Petra Kersten

Genetic variability and structure of common carp (Cyprinus carpio) populations throughout the distribution range inferred from allozyme, microsatellite and mitochondrial DNA markers

Domesticated/captive stocks and wild/feral populations of common carp from Europe, Central Asia and East/South-East Asia were examined for allozyme (23 populations), microsatellite (11 populations) and mitochondrial DNA (21 populations) variation. Allozyme variability (1.06–1.81 alleles per locus, expected heterozygosity 0.006–0.136 at 16 loci) was much lower than microsatellite variability (2.5–14.0 alleles per locus, expected heterozygosity 0.426–0.887 at four loci). Differences in variability between domesticated/captive stocks and wild-caught ones were more pronounced at microsatellite loci than at allozyme loci, suggesting that microsatellites are better suited to detect population bottlenecks and loss of variation due to inbreeding. All but one European population were fixed for a single composite mtDNA haplotype, which also dominated in Central Asia but was completely missing in East/South-East Asia, indicating a single origin of European carp in Central Asia. All three classes of genetic markers clustered populations into two highly divergent groups: Europe/Central Asia and East/South-East Asia. Hierarchical partition of genetic diversity showed that for microsatellite loci most of variation was due to the within-population component while the highest proportion of mtDNA variation and substantial proportion of allozyme variation was accounted for by differences between geographical regions. Genetic data support the subspecies status of C. c. carpio assigned to the European carp and C. c. haematopterus assigned to the East/South-East Asian carp but do not justify a separate subspecies status (C. c. aralensis) for the Central Asian carp. As demonstrated for a wild/feral carp population from R. Danube, Germany, the genetic markers used in our study may be effectively applied to detect mixing and introgression of intra-species units in the presence of sufficient genetic differentiation.

Recreational fishing selectively captures individuals with the highest fitness potential

Fisheries-induced evolution and its impact on the productivity of exploited fish stocks remains a highly contested research topic in applied fish evolution and fisheries science. Although many quantitative models assume that larger, more fecund fish are preferentially removed by fishing, there is no empirical evidence describing the relationship between vulnerability to capture and individual reproductive fitness in the wild. Using males from two lines of largemouth bass (Micropterus salmoides) selectively bred over three generations for either high (HV) or low (LV) vulnerability to angling as a model system, we show that the trait “vulnerability to angling” positively correlates with aggression, intensity of parental care, and reproductive fitness. The difference in reproductive fitness between HV and LV fish was particularly evident among larger males, which are also the preferred mating partners of females. Our study constitutes experimental evidence that recreational angling selectively captures individuals with the highest potential for reproductive fitness. Our study further suggests that selective removal of the fittest individuals likely occurs in many fisheries that target species engaged in parental care. As a result, depending on the ecological context, angling-induced selection may have negative consequences for recruitment within wild populations of largemouth bass and possibly other exploited species in which behavioral patterns that determine fitness, such as aggression or parental care, also affect their vulnerability to fishing gear.

Genetic variability of German and foreign common carp (Cyprinus carpio L.) populations

Abstract In order to describe their genetic variability the polymorphisms of 8 enzymatic systems representing 23 gene loci were studied in 11 German and 5 foreign common carp lines using horizontal starch gel electrophoresis. The highest variability measured by the mean number of alleles per locus and the percentage of polymorphic loci was observed in Vietnamese wild carp (1.9 and 50%, respectively) followed by carp from River Rhine (1.8 and 45%, respectively). The lowest variability was found in all domesticated stocks (1.4 to 1.5 and 25 to 40%, respectively) and could be attributed to a loss of rare alleles. The mean observed heterozygosities ranged from 0.112 to 0.256 for all populations examined. The calculation of Neis unbiased genetic distances [Nei, M., 1978. Estimation of average heterozygosity and genetic distance from a small number of individuals. Genetics 89, 583-590] revealed three pairs of genetically identical populations. All of them were German mirror carp stocks. The largest genetic distance was found between Japanese Koi carp and German domesticated scaly carp (D=0.133). A dendrogram based on these genetic distance measures showed that all populations could be assigned to two clearly distinct groups. One consisted of the German stocks and the Israeli Dor-70 carp (European group). The other one was formed by Koi carp, Vietnamese and River Amur wild carp, and the Ropsha carp (Asian group). Within the European group the carp from River Rhine were the most distinct ones. Their relatively separate position was mainly caused by the presence of alleles at four loci which could not be found in the majority of the domesticated European stocks.

PCR–RFLP analysis of the mitochondrial ND-3/4 and ND-5/6 gene polymorphisms in the European and East Asian subspecies of common carp (Cyprinus carpio L.)

Abstract Polymorphism within the mitochondrial NADH-3,4 dehydrogenase ( ND-3/4 ) and NADH-5,6 dehydrogenase ( ND-5/6 ) gene regions was studied by polymerase chain reaction–restriction fragment length polymorphism (PCR–RFLP) analysis among common carp populations belonging to the European (two farmed strains and three wild populations) and East Asian (Amur wild carp, Vietnamese wild carp and Japanese Koi carp) subspecies, Cyprinus carpio carpio and C. c. haematopterus , respectively. Polymorphism was detected using eight and six restriction enzymes, respectively, and a total of seven composite haplotypes were identified. Both distance-based and maximum likelihood phylogenetic inference methods clustered the haplotypes into four distinct groups—the European (two haplotypes), Amur (two haplotypes), Vietnamese (two haplotypes) and Koi (one haplotype), and their distributions strictly follow the geographic origin of populations. The populations are clustered into two highly divergent groups (average net nucleotide divergence, 2.4%), the European and the East Asian populations, suggesting an ancient separation. Six enzymes ( Hin fI, Alu I, Hpa II and Taq I at ND-3/4 ; Eco 47I and Bsu RI at ND-5/6 ) yielded diagnostic restriction sites for discriminating between the European and East Asian maternal lineages that can be applied to monitoring of genetic purity of the European farmed strains.

Genetic characterization of wild and domesticated common carp (Cyprinus carpio L.) populations from Uzbekistan

Abstract One domesticated and five wild common carp populations from Uzbekistan have been genetically characterized by examining variability at 22 allozyme loci. The observed level of polymorphism was high (1.4–1.7 alleles per locus, 26.3–42.1% polymorphic loci and expected heterozygosities from 0.098 to 0.146) and similar to that previously found in German or East Asian populations. The Uzbek wild populations, with the exception of the paired populations of Lake Arnasaiskie and Syr-Darya channels, were genetically very similar to each other as reflected by nonsignificant F ST values and clustering into one distinct group with high bootstrap support. In contrast, the differentiation between all Uzbek wild and the Uzbek domesticated carp was highly significant as well as the differentiation between Uzbek and German, Uzbek and East Asian, and German and East Asian populations. The Uzbek domesticated carp clustering with River Amur wild carp could be explained by their proposed crossing with Ropsha carp (a derivative of Amur wild carp), which could have taken place in their breeding history. Allelic distribution at some loci is consistent with introgressive hybridization between Uzbek domesticated carp and Syr-Darya channels wild carp. Considering that wild common carp has already disappeared, is endangered or has mixed with domesticated carp in many other parts of its natural distribution area, it is very important to conserve the wild populations in Uzbekistan in order to maintain the genetic diversity of the species.

Isolation and characterization of nine microsatellite loci from the pike-perch, Sander lucioperca (Linnaeus, 1758).

In order to facilitate studies on the genetic structure of wild populations as well as to monitor genetic changes in cultured stocks, nine polymorphic microsatellite loci were isolated from pike‐perch (Sander lucioperca). Single loci allele numbers varied between two (loci MSL‐3 and MSL‐7) and six (loci MSL‐1 and MSL‐2), and observed heterozygosities ranged from 0.36 (locus MSL‐2) to 1.00 (locus MSL‐9) in a test panel of 25 individuals. Only one pair of loci (MSL‐5 and MSL‐8) displayed significant linkage disequilibrium after sequential Bonferroni corrections. Hardy–Weinberg tests revealed significant excesses of heterozygotes at three loci (MSL‐1, MSL‐7, and MSL‐9).

Genetic variability and differentiation of wild and cultured tench populations inferred from microsatellite loci

Nine species-specific microsatellites were used to characterize 792 tench, Tinca tinca (L.), from 21 wild and cultured populations. Seven loci were polymorphic expressing four to 22 alleles. A Spanish cultured strain was homozygous at all loci for all individuals studied. Low variability was also observed in a wild population from Sapanca Lake, Turkey and a Chinese cultured strain. In contrast, the highest variabilities were found in wild tench from lake Felchowsee (average number of alleles), and the cultured strain from Königswartha (average heterozygosity), both from Germany. Genetic differentiation between populations was moderate to high. The smallest genetic distances were found between the geographically most distant populations. A Neighbor-Joining tree showed only two major clades consisting of 4 and 17 populations, respectively. Within the smaller clade the Turkish wild and Spanish and Chinese cultured tench formed a sub-cluster with 100% bootstrap support. Possible reasons for the latter unexpected grouping are discussed.

Microsatellite loci in tench: isolation and variabilityin a test population

Because of their high variability and rapid evolution, microsatellites became increasingly important in genetic research, e.g. population structure and differentiation studies, gene mapping and parentage analysis. However, such loci have not been isolated in tench so far. Applying a PCR based method of generating microsatellite enriched DNA fragment libraries we were able to identify nine loci (MTT-1 to MTT-9). The variability of these microsatellite loci was determined in 50 tench individuals originating from a wild population of Lake Döllnsee, Germany. Three loci were found to be monomorphic. The remaining six loci segregated for two to nine alleles. The observed heterozygosities at polymorphic loci were high (0.500–0.959) with only one exception: locus MTT-8 (0.167). These polymorphic microsatellite loci showed a much higher level of genetic variability than the allozyme loci previously studied in the same individuals. Thus, they seem to be more suitable for genetic studies of tench. On the other hand, it remains to be checked in other populations if the three loci that did not show any variation in this population are generally monomorphic in this species.

Population differentiation of zander (Sander lucioperca) across native and newly colonized ranges suggests increasing admixture in the course of an invasion

In addition to ecological factors, evolutionary processes can determine the invasion success of a species. In particular, genetic admixture has the potential to induce rapid evolutionary change, which can result from natural or human‐assisted secondary contact between differentiated populations. We studied the recent range expansion of zander in Germany focusing on the interplay between invasion and genetic admixture. Historically, the rivers Elbe and Danube harboured the most north‐western source populations from which a north‐westward range expansion occurred. This was initiated by introducing zander outside its native range into rivers and lakes, and was fostered by migration through artificial canals and stocking from various sources. We analysed zander populations of the native and invaded ranges using nuclear and mitochondrial genetic markers. Three genetic lineages were identified, which were traced to ancestral ranges. Increased genetic diversity and admixture in the invaded region highlighted asymmetric gene flow towards this area. We suppose that the adaptive potential of the invading populations was promoted by genetic admixture, whereas competitive exclusion in the native areas provided a buffer against introgression by novel genotypes. These explanations would be in line with evidence that hybridization can drive evolutionary change under conditions when new niches can be exploited.

Genetic variability in tench (Tinca tinca L.) as revealed by PCR-RFLP analysis of mitochondrial DNA

Four mitochondrial DNA segments, ND1, ND6, cyt b and D-loop, were analyzed by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in 14 tench (Tinca tinca L.) populations located in Europe and Asia; data on 5 Italian populations previously analyzed for the same mtDNA segments were also included in the study. All the considered segments were polymorphic and originated a total of 9 composite haplotypes which were clustered into 2 haplogroups, A and B, possibly corresponding to the Western and Eastern phylogroups previously described in tench. Nine out of 19 populations showed polymorphism, with haplotype diversity ranging from 0.246 to 0.643 and nucleotide diversity from 0.009 to 0.078. Seventy-five percent of the pairwise comparisons were significant, indicating a high between-population variability. The Neighbour-Joining tree revealed the presence of 3 clusters, including pure populations, with only a A or B haplogroup, and mixed populations, with both haplogroups. The possibility of identifying populations with different haplotypes has practical implications for both conservation and supportive stocking.