The example of a species that survived past climate change in refuges and benefited from reverse climatic changes by range expansion despite low dispersal power may give hope for conservation. However, C. v. nodulosus, like many other postglacial populations, shows reduced genetic variability (Hewitt 2001), which implies certain risks for long-term survival. Hence, the maintenance of genetic diversity within species is one important goal of biodiversity conservation.
As the Southern Slovenian populations are a distinct genetic unit holding genetic diversity not found in Central European populations, they should consequently be granted special protection alongside the Central European samples. To conserve the remaining genetic diversity, as many of the relict populations as possible should be targeted, since more than 45% of the total allozyme variance of C. v. nodulosus is found among populations (Matern et al. 2009). Where possible, a cautious enlargement of the habitat patches may also be attempted.
If further populations within or close to the core of the subspecies range could be found that display high genetic diversity (owing to their location in glacial refuges, for example), these of course would have an especially high conservation priority. Locations of all current relict populations of C. variolosus (and of other flightless, sensitive species) may also be an indicator of unique environmental conditions not affected by disturbance and demonstrate the general continuity (stability) of habitats. These occurrences can therefore be used to identify valuable habitats for the conservation of entire species communities.
This study provides an example of increased knowledge and sensible conservation strategies that were derived from a combination of diverse methodological approaches offering different perspectives. The contribution of ecological knowledge is essential where knowledge on a species is scant. Details on the habitat preference and habitat use of C. variolosus are crucial for an assessment of factors influencing the incidence and distribution pattern of the species. In the case of
C. variolosus this information especially emphasises the urgency to assess population sizes and the necessity to enlarge populations. The analysis of COI provides valuable information on long-term population history that was not available from allozyme analysis. Moreover, it strongly supports the allozyme results which already suggested that the Southern Slovenian populations are a differentiated entity, with relevance for conservation (Moritz 1994). The identification of differentiated population groups is considered crucial for the conservation of the genetic diversity of species (e.g. Ryder 1986; Moritz 1995) and provides important data in rescue efforts of species by means of translocations (e.g. Avise 1996). While mtDNA sequence data contribute additional information on population differentiation and genetic diversity, they should not be used exclusively in the discussion of conservation priorities. It is the population genetic approach with nuclear markers that offers an advanced insight into the isolation of populations and the level and overall distribution of genetic diversity within and across populations. The allozyme results underline the need for recognition of distinct Management Units even at adjacent sites within the same drainage system.
In the context of the EU Habitats Directive and Natura 2000 Network it is now important to extend analyses to the Eastern subspecies C. v. variolosus. Further allozyme and DNA analyses to unravel the phylogeny and discover subspecific population structure will show whether the conservation measures established for C. v. nodulosus are also valid for C. v. variolosus. One important clue, however, is already given by the current COI analysis: sequence divergence between the two taxa is surprisingly low. As the amount of sequence divergence is extremely variable in different lineages, it is impossible to apply a general threshold value to justify taxonomic distinction at the species level (Vogler et al. 1993). Some molecular taxonomists have (controversially) used a 3 or 2% COI divergence for species delimitation across a wide range of organisms including insects (cf. Duckett and Kjer 2003; Hebert et al. 2003, 2004; Moritz and Cicero 2004). Comparisons of mtDNA studies find sequence divergence of less than 2% primarily on an intraspe-cific level (Vogler and DeSalle 1994; Avise 2000; Woodcock et al. 2007). This is also the case among populations of another ground beetle species, Nebria rufe-scens, which are not formally distinguished at the species or subspecies level and display a mean mtDNA-sequence divergence (ND1) of 1.3% (Schmitt et al. this book). Although the two taxa of C. variolosus are "diagnosable" under a phyloge-netic species concept (Vogler and DeSalle 1994), their divergence is low and only slightly greater than the striking separation of the Central European and Southern Slovenian populations. This finding may support the older classification as subspecies (cf. Breuning 1926), settle the past discussion on the potential species rank of C. v. nodulosus and counteract taxonomic inflation (cf. Isaac et al. 2004).
Future genetic assessment of C. variolosus will be necessary to study the success of conservation recommendations such as population increase or population connectivity and thus augment ecological monitoring. Moreover, it may also enhance our knowledge on the relationship between population sizes and the maintenance of genetic diversity and probably their influence on the persistence of these populations.
Acknowledgements We are grateful to Bozidar Drovenik, Daniela Eisenacher, Jens Günther, Michael Franzen, Istvan Mathe, Wolfgang Paill, Laszlo Rakosy, Annette Ehrhardt-Renken, and Marco Zimmermann for their assistance in sampling and valuable exchange of information and to Dietrich Mossakowski for providing us with an additional specimen from Romania. For technical assistance in the lab we thank Marianne Peters, Beatrice Dames, and Gunnar Siedenschnur. We cordially thank Anna Papadopoulou at the Natural History Museum London, who helped with mtDNA sequencing and analysis. We also thank an anonymous reviewer for valuable comments on the manuscript. A. Matern was funded by the German Federal Environmental Foundation (DBU).
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