Effect of hybridization of the Quercus crassifolia×Quercus crassipes complex on the community structure of endophagous insects

Abstract

In a previous study, we showed that the geographic proximity of hybrid plants to the allopatric areas of parental species increases their morphological and genetic similarity with them. In the present work, we explored whether the endophagous fauna of hybrid plants show the same pattern. We studied the canopy species richness, diversity and composition of leaf-mining moths (Lepidoptera: Tischeridae, Citheraniidae) and gall-forming wasps (Hymenoptera: Cynipidae) associated with two species of red oaks (Quercus crassifolia and Quercus crassipes) and their interspecific hybrid (Quercusxdysophylla Benth pro sp.) in seven hybrid zones in central Mexico, during four seasons in 2 years. The study was conducted on 194 oak trees with known genetic status [identified by leaf morphology and molecular markers (random amplified polymorphic DNAs)], and the results indicate a bidirectional pattern of gene flow. Hybrid plants supported intermediate levels of infestation of gall-forming and leaf-mining insects compared to their putative parental species. The infestation level of leaf-mining insects varied significantly following the pattern: Q. crassifolia>hybrids>Q. crassipes, whereas the gall-forming insects showed an inverse pattern. A negative and significant relationship was found between these two types of insect guilds in each host taxa, when the infestation percentage was evaluated. It was found that 31.5% (n=11) of the endophagous insects were specific to Q. crassipes, 22.9% (n=8) to Q. crassifolia, and 8.6% (n=3) to hybrid individuals. The hybrid bridge hypothesis was supported in the case of 25.7% (n=9) of insects, which suggests that the presence of a hybrid intermediary plant may favor a host herbivore shift from one plant species to another. Greater genetic diversity in a hybrid zone is associated with greater diversity in the endophagous community. The geographic proximity of hybrid plants to the allopatric site of a parental species increases their similarity in terms of endophagous insects and the Eje Neovolcánico acts as a corridor favoring this pattern.

Diversity of galls induced by wasps (Hymenoptera: Cynipidae, Cynipini) associated with oaks (Fagaceae: <em>Quercus</em>) in Mexico

“…These zones are also suggested by the Q. crassifolia × Q. crassipes complex (TovarSánchez & Oyama 2004) in which three gall morphotypes were exclusively associated with the hybrid individuals found there (Tovar-Sánchez & Oyama 2006). However, this pattern cannot be generalized, since in another hybrid complex formed by Q. affinis × Q. laurina (González-Rodríguez et al 2004, only one gall morphotype was found in each of the species in this study (see Table 1).…”

Genetic structure of a foundation species: scaling community phenotypes from the individual to the region

“…For example, Shuster et al (see Tables 1 and 2 in Shuster et al, 2006) found that 57% of community phenotype variation was due to the genetic differences among genotypes within either pure P. fremontii or P. angustifolia, which was 3 Â greater than community variation between these two species and their hybrids (19%). Moreover, many community metrics scale across the plant taxonomic hierarchy at large geographic scales from genera to the species level (e.g., genera: Brändle and Brandl, 2006;hybrids: Wimp et al, 2004;Tovar-Sánchez and Oyama, 2006;Bangert et al, 2006b;species: Whitham et al, 2006). Thus, genetic scaling has been detected in both phylogenetic and spatial analyses.…”

“…Studies in five different systems found that plots with the highest plant genetic diversity supported significantly greater invertebrate species richness than plots with low genetic diversity in both hybridizing and single species systems (Wimp et al, 2004;Reusch et al, 2005;Crutsinger et al, 2006;Johnson et al, 2006;Tovar-Sánchez and Oyama, 2006). Moreover, analyses of arthropod communities in the wild and in common gardens show that many arthropod species are tree genotype dependent (McIntyre and Wimp et al, 2005).…”

“…Ecological systems are highly complex, and structured by multiple interacting factors whose effects are variable through space and time (Wiens, 1989;. Simple evolutionary principles are not generally included in explanations of community dynamics or patterns of community structure (e.g., Jones and Lawton, 1995;Hubbell, 2001;Kinzig et al, 2001), and until recently studies of communities have lacked a genetic perspective (but see Dungey et al, 2000;Whitham et al, 2003Whitham et al, , 2006Hochwender and Fritz, 2004;Johnson and Agrawal, 2005;Bangert et al, 2005Bangert et al, , 2006aWimp et al, 2004Wimp et al, , 2005Johnson et al, 2006;Tovar-Sánchez and Oyama, 2006;Shuster et al, 2006). Although there has been an explicit incorporation of scale into ecological studies (Wiens, 1989) the integration of genetics and scaling (i.e., genetic scaling; see Table 1 for definitions used throughout this paper) has received little attention (but see Bailey et al, 2004a).…”

“…However, if P 2 is completely dominant to P 1 (F 1 trait value ¼ 2), population mean and variance change to 1.2 and 1.01, respectively, illustrating that both a population's trait mean and variance are functions of gene action. If arthropods depend on these trait values, then we would expect arthropod community structure (abundance of each species on the tree population) to scale with the plant population's trait mean and species richness (number of species) to scale with plant population's trait variance (e.g., Wimp et al, 2004;Johnson et al, 2006;Tovar-Sánchez and Oyama, 2006), such that richness in the scenario with P 2 dominant would be greater than the scenario where there is just additive gene action. Thus, if we can calculate the mean and variance for a trait as a function of the frequencies of each cross type and gene action (additive, dominance, and so on), we can predict species richness using the genetically based ecological scaling relationship S ¼ cA ðz 0 þmðV g þV e ÞÞ as previously defined.…”