Transcriptomics of host adaptation, early results: Gene expression patterns of the cactophilic fly Drosophila buzzatii in its natural breeding and feeding resources

DE PANIS D, P FURIÓ, J PADRÓ, I SOTO, S TARAZONA, H DOPAZO, A CONESA, E HASSON

Rosario

Congreso; 4to Congreso Argentino de Bioinformática; 2013

Asociación Argentina de Bioinformática y Biología Computacional

Cactophilic species of the subgenus Drosophila have been a model for the study of ecological adaptation and speciation for several decades. Drosophila buzzatii primarily uses decomposing cacti of different species of the Opuntia genus as breeding substrates, while its sibling species, Drosophila koepferae, utilizes columnar cacti of the genera Cereus and Trichocereus. However, some degree of niche overlapping has been described between these two species. Previous studies have shown that fitness components were heavily affected by host shifts in both species, leading to the proposal of the hypothesis that breeding in asecondary host is stressful for D. buzzatii, specially due to the presence of alkaloids [1].Our project seeks to study the genetic responses to environmental change and its implication in speciation by ecological specialization through transcriptome analysis of these closely related species by RNA-Seq. Transcriptomes of 3rd instar larvae raised in native conditions, and complemented with nutritional supplements and an alkaloid fraction extracted from Trichocereus terschekii, were sequenced with Illumina Hi-Seq 2000, each species in both cacti, and each cacti in every treatment, with 3 biological replicates. Here we show early results of some treatments in one of the two studied species, D. buzzatii. The ~80 million high quality paired-end reads obtained for the treatments shown below (Fig.1) were mapped against the D. buzzatii reference genome (unreleased) with the program TopHat, then the mapped reads were counted using a genome annotation reference of 12,102 genes (unreleased) using HTSeq-count software. Differential expression analysis was performed by NOISeq-BIO R-package [2]. Fig.1. A,B: Differential expression plot.There are 696 differentially expressed genes between the treatments of eachcactus with nutritional supplements (A), while only 3 genes in the same treatments with Trichocereus alkaloids fraction added in the same final concentration (B). C: Venn  diagrams. Overexpressed genes are shown in red, underexpressed in blue. The intersection shows the 2 shared differentially expressed genes between the two pair of treatments. ConclusionThese first results show that the differential expression observed in the treatments of each cactus with nutritional supplements in the native concentration of alkaloids is no longer observed when  alkaloids are added in those same treatments in such a way that both are in the same concentration. This suggest that the natural alkaloids present in T. terschekii  modify the expression of particular genes in D. buzzatii. Further detailed analysis will be perform with the complementary treatments of the project to validate these results.