Rosa Graciela Cohen

Preliminary characterization of some Argentinean Artemia populations from La Pampa and Buenos Aires provinces

Artemia populations were sampledin four hypersaline ecosystems in continentalevaporitic basins from the Argentinean provinces of LaPampa and Buenos Aires. Biometrics of cysts andnauplii were performed. The morphometrics of adultfemales under standard culture conditions, studied bymultivariate discriminant analysis, provided evidencethat these populations belonged to the species A.persimilis; this was further supported bycross-breeding tests established between one of thesepopulations (Salinas Grandes de Hidalgo, province ofLa Pampa) and a population of A. franciscanafrom San Francisco Bay (California, USA), which showedreproductive isolation and barriers to gene flowbetween both populations.

MITOTIC AND MEIOTIC CHROMOSOMES OF ARTEMIA (BRANCHIOPODA) FROM POPULATIONS OF LA PAMPA PROVINCE, ARGENTINA

Three populations of Artemia from La Pampa Province, Argentina, were cytogenetically analyzed: Salinas Grandes de Hidalgo, Laguna Callaqueo, and Laguna Colorada Chica. Both mitotic and male meiotic chromosomes were studied. All 3 populations share the same diploid (2n = 44) and/or haploid chromosome number (n = 22), and hence were determined as Artemia persimilis Piccinelli and Prosdocimi. Although bivalents decrease gradually in size, differences among the larger and the smaller ones were apparent. So far, no cytogenetic differences have been detected among the 3 populations. Chromosomes with metacentric, submetacentric, and telocentric morphology were detected in mitotic prometaphase cells, suggesting that chromosomes of Artemia may be monocentric. The anostracan genus Artemia is taxonomically regarded as a group of several reproductively isolated sibling species, distributed worldwide, except for the Antarctic continent. In the New World, the genus is represented by three endemic bisexual species: A. franciscana Kellogg, 1906, A. persimilis Piccinelli and Prosdocimi, 1968, and A. monica Verrill, 1869.

Redescription of Branchinecta granulosa Daday, 1902 from Argentina (Crustacea: Branchiopoda)

The species Branchinecta granulosa Daday 1902, is redescribed on the basis of adult material from near Facundo (Chubut Province, Argentina). Its relationship to its regional congeners is outlined.

Description of a new subgenus and a new species of Thamnocephalus (Crustacea: Branchiopoda, Anostraca) from the Salinas Grandes Basin, Córdoba Province, Argentina

At present, the American genus Thamnocephalus has three species, recorded from several states of U.S.A., México and Venezuela: Thamnocephalus platyurus Packard, T. mexicanus Linder and T. venezuelensis Belk & Pereira. The new species Thamnocephalus salinarum, from a turbid saline temporary pond inside the Salinas Grandes of Córdoba, Argentina is described here. The new species differs from all other congeners by the presence in the male, of an unbranched frontal appendage and a pair of soft cordiform parapenial lobes; also, by the sexually dimorphic caudal fin-like lobe. This new species may represent a new genus, however since only five specimens were collected it was not possible to observe if the penial ornamentation conforms to the Thamnocephalus type. Therefore, a conservative position is taken until new material allows proper analysis, by keeping the new species in the genus Thamnocephalus under the new subgenus Simplicephalus.

The post-embryonic development of Artemia persimilis Piccinelli & Prosdocimi

The post-embryonic development of Artemia persimilis Piccinelli & Prosdocimi, reared under laboratory conditions, is described. Larval development is typical of branchiopods. It comprises 17 identifiable instars, which may be grouped into four periods. A comparison is made with Artemia franciscana Kellogg.

Morphological Diversity Displayed by High Altitude Branchinecta papillata (Anostraca) and Additional Morphological Comparisons with Branchinecta achalensis

ABSTRACT Populations of the high altitude anostracan Branchinecta papillota from the type locality in the Atacama Altiplano (Iquique province, Chile) and from the Cumbres Calchaquíes (Tucumán province, Argentina) and specimens of B. achalensis from the type locality (La Posta, Pampa de Achala, Córdoba province, Argentina) were compared and new observations on the morphological diversity of the species were made. A basal branching in the male antenna 2 distal article, only observed in one branchinectid to date, was found in the Argentinean populations of both species.

Reproductive and brood cycles of Artemia persimilis Piccinelli & Prosdocimi from Colorada Chica Lake (Province of La Pampa, República Argentina), under laboratory conditions

The brood cycle in anostracans results from the overlapping of two successive reproductive cycles in the genital tract of females. While a clutch of oocytes begins to mature at the ovaries (ovarian period), the nauplii, cysts or unfertilised products of a previous clutch are developing in the ovisac or being released to the medium (oviduct-ovisac period). Models are proposed for the sequence of stages and their duration in a complete brood cycle under two treatments, i.e., females with males (1:1 ratio), and isolated virginal females of Artemia persimilis in laboratory conditions. The whole brood cycle in both treatments took 6 days, however, they differed in the duration of some stages. The differences are discussed and observations on amplexus are added.

Concerning the identity ofBranchinecta santacrucensis Csar, 1987

The type series of the speciesBrachinecta santacrucensis César 1987, is compared with specimens ofBranchinecta granulosa Daday 1902 collected near Facundo, Chubut Province, Argentina. The great resemblance between them suggest that both sets of material belong to the same species and therefore,B. santacrucensis andB. granulosa are synonyms.

Heterochromatin variation in Artemia populations

Abstract The genus Artemia is an interesting model organism for evolutionary studies since many factors driving speciation have been observed in the genus. It has been suggested that in this genus heterochromatin content could be a reliable criteria to establish taxonomic identity of populations. In the present work the heterochromatin content was determined in 4 populations of A. franciscana and seven populations of A. persimilis, six from Argentina and one from Chile. Heterochromatin was revealed by C-banding and the heterochromatin content (measured as chromocenter number and C-positive area in nauplii interphase nuclei) was compared. A standardized procedure to evaluate the heterochromatin content is here proposed so that the results from different laboratories could be compared. We analyze the intra and interspecific variation in heterochromatin content in the different Artemia populations and we discuss the value of this trait as a population and/or specific cytogenetic marker.

Redescription of Dendrocephalus Affinis (Anostraca: Thamnocephalidae): First Record of the Species from Colombia and Additional Morphological Observations Useful in Taxonomy

The finding of a fairy shrimp population belonging to the genus Dendrocephalus in a temporary pond from the La Guajira Department of Colombia promoted the interest in evaluating this resource for its potential use for aquaculture purposes. In the present paper the population was allocated to Dendrocephalus affinis Pereira, 1984, only known so far from the type locality in Venezuela. The species was redescribed, providing new morphological observations on the male, useful in taxonomy. In addition, two characters on the female, not mentioned up to now in the genus, the presence of a baso-lateral short process with a spine in the endopod of the first thoracopod, and the presence of one square cell among all the pentagonal ones in the polyhedral resting egg, could help in the specific identification of dendrocephalid samples without males. The present is the first record of the species from Colombia.