Gill‐filament ossifications: a possible morphological synapomorphy uniting the families Balitoridae and Cobitidae (Ostariophysi: Cypriniformes)

Ossifications associated with the gill filaments of members of the Balitoridae and Cobitidae are described for the first time. Although gill‐filament ossifications are common in teleosts, similar ossifications were not observed in other members of the order Cypriniformes. Their presence is interpreted as a shared and derived character uniting the families Balitoridae and Cobitidae as a monophyletic group.     

Microsatellite variation among River Sturgeons of the genus Scaphirhynchus (Actinopterygii: Acipenseridae): a preliminary assessment of hybridization*

Microsatellite variation from 13 disomic loci is reported for a total of 208 individuals of the genus Scaphirhynchus. This includes 105 individuals of the pallid sturgeon (Scaphirhynchus albus) from the lower Mississippi River, 11 pallid sturgeon from the Upper Mississippi and Missouri rivers, 65 shovelnose sturgeon (S. platorynchus) from the lower Mississippi River, six Alabama sturgeon (S. suttkusi), and 21 individuals of sturgeon identified as intermediate between S. albus and S. platorynchus. Results indicate that all five of the above population/species units are significantly differentiated from one another based on pairwise F_ST estimates. Locus Spl‐7 was diagnostic for the Alabama sturgeon and serves to further differentiate this allopatric species from other Scaphirhynchus. Classification of genotypes with and without a priori designations failed to clearly delineate the species and intermediates in the latter case but was successful for the species but not in the intermediates in the former case. The presence of six unique alleles in five of the 21 morphologically ‘intermediate’ sturgeon examined requires additional evaluation but suggests that these individuals are possibly not the result of hybridization. We hope that raising these important issues will bring all stakeholders to the table to establish a concerted effort needed for both morphological and molecular analyses to adequately address the question of hybridization and the origin of the morphological variation in these fishes.     

Molecular systematics of Scaphirhynchinae: an assessment of North American and Central Asian Freshwater Sturgeon Species

The sturgeon subfamily Scaphirhynchinae contains two genera of obligate freshwater sturgeon: Scaphirhynchus and Pseudoscaphirhynchus, from North America and Central Asia, respectively. Both genera contain morphologically variable species. A novel data set containing multiple individuals representing four diagnosable morphological variants for two species of Pseudoscaphirhynchus, P. hermanni and P. kaufmanni, was generated. These data were used to test taxonomic hypotheses of monophyly for the subfamily Scaphirhynchinae, monophyly of both Scaphirhynchus and Pseudoscaphirhynchus, monophyly of P. hermanni and P. kaufmanni, and monophyly of the recognized morphological variants. Monophyly of the subfamily Scaphirhynchinae is consistently rejected by all phylogenetic reconstruction methodologies with the molecular character set while monophyly of both river sturgeon genera is robustly supported. The molecular data set also rejects hypotheses of monophyly for sampled species of Pseudoscaphirhynchus as well as monophyly for the recognized intraspecific morphological variants. Interestingly both Scaphirhynchus and Pseudoscaphirhynchus demonstrate the same general pattern in reconstructed topologies; a lack of phylogenetic structure in the clade with respect to recognized diversity. Despite rejection of monophyly for the subfamily Scaphirhynchinae with molecular data, reconstructed hypotheses from morphological character sets consistently support monophyly for this subfamily. Disparities among the data sets, as well as reasons for rejection of monophyly for Scaphirhynchinae and species of Scaphirhynchus and Pseudoscaphirhynchus with molecular characters are examined and a decreased rate of molecular evolution is found to be most consistent with the data.     

Food habits of the endangered Alabama Sturgeon, Scaphirhynchus suttkusi Williams and Clemmer, 1991 (Acipenseridae)

The gut contents of 12 museum specimens of the federally (USA) endangered Alabama sturgeon were analyzed. This collective series represents 32% of the known museum specimens. Gut contents were dominated by aquatic insects and fishes. At the taxonomic level of insect orders, Dipterans (174.3/fish) were the most numerically abundant food item consumed, followed by Ephemeroptera (19.0/fish), Trichoptera (4.0/fish), Coleoptera (2.4/fish), and Odonata (2.0/fish). Weight, which better reflects the caloric value of food items consumed, showed a similar consumption pattern. Dipterans (12.5%) made up the largest percentage of the total weight of insect prey, followed by Ephemeroptera (8.9%), Trichoptera (6.0%), Odonata, (4.5%) and Coleoptera (0.9%). Volumetric values were substantially higher than weights for Odonata (13.4%) and Ephemeroptera (14.3%), but were comparable for Diptera (10.6%), Trichoptera (4.7%), and Coleoptera (2.2%). The diet of the Alabama sturgeon is similar to the pallid and shovelnose sturgeon, eating both aquatic invertebrates and fish. In terms of piscivory, the volume of fish in the diet of the Alabama sturgeon (34.5%) is intermediate between that of the shovelnose (0% fish) and the pallid sturgeon (60% fish). Based upon the habitat preference of the prey family assemblages present from the 12 guts examined, probable feeding habitats of this sturgeon include sandy to rocky bottoms, slow to swift water velocities, and the water column. Conservation of fish prey may be important to the survival and recovery of the Alabama sturgeon.     

Comparative neuromorphology of the telencephalon of sturgeon of the genera Acipenser, Huso and Scaphirhynchus (Actinopterygii; Acipenseridae)

Brain anatomy and structure, composition of the neurons, and cytoarchitectural maps were compared between five species of Acipenser, one species of Huso and two species of Scaphirhynchus. Morphological differences in the forebrain structure between species and genera were apparent. The evolutionary history of the Acipenseridae has been marked by an extensive mosaic radiation in the evolutionary development of the inner structure of their brains. Members of Scaphirhynchus have a very simple telencephalon structure differing significantly from that of Huso and Acipenser. It is clear that neuromorphological variation of sturgeon species will serve as an additional data useful in understanding the evolutionary processes and history associated with the speciation in Acipenseridae.     

Speciation and anagenesis in the genus Cyprinella of Mexico (Teleostei: Cyprinidae): a case study of Model III allopatric speciation

Allozyme variation at 42 presumptive gene lociis presented for members of the C. formosa species group. This group iscorroborated as a monophyletic assemblage whosecommon ancestor occupied pluvial Lake Palomasof the Guzman Basin. With increasingaridity during the Pleistocene this basin andassociated populations of this commonancestor were fragmented into several lineagesthat diverged independently of oneanother. The pattern of relationships andlevels of anagenetic change observed inindependent lineages for this clade are notconsistent with expectations of the mostcommon modes of speciation, Model I large-scalevicariance or Model II peripheralisolation. Rather, divergence in these fishlineages is consistent with the rarely observedModel III allopatric speciation. Consistentwith predictions of this model, thephylogenetic pattern recovered revealspolychotomous relationships (a hard polytomy)and varied rates of anagenetic change acrossexamined lineages.     

Mitochondrial haplotype variation in wild trout populations (Teleostei: Salmonidae) from northwestern Mexico

The variation and composition of Mexican wild trout mitochondrial DNA haplotypes throughout northwestern Mexico was determined by means of polymerase chain reaction–restriction fragment polymorphism analysis (PCR–RFLP), of one region of mitochondrial DNA between cytochrome b and the D-loop. This analysis was based on 261 specimens taken in 12 basins and four hatcheries from northwestern Mexico. From 23 haplotypes, 15 wild trout haplotypes were identified and classified in four groups: (1) one restricted to Nelson’s trout (Oncorhynchus mykiss nelsoni), (2) four restricted to Río Mayo and RíoYaqui trout (O. mykiss sspp.), (3) six to Mexican golden trout (O. chrysogaster) with two subgroups, and (4) one exclusive to Río Piaxtla trout. Distributions of native haplotypes broadly overlap the distribution of non-native hatchery rainbow trout reflecting the historical management of introductions of exotic rainbow trout and the artificial transference of these trout among basins.     

Phylogenetic Relationships of the Creek Chubs and the Spine-Fins: an Enigmatic Group of North American Cyprinid Fishes (Actinopterygii: Cyprinidae)

Phylogenetic analyses based on the complete nucleotide sequence of the mitochondrial 12S ribosomal RNA gene were performed for representatives of major North American cyprinid clades. These analyses resolved four monophyletic groups: (1) Western Clade, represented by Acrocheilus and Gila , (2) Creek Chub Clade, represented by Couesius, Hemitremia, Semotilus , and Margariscus , (3) Open Posterior Myodome Clade, represented by Campostoma, Phenacobius, Cyprinella, Notropis, Platygobio , and Rhinichthys , and (4) Plagopterin Clade, represented by Snyderichthys, Lepidomeda , and Meda . The overall results of these analyses refute previous hypotheses of relationships of North American Cyprinidae based on morphological data. Our analyses support recognition of Snyderichthys , formerly considered a subgenus of Gila, and indicate that the Plagopterin Clade is sister to the Creek Chub Clade. Furthermore, this analysis indicates that hypotheses of relationship between plagopterins and other Western taxa are unsupported and the Open Posterior Myodome Clade is a monophyletic group.     

Microanatomy of the paired‐fin pads of ostariophysan fishes (Teleostei: Ostariophysi)

Members of the teleost superorder Ostariophysi dominate freshwater habitats on all continents except Antarctica and Australia. Obligate benthic and rheophilic taxa from four different orders of the Ostariophysi (Gonorynchiformes, Cypriniformes, Characiformes, and Siluriformes) frequently exhibit thickened pads of skin along the ventral surface of the anteriormost ray or rays of horizontally orientated paired (pectoral and pelvic) fins. Such paired‐fin pads, though convergent, are externally homogenous across ostariophysan groups (particularly nonsiluriform taxa) and have been considered previously to be the result of epidermal modification. Histological examination of the pectoral and/or pelvic fins of 44 species of ostariophysans (including members of the Gonorynchiforms, Cypriniformes, Characiformes, and Siluriformes) revealed a tremendous and previously unrecognized diversity in the cellular arrangement of the skin layers (epidermis and subdermis) contributing to the paired‐fin pads. Three types of paired‐fin pads (Types 1–3) are identified in nonsiluriform ostariophysan fishes, based on differences in the cellular arrangement of the epidermis and subdermis. The paired‐fin pads of siluriforms may or may not exhibit a deep series of ridges and grooves across the surface. Two distinct patterns of unculus producing cells are identified in the epidermis of the paired‐fin pads of siluriforms, one of which is characterized by distinct bands of keratinization throughout the epidermis and is described in Amphilius platychir (Amphiliidae) for the first time. General histological comparisons between the paired fins of benthic and rheophilic ostariophysan and nonostariophysan percomorph fishes are provided, and the possible function(s) of the paired‐fin pads of ostariophysan fish are discussed. J. Morphol. 2012. © 2012 Wiley Periodicals, Inc.