What is ecological speciation

Evolutionary changes in traits that affect both ecological divergence and mating signals could lead to reproductive isolation and the formation of new species. Insect cuticular hydrocarbons (CHCs) are potential examples of such dual traits. They form a waxy layer on the cuticle of the insect to maintain water balance and prevent desiccation, while also acting as signaling molecules in mate recognition and chemical communication. Because the synthesis of these hydrocarbons in insect oenocytes occurs through a common biochemical pathway, natural or sexual selection on one role may affect the other. In this review, we explore how ecological divergence in insect CHCs can lead to divergence in mating signals and reproductive isolation. We suggest that the evolution of insect CHCs may be ripe models for understanding ecological speciation.

https://onlinelibrary.wiley.com/doi/pdf/10.1002/bies.201500014

Wax, sex and the origin of species: Dual roles of insect cuticular hydrocarbons in adaptation and mating

Intense use of insecticides has resulted in the selection of extreme levels of resistance in insect populations. Therefore understanding the molecular basis of insecticide resistance mechanisms becomes critical. Penetration resistance refers to modifications in the cuticle that will eventually slow down the penetration of insecticide molecules within insects' body. So far, two mechanisms of penetration resistance have been described, the cuticle thickening and the altering of cuticle composition. Cuticular modifications are attributed to the over-expression of diversified genes or proteins, which belong to structural components (cuticular proteins mainly), enzymes that catalyze enzymatic reactions (CYP4G16 and laccase 2) or ABC transporters that promote cuticular translocation. In the present review we summarize recent studies and discuss future perspectives.

Insect cuticle: a critical determinant of insecticide resistance.

Speciation can involve a transition from a few genetic loci that are resistant to gene flow to genome-wide differentiation. However, only limited data exist concerning this transition and the factors promoting it. Here, we study phases of speciation using data from >100 populations of 11 species of Timema stick insects. Consistent with early phases of genic speciation, adaptive colour-pattern loci reside in localized genetic regions of accentuated differentiation between populations experiencing gene flow. Transitions to genome-wide differentiation are also observed with gene flow, in association with differentiation in polygenic chemical traits affecting mate choice. Thus, intermediate phases of speciation are associated with genome-wide differentiation and mate choice, but not growth of a few genomic islands. We also find a gap in genomic differentiation between sympatric taxa that still exchange genes and those that do not, highlighting the association between differentiation and complete reproductive isolation. Our results suggest that substantial progress towards speciation may involve the alignment of multi-faceted aspects of differentiation.

/pdf/transitions-between-phases-of-genomic-differentiation-during-10coii5nul.pdf

Transitions between phases of genomic differentiation during stick-insect speciation

Insect pheromones: An overview of function, form, and discovery.

Evolutionary changes in traits involved in both ecological divergence and mate choice may produce reproductive isolation and speciation. However, there are few examples of such dual traits, and the genetic and molecular bases of their evolution have not been identified. We show that methyl-branched cuticular hydrocarbons (mbCHCs) are a dual trait that affects both desiccation resistance and mate choice in Drosophila serrata. We identify a fatty acid synthase mFAS (CG3524) responsible for mbCHC production in Drosophila and find that expression of mFAS is undetectable in oenocytes (cells that produce CHCs) of a closely related, desiccation-sensitive species, D. birchii, due in part to multiple changes in cis-regulatory sequences of mFAS. We suggest that ecologically influenced changes in the production of mbCHCs have contributed to reproductive isolation between the two species.

https://science.sciencemag.org/content/sci/343/6175/1148.full.pdf

Kathy Vaccarro

Papers

A single gene affects both ecological divergence and mate choice in Drosophila