Assessing the taxonomic status ofOsmoderma cristinae(Coleoptera: Scarabaeidae), endemic to Sicily, by genetic, morphological and pheromonal analyses

Abstract

Resolving complexes of closely related and cryptic insect species can be challenging, especially when dealing with rare and protected taxa that are difficult to collect for genetic and morphological analyses. Until recently, populations of the genus Osmoderma (Scarabaeidae), widespread in Europe, were treated as a single species O. eremita (Scopoli, 1763) in spite of observed geographic variation in morphology. A previous survey using sequence data from the mtDNA cytochrome C oxidase I gene (COI) revealed the occurrence of at least two distinct lineages within this species complex: O. eremita in the west and O. barnabita Motschulsky, 1845, in the east. Interestingly, beetles confined to Sicily have been described as a distinct species, O. cristinae Sparacio, 1994, based on morphological traits. Only few Sicilian specimens were included in the former genetic analysis, and the results led to a still questionable taxonomic rank for these populations. To explore the robustness of the previous taxonomic arrangement for O. cristinae, a combination of genetic, morphological and pheromonal analyses was used. A 617‐bp fragment of the COI gene, aligned with O. cristinae and O. eremita sequences already available in GenBank, showed a clear genetic divergence between the two species (interspecific mean distance = 6.6%). Moreover, results from AFLP markers sustained the distinction of the two species. In addition, geometric morphometric analyses of the shape of male genitalia revealed a clear differentiation between the two species. Via scent analysis and field trapping, we demonstrated the production of the sex pheromone (R)‐(+)‐γ‐decalactone by males of O. cristinae, the attraction by conspecific individuals (mostly females) to this compound, and a lack of antagonistic effect of (S)‐(–)‐γ‐decalactone. The fact that O. eremita and O. eremita use the same compound for mate finding suggests that this sex pheromone has not undergone a differentiation and probably the allopatry of these two species compensates for the absence of a mechanism to avoid cross‐attraction. Our genetic and morphological data support the divergence of the two species and confirm the species status for O. cristinae, while sex pheromones are confirmed to be invariant among different species of the genus Osmoderma.

Guidelines for the monitoring of Osmoderma eremita and closely related species

“…An integrated approach to the Italian populations, based on morphological and molecular analyses (Zauli et al 2016a), suggested that both the genetic distance (COI and AFLP markers) and morphological divergence (particularly the shape of male genitalia) support the validation of species rank for O. cristinae, despite the close relationship between this Sicilian endemic taxon and the widespread O. eremita. Additional poorly investigated taxa occur from the Balkan peninsula to the Caucasus mountains (apart from O. lassallei and O. barnabita): at least one undescribed species or semispecies, related to O. lassallei, in southern Greece (P. Audisio, P. Petrakis and G.M.…”

“…The problem arises when a locality is situated in the overlapping area between the ranges of two parapatric species, as in the case of O. eremita and O. barnabita in central Europe and the Balkans, where the possibility cannot be ruled out that they mated with each other. The less variable trait for separation of these two species is perhaps the shape of the parameres of the male genital organ (Krell 1997, Lüchte and Klausnitzer 1998, Sparacio 2000, Zauli et al 2016a according to the following key (see also Figure 3 The male genitalia also allow the separation of O. eremita and O. barnabita from O. cristinae, as the latter does not show a real upward extension on parameres but only a moderate swelling followed by a straight or very slightly convex slope continuing up to the base (Figure 4). However, genitalia shape cannot be used for monitoring populations because it requires dead specimens.…”

“…Therefore, click-beetle females use the sexual pheromone of the hermit beetle males as a kairomone in order to lay eggs in suitable tree cavities, already inhabited by the favourite prey for their offspring (Svensson et al 2004, 2011, 2016c. Field trials, scent collection and biochemical analysis on O. barnabita and O. cristinae, showed that these species use exactly the same sex pheromone compound as O. eremita, demonstrating a strong conservation of this sexual trait within the genus throughout Europe (Landvik et al 2015, Zauli et al 2016a. Besides, as suggested by , the maleproduced pheromone in Osmoderma beetles may function as a territorial signal instead of a classical sex pheromone used for species discrimination and the selection pressure to change the signal may be weak or absent.…”

Spatial analysis of the habitat and distribution of Osmoderma eremita (Scop.) in trees outside of woodlands

“…Other techniques confirmed this range of dispersal: 190m (Ranius and Hedin 2001) and 2,090m (Valainis et al 2015) with markrecapture studies, about 500m calculated with DNA markers (Oleksa et al 2013) and a maximum single flight distance of 1,454m and a maximum cumulative flight distance of 2,361m obtained with a flight mill (Dubois et al 2010). Dispersal is probably guided by the (R)-(+)-γ-decalactone, a pheromone emitted by males to attract females and sometimes also males in various other species of Osmoderma (Larsson et al 2003, Svensson et al 2009, Zauli et al 2016.…”

“…Sparacio, 2000, O. cristinae Sparacio, 1994and O. lassallei Baraud & Tauzin, 1991, respectively endemic to the Italian peninsula, Sicily and Greece and European Turkey (Sparacio 2000, Ranius et al 2005, Audisio et al 2007, Landvik et al 2013, Zauli et al 2016. Osmoderma species live in the cavities of large and old broad-leaved trees and, very likely, they all have the same biological requirements.…”