Reciprocal diversification in a complex plant-herbivore-parasitoid food web

Abstract

Background: Plants, plant-feeding insects, and insect parasitoids form some of the most complex and species-rich food webs. According to the classic escape-and-radiate (EAR) hypothesis, these hyperdiverse communities result from coevolutionary arms races consisting of successive cycles of enemy escape, radiation, and colonization by new enemy lineages. It has also been suggested that "enemy-free space" provided by novel host plants could promote host shifts by herbivores, and that parasitoids could similarly drive diversification of gall form in insects that induce galls on plants. Because these central coevolutionary hypotheses have never been tested in a phylogenetic framework, we combined phylogenetic information on willow-galling sawflies with data on their host plants, gall types, and enemy communities.

North European gall-inducing Euura sawflies (Hymenoptera, Tenthredinidae, Nematinae)

“…Genetic data. The COI barcode of a single specimen identified as virilis (GenBank accession EU084002, from Germany) diverges from the next nearest of other dolichura group species by approximately 4.9% (see also Nyman et al 2007). However, newer COI sequences of dolichura group larvae collected from S. purpurea (which should therefore be E. virilis), locate at two different positions in the tree (Nyman, unpublished).…”

“…Euura plicalapponum (Kopelke, 2007) examined. Female and male: too few specimens were examined to allow an assessment of variability.…”

“…Euura ischnocera (Thomson, 1863) Euura plicadaphnoides (Kopelke, 2007) Phyllocolpa plicadaphnoides Kopelke, 2007a: 97-99. Described: ♀, ♂, gall, recorded host: Salix daphnoides.…”

“…Euura plicaphylicifolia (Kopelke, 2007) Kopelke (2007a). Five males reared from German localities in Mecklenburg and BadenWürttemberg bear determination labels by Kopelke "Phyllocolpa anomaloptera /S.…”

Partitioning of herbivore hosts across time and food plants promotes diversification in the Megastigmus dorsalis oak gall parasitoid complex

“…Megastigmus dorsalis sp.2 also contains two divergent genetic lineages that attack galls on different host‐plant taxa, with one host race attacking galls on section Cerris oaks and the other attacking galls on section Quercus oaks. These results show that some of the same host traits structure both intraspecific genetic diversity and multispecies composition in the oak gall parasitoid community (Bailey et al., 2009), highlighting the importance of tri‐trophic niches in promoting cascades of diversification across interacting trophic levels (Feder & Forbes, 2010; Forbes et al., 2009; Hood et al., 2015; Nyman, Bokma, & Kopelke, 2007; Stireman et al., 2006). Our results also underline the need for more data, even in systems such as the oak gall wasp community that are relatively well known, in order for the subtleties of HAD to be revealed.…”