Description, biology and molecular characterisation of Serpentirhabdias moi n. sp. (Nematoda: Rhabdiasidae) from Chironius exoletus (Serpentes: Colubridae) in Brazil.

A new species of the genus Serpentirhabdias Tkach, Kuzmin et Snyder, 2014, S. moi n. sp., is described from a colubroid snake Chironius exoletus from Caxiuanã National Forest, State of Pará, Brazil. The species is characterised by having a triangular oral opening, absence of the buccal capsule, presence of six minute onchia in the oesophastome, and excretory glands of approximately the same length as the oesophagus. These qualitative morphological characters, as well as some measurements, differentiate the new species from other Neotropical and Nearctic Serpentirhabdias spp. The morphological description of parasitic adults of S. moi n. sp. is complemented by the description of free-living stages including males, females, and infective larvae. Comparative analysis of partial sequences of cox1 and 12S mitochondrial genes strongly supported the status of S. moi n. sp. as a new species. Molecular phylogeny based on sequences of the nuclear DNA region spanning the 3' end of the 18S nuclear rRNA gene, ITS region (ITS1 + 5.8S + ITS2) and 5' end of the 28S gene supported monophyly of all rhabdiasid genera included in the analysis and placed the new species into the Serpentirhabdias clade as sister taxon to S. fuscovenosa.

Rhabdias rhampholeonis n. sp. and Rhabdias mariauxi n. sp. (Nematoda, Rhabdiasoidea), first lung worms from leaf chameleons: description, molecular evidence and notes on biology.

Rhabdias rhampholeonis n. sp. from Rhampholeon (Rh.) spectrum, Cameroon, and Rhabdias mariauxi n. sp. from Rieppeleon brevicaudatus, Tanzania, are the first lung worms from leaf chameleons. The new species are similar to the majority of species parasitic in chamaeleonids by having a long (>or=10 mm) and thick body (>or=500 microm), long oesophagus (>or=800 microm), wide buccal capsule (>or=40 microm) and low buccal ratio (<0.5). They most closely resemble Rhabdias chamaeleonis and Rhabdias cristati parasitic in Trioceros spp. from East Africa and Cameroon, respectively. Main distinctive characters are a buccal capsule composed of two segments and the head shape. The dorso-ventrally flattened buccal capsule of R. mariauxi n. sp. is unique in Rhabdias parasitising Chamaeleonidae. Sequences of the 12S rDNA and mitochondrial cytochrome c oxidase subunit 1 (coxI) genes were obtained and compared to those of Rhabdias okuensis, the only sequences published for chamaeleonid lung worms. The smallest nucleotide interspecific distances were found between R. mariauxi n. sp. and the former species of Trioceros from Cameroon. Hermaphroditism in females in the lungs, and R. mariauxi n. sp. free-living stages are like in other species from Chamaeleonidae, but the number of infective larvae produced per free-living female (one or two) was not fixed.

Exposure of leopard frogs to a pesticide mixture affects life history characteristics of the lungworm Rhabdias ranae.

We tested the hypothesis that exposure of leopard frogs ( Rana pipiens) to agricultural pesticides can affect the infection dynamics of a common parasite of ranid frogs, the lungworm Rhabdias ranae. After a 21-day exposure to sublethal concentrations of a pesticide mixture composed of atrazine, metribuzin, aldicarb, endosulfan, lindane and dieldrin, or to control solutions (water, dimethyl sulfoxide), parasite-free juvenile frogs were challenged with 30 infective larvae of R. ranae. Approximately 75% of the larvae penetrated the skin and survived in both exposed and control animals, suggesting that pesticides did not influence host recognition or penetration components of the transmission process. Rather, we found that the migration of R. ranae was significantly accelerated in hosts exposed to the highest concentrations of pesticides, leading to the establishment of twice as many adult worms in the lungs of frogs 21 days post-infection. Pesticide treatment did not influence the growth of lungworms but our results indicate that they matured and reproduced earlier in pesticide-exposed frogs compared to control animals. Such alterations in life history characteristics that enhance parasite transmission may lead to an increase in virulence. Supporting evidence shows that certain components of the frog immune response were significantly suppressed after exposure to the pesticide mixture. This suggests that the immune system of anurans exerts a control over lungworm migration and maturation and that agricultural contaminants can interfere with these control mechanisms. Our results also contribute to the ongoing debate regarding the role that anthropogenic factors could play in the perplexing disease-related die-offs of amphibians observed in several parts of the world.

Experimental population dynamics of Rhabdias bufonis (Nematoda) in toads (Bufo bufo): density-dependence in the primary infection.

Density-dependence in worm establishment, numbers, biomass and larval production were examined in primary infections of 0, 10, 40, 80 and 160 larvae of the lung nematode, Rhabdias bufonis in the common toad, Bufo bufo. The infection procedure established 4 non-overlapping levels of infection which persisted until 6 weeks post-infection (p.i.), after which there was an overall decline up to 12 weeks p.i. Worm numbers had no direct effect on adult worm survival but temporal changes in worm weight were density-dependent. Adult worm establishment in the lungs declined significantly as the numbers of worms in the lungs increased. At the lowest exposure dose, 86% of the larvae administered reached maturity in the lungs while at the highest, only 37% did so. Also, the numbers of immature larvae outside the lungs increased as adult worm numbers increased. Both features provide evidence for a threshold limit to the numbers of worms maturing in the lungs. Worm numbers also affected larval output per host and per capita fecundity. A significant positive relationship between per capita fecundity and per capita worm weight suggested that density-dependence acted primarily to constrain the growth of individual worms. Finally, the constraints imposed on worm growth and fecundity were apparently relaxed when worm density decreased, providing evidence for density-dependent flexibility in per capita fecundity. Density-dependence in worm establishment and per capita fecundity are mechanisms which may potentially regulate this host-parasite interaction in the field. Both mechanisms may be functionally related to physical space limitations in the lungs, within which worms must compete for finite nutrients.