Heredity (2002) 89, 163–170 2002 Nature Publishing Group All rights reserved 0018-067X/02 $25.00 www.nature.com/hdy Differences in levels of heterozygosity in populations of the common gudgeon (Gobio gobio, Cyprinidae) among adjacent drainages in Central Europe: an effect of postglacial range dynamics? A Schreiber Institute of Zoology, University of Heidelberg, Heidelberg, Germany Twenty-nine allozyme loci analyzed in 295 common gudg- of the postglacial immigrants into the Atlantic drainages of eons (Gobio gobio) from the Rhine, the upper Danube and the study area. Refugial bottlenecking of gudgeons from the Elbe river systems revealed variability measures of P = Atlantic drainages in a Pleistocene refuge located in oceanic = = 0.590, He 0.066, and GST 0.1415. Gene flow was esti- northwest Europe also seems possible. Slightly deeper gen- = = mated at Nem 1.88 over 223 river km in the Danube basin, etic lineages in the Danube (GST 0.0859) than in the Rhine = = and at Nem 1.96 over 300 river km in the Rhine system. (GST 0.0793) agree with this explanation, as does the Isolation-by-distance was not observed. Danubian gudgeons greater mean genetic distance among pairs of population = = proved significantly more heterozygous (He 0.106) than samples from the Danube (D 0.0138) than from the Rhine = = = those from the Rhine (He 0.057) or the Elbe drainages (D 0.0054). A genetic distance of D 0.0085 separated = (He 0.029). Nine polymorphic enzymes contributed to this Rhenish and Danubian gudgeons. difference, which probably indicates dispersal bottlenecking Heredity (2002) 89, 163–170. doi:10.1038/sj.hdy.6800109 Keywords: phylogeography; Gobio gobio; Cyprinidae; range dynamics; allozymes Introduction observed by Reinig (1938), dispersal bottlenecking also holds true for freshwater fish. The 42 Holarctic fish spe- Pleistocene glaciations have complicated the zoogeo- cies reviewed by Bernatchez and Wilson (1998) revealed graphy of the Holarctic fish fauna, by the retreat of ther- significantly reduced levels of mtDNA nucleotide diver- mophilous species to southern refugial areas at the onset sity with geographical latitude, and northern species/ of each glaciation phase, and their eventual recoloniz- populations that have immigrated into previously glaci- ation following deglaciation (Reinig, 1937; Thienemann, ated rivers are, as a rule, genetically more uniform than 1950; Banarescu, 1991). These range dynamics of the those from glacial refuges. Quaternary and early Holocene imply the evolution of In Europe the watersheds of rivers draining into the zones secondary population contact, which are of interest Atlantic and into the Mediterranean Sea or the Black Sea for genetics and taxonomy, and for fisheries or species could be of particular importance in this regard, because conservation management. A number of genetic studies they represent a major secondary contact zone of fish have reconstructed postglacial recolonization routes, and invading from different refuges (Riffel and Schreiber, zones of population hybridization, of European fresh- 1995; Schreiber et al, 1998). In each glacial cycle fish could water fish (eg, Riffel and Schreiber, 1995; Riffel et al, 1995; have avoided the periglacial upper Danube, which was Durand et al, 1999; Nesbo et al, 1999; Koskinen et al, 2000). influenced by the melting waters and moraine gravel of Another genetic aspect of this range dynamics has the nearby Alpine glaciers, by descending downstream received little attention from fish biologists. The to the Black Sea basin which has retained temperate-zone reduction of the population genetic variability during conditions for limnofauna throughout the Pleistocene. range expansion by dispersal bottlenecking and genetic They were able to recolonize, upon deglaciation, along drift has, in many animal groups, created a continent- the same route without meeting physical obstacles wide biogeographical pattern of southern richness and (Thienemann, 1950). By contrast, the northwardly northern purity (Rensch, 1939; Hewitt, 1999). Northern directed Rhine retained only cold-adapted fish after the species may, however, display the reverse pattern of Wu¨ rm glaciation at 10 000 years b.p. (Torke, 1998). Immi- what is sometimes a pronounced homozygosity in their grants had to be able to traverse marine waters, or to extreme southern populations (Schreiber et al, 1996). First surmount the watersheds to the south (Rhoˆne, Danube) or the east (Elbe). The upper Danube is inhabited by 50 fish species, including endemics, but the adjacent Rhine, Correspondence: A Schreiber, Institute of Zoology, University of Heidel- berg, Im Neuenheimer Feld 230, D-169120 Heidelberg, Germany. E-mail: which offers a similar range of biotopes, has only 42 spe- [email protected] cies, none of them endemic (Berg et al, 1989). The relative Received 12 November 2001; accepted 23 April 2002 species richness is due to several late postglacial invaders Phylogeographical bottlenecking in common gudgeon A Schreiber 164 which have reached the upper Danube but not (yet) the Table 1 Locations and sizes of 17 population samples of the com- Rhine system (Thienemann, 1941). At the population gen- mon gudgeon (Gobio gobio) from the Rhine and Danube river sys- etic level, comparisons of Rhenish and Danubian fish tems have been confined to trout (Riffel et al, 1995), sculpin (Riffel and Schreiber, 1995), chub (Ha¨nfling and Brandl, River system/Region Collection sites No. 1998), and grayling (Gross et al, 2001), ie to species which = have survived the Wu¨rm glaciation in Central Europe Rhine (n 199) (Torke, 1998). These are unsuitable candidates to investi- Hochrhein Rheinfelden (RHE) 11 Oberrhein Istein (IST) 10 gate dispersal bottlenecking. The present study maps the Riegel (RIE) 19 allozyme variability of the common gudgeon (Gobio Weschnitz (WES) 7 gobio) which is absent from the very rich late Pleistocene Mittelrhein Nette (NET) 30 record of fossil fish in the Rhine/Danube contact area (Torke, 1998). It is shown that the gudgeon populations Neckar Stunzach (STU) 14 from two Atlantic drainages, ie the Rhine and the Elbe, Haigerloch/Rottenburg (ROT) 11 Murr (MUR) 49 contain significantly reduced levels of allozyme hetero- Zaber (ZAB) 21 zygosity when compared with gudgeons from the Bu¨hler/Kocher (BU¨ H) 6 Danube. It is suggested that this difference can be under- Main Gersprenz (GER) 21 stood as the effect of postglacial range dynamics. Gobio gobio is a taxonomically difficult species which Danube (n = 55) shows an extraordinary phenotypic diversity, but the val- uppermost Danube Beuron (BEU) 19 Neuburg (NEU) 8 idity of many of its nominal subspecies continues to be Westernach/Rot (WEN) 20 controversial (Banarescu and Nalbant, 1973; Banarescu et Isar Mu¨hlbach (ISA) 8 al, 1999). Therefore, genetic data are of interest to identify population units for conservation management. Lotic Elbe (n = 41) (rheophilic) morphotypes have a longer tail peduncle, Mittelelbe Oessau (OES) 15 more deeply forked caudal fins, longer paired fins and Gross-Rosenburg (ROS) 26 barbels, and are darker than the lentic (limnophilic) still- water forms from the same general area, which have a higher body shape and rounded caudal fins (Banarescu standard zymography (Harris and Hopkinson, 1976). The et al, 1999). The heritabillity of this morphotypic dichot- alleles were designated by their electrophoretic mobility omy is uncertain. Gudgeons are unattractive to the fish- in relation to the mobility of the most frequent variant ing industry or for sportsfishing, and therefore the spe- which was defined as 100%. Migration to the cathode is cies is neither hatchery-bred nor stocked anywhere in the indicated by a negative sign. study area, or likely to have been in the past, at any sig- nificant level. Its genetic population structure should Statistics reflect natural patterns rather than the consequence of Diversity measures for entire drainages have been human management. derived after pooling all specimens from the respective river systems. Genetic distances are unbiased standard Materials and methods distances (Nei, 1978). Hierarchical gene diversity analysis followed Chakraborty and Leimar (1987), and used Populations unbiased esimates which weighted samples of varying Gobio gobio were collected by electrofishing at 17 size equally (Nei and Chesser, 1983). Chi-square tests of localities, chiefly in 1998/1999 (Table 1, Figure 1). Most Hardy-Weinberg equilibrium used the sequential Bonfer- local samples were acquired from within a few 100 m of roni and the Yates corrections (Lessios, 1992). Heterogen- river length, but two of them were assembled over tens eity analysis of genotype distibutions, or allele fre- of river km, and at two sampling dates each, ie Murr quencies, followed Workman and Niswander (1970). (n = 24 in 1996, and n = 25 in spring 1999) and Nette (n = = Gene flow was estimated from gene diversity indices 4 in the early 1990s, and n 26 in 1999). The contro- (Wright, 1951). Principal component analysis (PCA) was versial species identity of gudgeons from the Danube performed on the arcsine-transformed allele frequencies (Berg et al, 1989) was determined by inspecting the mor- using the SSPS software package. The matrix correlation phological characters summarized by Wanzenbo¨ck et al of geographical and genetic distances (Mantel, 1967) used (1989) and Banarescu et al (1999). Their zymograms were NTSYS/PC 2.02f software (Rohlf, 1998), after data trans- also compared with those of confirmed reference speci- formation to adjust