Zoologischer Anzeiger - A Journal of Comparative Zoology
A multisource solution for a complex problem in biodiversity research: Description of the cryptic ant species Tetramorium alpestre sp.n. (Hymenoptera: Formicidae)
Introduction
Recently, the approach of combining data from multiple sources including molecular genetics has been shown to improve the success in disclosing cryptic biodiversity to an unparalleled degree (e.g., Bickford et al., 2007, Moreau, 2009, Seifert, 2009, Bernasconi et al., 2010, Schlick-Steiner et al., 2010). Discovery of cryptic species frequently marks the first step in resolving longstanding taxonomic disputes. However, cryptic-species identification as made plausible by modern approaches but yet to be linked to Linnean nomenclature represents special challenges to alpha taxonomy (Schlick-Steiner et al., 2007). Achieving this link is highly desirable: in taxonomy, any species delimitation and characterisation is available, and thus open to further scrutiny, only if it is associated with a formal name published in accord with nomenclature (International Commission on Zoological Nomenclature, 1999), such publications having “eternal life” (Boero, 2001). We here contribute to settling the taxonomic dispute surrounding the pavement ants, Tetramorium caespitum (Linnaeus, 1758), T. impurum (Foerster, 1850), and the cryptic species formerly attributed to these species.
Linnaeus's (1758) name caespitum was the starting point of the taxonomic dispute, followed by descriptions of numerous similar taxa, as well as constant revisions (for a summary, see Bolton et al., 2007). By the end of the millennium, taxonomists had come to believe there were just two species in the montane and subalpine altitudinal zone of Central Europe, T. caespitum and T. impurum. Disconcertingly, some samples did not fit the keys (Seifert, 1996): for example, both states of the main distinguishing character, viz. the absence and presence of rugae on the crests of petiole and postpetiole, were found within some nests (Schlick-Steiner and Steiner, 1999). In addition, Sanetra and Buschinger (2000) presented allozyme patterns for 14 Palearctic Tetramorium species and found the highest variability in T. caespitum and T. impurum (most of the species characterised by Schlick-Steiner et al. (2006) were included; for details, see Appendix A of Schlick-Steiner et al. (2006)). It was the multidisciplinary approach, starting from tentative semiochemical findings (Steiner et al., 2002), which began to shed light on the systematic enigma and revealed cryptic diversity (Schlick-Steiner et al., 2006). Sociobiology data contributed, with partial differences in the number of nest queens (Steiner et al., 2003). Findings from mitochondrial DNA (mtDNA) revealed at least seven groups, but the pattern alone was inconclusive in that divergences within groups partly exceeded those between them (Schlick-Steiner et al., 2006). Male genital morphology showed diagnostic characters for four of the groups, but could not distinguish two of them (the males of one entity remaining unknown); refined morphometrics of workers were in line with the seven-group hypothesis (Schlick-Steiner et al., 2006). But were the groupings species or did they reflect intraspecific variants? Biogeography shed some light on this question, showing sympatry for the species. In sum, these studies demonstrated that the combined evidence was required to overcome the deficits of single disciplines in this species complex. The study by Schlick-Steiner et al. (2006) resulted in neotype designations and redescriptions of T. caespitum and T. impurum. It also led to the characterisation of a further five species, under code names, A–E, because “a taxonomic decision on species A–E would require the revision of about 50 names which come into question for Palearctic Tetramorium species (Bolton, 1995).”
Here, we start to resolve the revealed cryptic diversity in nomenclatural terms by tackling the case of the alpine species Tetramorium sp. A. Applying a multisource approach that takes advantage of interdisciplinary complementarity, we first use information from morphology (male genitalia, worker morphometrics), ecology (thermal niche) and molecular genetics (mtDNA) separately and then integrate it. We focus on the species which co-occur with Tetramorium sp. A and use samples from their entire distribution ranges. In detail, there are two steps:
- (i)
Species delimitation: Starting from the findings of Schlick-Steiner et al. (2006) we go beyond that study by analysing a larger sample, thus increasing the system's robustness, allowing for intraspecific variation to be examined, and reducing the error rate in identifications.
- (ii)
Nomenclature: Building on the results from (i), we consider the relevant available names of taxa that could potentially be conspecific with Tetramorium sp. A. Following demonstration that Tetramorium sp. A represents an as yet undescribed species based on biogeographic, thermal-niche and worker-morphometric arguments, we present the taxonomic description of Tetramorium alpestre sp.n., in terms of morphology, ecology and molecular genetics.
Section snippets
The Tetramorium caespitum/impurum complex
Bolton, 1976, Bolton, 1977, Bolton, 1979, Bolton, 1980 outlined the Palearctic T. caespitum group by means of morphological characters and included 55 species (Bolton, 1995). Within this group, the species with strongest resemblance to T. caespitum and T. impurum have been termed the T. caespitum/impurum complex (Schlick-Steiner et al., 2006). Workers of the T. caespitum/impurum complex range from small to large and from light brown to black; the head is often strongly, less frequently weakly
Species concept and species delimitation criteria
We applied the unified species concept (USC; de Queiroz, 2007). The USC has been defined to accommodate the core common to all species concepts and considers a separately evolving metapopulation lineage as the only necessary conceptual property of species. The justification of a particular delimitation in practice is then based on any or several of the properties of species that other species concepts consider (Hey, 2006, de Queiroz, 2007).
As delimitation criteria we used phenotypic
Species delimitation
Type specimens of T. banyulense, T. caespitum var. fusciclavum, T. caespitum var. penninum, T. semilaeve var. kutteri and T. semilaevis subsp. italica were not included in the basic data set for species delimitation, but are checked for conspecificity with the here delimited species in Section 4.2. Four of the other nests (#260, #261, #i548, #i613) could not be tentatively identified as either Tetramorium sp. A, T. caespitum et sp. B or T. impurum (but were not identified as any of the other
Discussion
Our analyses resulted in the delimitation of Tetramorium sp. A sensu Schlick-Steiner et al. (2006) against the species of the T. caespitum/impurum complex which co-occur with it, as well as in the exclusion of all relevant available names as names for T. sp. A. Prior to the formal species description (Section 6), we give some considerations on species concepts, species-delimitation criteria and data analyses, discuss the six ambiguous nests, and highlight some aspects of the multisource
Formal description
Tetramorium alpestre sp.n. Steiner, Schlick-Steiner and Seifert (Fig. 2, Fig. 3, Fig. 4, Fig. 5, Fig. 6, Fig. 7, Fig. 8, Fig. 9; Table 1, Table 2)
Type locality. Austria (Tyrol): Vent, 46.8548°N, 10.9097°E, 2000 m a.s.l.; immediately above timber line; vegetation mainly grass with interspersed dwarf shrubs (Erica sp. and others; ca. 10–20 cm high) and patches free of vegetation (small rocks, stones, bare soil); holotype nest large (ca. 3 m2); other ant species found close to holotype nest: Formica
Acknowledgements
More than 150 persons have provided material to our ongoing study on Palearctic Tetramorium which was used for establishing the phylogenetic framework published by Schlick-Steiner et al. (2006). The description of T. alpestre would not have been possible without their assistance. We are especially grateful to the following persons who contributed material for the present work: C. Bernasconi, A. Buschinger, D. Cherix, A. Freitag, R. Göls, G. Heller, H. Müller, R. Neumeyer, A. Schulz and J.
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2021, Zoologischer AnzeigerCitation Excerpt :Therefore, the distribution area of T. ferox, the putatively socially parasitic species, is hypothesized to fully overlap with or to be contained within the distribution area of T. moravicum, its putative host. Distribution data of Tetramorium moravicum and T. ferox were taken from the available literature (Antonova & Penev 2006; Borowiec & Salata 2018, 2012; Bračko 2019; Bračko et al. 2016, 2014; Bregant 1998; Cordonnier et al. 2018; Csősz et al. 2014, 2007; Csősz & Schulz 2010; Dvořák et al. 2008; Güsten et al. 2006; Karaman et al. 2014; Karaman 2011; Kiran et al. 2017; Kiran & Aktaç 2006; Kiran & Karaman 2020; Lapeva-Gjonova et al. 2012, 2010; Lapeva-Gjonova & Kiran 2012; Mohseni et al. 2019; Nezhad et al. 2012; Paknia et al. 2008; Radchenko 2016; Ruzsky 1903; Salata et al. 2020; Salata & Borowiec 2019; Schlick-Steiner et al. 2007, 2005 2003; Steiner et al. 2010; Tirgari & Paknia 2004; Wagner 2012; Wagner et al. 2018b; Wiezik et al. 2015) and the database of B. C. Schlick-Steiner & F. M. Steiner. To complement literature search, https://antmaps.org was used.
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These authors contributed equally to this work.