Predation on Rose Galls: Parasitoids and Predators Determine Gall Size through Directional Selection

Abstract

Both predators and parasitoids can have significant effects on species’ life history traits, such as longevity or clutch size. In the case of gall inducers, sporadically there is evidence to suggest that both vertebrate predation and insect parasitoid attack may shape the optimal gall size. While the effects of parasitoids have been studied in detail, the influence of vertebrate predation is less well-investigated. To better understand this aspect of gall size evolution, we studied vertebrate predation on galls of Diplolepis rosae on rose (Rosa canina) shrubs. We measured predation frequency, predation incidence, and predation rate in a large-scale observational field study, as well as an experimental field study. Our combined results suggest that, similarly to parasitoids, vertebrate predation makes a considerable contribution to mortality of gall inducer larvae. On the other hand, its influence on gall size is in direct contrast to the effect of parasitoids, as frequency of vertebrate predation increases with gall size. This suggests that the balance between predation and parasitoid attack shapes the optimal size of D. rosae galls.

Trade‐off between fecundity and survival generates stabilizing selection on gall size

“…Most gall wasp populations are attacked by large communities of natural enemies, including parasitoids, inquilines, and larger vertebrate predators, which as a whole can inflict high levels of mortality (sometimes as high as 99%; Egan et al, unpublished data). Our study is one of only a few to document vertebrate predation on galls including birds (Hails & Crawley, 1992; László et al., 2014; Schönrogge et al., 2013; Tscharntke, 1992) and squirrels (Shealer, Snyder, Dreisbach, Sunderlin, & Novak, 1999), which has rarely been studied in gall wasps (Stone et al., 2002), and further document the important role that vertebrates can plan in the evolution of gall morphology (Abrahamson & Weis, 1997). In addition to protection from natural enemies, gall formers receive nutrition from their host plant and protection from challenging environmental conditions.…”

“…We first present observational studies that estimate the association between gall size and chamber number, a proxy for fecundity, in the absence of bird predation. We then measure the association between gall size and the probability of predation by birds, an important, albeit understudied, source for gall former mortality (Hails & Crawley, 1992;László, Sólyom, Prázsmári, Barta, & Tóthmérész, 2014;Schönrogge, Begg, & Stone, 2013;Tscharntke, 1992). Next, following Mitchell-Olds and Shaw (1987), which recommended experimental manipulation to accompany observational analysis of selection, we performed a manipulative experiment that excluded predation by birds from the canopy of 11 large live oak trees to test for the effects of relaxed directional selection on gall size based on our predictions from natural populations.…”

The community components associated with two common rose gall wasps (Hymenoptera: Cynipidae: Diplolepidini) in Turkey

“…These communities include gall makers, phytophagous inquilines, primary and secondary parasitoids, and various predators (Stone et al, 2002;Csóka et al, 2005;László et al, 2014).…”

“…Diplolepis galls, like other cynipid galls, support species-rich communities (Shorthouse, 1973;Stone et al, 2002;Csóka et al, 2005), and this feature makes them model systems for community ecology (Shorthouse, 1973). These communities include gall makers, phytophagous inquilines, primary and secondary parasitoids, and various predators (Stone et al, 2002;Csóka et al, 2005;László et al, 2014).…”

“…), and are known to be the two most important pests of dog roses in Turkey (Güçlü et al, 2008).Diplolepis galls, like other cynipid galls, support species-rich communities (Shorthouse, 1973;Stone et al, 2002;Csóka et al, 2005), and this feature makes them model systems for community ecology (Shorthouse, 1973). These communities include gall makers, phytophagous inquilines, primary and secondary parasitoids, and various predators (Stone et al, 2002;Csóka et al, 2005;László et al, 2014).Anatolia was an important refugium for rose gall wasps and their host plants, as it was for many other terrestrial animals and plants, during the glacial periods in the Pleistocene, along with some of the southern parts of Europe (southern Iberian Peninsula, Italy, and the Balkans) and the Caucasus (Stone et al, 2001;Rokas et al, 2003;Demirsoy, 2008). The results of some important studies on gall wasps have indicated that Anatolia has been the main speciation center of the gall wasps in the past (Stone et al, 2001;Rokas et al, 2003).…”