape analysis also demonstrates that D. mauritiana eyes are specifically enlarged in the dorsal region. Intriguingly, this dorsal enlargement is associated with enhanced expression of rhodopsin 3 in D. mauritiana. In summary, our data suggests that the morphology and functional properties of the compound eyes vary considerably within and among these closely related Drosophila species and may be part of coordinated morphological changes affecting the head capsule.

Dissection of the complex genetic basis of craniofacial anomalies using haploid genetics and interspecies hybrids in Nasonia wasps

“…Further genetic and molecular analysis of the head shape differences will contribute to the growing number of studies examining the evolutionary genetics of shape and form. In particular, our analyses will complement similar approaches in understanding the patterning differences between closely (Arif et al, 2013; Posnien et al, 2012) and distantly (Carr et al, 2005) related flies with subtle and extreme, respectively, head shape differences.…”

The evolutionary diversity of insect retinal mosaics: common design principles and emerging molecular logic

“…The ratio of ommatidial subtypes is stable amongst higher Diptera [33,108,109], yet subtle differences amongst drosophilids have been reported [110,111]. The data from more distantly related insects reviewed here show that some stochastic mosaics look surprisingly similar (honeybee workers, butterflies, and locusts), raising the possibility that patterning via factors similar to Spineless could be conserved.…”

Rhodopsin coexpression in UV photoreceptors of Aedes aegypti and Anopheles gambiae mosquitoes

“…Phylogenetic analysis shows that these Op10 rhodopsins are orthologs of the Drosophila Rh7 rhodopsin (Nene et al, 2007). This rhodopsin family is known to be present in the three mosquito species and the 12 Drosophila species for which there are characterized genomes (Posnien et al, 2012). The conservation of this rhodopsin family suggests that they may have a unique role in mosquito visual system function.…”

“…Sequence comparison (Nene et al, 2007) showed that this Op10 rhodopsin belongs to a divergent group with greatest similarity to Drosophila Rh7, a rhodopsin of unknown function (Posnien et al, 2012). To initiate the study of this rhodopsin group, we characterized the expression profile of these mosquito genes.…”