Insights in KIR2.1 channel structure and function by an evolutionary approach; cloning and functional characterization of the first reptilian inward rectifier channel KIR2.1, derived from the California kingsnake (Lampropeltis getula californiae)

Potassium inward rectifier K_IR2.1 channels contribute to the stable resting membrane potential in a variety of muscle and neuronal cell-types. Mutations in the K_IR2.1 gene KCNJ2 have been associated with human disease, such as cardiac arrhythmias and periodic paralysis. Crystal structure and homology modelling of K_IR2.1 channels combined with functional current measurements provided valuable insights in mechanisms underlying channel function. K_IR2.1 channels have been cloned and analyzed from all main vertebrate phyla, except reptilians. To address this lacuna, we set out to clone reptilian K_IR2.1 channels. Using a degenerated primer set we cloned the KCNJ2 coding regions from muscle tissue of turtle, snake, bear, quail and bream, and compared their deduced amino acid sequences with those of K_IR2.1 sequences from 26 different animal species obtained from Genbank. Furthermore, expression constructs were prepared for functional electrophysiological studies of ectopically expressed K_IR2.1 ion channels. In general, KCNJ2 gene evolution followed normal phylogenetic patterns, however turtle K_IR2.1 ion channel sequence is more homologues to avians than to snake. Alignment of all 31 K_IR2.1 sequences showed that all disease causing K_IR2.1 mutations, except V93I, V123G and N318S, are fully conserved. Homology models were built to provide structural insights into species specific amino acid substitutions. Snake K_IR2.1 channels became expressed at the plasmamembrane and produced typical barium sensitive (IC₅₀ ∼6 μM) inward rectifier currents.     

Success of embryonic development of reciprocal hybrids of bream Abramis brama (L.) and white bream Blicca bjoerkna (L.)

Success of embryonic development of reciprocal hybrids of bream Abramis brama and white bream Blicca bjoerkna was tested under laboratory conditions. Fertilization and embryonic development success of hybrids until hatching was high and comparable to that of pure species.     

Assessment of Grey Heron predation on fish communities: the case of the largest European colony

The fish predation rate by Grey Heron Ardea cinerea was studied during two breeding seasons (1987–88) in the largest European colony at the Lake of Grand-Lieu (Loire-Atlantique, France). The herons' diet was compared to the available fish population of its main feeding area, the marsh of Bourgneuf (16000 ha) which is composed of former salt pans and meadows drained by a dense network of shallow ditches. This study is the first attempt to assess the predation exerted by an ardeid colony on a fish community over such an extensive natural environment. It also provides the first data about the abundance and the structure of fish communities in shallow coastal dyked marshes. For this purpose, two different sampling methods were used according to the water's salinity. In fresh waters, electrofishing was used as the removal method, and density estimates were calculated with Carle & Strub estimator (1978). Fish were caught in randomly selected stations (sections of ditches enclosed by two 5 mm mesh nets). In brackish waters, pools and ditches were drained. The distribution of the herons at the feeding areas was determined by direct observations, by counting flights from the colony, and by radio-tracking. The diet was investigated by observing adult herons on the foraging areas, and by analyzing the prey regurgitations of the young at the nests. The global food consumption was assessed from Marion (1988), according to the birds' activity determined during 5 years of radio-tracking. Altogether, at least 39 species of fish were available in the herons' feeding area (during the reference period, 87–88) and the mean fish biomass was 270 kg per ha of open water, or 30 kg per ha of marsh (open water = 11.2% of the marsh area). The fish community was dominated by eel Anguilla anguilla (145 kg ha^–1, 50,8% of the total biomass), and catfish Ictalurus melas (40 kg ha^–1, 14%). Except for small and inaccessible species (living in the deepest parts of the marsh), heron diet was very similar to fish species composition of the community occurring in the marsh. The catfish was the species captured most frequently by the heron (45% of the mass), the eel was second with 28% of the mass. The catfish was probably over represented in the diet considering that they are caught in catfish-dumps created by professional fishermen at Grand-Lieu lake, in order to reduce the density of this undesirable species. Inversely, small species such as Gasterosteus aculeatus were not found in the diet whereas they are very numerous in the marsh. On average herons of Grand-Lieu colony catch 1.92 kg of fish per ha of marsh (6% of the fish standing crops in the marsh) during the breeding season, the main predation period.     

Male primer endocrine responses to preovulatory female cyprinids under natural conditions in Sweden

This study investigated two related aspects of male-female reproductive interactions in the family Cyprinidae: (1) whether ovulating female rudd Scardinius erythrophthalmus (subfamily Leuciscinae) induce endocrine and gonadal priming responses in conspecific males, a phenomenon which has been described only in species from the subfamily Cyprininae such as goldfish, Carassius auratus, crucian carp Carassius carassius and common carp, Cyprinus carpio and (2) whether the stimuli mediating these responses are species-specific. Field studies of three sympatric European cyprinids, two leuciscins (S. erythrophthalmus and white bream Blicca bjoerkna) and one cyprinin (C. carassius), were conducted on fishes captured in Sweden in the spawning season and held in net pens under natural conditions. As previously reported in C. carassius, male S. erythrophthalmus increased milt (sperm and seminal fluid) volume and plasma concentrations of the sperm maturation hormone 4-pregnen-17,20β-diol-3-one (17,20β-P) when they were held with female S. erythrophthalmus induced to ovulate by injection of Ovaprim (GnRH analogue plus dopamine antagonist). Male S. erythrophthalmus had larger milt volumes than male C. carassius prior to and following exposure to ovulatory conspecifics, but exhibited a smaller proportional milt increase in response to stimulation, suggesting species differences in sperm allocation at spawning. The presence of female S. erythrophthalmus and B. bjoerkna did not affect milt volumes of C. carassius under two experimental conditions: (1) ovulating S. erythrophthalmus and B. bjoerkna did not increase the milt volumes of C. carassius and (2) S. erythrophthalmus and B. bjoerkna did not interfere with the milt volume increase induced in male C. carassius by ovulating conspecifics. These results suggest that, as in C. auratus, C. carassius and C. carpio (subfamily Cyprininae), female S. erythrophthalmus (subfamily Leuciscinae) release a preovulatory pheromone that exerts priming effects on male hormones and sperm allocation. The findings also indicate that C. carassius discriminate between the reproductive odours of conspecifics and heterospecifics.     

Diel distribution patterns of fishes in a temperate large lowland river

During the day, juveniles and typical inshore species in the lower Oder River, Germany, inhabited the littoral (0·05–1·50 m deep) while potamal species inhabited the mid‐channel (40–100 m from the banks). During the night, two behavioural groups were distinguished: 1) potamal species and large individuals of other species, moved from offshore to the littoral, and 2) nocturnal foraging species, became active and increased in inshore and offshore habitats. Inshore, the most significant differences at night was the increasing density of silver bream Blicca bjoerkna increasing both total biomass and total length of fishes caught. Offshore, the increasing density of whitefin gudgeon Gobio albipinnatus at night was most significant. Additional night electrofishing improved the assessment of the abundance, age and size structure of typical potamal fish species. It should be incorporated in large river fish monitoring programmes.     

New insights into the migration and habitat use by bream and white bream in the floodplain of the River Rhine

Bream Abramis brama , white bream Blicca bjoerkna and roach Rutilus rutilus all undertook spawning migrations from the River Rhine into oxbows. Adult white bream and roach returned to the river after spawning. This indicates an annual change of habitat allowing the use of optimal conditions in oxbows for spawning and growth of juvenile fish, and the use of feeding grounds rich in benthos in the main river by the adults. In contrast, adult bream were still present in large numbers in the oxbows over the summer. Juvenile bream (0+ and 1+) migrated to the main river. Bream aged 2+ to 4+ were not found in the oxbows, whereas they occurred frequently in the river. Thus bream show ontogenetic changes in their use of the main river and oxbows. The young fish spend their long juvenile phase in the river after leaving the oxbows. Reproduction in oxbows is ensured by mature fish migrating in for a short period from the river as well as by other adults (≥5+) that live permanently in the oxbows. The strong tendency of adult bream to develop permanent stocks in the oxbows gives this species a reproductive advantage, since many oxbows are accessible to Rhine fish only occasionally in the present hydrological situation.     

How dams on the River Danube might have caused hybridization and influenced the appearance of a new cyprinid taxon

Synopsis When a new species is found, or a known one collected outside its recognized distribution, most people either assume that the species has been overlooked in the past or that it has recently invaded the area in question from elsewhere. While other, more evolutionary explanations are possible, these are nearly always ignored, in spite of the common perception that animals are constantly in states of change. Recent findings in the Danube River are used as examples for such alternative interpretations. The case of two forms of Vimba — short and long snouted — which live in sympatry in the upper Danube is dispelled, as one of them is identified as a hybrid between female V. vimba and male Blicca bjoerkna. Frequent occurrences of this hybrid (and a few of its backcrosses) in recent times are explained by man-induced alteration of reproductive isolation between their parent species, caused by the impoundment of the river by dams built as part of the Rhein-Main-Donau Kanal. These impoundments, however, might be responsible not only for the creation of hybrids but also for direct speciation, as the case of Gobio albipinnatus may represent. The ability for epigenetic creation of two alternative life-history states (as part of the theory of alprehost) and the survival of an alternative state when environmental conditions change might be ultimately responsible for the appearance of a new taxon.