Major morphological changes in a Lake Victoria cichlid fish within two decades

During the upsurge of the introduced predatory Nile perch in Lake Victoria in the 1980s, the zooplanktivorous Haplochromis ( Yssichromis ) pyrrhocephalus nearly vanished. The species recovered coincident with the intense fishing of Nile perch in the 1990s, when water clarity and dissolved oxygen levels had decreased dramatically due to increased eutrophication. In response to the hypoxic conditions, total gill surface in resurgent H. pyrrhocephalus increased by 64%. Remarkably, head length, eye length, and head volume decreased in size, whereas cheek depth increased. Reductions in eye size and depth of the rostral part of the musculus sternohyoideus, and reallocation of space between the opercular and suspensorial compartments of the head may have permitted accommodation of larger gills in a smaller head. By contrast, the musculus levator posterior, located dorsal to the gills, increased in depth. This probably reflects an adaptive response to the larger and tougher prey types in the diet of resurgent H. pyrrhocephalus . These striking morphological changes over a time span of only two decades could be the combined result of phenotypic plasticity and genetic change and may have fostered recovery of this species.  © 2008 The Linnean Society of London, Biological Journal of the Linnean Society , 2008, 94 , 41–52.     

A functional analysis of the shift from gill- to lung-breathing during the evolution of land crabs (Crustacea, Decapoda)

The evolution of air-breathing in land crabs is associated with a progressive shift in the primary site of respiratory gas exchange from the diffusion-limited gills used for water-breathing, via a simple 'cutaneous' lung surface to the perfusion-limited, invaginated lung described in the mountain crab, Pseudothelphusa garmani. The reduced diffusion limitation over the lungs facilitates oxygen transfer from air to the tissues at lower ventilation rates but is associated with accumulation of carbon dioxide. A potential respiratory acidosis is buffered by the respiratory pigment haemocyanin and by elevation of haemolymph bicarbonate levels. These changes parallel those described in vertebrates but air-breathing crustaceans maintain relatively low carbon dioxide levels in the haemolymph, either by retaining an aquatic route for its elimination over the reduced gills or by blowing it off across the lung. Maintenance of low carbon dioxide levels may be associated with a limited capacity to buffer against an acidosis due to low levels of circulating haemocyanin (i.e. crustaceans lack red blood cells). This may ultimately limit their survival in air as an acidosis will reduce oxygen transport due to a marked Bohr effect on haemocyanin. The primary role of an invaginated lung may be to reduce rates of water loss in air.     

Sound physiological knowledge and principles in modeling shrinking of fishes under climate change

One of the main expected responses of marine fishes to ocean warming is decrease in body size, as supported by evidence from empirical data and theoretical modeling. The theoretical underpinning for fish shrinking is that the oxygen supply to large fish size cannot be met by their gills, whose surface area cannot keep up with the oxygen demand by their three‐dimensional bodies. However, Lefevre et al. (Global Change Biology, 2017, 23, 3449–3459) argue against such theory. Here, we re‐assert, with the Gill‐Oxygen Limitation Theory (GOLT), that gills, which must retain the properties of open surfaces because their growth, even while hyperallometric, cannot keep up with the demand of growing three‐dimensional bodies. Also, we show that a wide range of biological features of fish and other water‐breathing organisms can be understood when gill area limitation is used as an explanation. We also note that an alternative to GOLT, offering a more parsimonious explanation for these features of water‐breathers has not been proposed. Available empirical evidence corroborates predictions of decrease in body sizes under ocean warming based on GOLT, with the magnitude of the predicted change increases when using more species‐specific parameter values of metabolic scaling.     

Differences in protein patterns of gill epithelial cells of the fish Gillichthys mirabilis after osmotic and thermal acclimation

Different protein patterns in gill epithelium of a euryhaline and eurythermal teleost fish (Gillichthys mirabilis, Family Gobiidae) in response to long-term (2 months) osmotic and thermal acclimation were found for the first time. Gill epithelial cells were isolated to remove extracellular proteins and quantify specialized cell types. Chloride cells were identified on the basis of size (>10 m) and bright appearance after [2-(p-dimethylaminostyryl)-1-methyl-pyridinium-iodine] staining. Small mitochondria-rich cells were <5 m in diameter and showed intermediate fluorescence. Abundance of chloride cells and small mitochondria-rich cells was significantly influenced by osmotic but not thermal acclimation (dilute seawater/25°C: 1.4±0.2% chloride cells, 11.9±4.6% small mitochondria-rich cells; seawater/25°C: 2.4±0.6% chloride cells, 2.2±1.3% small mitochondria-rich cells; seawater/10°C: 2.9±0.3% chloride cells, 1.2±0.7% small mitochondria-rich cells). Pavement cells, identified by low fluorescence and intermediate size (5–10 m), largely predominated under all conditions (>85% of cells). Thus, they represented the major protein source in gill epithelium. Differences in protein patterns were detectable using two-dimensional but not one-dimensional electrophoresis. Of 602 proteins identified by charge and molecular weight properties, only two were induced by high temperature (25°C) and three in response to cold acclimation (10°C). Nine proteins were induced in diluted seawater-acclimated fish, whereas no seawater-induced proteins were found. We hypothesize that proteins induced under dilute seawater conditions are important for the function of pavement cells in gills of hyper-osmoregulating G. mirabilis.Abbreviations BCA bicinchoninic acid - BSS balanced salt solution - CC chloride cells - CLB cell lysis buffer - DASPMI [2-(p-dimethylaminostryryl)-1-methylpyridinium-iodine] - DSW diluted sea water - DTT dithiothreitol - EDTA ethylene-diaminetetraacetate - FW fresh water - IEF isoelectric focusing - PC pavement cells - PDA diacrylpiperazine - pI isoelectric point(s) - PMSF phenylmethanesulphonylfluoride - SDS sodium dodecyl sulfate - SMRC small mitochondria-rich cells - SW sea water - TEMED tetramethylenediamine     

Hypoxia and interdemic variation in Poecilia latipinna

Variation in respiratory traits was quantified between two populations of the sailfin molly Poecilia latipinna (one from a periodically hypoxic salt marsh, Cedar Key, and one from a chronically normoxic river site, Santa Fe River). Two suites of characters were selected: traits that may show both short‐term acclimation response and interdemic variation in acclimation response (metabolic rate, critical oxygen tension and respiratory behaviour), and those that are not likely to respond to short‐term acclimation but may vary among populations (gill morphometric characters). Sailfin mollies from the salt marsh, acclimated to hypoxia (1 mg l⁻¹, c . 20 mmHg) for 6 weeks, spent less time conducting aquatic surface respiration and had lower gill ventilation rates than hypoxia‐acclimated conspecifics from the well‐oxygenated river site. Poecilia latipinna acclimated to hypoxia exhibited a lower critical oxygen tension ( P _c) than fish acclimated to normoxia; however, there was also a significant population effect. Poecilia latipinna from Cedar Key exhibited a lower P _c than fish from the Santa Fe River, regardless of acclimation. Cedar Key fish had a 14% higher mean gill surface area relative to fish from the Santa Fe River, a character that could account, at least in part, for their greater tolerance to hypoxia.     

Ultrastructural effects on gill tissues induced in red tilapia Oreochromis sp. by a waterborne lead exposure

Experiments on hybrid red tilapia Oreochromis sp. were conducted to assess histopathological effects induced in gill tissues of 96 h exposure to waterborne lead (5.5 mg/L). These tissues were investigated by light and scanning electron microscopy. Results showed that structural design of gill tissues was noticeably disrupted. Major symptoms were changes of epithelial cells, fusion in adjacent secondary lamellae, hypertrophy and hyperplasia of chloride cells and coagulate necrosis in pavement cells with disappearance of its microridges. Electron microscopic X-ray microanalysis of fish gills exposed to sublethal lead revealed that lead accumulated on the surface of the gill lamella. This study confirmed that lead exposure incited a difference of histological impairment in fish, supporting environmental watch over aquatic systems when polluted by lead.     

Accumulation et excrétion de substances organiques par les cellules à chlorure de la branchie d'Anguilla anguilla L. adaptée à l'eau de mer

Résumé Les sites branchiaux d'accumulation de certaines substances (bleu de méthylène, urée, paraaminohippurate et inuline) injectées dans la circulation générale ont été localisés sur des anguilles adaptées à l'eau de mer. Le bleu de méthylène est accumulé et excrété par les cellules à chlorure. Les autoradiographies des corps marqués au ¹⁴C: inuline, PAH et urée, faites après cryodessication montrent que les cellules à chlorure accumulent ces substances. La signification de ces résultats est discutée.

---

Accumulation and excretion of organic substances by the branchial chloride cells in sea-water adapted eel (anguilla anguilla L.)

Summary The branchial site of accumulation of various organic substances (methylene blue, urea, inulin and paraaminohippurate) following intracardiac injection has been localised in sea-water adapted eels. Methylene blue is concentrated and excreted by chloride cells. By combining freeze-drying and radioautographic technique it was possible to demonstrate that chloride cells concentrate urea, inulin and paraaminohippurate. The signification of these results is discussed in relation with the branchial excretion of organic substances.

     

Structural and ultrastructural analysis of gills and gut of Hexagenia rigida nymphs (ephemeroptera) in relation to contamination mechanisms

In the context of an experimental approach to organic and inorganic mercury bio-accumulation by burrowing mayfly nymphs-Hexagenia rigida-, gills and different parts of the gut were investigated by light and electron microscopes. In the gut, two regions were studied: (1) mesenteron (midgut) characterized by cells with microvilli and a peritrophic membrane throughout this part, a lot of fungal hyphae being found on it; (2) proctodeum (hindgut) characterized by macrovilli, the apical face of cells being covered by a thick layer of chitin; many bacteria were observed at the bottom of macrovilli. The stomodeum (foregut) is extremely short. The gills are made up of six pairs of lamellae fringed with long filaments which are arranged on both sides of the long axis. Gills are constituted by tracheae and tracheoles, with a large canal for haemolymph circulation; muscle masses and nerve bundles were also observed. This structural approach shows that the nymph interface with the external environment, at gill and gut barrier levels, are quite different. Links between this structural and ultrastructural analysis and contamination mechanisms, via the trophic or direct route, are discussed; gills and gut could be transfer routes for mercury absorption, but also target organs for metal accumulation.     

Identification of apical membranes from tight epithelia using spin-labeled amiloride and electron paramagnetic resonance spectroscopy

Summary Apical cell membranes from Na⁺-transporting epithelia were identified in centrifugal fractions prepared from homogenates of rainbow trout kidney, gill and frog skin using a spinlabeled, nitroxide derivative of amiloride and electron paramagnetic resonance spectroscopy. Spin-labeled amiloride (ASp) is a potent inhibitor of Na⁺ transport. Frog skin shortcircuit current was inhibited by 50% in the presence of 7×10^–8 m ASp, whereas 4×10^–7 m amiloride was required to obtain the same effect. ASp is a suitable probe for the amiloride binding site based on analytical criteria: Unbound ASp produces an EPR signal linear with concentration and detectable at micromolar concentrations. Estimates of ASp binding can usually be made on less than 100 g of membrane protein. While ASp binds nonspecifically to many materials, amiloride- or benzamil-displaceable binding occurred only in trout gill and kidney, and in frog skin, but not in trout skeletal muscle. ASp binds to membrane fractions produced by differential centrifugation of trout gill, kidney and frog skin. In trout gill and kidney, 81% and 91%, respectively, of the amiloride-displaceable ASp binding is found in the 10,000 xg fraction. All of the ASp binding in frog skin is found in the 10,000 xg fraction. These data indicate that spin-labeled amiloride is a useful probe for the identification of the amiloride binding site, and electron paramagnetic resonance spectroscopy will allow the amiloride binding site to be used as a molecular marker for apical membranes.     

Concept formation in neural networks: Implications for evolution of cognitive functions

Parallel systems composed of many interconnected elements are both simple brain models and possible novel computer architectures. Potential advantages of such systems are massive parallelism with resulting speedup of computation as well as general ability to compute with noisy, corrupted, or missing data. Parallel, distributed, associative models have pronounced psychologies. Some ways of handling information are natural for them, and some things that we might want them to do are unnatural and quite difficult to do. A question of considerable interest is whether the models’ capabilities and limitations are features of human psychology. Such systems form categories based on the structure their inputs and display behavior that looks as if they form and use simple concepts. However, if noisy examples are learned, an initially stable concept structure may break up. One very simple function of names attached to categories — i.e. a rudimentary language — could be to stabilize a concept structure against fragmentation. In addition, if the statistical structure of the names reflects the statistical structure of the inputs, capacity and reliability of categorization and recognition is enhanced.