Chiara De Pasqual (she/her) provides the story behind her paper, “Morph-linked variation in female pheromone signaling and male response in a polymorphic moth“, which was shortlisted for this year’s Elton Prize. We also hear a little about her journey into animal ecology.

About the paper

Phenotypic color variation is common in natural populations and is often maintained by complex interactions among multiple selective pressures. Color traits can be involved both in intra- and inter-specific communication and, genetic associations with other traits, such as behavior, physiology and chemical signals can affect mate choice and individual fitness. In our study, we explored potential associations between three color genotypes and variation in female pheromone signaling and male’s ability to reach females. While previous work have typically focused on the signaler side, our study investigated associations between color morphs and both female pheromone signaling and male’s antennal morphology, which has virtually never been done.

In moths, females signal their willingness to mate by releasing sex pheromones, which are blends of chemical compounds. Males perceive the sex pheromones through their antennae, impressive sensory organs that are able to perceive minute quantities of pheromones. While it is known that variation in female chemical signals influences mate choice, much less investigated is the role of variation in male’s antennae in mate choice. Yet, both sexes interact in the wild.

For my PhD I joined Johanna Mappes’ research group (@aplantaginis.bsky.social) and used the wood tiger moth (Arctia plantaginis) as study system. Male hindwing coloration is dimorphic and genetically determined in a Mendelian way, with white (WW, Wy) and yellow (yy) color morphs. Although this color polymorphism is sex-limited, and females have orange/red hindwings, they carry the male’s color alleles and can be genetically classified as WW, Wy, and yy.

In this study, to test for associations between color morphs and chemical communication and their consequences for intra-population dynamics and the maintenance of phenotypic variation, we baited traps with females of known genotype and tested their attractiveness and the males ability to reach females based on their color morph and antennal characteristics (length, area and number of lamellae). The experiment was done both in a high (semi-natural setup)- and low (field setup)- population density scenario.

Before we dive into the results, let me make a digression. I think there is something extremely fascinating about chemical communication. Moths, and insects in general, have evolved this amazing communication skill that travels far and allows for recruitment over very long distances (up to kilometres!). During the field experiment, I stood close to the traps to observe how males behave once they have detected the female pheromone. I quickly learned that males seem to make their decision from quite far away and once they are locked on their preferred pheromone plume they fly straight to the trap. There is no probing between traps. I also found extremely fascinating the zig-zag flight pattern and the rapid wing flapping when they reach the trap with the female.

Alright, now back to the science! We found that yy females were more attractive than the other two genotypes, likely due to the combination of female weight, early pheromone release during the night and higher population density. Male’s searching success was instead likely affected by morph-specific behavioral strategies and local population density. White males were faster to locate females in high density population whereas yellow males were faster in low population density. While antennal area and length did not affect male’s searching behavior, males with a higher number of antennal lamellae located females faster. This makes sense, as the lamellae house the sensory neuron cells response responsible for detecting female pheromone.

This study provides a rare example of the interplay between morph-related precopulatory strategies and variation in chemical communication channels, which may offer an additional mechanism for the maintenance of phenotypic variation. It also shows that to understand how complex polymorphisms are maintained, we need to understand how the genetic architecture of the trait and the ecology of the species are interrelated.

I think, in the future, it would be interesting to explore the behavioral mechanisms that led to morph-specific advantages in the different contexts and also to investigate whether there are fitness costs for males with bigger and more sensitive antennae.

About the author

Chiara (@chiaradp.bsky.social) is currently a Postdoctoral Researcher at the Department of Plant Protection Biology at the Swedish University of Agricultural Sciences (SLU). Her work focuses on identifying the ecological factors that promote balancing selection in natural and agricultural systems. In natural systems, she focuses on the ecological factors that contribute to the maintenance of genetic and phenotypic variation. In agricultural contexts, she explores factors that limit the evolutionary potential of pathogens to reduce the reliance on agrochemical for environmentally sustainable crop protection. In her free time, Chiara enjoys cooking, hiking in nature, and solving jigsaw puzzles.