How many Buthus species are there in Europe and how did they evolve?

 

As mentioned in  previous post, the number of Buthus Leach, 1815 (Buthidae) species in Europe grew from one single species to more than 20. Earlier this year, this number was reduced to nine valid species. This decision was based on  rigorous phylogenetic analyses combining morphology, nuclear and mitochondrial DNA sequences, morphometric analyses, and ecological data.

In a new study, which was supposed to be published before the article mentioned above, Javier Blasco-Aróstegui and co-workers looks more deeply into the DNA og genetics of the Iberian Buthus species. This is complex stuff, way beyond my knowledge. I have therefor asked co-author Yuri simon to explain this article for us in more laymen terms:

 In this study, the authors re-examined the number of species within the European Buthus scorpions. Over the years, the group experienced a rapid increase in the number of described species, mostly because they show a great morphological diversity. 

However, this high morphological diversity is not always reflected in their DNA. The fast-changing mitochondrial DNA (inherited only from the mother) often suggests many species, while the more slowly evolving nuclear DNA (inherited from both parents) tells a different story. When these two genetic signals disagree, a situation known as mito-nuclear discordance, making difficult to define clear species boundaries. Moreover, since the past climate changes and the region’s complex landscape repeatedly separated and later reconnected populations, these scorpions sometimes met again after long periods apart and interbred creating in some cases hybrid populations showing some morphological intermediate characters which has contributed to the large number of taxa described. 

By combining genetic evidence with morphology and species distribution modelling, we found that the evolutionary history of Buthus in Iberia is far more complex than a simple “split and diverge” story. It involves repeated cycles of isolation, reconnection, and hybridization. Our results show that no single source of data—neither morphology nor mitochondrial or nuclear DNA alone—is sufficient to accurately define these species. Instead, an integrative approach is necessary. Using this approach, we concluded that the number of valid European Buthus species is likely much lower than previously thought, reducing it from around 20 to roughly half.

Abstract:
Mito-nuclear (or cytonuclear) discordance, evolutionary incongruence between the mitochondrial and nuclear genomes, is a widespread but underappreciated phenomenon that may obscure signals of introgression and hybridization important for understanding evolutionary trajectories and species boundaries. The present study explored the roles of secondary contact and introgressive hybridization in the diversification of Buthus Leach, 1815 scorpions in the Iberian Peninsula, a hotspot for mito-nuclear discordance, in which complex topography and glacial history facilitated repeated cycles of isolation and secondary contact. Patterns of mito-nuclear discordance were predicted to be consistent with overlapping distributions, similar ecological niches, and intermediate phenotypes. By integrating genomic, morphological, and ecological data, the intricate evolutionary history of Buthus, shaped by vicariance, reticulation and ecological opportunity, was revealed. The results underscore the role of introgressive hybridization in shaping patterns of biodiversity and the need to consider mito-nuclear discordance in species delimitation. 

Reference:
Blasco-Aróstegui J, Simone Y, Paulo OS, Prendini L. Mito-nuclear discordance reveals introgressive hybridization following vicariance and secondary contact in Iberian scorpions (Buthidae: Buthus). BMC Ecol Evol. 2025;25(1):112. [Open access]

Thanks to Yuri for sending me their article and for for writing a layman version of a summary for the article!