Experimental hybridization and reproductive isolation between two sympatric species of tephritid fruit flies in the Anastrepha fraterculus species group

Abstract

Among tephritid fruit flies, hybridization has been found to produce local adaptation and speciation, and in the case of pest species, induce behavioral and ecological alterations that can adversely impact efficient pest management. The fraterculus species group within Anastrepha (Diptera: Tephritidae), is a rapidly radiating aggregate, which includes cryptic species complexes, numerous sister species, and several pest species. Molecular studies have highlighted the possibility of introgression between A. fraterculus and A. obliqua. Reproductive isolation has been studied among morphotypes of the A. fraterculus species complex as a tool for species delimitation. Here we examined the existence and strength of prezygotic and postzygotic isolation between sympatric populations of two closely related species within the highly derived fraterculus group (A. fraterculus and A. obliqua), coexisting in nature. Although adults of both species showed a strong tendency for assortative mating, a small proportion of hybrid pairings in both directions were observed. We also observed asymmetric postzygotic isolation, with one hybrid cross displaying a strong reduction in fecundity and F1 egg fertility. Survival was greater for the progeny of homotypic and hybrid crosses in the maternal host. There was a marked female biased sex ratio distortion for both F1 hybrid adults. Hybridization between A. fraterculus and A. obliqua in nature may be difficult but possible; these two species display stronger reproductive isolation than all pairs of species previously examined in the A. fraterculus species complex. Asymmetric postzygotic isolation is suggestive of Wolbachia mediated cytoplasmic incompatibilities that may be exploited in area-wide pest management.

Evidence for Introgression Among Three Species of the Anastrepha fraterculus Group, a Radiating Species Complex of Fruit Flies

“…Our method has proved to be highly effective as was evidenced from the analyses of haplotype networks, which followed coalescent expectations rather than a potential pooling bias, as well as from the consistency of several methods pointing to the same final conclusions. Furthermore, these results are in agreement with what has been suggested elsewhere from multiple disciplines ( McPheron et al, 1999 ; Selivon et al, 1999 ; Santos et al, 2001 ; Smith-Caldas et al, 2001 ; Vaníèková et al, 2015 ; Scally et al, 2016 ; Rull et al, 2017 ).…”

“…Evidence of introgression among Anastrepha species is not surprising since reciprocal hybrids have been produced in laboratory, even though there is a Haldane’s rule when crossing A. fraterculus or A. sororcula females and A. obliqua males ( Selivon et al, 1999 ; Santos et al, 2001 ; Rull et al, 2017 ). This is why introgression between A. fraterculus and A. obliqua has been recently proposed as a potential cause of some discrepancies in the relationships among A. obliqua populations ( Scally et al, 2016 ).…”

Reproductive compatibility among Mexican populations of Anastrepha obliqua: theoretical and management implications

“…(), introgression, particularly between A. obliqua and A. fraterculus , may be one explanation for the discrepancy and the high mitochondrial diversity reported for A. obliqua could be the result of incomplete lineage sorting. These two species have been found to mate and interbreed under artificial conditions (Rull et al., ; Santos et al., ) and could potentially hybridize in nature.…”

“…Using smaller cages allowed higher replication and environmental control, which was key for synchronization of sexual receptivity of adults from geographically disjunct populations. Our cages had been successfully used to test reproductive isolation between A. fraterculus and A. obliqua (Rull et al, 2017), and we feel confident that results obtained using such cages reflect existing patterns among populations. A white light lamp (960 lm) was hung in the centre top of each cage, at a distance of 15 cm above the cage ceiling.…”

“…Nevertheless, more recently Scally et al (2016), using a multilocus data set comprising nuclear and mitochondrial loci, suggested that A. obliqua is a monophyletic group. They attributed prior results to possible introgression and interbreeding between different Anastrepha species, which has been shown to be possible in the laboratory (Rull et al, 2017;Santos, Uramoto, & Matioli, 2001).…”