Dorcadionini

Caba, Florina-Georgiana & Dascălu, Maria-Magdalena, 2024, Dissecting natural hybridisation in longhorned beetles through an integrative approach: Further proof of reticulate evolution in Dorcadionini (Cerambycidae, Lamiinae), Zoologica Scripta 53 (5), pp. 665-687 : 682

4.5 | Reticulate evolution in Dorcadionini

The mtDNA of D. lugubre minkovae is very divergent from the nominal subspecies (at 7.1%), which would mean that these are two different and very distinct species—according to Hebert et al. (2003) between two species the value of the genetic distance in COI is larger than 2%–3%. Consequently, we searched in GenBank for sequences similar to our COI sequences of D. lugubre minkovae ; the nearest match was D. aethiops sequences from Dascălu et al. (2022). These results are not surprising because, in our previous study, we discovered that D. aethiops (from subgenus Carinatodorcadion ) has captured mitochondria from an unknown species in the subgenus Cribridorcadion ( Dascălu et al., 2022) . The exact origin of mtDNA of D. aethiops remained unknown because of conflicting information between the phylogenetic analyses and genetic distances. The present study narrowed down the ‘circle of suspects’ to the mitochondrial lineage of D. lugubre minkovae with whom D.aethiops has a similarity of 97.57% (2.43% divergence), the two being recovered as sister taxa (Figure S2).

Even though we do not have genomic data to prove the hybrid origin of the nuclear genome, we believe that it is not a mere coincidence that D. aethiops is similar in external features exactly to the taxon from which it took the mitochondria. The alternative explanation that D.aethiops is a stable taxon which simply captured foreign mitochondria followed by a mitochondrial sweep ( Bonnet et al., 2017) does not explain the resemblance of D. aethiops with D.lugubre minkovae , unless at least some nuclear introgression had taken place. Even if D.aethiops is an intersubgeneric hybridogenic species, it is correctly classified to subgenus because the subgeneric classification is based on male genitalia ( Breuning, 1943; Danilevsky et al., 2005). It has both the apex of the aedeagus ( Pesarini & Sabbadini, 2007) and the endophallus ( Danilevsky et al., 2005) typical for Carinatodorcadion .

There is more and more evidence that in Dorcadion and its flightless relatives, similar to the genus Carabus which is a much better studied group ( Deuve et al., 2012), hybridisation is relatively frequent, and their evolution is often reticulate. If this is true, new taxa can appear through introgressive hybridisation and the phylogeny of Dorcadionini is not strictly dichotomous ( Mallet et al., 2016), promising to be difficult to reconstruct. In addition to the evidence from hybrids found in nature, evidence of molecular genetics is beginning to accumulate. Thus, this work demonstrates for the first time using molecular markers that a specimen with an atypical and intermediate phenotype is a hybrid, and that D.lugubre lugubre is very likely a hybridogenic taxon. Not long ago, Dascălu et al. (2022) showed that D. axillare moldavicum Dascălu & Fusu , D. pusillum ochrolineatum Dascălu and D. pusillum vasiliscus Dascălu are hybridogenic taxa. We believe that the morphologically distinct populations originated from introgression with another species are best classified as subspecies to highlight their distinctiveness but at the same time to emphasise that they are not reproductively isolated.

This phenomenon is not limited to the western Palearctic, as Karpiński, Gorring, and Cognato (2023) described the case of introgression in the Mongolian Eodorcadion intermedium species group. While in taxa with distinct morphology hybridisation is a wellknown fact, in those with cryptic morphologies (such as Dorcadion ), this phenomenon is much more difficult to detect ( Macholán, 2013; Mallet, 2005), and information only starts to accumulate through the introduction of genetic techniques.