Fruit odor discrimination and sympatric host race formation in Rhagoletis

Abstract

Rhagoletis pomonella is a model for incipient sympatric speciation (divergence without geographic isolation) by host-plant shifts. Here, we show that historically derived apple-and ancestral hawthorn-infesting host races of the fly use fruit odor as a key olfactory cue to help distinguish between their respective plants. In flight-tunnel assays and field tests, apple and hawthorn flies preferentially oriented to, and were captured with, chemical blends of their natal fruit volatiles. Because R. pomonella rendezvous on or near the unabscised fruit of their hosts to mate, the behavioral preference for apple vs. hawthorn fruit odor translates directly into premating reproductive isolation between the fly races. We have therefore identified a key and recently evolved (<150 years) mechanism responsible for host choice in R. pomonella bearing directly on sympatric host race formation and speciation.

Chemical ecology of insect–plant interactions: ecological significance of plant secondary metabolites

“…The phytochemical mediation of sexual communication, including rendezvous cues (IV-2) in conjunction with host recognition (I-1, I-2), may be of great importance particularly at the initial stage of speciation, although such a process has not been well understood. 75,79) On another front, phytochemical cues and their derivatives also provide us with innovative tools for pest management. However, in the case of fruit fly attractants, such as the synomones mediating orchid-fruit fly interactions, the intensive use of such allelochemicals in RK-sensitive RK-sensitive ME-sensitive + Fig.…”

“…79) Divergence of incipient populations and speciation in phytophagous insects may be driven by such hostrelated chemical cues, both in habitat-specific mating choice and in host preference by ovipositing females, although this warrants further in-depth investigations.…”

Conserved oviposition preferences in alpine leaf beetle populations despite host shifts and isolation

“…Changes in specificity are more common than alterations to plant ranking ( Jaenike, 1990;Funk & Bernays, 2001 ). Both can evolve rapidly ( Thomas et al , 1987;Singer et al , 1993 ) and can differ even between sympatric populations ( Prokopy et al , 1988;Craig et al , 1993;Via, 1999 ;Linn et al , 2003), yet species sometimes show conserved preferences ( Thompson, 1993;Wehling & Thompson, 1997 ). Several explanations have been proposed for conservatism ( Thompson, 1993;Wehling & Thompson, 1997 ).…”

On the scent of speciation: the chemosensory system and its role in premating isolation

“…It has been shown that that volatiles emitted from the surface of ripening fruit are important long-and short-range chemosensory cues used to discriminate among potential host plants (Frey and Bush, 1990). More specifically, it was shown that, in both field and wind-tunnel experiments, apple flies are more attracted to volatile chemicals that are typical of apples than they are to those of hawthorn fruit (Linn et al, 2003). Hawthorn flies and the closely related flowering dogwood fly, Rhagoletis sp.…”