Evolution of pre‐zygotic and post‐zygotic barriers to gene flow among three cryptic species within the <i><scp>A</scp>nastrepha fraterculus</i> complex

Abstract

Abstract Tropical tephritids are ideally suited for studies on population divergence and speciation because they include species groups undergoing rapid radiation, in which morphologically cryptic species and sister species are abundant. The fraterculus species group in the N eotropical genus A nastrepha is a case in point, as it is composed of a complex of up to seven A . fraterculus morphotypes proposed to be cryptic species. Here, we document pre‐ and post‐zygotic barriers to gene flow among adults of the M exican A . fraterculus morphotype and three populations ( A rgentina, B razil, and P eru) belonging to two separate morphotypes ( B razilian 1 and P eruvian). We unveiled three forms of pre‐zygotic reproductive isolation resulting in strong assortative mating. In field cages, free‐ranging male and female A . fraterculus displayed a strong tendency to form couples with members of the opposite sex belonging to their own morphotype, suggesting that male pheromone emission, courtship displays, or both intervene in shaping female choice before actual contact and coupling. In addition, males and females of the Peruvian morphotype became receptive and mated significantly later than adults of the M exican and B razilian 1 morphotypes. After contact, M exican females exhibited greater mating discrimination than males when facing adults of the opposite sex belonging to either the P eruvian or the B razilian 1 morphotype as evidenced by vigorous resistance to penetration once they had been forcefully mounted by heterotypic males. Forced copulations resulted in production of F1 hybrids that were either less viable (and partially fertile) than parental crosses or even sterile. Our results suggest that the M exican morphotype is a distinct biological entity and that pre‐zygotic reproductive isolation through divergence in courtship or male‐produced pheromone and other mechanisms appear to evolve faster than post‐zygotic isolation in the fraterculus species group.