Impact of elevated CO2 level and egg quiescence duration on gene expression in the peripheral olfactory system of Aedes aegypti

Abstract

Elevation in CO₂ can significantly impact the biology of various organisms, affecting life-history traits of both aquatic and terrestrial forms, including disease-vectoring mosquitoes. For mosquitoes, this effect is accentuated by egg quiescence duration, resulting in a change in foraging of adult females. Female mosquitoes rely on their olfactory system for locating resources, such as nectar and blood. This study employs a transcriptomic approach to investigate how a projected elevation in CO₂ level, under a worst-case scenario, interacts with extended egg quiescence duration to modulate the molecular machinery of the peripheral olfactory system, the antennae and maxillary palps, of the yellow fever mosquito, Aedes aegypti. The transcriptome analysis demonstrates significant changes in the abundance of genes related to metabolism, xenobiotics degradation and chemosensory function, with the most pronounced effects observed in the CO₂ sensing tissue, the maxillary palp. The study provides novel insights into how anthropogenic climate change can modulate the olfactory sensory system of disease vectors, which may have cascading effects on resource-seeking behaviour.

Keywords: Carbon dioxide; Climate change; Egg quiescence; Mosquitoes; Olfactory system; Transcriptome.

Fig. 1

Elevated CO₂, but not egg quiescence, differentially affects overall gene expression in the peripheral olfactory organs of Aedes aegypti. Principal component analysis of antennal and maxillary palp libraries of females emerging from new and older eggs, with short and extended egg quiescent duration, respectively, reared under ambient and elevated CO₂ conditions. A total of 29 libraries were analysed to estimate the change in overall gene expression, in which Principal Component (PC) 1 (43.2%) and PC 9 (1.9%) accounted for the variance between the libraries.

Fig. 2

Gene ontology analysis of differentially expressed genes in the antennae and maxillary palps of Aedes aegypti. The olfactory tissues were collected from females reared under ambient and elevated CO₂ conditions, as well as short and extended egg quiescence duration, referred to as new and older eggs, respectively. Pairwise comparisons are arranged in a matrix in response to CO₂ conditions and egg quiescence period. The differentially expressed genes are classified into molecular function ontology, using gene ontology slim categorisation. n.s.: non-significant.

Fig. 3

Kyoto Encyclopedia of Genes and Genomes pathway analysis of differentially expressed genes in the antennae and maxillary palps of Aedes aegypti. The olfactory tissues were collected from females reared under ambient and elevated CO₂ conditions, as well as short and extended egg quiescence duration, referred to as new and older eggs, respectively. Pairwise comparisons are arranged in a matrix in relation to the response to CO₂ conditions (eCO₂) and egg quiescence period. The categories are annotated from Vectorbase and further classified into pathways designated by Kyoto Encyclopedia of Genes and Genomes database (https://www.genome.jp/kegg/).

Fig. 4

Differential abundance of chemosensory genes in Aedes aegypti in response to elevated CO₂ conditions and extended egg quiescence period. The olfactory tissues were collected from females reared under ambient and elevated CO₂ conditions, as well as short and extended egg quiescence duration, referred to as new and older eggs, respectively. The abundance of reliably expressed (> 1 transcript per million) chemosensory genes compared between ambient and elevated CO₂ (eCO₂) levels, as well as egg quiescent periods, in the antennal (a) and maxillary palp (b) libraries, and demonstrated by fold-change (> 1.5-fold change; FDR > 0.05). Asterisks on fold change denote significant differences between pairwise comparisons.