167 research outputs found
Description of five new species of Acestrocephalus Eigenmann and redescription of A. sardina and A. boehlkei (Characiformes: Characidae)
A ‘living fossil’ eel (Anguilliformes: Protanguillidae, fam. nov.) from an undersea cave in Palau
We report the discovery of an enigmatic, small eel-like fish from a 35 m-deep fringing-reef cave in the western Pacific Ocean Republic of Palau that exhibits an unusual suite of morphological characters. Many of these uniquely characterize the Recent members of the 19 families comprising the elopomorph order Anguilliformes, the true eels. Others are found among anguilliforms only in the Cretaceous fossils, and still others are primitive with respect to both Recent and fossil eels. Thus, morphological evidence explicitly places it as the most basal lineage (i.e. the sister group of extant anguilliforms). Phylogenetic analysis and divergence time estimation based on whole mitogenome sequences from various actinopterygians, including representatives of all eel families, demonstrate that this fish represents one of the most basal, independent lineages of the true eels, with a long evolutionary history comparable to that of the entire Anguilliformes (approx. 200 Myr). Such a long, independent evolutionary history dating back to the early Mesozoic and a retention of primitive morphological features (e.g. the presence of a premaxilla, metapterygoid, free symplectic, gill rakers, pseudobranch and distinct caudal fin rays) warrant recognition of this species as a ‘living fossil’ of the true eels, herein described as Protanguilla palau genus et species nov. in the new family Protanguillidae
A review of the Cis-Andean species of Hemibrycon Günther (Teleostei: Characiformes: Characidae: Stevardiinae), with description of two new species
Minimum requirements for publishing hydrogen, carbon, nitrogen, oxygen and sulfur stable-isotope delta results (IUPAC Technical Report)
Stable hydrogen, carbon, nitrogen, oxygen and sulfur (HCNOS) isotope compositions expressed as isotope-delta values are typically reported relative to international standards such as Vienna Standard Mean Ocean Water (VSMOW), Vienna Peedee belemnite (VPDB) or Vienna Cañon Diablo Troilite (VCDT). These international standards are chosen by convention and the calibration methods used to realise them in practice undergo occasional changes. To ensure longevity and reusability of published data, a comprehensive description of (1) analytical procedure, (2) traceability, (3) data processing, and (4) uncertainty evaluation is required. Following earlier International Union of Pure and Applied Chemistry documents on terminology and notations, this paper proposes minimum requirements for publishing HCNOS stable-isotope delta results. Each of the requirements are presented with illustrative example
Fine-Scale in Situ Measurement of Riverbed Nitrate Production and Consumption in an Armored Permeable Riverbed
Alteration of the global nitrogen cycle by man has increased nitrogen loading in waterways considerably, often with harmful consequences for aquatic ecosystems. Dynamic redox conditions within riverbeds support a variety of nitrogen transformations, some of which can attenuate this burden. In reality, however, assessing the importance of processes besides perhaps denitrification is difficult, due to a sparseness of data, especially in situ, where sediment structure and hydrologic pathways are intact. Here we show in situ within a permeable riverbed, through injections of 15N-labeled substrates, that nitrate can be either consumed through denitrification or produced through nitrification, at a previously unresolved fine (centimeter) scale. Nitrification and denitrification occupy different niches in the riverbed, with denitrification occurring across a broad chemical gradient while nitrification is restricted to more oxic sediments. The narrow niche width for nitrification is in effect a break point, with the switch from activity “on” to activity “off” regulated by interactions between subsurface chemistry and hydrology. Although maxima for denitrification and nitrification occur at opposing ends of a chemical gradient, high potentials for both nitrate production and consumption can overlap when groundwater upwelling is strong
Charax goeldii Fowler, 1913 a valid species of Galeocharax Fowler (Characiformes: Characidae)
Iron-Responsive Olfactory Uptake of Manganese Improves Motor Function Deficits Associated with Iron Deficiency
Iron-responsive manganese uptake is increased in iron-deficient rats, suggesting that toxicity related to manganese exposure could be modified by iron status. To explore possible interactions, the distribution of intranasally-instilled manganese in control and iron-deficient rat brain was characterized by quantitative image analysis using T1-weighted magnetic resonance imaging (MRI). Manganese accumulation in the brain of iron-deficient rats was doubled after intranasal administration of MnCl2 for 1- or 3-week. Enhanced manganese level was observed in specific brain regions of iron-deficient rats, including the striatum, hippocampus, and prefrontal cortex. Iron-deficient rats spent reduced time on a standard accelerating rotarod bar before falling and with lower peak speed compared to controls; unexpectedly, these measures of motor function significantly improved in iron-deficient rats intranasally-instilled with MnCl2. Although tissue dopamine concentrations were similar in the striatum, dopamine transporter (DAT) and dopamine receptor D1 (D1R) levels were reduced and dopamine receptor D2 (D2R) levels were increased in manganese-instilled rats, suggesting that manganese-induced changes in post-synaptic dopaminergic signaling contribute to the compensatory effect. Enhanced olfactory manganese uptake during iron deficiency appears to be a programmed “rescue response” with beneficial influence on motor impairment due to low iron status
Taxonomic review of Colombian Parodon (Characiformes: Parodontidae), with descriptions of three new species
Feeding of two sympatric species of Characidium, C. lanei and C. pterostictum (Characidiinae) in a coastal stream of Atlantic Forest (Southern Brazil)
The indirect response of an aquatic ecosystem to long-term climate-driven terrestrial vegetation in a subalpine temperate lake
Aim: To assess whether climate directly influences aquatic ecosystem dynamics in
the temperate landscape of Tasmania or whether the effects of long-term climatic
change are mediated through the terrestrial environment (indirect climate influence).
Location: Paddy’s Lake is located at 1065 m a.s.l. in temperate north-west Tasmania,
a continental island south-east of mainland Australia (41°15–43°250 S; 145°00–
148°150 E).
Methods: We developed a new 13,400 year (13.4 kyr) palaeoecological dataset of
lake sediment subfossil cladocerans (aquatic grazers), bulk organic sediment carbon
(C%) and nitrogen (N%) and d13C and d15N stable isotopes. Comparison of this new
data was made with a recently published pollen, geochemistry and charcoal records
from Paddy’s Lake.
Results: Low cladoceran diversity at Paddy’s Lake is consistent with other temperate
Southern Hemisphere lakes. The bulk sediment d15N values demonstrate a significant
lagged negative response to pollen accumulation rate (pollen AR).
Compositional shifts of dominant cladoceran taxa (Bosmina meridionalis and Alona
guttata) occur following changes in both pollen AR and pollen (vegetation) composition
throughout the 13.4 kyr record at Paddy’s Lake. The d15N values demonstrate
a significant positive lagged relationship to the oligotrophic:eutrophic cladoceran
ratio.
Main conclusions: Long-term changes in cladoceran composition lag changes in
both pollen AR and terrestrial vegetation composition. We interpret pollen AR as
reflecting climate-driven changes in terrestrial vegetation productivity and conclude
that climate-driven shifts in vegetation are the principal driver of the cladoceran
community during the last ca. 13.4 kyr. The significant negative lagged relationship
between pollen AR and d15N reflects the primary control of vegetation productivity
over within-lake nutrient status. Thus, we conclude that the effects of long-term climate
change on aquatic ecosystem dynamics at our site are indirect and mediated
by the terrestrial environment. Vegetation productivity controls organic soil development
and has a direct influence over lake trophic status via changes in the delivery
of terrestrial organic matter into the lake
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