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

Abstract

The thistle-infesting fruit fly Tephritis conura Loew (Diptera: Tephritidae) forms host races on the melancholy thistle, Cirsium hetewphyllum (L.) Hill (Asterales: Asteraceae) and the cabbage thistle, Cirsium olemceum (L.). Scop. Previous research indicates that the host shift occurred from C. hetewphyllum to C. oleraceum. In this paper we address whether the host shift involved physiological adaptations by studying oviposition acceptance and survival of the two host races on the derived host C. oleraceum. Performance differed significantly between host races. T. conura originating from C. oleraceum produced adults in 75% of all egg-laying trials in contrast to only 6.6% in T. conura originating from C. hetewphyllum. Population fitness components measured as a function of life-stage was linear decreasing for T. conura on C. oleraceum but stepwise for T. conura on C. heterophyllum. Low performance of T. conura on C. hetewphyllum was determined by low plant acceptance and high mortality during the larval stage, whereas hatching (at least one larva per batch) and pupae survival were not affected.

Non-parallel morphological divergence following colonization of a new host plant

“…]) support the presence of discrete genetic host races. Moreover, the flies also have poor performance on the alternate host plant (Diegisser et al, 2008). In light of this, the moderate host race divergence in morphology was unexpected, but this result is in line with the observation that parallelism in fitness is typically higher than for both phenotypic divergence and genetic divergence (Bolnick et al, 2018).…”

“…Potentially, the other traits measured are not important enough for host plant adaptation to result in strongly parallel divergence. Traits that have been shown to differ strongly between host races include female ovipositor length (Diegisser et al, 2007) and the larval ability to survive on the different host plant species (Diegisser et al, 2008), and these traits are more likely to show parallel divergence.…”

“…Here, we address how ecologically and putatively sexually selected traits evolve and diversify in allopatric and sympatric areas using two host races of the fly Tephritis conura . This species has recently undergone a host shift resulting in host races specializing on utilizing different Cirsium thistle species as larval food plants (Diegisser et al, 2006a, Diegisser et al, 2006b, Diegisser et al, 2007, Diegisser et al, 2008). Macroevolutionary analyses reveal that such host plant driven speciation is one of the main factors explaining the tremendous diversity of phytophagous insects, because many speciation events can be attributed to host plant shifts (Berlocher & Feder, 2002, Dres & Mallet, 2002, Nylin et al, 2014), and diversification rates are elevated in herbivorous insects compared to their non-herbivorous relatives (Mitter et al, 1988, Farrell, 1998, Wiens et al, 2015).…”

“…The two recently established host races inhabit two geographically isolated sympatric zones with adjacent allopatric populations, one East and one West of the Baltic Sea (Figure 2A). Tephritis conura females of the two host races are ovipositing into buds of either Cirsium heterophyllum (the ancestral host; Figure 2B) or C. oleraceum (the novel host; Figure 2C), and larvae show host specific performance and survival (Diegisser et al, 2008). During courtship, Tephritid flies performs a mating ritual that includes elaborate wing movements from both sexes (Sivinski, 2000, but see Briceno & Eberhard, 2017).…”

The evolution and ecology of individual specializations amongst a group of dietary generalists.

“…A marine snail, Littorina saxatilis, developed from genetically distinct morphs (Conde-Padín et al 2007) as well as several species of dipterans (Feder et al 2003;Diegisser et al 2007;Simard et al 2009) While the literature in Table 2 illustrates how sympatrically cladogenic polymorphisms develop, it does not demonstrate which mode of development more quickly leads to speciation. As a result of several factors, the dynamics of the transition from resource polymorphisms to daughter species will largely be system-dependent, with some genetic systems moving faster than some plastic systems and vice versa.…”