Molecular evidence of a reed warbler × great reed warbler hybrid (Acrocephalus scirpaceus × A. arundinaceus) in Belgium

Substantial genetic variation is hypothesised to be necessary for the long-term survival of species. Therefore, a major aim in conservation is to maintain and restore variation in small and endangered populations. However, in most populations the amount of genetic variation and, thus, the potential threats posed by limited variation are unknown. In the present study, we assess genetic variation, both at 10 microsatellite loci and at the major histocompatibility complex (MHC), in three closely related Acrocephalus warbler species with contrasting demographies. We found that the recently bottlenecked, island endemic, Seychelles warbler (A. sechellensis; SW) has substantially reduced microsatellite and MHC diversity compared to the widespread great reed warbler (A. arundinaceus; GRW). In contrast, another endangered species with a small breeding range, the Basra reed warbler (A. griseldis; BRW), harboured as much variation as did the GRW. This suggests that significant genetic variation and, therefore, adaptive potential, remains in the BRW -a situation that should hold as long as its habitat and numbers are maintained. Our study is one of the first to assess genetic variation at both 'non-critical' microsatellite markers and 'critical' MHC loci within endangered species. The two types of loci provided a similar picture of the genetic variation in the species we studied, but this has not been the case in studies of some other species. Using a combination of specific functional loci and genome-wide random markers appears to be the best way to assess the threat posed by reduced genetic diversity.

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“…Indeed, related Acrocephalus sp. may occasionally hybridise : Hansson, Roggeman & De Smet, 2004; c.f. Grant & Grant 1992).…”

Section: Discussionmentioning

confidence: 99%

Genetic variation in two endangered Acrocephalus species compared to a widespread congener: estimates based on functional and random loci

Hansson

Richardson

2005

Animal Conservation

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“…Some detail of juvenile bonelli · sibilatrix hybrids was given by Schneider (1969). As in many other Sylviidae and their hybrids, it would be difficult to identify these hybrids correctly in the field without capturing them (Hansson et al 2003(Hansson et al , 2004Beier et al 1997;Bensch et al 2002).…”

Section: Discussionmentioning

confidence: 98%

“…Cordero and Summers-Smith 1993;Becker 1995;Panov et al 2003). Recent examples for genetically proven hybridisations within the Sylviidae family included reed warbler · great reed warbler (Acrocephalus scirpaceus, A. arundinaceus) (Beier et al 1997;Hansson et al 2004), clamorous reed warbler · great reed warbler (A. stentoreus, A. arundinaceus) (Hansson et al 2003), and common chiffchaff [Phylloscopus [c.] collybita] · Iberian chiffchaff [P. (c.) brehmii] (Bensch et al 2002).…”

Section: Discussionmentioning

confidence: 99%

Genetically confirmed interbreeding between western Bonelli’s warbler (Phylloscopus bonelli) and wood warbler (P. sibilatrix)

Dietzen

Hackenberg²,

Heyne

et al. 2007

J Ornithol

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During May and June 2003, a mixed breeding pair consisting of a male western Bonelli's warbler (Phylloscopus bonelli) and a female wood warbler (P. sibilatrix) successfully raised six young in a broad-leafed forest near Jü nkerath, western Germany, an area far outside the regular breeding range of P. bonelli. The identity of the adult birds was confirmed by song, calls, colouration, and wing measurements. Based on blood samples taken from both parents and three juveniles, the potential interbreeding was analysed by molecular methods. Sequences of the mitochondrial cytochrome b gene differed between male and female by 8.7% and confirmed the identification of both parents. Sequences of the mitochondrial cytochrome b gene revealed that the male was a western Bonelli's and the female a wood warbler. The hybridisation and the parentage of male and female were corroborated by multilocus DNA fingerprinting. This is the first documented and genetically proven hybridisation event between these two warbler species.

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“…As mentioned above, the breeding ranges of great reed warblers and clamorous reed warblers overlap in southern Kazakhstan and a previous study has documented the occurrence of hybrids in a sympatric population [21] . Occasionally, heterospecific matings and/or viable hybrids have been documented also between other Acrocephalus species [19] , [44] , for example, between reed warbler and marsh warbler, A. scirpaceus and A. palustris [45] , and between reed warbler and great reed warbler [46] , [47] .…”

Section: Discussionmentioning

confidence: 99%

Hybridization but No Evidence for Backcrossing and Introgression in a Sympatric Population of Great Reed Warblers and Clamorous Reed Warblers

et al. 2012

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Hybridization is observed frequently in birds, but often it is not known whether the hybrids are fertile and if backcrossing occurs. The breeding ranges of the great reed warbler (Acrocephalus arundinaceus) and the clamorous reed warbler (A. stentoreus) overlap in southern Kazakhstan and a previous study has documented hybridization in a sympatric population. In the present study, we first present a large set of novel microsatellite loci isolated and characterised in great reed warblers. Secondly, we evaluate whether hybridization in the sympatric breeding population has been followed by backcrossing and introgression.We isolated 181 unique microsatellite loci in great reed warblers. Of 41 loci evaluated, 40 amplified and 30 were polymorphic. Bayesian clustering analyses based on genotype data from 23 autosomal loci recognised two well-defined genetic clusters corresponding to the two species. Individuals clustered to a very high extent to either of these clusters (admixture proportions ≥0.984) with the exception of four previously suggested arundinaceus–stentoreus hybrid birds that showed mixed ancestry (admixture proportions 0.495–0.619). Analyses of simulated hybrids and backcrossed individuals showed that the sampled birds do not correspond to first–fourth-generation backcrosses, and that fifth or higher generation backcrosses to a high extent resemble ‘pure’ birds at this set of markers.We conclude that these novel microsatellite loci provide a useful molecular resource for Acrocephalus warblers. The time to reach reproductive isolation is believed to be very long in birds, approximately 5 Myrs, and with an estimated divergence time of 2 Myrs between these warblers, some backcrossing and introgression could have been expected. However, there was no evidence for backcrossing and introgression suggesting that hybrids are either infertile or their progeny inviable. Very low levels of introgression cannot be excluded, which still may be an important factor as a source of new genetic variation.

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Molecular evidence of a reed warbler × great reed warbler hybrid (Acrocephalus scirpaceus × A. arundinaceus) in Belgium

Cited by 7 publications

References 11 publications

Genetic variation in two endangered Acrocephalus species compared to a widespread congener: estimates based on functional and random loci

Genetic variation in two endangered Acrocephalus species compared to a widespread congener: estimates based on functional and random loci

Genetically confirmed interbreeding between western Bonelli’s warbler (Phylloscopus bonelli) and wood warbler (P. sibilatrix)

Hybridization but No Evidence for Backcrossing and Introgression in a Sympatric Population of Great Reed Warblers and Clamorous Reed Warblers

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