Lamellodiscus euzeti n. sp. (Monogenea:Diplectanidae), a parasite from Dentex canariensis and D. gibbosus (Teleostei:Sparidae) in the Atlantic Ocean and Mediterranean Sea

Lamellodiscus euzeti n. sp. (Monogenea:Diplectanidae) is described from the gills of two sparid fishes, Dentex canariensis (Steindachner) off Senegal and Ivory Coast and D. gibbosus (Rafinesque) off Senegal and Tunisia. The new species belongs to the "ignoratus" group, characterized by a lamellodisc with complete lamellae, a "lyre" shaped male copulatory organ type, and the "ignoratus" sensu stricto subgroup, characterized by a haptor with simple lateral dorsal bars. Lamellodiscus euzeti n. sp can be distinguished from all the congeneric species of the "ignoratus" subgroup by the presence of a prominent protuberance at the base of the curved part of the simple piece of the male copulatory organ (MCO), a large bulb at the base of the bifurcated piece of the MCO and the presence of 5-6 spines in the distal portion of the axial branch of the bifurcated piece of the MCO. Specificity and biogeography of Lamellodiscus species from sparid fishes are discussed.     

Description of Lamellodiscus confusus n. sp, (Monogenea: Diplectanidae), parasite of Sarpa salpa (Teleostei: Sparidae)

Lamellodiscus confusus n. sp., a diplectanid gill parasite of Sarpa salpa Linnaeus, 1758 (Sparidae) from the coast of Algeria, is described. This monogenean has been previously reported in Sarpa salpa, by various authors, under the name L. ignoratus. L. confusus n. sp. is included (among other Lamellodiscus of Mediterranean sparids) in the "ignoratus" sub-group (Amine & Euzet, 2005). L. confusus n. sp. can be distinguished from L. ignoratus by the shape and size of the haptoral ventral bar and the male copulatory organ. For comparison, illustrations of the ventral bar and the male copulatory organ of all Mediterranean species of the "ignoratus" sub-group are provided. The question of the host specificity of L. ignoratus is discussed.     

Evolution and determinants of host specificity in the genus Lamellodiscus (Monogenea)

The evolution and determinants of host specificity in Lamellodiscus species (Monogenea, Diplectanidae) were investigated. The 20 known Mediterranean species were studied, all parasites of fishes from the family Sparidae (Teleostei). An index of specificity, which takes into account the phylogenetic relationships of their fish host species, was defined. The link between specificity and its potential determinants was investigated in a phylogenetic context using the method of independent contrasts. Host specificity in Lamellodiscus species appeared to be highly constrained by phylogeny, but also linked to host size. Mapping specificity onto the parasite phylogenetic tree suggests that specialist species do not represent an evolutionary dead end, and that specialization is not a derived condition. It is hypothesized that the ability to be generalist or specialist in Lamellodiscus is controlled by intrinsic, phylogenetically-related characteristics, and that specialist species tend to use large hosts, which may be more predictable.  © 2002 The Linnean Society of London, Biological Journal of the Linnean Society , 2002, 77, 431−443.     

Lamellodiscus sanfilippoi n. sp. (Monogenea, Diplectanidae) parasite from the gills of Diplodus sargus (Teleostei, Sparidae) in Mediterranean Sea

Lamellodiscus sanfilippoi n. sp. takes place, among the other species of Lamellodiscus, in the "ergensi" sub-group (Amine et Euzet, 2005) characterized by the morphology of the dorsal lateral bars of the haptor. This sub-group comprises, in the Mediterranean, L. ergensi Euzet and Oliver, 1966, L. kechemirae Amine and Euzet, 2005, L. tomentosus Amine and Euzet, 2005, all parasite of Diplodus sargus, and L. baeri Oliver, 1974 parasite of Pagrus pagrus. L. sanfilippoi can be distinguished from the previous species by the morphology and size of the dorsal lateral bars. The new species is close to Lamellodiscus furcillatus Kritsky, Jiménez-Ruiz and Sey, 2000, a parasite of Diplodus noct in the Persian Gulf, but differs by the size of the haptoral sclerotised pieces and the morphology of the male copulatory apparatus. Lamellodiscus gussevi Sanfilippo (1978) et Lamellodiscus abbreviatus Sanfilippo (1978) are considered as nomina nuda.     

Coevolution of the Monogenoidea (Platyhelminthes) based on a revised hypothesis of parasite phylogeny

A revised hypothesis for the phylogeny of the Subclass Polyonchoinea (Monogenoidea) was contructed employing phylogenetic systematics. The Acanthocotylidae (formerly of the Order Capsalidea) is transferred to the Order Gyrodactylidea based on this analysis. The new phylogeny is used to determine coevolutionary relationships of the familial taxa of Monogenoidea with their hosts. The coevolutionary analysis suggests that the Monogenoidea apparently underwent sympatric speciation or dispersal while parasitic on ancestral Guathostomata, resulting in two primary clades: the Polyonchoinea and the Oligonchoinea + Polystomatoinea. The two parasite clades apparently cospeciated independently with divergence of the Chondrichthyes and Osteichthyes. In the Polyonchoinea, the clade associated with Chondrichthyes experienced primary extiaction within the Holocephala, but coevolved into the Loimoidae and Monocotylidae in the Galeomorphii and Squalea (Elasmobranchii), respectively. Within the Osteichthyes, polyonchoineans experienced primary extinction with the divergence of Sarcopterygii, Polypteriformes and Acipenseriformes. They demonstrate primary dispersal from the Neopterygii into the Squalea (as Amphibdellatinea), Actinistia (as Neodactylodiscinea) and Urodela (as Lagarocotylidea). Secondary dispersals of polyonchoineans occurred in the Gyrodactylidae to the Polypteriformes, Urodela and Anura; in the Acanthocotylidae to the Myxinoidea and Squalea; in the Capsalidae to the Acipenseriformes and Elasmobranchii; and in the Monocotylidae to the Helocephala. The Oligonchoinea and Polystomatoinea developed upon divergence of the Chondrichthyes and Osteichthyes. Oligonchoineans cospeciated within the Chondrichthyes, with the Chimaericolidea developing within the Helocephala and the ancestor of the Diclybothriidea + Mazocraeidea within the Elasmobranchii. Two cases of primary dispersal occurred within this clade: the Diclybothriidae to the Acipenseriformes and the ancestor of mazocracidean families to the Neopterygii (both Osteichthyes). Secondary dispersal within the Oligonchoinea includes host switching of the common ancestor of Callorhynchocotyle (Hexabothriidae) to the Holocephala. Polystomatoineans coevolved within the Osteichthyes, but experienced primary extinctions in the Actinopterygii, Actinistia, Dipnoi and Amniota. Coevolution of the Sphyranuridae and Polystomatidae occurred with divergence of the Urodela and Anura, respectively. Secondary dispersal of polystomatids to the Urodela, Dipnoi and Amniota is suggested. A preliminary phylogenetic analysis of the Polystomatoinea suggests that primary extinction with secondary dispersal of polystomatids to the Dipnoi may not be necessary to explain extant parasite distributions, since Concinnocotyla (Concinnocotylinae) appears to represent the sister taxon of the remaining Polystomatidae + Sphyranuridae.     

A species complex within the isopod genus Haploniscus (Crustacea: Malacostraca: Peracarida) from the Southern Ocean deep sea: a morphological and molecular approach

Seven new species of the genus Haploniscus from the deep Scotia and Weddell Seas are presented, combining morphological and molecular data (mitochondrial 16S rDNA and nuclear 18S rDNA). Haploniscus cassilatus sp. nov. , H. cucullus sp. nov. , H. weddellensis sp. nov. , H. procerus sp. nov. and H. kyrbasia sp. nov. are characterized by a prominent rostral process, the size and shape of which vary among species. The rostrum of H. microkorys sp. nov. is distinctly smaller than that of the former species, while H. nudifrons sp. nov. does not possess a rostrum. The status of the latter as separate species is obvious, owing to the stronger morphological differences. DNA was sequenced from three of the other five species. Genetic distances together with the more subtle morphological variation justify the erection of separate species. Overall morphological variations between these species are small yet noticeable and include, among others, the rostrum, the shape of the pleotelson and setation of pereopods. Our molecular data sets reveal detailed phylogenetic insights within the Haploniscus cucullus complex, supporting the monophyly of all species. We found p -distances of at least 0.0732 (16S rDNA) and 0.0140 (complete 18S rDNA) between pairs of species and show that both genes can be used as a marker for DNA taxonomy.  © 2008 The Linnean Society of London, Zoological Journal of the Linnean Society , 2008, 152 , 655–706.     

Discord in the family Sparidae (Teleostei): divergent phylogeographical patterns across the Atlantic-Mediterranean divide

The Strait of Gibraltar has been proposed to be the divide between two marine biogeographical regions, the Mediterranean Sea and the Northeast Atlantic. Intraspecific studies have shown, for several of the examined species, a reduction of gene flow between the two basins. The present study examines genetic variation at nuclear and mitochondrial loci in five marine teleost species belonging to the family Sparidae. Four samples for each species were analysed spanning the Northeast Atlantic and the Mediterranean. For all individuals 17 allozyme loci were scored and a combined single strand conformation polymorphism-sequencing approach was used to survey approximately 190 bp of the mitochondrial DNA (mtDNA) D-loop region. All five species share similar biological features. For three species, namely Lithognathus mormyrus, Spondyliosoma cantharus, and Dentex dentex, large mtDNA divergence was observed between Atlantic and Mediterranean samples. Little or no mtDNA differentiation was found in the other two species, Pagrus pagrus and Pagellus bogaraveo. Allozyme data revealed strong differentiation when comparing Atlantic and Mediterranean samples of L. mormyrus and D. dentex, moderate for P. pagrus, and no differentiation for P. bogaraveo and S. cantharus. These results provide evidence for a sharp phylogeographical break (sensu Avise) between the Atlantic and the Mediterranean for two (or possibly three) sparid species of the five investigated. At the same time, the obtained results for the other two species raise the question on which ecological/historical factors might have caused the observed discrepancy in the geographical distribution of genetic variation among otherwise biologically similar species.     

Speciation and host-parasite relationships in the parasite genus Gyrodactylus (Monogenea, Platyhelminthes) infecting gobies of the genus Pomatoschistus (Gobiidae, Teleostei)

Using species-level phylogenies, the speciation mode of Gyrodactylus species infecting a single host genus was evaluated. Eighteen Gyrodactylus species were collected from gobies of the genus Pomatoschistus and sympatric fish species across the distribution range of the hosts. The V4 region of the ssrRNA and the internal transcribed spacers encompassing the 5.8S rRNA gene were sequenced; by including published sequences a total of 30 species representing all subgenera were used in the data analyses. The molecular phylogeny did not support the morphological groupings into subgenera as based on the excretory system, suggesting that the genus needs systematic revisions. Paraphyly of the total Gyrodactylus fauna of the gobies indicates that at least two independent colonisation events were involved, giving rise to two separate groups, belonging to the subgenus Mesonephrotus and Paranephrotus, respectively. The most recent association probably originated from a host switching event from Gyrodactylus arcuatus, which parasitises three-spined stickleback, onto Pomatoschistus gobies. These species are highly host-specific and form a monophyletic group, two possible ‘signatures’ of co-speciation. Host specificity was lower in the second group. The colonising capacity of these species is illustrated by a host jump from gobiids to another fish order (Anguilliformes), supporting the hypothesis of a European origin of Gyrodactylus anguillae and its intercontinental introduction by the eel trade. Thus, allopatric speciation seems to be the dominant mode of speciation in this host–parasite system, with a possible case of sympatric speciation.     

Cophylogenetic analysis of the relationship between anemonefish Amphiprion (Perciformes: Pomacentridae) and their symbiotic host anemones (Anthozoa: Actiniaria)

ABSTRACT

The association between anemonefish and anemone is a classical example of mutualism in coral reefs. Although mutualism is probably the key innovation that triggered the adaptive radiation of anemonefish into a wide range of habitats, the coevolutionary history between the groups has not been thoroughly tested in a phylogenetic framework. We examined the evolutionary history of the association via distance-based (Parafit and PACo) and event-based methods (Core-PA, Jane). Mitochondrial DNA sequences (COI mtDNA, Cytb, 16S rDNA and 12S rDNA) were used to reconstruct the phylogenies of tropical Amphiprion species and their host anemones by using maximum likelihood with best-fit models selected. Neither distance-based analyses nor event-based analyses revealed global significant congruence between the phylogenies of the hosts and the symbionts, and thus no evidence for coevolution between anemone-anemonefish. However, at the individual pair level, the fish showed some dependence on anemone hosts. Even though living in close association and benefiting from each other, the change of genetic composition of one species (anemonefish) does not always evolve in response to changes in the other (anemones). These findings expand our understanding of the pattern and the role of evolutionary events to allow a better prediction of the future of the anemonefish-anemone relationship.     

Optimization of single-strand conformation polymorphism and sequence analysis of the mitochondrial control region in Pagellus bogaraveo (Sparidae, Teleostei): rationalized tools in fish population biology

We report the isolation and sequencing of 400–550 base pairs (bp) of the mitochondrial DNA (mtDNA) control region of eight species of Sparidae (Perciformes, Teleostei). This sequence information allowed us to design specific primers to one of these species (Pagellus bogaraveo). The new set of primers was used to test a rationalized approach to study the mtDNA nucleotide variability at the intraspecific level. The single-strand conformation polymorphism (SSCP) technique was applied to detect sequence variation in two non-overlapping fragments of the control region of 32 individuals of P. bogaraveo. To assess the sensitivity of the method, the nucleotide sequence of the analysed region was determined for all the specimens. The results showed that, for one of the two fragments, SSCP analysis was able to detect 100% of the underlying genetic variability. In sharp contrast, nucleotide variation of the second DNA fragment was completely unresolved by SSCP under different experimental conditions. This suggests that the resolution power of SSCP is crucially dependent on the nature of the fragment subjected to the analysis; therefore, a preliminary test of the sensitivity of the method should be performed on each specific DNA fragment before starting a large-scale survey. A rationalized approach, combining the SSCP technique and a simplified sequencing procedure, is proposed for studying intraspecific polymorphism at the mtDNA control region in fish.     

Phylogeny and taxonomy of the genus Ilyodon Eigenmann, 1907 (Teleostei: Goodeidae), based on mitochondrial and nuclear DNA sequences

Taxonomy of the live‐bearing fish of the genus Ilyodon Eigenmann, 1907 (Goodeidae), in Mexico, is controversial, with morphology and mitochondrial genetic analyses in disagreement about the number of valid species. The present study accumulated a comprehensive DNA sequences dataset of 98 individuals of all Ilyodon species and mitochondrial and nuclear loci to reconstruct the evolutionary history of the genus. Phylogenetic inference produced five clades, one with two sub‐clades, and one clade including three recognized species. Genetic distances in mitochondrial genes (cytb: 0.5%–2.1%; coxI: 0.5%–1.1% and d‐loop: 2.3%–10.2%) were relatively high among main clades, while, as expected, nuclear genes showed low variation (0.0%–0.2%), with geographic concordance and few shared haplotypes among river basins. High genetic structure was observed among clades and within basins. Our genetic analyses, applying the priority principle, suggest the recognition only of Ilyodon whitei and Ilyodon furcidens, with I. cortesae relegated to an invalid species, the populations of which belong to I. whitei.     

Cytogenetic analysis of three species of the genus <Emphasis Type="Italic">Haemulon</Emphasis> (Teleostei: Haemulinae) from Margarita Island,Venezuela

This paper describes the karyotype analysis of Haemulon aurolineatum, Haemulon bonariensis and Haemulon plumierii, by Giemsa staining, C-banding, Ag-staining and fluorescent in situ hybridization (FISH), to locate the 18S and 5S rRNA genes. Diploid modal count in the three species was 2n = 48 acrocentric elements. Except for pair 24, which exhibited an unmistakable secondary constriction in all three species, it was not possible to classify them as homologous to each other because differences in chromosome size were too slight between adjacent pairs within a size-graded series. Ag-NOR clusters were located in pair 24 in the three species with signal located on the secondary constriction of these chromosomes. C-banding demonstrated that the three species share the same distribution pattern of the constitutive heterochromatin with centromeric heterochromatic blocks in the 23 chromosome pairs and a pericentromeric block in pair 24 which is coincident with the NORs. FISH experiments showed that 18S rDNA sequences were located coincident with the Ag-NOR site in the three species; however, differences in both the number and chromosome distribution of 5S-rDNA cluster were detected among them. Our data suggest that chromosome evolution of Haemulon has been preserved from major changes in the karyotypic macrostructure, whereas microstructural changes have occurred.     

Sex chromosome system ZZ/ZW in Apareiodon hasemani Eigenmann, 1916 (Characiformes,Parodontidae) and a derived chromosomal region

Parodontidae fish show few morphological characteristics for the identification of their representatives and chromosomal analyses have provided reliable features for determining the interrelationships in this family. In this study, the chromosomes of Apareiodon hasemani from the São Francisco River basin, Brazil, were analyzed and showed a karyotype with 2n = 54 meta/submetacentric chromosomes, and a ZZ/ZW sex chromosome system. The study revealed active NORs located on pair 11 and additional 18S rDNA sites on pairs 7 and 22. The 5S rDNA locus was found in pair 14. It showed a pericentric inversion regarding the ancestral condition. The satellite DNA pPh2004 was absent in the chromosomes of A. hasemani, a shared condition with most members of Apareiodon. The WAp probe was able to detect the amplification region of the W chromosome, corroborating the common origin of the system within Parodontidae. These chromosomal data corroborate an origin for the ZW system of Parodontidae and aid in the understanding of the differentiation of sex chromosome systems in Neotropical fishes.     

Karyotypic conservatism in samples of Characidium cf. zebra (Teleostei, Characiformes, Crenuchidae): Physical mapping of ribosomal genes and natural triploidy

Basic and molecular cytogenetic analyses were performed in specimens of Characidium cf. zebra from five collection sites located throughout the Tietê, Paranapanema and Paraguay river basins. The diploid number in specimens from all samples was 2n = 50 with a karyotype composed of 32 metacentric and 18 submetacentric chromosomes in both males and females. Constitutive heterochromatin was present at the centromeric regions of all chromosomes and pair 23, had additional interstitial heterochromatic blocks on its long arms. The nucleolar organizer regions (NORs) were located on the long arms of pair 23, while the 5S rDNA sites were detected in different chromosomes among the studied samples. One specimen from the Alambari river was a natural triploid and had two extra chromosomes, resulting in 2n = 77. The remarkable karyotypic similarity among the specimens of C. cf. zebra suggests a close evolutionary relationship. On the other hand, the distinct patterns of 5S rDNA distribution may be the result of gene flow constraints during their evolutionary history.     

Unexpected prey of juvenile spotted scat (Scatophagus argus) near a wharf: The prevalence of fouling organisms in stomach contents

A knowledge of fish diets can contribute to revealing the trophic role and ecological function of species in aquatic ecosystems. At present, however, there are no efficient or comprehensive methods for analyzing fish diets. In this study, we investigated the diets of juvenile Scatophagus argus collected near a wharf in Daya Bay, China, by dissection and high‐throughput sequencing (HTS) using the 18S rDNA V4 region. Microscopy disclosed large amounts of bryozoans and unrecognizable detritus. In contrast, HTS analysis indicated that the fish diets were considerably more diverse than visual inspection suggested. After eliminating fish sequences, approximately 17,000 sequences from taxa in nine phyla (Ciliophora, Bryozoa, Annelida, Bacillariophyta, Chlorophyta, Arthropoda, Dinoflagellata, Tunicata, and Phaeophyta) were identified from the analysis of stomach contents. Twenty‐one food categories were identified, most of which (95.2%) were benthic fouling organisms that could easily be collected around wharfs. These consisted of bryozoans (31.9%), ciliates (45.7%), polychaetes (14.6%), and green algae (3.0%). Therefore, to adapt to anthropogenic habitat modification, the fish had probably shifted from planktonic to benthic feeding. The prevalence of fouling organisms in the stomachs of juvenile S. argus indicates that the fish have responded to habitat changes by widening their food spectrum. This adaptation may have increased their chances of survival. The fouling organisms that inhabit highly perturbed coastal ecosystems could represent a food source for animals at higher trophic levels. Our results accordingly suggest that human activity might significantly influence fish feeding behavior and material transfer along the food chain.     

The evolution of ecologically important characters in Heliconius butterflies (Lepidoptera: Nymphalidae): a cladistic review

The biology of Heliconius butterflies has provided a rich source of data to test theories of ecological genetics, coevolution and community ecology. Many putatively adaptive characters have been discussed with reference to a phylogenetic hypothesis based on a variety of morphological and life-history traits interpreted from an evolutionary taxonomic perspective. Here, alternate interpretations of characters on the traditional tree and a more recent mitochondrial DNA cladogram with a substantially different topology are compared and contrasted. It is shown that many characters ostensibly providing support for the traditional phylogenetic hypothesis are almost equally parsimoniously distributed and in some cases more parsimoniously distributed on the mtDNA tree than on the tree inferred from those characters. Discussion of alternate evolutionary scenarios based on the mDNA-based topology is presented for pupal mating, pollen feeding, foodplant coevolution, and other ecologically significant features.     

Phylogenetic analysis of anostracans (Branchiopoda: Anostraca) inferred from nuclear 18S ribosomal DNA (18S rDNA) sequences

The nuclear small subunit ribosomal DNA (18S rDNA) of 27 anostracans (Branchiopoda: Anostraca) belonging to 14 genera and eight out of nine traditionally recognized families has been sequenced and used for phylogenetic analysis. The 18S rDNA phylogeny shows that the anostracans are monophyletic. The taxa under examination form two clades of subordinal level and eight clades of family level. Two families the Polyartemiidae and Linderiellidae are suppressed and merged with the Chirocephalidae, of which together they form a subfamily. In contrast, the Parartemiinae are removed from the Branchipodidae, raised to family level (Parartemiidae) and cluster as a sister group to the Artemiidae in a clade defined here as the Artemiina (new suborder). A number of morphological traits support this new suborder. The Branchipodidae are separated into two families, the Branchipodidae and Tanymastigidae (new family). The relationship between Dendrocephalus and Thamnocephalus requires further study and needs the addition of Branchinella sequences to decide whether the Thamnocephalidae are monophyletic. Surprisingly, Polyartemiella hazeni and Polyartemia forcipata ("Family" Polyartemiidae), with 17 and 19 thoracic segments and pairs of trunk limb as opposed to all other anostracans with only 11 pairs, do not cluster but are separated by Linderiella santarosae ("Family" Linderiellidae), which has 11 pairs of trunk limbs. All appear to be part of the Chirocephalidae and share one morphological character: double pre-epipodites on at least part of their legs. That Linderiella is part of the Polyartemiinae suggests that multiplication of the number of limbs occurred once, but was lost again in Linderiella. Within Chirocephalidae, we found two further clades, the Eubranchipus-Pristicephalus clade and the Chirocephalus clade. Pristicephalus is reinstated as a genus.     

Molecular systematics of the suborder Trogiomorpha (Insecta: Psocodea: 'Psocoptera')

Phylogenetic relationships among extant families in the suborder Trogiomorpha (Insecta: Psocodea: 'Psocoptera') were inferred from partial sequences of the nuclear 18S rDNA and Histone 3 and mitochondrial 16S rDNA genes. Analyses of these data produced trees that largely supported the traditional classification; however, monophyly of the infraorder Psocathropetae (= Psyllipsocidae + Prionoglarididae) was not recovered. Instead, the family Psyllipsocidae was recovered as the sister taxon to the infraorder Atropetae (= Lepidopsocidae + Trogiidae + Psoquillidae), and the Prionoglarididae was recovered as sister to all other families in the suborder. Character states previously used to diagnose Psocathropetae are shown to be plesiomorphic. The sister group relationship between Psyllipsocidae and Atropetae was supported by two morphological apomorphies: the presence of a paraproctal anal spine and an anteriorly opened phallosome. Based on these sequence data and morphological observations, we propose a new classification scheme for the Trogiomorpha as follows: infraorder Prionoglaridetae (Prionoglarididae), infraorder Psyllipsocetae (Psyllipsocidae), infraorder Atropetae (Lepidopsocidae, Trogiidae, Psoquillidae).  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 287–299.     

Genetic admixture of burbot (Teleostei: Lota lota) in Lake Constance from two European glacial refugia

The burbot, Lota lota, is the only freshwater species of the codfish family and has a Holarctic distribution. Pleistocene glaciations caused significant geographical differentiation in the past, but its life history characterized by winter spawning migrations over large distances is likely to homogenize populations by contemporary gene flow. We investigated the population genetic structure of 541 burbots from Lake Constance and adjacent Rhine and Danube tributaries in Europe using the entire mitochondrial DNA (mtDNA) control region and 11 microsatellites. Microsatellites revealed considerable population divergence (F(ST) = 0.26) and evidenced recent bottlenecks in two Central European rivers. In accordance to previous evidence two main phylogeographic lineages (Atlantic and Danubian) were found co-occurring at similar frequencies in Lake Constance, where they currently undergo random mating as indicated by microsatellites. The Danubian lineage contributed only a small proportion to the lake's mtDNA diversity, and probably expanded within the lake shortly after its formation approximately 10,000-15,000 BP. The larger Atlantic haplotype diversity suggested a population expansion older than the lake itself. Levels of admixture at microsatellite loci were less obvious due to their high variability, and coalescence methods were used to estimate past admixture proportions. Our results reinforce a model of a two-step colonization of Europe by burbot from an ancestral Danubian refuge, and confirm the persistence of a secondary Atlantic refuge, as proposed to exist for other freshwater fish. We conclude that the present-day burbot population in Lake Constance bears the genetic signature of both contemporary gene flow and historical separation events.