Browsing by Author "Ojeda, FP"

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    Altered dopamine levels induced by the parasite Profilicollis antarcticus on its intermediate host, the crab Hemigrapsus crenulatus
    (2005) Rojas, JM; Ojeda, FP
    A scrotonergic pathway is apparently involved in parasite-host interactions. Previous studies conducted in our laboratory showed increased rates in oxygen consumption and alterations in body posture in the crab Hemigrapsus crenulatus parasitized by the acanthoceplialan, Profilicollis antarcticus. Such changes may be related to the functions described for biogenic amines in crustaceans. During the infective stage the acanthocephalans live freely in the hemocelomic cavity, suggesting that the possible alteration induced by biogenic amines may be related to their neurohormonal function in crustaceans. To test whether the presence of P. antarcticus produced neurohormonal changes in its intermediate host, H. crenulatus, we analyzed serotonin and dopamine levels in the host using HPLC with electrochemical detection. Two groups of 11 female crabs were studied one group was artificially inoculated with two cystacanths while the other was used as the control. Our results show a dramatic increase in hemolymph dopamine, but not serotonin in H. crenulatus parasitized by the acanthocephalan P. antarcticits. Our results, along with those reported by Maynard (1996), suggest a parasite-specific strategy involved in the behavior alteration caused by the acanthocephalans on their intermediate host. The use of a biogenic amine as a mechanism of interaction by the parasites gives them an endless number of alternative potential actions on their intermediate hosts.
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    Behavioral thermoregulation in the intertidal fish Girella laevifrons (Kyphosidae)
    (1999) Pulgar, J; Bozinovic, F; Ojeda, FP
    One of the key factors that determine an animal's distribution and abundance is environmental temperature. This factor affects all the components of an organism's energy budget and fitness. In this study, we tested the effect of water temperature and starvation on patterns of space use in the intertidal fish Girella laevifrons. We postulated that starved animals would select cold temperatures as a mechanism of energy conservation while fed animals would prefer higher temperatures as a mechanism to facilitate digestive processes. In a thermal gradient tank, fishes, irrespective of treatment (fed and starved), actively selected temperatures between 15 and 18 degrees C. Starvation did not affect temperature selection, although it did alter the time and number of visits to thermal gradient extremes. Starved fishes stayed longer in, and visited the warmer temperatures of the gradient more frequently. In contrast, fed fishes stayed longer in, and visited cold temperatures more frequently. We discuss the ecological consequences of temperature selection and the possible relationship between water temperature, food selection and digestive processes.
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    Biogeographic patterns of Chilean littoral fishes
    (2000) Ojeda, FP; Labra, FA; Muñoz, AA
    In this study, we analyzed the biogeographic patterns of the Chilean littoral fish fauna, including latitudinal trends in teleost and chondrichhyan fish species richness, their distribution range patterns, and their level of endemism, both to the Chilean coast and the Southeastern Pacific. We determined the number and percentage of fish taxa within four different groups based on their biogeographic affinities. This was done, both for teleost and chondrichthyan fishes, at the species, genus and family level. In order to recognise the existence of biogeographic regions, we applied cluster and ordination analyses to the distribution data, using objective bootstrapping techniques at the three taxonomic levels used. We found that littoral fish diversity remains fairly constant along the coast down to around 40 degrees S, declining south of this latitude. We detected two biogeographic regions along the Chilean coast, with a break between them at 40 degrees S. These results lend support to previously recognized biogeographic provinces or faunistic units. These two biogeographic regions are a reflection of the mixed origin of the Chilean littoral ichthyofauna, consisting of northern warm-temperate fishes of subtropical origin and southern cold-temperate fishes of subantarctic origin. While the percentage of fishes endemic to the Chilean coast is not high (18%), a large percentage of teleost species inhabiting Chilean littoral waters are endemic to the Southeastern Pacific (44%). Dispersal and evolutionary history, rather that other factors, seem to explain the observed patterns of distribution of this: particular fish fauna. This study represents a necessary first step towards understanding the biogeography of Southeastern Pacific marine fishes.
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    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
    (2001) Balboa, L; George-Nascimento, M; Ojeda, FP
    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.
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    Divergence and zoogeography of mole crabs, Emerita spp (Decapoda: Hippidae), in the Americas
    (1996) Tam, YK; Kornfield, I; Ojeda, FP
    Six of the nine described species of the mole crab genus Emerita are distributed in the Americas, two [E. analoga (Stimpson, 1857) and E. rathbunae Schmitt, 1935] on the west coast, and four [E. benedicti Schmitt, 1935, E. brasiliensis Schmitt, 1935, E. portoricensis Schmitt, 1935 and E. talpoida (Say, 1817)] on the east. The presence of an extended planktonic larval stage in all Emerita species suggests high dispersal potential and the possibility of extensive gene flow among conspecific populations. Two taxa were sampled to study the extent of gene flow between widely separated conspecific populations: E. analoga (California and Chile) and E. talpoida (Massachusetts, South Carolina, and the west coast of Florida), while all other taxa were characterized from a single location. Portions of two mitochondrial genes, cytochrome oxidase I(COI) and 16S ribosomal RNA (16S rRNA) were sequenced. For data analysis, approximately 500 bp (COI) and 400 bp (16S rRNA) were examined. Estimated genetic divergence of 5.41% in COI between E. talpoida populations sampled from the Gulf of Mexico and the Atlantic coast, and 3.47% between E. analoga sampled in Chile and California, indicates that in both cases there has been no recent gene flow between disjunct populations. Additional molecular and morphological studies are necessary to decide whether disjunct populations should be accorded specific status. We predict that many marine invertebrates with antitropical distributions similar to E. analoga may consist of sibling species. In contrast to relationships inferred earlier from distribution patterns, parsimony analyses of both COI and 16S rRNA data yield similar phylogenetic trees in which E. analoga is separated from a clade composed of other species in the Americas; a bootstrap value (67%) in the COI inferred tree marginally supports the separation, but the same tree topology with a higher bootstrap value (84%) is obtained with 16S rRNA sequence data. Genetic divergence among the taxa indicates that the Emei ita species constitute an old group and that distribution of species has been modified by past climatic and geological events.
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    Does food quality influence thermoregulatory behavior in the intertidal fish Girella laevifrons?
    (2003) Pulgar, JM; Aldana, M; Bozinovic, F; Ojeda, FP
    Algal and invertebrate species are less abundant towards higher zones of the intertidal, where the greatest variations in physical environmental conditions occur. Mobile predators such as fishes that inhabit high intertidal rockpools are thus exposed to wide variations in physical conditions and to a low abundance and quality of food. We used an aquarium with a temperature gradient in the laboratory to assesed whether dietary quality differences modify temperature preferences of Girella laevifrons, one of the most abundant transitory fishes inhabiting rocky shores along the coast of Chile. Our results indicate that food quality clearly modifies temperature preferences in this species. Animals fed on high quality bivalves selected intermediate temperatures (16-18degreesC) while those fed on lower quality algae selected lower temperatures (10-12degreesC). Control fish not subjected to the temperature gradient did not select portions of the aquarium differentially. The thermal selectivity of G. laevifons in relation to the optimization of digestive processes and mechanisms of energy conservation are discussed. (C) 2003 Elsevier Ltd. All rights reserved.
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    Feeding selectivity of the herbivorous fish Scartichthys viridis
    (1999) Ojeda, FP; Muñoz, AA
    The ecological importance of fish herbivory was examined in a temperate rocky intertidal zone along the central Chilean coast. In this system, the blenny Scartichthys viridis is the most abundant and only herbivorous fish. We describe its diet, determine its field food selectivity (gut contents vs macroalgal field availability comparison), and report on its laboratory dietary preferences in a multiple-choice feeding experiment. Finally, we evaluate the relative effects of fish herbivory and grazing invertebrates on macroalgal abundance, distribution and diversity patterns in the field, using replicated exclusion cages to manipulate grazing intensity. S. viridis was found to be a selective grazer; its diet was dominated by 2 macroalgae: the green Ulva and the red Gelidium, representing 32.6 and 41.4% of its total gut content biomass, respectively. Ulva was consumed much above its field availability while Gelidium was selected only during fall-winter. In the laboratory, S. viridis selected the green macroalgae Ulva rigida and Codium dimorphum and avoided Gelidium chilense. We suggest that Gelidium may be included in its diet due to the limited availability of Ulva in the field. Experimental exclusion of this fish from rocky surfaces resulted in increased abundance of green foliose macroalgae (U. rigida and Enteromorpha linza), and, to a much lesser extent, of the red foliose macroalgae G. chilense, Porphyra columbina, and Mazzaella laminarioides, and of the brown macroalgae Colpomenia phaeodactyla and Petalonia fascia, as well as an extension of the distribution of P. columbina from the high intertidal to the mid intertidal zone, where it normally does not occur. Exclusion of grazing invertebrates resulted in a decrease in foliose macroalgal species richness, but had no effect on biomass. To our knowledge, this is the first experimental demonstration of the effect of an herbivorous fish on macroalgal community structure in a temperate rocky intertidal area. The selective feeding displayed by S, viridis, its high numerical abundance, and the results of the herbivore exclusion experiment suggest its importance in maintaining the low abundance of foliose macroalgae and the high relative cover of brown and red crustose macroalgae, characteristic of many low to mid rocky intertidal areas along the coast of central Chile.
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    Intraspecific geographic and seasonal physiological variability in an intertidal fish, Girella laevifrons, along a climatic gradient
    (2006) Pulgar, JM; Ojeda, FP; Bozinovic, F
    Metabolic rate and condition factor (K) of juvenile Girella laevifrons were highest in southern populations along the Chilean coast. Since adults of G. laevifrons complete their life cycle in subtidal waters, the results suggest a metabolic cold adaptation in juveniles of this species and physiological compensation that enable them to move early to subtidal environments for reproduction. (c) 2006 The Fisheries Society of the British Isles.
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    Morphometric and parasitological evidence for ontogenetic and geographical dietary shifts in intertidal fishes
    (2002) Aldana, M; Pulgar, JM; Ogalde, F; Ojeda, FP
    Studies on the feeding ecology of intertidal fish assemblages have indicated the existence of three trophic groups: herbivores, omnivores and carnivores. This classification has enabled researchers to establish some ecological relationships among their components. However, temporal and spatial variations in the use of food resources have rarely been addressed. In this study, ontogenetic and geographical variations in the diet of two inter-tidal fish species: Girella laevifrons and Graus nigra were evaluated through an integrative analysis of their diet, relation between intestinal length/body length, and their parasite fauna. Results of this combined analysis suggest ontogenetic and geographical variations in the diet of G. laevifrons. In G. nigra, no evidence of ontogenetic dietary shifts was found, but marked differences in diet were detected among localities. However, parasitological evidence does not reflect the geographical differences in its diet. Omnivory of G. nigra at two localities (viz Caleta Errazuriz and El Tabo) may be indicative of the opportunistic nature of this species related to the greater availability of macroalgae at these localities. The assessment of intestinal length of G. nigra highlights the importance of considering macroalgal species composition, and not only their abundance as a group, when estimating the quality of the diet of a given fish species. In general, the geographical differences in diet, length of the intestine and parasitofauna of G. laevifrons and G. nigra together suggest that a species' diet is a dynamic feature that may be related to variations in the availability of food resources in the environment.
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    Ontogenetic changes in the diet of the herbivorous Scartichthys viridis in a rocky intertidal zone in central Chile
    (2000) Muñoz, AA; Ojeda, FP
    Scartichthys viridis maintains a herbivorous diet following recruitment to rocky intertidal areas, where it consumes almost exclusively macroalgae. The sheet-like green macroalgae Ulva and Enteromorpha were the main items consumed by individuals <130 mm L-T. The tough branching red macroalga Gelidium made the bulk of the gut contents of specimens >220 mm L-T, Ulva being consumed to a much lesser extent. Further, Gelidium increased in importance in the total gut contents during ontogeny. In contrast, both small (70-120 mm L-T) and medium-sized (140-210 mm L-T) S. viridis individuals preferred Ulva in the laboratory. It is suggested that the increasing consumption of Gelidium along the ontogeny of S. viridis results from the limited availability of Ulva in the field. Large S. viridis individuals possessed longer guts relative to their body length, in comparison with small individuals. (C) 2000 The Fisheries Society of the British Isles.
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    Origin, diversification, and historical biogeography of the genus Trachurus (Perciformes: Carangidae)
    (2005) Cárdenas, L; Hernández, CE; Poulin, E; Magoulas, A; Kornfield, I; Ojeda, FP
    We addressed phylogenetic relationships in the genus Trachurus using cytochrome b gene and D-loop sequences. The trees showed five groups: (1) the Southwest Pacific species (T. japonicus, T. novaezelandiae, and T. declivis); (2) The Mediterranean Sea and Eastern Atlantic species (T. mediterraneus); (3) The Atlantic Ocean species (T. lathami and T trecae); (4) Eastern Atlantic species (T. trachurus and T. capensis); and (5) a group of highly mobile pelagic species, two from the Eastern Pacific (T. symmetricus and T. murphyi) and one from the Eastern Atlantic (T. picturatus). The phylogeny based on Cyt b, supports the molecular clock hypothesis and our results agree with the reported fossil indicating that the origin of this genus occur when the Thetys Sea closed (around 18.4 MYA). In addition, a very slow neutral substitution rate is reported identified only two periods of maximum diversification: the first occurring between 18.4 and 15.0 MYA and the second between 8.4 MYA and present day. (c) 2005 Elsevier Inc. All rights reserved.