Experimental evidence for interspecific directional selection on moth pheromone communication

Department of Entomology and W. M. Keck Center for Behavioral Biology, North Carolina State University, Raleigh, NC 27695-7613

Edited by May R. Berenbaum, University of Illinois at Urbana–Champaign, Urbana, IL, and approved February 27, 2006 (received for review October 28, 2005)

Abstract

The chemical composition of the sexual communication signals of female moths is thought to be under strong stabilizing selection, because females that produce atypical pheromone blends suffer lower success in finding mates. This intraspecific selection pressure cannot explain the high diversity of moth pheromone blends found in nature. We conducted experiments to determine whether communication interference from males of closely related species could exert strong enough directional selection to cause evolution of these signals. Attraction and mating success of Heliothis subflexa (Hs) females with a normal quantitative trait locus for production of acetate pheromone components (norm-OAc) were compared with Hs females with an introgressed quantitative trait locus from Heliothis virescens (Hv) that dramatically decreased the amount of acetate esters in their pheromone glands (low-OAc). In field experiments with natural Hv and Hs populations, 10 times more Hv males were captured in traps baited with live low-OAc Hs females than in traps with norm-OAc Hs females. This pattern was confirmed in mate-choice assays in cages. Hybrids resulting from Hv–Hs matings have effectively zero fitness in the field. Combining our results with the extensive data set gathered in the past 40 years on the reproductive biology of Hv, we can quantitatively estimate that the directional selection exerted by Hv males on Hs females to produce relatively high amounts (>5%) of acetates can range from 0.135 to 0.231. Such intense interspecific selection may counteract intraspecific stabilizing selection that impedes evolutionary changes in pheromone blends and could lead to diversification of sexual signals.

Footnotes

*To whom correspondence should be addressed. E-mail: astrid_groot{at}ncsu.edu
Author contributions: A.T.G., C.S., and F.G. designed research; A.T.G., J.L.H., J.H., and R.G.S. performed research; J.L.H. contributed new reagents/analytic tools; A.T.G., J.L.H., C.S., and F.G. analyzed data; and A.T.G., C.S., and F.G. wrote the paper.
Conflict of interest statement: No conflicts declared.
This paper was submitted directly (Track II) to the PNAS office.
Abbreviations:

Abbreviations:

Hs,

Heliothis subflexa;

Hv,

Heliothis virescens;

QTL,

quantitative trait locus