1. Department of Entomology, The Pennsylvania State University, 501 ASI Building, University Park, Pennsylvania 16803, USA
2. †Present address: Department of Surgery, University of Pittsburgh, 200 Lothrop St, Pittsburgh, Pennsylvania 15213, USA

Correspondence to: Dietmar Schwarz¹ Correspondence and requests for materials should be addressed to D.S. (Email: dxs332@psu.edu).

Abstract

Speciation in animals is almost always envisioned as the split of an existing lineage into an ancestral and a derived species. An alternative speciation route is homoploid hybrid speciation¹ in which two ancestral taxa give rise to a third, derived, species by hybridization without a change in chromosome number. Although theoretically possible it has been regarded as rare¹ and hence of little importance in animals. On the basis of molecular and chromosomal evidence, hybridization is the best explanation for the origin of a handful of extant diploid bisexual animal taxa^{2, 3, 4, 5, 6}. Here we report the first case in which hybridization between two host-specific animals (tephritid fruitflies) is clearly associated with the shift to a new resource. Such a hybrid host shift presents an ecologically robust scenario for animal hybrid speciation because it offers a potential mechanism for reproductive isolation through differential adaptation to a new ecological niche⁷. The necessary conditions for this mechanism of speciation⁷ are common in parasitic animals, which represent much of animal diversity⁸. The frequency of homoploid hybrid speciation in animals may therefore be higher than previously assumed.

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