Within-population variability in a moth sex pheromone blend: genetic basis and behavioural consequences

Abstract

Evolutionary diversification of sexual communication systems in moths is perplexing because signal and response are under stabilizing selection in many species, and this is expected to constrain evolutionary change. In the moth Heliothis virescens, we consistently found high phenotypic variability in the female sex pheromone blend within each of four geographically distant populations. Here, we assess the heritability, genetic basis and behavioural consequences of this variation. Artificial selection with field-collected moths dramatically increased the relative amount of the saturated compound 16:Ald and decreased its unsaturated counterpart Z11-16:Ald, the major sex pheromone component (high line). In a cross between the high-and low-selected lines, one quantitative trait locus (QTL) explained 11-21% of the phenotypic variance in the 16:Ald/Z11-16:Ald ratio. Because changes in activity of desaturase enzymes could affect this ratio, we measured their expression levels in pheromone glands and mapped desaturase genes onto our linkage map. A delta-11-desaturase had lower expression in females producing less Z11-16:Ald; however, this gene mapped to a different chromosome than the QTL. A model in which the QTL is a trans-acting repressor of delta-11 desaturase expression explains many features of the data. Selection favouring heterozygotes which produce more unsaturated components could maintain a polymorphism at this locus.

Key genes of the sex pheromone biosynthesis pathway in female moths are required for pheromone quality and possibly mediate olfactory plasticity in conspecific male moths in Spodoptera litura

“…Our results are consistent with previous studies that showed that different geographical populations of Helio. virescens exhibit great variations in Z11‐16:Ald and 16:Ald proportions, which are the result of an expression level change in △ 11‐desaturase (Groot et al ., ). The differential expression of the pheromone biosynthesis pathway genes probably caused changes in the ratio of the sex pheromones released in the different geographical populations, which thus led to the coevolution of the S. litura mating and pheromone recognition systems and resulted in segregated populations and promotion of species evolution (Roelofs et al ., ).…”

Beyond species recognition: somatic state affects long-distance sex pheromone communication

“…Nevertheless, various studies found considerable interindividual variation in the amount and ratio of pheromone components [20]. Although such variation can be caused by local environmental factors or due to heterozygote advantage [21], there is certainly the possibility that long-range sex pheromones covary positively with the condition of the sender and serve as reliable indicator of mate quality [22,23], especially if produced and emitted by the less limiting sex (usually the males). More importantly, we know from studies on acoustic signals used to attract conspecific mates that selection on species recognition does not necessarily preclude sexual selection (e.g.…”

Evolution of moth sex pheromone composition by a single amino acid substitution in a fatty acid desaturase

“…Pheromone biosynthesis involves modifications of fatty acyl substrates, such as chain shortening and elongation, reduction, acetylation, oxidation, and desaturation (11). SP biosynthetic enzymes [i.e., FA reductases (8), FA chain-shortening enzymes (12, 13), and particularly FA desaturases (FADs) (7,9,(14)(15)(16)(17)] are the most commonly discovered traits underlying SP divergence in moths.Manduca sexta females attract males by releasing an SP containing in addition to mono-and diunsaturated aldehydes, which are typical structural themes in SPs of Bombycoidea moths (10), also uncommon conjugated triunsaturated aldehydes. The production of triunsaturated SPCs represents an easily traceable phenotype, thus making M. sexta a convenient yet unexploited model organism for unraveling the mechanisms of chemical communication evolution via novel SPC recruitment.…”

“…Pheromone biosynthesis involves modifications of fatty acyl substrates, such as chain shortening and elongation, reduction, acetylation, oxidation, and desaturation (11). SP biosynthetic enzymes [i.e., FA reductases (8), FA chain-shortening enzymes (12,13), and particularly FA desaturases (FADs) (7,9,(14)(15)(16)(17)] are the most commonly discovered traits underlying SP divergence in moths.…”