The relationship between ontogeny, morphology, and diet in the Chinese hook snout carp (Opsariichthys bidens)

The relationship of changes of body and mouth shape with diet during ontogeny in the Chinese hook snout carp Opsariichthys bidens was examined. Shape changes were analyzed using geometric morphometrics. Body shape changed from a shallow body to a deep body as size increased. Similarly, the head of O. bidens changed from an upward-pointing direction to a downward-pointing directing as size increased. The position of the eye also changed during ontogeny, with large individuals having an eye situated higher on the head than small individuals. The conspicuous symphyseal knob on the lower jaw of O. bidens results in a typical zigzag pattern of the jaw. The zigzag pattern became more pronounced as fish grew larger. No difference in body shape or jaw shape was found between males and females. The shape changes were associated with changes in diet, suggesting that diet choice over the course of ontogeny has a strong impact on body shape. Benthic macroinvertebrates and zooplankton dominated the diet of small individuals, medium-size individuals specialized in benthic macroinvertebrates, and fish dominated the diet of large individuals.     

The complete mitochondrial genome of the Chinese hook snout carp Opsariichthys bidens (Actinopterygii: Cypriniformes) and an alternative pattern of mitogenomic evolution in vertebrate

The complete mitochondrial genome sequence of the Chinese hook snout carp, Opsariichthys bidens, was newly determined using the long and accurate polymerase chain reaction method. The 16,611-nucleotide mitogenome contains 13 protein-coding genes, two rRNA genes (12S, 16S), 22 tRNA genes, and a noncoding control region. We use these data and homologous sequence data from multiple other ostariophysan fishes in a phylogenetic evaluation to test hypothesis pertaining to codon usage pattern of O. bidens mitochondrial protein genes as well as to re-examine the ostariophysan phylogeny. The mitochondrial genome of O. bidens reveals an alternative pattern of vertebrate mitochondrial evolution. For the mitochondrial protein genes of O. bidens, the most frequently used codon generally ends with either A or C, with C preferred over A for most fourfold degenerate codon families; the relative synonymous codon usage of G-ending codons is greatly elevated in all categories. The codon usage pattern of O. bidens mitochondrial protein genes is remarkably different from the general pattern found previously in the relatively closely related zebrafish and most other vertebrate mitochondria. Nucleotide bias at third codon positions is the main cause of codon bias in the mitochondrial protein genes of O. bidens, as it is biased particularly in favor of C over A. Bayesian analysis of 12 concatenated mitochondrial protein sequences for O. bidens and 46 other teleostean taxa supports the monophyly of Cypriniformes and Otophysi and results in a robust estimate of the otophysan phylogeny.     

Mitochondrial diversity of Opsariichthys bidens (Teleostei, Cyprinidae) in three Chinese drainages

We describe the phylogeographic structure of 28 Chinese populations of the cyprinid Opsariichthys bidens across three main Chinese river drainages. Our study is based on the phylogenetic analysis of the complete mitochondrial cytochrome b gene (1140 bp). We combined this analysis with population processes inferred from nested clade analysis (NCA) and mismatch distributions. Both analyses showed that Chinese O. bidens consists of five mtDNA lineages (Opsariichthys 1-5) with high genetic divergence among them. Molecular divergences (TrN+G) higher than 20% among the Opsariichthys 1-5 mtDNA lineages suggest a taxonomic underestimation at the species level. About 92% of the genetic variance among samples was explained by differences among Opsariichthys mtDNA lineages. Drainage-restricted haplotypes with high frequencies and moderate nucleotide diversity show that Opsariichthys populations have evolved independently. NCA results were congruent with the phylogeny, and unimodal mismatch distributions with negative Tajima's D values suggest population expansions in some Opsariichthys lineages. The phylogeographic structure of the Opsariichthys 1-5 mtDNA lineages appears to be related to their long-term interruption of gene flow (theta(ST)>0.97). Our results suggested that fragmentation of ancestral ranges might have caused Opsariichthys diversification in Chinese waters. However, current distribution of common haplotypes across the Yangtze and Pearl drainages suggests a recent river connection that could have favoured gene flow across drainages. Overall, the results indicated that the richness of current Asian widespread species might have been underestimated, and that the cyprinid populations of O. bidens in the Yangtze, Pearl and Hai He drainages may correspond to five species.     

Habitat-specific morphological variation among threespine sticklebacks (Gasterosteus aculeatus) within a drainage basin

Habitat-specific morphological variation, often corresponding to resource specialization, is well documented in freshwater fishes. In this study we used landmark based morphometric analyses to investigate morphological variation among threespine sticklebacks (Gasterosteus aculeatus L.) from four interconnected habitat types within a single lowland drainage basin in eastern England. These included the upper and lower reaches of the river, the estuary, a connected ditch network and a coastal salt marsh. We found significant habitat-specific differences in morphology, with three axes of variation describing differences in orbit diameter, body depth, caudal peduncle shape and pectoral fin positioning as well as variation in relative dorsal and pelvic spine size. Interestingly, the ditch system, an artificial and heavily managed habitat, is populated by sticklebacks with a characteristic morphology, suggesting that human management of habitats can in some circumstances lead to morphological variation among the animals that inhabit them. We discuss the mechanisms that conceivably underlie the observed morphological variation and the further work necessary to identify them. Finally, we consider the implications of habitat-specific body shape variation for the behavioural ecology of this ecologically generalist species.     

Comparative phylogeography of Zacco platypus and Opsariichthys bidens (Teleostei, Cyprinidae) in China based on cytochrome b sequences

We compared the phylogenetic relationships and the population structure of the sympatric cyprinids Opsariichthys bidens and Zacco platypus across the Yangzte, Pearl and Hai He drainages in Mainland China. We used the mitochondrial cytochrome b gene to evaluate their phylogeographical structure and to discuss further systematic implications. We sequenced 71 new individuals of Z. platypus to add to a previous study and to construct a geographically comparable data set with O. bidens (Mol. Phylogenet. Evol. 31, 2004, 192; Mol. Phylogenet. Evol. 37, 2005, 920). Phylogeographic analysis of Z. platypus identified two additional mtDNA lineages (Zacco E and F) in addition to the previously recovered lineages (Zacco A–D). The geographical range of the Zacco A was extended across the Pearl drainage, broadening considerably the previous distribution that was circumscribed to the Yangtze drainage. Our results show high molecular divergence between all Zacco A–F mtDNA lineages (mean TrN + I + G distance 17.7%, range 4.4–30.8%), and the population analyses showed that most of the genetic variation was found among major river tributaries (90.2%). Values of θ_ST higher than 0.97 corroborated this interruption of gene flow between Zacco A–F mtDNA lineages. Nested clade analysis results were also concordant with the phylogenetic relationships recovered. We found similar phylogeographic patterns in Z. platypus and O. bidens: they exhibited two widespread and common lineages (Zacco A and Opsariichthys 1) ranging across the Yangtze and Pearl drainages, and both taxa had Northern lineages (Zacco F and Opsariichthys 5) clearly differentiated. Similar phylogeographic patterns suggest that common historical factors have shaped current Zacco and Opsariichthys diversity. High genetic distances and θ_ST values suggested that differentiation of Zacco A–F mtDNA lineages and Opsariichthys 1–5 was not recent and was probably favoured by old geological events. However, population parameters and low genetic differentiation inside Zacco A and Opsariichthys 1 suggest a recent gene flow across river drainages. Mitochondrial‐based phylogenies for the combined data sets of Zacco A–F and Opsariichthys 1–5 mtDNA lineages always recovered both taxa as paraphyletic, highlighting the notion that their current systematics need a revision.     

Habitat-specific adaptation of immune responses of stickleback (Gasterosteus aculeatus) lake and river ecotypes

Freshwater populations of three-spined sticklebacks (Gasterosteus aculeatus) in northern Germany are found as distinct lake and river ecotypes. Adaptation to habitat-specific parasites might influence immune capabilities of stickleback ecotypes. Here, naive laboratory-bred sticklebacks from lake and river populations were exposed reciprocally to parasite environments in a lake and a river habitat. Sticklebacks exposed to lake conditions were infected with higher numbers of parasite species when compared with the river. River sticklebacks in the lake had higher parasite loads than lake sticklebacks in the same habitat. Respiratory burst, granulocyte counts and lymphocyte proliferation of head kidney leucocytes were increased in river sticklebacks exposed to lake when compared with river conditions. Although river sticklebacks exposed to lake conditions showed elevated activation of their immune system, parasites could not be diminished as effectively as by lake sticklebacks in their native habitat. River sticklebacks seem to have reduced their immune-competence potential due to lower parasite diversity in rivers.     

Microsatellite analysis of variation among wild,domesticated,and genetically improved populations of blunt snout bream(Megalobrama amblycephala)

In the present study,the genetic diversity of one selected strain(Pujiang No.1),two domesticated populations(GA and HX)and four wild populations(LZ,YN,SS and JL)of blunt snout bream(Megalobrama amblycephala)was analyzed using 17microsatellite markers.The results showed that an average of 4.88-7.65 number of alleles(A);an average of 3.20-5.33 effective alleles(Ne);average observed heterozygosity(Ho)of 0.6985-0.9044;average expected heterozygosity(He)of 0.6501-0.7805;and the average polymorphism information content(PIC)at 0.5706-0.7226.Pairwise FST value between populations ranged from0.0307-0.1451,and Nei’s standard genetic distance between populations was 0.0938-0.4524.The expected heterozygosities in the domesticated populations(GA and HX)were significantly lower than those found in three wild populations(LZ,SS and JL),but no difference was detected when compared with the wild YN population.Likewise,no difference was found between the four wild populations or two domesticated populations.The expected heterozygosity in Pujiang No.1 was higher than the two domesticated populations and lower than the four wild populations.Regarding pairwise FST value between populations,permutation test P-values were significant between the GA,HX and PJ populations,but not between the four wild populations.These results showed that the expected heterozygosity in the selected strain of blunt snout bream,after seven generations of selective breeding,was lower than that of wild populations,but this strain retains higher levels of genetic diversity than domesticated populations.The genetic differences and differentiation amongst wild populations,domesticated populations and the genetically improved strain of blunt snout bream will provide important conservation criteria and guide the utilization of germplasm resources.     

Thermoregulatory variation among populations of bats along a latitudinal gradient

Most studies of hibernation physiology sample individuals from populations within a single geographic area, yet some species have large ranges meaning populations likely experience area-specific levels of energetic challenges. As well, few studies have assessed within-season variation. Since physiological adjustments often are influenced by environmental factors, and the types of environments vary with geography, we expected variance in hibernation patterns among geographically separated populations. Our specific goal was to measure intraspecific variation in torpid metabolic rate (TMR) and body temperature (T _b) as a function of ambient temperature (T _a) for a non-migratory and migratory species to determine whether there is a continuum in physiological responses based on latitude. We chose big brown (Eptesicus fuscus) and eastern red bats (Lasiurus borealis) as model species and sampled individuals from populations throughout each species’ winter range. In both species, individuals from southern populations maintained higher TMR at cooler T _as and lower TMR at warmer T _as than those from northern populations. Big brown bats from southern populations regulated T _b during torpor at higher levels and there was no significant difference in T _b between populations of eastern red bats. Although metabolic responses were similar across the gradient between species, the effect was more dramatic in big brown bats. Our data demonstrate a continuum in thermoregulatory response, ranging from classic hibernation in northern populations to a pattern more akin to daily torpor in southern populations. Our research highlights the potential usefulness of bats as model organisms to address questions about within-species physiological variation in wild populations.     

Life history variation in males of the river sculpin,Cottus hangiongensis,along the course of a river

Synopsis Body size at maturity, individual growth, upstream migration and spatial stability in males of the amphidromous sculpin,Cottus hangiongensis (Cottidae), were investigated in the Daitobetsu River of southern Hokkaido, Japan. The body size of males at first maturity varied gradually along the course of the river, from approximately 70 mm SL in the lowest reaches (0.2 km up from the river mouth) to about 120 mm SL in the uppermost reaches (about 6 km up from the river mouth). The age at first maturity was estimated as 2 to 3 years in the lower reaches and as 4 to 5 years in the upper reaches. Individual growth rate tended to increase upstream, while population density decreased. These results suggest that the male life-history pathway varies along the course of the river and so allows one to consider the relationships to the polygynous mating system of this species in terms of current hypotheses regarding alternative reproductive tactics.     

D-glucose permeability in river lamprey (Lampetra fluviatilis) and carp (Cyprinus carpio) erythrocytes.

1. The transport of 3-O-methyl-D-glucose (3-OMG) in lamprey and carp erythrocytes was studied. 2. In lamprey erythrocytes the half-time for the equilibration of 3-OMG was fast, approx. 8 min. In contrast, the erythrocytes of carp were almost impermeable to 3-OMG, with a half-time for equilibration of 14.2 hr. 3. 3-OMG was taken up by lamprey erythrocytes both by facilitated diffusion and simple diffusion. The presence of carrier-mediated transport was indicated by saturation kinetics and by inhibition by phloretin. The Km and Vm of the saturable component of 3-OMG transport were 1.6 mmol/l and 12.4 mmol/kg packed cells/hr. 4. Since the 3-OMG transport in carp erythrocytes showed no sign of saturation kinetics, it appears to proceed by simple diffusion only. 5. These results suggest that, as for most other teleost fish so far studied, low glucose permeability is insufficient to maintain normal energy metabolism in carp erythrocytes. In contrast, in agnathans facilitated glucose transport seems to be quite effective.     

Size variation ofAcacia caven (leguminosae) pods along a climatic gradient in Chile

A southward tendency of increment in pod-length is shown for 11 populations ofAcacia caven (Mol.) Hook et Arn. localized along a climatic gradient of increasing annual rainfall in Chile. This fact would suggest thatA. caven populations occurring in the south are in better conditions for reproduction than northern populations, since pod-length is related to the amount of seeds inside the pods. The possible bearing of this southward tendency of increasing seed production upon the expansion ofA. caven toward the more humid zones in southern Chile is discussed.     

Limited gene flow in Uca minax (LeConte 1855) along a tidally influenced river system

For crab larvae, swimming behaviors coupled with the movement of tides suggests that larvae can normally move upstream within estuaries by avoiding ebb tides and actively swimming during flood tides (i.e., flood-tide transport [FTT]). Recently, a 1-D transport model incorporating larval behavior predicted that opposing forces of river discharge and tidal amplitude in the Pee Dee River/Winyah Bay system of South Carolina, USA, could limit dispersal within a single estuary for downstream transport as well as become a dispersal barrier to recruitment of late stage larvae to the freshwater adult habitats of Uca minax (LeConte 1855). We sequenced 394-bp of the mitochondrial cytochrome apoenzyme b for 226 adult U. minax, from four locales along a 49-km stretch of the Pee Dee River/Winyah Bay estuary, above and below the boundary of salt intrusion. Results of an analysis of molecular variance (AMOVA) and an exact test of population differentiation showed a small, but statistically significant (α=0.05) population subdivision among adults of the 4 subpopulations, as well as all subpopulations being significantly differentiated (α=0.05). This pattern fitted with model predictions, which implies that larval transport within the tidally influenced river system is limited.     

Longitudinal variation in food sources and their use by aquatic fauna along a subtropical river in Taiwan

1. River food webs rely on two major food sources: autochthonous primary production within the river and allochthonous organic matter transferred to the river. We characterised the consumer communities and assessed the food sources of dominant consumers along a subtropical mountainous river (the Lanyang River of north‐eastern Taiwan) at the catchment scale from the headwater to the estuary using natural abundances of stable carbon and nitrogen isotopes. 2. The downstream transport of fine particulate organic matter (FPOM) was two orders of magnitude greater than that of coarse particulate organic matter (CPOM). Transport of both materials increased from the headwater and reached a maximum in the midstream reach. CPOM composition exhibited a gradual shift from leaves and branches in the headwater, an area characterised by high canopy cover, to algae in the midstream reaches and marsh plants in the downstream reaches. 3. Consumer communities can be classified into two regional categories: the upland category in the headwater and upstream and midstream reaches and the lowland category comprised of samples from the downstream reach and estuary. The upland category revealed a clear and gradual seasonal shift in community composition, but a seasonal shift was not apparent for the lowland category. Nutrient concentrations and water temperature were the main factors explaining longitudinal and seasonal variations. 4. The use of sources of organic matter by dominant consumers along the Lanyang River was primarily determined by their availability. Riparian C₃ plants were the major food sources in the headwater, upstream reach and estuary, but the contribution of periphyton increased in the upper midstream reach where the river flows through an agricultural area. In the lower midstream and downstream reaches, the contribution of riparian C₄ plants became dominant. 5. The trophic transfer of organic materials in the Lanyang River may be influenced by the fast current velocity and by sewage nutrient loading in the river, both of which have important implications for predicting how the functioning of subtropical river food webs will respond to human‐related changes in land use.     

Growth differences in males of the river-sculpin Cottus hangiongensis along a river course,a correlate of life-history variation

Synopsis Growth patterns of the 1982 year-class, individual growth patterns, age at sexual maturity and longevity in the river-sculpin, Cottus hangiongensis (Cottidae), were investigated along the course of the Daitobetsu River of southern Hokkaido, Japan. Slow growth occurred in males from the lower reaches, while more rapid growth was found in males from upstream areas. Age at first sexual maturity in males generally increased from 2 or 3 years in downstream areas to 4–6 years in upstream sites. Longevity was estimated as 7 years throughout the river course except in the uppermost site where it was 6 years. The growth differences evident in male C. hangiongensis are likely a result of differences in sculpin population density and/or food abundance along the river course, and are apparently reflected in variation in their life-history as well.     

Morphometric variation among river sturgeons (Scaphirhynchus spp.) of the Middle and Lower Mississippi River

Pallid sturgeon (Scaphirhynchus albus) captured in the Middle and Lower Mississippi River (i.e. below St. Louis, MO, USA) are morphologically very similar to shovelnose sturgeon (Scaphirhynchus platorynchus). Available empirical data are limited to a few studies based on low sample sizes from disjointed populations. Geneticists are currently searching for markers that will differentiate the two species, but the need for unequivocal species‐specific field characters remains. Continuation of commercial fishing for shovelnose sturgeon in some states necessitates an immediate means for accurate field identifications. Previous studies of lower basin river sturgeon classified individuals with simple morphometric character indices and interpreted intermediacy as interspecific hybridization. In this study, morphometric variation among Scaphirhynchus specimens from the Middle and Lower Mississippi River is examined for evidence of hybridization. Data are compared for large (>250‐mm standard length) hatchery‐reared and wild pallid specimens and wild shovelnose specimens. Specimens are compared using two morphometric character indices, two morphometric/meristic character indices and principal components analysis. Results indicate substantial morphological variation among pallid sturgeon below the mouth of the Missouri River. The amount of variation appears to decrease downstream in the Mississippi River. Sheared principal components analysis of morphometric data shows complete separation of shovelnose and pallid sturgeon specimens, whereas character indices indicate overlap. Both character indices and sheared principal components analysis demonstrate that pallid sturgeon in the Lower Mississippi River are morphologically more similar to shovelnose sturgeon than are pallids from the Upper Missouri River. This similarity, explained in previous studies as hybridization, may be the result of latitudinal morphometric variation and length‐at‐age differences between populations of the upper and lower extremes of the range.     

Sequence variation and gene duplication at MHC DQB loci of baiji (Lipotes vexillifer), a Chinese river dolphin

The major histocompatibility complex (MHC) is a fundamental part of the vertebrate immune system, and the high variability in many MHC genes is thought to play an important role in the recognition of parasites. Baiji (Lipotes vexillifer) is one of the most endangered species in the world. Its wild population has declined to fewer than 100 individuals and has a very high risk of becoming extinct in the near future. In this study we present a first step in the molecular characterization of a DQB-like locus of baiji by nucleotide sequence analysis of the polymorphic exon 2 segments. In the examined 172 bp sequences from a group of 18 incidentally captured or stranded individuals, 48 variable sites were determined and 43 alleles were identified, many of which were represented by only one clone. Three to seven alleles were found in each individual, suggesting gene duplications. No deletion, insertion, or exceptional stop codon was detected, suggesting these alleles function in vivo. Phylogenetic reconstruction using neighbor joining grouped the 43 alleles into two distinct lineages, differing by seven nucleotides and four amino acids. Substitutions of amino acids tend to be clustered around sites postulated to be responsible for selective peptide recognition. In the peptide-binding region (PBR) of the DQB locus, the average number of nonsynonymous substitutions per site is greater than that of synonymous substitutions per site (0.1962 versus 0.0256, respectively). Nucleotide and amino acid sequences both showed a relatively high level of similarity (nucleotides 90.6%; amino acids 80.6%) to those of beluga whale (Delphinapterus leucas) and narwhal (Monodon monoceros). The high level of baiji MHC polymorphism revealed in the present study has not been reported in other cetaceans and could be a consequence of the small baiji population adapting to freshwater with a relatively high level of pathogens.     

Genetic variation in the diatomFragilaria capucina (Fragilariaceae) along a latitudinal gradient across North America

Genetic variation in 126 clones of the planktonic diatom,Fragilaria capucina, collected from seven lakes from Manitoba to Texas, was determined by RAPD analysis. Five primers yielded 48 scorable RAPD fragments in 123 unique combinations. Patterns of genetic variation were analysed by cluster analysis, which showed that most clones grouped together according to the site from which they were collected. This pattern in genetic variation may be a result of the geographically disjunct nature of these populations and/or the different environmental conditions, especially temperature, in the different lakes.     

Seed-bank and dynamics of a Polygonum hydropiper L. community along the Po river (Central-West Italy)

ABSTRACT

The seed-bank and the dynamics of a Polygonum hydropiper L. community were investigated. The study area is located along the Po river in the Central-West Po plane (Northern Italy), in Piedmont, near Alessandria. The seed-bank in the soil was investigated by means of a simplified procedure of seasonal sampling and germination tests while the dynamics of the Polygonum community was investigated within a permanent square. Results indicate that: i) The Polygonum hydropiper community has strong growth potential because it has a source of biodiversity in its reservoir of germinable seeds of different species. River overflows act both as disturbance and as vectors for propagules, selecting the species that can grow and develop within the vegetation, and the species that will be left as seeds in the soil; ii) species diversity and dominance vary with vegetation stage (seed bank, pioneer stages and mature stages); iii) two types of seed-bank were present in the soil we analysed: a transient one and a persistent one.     

Morphological variation does not influence locomotor performance within a cohort of hatchling lizards (Amphibolurus muricatus, Agamidae)

A causal link between morphology and performance is a central tenet of ecomorphological analyses, but there are few detailed analyses of exactly how morphological variation within a hatchling cohort maps onto locomotor performance, and especially whether or not different tasks favour different morphologies (or vice versa). We measured morphological traits (including body length, mass, head size, limb proportions and fluctuating asymmetry [FA]) on a large sample of laboratory-incubated hatchling lizards ( Amphibolurus muricatus , Agamidae), and used principal component analysis to reduce this data set to four major axes of variation (size, shape and two FA axes). Running speeds of each lizard were measured on raceways at four inclines, from level (0°) through to steep (45°). Unsurprisingly, steeper inclines reduced locomotor speeds. Absolute body size was the only morphological trait that was consistently related to sprinting performance, and the relationships were similar at each incline. Within-cohort variation in body shape and FA among this large sample was unrelated to locomotor speeds, thus challenging the common assumption of a causal link between these variables. The only exception was a weak trend for greater hind limb length to enhance locomotor performance more at steep inclines than at shallower angles. In general, our data suggest that different morphological traits do not differentially maximize locomotor performance up variable inclines. Overall, our data provide a cautionary note about the generality of causal connections between within-cohort morphological variation and locomotor performance under different environmental contexts.