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One mechanism, rarely found outside of disease resistance studies, describes the most genetically variable individuals to have higher reproductive success, promoting the maintenance of genetic variation in the population. In addition, individuals with different genetic backgrounds benefit from reproductive advantages that varies according to the context.

Populations formed by organisms that present variation in genetically determined traits are ideal systems to study how interactions between individuals and the environment can contribute to maintain genetic diversity in natural populations. The wood tiger moth (Arctia plantaginis) hindwing (i.e, back wings) coloration is genetically determined by two color alleles, which translate into white (genotype; WW, Wy) or yellow (genotype; yy) moths. Mating experiments involving moths of all genotypes, that span from finding a potential mating partner to producing offspring can shed light on the maintenance of genetic diversity.

Heterozygote advantage as a powerful mechanism to preserve genetic variation

In her dissertation, De Pasqual showed two mechanisms that contribute to maintain the different color alleles. The thesis found a strong contribution of a mechanism called “heterozygote advantage”. The key feature of this mechanism describes the genetically more variable individuals to benefit from a reproductive advantage, promoting the maintenance of genetic variation in the population. This mechanism is typically related to disease resistance and rarely shown for natural populations. Well known is the case of the sickle cell anemia. In countries where malaria is prevalent, individuals that carry two types of red blood cells (thus heterozygote individuals) have significantly increased chances to survive the disease compared to individuals that have one type of red blood cells. In the case of the wood tiger moth, females carrying two different color alleles (i.e., Wy) had a higher offspring number than the other genotypes. Since the yellow (y) allele is related to low reproductive success, heterozygote advantage is a mechanism that prevent this allele from disappearing from the population. Heterozygote advantage thus allows both color alleles to remain in the same population, and preserve genetic variation.

The importance of considering multiple steps of the reproductive sequence

Across the thesis, De Pasqual also found that, in general, differently colored individuals, thus with different genetic backgrounds, were favored at different stages of the reproductive sequence. When searching for a potential partner, white (WW, Wy) males were faster in reaching females in high population density, whereas yellow (yy) males were more successful in low population densities. Yellow (yy) females were typically more attractive than white females due to a strategy of earlier sexual advertisement during the night. Finally, once mated, heterozygote (Wy) females had more offspring. This, as well, can contribute to maintain the genetic diversity through advantages that are context-specifics.

This thesis showed that a small genetic region, such as the color gene, can have profound effects on the biology of the species, affecting the individual’s behavior and reproductive success. In turn, this contributes to maintain genetic diversity in the population. Furthermore, the thesis highlighted the importance of understanding the complex interactions between the genetic basis of traits, animal behavior, and the environment to deeply understand how genetic variation persists in nature.

The thesis is published in the JYU Dissertations as a number 579, Jyväskylä 2022, ISBN 978-951-39-9244-6 (PDF), URN:ISBN:978-951-39-9244-6, ISSN 2489-9003. Link to publication:

Chiara De Pasqual will defend her doctoral thesis titled “On the maintenance of intrapopulation genetic variation: the interplay between sexual selection, chemical communication, and fitness in the wood tiger moth (Arctia plantaginis)” on December 2^nd, 2022. The public dissertation will be held in Seminarium, Old Festival Hall (S212, Seminarinmäki), starting at 12.00. The Opponent is Associate Professor Matthew Symonds from Deakin University, Australia and the Custos is Academy Professor Johanna Mappes from University of Helsinki and Jyväskylä. The doctoral dissertation is held in English.