Natural Hybridization and Speciation in Rhagoletis (Diptera: Tephritidae)

Open Access
Author:
Schwarz, Dietmar
Graduate Program:
Entomology
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
August 26, 2004
Committee Members:
  • Bruce A Mc Pheron, Committee Chair
  • Ottar N Bjornstad, Committee Member
  • Warren G Abrahamson Ii, Committee Member
  • Thomas Charles Baker, Committee Member
  • Stephen Wade Schaeffer, Committee Member
Keywords:
  • speciation via hybridization in a diploid and bise
  • sympatric speciation
  • introgressive hybridization
  • population genetics
  • host choice and acceptance behavior
  • Rhagoletis pomonella species group
Abstract:
Hybridization has long been regarded as an important source of evolutionary novelty in plants. Zoologists, in contrast, have regarded hybridization merely as an artifact of incomplete reproductive isolation. Especially the formation of new animal species via hybridization has been deemed highly unlikely (unless it results in parthenogenetic, polyploid taxa). Here I present the first case of hybridization in an insect that has resulted in an isolated, diploid and bisexually reproducing population. I discovered the infestation of invasive honeysuckle, Lonicera spp., by flies belonging to the R. pomonella species complex (Diptera: Tephritidae). Because all members of this species complex are native to North America, the infestation of Lonicera has to be the result of a recent host shift. Multilocus nuclear genotypes and mitochondrial DNA sequences showed that the Lonicera Fly originated via hybridization between the blueberry maggot R. mendax and the snowberry maggot R. zephyria. The same data also provide indirect evidence for the reproductive isolation of the Lonicera Fly from its parent taxa. I tested the acceptance of different host fruits by the Lonicera Fly, R. mendax and R. zephyria in behavioral experiments. These experiments suggest that, compared to host races and described sibling parent species, the Lonicera Fly shows an intermediate level of behavioral isolation from its parent taxa. At the same time, the Lonicera Fly's host selection behavior indicated a higher phenotypic variability when compared to R. mendax and R. zephyria. This unique combination of host shift and hybridization suggests sympatric speciation via host shift as the mechanism by which the hybrid Lonicera Fly formed. I discuss how the increased phenotypic variability of hybrid origin populations could facilitate adaptive speciation. I further argue that hybrid speciation in parasitic animals could be common because the ecological conditions of the Lonicera Fly system are frequently encountered in nature. Finally I integrate the findings of this study with previous results on speciation and hybridization in the genus Rhagoletis and other animal taxa. I propose the term “biological metaspecies” to describe the evolution of the Rhagoletis pomonella species group. A biological metaspecies is a group of ecologically differentiated sibling taxa that are linked by occasional hybridization. Each single taxon might lack the necessary variation to colonize a new niche, but such variation could be maintained on the metaspecies level and become mobilized by hybridization.