Contributions to Zoology, 79 (3) – 2010Peer Martin; Nathan J. Dorn; Tadashi Kawai; Craig van der Heiden; Gerhard Scholtz: The enigmatic Marmorkrebs (marbled crayfish) is the parthenogenetic form of Procambarus fallax (Hagen, 1870)

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Results

Morphological comparisons reveal detailed similarities between Procambarus fallax and Marmorkrebs

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Concerning morphological characters the Marmor­krebs identifies closely with P. fallax and is quite distinct from P. alleni (Figs 2, 3). The Marmorkrebs annulus ventralis lacks the characteristic scooped ‘wings’ on the lateral parts and the anterior portion is not peaked like the annulus ventralis of P. alleni (Fig. 2A vs. B-C). In contrast, the Marmorkrebs annulus ventralis closely resembles the flatter, bell-shaped annulus ventralis of P. fallax (see also Hobbs, 1942; Kawai et al., 2009) (Fig. 2). Furthermore, the Marmorkrebs annulus ventralis does not closely resemble that of any other North American members of the genus Procambarus (Hobbs, 1989). The overall coloration pattern of P. fallax (Fig. 3), including a ‘marbled’ carapace and lateral dark stripes, is consistent with the coloration of Marmorkrebs from the Berlin laboratory culture, in published photos (Scholtz et al., 2003; Seitz et al., 2005; Vogt et al., 2008; Kawai et al., 2009), and with those on the internet. The dark lateral horizontal stripes through the cephalothorax and abdomen on P. fallax (Fig. 3B) can vary in intensity between individuals (or populations), but a distinct stripe is a good indication that the crayfish is P. fallax (Fig. 3B) rather than P. alleni (Fig. 3A). Specimens of Procambarus alleni have conspicuous dark spots ventral to the bases of the eye stalks and anterior to the oral cavity (Fig. 3A) while those of P. fallax do not (Fig. 3B). This was first pointed out by Hendrix and Loftus (2000) and after seeing thousands of individuals of these species we can further attest to the uniformity of this difference in south Florida (N. Dorn, pers. obs.). All the Marmorkrebs individuals studied in the laboratory culture in Berlin lack these conspicuous spots (Fig. 3C). The absence of these spots can also be clearly seen in Kawai et al. (2009) from Marmorkrebs from the Japanese aquarium trade (Fig. 3D).

Molecular analysis shows a high degree of DNA sequence correspondence between Procambarus fallax and Marmorkrebs

The molecular analysis shows distances of the COI sequences (total length 675 base pairs) between P. alleni and P. fallax ranging from 6.40 to 7.24% (mean 6.88 ± 1.01%), between P. alleni and Marmorkrebs from 6.75 to 7.24% (mean 6.88 ± 1.05%), and between P. fallax and Marmorkrebs from 0.60 to 0.75 (mean 0.67 ± 0.24%). Within the species, the values are 0.00-1.36% (mean 0.79 ± 0.25%) in P. alleni and 0.00-1.05% (mean 0.57 ± 0.19%) in P. fallax. The 12S sequences (381 base pairs) of P. fallax and Marmorkrebs are identical. This is also true for the P. alleni specimens, where uniform sequences are found except in specimen pal-10, which shows a single substitution. The distance between the P. fallax / Marmorkrebs complex and the P. alleni population ranges from 2.95 to 3.27% (mean 3.02 ± 0.92%). The two Marmorkrebs specimens are identical in the COI and 12S sequences over a total length of 1057 base pairs (see also Martin et al., 2010).

For tree reconstruction, a total data set consisting of the combined COI and 12S sequences of the specimens listed in Table 2 and a selection of several species from GenBank^® of 927 nucleotides was available after pruning the DNA alignments with the program Gblocks 0.91b. The resulting tree shows that the two Marmorkrebs specimens nest clearly within the P. fallax representatives (Fig. 4). The same result was obtained if each gene alone was used for tree reconstruction (not shown).

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