Genetic characterization of Western European noble crayfish populations (Astacus astacus) for advanced conservation management strategies

Abstract

One central goal of conservation biology is to conserve the genetic diversity of species in order to protect their adaptive potential. The main objective of this study was to identify management units (MUs) for the threatened noble crayfish (Astacus astacus) in Western Europe by utilizing sequence and microsatellite analysis to determine populations in need of focused conservation programs. With the analysis of noble crayfish from 31 sampling sites from Belgium, France, The Netherlands and Germany, and further comparison of this data with a European-wide dataset, we propose four distinct MUs: the French Meuse (MU 1), the French Rhine (MU 2), the Belgian Scheldt and Meuse (MU 3) as well as populations from the French Seine (MU 4). This knowledge enables advanced A. astacus conservation management practises in these catchments by distinguishing between outbreeding and inbreeding populations and by preserving the maximum genetic diversity. When required, a high genetic diversity can be conserved by strengthen existing populations via stocking with populations that either bear the most common haplotype or population-specific private haplotypes in order to maintain recent and regional adaptions. Above all, stocking with populations that exhibit haplotypes from outside Western Europe should be avoided in these catchments. This study supports the preservation of the genetic diversity of noble crayfish in Western Europe and provides thus a proposition for advanced conservation management.

Appendices

Appendix 1

See Table 4.

Table 4 Pairwise FST- and ΦST-values between sampling sites calculated with ARLEQUIN, v. 3.11

Appendix 2

Detailed discussion about the stocking history of the analyzed populations

Our study benefits from detailed information about the history of the studied populations. The differentiated Hap41 found in the Meisenthal hatchery (F1) and in a natural population in the Rhine catchment in France (F7, Lemberg) indicates a stocking event because this haplotype and related ones are frequently distributed in the Croatian Danube catchment (Hap 41 in Fig. 6 and in Schrimpf et al. 2014). A parallel evolution of Hap41 is highly unlikely because it differs from the most common haplotype Hap01 by 10 mutations. The hatchery (F1) was founded with crayfish from the Meisenthal brook in the Vosges, where ponds were dug out in the past to supply power to the local glass industry (Franckhauser, personal communication). We thus assumed that the population from the hatchery was stocked with Danubian crayfish. In its geographic vicinity, sampling site F6 (Sturzelbronn in the Vosges, Fig. 1) is located, which belongs to the same MU (Fig. 4). Noble crayfish were present in the former Sturzelbronn abbey estate already in 1594 and 1789 (Jehin 2006–2007). Therefore, it is most probable that population F6, characterized by the Western-European haplotype Hap31, existed here already historically. It should be preserved by priority. The presence of F6 should explain the presence of both Hap31 and Hap41 in the F7 population. Because noble crayfish stockings likely occurred many times in this region more natural populations from the French Rhine should be analysed to estimate the influence of stockings from the past.

Although some of the sampled populations, especially those harboured in water-filled quarries such as B6 and B9 on the one hand and B11 and B17 on the other hand (all Scheldt catchment) live only a few hundred meters apart from each other in a same locality, they were stocked independently (Table 1), from a distinct origin and in distinct quarries without any exchange between them. While the origin of B9 and B11 is unknown, the origin of B17 is a pond in the Haine-Scheldt catchment. However, as this population may have been stocked in past times, its very first origin is unknown. Interestingly, these stocked populations and the fish farm B3 (Meuse catchment) all carried the haplotype Hap35, which was previously found in the Romanian Danube catchment (Schrimpf et al. 2014). However, since haplotype Hap35 differed by only one base pair exchange from Hap01 it is possible that Hap35 has evolved independently twice. In this case the occurrence in both regions would not necessarily be a sign for a translocation of noble crayfish from Romania to Belgium, but could be an indication of a relationship between the Belgian populations. According to the msat data, the respective Belgian populations (B3, B9, B11, B17) were distinct from noble crayfish from the Black Sea catchment, but they did show some similarity to the remaining noble crayfish from central and Western Europe (Fig. 3). Especially interesting is population B11, which additionally holds two private haplotypes (Hap47, Hap48), that have not been found elsewhere in Europe before. The private haplotypes explain the high Φ_ST-values between B11 and all other populations (Table 4 in Appendix 1). As long as we cannot provide evidence for an alien origin of these private haplotypes we recommend special protection of population B11 in the Scheldt catchment.

Population B13 was highly differentiated from all other populations (high Φ-values and F_ST-values, Table 4; Figs. 4, 5), even from the geographically very close and presumably autochthonous population B18. All 10 sequenced individuals of population B13 carried a haplotype (Hap40, Table 2) that was previously found in the Romanian Danube catchment (Schrimpf et al. 2014). Interestingly, this population was stocked with crayfish purchased in a Belgian food store in the 1970s (S. Kanjester, personal communication; Table 1). Since both the historic record and the genetic results indicate an allochthonous origin, population B13, along with other populations with allochthonous haplotypes (populations F1, F7), should not be used for further stockings in Belgium. Also other crayfish with Danubian (see Schrimpf et al. 2014) or other foreign origin should not be used.

Small isolated populations like the last known Dutch noble crayfish population (NL) are at high risk from inbreeding depression (Frankham et al. 2012). Individuals in small populations have a lower fitness and the extinction probability is increased especially in changing environments (Willi et al. 2006). Haplotype and allele diversities are indeed already low in the Dutch population (Table 2). Additionally, as for the Belgian and the French Oise catchment populations, the extinction risk for noble crayfish in The Netherlands is especially high due to the wide distribution of American crayfish species (Koese and Soes 2011) and the crayfish plague (Tilmans et al. 2014). Consequently, this population should be a focus of special management.