Context-Dependence in parasite effects on keyhole limpets.

Parasites alter the reproductive performance of their hosts, limit their growth, and thereby modify the energy budget of these hosts. Experimental studies and theoretical models suggest that the outcome of the host-parasite interactions could be determined by ecological factors such as food availability levels in the local habitats. Nutrient inputs may affect the host's food resource availability with positive or negative effects on parasite infection rates and tolerance of infection, however this has not been specifically evaluated in natural systems. In this study, we evaluate the effects of parasitism by Proctoeces humboldti on body size, gonadosomatic index (GSI), and metabolic rate (oxygen consumption) of their second intermediate host Fissurella crassa limpets, under contrasting natural conditions of productivity (upwelling center vs upwelling shadow sites). Our results evidenced that parasitized limpets collected from the intertidal habitat influenced by coastal upwelling site showed greater shell length, muscular foot biomass and GSI as compared to non-parasitized limpets collected in the same site, and compared to parasitized and non-parasitized limpets collected from the sites under the influence of upwelling shadow conditions. Oxygen consumption was lower in parasitized limpets collected from the upwelling-influenced site than in the other groups, independent of age, suggesting reduced metabolic stress in infected individuals inhabiting these productive sites. Our results suggest that increased productivity in upwelling sites could mitigate the conflict for resources in the P. humboldti - F. crassa system, influencing where such interaction is found in the continuum between parasitism and mutualism. Since parasitism is ubiquitous in natural systems, and play important roles in ecological and evolutionary processes, it is important to analyze host-parasite interaction across a variety of ecological conditions, especially in biological conservation.

Role of temperature and carbonate system variability on a host-parasite system: Implications for the gigantism hypothesis.

Biological interactions and environmental constraints alter life-history traits, modifying organismal performances. Trematode parasites often impact their hosts by inducing parasitic castration, frequently correlated with increased body size in the host (i.e., gigantism hypothesis), which is postulated to reflect the re-allocation of energy released by the reduction in the reproductive process. In this study, we compared the effect of a trematode species on shell size and morphology in adult individuals of the intertidal mussels Perumytilus purpuratus (>20 mm) collected from two local populations of contrasting environmental regimes experienced in central-southern Chile. Our field data indicates that in both study locations, parasitized mussels evidenced higher body sizes (shell length, total weight and volume) as compared with non-parasitized. In addition, parasitized mussels from the southern location evidenced thinner shells than non-parasitized ones and those collected from central Chile, suggesting geographical variation in shell carbonate precipitation across intertidal habitats of the Chilean coast. In laboratory conditions, mussels collected from a local population in central Chile were exposed to two temperature treatments (12 and 18 °C). Parasitized mussels showed higher growth rates than non-parasitized, regardless of the seawater temperature treatments. However, the metabolic rate was not influenced by the parasite condition or the temperature treatments. Our field and laboratory results support the parasite-induced gigantism hypothesis, and suggest that both the thermal environment and geographic location explain only a portion of the increased body size, while the parasitic condition is the most plausible factor modulating the outcome of this host-parasite interaction.

Morphometrical and molecular evidence suggests cryptic diversity among hookworms (Nematoda: Uncinaria) that parasitize pinnipeds from the south-eastern Pacific coasts.

Hookworms of the genus Uncinaria parasitize pinniped pups in various locations worldwide. Four species have been described, two of which parasitize pinniped pups in the southern hemisphere: Uncinaria hamiltoni parasitizes Otaria flavescens and Arctocephalus australis from the South American coast, and Uncinaria sanguinis parasitizes Neophoca cinerea from the Australian coast. However, their geographical ranges and host specificity are unknown. Uncinaria spp. are morphologically similar, but molecular analyses have allowed the recognition of new species in the genus Uncinaria. We used nuclear genetic markers (internal transcribed spacer (ITS) and large subunit (LSU) rDNA) and a mitochondrial genetic marker (cytochrome c oxidase subunit I (COI)) to evaluate the phylogenetic relationships of Uncinaria spp. parasitizing A. australis and O. flavescens from South American coasts (Atlantic and Pacific coasts). We compared our sequences with published Uncinaria sequences. A Generalized Mixed Yule Coalescent (GMYC) analysis was also used to delimit species, and principal component analysis was used to compare morphometry among Uncinaria specimens. Parasites were sampled from A. australis from Peru (12°S), southern Chile (42°S), and the Uruguayan coast, and from O. flavescens from northern Chile (24°S) and the Uruguayan coast. Morphometric differences were observed between Uncinaria specimens from both South American coasts and between Uncinaria specimens from A. australis in Peru and southern Chile. Phylogenetic and GMYC analyses suggest that south-eastern Pacific otariid species harbour U. hamiltoni and an undescribed putative species of Uncinaria. However, more samples from A. australis and O. flavescens are necessary to understand the phylogenetic patterns of Uncinaria spp. across the South Pacific.

Molecular evidence confirms that Proctoeces humboldti and Proctoeces chilensis (Digenea: Fellodistomidae) are the same species.

Two species of Proctoeces Odhner, 1911 have been described in marine organisms from Chile: P. humboldti George-Nascimento & Quiroga (1983), parasitizing the gonads of keyhole limpets (Fissurella spp.), and P. chilensis Oliva (1984), an intestinal parasite of Sicyases sanguineus (Teleostei); both species were subsequently considered as P. lintoni Siddiqi & Cable (1960). To assist in the resolution of the taxonomic identification of Proctoeces species in marine organisms from Chile, phylogenetic studies using DNA sequences from the V4 region of the SSU rRNA gene were performed. Several specimens of P. lintoni were isolated from keyhole limpets (Fissurella spp.) and clingfish (S. sanguineus) from Bahia San Jorge (23°40'S) and Bahia Concepción (36°50'S). Phylogenetic analyses were conducted using three different approaches: a neighbour-joining (NJ), a maximum likelihood (ML) and Bayesian inference (BI). The phylogenetic analysis confirms that specimens of Proctoeces obtained from keyhole limpets and those specimens from the clingfish are in fact the same species. We prefer to consider our specimens as Proctoeces cf. lintoni, as the morphology of Proctoeces appears to be of doubtful value and genetic information about P. lintoni Siddiqi & Cable (1960) is not available. In addition, our results strongly suggest that there are at least three species in this genus.

Alloxenic distribution of cystacanths of two Profilicollis species in sympatric crustacean hosts in Chile.

The taxonomic status of Profilicollis ( = Falsifilicollis Webster, 1948) species in crustaceans in Chile is examined. Mole crabs, Emerita analoga (Stimpson 1857), living in the splash zone of a sandy beach at Lenga off the coast of central Chile, harbor Polymorphus (Profilicollis) bullocki Mateo, Córdova and Guzmán 1982, while the estuarine crabs, Hemigrapsus crenulatus (Milne-Edwards, 1837), living in an oligohaline inlet at the same site, harbor Profilicollis spp. cystacanths which cannot be distinguished specifically to either Profilicollis antarcticus or P. chasmagnathi Holcman-Spector, Mañé-Garzón and Dei-Cas 1977. We found no morphological data supporting records of P. altmani along the coast of Chile. Therefore, and after examination of both their morphology and the literature, we consider that P. bullocki must be reinstated as a valid species in the genus. There is a widespread distribution of habitats, such as sandy beaches and inlets, as well as a variety of host taxa involved in the life cycle of Profilicollis spp. Consequently, they provide an interesting scenario for testing hypotheses regarding the coevolution and host specificity of these parasites.

The effect of Anonchocephalus chilensis Riggenbach (Eucestoda: Bothriocephalidea) on infracommunity patterns in Genypterus maculatus Tschudi (Osteichthyes: Ophidiidae).

The use of parasite body size (i.e. body mass) is a promising proxy to improve the study of patterns in parasite infracommunities, which are usually analysed using only numerical descriptors. This study deals with the importance and effect of the presence of a large endoparasite species, the cestode Anonchocephalus chilensis in a marine fish species, Genypterus maculatus, on the structure of the parasite infracommunities. Numerical and volumetric measures of aggregated properties of parasite infracommunities were compared and their correlation examined. The highly dominant presence of A. chilensis by volume causes a dramatic change in the patterns observed, including a smaller total volume of the remaining species when this volumetrically dominant species is present. However, C-scores and V-ratios, both indices based on null models of species occurrence, do not support the idea of communities structured by interspecific competition. Analyses reveal that numerical and volumetric community descriptors are complementary ways to search for patterns and to reveal processes within these systems.

SSCP-based identification of members within the Pseudoterranova decipiens complex (Nematoda: Ascaridoidea: Anisakidae) using genetic markers in the internal transcribed spacers of ribosomal DNA.

The anisakid nematodes morphologically corresponding with Pseudoterranova decipiens sensu lato (s.l.) (Krabbe, 1878) from different seal or sea lion hosts and geographical origins, previously identified as Pseudoterranova krabbei, P. decipiens (s.s.), P. bulbosa, P. azarasi and P. cattani by multilocus enzyme electrophoresis, were characterized using a DNA approach. Also a population of P. decipiens (s.l.) from Chaenocephalus aceratus, the blackfin icefish, from Antarctica and another from Osmerus eperlanus, the European smelt, from Germany were included in the study. The first (ITS-1) and second (ITS-2) internal transcribed spacers (ITS) of ribosomal DNA (rDNA) were amplified by PCR from individual nematodes and analysed by single-strand conformation polymorphism (SSCP), followed by selective sequencing. While no variation in single-stranded ITS-1 and ITS-2 profiles was detected among samples representing each of the species or populations (with the exception of slight microheterogeneity), SSCP analysis of the ITS-2 amplicons allowed the unequivocal differentiation of all of the 5 sibling species of P. decipiens (s.l.) examined, which was supported by sequence differences in ITS rDNA. Samples representing the P. decipiens (s.l.) population from O. eperlanus had the same SSCP profile as those of P. decipiens (s.s.), which was supported by a lack of nucleotide difference in the ITS between them, suggesting that the former represented P. decipiens (s.s.). Based on SSCP results and ITS sequence data, P. decipiens (s.l.) from C. aceratus was genetically most distinct with respect to all other members of Pseudoterranova examined, which indicated that it may represent P. decipiens E (based on geographical origin) or a distinct species. These findings and the molecular approach taken should have important implications for studying the life-cycles, transmission patterns, epidemiology and population genetics of these anisakid nematodes, and the diagnosis of their infections.

Pseudascarophis genypteri n. sp. (Nematoda: Cystidicolidae) parasite from the red ling Genypterus chilensis off Chile.

A new nematode belonging to the Cystidicolidae is described, Pseudascarophis genypteri n. sp. was found in the intestine of the red ling Genypterus chilensis, sampled off Talcahuano, Chile. It is distinguished from Ascarophis species mainly by the absence of cephalic papillae and of submedial and medial labia. The other species in the genus, Pseudascarophis kyphosi Ko, Margolis, and Machida, 1985, found in Kyphosus cinerascens, and P. tropica (Solov'eva, 1996), found in Parupeneus chrysopleuron, differed principally from P. genypteri in the form of pseudolabia, number of pre- and postanal papillae, and length of spicules.

Differential precocious sexual development of Proctoeces lintoni (Digenea: Fellodistomidae) in three sympatric species of keyhole limpets Fissurella spp. may affect transmission to the final host.

The prevalence, abundance, and developmental status of the digenetic trematode Proctoeces lintoni Siddiqui et Cable 1960 were compared in 3 species of keyhole limpets Fissurella. A total of 197 limpets was collected at Caleta Chome, south-central Chile. Fissurella picta and F. costata had the highest prevalence of infection, whereas F. picta showed the greatest abundance of parasites, which increased with host shell length. However, the frequency of P. lintoni specimens with eggs in the uterus was greatest in F. costata. These results suggest that an increased rate of development of a parasite in the intermediate host may shorten the residence time necessary for maturation in the final host. Thus, faster development of the parasite in F. costata suggests the possibility that the parasites transmitted through this host species have shorter maturation times in clingfishes than individuals transmitted via other limpet species.

[Parasite fauna and food contents of Notothenia c.f. angustata Hutton, 1875 (Pisces: Nototheniidae) from two intertidal localities of the Arauco Gulf, Chile]. / Parasitofauna y alimentación de Notothenia c.f. angustata Hutton, 1875 (Pisces: Nototheniidae) en el intermareal de dos localidades del Golfo de Arauco, Chile.

We studied the parasite fauna and food contents of 38 juvenile of Notothenia c.f. angustata specimens captured in the intertidal of Island Santa María and Maule, in the Arauco Gulf, Chile. Trophic habits of Notothenia c.f. angustata were not different between localities, which was mainly algae. A total 11 parasitic taxa among were found with the digenean Lecitasther macrocotyle, cestode larvae Tetraphyllidea and Diphyllidea and nematode Ascarophis sp. being the dominant taxa. The abundance of parasites was similar in the two localities, although the infracommunity richness was higher in fish from Maule. The most abundant parasite was L. macrocotyle in hosts from Isla Santa María, while those from Maule they were the Diphyllidea larvae and nematodes Ascarophis sp. The body length of the hosts was not a good predictor of the variations in abundance and richness at infracommunities, probably because of the early ontogenetic stage of fishes.

Geographical variations in the jack mackerel Trachurus symmetricus murphyi populations in the southeastern Pacific Ocean as evidenced from the associated parasite communities.

The composition of the metazoan parasite communities within 2 fishing zones along the Chilean coast were compared to determine the population structure of the jack mackerel Trachurus symmetricus murphyi (Nichols) in these 2 geographical locations. More than 7,780 parasites belonging to 15 taxa were collected between 1990 and 1996 in 71 samples comprised of 3,946 hosts. The same taxa were found in both fishing zones. However, jack mackerel from northern Chile had a higher abundance of cymothoid isopods, Ceratothoa spp., whereas those from southern Chile had more Rhadinorhynchus trachuri, Hysterothylacium sp. larvae, and Anisakis type I larvae. Results were similar at all community levels because all parasites had low prevalence and infracommunities had low total abundance and richness. Analyses at the component community level may be more adequate for stock identification when infracommunities are simple. There were significant differences in composition of parasite communities between years in each fishing zone, presumably as a result of the increase in offshore catches since 1994. These results reinforce the hypothesis that more than 1 ecological stock of the jack mackerel exists in the southeastern Pacific and contradict the current assumption of a single stock in the management of this heavily exploited fish species.

Micro-evolutionary implications of allozymic and morphometric variations in sealworms Pseudoterranova sp. (Ascaridoidea: Anisakidae) among sympatric hosts from the southeastern Pacific Ocean.

We found significant morphometric and electrophoretic differences between sealworm larvae collected from four sympatric fish host species off the central coast of Chile. The South American sea lion, Otaria byronia, is a suitable host and most likely the only definitive host species in the study area. Morphological patterns of caudal papillae in adult males collected from sea lions and electrophoretic evidence from larvae and adults substantiate our conclusion that they belong to just one, new species yet to be described. The genetic and morphometric differences found between sealworm larvae from sympatric fish hosts may be due to selective pressures arising from the internal environment of the intermediate hosts, although they may serve only for passing sequential filters along the life cycle. The discussion deals with the roles that definitive and intermediate hosts may play in the micro-evolutionary processes of sealworms.

Trypanosoma humboldti n. sp. from the Chilean catshark, Schroederichthys chilensis (Guichenot, 1848).

The morphology of Trypanosoma humboldti n. sp. is described from living and stained specimens obtained from the blood of a catshark, Schroederichthys chilensis. This represents the first report of a trypanosome in fish from the eastern Pacific Ocean. It is distinguished by its size and apparent lack of pleomorphism. The presence of a leech, Branchellion ravenellii, attached to the catshark, raises the possibility that it can act as a vector. Additionally, this leech is recorded for the first time from the Pacific Ocean.