From Sea to Sea: Canada's Three Oceans of Biodiversity

Evaluating and understanding biodiversity in marine ecosystems are both necessary and challenging for conservation. This paper compiles and summarizes current knowledge of the diversity of marine taxa in Canada''s three oceans while recognizing that this compilation is incomplete and will change in the future. That Canada has the longest coastline in the world and incorporates distinctly different biogeographic provinces and ecoregions (e.g., temperate through ice-covered areas) constrains this analysis. The taxonomic groups presented here include microbes, phytoplankton, macroalgae, zooplankton, benthic infauna, fishes, and marine mammals. The minimum number of species or taxa compiled here is 15,988 for the three Canadian oceans. However, this number clearly underestimates in several ways the total number of taxa present. First, there are significant gaps in the published literature. Second, the diversity of many habitats has not been compiled for all taxonomic groups (e.g., intertidal rocky shores, deep sea), and data compilations are based on short-term, directed research programs or longer-term monitoring activities with limited spatial resolution. Third, the biodiversity of large organisms is well known, but this is not true of smaller organisms. Finally, the greatest constraint on this summary is the willingness and capacity of those who collected the data to make it available to those interested in biodiversity meta-analyses. Confirmation of identities and intercomparison of studies are also constrained by the disturbing rate of decline in the number of taxonomists and systematists specializing on marine taxa in Canada. This decline is mostly the result of retirements of current specialists and to a lack of training and employment opportunities for new ones. Considering the difficulties encountered in compiling an overview of biogeographic data and the diversity of species or taxa in Canada''s three oceans, this synthesis is intended to serve as a biodiversity baseline for a new program on marine biodiversity, the Canadian Healthy Ocean Network. A major effort needs to be undertaken to establish a complete baseline of Canadian marine biodiversity of all taxonomic groups, especially if we are to understand and conserve this part of Canada''s natural heritage.     

Speciation in parasites: a population genetics approach

Parasite speciation and host-parasite coevolution should be studied at both macroevolutionary and microevolutionary levels. Studies on a macroevolutionary scale provide an essential framework for understanding the origins of parasite lineages and the patterns of diversification. However, because coevolutionary interactions can be highly divergent across time and space, it is important to quantify and compare the phylogeographic variation in both the host and the parasite throughout their geographical range. Furthermore, to evaluate demographic parameters that are relevant to population genetics structure, such as effective population size and parasite transmission, parasite populations must be studied using neutral genetic markers. Previous emphasis on larger-scale studies means that the connection between microevolutionary and macroevolutionary events is poorly explored. In this article, we focus on the spatial fragmentation of parasites and the population genetics processes behind their diversification in an effort to bridge the micro- and macro-scales.     

Host population density as the major determinant of endoparasite species richness in floodplain fishes of the upper Paraná River, Brazil

A comparative analysis of parasite species richness was performed across 53 species of fish from the floodplain of the upper Paraná River, Brazil. Values of catch per unit effort, CPUE (number of individuals of a given fish species captured per 1000 m(2) of net during 24 h) were used as a rough measure of population density for each fish species in order to test its influence on endoparasite species richness. The effects of several other host traits (body size, social behaviour, reproductive behaviour, spawning type, trophic category, feeding habits, relative position in the food web, preference for certain habitats and whether the fish species are native or exotic) on metazoan endoparasite species richness were also evaluated. The CPUE was the sole significant predictor of parasite species richness, whether controlling for the confounding influences of host phylogeny and sampling effort or not. The results suggest that in the floodplain of the upper Paraná River (with homogeneous physical characteristics and occurrence of many flood pulses), population density of different host species might be the major determinant of their parasite species richness.     

Current status of embryo technologies in sheep and goat

This review presents an overview of the technical bases of in vivo and in vitro embryo production in sheep and goat. The current limitations of in vivo production, such as variability of response to the hormonal treatment, fertilization failure in females showing a high ovulatory response, and the importance of premature regressed CL in the goat, are described along with possibilities for improvement. The new prospects offered by in vitro embryo production, by repeated ovum pick-up from live females and by juvenile breeding, are presented along with their limiting steps and research priorities. The recent improvements of embryo production and freezing technologies could be used for constitution of flocks without risks of disease transmission and will allow wider propagation of valuable genes in small ruminants populations in the future.     

A general test of the interactive-isolationist continuum in gastrointestinal parasite communities of fish

Parasite communities are generally believed to lie somewhere along the interactive-to-isolationist continuum, i.e. from rich assemblages of species with high colonisation rates in which interspecific interactions play an important structuring role, to species-poor assemblages where interactions are unlikely. This framework has become one of the paradigms of parasite community ecology. There is, however, no objective way of ranking a set of parasite communities in terms of the extent of interactivity among their constituent species. Here, we propose a simple index of interactivity based on the general likelihood of species co-occurrence, and thus on the potential for interactions, and we apply it to component communities of gastrointestinal helminth parasites from 37 species of marine fish hosts. The index essentially collapses several features of parasite communities thought to influence the degree of interactivity into a single number independent of the number of hosts examined or the total number of species in a component community. The range of values obtained here suggests that the potential interactivity in helminth communities of fish covers almost the full spectrum of possibilities, i.e. from isolationist to highly interactive communities. Although derived from presence/absence data only, the index correlates relatively strongly with the total parasite abundance per host, as well as the total prevalence of infection and the mean infracommunity richness. In other words, it captures properties of the community that influence interactivity. The use of the index in comparative studies may help in determining whether interactive helminth communities are, as widely believed, more common in endothermic vertebrate hosts than in fish hosts.     

From first to second and back to first intermediate host: the unusual transmission route of Curtuteria australis (Digenea: Echinostomatidae)

The trematode Curtuteria australis uses the whelk Cominella glandiformis as first intermediate host and the cockle Austrovenus stutchburyi as second intermediate host before maturing in shorebirds. The whelk also happen to be an important predator of cockles on intertidal mudflats. In this study we show that whelks can act as temporary paratenic hosts for the trematode. A single whelk feeding on 1 cockle can ingest large numbers of metacercariae, which remain within the whelk for 1-3 days before passing out in feces. The viability of these metacercariae assessed as the percentage capable of successfully excysting under conditions simulating those inside a bird's digestive tract, is lower after passage through a whelk (48%) than before (59%). Still, given that shorebird definitive hosts prey on whelks as well as cockles, survival inside the whelk allows C. australis to complete its life cycle: overall, though, whelk predation is likely to be an important sink for the trematode population. To our knowledge, this is the first report of a trematode using a snail as both first intermediate host and paratenic host, offering an alternative transmission route for the parasite as a result of the unusual trophic relationships of its hosts.     

Larval helminths in intermediate hosts: does competition early in life determine the fitness of adult parasites?

Density-dependent effects on parasite fitness have been documented from adult helminths in their definitive hosts. There have, however, been no studies on the cost of sharing an intermediate host with other parasites in terms of reduced adult parasite fecundity. Even if larval parasites suffer a reduction in size, caused by crowding, virtually nothing is known about longer-lasting effects after transmission to the definitive host. This study is the first to use in vitro cultivation with feeding of adult trematodes to investigate how numbers of parasites in the intermediate host affect the size and fecundity of adult parasites. For this purpose, we examined two different infracommunities of parasites in crustacean hosts. Firstly, we used experimental infections of Maritrema novaezealandensis in the amphipod, Paracalliope novizealandiae, to investigate potential density-dependent effects in single-species infections. Secondly, we used the crab, Macrophthalmus hirtipes (Ocypodidae), naturally infected by the trematodes, M. novaezealandensis and Levinseniella sp., the acanthocephalan, Profilicollis spp., and an acuariid nematode. These four helminths all develop and grow in their crustacean host before transmission to their bird definitive host by predation. In experimental infections, we found an intensity-dependent establishment success, with a decrease in the success rate of cercariae developing into infective metacercariae with an increasing dose of cercariae applied to each amphipod. In natural infections, we found that M. novaezealandensis-metacercariae achieved a smaller volume, on average, when infrapopulations of this parasite were large. Small metacercariae produced small in vitro-adult worms, which in turn produced fewer eggs. Crowding effects in the intermediate host thus were expressed at the adult stage in spite of the worms being cultured in a nutrient-rich medium. Furthermore, excystment success and egg-production in M. novaezealandensis in naturally infected crabs were influenced by the number of co-occurring Profilicollis cystacanths, indicating interspecific interactions between the two species. Our results thus indicate that the infracommunity of larval helminths in their intermediate host is interactive and that any density-dependent effect in the intermediate host may have lasting effects on individual parasite fitness.     

Host specificity and molecular phylogeny of larval Digenea isolated from New Zealand and Australian topshells (Gastropoda: Trochidae)

The maintenance of strict host specificity by parasites when several closely related host species live in sympatry is poorly understood. Species of intertidal trochid snails in the genera Diloma, Melagraphia and Austrocochlea often occur together and are parasitised by a single digenean morphotype (Platyhelminthes, Trematoda), tentatively placed in Opecoelidae. Of the 10 trochid species (6 from New Zealand, 4 from Australia) we examined, six were found to be infected, and the prevalence of infection was as high as 17.5%. We obtained molecular data (mitochondrial 16S and nuclear rDNA internal transcriber spacer 2 sequences, representing 774 bp), to infer phylogenetic relationships amongst these Digenea. Our phylogeny separated the single morphotype into three clearly defined clades (which are almost certainly separate biological species): (i) those infecting two species of Austrocochlea from Tasmania, (ii) those infecting Diloma subrostrata in Otago and Southland, New Zealand, and (iii) those infecting all the parasitised New Zealand topshells (Melagraphia aethiops, D. subrostrata, Diloma nigerrima and Diloma arida) throughout the country. This last group comprised two subclades, one infecting only D. subrostrata and one infecting the other three species. Two D. subrostrata populations were each found to be infected by genetically distinct parasites, yet sympatric populations of the other snails were not necessarily infected. This study is thus the first to reveal cryptic species of digeneans in a single population of a molluscan first intermediate host. We point out also that the degree of host specificity would have been grossly underestimated if, in the absence of our genetic analysis, we had only considered digenean morphology. Our results shed light on the conditions that may favour switching among intermediate hosts in digeneans, and on the presence/absence of host specificity in these parasites.