Věra Šlechtová

Spatial heterogeneity in the Mediterranean Biodiversity Hotspot affects barcoding accuracy of its freshwater fishes

Incomplete knowledge of biodiversity remains a stumbling block for conservation planning and even occurs within globally important Biodiversity Hotspots (BH). Although technical advances have boosted the power of molecular biodiversity assessments, the link between DNA sequences and species and the analytics to discriminate entities remain crucial. Here, we present an analysis of the first DNA barcode library for the freshwater fish fauna of the Mediterranean BH (526 spp.), with virtually complete species coverage (498 spp., 98% extant species). In order to build an identification system supporting conservation, we compared species determination by taxonomists to multiple clustering analyses of DNA barcodes for 3165 specimens. The congruence of barcode clusters with morphological determination was strongly dependent on the method of cluster delineation, but was highest with the general mixed Yule‐coalescent (GMYC) model‐based approach (83% of all species recovered as GMYC entity). Overall, genetic morphological discontinuities suggest the existence of up to 64 previously unrecognized candidate species. We found reduced identification accuracy when using the entire DNA‐barcode database, compared with analyses on databases for individual river catchments. This scale effect has important implications for barcoding assessments and suggests that fairly simple identification pipelines provide sufficient resolution in local applications. We calculated Evolutionarily Distinct and Globally Endangered scores in order to identify candidate species for conservation priority and argue that the evolutionary content of barcode data can be used to detect priority species for future IUCN assessments. We show that large‐scale barcoding inventories of complex biotas are feasible and contribute directly to the evaluation of conservation priorities.

Synthesis of clonality and polyploidy in vertebrate animals by hybridization between two sexual species.

Because most clonal vertebrates have hybrid genomic constitutions, tight linkages are assumed among hybridization, clonality, and polyploidy. However, predictions about how these processes mechanistically relate during the switch from sexual to clonal reproduction have not been validated. Therefore, we performed a crossing experiment to test the hypothesis that interspecific hybridization per se initiated clonal diploid and triploid spined loaches (Cobitis) and their gynogenetic reproduction. We reared two F1 families resulting from the crossing of 14 pairs of two sexual species, and found their diploid hybrid constitution and a 1:1 sex ratio. While males were infertile, females produced unreduced nonrecombinant eggs (100%). Synthetic triploid females and males (96.3%) resulted in each of nine backcrossed families from eggs of synthesized diploid F1s fertilized by haploid sperm from sexual males. Five individuals (3.7%) from one backcross family were genetically identical to the somatic cells of the mother and originated via gynogenesis; the sperm of the sexual male only triggered clonal development of the egg. Our reconstruction of the evolutionary route from sexuality to clonality and polyploidy in these fish shows that clonality and gynogenesis may have been directly triggered by interspecific hybridization and that polyploidy is a consequence, not a cause, of clonality.

Top-crossing with paternal inheritance testing of common carp (Cyprinus carpio L.) progeny under two altitude conditions

Abstract Weight, survival and heterosis were tested in hybrids by means of top-crossing at low and high altitudes (350 and 750 m, respectively) above the sea level. A Hungarian mirror carp strain (HSM) was chosen for testing as a maternal strain. The HSM, a wild Amur carp strain (AC), Ropsha carp strain (ROP) and Tata carp strain (TAT) were used as the paternal strains. The first season of the top-crossing test was performed by means of separate rearing of each group of fry with controls in four ponds at each altitude. In the second and third seasons, up to 3-year-old carp were grown in communal stocks for all groups in three ponds at each altitude. The highest significant corrected weight gain and survival in low and high altitudes during three seasons were obtained with the HSM×ROP and HSM×AC crossbreds. The lowest significant corrected weights were obtained with the HSM×TAT crossbred and HSM purebred, respectively. The highest significant heterosis effect both at low and high altitudes was obtained for both HSM×ROP and HSM×AC crossbreds compared to the HSM×TAT crossbred as predicted from the genetic distances between the strains. Moreover, the HSM×ROP crossbred was best adapted for altitude, regions or management in pond stations.

Genetic resources of commercially important fish species in the Czech Republic: present state and future strategy

Abstract Since 1996, the Czech governmental programme on gene resources conservation of commercially important fish species has supported in situ conservation of rare/endangered breeds of common carp ( Cyprinus carpio ; nine breeds) and of rainbow trout ( Oncorhynchus mykiss ; three breeds) by keeping broodstock of each as live gene banks on selected farms. Effective population size ( N e ) is maintained at 120. As fish are not included yet in the Czech animal breeding act, the programme encourages fisheries policy makers and farm managers to protect pure local breeds parallely to a general tendency to import breeds, use crossbreds for production or move breeds among farms. Since most breeds are defined by reproductive and performance traits only, their genetic structure is currently being investigated by enzyme polymorphism analysis to determine their value to the programme. A data records system is being introduced to the breeders that combines fish tagging and a locally-developed computer programme to store information. The experimental cryopreserved sperm bank is being extended to meet the needs of ex situ conservation. Since 1997, the programme has expanded to include eight strains of tench ( Tinca tinca ), two strains of wels ( Silurus glanis ), two coregonid species ( Coregonus lavaretus maraena and Coregonus peled ) and two acipenserid species ( Acipenser ruthenus and Huso huso ).

Rare and asymmetrical hybridization of the endemic Barbus carpathicus with its widespread congener Barbus barbus.

In endemic species that co-occur with widespread congeners, hybridization can lead to an influx of novel and beneficial genetic variation, but high rates of introgression may cause genetic swamping of the endemic species and have detrimental effects on its survival potential. This study examines hybridization between sympatric populations of the Carpathian barbel Barbus carpathicus, a recently discovered cryptic species with a restricted range, and the widespread common barbel Barbus barbus. Based on six diagnostic allozyme loci, a microsatellite locus and mtDNA, hybrids were found to be present at multiple localities within the Vistula River drainage (Baltic Sea) as well as in the Tisza River system of the Danube River drainage (Black Sea). However, the numbers of hybrids were very low; four individuals of 230 fish sampled from the Vistula drainage. Bayesian assessment of their nuclear genotypes suggested that two hybrids in the Vistula drainage and nine in the Tisza system were F1 generation, and one in the Vistula drainage and one in the Tisza system were backcrosses (BC) to B. barbus, while no F2 or BC to B. carpathicus were detected. No hybrid carried B. carpathicus mtDNA and cytonuclear linkage disequilibria showed significant positive associations between hybrid genotypes and B. barbus mtDNA, suggesting unidirectionality in the interspecific mating with a disproportionate contribution of B. barbus mothers. Despite geographically broad occurrence of hybrids, these data provide evidence of strong constraints on hybridization in the native breeding habitats and the lack of introgression towards B. carpathicus.

Hybrid asexuality as a primary postzygotic barrier between nascent species: On the interconnection between asexuality, hybridization and speciation

Although sexual reproduction is ubiquitous throughout nature, the molecular machinery behind it has been repeatedly disrupted during evolution, leading to the emergence of asexual lineages in all eukaryotic phyla. Despite intensive research, little is known about what causes the switch from sexual reproduction to asexuality. Interspecific hybridization is one of the candidate explanations, but the reasons for the apparent association between hybridization and asexuality remain unclear. In this study, we combined cross‐breeding experiments with population genetic and phylogenomic approaches to reveal the history of speciation and asexuality evolution in European spined loaches (Cobitis). Contemporary species readily hybridize in hybrid zones, but produce infertile males and fertile but clonally reproducing females that cannot mediate introgressions. However, our analysis of exome data indicates that intensive gene flow between species has occurred in the past. Crossings among species with various genetic distances showed that, while distantly related species produced asexual females and sterile males, closely related species produce sexually reproducing hybrids of both sexes. Our results suggest that hybridization leads to sexual hybrids at the initial stages of speciation, but as the species diverge further, the gradual accumulation of reproductive incompatibilities between species could distort their gametogenesis towards asexuality. Interestingly, comparative analysis of published data revealed that hybrid asexuality generally evolves at lower genetic divergences than hybrid sterility or inviability. Given that hybrid asexuality effectively restricts gene flow, it may establish a primary reproductive barrier earlier during diversification than other “classical” forms of postzygotic incompatibilities. Hybrid asexuality may thus indirectly contribute to the speciation process.