RESUMO
The aim of this study was to investigate the tolerance of Hypsolebias radiseriatuslarvae to different salinities, and the effects of different prey concentrations and water salinities on the larviculture of this species. Salinity tolerance was tested by subjecting newly-hatched larvae to 96 hours of osmotic shock testing (experiment I) and gradual acclimatization (experiment II) of the following salinities: freshwater (control), 2, 4, 6 and 8 g of salt L-1. A third experiment (experiment III) evaluated three water salinities (S0-freshwater, S2-2 g of salt L-1and S44 g of salt L-1) and three initial daily prey concentrations (100, 300 and 500 artemia nauplii larva-1). In experiments I and II, survival was only influenced by the salinity of 8 g of salt L-1(p < 0.01). After 35 days, weight was only influenced by prey concentration (p < 0.05), with the highest value being with 500 artemia nauplii larva-1. The lowest survival was for 4 g of salt L-1and for 100 artemia nauplii larva-1. H. radiseriatuslarviculture can be carried out in salinity of up to 2 g of salt L-1and initial daily prey concentrations with 500 artemia nauplii larva-1.
Assuntos
Animais , Peixes Listrados/fisiologia , Pressão Osmótica , Salinidade , Tolerância ao SalRESUMO
The aim of this study was to investigate the tolerance of Hypsolebias radiseriatuslarvae to different salinities, and the effects of different prey concentrations and water salinities on the larviculture of this species. Salinity tolerance was tested by subjecting newly-hatched larvae to 96 hours of osmotic shock testing (experiment I) and gradual acclimatization (experiment II) of the following salinities: freshwater (control), 2, 4, 6 and 8 g of salt L-1. A third experiment (experiment III) evaluated three water salinities (S0-freshwater, S2-2 g of salt L-1and S44 g of salt L-1) and three initial daily prey concentrations (100, 300 and 500 artemia nauplii larva-1). In experiments I and II, survival was only influenced by the salinity of 8 g of salt L-1(p < 0.01). After 35 days, weight was only influenced by prey concentration (p < 0.05), with the highest value being with 500 artemia nauplii larva-1. The lowest survival was for 4 g of salt L-1and for 100 artemia nauplii larva-1. H. radiseriatuslarviculture can be carried out in salinity of up to 2 g of salt L-1and initial daily prey concentrations with 500 artemia nauplii larva-1.(AU)
Assuntos
Animais , Salinidade , Peixes Listrados/fisiologia , Tolerância ao Sal , Pressão OsmóticaRESUMO
Dietary specialization on hard prey items, such as mollusks and crustaceans, is commonly observed in a diverse array of fish species. Many fish consume these types of prey by crushing the shell to consume the soft tissue within, but a few fishes extricate the soft tissue without breaking the shell using a method known as oral shelling. Oral shelling involves pulling a mollusc from its shell and it may be a way to subvert an otherwise insurmountable shell defence. However, the biomechanical requirements and potential adaptations for oral shelling are unknown. Here, we test the hypothesis that a novel nasal protrusion is an adaptation for oral shelling in the durophagous pupfish (Cyprinodon brontotheroides). We first demonstrate oral shelling in this species and then predict that a larger nasal protrusion would allow pupfish to consume larger snails. Durophagous pupfish are found within an endemic radiation of pupfish on San Salvador Island, Bahamas. We took advantage of closely related sympatric species and outgroups to test: (a) whether durophagous pupfish shell and consume more snails than other species, (b) if F1 and F2 durophagous hybrids consume similar amounts of snails as purebred durophagous pupfish, and (c) if nasal protrusion size in parental and hybrid populations increases the maximum size of consumed snails. We found that durophagous pupfish and their hybrids consumed the most snails, but did not find a strong association between nasal protrusion size and maximum snail size consumed within the parental or F2 hybrid population, suggesting that the size of their novel nasal protrusion does not provide a major benefit in oral shelling. Instead, we suggest that the nasal protrusion may increase feeding efficiency, act as a sensory organ, or is a sexually selected trait, and that a strong feeding preference may be most important for oral shelling.
Assuntos
Adaptação Fisiológica , Distribuição Animal , Comportamento Alimentar/fisiologia , Peixes Listrados/anatomia & histologia , Peixes Listrados/fisiologia , Animais , Bahamas , SimpatriaRESUMO
Oxidative stress plays an important role in the evolution of aging and life history. High investments in life-history traits and environmental conditions can be associated with increased oxidative stress and aging process. However, to date, most studies that investigated variations in oxidative status were performed with long-lived vertebrates. Studies with short-lived vertebrates in wild are nonexistent. Annual killifishes have the shortest lifespans among vertebrates and inhabit temporary ponds subject to large variations in environmental conditions. In this sense, we investigated whether the high investment in growth and reproduction in a short-lived vertebrate and the large variations in environment has any cost in susceptibility to oxidative stress. We assessed the seasonal variation and the environmental correlates of four different oxidative status markers (lipid peroxidation and activity of the antioxidant enzymes Superoxide Dismutase, Catalase and Glutathione S-Transferase) along the life cycle of wild individuals of the Neotropical annual fish Austrolebias minuano. Males showed reduction in all biomarkers (except proteins) along their life cycle, while females showed increased oxidative stress only in the growth period. In addition, we showed that water physicochemical parameters, habitat structure and presence of co-occurring killifish species influenced the seasonal variation of the biomarkers. A. minuano showed an efficient antioxidant system for most part of their life cycle (mainly in males), suggesting a well-developed oxidative stress regulation system. We also show that annual fish mortality (mainly in males) apparently is not related to oxidative stress. Thus, environmental factors should drive annual fish aging and mortality.
Assuntos
Peixes Listrados/fisiologia , Longevidade , Estresse Oxidativo , Fatores Etários , Animais , Biomarcadores/metabolismo , Catalase/metabolismo , Meio Ambiente , Feminino , Glutationa Transferase/metabolismo , Peixes Listrados/metabolismo , Peroxidação de Lipídeos , Masculino , Estações do Ano , Fatores Sexuais , Superóxido Dismutase/metabolismoRESUMO
Aging processes have become an attractive field for researchers and annual fish have been used as biological models. However, the study on the changes in age-associated markers during the normal aging in wild populations of annual fish remains open. Austrolebias is a genus of Neotropical annual killifishes, distributed mainly in ephemeral pools across grassland floodplains of temperate South America and represent an emerging biological model for aging research, but studies investigating rapid aging and senescence in this genus of annual fish are almost non-existent. This study was undertaken to examine the changes in age-associated liver markers at the different developmental stages in wild populations of Austrolebias minuano. We demonstrate that A. minuano has a number of liver alterations of different severities throughout the life cycle, suggesting that these changes tend to increase with age. Our results revealed that > 70% of the analyzed livers presented alterations. Thus, our study should instigate new approaches on aging using Neotropical annual fish, and could be useful to improve the knowledge already provided by consecrated biological aging models as e.g. Nothobranchius killifishes.
Assuntos
Envelhecimento/fisiologia , Fígado Gorduroso/metabolismo , Peixes Listrados/fisiologia , Lipofuscina/análise , Fígado/metabolismo , Animais , Biomarcadores/metabolismo , Fundulidae , Modelos Biológicos , beta-Galactosidase/análiseRESUMO
Cellular aspects of oocyte development of the Mexican rivulus Millerichthys robustus were morphologically described in order to analyze ovarian function and the cellular recruitment dynamics associating it with life history strategies of annual killifishes. Millerichthys is an iteroparous batch spawner with continuous oocyte recruitment and indeterminate fecundity with asynchronous development of the follicles. It has two ovaries of cystovarian type, with a central lumen, which communicates with the outside through the caudal region of the ovary, that is, the gonoduct. From the walls of the ovary, irregular lamellae composed of germinal epithelium and vascularized stroma project. Oogenesis starts with oogonial proliferation, found alone or in nests within the germinal epithelium. The oogonia come into meiosis becoming oocytes and advancing to the chromatin nucleolus stage and to early primary growth stage. Folliculogenesis is completed in the primary growth stage and cortical alveoli step. Follicles moves toward the stroma, but they continue to be attached to the germinal epithelium through the basement membrane until ovulation. The inclusion of fluid yolk in the follicles during the secondary growth stage was observed. During ovulation, the follicle collapsed, the oocyte was released into the lumen, and the constitutive elements of the post-ovulatory follicle complex remained in the stroma.
Assuntos
Peixes Listrados/anatomia & histologia , Peixes Listrados/fisiologia , Oogênese/fisiologia , Ovário/anatomia & histologia , Animais , Feminino , MéxicoRESUMO
The name killifish refers to the oviparous secondary freshwater fishes in the order Cyprinodontiformes. Killifishes are abundant in Mexico and are represented by four extant families, Rivulidae, Profundulidae, Fundulidae and Cyprinodontidae, comprising > 50 species in a wide variety of habitats. This paper reviews the current classification of the killifishes of Mexico, as well as aspects of their distribution, biology, ecology and current population conservation status.
Assuntos
Biodiversidade , Peixes Listrados/classificação , Peixes Listrados/fisiologia , Distribuição Animal , Animais , Ecologia , México , Filogenia , Densidade Demográfica , Especificidade da EspécieRESUMO
The colonization of new adaptive zones is widely recognized as one of the hallmarks of adaptive radiation. However, the adoption of novel resources during this process is rarely distinguished from phenotypic change because morphology is a common proxy for ecology. How can we quantify ecological novelty independent of phenotype? Our study is split into two parts: we first document a remarkable example of ecological novelty, scale-eating (lepidophagy), within a rapidly-evolving adaptive radiation of Cyprinodon pupfishes on San Salvador Island, Bahamas. This specialized predatory niche is known in several other fish groups, but is not found elsewhere among the 1,500 species of atherinomorphs. Second, we quantify this ecological novelty by measuring the time-calibrated phylogenetic distance in years to the most closely-related species with convergent ecology. We find that scale-eating pupfish are separated by 168 million years of evolution from the nearest scale-eating fish. We apply this approach to a variety of examples and highlight the frequent decoupling of ecological novelty from phenotypic divergence. We observe that novel ecology is not always tightly correlated with rates of phenotypic or species diversification, particularly within recent adaptive radiations, necessitating the use of additional measures of ecological novelty independent of phenotype.
Assuntos
Adaptação Biológica , Especiação Genética , Peixes Listrados/classificação , Filogenia , Animais , Bahamas , Ecossistema , Comportamento Alimentar , Feminino , Peixes Listrados/fisiologia , Masculino , Fenótipo , Especificidade da Espécie , Fatores de TempoRESUMO
Since many traits are involved in both female mating decisions and male contest outcomes, female mate choice and male competition can act in concert to intensify sexual selection on male traits, or in opposition to weaken it. In the sexually dimorphic annual killifish, Austrolebias charrua, we evaluated the effect of male body size on female mate choice, male-male competition, and their interaction. We carried out an experiment with three consecutive stages: (i) female choice test between males of different size in a classic two-choice device, (ii) agonistic interactions between males used in the previous stage, and (iii) a second female choice test to evaluate preference consistency in females that either were allowed or were prevented from observing the male competition. Larger males were preferred by females and became socially dominant in agonistic interactions. Further, females were consistent in their choices, and this consistency was independent of whether they had observed or not the male contest. Our research shows that, in A. charrua, intrasexual competition and female mate choice act in concert with respect to male body size. The unique life-history of Austrolebias and the high repeatability of mate-choice assays make this system a promising candidate for studies of behavioural evolution.
Assuntos
Tamanho Corporal/fisiologia , Peixes Listrados/fisiologia , Preferência de Acasalamento Animal/fisiologia , Animais , Evolução Biológica , Comportamento de Escolha/fisiologia , Feminino , Masculino , FenótipoRESUMO
The relationship between phenotype and fitness can be visualized as a rugged landscape. Multiple fitness peaks on this landscape are predicted to drive early bursts of niche diversification during adaptive radiation. We measured the adaptive landscape in a nascent adaptive radiation of Cyprinodon pupfishes endemic to San Salvador Island, Bahamas, and found multiple coexisting high-fitness regions driven by increased competition at high densities, supporting the early burst model. Hybrids resembling the generalist phenotype were isolated on a local fitness peak separated by a valley from a higher-fitness region corresponding to trophic specialization. This complex landscape could explain both the rarity of specialists across many similar environments due to stabilizing selection on generalists and the rapid morphological diversification rate of specialists due to their higher fitness.
Assuntos
Adaptação Fisiológica/genética , Evolução Biológica , Aptidão Genética , Peixes Listrados/genética , Peixes Listrados/fisiologia , Animais , Bahamas , Cruzamentos Genéticos , Ecossistema , Meio Ambiente , Feminino , Especiação Genética , Hibridização Genética , Lagos , Masculino , Modelos Biológicos , Fenótipo , Seleção GenéticaRESUMO
A fundamental question in sympatric speciation is how trophic divergence is achieved. We used an extremely young (<8,000 years) species flock of pupfish (Cyprinodon spp.) from Laguna Chichancanab in south-eastern Mexico to examine divergent evolution of preferences for different feeding substrates. In a test aquarium, we presented four feeding substrates (sand, gravel, a plastic plant, and blank bottom), but no actual food was offered. The four feeding substrates were chosen to mirror the most common substrate types in Laguna Chichancanab. Previous studies demonstrated that benthic food items prevail in the diet of most Cyprinodon species. C. beltrani preferred sand, whereas C. labiosus preferred gravel. F(1) hybrids of both species showed intermediate preferences. C. maya searched for food equally at all substrates. As the test fish were reared under identical laboratory conditions (i.e., in the absence of feeding substrates), the species-specific preferences appear to be genetically fixed, suggesting rapid divergent evolution of feeding behaviors.
Assuntos
Comportamento Alimentar/fisiologia , Peixes Listrados/fisiologia , Filogenia , Ração Animal , Animais , Evolução Biológica , Tamanho Corporal , Comportamento de Escolha , Peixes Listrados/anatomia & histologia , Peixes Listrados/classificação , MéxicoRESUMO
The Cyprinodon species flock from Laguna Chichancanab, aged 8000 years, provides another potential case of sympatric speciation. The flock consists of seven morphologically distinct species, each within partially different trophic niches, and a group of specimens which cannot unequivocally be assigned to one of these species. Genetic analyses, based on mtDNA and five microsatellite loci, revealed significant genetic differentiation of one species, C. maya, from other members of the species flock, providing strong evidence for reproductive isolation. For the remaining members of the flock significant genetic structuring was detected, with some evidence of gene flow with the most abundant species C. beltrani. These analyses suggest that speciation proceeds with ongoing hybridisation, and further suggest that the morphologically unidentifiable specimens found in the lake are probably hybrids. I propose that in the Cyprinodon species flock besides disruptive selection sexual selection plays an important part in achieving and maintaining reproductive isolation.