Host shift to an invasive plant triggers rapid animal hybrid speciation

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 speciation 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 rare 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. 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 niche. The necessary conditions for this mechanism of speciation are common in parasitic animals, which represent much of animal diversity. The frequency of homoploid hybrid speciation in animals may therefore be higher than previously assumed.

Recent, Allopatric, Homoploid Hybrid Speciation: The Origin of Senecio Squalidus (Asteraceae) in the British Isles From a Hybrid Zone on Mount Etna, Sicily

“…Other examples of recent homoploid hybrid speciation have been reported in the genus Scaveola (Goodeniaceae) in the Hawaiian Islands (Howarth and Baum 2005) and within the Rhagoletis pomonella species complex of tephritid fruitflies in the northeastern United States (Schwarz et al 2005). These discoveries of homoploid hybrid neospecies are important in that further research on such material should lead to an improved understanding of what promotes the origin and establishment of homoploid hybrid species in the wild.…”

Genetically differentiated races and speciation-with-gene-flow in the sunflower maggot, Strauzia longipennis

“…Such models strongly imply that complete reproductive isolation is not necessary for genetic divergence, and that divergent lineages may experience even relatively high rates of gene flow without consequent lineage fusion (Nosil 2008). To date, such patterns have been elegantly documented in a range of phytophagous insects, including Anopheles mosquitoes (Turner et al 1999;White et al 2010), Acyrthosiphon pea aphids (Via and West 2008), Neochlamisus leaf beetles (Funk et al 2011), and Rhagoletis fruit flies (Schwarz et al 2005;Michel et al 2010), and early indications are that reduced recombination in some number of genomic regions ''protect'' important allelic combinations. The study of organisms at various stages along the so-called ''speciation continuum'' (Hendry et al 2009), ultimately allows for a better understanding of how reproductive isolating barriers arise and are maintained.…”

Natural hybridization generates mammalian lineage with species characteristics

“…Artibeus | Chiroptera | hybrid speciation | reticulate evolution | transgressive segregation D espite empirical studies documenting the establishment of animal hybrid lineages (1)(2)(3)(4)(5)(6)(7)(8), the evolutionary importance of speciation by natural hybridization in animals is unknown and often is considered minor because the offspring of such crosses typically are less fit than either parental species (9,10). Nearly all reported cases of homoploid speciation events (hybrid speciation without change in chromosome number) (11) in animals are among species of insects or fish (12), and there are only a handful of suspected cases in mammals (13)(14)(15)(16)(17).…”