Visual cues during the alarm reaction of Gymnocharacinus bergi (Pisces, Characidae)

Gymnocharacinus bergi (Pisces, Characidae), an endemic fish in the headwaters of the Valcheta stream in northern Patagonia, displays a fright reaction. As this species inhabits a rapid stream, we hypothesized that the alarm reaction might be socially transmitted through visual information, because the detection of alarm pheromone would be restricted to those fish located downstream from the releaser. Alarm substances elicited a decrease in the swimming activity and a tendency to remain at the bottom of the aquarium. Individuals that observed the fright reaction, but were not exposed to the pheromone, spent significantly more time at the bottom of the aquarium imitating the alarm response, and tended to approach the others. Gregarious behaviour was observed; however, interactions (number of approaches) were stronger between those fish held prior to testing in the same aquarium; smaller fish in particular tended to get closer to bigger ones. Greater group cohesion was found between individuals that were exposed to the alarm pheromone.     

Lethal temperatures of a Neotropical fish relic in Patagonia, the scale-less characinid Gymnocharacinus bergi

Southern South America has a rather low fish species diversity. Gymnocharacinus bergi, the southernmost characid fish of the world, is the only member of Characoidei in the Argentine Patagonia. The isolation of this species in an endorheic stream has been linked to the thermal conditions of its habitat, the head-waters of the Valcheta Stream, which is the only site where this species occurs. We provide information on the distribution and thermal habitat of this species and other fishes in the Valcheta Stream. The responses of G. bergi to high and low temperatures were assessed in the laboratory under different temperatures and heating and cooling rates. Our results suggest that G. bergi is unable to extend its distribution to the colder waters nearby, as well as to waters with greater temperature fluctuations. We discuss the implications of our experimental data, the habitat of G. bergi, and the known responses of a few other paranensean fishes to temperature, within the framework of the thermal ecology of freshwater fishes.     

Fright Reaction in Gymnocharacinus bergi (Pisces, Characidae), A Relic Fish from Patagonia

Fright reaction, mediated by pheromones, is an antipredatory mechanism in the scale-less mojarra Gymnocharacinus bergi (Pisces, Characidae). The aim of this study was to characterise and quantify the fright reaction of this species and to analyse the alarm response to different doses of alarm substance. The alarm response consisted in a general decrease in the swimming speed and a tendency to remain at the bottom of the test aquarium. A threshold effect was induced by a very low dose of alarm substance, and the intensity of the fright reaction was positively correlated to the dose concentration. The main characteristics of the alarm response appear to be consistent with G. bergi's environmental conditions such as: a higher predation risk in the upper stratum, the abundant pond-weeds of the stream and the great flow and fast speed of the clear waters.     

Morphology of the inner ear of mammals in ontogeny

In both phylogenesis and ontogenesis, the inner ear is formed first as a core, which, phylogenetically, is the most ancient part of the peripheral region of the auditory system. Along with the development of the inner ear, other links of different evolutionary ages (the auricle is a phylogenetically young link) begin to form in the peripheral auditory system.     

Appendicular skeleton in Bachia bicolor (Squamata: Gymnophthalmidae): osteology,limb reduction and postnatal skeletal ontogeny

The osteology of the appendicular skeleton and its postnatal development are described in Bachia bicolor, a serpentiform lizard with reduced limbs. The pectoral girdle is well developed and the forelimb consists of a humerus, ulna, radius, five carpal elements (ulnare, radiale, distal carpals 4–3, centrale), four metacarpals (II, III, IV, V) and phalanges (phalangeal formula X‐2‐2‐2‐2). In the hindlimb, the femur is small and slender, and articulates distally with a series of ossified amorphous and extremely reduced elements that correspond to a fibula, tibia and proximal and distal tarsals 4 and 3. The pelvic girdle consists of ischium, pubis and ilium, but its two halves are widely separated; the ilium is the least reduced element. We describe the ossification and development during postnatal skeletal ontogeny, especially of epiphyseal secondary centres, ossifications of carpal elements, apophyseal ossifications and sesamoids. Compared to other squamates, B. bicolor shows an overall reduction in limb size, an absence of skeletal elements, a fusion of carpal elements, an early differentiation of apophyseal centres, and a low number of sesamoids and apophyseal centres. These observations suggest that the reductions are produced by heterochronic changes during postnatal development and probably during embryonic development; therefore the appendicular skeleton exhibits a pattern of paedomorphic features.     

Steganoderma (Steganoderma) valchetensis n. sp. (Digenea: Zoogonidae) from the relict fish Gymnocharacinus bergi (Osteichthyes: Characidae) in Argentina

A new species of Steganoderma (Steganoderma) (Digenea: Zoogonidae) was found in the digestive tract of the southernmost, endemic and scale-less characid, Gymnocharacinus bergi, inhabiting thermal headwaters of the Valcheta Creek in northern Patagonia, Argentina. Steganoderma valchetensis n. sp. is included in the subgenus Steganoderma because of having a sessile ventral sucker and caeca reaching to the testes. This new species can be distinguished from other species of this genus on the basis of body-length, sucker-ratio, the length of the cirrus-sac, the morphology of the seminal vesicle and gonads, and the location of the vitelline follicles and genital pore. The taxonomic status of the species of Steganoderma, parasitising the freshwater fishes of Patagonia, in southern Argentina, and Chile, is also discussed.     

Campynemanthe (Campynemaceae): Morphology, microsporogenesis, early ovule ontogeny and relationships

Campynemanthe Baill. consists of three species endemic to New Caledonia. Two species are studied and compared. The tapetum is secretory with 2-nucleate tapetal cells. Microsprogenesis is successive, microspore tetrads are isobilateral and the pollen grains are free and inaperturate or have a weakly defined aperture. Placentation is axile with 3–4 ovules in each of the three locules. Ovules are anatropous and crassinucellate with the micropyle formed by the inner integument alone. The archesporial cell cuts off a parietal cell, which divides to form a parietal tissue. The nucellar epidermis divides periclinally at the nucellar apex to become 2-layered. The megaspore tetrad is T-shaped, in which the micropylar megaspore cells are separated by an oblique wall. The chalazal megaspore enlarges and apparently developes into a Polygonum-type embryo sac, but a mature embryo sac has not been seen. The ripe seeds are pale and non-phytomelaniferous. They have copious endosperm rich in fatty oils. The embryo is minute. These characters and gross morphological similarities support relationship with Campynema Labill., but there are also conspicuous differences. The two genera are considered related. They also closely approach genera of the variable family Melanthiaceae and there are reasons to include them in this family.     

Visual discrimination by the spraying characid,Copeina arnoldi Regan

Visual discrimination by male spraying characids, Copeina arnoldi, during spawn splashing was studied. Apparently the spawn is not used per se in directing parental splashing. Males discriminated between the standard 12·7-cm disc and a square, a triangle, a white disc, and a small disc in successive and/or simultaneous presentations. They did not discriminate between the standard disc and a large disc in succession, nor between the standard (green) disc and a white disc presented simultaneously. Although they can discriminate between objects differing in shape, colour, and/or brightness, these are probably not the major cues used in nature for selecting the spawn substrate from other proximal stimuli. However, large size differences may be important in spawn substrate discrimination.     

Morphology and ontogeny of single-walled multiporous sensilla of hemimetabolous insects

Comparative morphological investigations were made to determine the common organization plan of single-walled multiporous sensilla. The development of multiporous chemoreceptive sensilla of Gryllus, Oncopeltus and Lepisma follows the same path. Each chemoreceptive sensillum is associated with four types of enveloping cell. During ontogeny, enveloping cell 1 secretes the dendritic sheath. Enveloping cell 4 builds the connection of the hair base with the antennal cuticle. In Gryllus and Oncopehus, enveloping cells 2 and 3 build the hair shaft, the wall pores and pore tubules in nearly equal parts. Enveloping cells 2 and 3 lie side by side in the hair process, in which enveloping cell 2 produces the inner part, enveloping cell 3 the outer part of the hair shaft. In Lepisma the predominant part of the hair shaft with the wall pores is formed by the doubled enveloping cells 3. Interpreting our findings and the literature data, a new proposal is given for the homology of the enveloping cells. In singlewalled chemoreceptors, enveloping cell 1 is considered as thecogen and enveloping cell 4 as tormogen cell. Enveloping cell 2 is interpreted as inner trichogcn cell and enveloping cell 3 as outer trichogen cell.     

Morphology, ontogeny and histochemistry of secretory trichomes of Geranium robertianum (Geraniaceae)

Geranium robertianum bears three types of glandular uniseriate trichomes which originate from a single protodermal cell and develop through periclinal divisions. Type I trichomes are procumbent and have an oval apical cell, two stalk cells and a basal cell. Type II trichomes are erect and have a pear shaped apical cell, two stalk cells and a basal cell. Type III trichomes are much longer than the other two types and have an elongated apical cell, five long stalk cells and a basal cell. Type I and type II trichomes are common on leaves while III trichomes are more abundant on flower structures.
Type I and type II trichomes secrete terpenoids and phenols. Type III trichomes are characterized by the accumulation of anthocyanins in the apical cell and secrete flavonoids.     

Ontogenic diet shifts and scale-eating in Roeboides dayi, a Neotropical characid

Scale feeding (lepidophagy) has been documented for a variety of Neotropical fish taxa, including the characid genus Roeboides. Ontogenetic differentiation of jaws and snout teeth allow larger Roeboides to remove scales, however, the less specialized tooth/jaw structure in Roeboides dayi, indicates that it may be a facultative scale feeder. Population dynamics and diets of R. dayi in a Venezuelan lowland swamp/creek and a piedmont stream were compared over an annual cycle. Juvenile R. dayi consumed aquatic insect larvae and microcrustacea, and although spawning was year-round at both sites, most reproduction occurred during the wet season when the availability of these resources was greatest for juveniles. At both sites, larger R. dayi fed on a combination of invertebrate prey and fish scales, the former being more important at the piedmont site, and the latter being especially important during initial low water conditions at both sites. In the lowland stream, the reduction of aquatic habitat during the early dry season created higher fish densities and a more profitable environment for scale-feeders. Insectivory probably was less profitable during this early low water period due to interspecific competition for reduced aquatic insect stocks.     

Morphology of juvenile stages of Kuschelina bergi (Harold) with biological information (Coleoptera,Chrysomelidae, Alticini)

Kuschelina bergi (Harold, 1881) is being studied to be evaluated as a natural enemy of Phyla nodiflora var. minor (Hook.) N. O’Leary & Múlgura (Verbenaceae), an invasive weed in Australia. Eggs, and 1^st and 3^rd instar larvae are described and illustrated for the first time. The following characters distinguish Kuschelina bergi: presence of two medial setae in prosternum, mesosternum and metasternum, absence of tubercle on sternum I and eight setae in abdominal segment IX. The 3^rd instar larvae of Kuschelina bergi resemble Kuschelina gibbitarsa (Say) larvae: the body shape and details of mouthparts are similar, but the morphology of the mandible is different, as is the tarsungulus which has a single seta. Differences between Kuschelina bergi and other known larvae of Oedionychina are discussed. New biological data based on laboratory rearing and field observation are also presented and discussed.     

Morphology and ontogeny of Cretaceous ostracods with preserved appendages from Brazil

The Lower Cretaceous ostracod Pattersoncypris micropapillosa Bate is redescribed, and Reconcavona sp. indet. with appendages preserved is described for the first time. The morphology of the carapace and especially of the appendages of P. micropapillosa is compared in detail with that of the Recent Cyprididae Eucypris virens , which demonstrates that there are substantial similarities. In addition to the adults of P. micropapillosa , a number of juveniles have also been recovered and described, and these are compared with the juveniles of E. virens . The ontogenetic development of P. micropapillosa is shown to be very similar to that of Recent Cyprididae. This has highlighted that this group of ostracods has changed very little over the last 100 My. P. micropapillosa is tentatively placed in the subfamily Cyprinotinae, based on features of the upper lip. As the morphology of the appendages and the ontogeny of P. micropapillosa are very similar to those of Recent forms, it is postulated that the function of the limbs and lifestyle were also similar, i.e. it was nektobenthic and an opportunistic detritus feeder.     

Morphology,ontogeny, and heterochrony in lower and middle Cambrian Gogiids (Eocrinoidea,Echinodermata) from Guizhou Province,China

Gogiid eocrinoids from the Lower Cambrian (Balang Formation — Guizhoueocrinus) and basal Middle Cambrian (Kaili Formation — Sinoeocrinus, Globoeocrinus) in Guizhou Province, China are found in great numbers and are extremely well preserved as high fidelity molds in shale/mud sized siliciclastics. Because of their numbers, complete ontogenetic growth sequences have been observed. Significant differences in growth patterns (heterochrony) are present between Lower and Middle Cambrian genera: thecal plates tend to be paedomorphic in development, while the sutural pores developed between them are peramorphic in their development. Because of the large surface area of theca and brachioles relative to the size of the attachment area, considerable drag in ambient currents would necessitate a strong attachment medium. Anchoring by “biogluing”, possibly by collagen, directly to the substrate or to biodetritus is proposed as the method of attachment.