The implications go beyond making a better dating app for bugs. Now scientists can begin to ask why mating signals and mating preferences change in the first place, which is a long-standing paradox since any change could reduce the ability of an organism to successfully mate. Knowledge of these two genes will provide a better understanding of how the pheromones of the 160,000 moth species have evolved.
Of course, one important role for mating preferences is to make sure you are not matching up with a completely different species. The signal sent by females must be preferred by males of the same species, a mechanism called assortative mating. The European corn borer is interesting because there are two types, called E and Z, with assortative mating within each type. Even though the two types can be mated to each other in captivity, E mostly mates with E, and Z with Z in the field. For this reason, the European corn borer has been used as a model for how one species can split into two, ever since the two pheromone types were first discovered 50 years ago.
'That means we now know – at the molecular level – how chemical matchmaking aids in the formation of new species. Similar genetic changes to pheromone preference could also be keeping tens of thousands of other moth species separate,' says Erik Dopman, professor of biology at Tufts University and corresponding author of the study. Different aspects of the research were conducted by the three co-first authors Fotini Koutroumpa of University of Amsterdam, Melanie Unbehend of the Max Planck Institute for Chemical Ecology, and Genevieve Kozak, a former post-doctoral scholar at Tufts University and now assistant professor at University of Massachusetts, Dartmouth.
Koutroumpa examined genes expressed in the male brain and antenna, Unbehend performed an elaborate set of crosses that narrowed down the chromosomal interval to a single gene, and Kozak used a population genomic approach to further pinpoint a single intron in the gene for its functional importance. 'Our study’s success can be attributed to a team with a common vision and strong sense of humor that helped make the science worthwhile and fun,' says Dopman.
'This is the first moth species out of 160,000 in which female signalling and male preference genes have both been identified,' says Prof. Astrid Groot from the UvA Institute for Biodiversity and Ecosystem Dynamics, who also helped identify the gene controlling the pheromone difference in E and Z females. 'That provides us with complete information on the evolution of mate choice and a way to measure how closely these choices are linked to evolving traits and populations.'
The ability to predict mating could also help control reproduction in pest insects. The European corn borer is a significant pest for many agricultural crops in addition to corn. In the U.S., it costs nearly $2 billion each year to monitor and control. It is also the primary pest target for genetically modified 'Bt corn' which expresses insecticidal proteins derived from the bacterium, Bacillus thuringiensis. While Bt corn remains an effective control of the corn borer moth in the U.S., corn borers in Nova Scotia are now evolving resistance to another variety of Bt corn.
'Our results can help to predict whether Bt resistance could spread from Nova Scotia to the Corn Belt of the U.S., or whether assortative mating could prevent or delay it', says David Heckel from the Max Planck Institute for Chemical Ecology, who also studies how insects evolve resistance to Bt. 'Bt corn has enabled a huge reduction in the use of chemical insecticides, and it should be a high priority to preserve its ecological benefits as long as possible.'
Melanie Unbehend, Genevieve M. Kozak, Fotini Koutroumpa, Brad S. Coates, Teun Dekker, Astrid T. Groot, David G. Heckel, Erik B. Dopman: 'Bric à brac controls sex pheromone choice by male European corn borer moths,' in Nature Communications (14 May 2021). DOI: https://doi.org/10.1038/s41467-021-23026-x