Osteology of the South Asian Genus Psilorhynchus McClelland, 1839 (Teleostei: Ostariophysi: Psilorhynchidae), with investigation of its phylogenetic relationships within the order Cypriniformes

Members of the genus Psilorhynchus are small benthic fishes, commonly referred to as torrent minnows, which inhabit the fast to swift flowing water bodies of the Indo‐Burma region and the Western Ghats of Peninsular India. Despite being described scientifically in the mid 18^th century, the morphology of Psilorhynchus remains poorly known and its phylogenetic placement within the order Cypriniformes is a matter of considerable debate. In this paper the osteology of Psilorhynchus sucatio is described and illustrated in detail. Notes and/or illustrations on the osteology of 12 other species of Psilorhynchus are also provided for the first time. A phylogenetic investigation of the position of Psilorhynchus within the order Cypriniformes is also conducted. Analysis of 127 morphological characters scored for 52 ingroup taxa (including 12 species of Psilorhynchus) and four outgroup taxa resulted in 14 equally parsimonious cladograms (287 steps long; consitency index, CI = 0.48; retention index, RI = 0.88). Psilorhynchus is recovered as the sister group to the family Cyprinidae, and is regarded as a member of the superfamily Cyprinoidea, which forms the sister group to the Cobitoidea (including all other cypriniform families). The sistergroup relationship between Psilorhynchus and Cyprinidae is supported by eight derived characters (five of which are homoplastic within the order Cypriniformes). The monophyly of Psilorhynchus is supported by 16 derived characters (eight of which are homoplastic within Cypriniformes). Three species groups of Psilorhynchus are proposed, the Psilorhynchus balitora group (including P. amplicephalus, P. balitora, P. breviminor, P. nepalensis, P. rahmani, P. pavimentatus, and P. brachyrhynchus), the Psilorhynchus gracilis group (including P. gracilis, P. melissa, P. robustus, and P. tenura), and the Psilorhynchus homaloptera group (including P. arunachalensis, P. homaloptera, P. microphthalmus, and P. pseudecheneis). The continued use of the family group name Psilorhynchidae is recommended. Comments on the interrelationships of the Cypriniformes are also provided. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011.     

Moxostoma的磷酸葡萄糖异构酶电泳研究

用水平淀粉凝胶电泳对290尾Moxostoma属3个种的胭脂鱼进行了磷酸葡萄糖异构酶(PGI)的研究,得到10种电泳表现型(Phenotype),由A与B两个位点控制。A位点向阳极迁移,有a、b、c、d及e5个等位基因;B位点向阴极迁移,有f及g两个等位基因。种间差异明显。 不同采集地区(德克萨斯、佛罗里达及路易斯安那)的鱼类,新鲜材料、冰冻材料及雌雄之间电泳结果无差异。     

Comparison of quantitative light microscopy techniques used in diet studies of detritus-consuming omnivores

The assumptions and performances of three light microscope techniques for measuring the amount of detritus in the diets of omnivorous fish were compared: area estimation, volume estimation with subsequent estimation of weight, and weight difference determination. Accuracy of the area method depends on the improbable assumption that the volume or weight of detritus particles in the diet is directly proportional to particle area. Accuracy of the difference determination is limited by the accumulation of measurement errors associated with each component of the calculation. Direct estimation of volume with subsequent conversion to ash free dry weight requires the fewest assumptions and offers greatest accuracy. Precision was greatest for the volume estimation technique and lowest for the difference determination. Time required per sample can be substantially reduced by using a digitizer for measurement and a microcomputer for calculations.     

Physiological tolerances of juvenile robust redhorse, Moxostoma robustum: conservation implications for an imperiled species

The robust redhorse, Moxostoma robustum (Teleostei: Catostomidae), is an imperiled sucker native to large rivers of the Atlantic slope of the southeastern United States. Juvenile M. robustum were tested for tolerances to temperature, salinity, pH, and hypoxia in order to evaluate basic early life-history requirements. Static (acute) tests resulted in estimates of mean lower temperature tolerances (5.3–19.4 °C) that varied with prior thermal acclimation and indicated no apparent difference in tolerance among fish 30, 60, and 90 days old. Fish acclimated to 20 °C and 30 °C had significantly different mean critical thermal maxima (34.9 °C and 37.2 °C, respectively) and exhibited pronounced increased opercular ventilation rates with elevated temperatures. Fish exposed to acute and chronic increases in salinity showed unusual patterns of mortality above the isosmotic point (9 ppt) that reflected possible differences in body mass and prior acclimation conditions (i.e., water ionic composition); small fish and those held in soft water were the least tolerant of increased salinity. Abrupt exposure to extreme pH values resulted in greater than 50% mortality at pH values below 4.3 and above 9.5 within a 96-hour period. Fish exposed to progressive hypoxia utilized aquatic surface respiration at a mean oxygen concentration of 0.72–0.80 mg O₂ l^-1 (20 °C and 30 °C acclimated fish, respectively), and lost equilibrium at 0.54–0.57 mg O₂ l^-1. Juvenile M. robustum are moderately tolerant of a wide range of ambient physicochemical parameters, but further research is needed to determine how both abiotic and biotic factors have contributed to population decline and extirpation of this species.     

Morphological variation in the Weberian apparatus of Cypriniformes

Cypriniformes (which includes the minnows, carps, loaches, algae-eaters, stone loaches, and suckers) is a morphologically diverse and incredibly speciose order of teleosts. It has been suggested that a number of evolutionary innovations, key to improved hearing and feeding, have played an important role in cypriniform fishes' success. One such innovation, the Weberian apparatus, is a novel assemblage of vertebral elements and modified ribs that relay and amplify sound pressure changes from the gas bladder to the inner ear. The Weberian apparatus unites Cypriniformes with other major orders into an extremely species-rich group of fishes, the Otophysi. Together, otophysan fishes comprise one of the largest groups of fishes in the world, as well as the majority of freshwater fishes. Here we present a detailed comparison of the Weberian apparatus in a number of cypriniform families using cleared and stained specimens. We present data regarding inter- and intrafamilial morphological variation within Cypriniformes. With few, but evolutionarily important, exceptions we find that diagnostic features of the Weberian apparatus characterize each family. Interspecific variation within each of the families Balitoridae, Gyrinocheilidae, and Catostomidae is only slight, whereas variation among subfamilies within Cyprinidae and Cobitidae is far more significant. This comparative study identifies a number of distinct morphologies, some of which appear highly correlated with ecological niche. For example, inhabiting swift-moving waters appears to be a key factor in the encapsulation of the anterior gas bladder in some cobitids, balitorids, and gobionin cyprinids.     

Phylogenetic relationships of Moxostoma and Scartomyzon (Catostomidae) based on mitochondrial cytochrome b sequence data

A recent phylogenetic study based on morphological, biochemical and early life history characters resurrected the genus Scartomyzon (jumprock suckers, c . eight−10 species) from Moxostoma (redhorse suckers, c . 10–11 species) and advanced the understanding of relationships among species in these two genera, and the genealogical affinities of these genera with other evolutionary lineages within the tribe Moxostomatini in the subfamily Catostominae. To further examine phylogenetic relationships among moxostomatin suckers, the complete mitochondrial (mt) cytochrome b gene was sequenced from all species within this tribe and representative outgroup taxa from the Catostomini and other catostomid subfamilies. Phylogenetic analysis of gene sequences yielded two monophyletic clades within Catostominae: Catostomus + Deltistes + Xyrauchen + Erimyzon + Minytrema and Moxostoma + Scartomyzon + Hypentelium + Thoburnia . Within the Moxostomatini, Thoburnia was either unresolved or polyphyletic; Thoburnia atripinnis was sister to a monophyletic Hypentelium . In turn, this clade was sister to a monophyletic clade containing Scartomyzon and Moxostoma . Scartomyzon was never resolved as monophyletic, but was always recovered as a polyphyletic group embedded within Moxostoma , rendering the latter genus paraphyletic if ' Scartomyzon ' continues to be recognized. Relationships among lineages within the Moxostoma and' Scartomyzon 'clade were resolved as a polytomy. To better reflect phylogenetic relationships resolved in this analysis, the following changes to the classification of the tribe Moxostomatini are proposed: subsumption of' Scartomyzon 'into Moxostoma ; restriction of the tribe Moxostomatini to Moxostoma ; resurrect the tribe Erimyzonini, containing Erimyzon and Minytrema , classified as incertae sedis within Catostominae; retain the tribe Thoburniini.     

Genetic relationships among the torrent suckers, genus Thoburnia

Population samples of the three species of the tetraploid catostomid genus Thoburnia were electrophoretically studied to detect isozyme variability resolving the products of 54 alleles encoded by 34 presumptive loci. Species of Thoburnia express only about one-third of their loci in duplicate suggesting a high level of evolutionary advancement within the Catostomidae. Thoburnia hamiltoni and T. rhothoeca are phenetically close compared to T. atripinne. Cladistic analyses of the genetic data reveal that T. rhothoeca exhibits a relatively high degree of plesiomorphy while T. hamiltoni and T. atripinne represent extremes of separate lineages. A phylogenetic treatment of the genetic data yields a hypothetical phylogeny congruent with that based on morphological criteria.     

No Genetic Evidence for Hybridization Between Rio Grande Sucker, Catostomus Plebeius, and the Introduced White Sucker, Catostomus Commersoni, in the Rio Grande

Hybridization with the introduced white sucker, Catostomus commerson, has been blamed in part for the decline of the Rio Grande sucker, C. plebeius, in the upper Rio Grande basin of Colorado and New Mexico but without convincing evidence. Here we report results from a genetic study of hybridization between the two species across their sympatric range in New Mexico. We used two nuclear microsatellite markers and one mitochondrial DNA marker to identify hybrids. These genetic methods detected no F1 or backcross hybrids in larvae, young-of-the-year or adults from the upper Rio Grande basin. This indicates that hybridization between the two species occurs rarely, if ever.     

Spatial and temporal segregation of spawning habitat by catostomids in the Savannah River, Georgia and South Carolina, U.S.A.

Spawning aggregations of five species of catostomids were observed on the two mid-channel gravel bars of the Savannah River, Georgia and South Carolina, in 2004 and 2005 to assess the degree of spatial and temporal overlap in the use of this habitat and determine the habitat preferences leading to segregation. Spawning catostomids showed a considerable amount of temporal overlap in their use of these mid-channel gravel bars. The observed temporal overlap was consistent between 2004 and 2005 and corresponded to temperatures at which species were present. The distribution of catostomids was not uniform at the upstream gravel bar. Carpsuckers Carpiodes sp., spotted sucker Minytrema melanops and robust redhorse Moxostoma robustum both demonstrated some spatial overlap with notchlip redhorse Moxostoma collapsum ; however, their overall distributions were different from one another. Northern hogsucker Hypentelium nigricans was present across the gravel bars, apparently as an egg predator. Spawning catostomids segregated based on flow, depth, slope and substratum size. Whether due to limited habitat availability or changes in the timing of reproduction due to altered cues, temporal and spatial overlap occurs between spawning catostomids despite the apparent partitioning of available spawning habitat. It is unclear, however, if this overlap results in excessive mortality in the early life-history stages of these species. Results suggest spatial overlap among catostomid species was minimized due to species spawning in areas within a narrow range of conditions. Intraspecific interactions such as nest site superimposition or disturbance may be a concern.     

Differences in Swimming Ability and Behavior in Response to High Water Velocities among Native and Nonnative Fishes

We conducted swimming performance tests on native and nonnative fishes commonly found in Arizona streams to evaluate the extent of differences in swimming ability among species. Fishes with similar mean lengths were subjected to stepwise increases in water velocity in a laboratory swim tunnel until fish could no longer maintain position. Nonnative fathead minnows Pimephales promelas and red shiners Cyprinella lutrensis exhibited swimming abilities similar to native longfin dace Agosia chrysogaster, speckled dace Rhinichthys osculus and spikedace Meda fulgida. Nonnative mosquitofish Gambusia affinis exhibited swimming ability similar to native Gila topminnows Poeciliopsis occidentalis. Desert suckers Catostomus clarki, bluehead suckers Catostomus discobolus and speckled dace exhibited behavioral responses to high water velocities that may confer energetic advantages in swift water. Differences in swimming ability do not appear to adequately explain the disproportionate removal of nonnative fishes via flooding. Behavioral responses to high flows are more likely the mechanism that allows native fish to persist in streams during flood events.