Multiple loci linked to inversions are associated with eye size variation in species of the Drosophila virilis phylad

Abstract

The size and shape of organs is tightly controlled to achieve optimal function. Natural morphological variations often represent functional adaptations to an ever-changing environment. For instance, variation in head morphology is pervasive in insects and the underlying molecular basis is starting to be revealed in the Drosophila genus for species of the melanogaster group. However, it remains unclear whether similar diversifications are governed by similar or different molecular mechanisms over longer timescales. To address this issue, we used species of the virilis phylad because they have been diverging from D. melanogaster for at least 40 million years. Our comprehensive morphological survey revealed remarkable differences in eye size and head shape among these species with D. novamexicana having the smallest eyes and southern D. americana populations having the largest eyes. We show that the genetic architecture underlying eye size variation is complex with multiple associated genetic variants located on most chromosomes. Our genome wide association study (GWAS) strongly suggests that some of the putative causative variants are associated with the presence of inversions. Indeed, northern populations of D. americana share derived inversions with D. novamexicana and they show smaller eyes compared to southern ones . Intriguingly, we observed a significant enrichment of genes involved in eye development on the 4th chromosome after intersecting chromosomal regions associated with phenotypic differences with those showing high differentiation among D. americana populations. We propose that variants associated with chromosomal inversions contribute to both intra- and interspecific variation in eye size among species of the virilis phylad.

Investigating subtle changes in facial expression to assess acute pain in Japanese macaques

“…One approach to remove the artificial variation of orientation is to use regression before comparing groups. Therefore, to mitigate the effects of subject orientation we calculated the residuals of the within-group pooled regression between Procrustes coordinates and the respective PCs 38 . The resulting dataset containing the residuals produced by the regression was used to generate a covariance matrix and a new PCA was then performed.…”

Divergence and introgression among the virilis group of Drosophila

“…Additionally, our data do not allow us to characterize or describe inversions despite their prevalence in the virilis group (Reis et al. 2018 , 2020 ).…”

“…But there has been extensive introgression between the X chromosomes of D. borealis and D. lacicola. Additionally, our data do not allow us to characterize or describe inversions despite their prevalence in the virilis group (Reis et al 2018(Reis et al , 2020.…”

Looking across the gap: Understanding the evolution of eyes and vision among insects

“…[ 3 ] This suggests that changes in ey regulation could be an evolutionary hotspot, at least among Drosophila species, and it would be interesting to test whether this regulatory mechanism is involved in eye size differences in other insects. However, differences in Drosophila ommatidia number have been found to be polygenic [ 3,48,49 ]. Consistent with this, the nucleotide change in ey alone does not explain the full ommatidia number difference in the focal strains studied by Ramaekers et al.…”

“…The studies above demonstrate the enormous potential to decipher the genetic basis of differences in eye size and structure among other Drosophila species [43,45,48] and this could help to pinpoint the nodes of evolution to better understand how GRNs evolve more generally. While much less is known in other insects, models generated for eye development such as beetles, bees, and butterflies are already demonstrating their great potential to identify and investigate candidate genes to test mechanisms from Drosophila and more fully explain diversification of eye morphology among insects.…”