Geographic variation in fruit volatiles emitted by the hawthorn Crataegus mollis and its consequences for host race formation in the apple maggot fly, Rhagoletis pomonella

Abstract

The shift of the apple (AP) maggot fly, Rhagoletis pomonella (Walsh) (Diptera: Tephritidae), from its ancestral host downy hawthorn, Crataegus mollis (DH) (Torr. & A. Gray) Scheele, to introduced domesticated AP, Malus domestica Borkh. (both Rosaceae), is a model for ecological divergence and incipient sympatric speciation with gene flow. However, a portion of the variation contributing to the sympatric host shift from DH to AP appears to have a different biogeographic history, pre‐dating the shift. One potential source of standing variation may trace to a number of different native hawthorn species infested by R. pomonella in the southern USA, where the AP‐attacking race is absent. Herein, we investigate this possibility for the southern red hawthorn (SR) endemic to Texas, Crataegus mollis var. texana (Buckl.), which has been described as a member of the Molles series that includes the more northern distributed DH. We report results from chemical analyses of host fruit volatiles, fly behavioural responses to synthetic fruit blends, and microsatellite surveys of fly populations, implying that R. pomonella infesting SR may behaviourally and genetically represent a native host race differing from the DH‐infesting fly. No fly reared from SR responded to AP fruit volatiles in flight tunnel assays. However, coupled gas chromatographic‐electroantennographic detection (GC‐EAD) profiles for SR fruit contain all five of the component esters that comprise the standard AP volatile blend inducing behavioural orientation for AP‐infesting flies, compounds that appear to be largely missing from volatile profiles for DH fruit. Thus, SR‐infesting flies do not represent a source for a preassembled AP‐accepting phenotype. However, they may help explain why the ancestral DH race that shifted to AP in the northeastern USA had the ability to recognize AP fruit esters, potentially enabling the shift to AP. Our results highlight how categorizing speciation into different geographic modes may not adequately describe the evolutionary origins of important genetic variation fuelling adaptive radiation and the genesis of new biodiversity.

Sensory specificity and speciation: a potential neuronal pathway for host fruit odour discrimination in Rhagoletis pomonella

“…Thus, there is an evolutionary legacy for why OSNs for butyl hexanoate and 3-methyl-1-butanol could be important as pathways for information prompting specific behaviours; both serve in the recognition of southern hawthorn fruit. This does not explain how butyl hexanoate evolved to act as an antagonist for northern downy hawthorn flies, when it is not for southern hawthorn flies [32,53]. It may be that in the northeastern USA the compound is associated with a less suitable host fruit for fly survivorship, such as various native crabapple species that are absent from the south [33], and thus butyl hexanoate was selected to be a behavioural antagonist.…”

“…texana ). Data were compiled from [13,15,16,30–32]. volatiledowny hawapplegreen hawblueberry haweastern mayhawwestern mayhawhybrid mayhawsouthern red hawbutyl butyrate1019.59126545propyl hexanoate41.51610.3butyl hexanoate0.01372416.825262320hexyl butyrate442416.8912614pentyl hexanoate52.5230.63-methyl-1-butanol450.624410.4butyl acetate5047579pentyl acetate3.526…”

GENETIC DIVERGENCE ALONG THE SPECIATION CONTINUUM: THE TRANSITION FROM HOST RACE TO SPECIES INRHAGOLETIS(DIPTERA: TEPHRITIDAE)

“…a = Berlocher (); b = Michel et al (); c = Cha et al (); d = Feder et al (); e = Feder and Bush (); f = Berlcoher and McPheron ().…”

Utilização diferencial de frutos hospedeiros por Anastrepha sp. 1 affinis fraterculus (Diptera, Tephritidae): aspectos morfológicos e reprodutivos

“…Número de fêmeas e machos emergidos (♀♀, ♂♂). Selivon et al 2004Selivon et al , 2005aSelivon et al , 2005bCha et al 2012;Powel et al 2014;De Meyer et al 2015;Gomes-Cendra et al 2016;Ragland et al 2016).…”

“…Raças-hospedeiro, além de poderem apresentar diferenças genéticas, tendem a apresentar diferenças na escolha do hospedeiro, tempo de eclosão, comportamento de corte e cópula (Berlocher e Feder, 2002;Fordyce 2010;Cha et al, 2012. (Prokopy et al 1982(Prokopy et al , 1986. Essa pode ser a mesma explicação do reconhecimento e preferência em acasalar com machos provenientes do mesmo fruto hospedeiro, uma vez que o reconhecimento de parceiros e "aparentados" se dá por meio da identificação de feromônios e hidrocarbonetos de cutícula.…”