Completing the hybridization triangle: the inheritance of genetic incompatibilities during homoploid hybrid speciation in ragworts (Senecio)

Hybridization is an important contributor to biodiversity and speciation, with approximately 25 % of all plant species and 10 % of all animal species estimated to have experienced hybridization during their evolution. Although genome duplication following hybridization is a frequent mode of speciation in plants, hybrid speciation can also occur without a change in ploidy, i.e. homoploid hybrid speciation. The identification of homoploid hybrid species has been difficult in the past but improved genetic technologies are helping to identify further examples of this form of speciation.

The hybrid ragwort species Senecio squalidus
The hybrid species Senecio squalidus. Image credit: Brennan et al.

In a recent study by Brennan et al. published in AoBP, a genetic mapping approach was taken to study the inheritance of genetic incompatibilities between a new homoploid hybrid species, Senecio squalidus, and its two progenitor species. Multiple genomic regions, including genomic rearrangements, were found to contribute to hybrid incompatibility between these species. In particular, the new hybrid species had inherited a mix of genetic incompatibilities against both parents. These findings suggest that this young homoploid hybrid species has inherited a unique combination of genomic rearrangements and incompatibilities from its parents that contribute to its reproductive isolation.

Researcher highlight

Adrian Brennan

Adrian Brennan obtained an BA in Biological Sciences from Oxford University in 1999. He gained a PhD in Plant Sciences, also from Oxford University in 2004, under the supervision of Professors Stephen Harris and Simon Hiscock, during which he studied the population genetics of the self-incompatibility mating system of an invasive ragwort species. Following postdoctoral and fellowship positions at the universities of Bristol, St Andrews, and Durham and the research institutes, Royal Botanic Garden Edinburgh, and the DoƱana Biological Research Station at Seville, Adrian now holds an assistant professor position in the Biosciences Department, Durham University.

Adrian investigates evolutionary and ecological questions in the fields of speciation, plant breeding systems, hybridization, and invasiveness using combined population genetics and quantitative genetics approaches. His current projects include the genetic control of flower form in wild flax relatives, genetic variation contributing to local adaptation in flax and its wild relatives, and rapid evolution of reproductive isolation in the globally important weed, yellow starthistle.

Further reading

Brennan, A. C., Hiscock, S. J., & Abbott, R. J. (2019). Completing the hybridization triangle: the inheritance of genetic incompatibilities during homoploid hybrid speciation in ragworts (Senecio). AoB PLANTS, 11(1). https://doi.org/10.1093/aobpla/ply078