Lethal interactions between parasites and prey increase niche diversity in a tropical community.

Ecological specialization should minimize niche overlap, yet herbivorous neotropical flies (Blepharoneura) and their lethal parasitic wasps (parasitoids) exhibit both extreme specialization and apparent niche overlap in host plants. From just two plant species at one site in Peru, we collected 3636 flowers yielding 1478 fly pupae representing 14 Blepharoneura fly species, 18 parasitoid species (14 Bellopius species), and parasitoid-host associations, all discovered through analysis of molecular data. Multiple sympatric species specialize on the same sex flowers of the same fly host-plant species-which suggests extreme niche overlap; however, niche partitioning was exposed by interactions between wasps and flies. Most Bellopius species emerged as adults from only one fly species, yet evidence from pupae (preadult emergence samples) show that most Bellopius also attacked additional fly species but never emerged as adults from those flies.

Hawthorn-infesting populations of Rhagoletis pomonella in Mexico and speciation mode plurality.

Categorizing speciation into dichotomous allopatric versus nonallopatric modes may not always adequately describe the geographic context of divergence for taxa. If some of the genetic changes generating inherent barriers to gene flow between populations evolved in geographic isolation, whereas others arose in sympatry, then the mode of divergence would be mixed. The apple maggot fly, Rhagoletis pomonella, has contributed to this emerging concept of a mixed speciation mode "plurality." Genetic studies have implied that a source of diapause life-history variation associated with inversions and contributing to sympatric host race formation and speciation for R. pomonella in the United States may have introgressed from the Eje Volcanico Trans Mexicano (EVTM; a.k.a. the Altiplano) in the past. A critical unresolved issue concerning the introgression hypothesis is how past gene flow occurred given the current 1200-km disjunction in the ranges of hawthorn-infesting flies in the EVTM region of Mexico and the southern extreme of the U.S. population in Texas. Here, we report the discovery of a hawthorn-infesting population of R. pomonella in the Sierra Madre Oriental Mountains (SMO) of Mexico. Sequence data from 15 nuclear loci and mitochondrial DNA imply that the SMO flies are related to, but still different from, U.S. and EVTM flies. The host affiliations, diapause characteristics, and phylogeography of the SMO population are consistent with it having served as a conduit for gene flow between Mexico and the United States. We also present evidence suggesting greater permeability of collinear versus rearranged regions of the genome to introgression, in accord with recent models of chromosomal speciation. We discuss the implications of the results in the context of speciation mode plurality. We do not argue for abandoning the terms sympatry or allopatry, but caution that categorizing divergence into either/or geographic modes may not describe the genetic origins of all species. For R. pomonella in the United States, the proximate selection pressures triggering race formation and speciation stem from sympatric host shifts. However, some of the phenological variation contributing to host-related ecological adaptation and reproductive isolation in sympatry at the present time appears to have an older history, having originated and become packaged into inversion polymorphism in allopatry.