RESUMO
A common evolutionary response to predation pressure is increased investment in reproduction, ultimately resulting in a fast life history. Theory and comparative studies suggest that short-lived organisms invest less in defence against parasites than those that are longer lived (the pace of life hypothesis). Combining these tenets of evolutionary theory leads to the specific, untested prediction that within species, populations experiencing higher predation pressure invest less in defence against parasites. The Trinidadian guppy, Poecilia reticulata, presents an excellent opportunity to test this prediction: guppy populations in lower courses of rivers experience higher predation pressure, and as a consequence have evolved faster life histories, than those in upper courses. Data from a large-scale field survey showed that fish infected with Gyrodactylus parasites were of a lower body condition (quantified using the scaled mass index) than uninfected fish, but only in lower course populations. Although the evidence we present is correlational, it suggests that upper course guppies sustain lower fitness costs of infection, i.e. are more tolerant, than lower course guppies. The data are therefore consistent with the pace of life hypothesis of parasite defence allocation, and suggest that life-history traits mediate the indirect effect of predators on the parasites of their prey.
Assuntos
Interações Hospedeiro-Parasita , Estágios do Ciclo de Vida/fisiologia , Poecilia/parasitologia , Comportamento Predatório , Animais , Evolução Biológica , Peso Corporal , Ecossistema , Feminino , Masculino , Poecilia/fisiologia , Rios , Trinidad e TobagoRESUMO
Riverine fish populations are traditionally considered to be highly structured and subject to strong genetic drift. Here, we use microsatellites to analyse the population structure of the guppy (Poecilia reticulata), focussing on the headwater floodplain area of the Caroni drainage in Trinidad. We also analyse the population genetics of guppies in the Northern Drainage in Trinidad, a habitat characterized by rivers flowing directly into the sea, and a small isolated population in Tobago. Upland Caroni populations are highly differentiated and display low levels of genetic diversity. However, we found no evidence to suggest that these upland populations experienced recent population crashes and the populations appear to approach mutation-drift equilibrium. Dominant downstream migration over both short- and long-time frames has a strong impact on the population genetics of lowland Caroni populations. This drainage system could be considered a source-sink metapopulation, with the tributary furthest downstream representing a 'super sink', receiving immigrants from rivers upstream in the drainage. Moreover, the effective population size in the lowlands is surprisingly low in comparison with the apparently large census population sizes.
Assuntos
Efeito Fundador , Fluxo Gênico , Genética Populacional , Repetições de Microssatélites/genética , Poecilia/genética , Alelos , Migração Animal , Animais , Variação Genética , Heterozigoto , Dinâmica Populacional , Trinidad e TobagoRESUMO
Results of groundwater and seawater analyses for radioactive (3H, 222Rn, 223Ra, 224Ra, 226Ra, and 228Ra) and stable (D and 18O) isotopes are presented together with in situ spatial mapping and time series 222Rn measurements in seawater, direct seepage measurements using manual and automated seepage meters, pore water investigations using different tracers and piezometric techniques, and geoelectric surveys probing the coast. This study represents first time that such a new complex arsenal of radioactive and non-radioactive tracer techniques and geophysical methods have been used for simultaneous submarine groundwater discharge (SGD) investigations. Large fluctuations of SGD fluxes were observed at sites situated only a few meters apart (from 0 cm d(-1) to 360 cm d(-1); the unit represents cm3/cm2/day), as well as during a few hours (from 0 cm d(-1) to 110 cm d(-1)), strongly depending on the tidal fluctuations. The average SGD flux estimated from continuous 222Rn measurements is 17+/-10 cm d(-1). Integrated coastal SGD flux estimated for the Ubatuba coast using radium isotopes is about 7x10(3) m3 d(-1) per km of the coast. The isotopic composition (deltaD and delta18O) of submarine waters was characterised by significant variability and heavy isotope enrichment, indicating that the contribution of groundwater in submarine waters varied from a small percentage to 20%. However, this contribution with increasing offshore distance became negligible. Automated seepage meters and time series measurements of 222Rn activity concentration showed a negative correlation between the SGD rates and tidal stage. This is likely caused by sea level changes as tidal effects induce variations of hydraulic gradients. The geoelectric probing and piezometric measurements contributed to better understanding of the spatial distribution of different water masses present along the coast. The radium isotope data showed scattered distributions with offshore distance, which imply that seawater in a complex coast with many small bays and islands was influenced by local currents and groundwater/seawater mixing. This has also been confirmed by a relatively short residence time of 1-2 weeks for water within 25 km offshore, as obtained by short-lived radium isotopes. The irregular distribution of SGD seen at Ubatuba is a characteristic of fractured rock aquifers, fed by coastal groundwater and recirculated seawater with small admixtures of groundwater, which is of potential environmental concern and has implications on the management of freshwater resources in the region.
Assuntos
Radioisótopos/análise , Água do Mar/análise , Navios , Poluentes Radioativos da Água/análise , Brasil , Geografia , Rádio (Elemento)/análise , Radônio/análise , Trítio/análise , Movimentos da ÁguaRESUMO
There is large spatial and temporal variation in the Gyrodactylus parasite fauna across natural guppy (Poecilia reticulata) populations in Trinidad. The life history evolution of these fish could be affected differently in the various habitats depending on the local parasite selection pressure. Here, we experimentally infected three guppy populations with three gyrodactylid strains in the laboratory and monitored the infection by recording the number of parasites and host mortality in a full factorial design. The origin of the guppy population and parasite strain, and the size of the hosts explained significant variation in the survival of hosts. Larger fish carried the highest parasite loads and experienced the highest mortality rates, which suggests that parasite-mediated selection may favour smaller phenotypes, possibly counter-balancing selection pressures by gape-limited predators, mate choice and female fecundity. We observed significant variation in virulence between parasite strains with the captive-bred experimental strain (Gt3) causing the highest mortality of hosts whilst reaching only relatively low maximum burdens. This suggests that adaptations to the captive environment and/or inbreeding depression may alter the virulence of such captive-bred parasites. There were significant differences in survival rate between guppy populations, with infected guppies from the large population of the Lower Aripo River showing a higher survival rate than the fish from the small and genetically less diverse Upper Aripo River population.
Assuntos
Poecilia/parasitologia , Trematódeos/patogenicidade , Animais , Tamanho Corporal , Feminino , Interações Hospedeiro-Parasita , Longevidade , Masculino , Análise de Sobrevida , Trinidad e Tobago , VirulênciaRESUMO
Gyrodactylids are ubiquitous fish parasites and yet, with the notable exception of Gyrodactylus salaris, few studies have reported the effect of these parasites on host survival in natural populations. Here, we assess the impact of the parasite load of gyrodactylids (G. turnbulli and G. bullatarudis) on the survival and migration of guppies (Poecilia reticulata) in their natural habitat of the Aripo River in Trinidad. The recapture rate of males declined by 19% with every additional parasite, a remarkably high figure given that the parasite load in this study ranged from zero to 20 worms. In addition, with an increased number of parasites, males were more prone to be recovered downstream. In contrast, no effect of parasitism was observed in females. The mean parasite load sharply declined after a series of flushing events during heavy seasonal downpours. The parasite load varied significantly between fish depending on their location in the river, and the size of the fish explained variation in parasite load between individuals. The present study indicates that tropical gyrodactylid parasites can play an important role in the ecology of natural fish populations, causing intense bouts of natural selection in guppies during heavy rains in the wet season.
Assuntos
Doenças dos Peixes/parasitologia , Poecilia/parasitologia , Trematódeos/crescimento & desenvolvimento , Infecções por Trematódeos/veterinária , Migração Animal , Animais , Ecossistema , Feminino , Masculino , Rios , Estações do Ano , Seleção Genética , Infecções por Trematódeos/parasitologia , Trinidad e Tobago , Clima TropicalRESUMO
Submarine groundwater discharge (SGD) is now recognized as an important pathway between land and sea. As such, this flow may contribute to the biogeochemical and other marine budgets of near-shore waters. These discharges typically display significant spatial and temporal variability making assessments difficult. Groundwater seepage is patchy, diffuse, temporally variable, and may involve multiple aquifers. Thus, the measurement of its magnitude and associated chemical fluxes is a challenging enterprise. A joint project of UNESCO and the International Atomic Energy Agency (IAEA) has examined several methods of SGD assessment and carried out a series of five intercomparison experiments in different hydrogeologic environments (coastal plain, karst, glacial till, fractured crystalline rock, and volcanic terrains). This report reviews the scientific and management significance of SGD, measurement approaches, and the results of the intercomparison experiments. We conclude that while the process is essentially ubiquitous in coastal areas, the assessment of its magnitude at any one location is subject to enough variability that measurements should be made by a variety of techniques and over large enough spatial and temporal scales to capture the majority of these changing conditions. We feel that all the measurement techniques described here are valid although they each have their own advantages and disadvantages. It is recommended that multiple approaches be applied whenever possible. In addition, a continuing effort is required in order to capture long-period tidal fluctuations, storm effects, and seasonal variations.
Assuntos
Ecologia/métodos , Meio Ambiente , Água Doce , Movimentos da Água , Brasil , Ecologia/estatística & dados numéricos , Geografia , Itália , Maurício , New York , Nações Unidas , Austrália OcidentalRESUMO
Gyrodactylus pictae n. sp. is recorded from Poecilia picta in heterospecific shoals with the guppy P. reticulata in Northern Trinidad. G. pictae is morphologically similar to G. turnbulli Harris, 1986, but the hamuli and marginal hooks are slightly smaller and more gracile. The toe and the point of the marginal hook have a distinctly different shape, providing the best morphological characters for distinguishing the two species. The rDNA ITS1 and ITS2 sequences differ from those of G. turnbulli (the closest relative) by >5, suggesting that these two taxa are not sibling species. The origin of the two species on poeciliids of the subgenus Micropoecilia is discussed, and it is suggested that this may represent a case of host-parasite co-evolution.
Assuntos
Poecilia/parasitologia , Trematódeos/isolamento & purificação , Animais , Sequência Consenso , Elementos de DNA Transponíveis/genética , DNA de Helmintos/genética , DNA Ribossômico/genética , Dados de Sequência Molecular , Homologia de Sequência , Especificidade da Espécie , Trematódeos/anatomia & histologia , Trematódeos/genética , Trinidad e TobagoRESUMO
Two new species of Gyrodactylus are described from the South American live-bearing fish Poecilia caucana from Venezuela. Gyrodactylus poeciliae n. sp. is characterised by conspicuous ventral bar processes and by marginal hooks in which the tips are barely curved. Morphologically, the species resembles G. bullatarudis and G. costaricensis, and its relationship to the former was confirmed by sequencing the Internal Transcribed Spacers (ITS-1 and ITS-2) and the 5.8S ribosomal gene of the ribosomal DNA. Gyrodactylus milleri n. sp. was characterised by large, sharply angled marginal hook sickles in which the tips overhang the toes. This species resembled most closely G. turnbulli from guppies. These descriptions confirm the occurrence of G. turnbulli and G. bullatarudis-like gyrodactylids on a range of South American poeciliid fishes.