Chalceus

Abstract: The jaw movement pattern and the timing of cranial muscle activity were studied during feeding on a variety of prey types in three characoid fishes: Lebiasina boruca, Hoplias malabaricus and Chalceus macrolepidotus. In Hoplias, the kinematic and electromyographic profiles do not vary with prey type or location. Mouth opening invariably occurs by synchronous activity in the levator operculi, sternohyoideus, geniohyoideus, epaxial and obliquus superioris muscles. Jaw movement and muscle activity patterns in Lebiasina vary dramatically and consistently with prey type and location. Elusive prey elicit an electromyographic pattern similar to that in Hoplias except that the geniohyoideus is inactive. During capture of less elusive prey (insect larvae), three distinct feeding patterns are seen depending on whether prey are located on the surface, in the midwater or on the bottom. The epaxial muscles are always active during surface feeding whereas they are silent during feeding from the bottom. Midwater strikes were highly variable, and asymmetrical activity between right- and left-side muscles was observed. Prey capture by Chalceus was highly variable and no particular muscle activity pattern could be correlated with a specific prey type or location. Asymmetrical activity between certain right- and left-side muscles was also found. The functional repertoire of Hoplias represents a subset of the broader repertoires seen in Lebiasina and Chalceus. Prey capture by high-speed inertial suction is of limited versatility and is correlated with a nearly invarient movement and electromyographic pattern.

Abstract: Enzyme and dispersal polymorphisms of the saltmarsh carabid beetles Pogonus chalceus and Dicheirotrichus gustavii were studied in European populations varying in size and in isolation in space and time. D. gustavii, a constantly fullwinged species, has a larger genetic diversity and a smaller genetic differentiation between populations than the wing-polymorphic P. chalceus. Clear relationships between population or site characteristics and genetic structure were not observed, except for the special position taken by some small populations in both species. The dispersal power of P. chalceus in small populations is larger than in large populations, suggesting that these populations are unstable and/or young. Small populations, however, do not always show a lower genetic diversity than large populations, as would be expected from genetic drift. Dispersal power in P. chalceus declines with increasing age of the saltmarsh, probably due to continuous emigration of winged individuals. Age and size of saltmarshes, although difficult to study independently, both appear to be important in determining the genetic structure of saltmarsh beetles. Maximum diversity in both parameters is therefore recommended as an optimal nature conservation strategy.

Abstract: Astyanax bimaculatus (Linnaeus, 1758) and Tetragonopterus chalceus Spix & Agassiz, 1829 are two important foraging species occurring at the Sao Francisco River basin. Specimens from both species were submitted to spawning induction through hypophysation, to study some reproductive features and to obtain subsidiary information for the definition of the artificial reproduction protocol. Males and females were treated with a single dose of crude carp pituitary extract (6 mg/ kg). In water at 26oC, the extrusion of the oocytes was made 12,8 and 11 hours after the hypophisis injection, for A. bimaculatus and T. chalceus respectively. More than 70% of the females of both species showed a positive response to the treatment and mean egg fertilization rates were above 70%. The eggs of A. bimaculatus and T. chalceus are yellow or medium brown, spherical, opaque, demersal, and slightly adhesive. The ova contained 4774 and 2563 eggs (mean values per gram) respectively. The embryonic development in both species was fast, lasting less than a day when water temperature was between 24 and 25oC.