Recent visitations by eels to Sable Island, Canada, confirmed by parasites

The presence of immature stages of Proteocephalus macrocephalus in nine-spined stickleback Pungitius pungitius , four-spined stickleback Apeltes quadracus , three-spined stickleback Gasterosteus aculeatus , and mummichog Fundulus heteroclitus from Sable Island ponds was confirmed using scolex morphology. The occurrence of this eel-specific parasite in these accidental hosts provides evidence for recent visits by eels Anguilla rostrata to the isolated island in the North-west Atlantic Ocean off the east coast of Canada.     

Environmental control of salinity preferences in four sympatric species of sticklebacks: Gasterosteus aculeatus, Gasterosteus wheatlandi, Pungitius pungitius and Apeltes quadracus

Salinity preferences of four sympatric species of sticklebacks ( Gasterosteus aculeatus, Gasterosteus wheatlandi, Pungitius pungitius, Apelles quadracus ) were studied after acclimation to different regimes of photoperiod and temperature. The results indicate that photoperiod and temperature influence salinity preferences of G. aculeatus, G. wheatlandi and A. quadracus but that they are virtually without effect in the case of P. pungitius. Moreover, the overall photoperiod effects on salinity preferences are in accordance with the migratory movements of G. aculeatus and A. quadracus. The effect of temperature was more difficult to analyse because of its unnatural timing. It is clear, however, that temperature is involved in the regulation of salinity preferences of G. aculeatus and perhaps of G. wheatlandi. The relative importance of external factors in the adjustment of salinity preferences differed for the four species. However, the results suggest that for G. aculeatus and A. quadracus salinity preferences are an important component of the orientation mechanisms used during their seasonal migrations.     

Parasite fauna in sticklebacks (Gasterosteidae) from bodies of water of the Kola region

The results of a parasitological study of the two species of sticklebacks (Pungitius pungitius and Gasterosteus aculeatus) inhabiting the Kola region are presented. The 42 and 14 species of parasite were found in the nine-spined and three-spined stickleback, respectively. The paucity of the parasite fauna in the three-spined stickleback is observed. Distribution of parasites in Kola waterbodies and ecological peculiarities in system "parasite-host" are presented.     

Parasitism and Shoal Size in Juvenile Sticklebacks: Conflicting Selection Pressures from Different Ectoparasites?

In gregarious animals, group size correlates negatively with infection levels by some kinds of parasites and positively with infection by others. Conflicting selection pressures can be exerted simultaneously on a host species by different parasite species. Among stationary, mixed-species shoals of juvenile threespine sticklebacks, Gasterosteus aculeatus , and blackspotted sticklebacks, Gasterosteus wheatlandi , shoal size correlated differently with levels of infection by two species of ectoparasites. Stickleback shoal size correlated positively with infection levels by the copepod Thersitina gasterostei , which is transmitted among fish by short-lived planktonic larvae. In contrast, infection levels by the highly mobile crustacean parasite Argulus funduli did not decrease as shoal size increased, as predicted from an earlier laboratory experiment. The species composition of the different stickleback shoals also had an influence on some aspects of infection by these two parasite species. The contrasting mode of transmission of the two parasites results in one parasite species having a higher transmission rate among fish within large shoals, whereas the success of the other parasite species is independent of fish shoal size. The two ectoparasites may thus exert different selection pressures on stickleback shoal sizes.     

A checklist of parasites recorded on sticklebacks (Actinopterygii: Gasterosteidae) from Poland

Parasites of the three-spined stickleback, Gasterosteus aculeatus (L.), and the nine-spined stickleback, Pungitius pungitius (L.), from brackish and freshwater habitats in Poland are listed. The following list was compiled from published records and own long-term studies. Parasites are listed alphabetically in meaningful groups of parasites with notes about their location on the host and distribution in Poland with references. A total of 51 species (taxa) of parasites were recorded on G. aculeatus (3 Apicomplexa, 1 Microsporidia, 3 Peritrichia, 1 Myxozoa, 7 Digenea, 2 Monogenea, 10 Cestoda, 10 Nematoda, 7 Acanthocephala, 3 Copepoda, 1 Branchiura, 2 Hirudinea, 1 Bivalvia) and 16 parasites on P. pungitius (1 Apicomplexa, 1 Microsporidia, 2 Peritrichia, 4 Digenea, 1 Monogenea, 2 Cestoda, 2 Nematoda, 1 Copepoda, 1 Branchiura, 1 Bivalvia).     

Observations on the host-parasite relations of Thersitina gasterostei (Crustacea: Copepoda)

This study seeks to analyse the degree of infection of a euryhaline fish with the parasitic copepod Thersitina gasterostei in an extensive brackish-water system. For this purpose, a survey of the occurrence of the parasite on three-spined sticklebacks in the Norfolk Broads was conducted in Spring 1969. An attempt was made to correlate the incidence levels of T. gasterostei with variations in salinity. In addition, observations were made upon the location of the parasite on its host, the changes in maturation of the parasite during the sampling period and the differences in infection between three- and nine-spined sticklebacks.     

Species difference in adaptive use of public information in sticklebacks

Animals foraging on variable food sources can refine their estimates of patch quality by monitoring the success of others (i.e. collect 'public information'). Here, we show that both three-spined sticklebacks (Gasterosteus aculeatus) and nine-spined sticklebacks (Pungitius pungitius) use past cues provided by others to locate food but only nine-spined sticklebacks use prior public information to assess patch quality, regardless of whether demonstrators were conspecifics or heterospecifics. Moreover, nine-spined but not three-spined sticklebacks preferentially hid in vegetation during the demonstration, a position from which they could observe both patches simultaneously and collect public information. We conclude that species differences in the use of public information can be explained by variations in habitat choice and response to predation. Our findings expand current understanding of the scope of public-information use in animals by showing that fishes can use public-information in a foraging context and from heterospecifics. The study suggests that public-information use is an adaptation that allows animals vulnerable to predation to acquire valuable foraging information at low risk.     

A receiver bias in the origin of three-spined stickleback mate choice

Receiver-bias models of signal evolution predict that male sexually selected traits evolve through prior selection for other functions. Female three-spined sticklebacks (Gasterosteus aculeatus) in many populations show a mating preference for males with a red throat and jaw. It has been proposed that this preference evolved because the choice of males with red coloration confers direct and indirect benefits to females in accordance with the Fisher-Zahavi model of sexual selection. We present indirect evidence that the preference is an effect of a receiver bias in the perceptual or cognitive system of G. aculeatus for the colour red, which may have arisen in the context of foraging. In laboratory trials, male and female three-spined and nine-spined sticklebacks (Pungitius pungitius) responded most strongly to red objects outside a mating context. This result demonstrates a correlation between a sexually selected trait and an intrinsic attraction to red objects, and supports the sensory-exploitation model for the evolution of red nuptial coloration in three-spined sticklebacks.     

Some effects of low oxygen tensions on the distribution of the three-spined stickleback Gasterosteus aculeatus L. and the nine-spined stickleback Pungitius pungitius (L.)

During extensive sampling of populations of sticklebacks for parasites, it became apparent that marked differences existed in the distribution of the 2 British freshwater species. Observation of the survival, respiratory rates and distribution of three- and nine-spined sticklebacks from a variety of habitats supports the suggestion that physiologically, the nine-spined stickleback is much better adapted to life in closed, shallow, weedy, eutrophic waters, depleted in oxygen. By comparison, Gasterosteus aculeatus favours more open well oxygenated water.     

Intraspecific variation in behaviour: effects of evolutionary history, ontogenetic experience and sex

Geographical variation in behaviour within species is common. However, how behavioural plasticity varies between and within locally adapted populations is less studied. Here, we studied behavioural plasticity induced by perceived predation risk and food availability in pond (low predation - high competition) vs. coastal marine (high predation - low competition) nine-spined sticklebacks (Pungitius pungitius) reared in a common garden experiment. Pond sticklebacks were more active feeders, more risk-taking, aggressive and explorative than marine sticklebacks. Perceived predation risk decreased aggression and risk-taking of all fish. Food restriction increased feeding activity and risk-taking. Pond sticklebacks became more risk-taking than marine sticklebacks under food shortage, whereas well-fed fish behaved similarly. Among poorly fed fish, males showed higher drive to feed, whereas among well-fed fish, females did. Apart from showing how evolutionary history, ontogenetic experience and sex influence behaviour, the results provide evidence for habitat-dependent expression of adaptive phenotypic plasticity.     

Quantitative effects of three species of parasites on a population of Three-spined sticklebacks, Gasterosteus aculeatus

The effects of Schistocephalus solidus, Diplostomum gasterostei and Echinorhynchus clavula on a population of Three-spined sticklebacks from a pond in Somerset were studied. Schistocephalus was present at the highest level of infection and had the greatest effects on the sticklebacks. It caused the fish to weigh less than uninfected ones of the same length, as shown by the lower condition factor, and to grow more slowly; and it delayed the sexual maturation of fish of both sexes and prevented many from breeding. Diplostomum also had a significant effect on the condition of the sticklebacks and all three parasite species probably caused death or predation of heavily infected fish. The quantitative effects of the parasites on the condition, length and weight of the fish were calculated; seasonal changes in the condition factor could then be seen, and the growth rates for both length and weight calculated.     

Parasites of freshwater resident and anadromous Arctic charr (Salvelinus alpinus) in Greenland

Twenty-one metazoan parasite species were found in Arctic charr at three coastal sites in west Greenland, including Neascus sp. and the nematode Pseudoterranova decipiens , new records for Arctic charr. Twelve species are new records for Arctic charr in Greenland. The quantitative composition of the parasite communities varied, but the freshwater species ( Diphyllobothrium ditremwn, Eubothriutn salvelini, Proteocephalus longicollis, Crepidostotnutn farianis ) were usually numerically dominant, even in anadromous fish. The absence from Greenland of Mysidacea, Amphipoda, Ephemeroptera and Odonata excludes parasites requiring such organisms as intermediate hosts, including the cestode Cyathocephalus truncatus , nematodes of the genus Cystidicola , and freshwater acanthocephalans.     

Contrasting growth strategies of pond versus marine populations of nine-spined stickleback (Pungitius pungitius): a combined effect of predation and competition?

Gigantism in isolated ponds in the absence of sympatric fish species has previously been observed in nine-spined sticklebacks (Pungitius pungitius). Patterns in sexual size dimorphism suggested that fecundity selection acting on females might be responsible for the phenomenon. However, the growth strategy behind gigantism in pond sticklebacks has not been studied yet. Here, we compared von Bertalanffy growth parameters of four independent nine-spined stickleback populations reared in a common laboratory environment: two coastal marine (typical size) and two pond (giant size) populations. We found that both pond populations had larger estimated final size than marine populations, which in turn exhibited higher intrinsic growth rates than the pond populations. Female growth strategies were more divergent among marine and pond populations than those of males. Asymptotic body size and intrinsic growth rate were strongly negatively correlated. Hence, pond versus marine populations exhibited different growth strategies along a continuum. Our data suggest that quick maturation—even with the cost of being small (low fecundity)—is favoured in marine environments. On the contrary, growth to a giant final size (high fecundity)—even if it entails extended growth period—is favoured in ponds. We suggest that the absence (ponds) versus presence (marine environment) of sympatric predatory fish species, and the consequent change in the importance of intraspecific competition are responsible for the divergence in growth strategies. The sex-dependence of the patterns further emphasizes the role of females in the body size divergence in the species. Possible alternative hypotheses are also discussed.     

Rainbow trout (Salmo gairdneri) stocking and Contracaecum spp

A stocking program with rainbow trout (Salmo gairdneri) at High Rock Lake, Manitoba failed due to infections with large numbers of Contracaecum spp. larvae. Nematode larvae in the intestinal tract, body cavity and musculature made the fish unmarketable. A combination of experimental infections of rainbow trout and pelicans (Pelecanus erythrorhynchos), observations on the behavior of fish-eating birds, and numbers of larval Contracaecum spp. in minnow species led to the following conclusions. The introduction of rainbow trout attracted large numbers of fish-eating birds, particularly pelicans. Concurrent predation by rainbow trout on fathead minnows (Pimephales promelas), five-spined sticklebacks (Culaea inconstans), and nine-spined sticklebacks (Pungitius pungitius), concentrated the parasites. The combined increase in densities of the introduced fish host and fish-eating birds, and the short life cycle of the parasite, increased the numbers of parasites in rainbow trout over a season and in the indigenous minnow species between years. Numbers of larvae in the indigenous minnow species declined when stocking of rainbow trout was stopped and use of the lake by fish-eating birds, particularly pelicans, returned to normal levels.     

Do heavy burdens of Schistocephalus solidus in juvenile threespine stickleback result in disaster for the parasite?

The diphyllobothriidean cestode Schistocephalus solidus typically infects threespine sticklebacks that are too small to allow the parasite to reach a mature size. As a result, the parasite must allow further growth of its host to reach the size at which it becomes competent to infect and reproduce in the definitive host. At times, however, intensity of infection can be high, leading to crowding among parasites and to heavy burdens causing mortality among hosts. Our data show that, during a previously observed epizootic, large percentages of plerocercoids (average 75% per host, 82% among all parasites pooled) did not grow to become massive enough in 1-yr-old threespine sticklebacks to be capable of establishment and maturation in the definitive host. Massive deaths of 1-yr-old sticklebacks due to infection during the epizootic resulted in the great misfortune of a disaster for a large number of parasites, resulting in dramatically reduced transmission of S. solidus.     

Low haemosporidian diversity and one key-host species in a bird malaria community on a mid-Atlantic island (São Miguel, Azores)

When host species colonize new areas, the parasite assemblage infecting the hosts might change, with some parasite species being lost and others newly acquired. These changes would likely lead to novel selective forces on both host and its parasites. We investigated the avian blood parasites in the passerine bird community on the mid-Atlantic island of S?o Miguel, Azores, a bird community originating from continental Europe. The presence of haemosporidian blood parasites belonging to the genera Haemoproteus, Plasmodium, and Leucocytozoon was assessed using polymerase chain reaction. We found two Plasmodium lineages and two Leucocytozoon lineages in 11 bird species (84% of all breeding passerine species) on the island. These lineages were unevenly distributed across bird species. The Eurasian Blackbird (Turdus merula) was the key-host species (total parasite prevalence of 57%), harboring the main proportion of parasite infections. Except for Eurasian Blackbirds, all bird species had significantly lower prevalence and parasite diversity compared to their continental populations. We propose that in evolutionary novel bird communities, single species may act as key hosts by harboring the main part of the parasite fauna from which parasites "leak" into the other species. This would create very different host-parasite associations in areas recently colonized by hosts as compared to in their source populations.     

Intraspecific divergence in the lateral line system in the nine-spined stickleback (Pungitius pungitius)

The mechanosensory lateral line system of fishes is an important organ system conveying information crucial to individual fitness. Yet, our knowledge of lateral line diversity is almost exclusively based on interspecific studies, whereas intraspecific variability and possible population divergence have remained largely unexplored. We investigated lateral line system variability in four marine and five pond populations of nine-spined stickleback (Pungitius pungitius). We found significant differences in neuromast number between pond and marine fish. In particular, three of seventeen lateral line regions (viz. caudal peduncle superficial neuromasts; canal neuromasts from the anterior trunk and caudal peduncle) showed strong divergence between habitats. Similar results were obtained with laboratory-reared individuals from a subset of populations, suggesting that the patterns found in nature likely have a genetic basis. Interestingly, we also found habitat-dependent population divergence in neuromast variability, with pond populations showing greater heterogeneity than marine populations, although only in wild-caught fish. A comparison of neutral genetic (F(ST)) and phenotypic (P(ST)) differentiation suggested that natural selection is likely associated with habitat-dependent divergence in neuromast counts. Hence, the results align with the conclusion that the mechanosensory lateral line system divergence among marine and pond nine-spined sticklebacks is adaptive.     

Infectivity of two nematode parasites, Camallanus lacustris and Anguillicola crassus, in a paratenic host, the three-spined stickleback Gasterosteus aculeatus

Three-spined sticklebacks Gasterosteus aculeatus are frequent paratenic hosts of the nematode parasites Anguillicola crassus and Camallanus lacustris. As paratenic hosts, sticklebacks could spread infection by carrying high numbers of infective stages. In contrast, low infective ability of either parasite for the paratenic host could hinder the spread of infection. In the present study, G. aculeatus was, for the first time, infected under controlled laboratory conditions with defined doses of the parasites. Sticklebacks were exposed to 6, 12, 18 and 24 parasite larvae to determine the infective ability of the 2 nematode species. There were significantly higher infection rates for C. lacustris (18 to 49%) than for A. crassus (4 to 14%) at each exposure dose. In C. lacustris-infected sticklebacks, infection rates tended to be highest after exposure to 12 C. lacustris larvae and lowest after exposure to 24 parasites. In A. crassus-infected sticklebacks, no effect of parasite exposure dose on infection rates was observed. Immunity parameters such as respiratory burst activity and lymphocyte proliferation of head kidney leukocytes recorded 18 wk post exposure were not significantly affected by either parasite or exposure dose. Granulocyte:lymphocyte ratios were elevated only within the stickleback group showing the highest infection intensity of C. lacustris, i.e. to those exposed 18 parasites.     

Evolutionary implications of the adaptation to different immune systems in a parasite with a complex life cycle

Many diseases are caused by parasites with complex life cycles that involve several hosts. If parasites cope better with only one of the different types of immune systems of their host species, we might expect a trade-off in parasite performance in the different hosts, that likely influences the evolution of virulence. We tested this hypothesis in a naturally co-evolving host-parasite system consisting of the tapeworm Schistocephalus solidus and its intermediate hosts, a copepod, Macrocyclops albidus, and the three-spined stickleback Gasterosteus aculeatus. We did not find a trade-off between infection success in the two hosts. Rather, tapeworms seem to trade-off adaptation towards different parts of their hosts' immune systems. Worm sibships that performed better in the invertebrate host also seem to be able to evade detection by the fish innate defence systems, i.e. induce lower levels of activation of innate immune components. These worm variants were less harmful for the fish host likely due to reduced costs of an activated innate immune system. These findings substantiate the impact of both hosts' immune systems on parasite performance and virulence.     

Characterization and evolutionary relevance of the sperm nuclear basic proteins from stickleback fish

We have characterized the sperm nuclear basic proteins (SNBPs) of the sticklebacks in the suborder Gasterosteoidei. The complete amino acid sequence of the protamines from Aulorhynchus flavidus, Pungitius pungitius, Gasterosteus aculeatus, (anadromous) and G. wheatlandi, as well as the sequences of the protamines of several species pairs of freshwater G. aculeatus, have been determined. Analysis of the primary structure of these proteins has shown that: a) despite the relatively low amino acid complexity and small molecular mass of these basic proteins, they are very good molecular markers at the generic level. The bootstrap parsimony analysis using their sequences provides a phylogenetic relationship for the old anadromous species of Gasterosteoidei which is identical to that obtained from morphological and behavioral analysis; b) the comparison of the sequences also suggests that protamines from the suborder Gasterosteoidei have most likely evolved from a common gene in the early Acanthopterygii by an extension of the carboxy terminal portion of the molecule; c) protamines are not good markers for recent postglacial freshwater isolates of G. aculeatus. However, in the unique case of Enos Lake (British Columbia), we have been able to detect an additional minor protamine component in the benthic forms of G. aculeatus that is not present in the limnetic forms. Thus, this new protamine must have appeared during the past 12,000 years concomitantly with the speciation of benthics and limnetics in this lake.