Marcelo Silva-Briano

Morphological and morphometrical variations of selected rotifer species in response to predation: a seasonal study of selected brachionid species from Lake Xochimilco (Mexico)

We observed different morphotypes of some species in the family Brachionidae from the seasonal plankton samples of Lake Xochimilco collected during 2002–2003. We measured the body length, width, and spine lengths (posterior and anterior spines) of Brachionus havanaensis, Keratella americana, K. cochlearis and K. tropica during the periods when the predator Asplanchna brightwellii was present in great abundance but also when it was nearly absent. In general, spines of most of the selected rotifer species were longer if A. brightwellii was abundant. Relatively, small spines were observed if the predator was rare. The body lengths of brachionid rotifers widely varied in samples with more and less abundant A. brightwellii. Morphometric data are interpreted in terms of morphological adaptations of Brachionus and Keratella in response to Asplanchna predation.

THE FRESHWATER CLADOCERA (ORDERS CTENOPODA AND ANOMOPODA) OF MEXICO, WITH COMMENTS ON SELECTED TAXA

Knowledge of the composition and distribution of the freshwater Cladocera in Mexico is still limited. All the available literature was reviewed and added to our own new records in different states of Mexico to present here a revised and updated list of the 110 species of the orders Ctenopoda and Anomopoda recorded for the country, with separate state records. Ecological, biogeographical, and taxonomic comments are made for selected taxa of the commonest neotropical groups: Sididae, Daphniidae, Bosminidae, Macrothricidae, and Chydoridae.

Bioconcentration and localization of lead in the freshwater rotifer Brachionus calyciflorus Pallas 1677 (Rotifera: Monogononta)

We studied how lead is bioconcentrated and distributed in the rotifer Brachionus calyciflorus using metal histochemistry to locate lead granules, Leadmium Green® analysis to establish the route of uptake, atomic absorption to determined the bioconcentration factor (BCF), and detected the presence of microelements in the cuticle by X-ray microanalysis with scanning electron microscopy. Our results indicate: (a) the digestive system is the main route of lead uptake in the rotifer B. calyciflorus, (b) after 24-h lead is deposited in granules in the mastax and vitellarium, (c) our energy-dispersive X-ray microanalysis indicates decalcification taking place in the cuticle of the rotifer after a 24-h lead exposure, and (d) we determined a BCF = 115 for lead after a 24 h exposure. However, the route of mobilization and storage of intracellular lead are still not fully understood in B. calyciflorus.

A note on El Niagara, a polluted reservoir in Aguascalientes, Mexico

Plankton, physical, chemical, and microbiological data, were taken from the polluted reservoir El Niagara during 1990. Chlorella spp and Euglena spp were the dominant phytoplankters. Zooplankton diversity and density were low: Brachionus spp, Asplanchna sieboldi, Moina affinis and Daphnia similis appeared seasonally; protozoans were present all year. Ten years earlier, the water quality and biota of the reservoir, then alreay degraded, were much better than today.

Wlassicsia, Bunops & Onchobunops (Anomopoda), three related genera

Comparison of the gross morphology and trunk limb ultrastructure of the macrothricid genera Wlassicsia, Bunops and Onchobunops by light and electron microscopy demonstrated their morphological similarity. We propose the synonymy of Onchobunops Fryer & Paggi with Bunops Birge on the basis of shared characteristics.

The copepod Balaenophilus manatorum (Ortíz, Lalana and Torres, 1992) (Harpacticoida), an epibiont of the Caribbean manatee

The harpacticoid copepod Balaenophilus manatorum (Ortíz, Lalana and Torres, 1992) was originally described based on a few specimens collected from a single manatee in Cuba. Since its description it has been recorded exclusively as a symbiont of sea turtles worldwide; there were no further records of this species from the manatee and this association remained unconfirmed. During a long-term survey on the biology and ecology of the manatee Trichechus manatus manatus L. in Mexican waters of the western Caribbean, epibionts were collected from 54 individuals, including males, females and juveniles. Many specimens of B. manatorum were recorded from several manatees and analysed morphologically; a comparison is made with specimens from turtles of the Mexican Pacific. Manatees captured in two different bay systems were examined, but only those from Chetumal Bay were positive for copepods. Infestation comprised 14 manatees (26%), eight females and six males; incidence was higher than that previously found for other crustacean epibionts. Copepods were found as soft yellowish masses arranged along skin folds and wrinkles of the muzzle, the base of the fins, and the nipple area; there was no evidence of skin damage caused by the copepod. The presence of B. manatorum on manatees is confirmed and the first data are provided on the prevalence of this epibiont in one of the main populations of this mammal in the western Caribbean.

THE AFRO-ASIAN MESOCYCLOPS ASPERICORNIS (DADAY) (COPEPODA, CYCLOPIDAE) IN MEXICO: COMMENTS ON MORPHOLOGY AND DISTRIBUTION

The known distribution of Mesocyclops aspericornis in the Americas included the central and northern areas of South America and the insular Caribbean. It had not been collected before in continental North America. The analysis of samples collected in a pond in the state of Sinaloa, on the Pacific coast of Mexico, yielded female individuals of this species. The Mexican individuals tended to be smaller than the African females (1.14-1.20 mm vs 1.3-1.5 mm), but the morphology of the Mexican specimens is identical in most characters to that described or depicted in previous works. This is the first morphological study of this species aided with SEM; it includes detailed data on several microstructures, some of which undescribed previously. It also is the first report of its effective occurrence in Mexico. All previous records of this species in the Americas are related to the Atlantic coasts. This record, in the Mexican Pacific area, suggests that this supposedly introduced Afro-Asian species had an alternative route of dispersion from the Pacific coast. This is also the second documented record of an introduced freshwater copepod in Mexico.La distribucion conocida de Mesocyclops aspericornis en el continente americano incluia las areas sur y central de America del Sur y del Caribe insular. No habia sido recolectada antes en America del Norte. El analisis de muestras recolectadas en un estanque en el estado de Sinaloa, costa pacifica de Mexico, produjo la identificacion de hembras de esta especie. Las hembras recolectadas en Mexico tiended a ser de menor talla que las africanas (1.14-1.20 mm vs 1.3-1.5 mm); sin embargo, la morfologia de los especimenes mexicanos es identica en practicamente todos los caracteres a las descripciones previas. Este es, sin embargo, el primer estudio morfologico auxiliado por microscopia electronica de barrido (MEB); incluye datos detallados sobre varias microestructuras, algunas previamente indescritas. Este es el primer registro efectivo de la presencia de esta especie en Mexico; todos los registros anteriores estaban relacionados con las costas del Oceano Atlantico. Este registro en el area del Pacifico Mexicano sugiere que esta especie Afro-asiatica supuestamente introducida tuvo una via alternativa de dispersion a partir de la costa del Pacifico Tropical Oriental. Este es, ademas, el segundo registro documentado de una especie de copepodo dulceacuicola introducida en Mexico.

Keratella mexicana sp. nov., a new planktonic rotifer from Aguascalientes, Mexico

A new species of Keratella is described from a small reservoir in Aguascalientes, Mexico. The species appears related to K. slacki Bērziņčss, 1963 and K. lenzi Hauer, 1953.

Sexual reproductive biology of twelve species of rotifers in the genera: Brachionus, Cephalodella, Collotheca, Epiphanes, Filinia, Lecane, and Trichocerca

Abstract We provide descriptions of the sexual reproductive biology of 12 species of rotifers from seven families and seven genera: Brachionus angularis, B. araceliae, B. ibericus, B. quadridentatus (Brachionidae); Cephalodella catellina (Notommatidae); Collotheca ornata (Collothecidae); Epiphanes brachionus (Epiphanidae), Filinia novaezealandiae (Trochosphaeridae); Lecane nana, L. leontina, L. bulla (Gosse 1851) (Lecanidae); and Trichocerca stylata (Trichocercidae). Data include: (a) video-recordings of 10 of the 12 species (the exceptions are two common species, B. angularis and B. ibericus), (b) scanning electron micrographs of B. araceliae, B. ibericus, C. catellina, and E. brachionus females, (c) light micrographs of C. catellina, C. ornata, F. novaezealandiae, L. bulla, L. leontina, L. nana, and T. stylata diapausing embryos, males, and unfertilized sexual eggs. This study challenges the common perception that mating behavior consists of five steps, and provides: (a) the first documentation of sexual cannibalism in C. catellina, (b) the first description of the sexual reproductive behaviors of C. ornata, L. bulla, L. leontina, L. nana, and T. stylata, (c) the first description of the males of F. novaezealandiae, L. leontina, L. nana, and T. stylata. Moreover, this study includes analyses of morphological and behavioral variation among males of the seven families studied.

Taxonomic revision of the Mexican Eucyclops (Copepoda: Cyclopoida) with comments on the biogeography of the genus

ABSTRACT Based on the examination of specimens deposited in different national and international biological collections, we reviewed the ca. 800 records of the genus Eucyclops in Mexico and compared them with the type material of presumedly widespread species. Resulting from our taxonomical analysis, in this contribution we recognise 17 species dwelling in Mexico. Complementary upgraded descriptions of eight species emphasising newly introduced taxonomic characters are also presented from the examination of Mexican specimens. These species include E. elegans, E. prionophorus, E. festivus, E. leptacanthus, E. torresphilipi, E. chihuahuensis, E. cuatrocienegas and the recently described E. tziscao and E. angeli. In addition, the use of upgraded descriptive standards involving new morphological characters allowed the discovery of six new species that are described in this work: E. alekseevi sp. nov., E. wixarica sp. nov., E. defayeae sp. nov., E. mittmanni sp. nov., E. estherae sp. nov. and E. ishidai sp. nov. Most of these species were previously recorded in Mexico under different names. The occurrence of E. pectinifer, E. elegans, E. prionophorus and E. leptacanthus in Mexico is herein confirmed. We propose the ornamentation patterns of the fourth swimming legs (i.e. basipodite, coxal plates) as reliable additional characters to recognise closely related species of Eucyclops. The importance of the antennal basis ornamentation in the taxonomy of the genus is supported by our data. We evaluated the taxonomic value of 113 morphometric and binary characters using statistical methods; results of this analysis showed that morphometric characters alone overlap and thus have a limited value to distinguish species of Eucyclops. We include comments on E. serrulatus s. str. in order to provide a complete comparison frame among members of the serrulatus-species complex, but we did not find the strict form in the samples examined. A key to the Mexican species of the genus is also provided.