Cristina De Villalobos

Toxicity of the herbicide glyphosate to Chordodes nobilii (Gordiida, Nematomorpha)

Nematomorpha (horsehair worms) is a poorly known group of worm-like animals similar to nematodes. Adults are free-living and reproduction takes place in freshwater environments, where preparasitic larvae undergo development. All species have a parasitic juvenil stage and infection may result in the hosts death, insects being the most frequent host. Most of the life cycle occurs in freshwater environments, which are often contaminated by different pollutants. Based on the lack of information on the toxicity of herbicides to horsehair worms, the objective of this study is to evaluate the effect of different concentrations of glyphosate (technical grade and formulated product) on Chordodes nobilii (Gordiida, Nematomorpha). Bioassays were performed with embryos and larvae (preparasitic stages), and adults (postparasitic stage). Test organisms were exposed for a short period of time to concentrations ranging between 0.1 and 8 mga.e.l(-1) of glyphosate (technical and formulated). Although embryo development was not inhibited, there was a significant decrease in the infective capacity of larvae derived from eggs that had been exposed to >or= 0.1mg/l. Similar results were obtained for directly exposed larvae. No differences in toxicity were detected between the active ingredient and formulated product. Adult exposed for 96 h to 1.76 mgl(-1) formulated Gly shown a mortality of 50%. Results indicate that C. nobilii is affected at glyphosate concentrations lower than those expected to be found in freshwater environments and those specified in the legislation.

Validation test with embryonic and larval stages of Chordodes nobilii (Gordiida, Nematomorpha): sensitivity to three reference toxicants.

Chordodes nobilii is a parasite whose pre- and postparasitic stages are found in different types of freshwater bodies. Due to the peculiarities of its life cycle, it acts as a link between freshwater bodies and terrestrial ecosystems. There is little toxicological information on the group Gordiida. It is only known that embryos and larvae of C. nobilii are sensitive to glyphosate and malathion at relevant concentrations in the environment. On this basis, the aims of this study were to characterize the sensitivity of the pre-parasitic stages of C. nobilii to three reference toxicants: sodium dodecyl sulfate (SDS), cadmium chloride and potassium dichromate (Cr(6+)), and to validate a previous experimental protocol for ecotoxicological risk assessment. The protocol involved acute exposure of early embryonic stages and larvae to the three toxicants for 96 h and 48 h, respectively. Embryo development was inhibited only by Cr(6+) which presented a IC(50) of 0.71 mg Cr(6+)L(-1). The development of the eggs exposed to SDS and those exposed to cadmium chloride showed no differences as compared to that of controls. However, the infective capacity of larvae derived from the eggs exposed to the three toxicants was lower than that of controls. Larval survival was affected even at the lowest concentration of the three toxicants assayed. In relation to other freshwater organisms, C. nobilii can be characterized as an organism medium to highly sensitive to the toxicants tested.

Larval survival strategy during winter of Chordodes nobilii Camerano, 1901 (Gordiida, Nematomorpha)

There are numerous open questions concerning the life cycle of Gordiida (Nematomorpha), especially about egg development and viability of larvae during winter, when the temperature of freshwater environments where they inhabit is low. On the basis of experimental studies we demonstrate that egg development of Chordodes nobilii takes 20–25 days at 22°C and 45–55 days at 5°C. We also observed that larvae of C. nobilii obtained from egg strings at 5°C and maintained at that temperature during six months remained inside their egg shells as a survival strategy.

FINDING OF GORDIUS AUSTRINUS DE VILLALOBOS, ZANCA & IBARRA - VIDAL, 2005 (GORDIIDA, NEMATOMORPHA) IN THE STOMACH OF SALMO TRUTTA (SALMONIFORMES) IN PATAGONIA

En trabajos de campo se pudo observar, por primera vez, casos de depredacion de Salmo trutta sobre Gordius austrinus en el Lago Risopatron, Region de Aysen, Chile. El analisis ultraestructural (MEB) realizado sobre los especimenes de gordiidos, colectados dentro del estomago de la trucha cafe, sobre las caracteristicas del extremo posterior y la cuticula, permitieron asignarlos a la especie Gordius austrinus. Asimismo, mostro que en algunos especimenes la cuticula de la region media del cuerpo y el extremo posterior presentaban alteraciones en su estructura, probablemente debidas a la accion de los jugos digestivos del pez. Este hallazgo implica la ampliacion del rango de distribucion de G. austrinus.

Ultrastructural study of the cuticle and epidermis in Pseudochordodes bedriagae

Abstract. The light-microscopic and ultrastructural characteristics of Nematomorpha (Gordiacea) integument are described. Nine male Pseudochordodes bedriagae specimens were collected in the 1997 spring-summer period from the Sauce Chico stream in the Sierra de la Ventana, province of Buenos Aires, Argentina. Of these samples, two were analyzed using scanning electron microscopy (SEM) and the other two using transmission electron microscopy (TEM) in order to establish their morphological characteristics. The morphology of the three integumentary components (epidermis, cuticle and epicuticle) is described. Comparing our findings with those of previous studies, numerous similarities are pointed out. Some variants found would probably be related more to the various criteria of interpreting cut incidences and/or fractures than to actual differences. We assume that the different zones of the cuticle and epicuticle are segregated at the germinal stratum level by the epidermal cells, which would later undergo a slow process of maturation until their exocytosis at the level of the free epicuticular surface.

Redescription and new records of freshwater Nematomorpha (Gordiida) from Chile, with the description of two new species

Hasta el momento solo han sido citadas para Chile cuatro especies de Gordiida (Nematomorpha). En este trabajo se describen dos especies nuevas, Gordionus enigmaticus y Gordius austrinus. Gordionus enigmaticus se caracteriza por la variacion en la forma de las areolas a lo largo del surco longitudinal ventral y porque en la region pre-cloacal del extremo posterior, los campos de cerdas estan ausentes. Gordius austrinus se distingue de otras especies de Gordius por la presencia de un reborde precloacal que limita la depresion del area cloacal, por la prominencia cuticular donde se encuentra la abertura cloacal y por el patron de distribucion de las cerdas en el extremo posterior. Asimismo se redescriben ultraestructuralmente a Gordius paranensis, G. robustus y Neochordodes meridionales y se senala la distribucion para Chile de cada especie

Revision of the genus Beatogordius (Gordiida, Nematomorpha): II. South american species with description of two new species

Seven species of Beatogordius (Nematomorpha) have been reported from South America. A reinvestigation could not reproduce a number of determinations indicated in the literature. B. deshayesi has been a misinterpretation and the status of B. irregularis appears to be very uncertain, because no generic characters could be found. The descriptions of B. alfredi and B. latastei confirm that these species belong to South America only. In B. abaiconus we found adhesive warts anterior of the male cloacal opening. These structures were to date only known from the genus Gordionus. In the posterior end of females from B. alfredi and B. variabilis, short paired rows of bristles were present which had to date only been known from the African species B. equinatus. Two new species, B. funis and B. palustre could be added to the genus.

U0ltrastructural description of the musculature, the intraepidermal nervous system, and their interrelation in Pseudochordodes bedriagae (Nematomorpha).

Abstract. The ultrastructure of the body wall muscles and the intraepidermal nervous system of the Gordiida Pseudochordodes bedriagae are described. The body wall muscles are of the circomyarian type, since the sarcomeres constitute a system of continuous peripheral helices. The organisation of the sarcomeres follows a pattern that resembles that of the striated muscles. The muscle fibres are separated into areas by invaginations formed exclusively by the plasma membrane (T component), while the sarcoplasmic reticulum lies at the sides of the Z granules forming subsarcolemmal cisternae, and in the zone near the nucleus, like flattened vesicles, contributing with the T component to the formation of dyads and triads. The muscle fibres present two types of adaptations for their innervation: (1) cytoplasmic projections towards the epidermis, and (2) invaginations of the plasmalemma. The motor peripheral nervous system is conformed by the nerve fibres that run within the epidermis and their projections towards the basal membrane in order to contact the adaptations of the muscle fibres in a basi-epidermal synapsis. The presence of an intraepithelial peripheral nervous system in Gordiida confirms a structural pattern common to other taxa of Nemathelminthes.

Effect of extreme temperature on egg development, larval and adult survival of Chordodes nobilii Camerano, 1901 (Gordiida, Nematomorpha)

On the basis of experimental studies we analyzed the effect of extreme temperatures on the aquatic free-living phases of the life cycle of Chordodes nobilii (Gordiida, Nematomorpha). Bioassays were performed with eggs, larvae, and adults. Eggs and larvae were exposed to 3°C below zero and 40.5°C; adults were exposed to 3°C below zero and to 38.5°C and 40.5°C. The results showed that egg development was inhibited in both tests. Exposed larvae showed a decrease in their infective capacity, which resulted almost null at 40.5°C. Adults exposed to 38.5°C showed mortality ≤10%, at 40.5°C the mortality was 100% and the adult’s mortality at 3°C below zero was 89%. Results indicate that free living stages of Chordodes nobilii are susceptible to extreme temperatures.

Susceptibility of Aedes aegypti larvae to parasitism by Paragordius varius under laboratory conditions

Abstract Six hundred larvae of all instars of Aedes aegypti Linnaeus, 1762 (Diptera: Culicidae) were experimentally infected with larvae of Paragordius varius (Leidy, 1851) (Gordiida: Nematomorpha). All A. aegypti larvae were examined under a light microscope in order to assess the percentage of parasitized larvae, the number of P. varius larvae per A. aegypti larva and their location (thorax and/or abdomen). ANOVA was used for statistical testing of treatment effects. Data of the number of P. varius larvae per A. aegypti larva were log transformed and analyzed by two-factors ANOVA (instars: 1st, 2nd, 3rd, 4th; position: thorax and abdomen). Means were compared by Tukey test and the significance level was set at P< 0.05. The results obtained showed that A. aegypti larval mortality, at 2h 30min after infection, was higher in parasitized larvae (42.5 %) than in the control group (3 %). First and 2nd instar larvae were the most susceptible to parasitism (52.15% and 46.67 % respectively). More than 90% of each instar A. aegypti larvae were parasitized and the percentage parasitism did not differ between instars. More parasitic larvae were found in 1st and 2nd instar A. aegypti larvae than in 3rd and 4th instars. Paragordius varius parasitize predominantly the abdomen. 9.1% 3rd instar and 68.4% 4th instar Aedes aegypti larvae induced an internal defense reaction (IDR). No infection was registered in the control group.