Morph-linked variation in female pheromone signaling and male response in a polymorphic moth

Understanding the maintenance of genetic variation in reproductive strategies and polymorphisms in the wild requires a comprehensive examination of the complex interactions between genetic basis, behavior, and environmental factors.

We tested the association between three color genotypes and variation in female pheromone signaling and male antennal morphology in the wood tiger moth ( Arctia plantaginis ). These moths have genetically determined white (WW, Wy) and yellow (yy) hindwings that are linked to mating success and fitness, with heterozygotes (Wy) having an advantage. We hypothesized that attractiveness and reproductive success are correlated, with Wy females being more attractive than the other two genotypes which could contribute to maintaining the polymorphism.

Female attractiveness was tested by baiting traps with females of the three color genotypes both in low-(i.e., field setup) and in high-population density (i.e., large enclosure setup). Male’s ability to reach females was correlated to their own color genotype and antennal morphology (length, area, and lamellae count).

Contrary to our prediction, morph-related reproductive success and attractiveness were not correlated. Heavier Wy females attracted a lower proportion of males compared to WW and yy females. Specifically, an increase in weight corresponded to a decreased Wy but increased yy female attractiveness. yy females were generally more attractive than others likely due to earlier pheromone release. In males, lamellae count and genetic color morph were linked to the male’s ability to locate females. Furthermore, male traits affected their ability to reach females in a context-specific way. Males with denser antennae (i.e., higher lamellae count) and white males reached the females faster than yellows in the enclosure, while yellow males located females faster than whites in the field.

Our results indicate that higher yy female attractiveness was likely affected by the combined effect of early pheromone release, female weight and higher population density. Males’ searching success was affected by morph-specific behavioral strategies and local population density. Ultimately, the combined effect of genotype-related pheromone signaling strategies of females together with environment-dependent male behavior affect male response and potentially contribute to maintaining variation in fitness-related traits.