Summary 1.The extent to which plant-herbivore feeding interactions are specialized is key to understand the processes maintaining the diversity of both tropical forest plants and their insect herbivores. However, studies documenting the full complexity of tropical plant-herbivore food webs are lacking. 2. We describe a complex, species-rich plant-herbivore food web for lowland rain forest in Papua New Guinea, resolving 6818 feeding links between 224 plant species and 1490 herbivore species drawn from 11 distinct feeding guilds. By standardizing sampling intensity and the phylogenetic diversity of focal plants, we are able to make the first rigorous and unbiased comparisons of specificity patterns across feeding guilds. 3. Specificity was highly variable among guilds, spanning almost the full range of theoretically possible values from extreme trophic generalization to monophagy. 4. We identify guilds of herbivores that are most likely to influence the composition of tropical forest vegetation through density-dependent herbivory or apparent competition. 5. We calculate that 251 herbivore species (48 of them unique) are associated with each rain forest tree species in our study site so that the 200 tree species coexisting in the lowland rain forest community are involved in 50 000 trophic interactions with 9600 herbivore species of insects. This is the first estimate of total herbivore and interaction number in a rain forest plant-herbivore food web. 6. A comprehensive classification of insect herbivores into 24 guilds is proposed, providing a framework for comparative analyses across ecosystems and geographical regions.

SummaryCannabis sativa is an economically important source of durable fibers, nutritious seeds, and psychoactive drugs but few economic plants are so poorly understood genetically.Marijuana and hemp were crossed to evaluate competing models of cannabinoid inheritance and to explain the predominance of tetrahydrocannabinolic acid (THCA) in marijuana compared with cannabidiolic acid (CBDA) in hemp. Individuals in the resulting F 2 population were assessed for differential expression of cannabinoid synthase genes and were used in linkage mapping. Genetic markers associated with divergent cannabinoid phenotypes were identified.Although phenotypic segregation and a major quantitative trait locus (QTL) for the THCA/ CBDA ratio were consistent with a simple model of codominant alleles at a single locus, the diversity of THCA and CBDA synthase sequences observed in the mapping population, the position of enzyme coding loci on the map, and patterns of expression suggest multiple linked loci. Phylogenetic analysis further suggests a history of duplication and divergence affecting drug content.Marijuana is distinguished from hemp by a nonfunctional CBDA synthase that appears to have been positively selected to enhance psychoactivity. An unlinked QTL for cannabinoid quantity may also have played a role in the recent escalation of drug potency.

Comparative population genetics of ecological guilds can reveal generalities in patterns of differentiation bearing on hypotheses regarding the origin and maintenance of community diversity. Contradictory estimates of host specificity and beta diversity in tropical Lepidoptera (moths and butterflies) from New Guinea and the Americas have sparked debate on the role of host-associated divergence and geographic isolation in explaining latitudinal diversity gradients. We sampled haplotypes of mitochondrial cytochrome c oxidase I from 28 Lepidoptera species and 1,359 individuals across four host plant genera and eight sites in New Guinea to estimate population divergence in relation to host specificity and geography. Analyses of molecular variance and haplotype networks indicate varying patterns of genetic structure among ecologically similar sympatric species. One-quarter lacked evidence of isolation by distance or host-associated differentiation, whereas 21% exhibited both. Fourteen percent of the species exhibited host-associated differentiation without geographic isolation, 18% showed the opposite, and 21% were equivocal, insofar as analyses of molecular variance and haplotype networks yielded incongruent patterns. Variation in dietary breadth among community members suggests that speciation by specialization is an important, but not universal, mechanism for diversification of tropical Lepidoptera. Geographically widespread haplotypes challenge predictions of vicariance biogeography. Dispersal is important, and Lepidoptera communities appear to be highly dynamic according to the various phylogeographic histories of component species. Population genetic comparisons among herbivores of major tropical and temperate regions are needed to test predictions of ecological theory and evaluate global patterns of biodiversity. community ecology | DNA barcoding | phylogeography | plant-insect interactions | speciation

Many oak species are interfertile, and morphological and genetic evidence for hybridization is widespread. Here we use DNA microsatellite markers to characterize hybridization between two closely related oak species in a mixed stand in central coastal California, Quercus lobata (valley oak) and Q. douglasii (blue oak) (Fagaceae). Genotypes from four microsatellite loci indicate that many alleles are shared between the two species. However, each species harbors unique alleles, and allele frequencies differ significantly. A Bayesian analysis of genetic structure in the stand identified two highly differentiated genetic clusters, essentially corresponding to species assignment based on morphology. Data from the four loci were sufficient to assign all 135 trees to one of the two species. In addition, five putative hybrid individuals having intermediate morphologies could be assigned genetically to one or the other species, and all but one had low probability of hybrid ancestry. Overally, only six (4.6%) trees showed >0.05 probability of hybrid ancestry, in all cases their probabilities for nonhybrid ancestry were substantially higher. We conclude that adult hybrids of Q. douglasii × Q. lobata are rare at this site and plasticity in morphological characters may lead to overestimates of hybridization among Quercus species.