Morphological adaptation in host races of Tephritis conura

Abstract

The present study investigates morphological differentiation among host races of the fruit fly Tephritis conura Loew (Diptera: Tephritidae) for two fitness‐related traits and whether these traits are host induced or genetically determined. Flies were analyzed from independent sympatric regions, and from one syntopic site where parental host plants [Cirsium heterophyllum (L.) Hill. and Cirsium oleraceum (L.) Scop. (Cardueae)] and hybrid plants (C. heterophyllum×C. oleraceum) co‐occur. As both host races may oviposit on hybrid plants and hybrid plants provide an identical environment for larvae of both host races, flies emerging from C. heterophyllum×C. oleraceum hybrids were used to assess whether host‐race morphological differences are genetically determined or due to phenotypic plasticity. No significant size (wing length) differences were found among host races, whereas flies emerging from C. heterophyllum had on average 8.4% longer ovipositors than flies emerging from C. oleraceum. The mean size‐corrected ovipositor length (i.e., the ratio ovipositor/wing length) was 10.3% longer. These proportions were repeated among host races emerging from hybrid plants. Although flies of the C. heterophyllum host race from hybrid plants were smaller than on parental host plants, the ratio ovipositor/wing length was constant. Hybrid flies (which emerged only on hybrid plants) were intermediate in relative and absolute ovipositor length. Thus, ovipositor‐length differences among T. conura host races most likely have a genetic basis. This suggests that host‐related differences in ovipositor length reflect adaptations to the respective host‐plant species, most likely to the host's flower‐head size, whereas both host races experience similar selection regimes on body size.

Performance of Host-Races of the Fruit Fly,Tephritis conuraon a Derived Host Plant, the Cabbage ThistleCirsium oleraceum: Implications for the Original Host Shift

“…Genetic analyses have shown that gene flow among T. conura infesting C. heterophyllum or C. oleraceum is severely restricted (Seitz and Komma 1984; Diegisser et al 2006a,b) and that host-specific morphological adaptations exist (Diegisser et al 2007). In hostchoice experiments, T. conura significantly preferred to fly to and to stay on the host-plant species from which they had emerged (Komma 1990; Diegisser 2005).…”

Shift in Egg-Laying Strategy to Avoid Plant Defense Leads to Reproductive Isolation in Mutualistic and Cheating Yucca Moths

“…Thus, the evolution of the ovipositor (egg-laying structure) is critical for a female insect's reproductive fitness. Examination of ovipositor morphology within insect lineages confirms that ovipositor morphology is under selection and responds evolutionarily to changes in host plant use (Price and Carr 2000;Jousselin et al 2006;Diegisser et al 2007;Joy and Crespi 2007;Leschen and Buckley 2007;Urban and Cryan 2007). For many insect groups, copulation must also occur through the same opening as egg deposition.…”

Infestation of a novel host plant by Tephritis conura (Diptera: Tephritidae) in northern Britain: host-range expansion or host shift?

“…Cirsium palustre has significantly smaller flower heads than C. heterophyllum (Hegi 1979). Consequently, flies exploiting both C. palustre and C. heterophyllum (British flies) are expected to evolve shorter oviscapes than flies exploiting only C. heterophyllum (continental flies) (Diegisser et al 2007). British T. conura have adapted the ovipositor length to exploit the more common C. palustre but this has not resulted in a detectable host-related genetic shift under the current ecological conditions.…”

“…Potential factors restricting diet breath include natural enemies (Menken et al 1992), interspecific competition (Denno et al 1995), physiological constraints (Rosenthal and Berenbaum 1992) or the need to adapt to the host's morphology (Diegisser et al 2007) or phenology (Feder et al 1993;Dambroski and Feder 2007). The most proximate cause determining an insect's host range, however, is its behaviour (Bernays and Chapman 1994;Gassmann et al 2006); whether or not a host plant is utilised as oviposition substrate depends on the female's host choice.…”

“…Morphological analyses of wing and ovipositor lengths have failed to find significant differences between British T. conura infesting C. palustre and C. heterophyllum, whereas continental flies, which infest C. heterophyllum but not C. palustre, have significantly larger ovipositors than British flies (Romstöck and Arnold 1987;Tritsch 2005). Ovipositor length in T. conura is under selection and correlated with the host's flower-head size (Romstöck-Völkl 1997;Diegisser et al 2007). Thus, British T. conura flies seem to have adapted the ovipositor length to small buds of the more common C. palustre at the expense of C. heterophyllum, thereby differentiating themselves significantly from continental flies that infest only C. heterophyllum.…”