Species-specific markers provide molecular genetic evidence for natural introgression of bullhead catfishes in Hungary.

Beatrix Béres,Béla Urbányi,László Orbán,Milán Farkas,Balázs Kovács,Ádám Staszny,Katalin Bakos,Dóra Kánainé Sipos,Tamás Müller

doi:10.7717/peerj.2804

Beatrix Béres, Béla Urbányi + Show 7 more

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https://doi.org/10.7717/peerj.2804

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Abstract

Since three bullhead catfish species were introduced to Europe in the late 19th century, they have spread to most European countries. In Hungary, the brown bullhead (Ameiurus nebulosus) was more widespread in the 1970s–1980s, but the black bullhead (Ameiurus melas) has gradually supplanted since their second introduction in 1980. The introgressive hybridization of the two species has been presumed based on morphological examinations, but it has not previously been supported by genetic evidence. In this study, 11 different Hungarian habitats were screened with a new species-specific nuclear genetic, duplex PCR based, marker system to distinguish the introduced catfish species, Ameiurus nebulosus, Ameiurus melas, and Ameiurus natalis, as well as the hybrids of the first two. More than 460 specimens were analyzed using the above markers and additional mitochondrial sequence analyses were also conducted on >25% of the individuals from each habitat sampled. The results showed that only 7.9% of the specimens from two habitats belonged to Ameiurus nebulosus, and 92.1% were classified as Ameiurus melas of all habitats, whereas the presence of Ameiurus natalis was not detected. Two specimens (>0.4%) showed the presence of both nuclear genomes and they were identified as hybrids of Ameiurus melas and Ameiurus nebulosus. An additional two individuals showed contradicting results from the nuclear and mitochondrial assays as a sign of a possible footprint of introgressive hybridization that might have happened two or more generations before. Surprisingly, the level of hybridization was much smaller than expected based on the analyses of the North American continent’s indigenous stock from the hybrid zones. This phenomenon has been observed in several invasive fish species and it is regarded as an added level of complexity in the management of their rapid adaptation.

Highlights

Signs of natural hybridization and introgression between species can be detected in many taxonomic groups (Rieseberg, 1997; Argue & Dunham, 1999) as 25% of plants and about 10% of animals are capable of forming interspecies hybrids (Mallet, 2005)
Two primers (CytB_L_14724F and Cytbasa_R) in addition to the universal 421 bp cytochrome b-specific fragment that was present in the PCR product of all three species, amplified an additional band from Ameiurus nebulosus and Ameiurus melas samples (Fig. S2)
The size of this additional fragment was considerably different in the two species: approximately 950 bp for Ameiurus nebulosus and nearly 800 bp for Ameiurus melas

Summary

Introduction

Signs of natural hybridization and introgression between species can be detected in many taxonomic groups (Rieseberg, 1997; Argue & Dunham, 1999) as 25% of plants and about 10% of animals are capable of forming interspecies hybrids (Mallet, 2005) This process may have several evolutionary and ecological consequences such as the merging of taxonomical groups which may lead to the appearance of new, reproductively isolated hybrid species, or to the transmission of characteristics important for adaptation which happen through introgression (Arnold & Martin, 2009). In some cases, this phenomenon may be linked to the invasion of species or to their human-mediated introduction (Jose Madeira, Gomez-Moliner & Barbe, 2005). In 1885, further shipments arrived in Germany as well and subsequent introductions may have taken place since (Pinter, 1976; Rutkayovaet al., 2013)

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