Characteristics of the reparative regeneration of fins in the polypterid fish (Polypteridae,Actinopterygii)

Epimorphic regeneration of fins was studied in different ray-finned fishes (Actinopterygii), but species representing the phylogenetically basal lineages of the taxon have remained outside the attention of researchers. Information on the regenerative abilities of these groups is important both for understanding the evolutionary origins of the epimorphic regeneration phenomenon and for assessing the universality of regenerative potencies in Actinopterygii. Addressing this problem, we studied for the first time fin regeneration in two members of the archaic family Polypteridae: the ropefish (Erpetoichthys calabaricus) and the Senegal bichir (Polypterus senegalus). Along with the ability to regenerate the bony rays of fins, widespread among Actinopterygii, polypterids show the ability to effectively regenerate the endoskeleton and musculature of their fins. This unusual feature allows us to suggest polypterids as new model organisms for the study of the mechanisms of vertebrate limb regeneration.     

Polypteridae (Actinopterygii: Cladistia) and DANA-SINEs insertions

SINE sequences are interspersed throughout virtually all eukaryotic genomes and greatly outnumber the other repetitive elements. These sequences are of increasing interest for phylogenetic studies because of their diagnostic power for establishing common ancestry among taxa, once properly characterized. We identified and characterized a peculiar family of composite tRNA-derived short interspersed SINEs, DANA-SINEs, associated with mutational activities in Danio rerio, in a group of species belonging to one of the most basal bony fish families, the Polypteridae, in order to investigate their own inner specific phylogenetic relationships. DANA sequences were identified, sequenced and then localized, by means of fluorescent in situ hybridization (FISH), in six Polypteridae species (Polypterus delhezi, P. ornatipinnis, P. palmas, P. buettikoferi P. senegalus and Erpetoichthys calabaricus) After cloning, the sequences obtained were aligned for phylogenetic analysis, comparing them with three Dipnoan lungfish species (Protopterus annectens, P. aethiopicus, Lepidosiren paradoxa), and Lethenteron reissneri (Petromyzontidae)was used as outgroup. The obtained overlapping MP, ML and NJ tree clustered together the species belonging to the two taxonomically different Osteichthyans groups: the Polypteridae, by one side, and the Protopteridae by the other, with the monotypic genus Erpetoichthys more distantly related to the Polypterus genus comprising three distinct groups: P. palmas and P. buettikoferi, P. delhezi and P. ornatipinnis and P. senegalus. In situ hybridization with DANA probes marked along the whole chromosome arms in the metaphases of all the Polypteridae species examined.     

A new polypterid fish: Polypterus faraou sp. nov. (Cladistia, Polypteridae) from the Late Miocene, Toros-Menalla, Chad

Polypterus faraou sp. nov. (Cladistia, Polypteridae) from the Late Miocene of Toros-Menalla (western Djourab, Chad) is described on the basis of a subcomplete articulated skeleton preserved in three dimensions. This is the first time such a complete fossil polypterid skeleton has been described. It is the only verifiable fossil record for the genus Polypterus . P. faraou closely resembles P. bichir and P. endlicheri , extant fish found in the Chad–Chari system. Intrarelationships among the polypterids are not yet resolved: however, P. faraou shows a primitive shape of the body and a primitive shape of the opening of the lateral line on the scales, similar to that of three living species ( P. bichir , P. endlicheri and P. ansorgii ).  © 2006 The Linnean Society of London, Zoological Journal of the Linnean Society , 2006, 146 , 227–237.     

Cytogenetic analysis in Polypterus ornatipinnis (Actinopterygii, Cladistia, Polypteridae) and 5S rDNA

Polypteridae is a family of archaic freshwater African fish that constitute an interesting subject for the study of the karyological evolution in vertebrates, on account of their primitive morphological characters and peculiar relationships with lower Osteichthyans. In this paper, a cytogenetic analysis on twenty specimens of both sexes of Polypterus ornatipinnis the ornate "bichir", coming from the Congo River basin, was performed by using both classical and molecular techniques. The karyotypic formula (2n=36; FN=72) was composed of 26 M+10 SM. The Alu I banding, performed to characterize heterochromatin in this species, was mainly centromeric. Both the chromosome location of the ribosomal 5S and 18S rRNA genes were examined by using Ag-NOR, classical C-banding, CMA(3) staining and FISH. CMA(3) marked all centromerical regions and showed the presence of two GC rich regions on the p arm of the chromosome pair n°1 and on the q arm of the pair n°14. Staining with Ag-NOR marked the only telomeric region of the chromosome n°1 p arm. After PCR, the 5S rDNA in this species was cloned, sequenced and analyzed. In the 665bp 5S rDNA sequence of P.ornatipinnis, a conserved 120bp gene region for the 5S rDNA was identified, followed by a non-transcribed variable spacer (NTS) which included simple repeats, microsatellites and a fragment of a non-LTR retrotransposon R-TEX. FISH with 5S rDNA marked the subtelomeric region of the q arm of the chromosome pair n°14, previously marked by CMA(3). FISH with 18S rDNA marked the telomeric region of the p arm of the pair n°1, previously marked both by Ag-NOR and CMA(3). The (GATA)(7) repeats marked the telomeric regions of all chromosome pairs, with the exclusion of the n°1, n°3 and n°14; hybridization with telomeric probes (TTAGGG)(n) showed signals at the end of all chromosomes. Karyotype evolution in Polypterus genus was finally discussed, including the new data obtained.     

Cellular and molecular processes of regeneration, with special emphasis on fish fins

The phenomenon of 'epimorphic regeneration', a complete reformation of lost tissues and organs from adult differentiated cells, has been fascinating many biologists for many years. While most vertebrate species including humans do not have a remarkable ability for regeneration, the lower vertebrates such as urodeles and fish have exceptionally high regeneration abilities. In particular, the teleost fish has a high ability to regenerate a variety of tissues and organs including scales, muscles, spinal cord and heart among vertebrate species. Hence, an understanding of the regeneration mechanism in teleosts will provide an essential knowledge base for rational approaches to tissue and organ regeneration in mammals. In the last decade, small teleost fish such as the zebrafish and medaka have emerged as powerful animal models in which a variety of developmental, genetic and molecular approaches are applicable. In addition, rapid progress in the development of genome resources such as expressed sequence tags and genome sequences has accelerated the speed of the molecular analysis of regeneration. This review summarizes the current status of our understanding of the cellular and molecular basis of regeneration, particularly that regarding fish fins.     

Das geruchsorgan der Polypteridae (Pisces,Brachiopterygii)

The olfactory organ of the Polypteridae (Brachiopterygii) was studied histologically. It differs fundamentally from the olfactory organ of the Teleostei (Actinopterygii) and resembles that of Latimeria (Crossopterygii). The size of the olfactory organ indicates that the Polypteridae are macrosmatic.

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Mit dankenswerter Unterstützung durch die Deutsche Forschungsgemeinschaft.     

Zenopsis conchifera (Lowe, 1852) (Pisces, Actinopterygii, Zeidae): a new alien fish in the Mediterranean Sea

The first documented occurrence of a silvery John dory, Zenopsis conchifera , in the Mediterranean Sea is reported. A female (645 mm total length, 3296 g body mass) of Z. conchifera was caught in July 2006 by a commercial bottom trawler off the northern Tunisian coast (central Mediterranean Sea).     

A single micropyle in the eggs of the most basal living actinopterygian fish, Polypterus (Actinopterygii, Polypteriformes)

Breeding of Polypterus , the most basal living actinopterygian, provided the opportunity to study the surface structure of its eggs with SEM for the first time. The investigation revealed the previously overlooked presence of a micropyle at the animal egg pole, thus rejecting recent textbook belief that the eggs of Polypterus slack a micropyle. Comparison with data for other gnathostomes demonstrates that eggs with a micropyle are a further synapomorphy for Actinopterygii and confirm membership of the Cladistia in that group.     

Major issues in the origins of ray‐finned fish (Actinopterygii) biodiversity

Ray‐finned fishes (Actinopterygii) dominate modern aquatic ecosystems and are represented by over 32000 extant species. The vast majority of living actinopterygians are teleosts; their success is often attributed to a genome duplication event or morphological novelties. The remainder are ‘living fossils’ belonging to a few depauperate lineages with long‐retained ecomorphologies: Polypteriformes (bichirs), Holostei (bowfin and gar) and Chondrostei (paddlefish and sturgeon). Despite over a century of systematic work, the circumstances surrounding the origins of these clades, as well as their basic interrelationships and diagnoses, have been largely mired in uncertainty. Here, I review the systematics and characteristics of these major ray‐finned fish clades, and the early fossil record of Actinopterygii, in order to gauge the sources of doubt. Recent relaxed molecular clock studies have pushed the origins of actinopterygian crown clades to the mid‐late Palaeozoic [Silurian–Carboniferous; 420 to 298 million years ago (Ma)], despite a diagnostic body fossil record extending only to the later Mesozoic (251 to 66 Ma). This disjunct, recently termed the ‘Teleost Gap’ (although it affects all crown lineages), is based partly on calibrations from potential Palaeozoic stem‐taxa and thus has been attributed to poor fossil sampling. Actinopterygian fossils of appropriate ages are usually abundant and well preserved, yet long‐term neglect of this record in both taxonomic and systematic studies has exacerbated the gaps and obscured potential synapomorphies. At the moment, it is possible that later Palaeozoic‐age teleost, holostean, chondrostean and/or polypteriform crown taxa sit unrecognized in museum drawers. However, it is equally likely that the ‘Teleost Gap’ is an artifact of incorrect attributions to extant lineages, overwriting both a post‐Palaeozoic crown actinopterygian radiation and the ecomorphological diversity of stem‐taxa.     

The occipital region in the basal bony fish Erpetoichthys calabaricus (Actinopterygii: Cladistia)

Erpetoichthys calabaricus has unusual cranio‐vertebral anatomy, with an occipital centrum forming a component part of the compound basiexoccipital bone, and a ‘free‐floating’ occipital neural arch that differs from accessory arches found in some teleosts. The occipital neural arch bears autapomorphic lateral projections that articulate with small rod‐like bones resembling the spatial relationship of parapophyses and ribs, a feature normally restricted to vertebral centra. Based on analyses of cleared and stained specimens, computed tomography and histology, it is hypothesized that the lateral projections and associated rod‐shaped bones are structures that share developmental homologies to the unique ‘dorsal ribs’ of Polypteridae.     

Interrelationships of Gasterosteiformes (Actinopterygii,Percomorpha)

Phylogenetic relationships of Gasterosteiformes were studied using osteological examination of representatives of 11 families of gasterosteiform fishes, as ingroups, and 5 families of other smegmamorph fishes (Atheriniformes, Elassomatiformes, and Synbranchiformes), as outgroups. Based on phylogenetic analysis of 110 informative osteological characters, nine synapomorphies were found to unite all Gasterosteiformes and support was provided to the hypothesis that the order Gasterosteiformes (including Hypoptychidae and Indostomidae) is a monophyletic group. Furthermore, based on the synapomorphies provided for the subgroups, three suborders in Gasterosteiformes are recognized: Hypoptychoidei, Gasterosteoidei, and Syngnathoidei.     

Regeneration of the caudal and pectoral fins of a bony fish, Gambusia (Haplochilus) schoelleri

The study showed that excision of the caudal fin at basal level was followed by complete regeneration in one and a half months, whereas if it was amputated at mid-fin level, complete regeneration took two months. The findings confirm that the greater the extent of amputation, the faster the rate of regeneration. In the case of the pectoral fin, only part of which was removed, it was found that the fin completely regenerated, with recovery of its original pattern, within two months after amputation.     

Brain Structure in Calamoichthys calabaricus Smith 1865 (Polypteridae,Brachiopterygii)

The brain of Calamoichthys calabaricus is reconstructed including the arrangement of the parts of the brain and the cranial nerves and their nuclei. Histologically, the analysis includes structure of the rhombencephalon with its cranial and tegmental nuclei, and the cerebellum.     

Re‐evaluation of the ontogeny and reproductive biology of the Triassic fish Saurichthys (Actinopterygii,Saurichthyidae)

Viviparity has evolved independently at least 12 times in ray‐finned fishes. However, the fossil record of actinopterygian viviparity is poor, with only two documented occurrences. Both of these are from the non‐teleost actinopterygian Saurichthys, and include S. curionii and S. macrocephalus from the Middle Triassic Meride Limestone (Monte San Giorgio, Switzerland). Here, we present new data on the reproductive biology of these species, giving unprecedented insights into their life‐history. Based on positional and preservational criteria, six specimens were identified as unambiguously gravid. Embryos were positioned dorsal to the gastrointestinal tract, parallel to the axial skeleton and to each other, in the posterior two‐thirds of the abdominal region. A minimum of 16 embryos are preserved in the most fecund females and, based on the largest preserved embryos and smallest preserved neonates, birth must have occurred at 7–12% of maternal fork length. Embryonic crania and teeth are relatively well‐ossified, however ossification of the parietal region is delayed. In the postcranium, the median scale rows and lepidotrichia are ossified, but not the lateral scale rows. Ossified squamation and gradual allometric growth suggests that neonates did not undergo metamorphosis and were relatively precocial. When considered in a phylogenetic context, neither live birth nor internal fertilization appears to represent the primitive state for saurichthyid fishes.     

A basal Pachyrhizodontid fish (Actinopterygii, Teleostei) from the Lower Cretaceous of the Tlayúa Quarry, Central Mexico

Michin csernai gen. et sp. nov. from the Early Cretaceous (Albian) limestones of the Tlayúa Quarry, Puebla State, Central Mexico, is assigned to the Teleost clade Pachyrhizodontoidei as it possesses the enlarged inner premaxillary tooth, which is a unique synapomorphy of this clade. Additionally, the occurrence of relatively primitive characters (e.g., united parietals, angular and articular completely fused, caudal fin with five uroneurals) suggests that Michin csernai represents the most basal representative of the pachyrhizodontids.