RESUMO
BACKGROUND: Analyses of spatial and temporal patterns and interactions are important for determining the abiotic factors limiting populations and the impact from other species and different anthropogenic stressors that promote the extirpation of species. The fish Hubbsina turneri de Buen (1940) was studied as a model species in a historical context at varying locations. Originally distributed only in the Lerma-Chapala basin, the main lake complex in Mexico, this species has not been collected from Lake Cuitzeo (LC) and now is restricted to Lake Zacapu (LZ). At present, the Highland splitfin is classified as critically endangered. METHODS: Historical information of LC and historical and current information from LZ were explored by applying cluster analysis and generalized additive mixed model (GAMM) to describe the biotic interactions among fish species and the relationship between density and environmental variables, respectively. The two lakes' contrasting abiotic/biotic characteristics provided elements to describe some species distribution limits in chemical ion gradients. Extirpation calendar dates were estimated using an optimal linear estimation method. Finally, a bibliographic review was conducted on the causes that promoted the extirpation and restriction of H. turneri and the prognosis for its reestablishment and conservation. RESULTS: Clusters showed the fishes relationship according to their distribution along the lakes. GAMM indicated that high H. turneri density is related to low hardness/fecal coliforms, medium depth/suspended solids, and high oxygen concentration. Estimated extirpation dates were between the years 2013 and 2018. The extirpation was linked to an abrupt drop in the LC volume, water quality degradation, increased biotic interactions within macrophytes habitats with native and introduced species, and fisheries bycatches. The current restricted range of H. turneri resulted from the draining of the larger lake, forcing the remaining populations to small spring-fed remnants. Recent samplings in LZ resulted in a low number of individuals. CONCLUSIONS: The integration of ecological interactions derived from statistical models, extirpation dates from nonparametric tests, and the exhaustive analysis of historical information can be applied to define the current situation of imperiled, ecologically relevant species, in different aquatic ecosystems. We are confident that this general framework is important for determining (1) the requirements and limitations of populations regarding abiotic variables, (2) biotic interactions (trophic and spatial) with native and introduced species, and (3) different anthropogenic stressors within and around the ecosystem. This knowledge will also allow understanding those aspects that contribute to the extirpation of populations and could help the restoration of the habitat and the reintroduction of extirpated species.
Assuntos
Ecossistema , Peixes , Animais , LagosRESUMO
Reproductive tactics and strategies contribute to the persistence and maintenance of long-term populations in fish species. Members of the subfamily Goodeinae are a group of small-bodied freshwater fish with specialized reproduction (viviparity-matrotrophy). They are found in the highlands of central Mexico, most of them endemic. The aim of this study was to conduct a comprehensive investigation to evaluate the annual reproductive cycle of seven species of goodeines (splitfins). We carried out our study in the subtropical Lake Zacapu, Mexico, with bi-monthly sampling from May 2019 to March 2020. We obtain the fertility, size at first maturity (L50), sex ratio, and gonadosomatic index. Our result shows that populations of goodeines have high fertility compared to other populations of the same species in other aquatic systems and also to other species of goodein. We found that males mature at smaller sizes than females, the observed proportion of females was greater than males in all the goodeines. Lake Zacapu goodeines have two reproductive peaks, one in spring (April to June) and another in fall (September to November). These tactics (fertility rates, sex ratio, reproductive period) and strategies (viviparity-matrotrophy) favor reproductive success in this environmentally stable subtropical lake in the highlands of Mexico.(AU)
Las tácticas y estrategias reproductivas contribuyen a la persistencia y el mantenimiento de las poblaciones a largo plazo en especies de peces. Miembros de la subfamilia Goodeinae son un grupo de peces de agua dulce con reproducción especializada (viviparidad-matrotrofia). Se encuentran en el centro de México, la mayoría de ellos endémicos. El objetivo de este estudio fue realizar una investigación integral para evaluar el ciclo reproductivo anual de siete especies de goodeines o mexclapiques. Realizamos nuestro estudio en el lago subtropical de Zacapu, México, con muestreo bimestral de mayo de 2019 a marzo de 2020. Nuestros resultados muestran que las poblaciones de goodeines tienen una alta fertilidad en comparación con otras poblaciones de la misma especie en otros sistemas acuáticos y también con otras especies de goodeines. Encontramos que los machos maduran en tamaños más pequeños que las hembras, la proporción observada de hembras fue mayor que los machos en todas las goodeines. Los goodeines del lago Zacapu tienen dos picos reproductivos, uno en primavera (abril a junio) y otro en otoño (septiembre a noviembre). Estas tácticas (fertilidad, proporción de sexos, período reproductivo) y estrategias (viviparidad-matrotrofia) favorecen el éxito reproductivo en este lago subtropical ambientalmente estable en el altiplano de México.(AU)
Assuntos
Animais , Reprodução , Maturidade Sexual/genética , Ciprinodontiformes , Fertilidade , Estações do Ano , Água DoceRESUMO
Globally, our knowledge on lake fisheries is still limited despite their importance to food security and livelihoods. Here we show that fish catches can respond either positively or negatively to climate and land-use changes, by analyzing time-series data (1970-2014) for 31 lakes across five continents. We find that effects of a climate or land-use driver (e.g., air temperature) on lake environment could be relatively consistent in directions, but consequential changes in a lake-environmental factor (e.g., water temperature) could result in either increases or decreases in fish catch in a given lake. A subsequent correlation analysis indicates that reductions in fish catch was less likely to occur in response to potential climate and land-use changes if a lake is located in a region with greater access to clean water. This finding suggests that adequate investments for water-quality protection and water-use efficiency can provide additional benefits to lake fisheries and food security.
Assuntos
Pesqueiros , Lagos/química , Animais , Mudança Climática , Ecossistema , Peixes/crescimento & desenvolvimento , Humanos , Temperatura , Qualidade da ÁguaRESUMO
Objetivo: Conocer el impacto en la calidad de vida a consecuencia de la mortalidad de dientes permanentes de los usuarios de las Unidades Comunitarias de Salud Familiar (UCSF) de Tamanique, Puerto Parada, San Rafael Cedros, Santiago Texacuangos y Facultad de Odontología de la Universidad de El Salvador (FOUES) en el año 2018. Metodología: La investigación corresponde a un estudio observacional descriptivo de corte transversal; en donde describe la relación entre las principales secuelas de mortalidad dental y el impacto en la calidad de vida, estuvo constituido por 720 personas de 15 a más de 60 años que cumplieron con criterios de inclusión. Se utilizó una guía de observación donde se recopilaron datos de mortalidad dental por medio del índice perdido, la calidad de vida por medio del Impact on Daily Performance (OIDP), variables sociodemográficas y evaluación clínica de las unidades de análisis. Se utilizó el programa Statical Package for the Social Sciences (SPSS) v25 para el vaciado, análisis e interpretación de resultados de la investigación. Resultados: De la población evaluada el 76.2% posee un nivel educativo entre primaria y bachillerato, las principales alteraciones más predominantes fueron mesializaciones 52.5%, ruidos articulares 45.9% y extrusiones 37.2% con un efecto muy ligero en la calidad de vida. Se encontró asociación entre las variables sociodemográfica de edad y mortalidad dental. La mayor pérdida dental se encontró en el sector posterior con un promedio de 4.22± 2.9. La prótesis más frecuentemente observada en maxilar superior fue prótesis parcial fija 8.8% y en maxilar inferior se observó con mayor frecuencia la prótesis parcial removible 4.7%. Conclusión: la mortalidad dental influye en la calidad de vida de la población, con un promedio global de 5 dientes perdidos y un promedio global de 36.06 de calidad de vida. La mayoría no presentan rehabilitación protésica, por ello no se resuelven las afecciones estéticas y funcionales.
Objective: Know the impact on the quality of life as a result of the mortality of permanent teeth of users of the Community Family Health Units (UCSF) of Tamanique, Puerto Parada, San Rafael Cedros, Santiago Texacuangos and Faculty of Dentistry of the University of El Salvador (FOUES) in 2018. (Unidades Comunitarias de Salud Familiar (UCSF) de Tamanique, Puerto Parada, San Rafael Cedros, Santiago Texacuangos y Facultad de Odontología de la Universidad de El Salvador (FOUES) en el año 2018). Methodology: The research corresponds to a cross-sectional descriptive observational study, which describes the relationship between the main effect of dental mortality, and the impact on the quality of life that was constituted by 720 people aged 15 to over 60 who met inclusion criteria. An observation guide was used to collect dental mortality data through the lost Index, quality of life through the Impact on Daily Perfomance (OIDP), sociodemographic variables and clinical evaluation of the units of analysis. The program used was, Statical Package for the Social Sciences (SPSS) v25 for emptying, analysis, and interpretation of research results. Results: From the population evaluated, 76.2% has an educational level between primary and high school, the main predominant alterations were mesializations 52.5%, articular noises 45.9% and extrusions 37.2% with a very slight effect on the quality of life. Association was found between the sociodemographic variables of age and dental mortality. The largest dental loss was found in the later sector with an average of 4.22± 2.9. The most frequently observed prosthesis in the upper jaw was a fixed partial prosthesis 8.8% and in the lower jaw the removable partial prosthesis was more frequently observed 4.7%. Conclusion: Dental mortality influences the quality of life of the population, with an overall average of 5 missing teeth and an overall average of 36.06 quality of life. Most of them do not have prosthetic rehabilitation, which is why aesthetic and functional conditions are not resolved.
Assuntos
Odontologia , Qualidade de Vida , Dentição Permanente , El SalvadorRESUMO
The ultimate step in the formation of thebaine, a pentacyclic opiate alkaloid readily converted to the narcotic analgesics codeine and morphine in the opium poppy, has long been presumed to be a spontaneous reaction. We have detected and purified a novel enzyme from opium poppy latex that is capable of the efficient formation of thebaine from (7S)-salutaridinol 7-O-acetate at the expense of labile hydroxylated byproducts, which are preferentially produced by spontaneous allylic elimination. Remarkably, thebaine synthase (THS), a member of the pathogenesis-related 10 protein (PR10) superfamily, is encoded within a novel gene cluster in the opium poppy genome that also includes genes encoding the four biosynthetic enzymes immediately upstream. THS is a missing component that is crucial to the development of fermentation-based opiate production and dramatically improves thebaine yield in engineered yeast.
Assuntos
Proteínas de Saccharomyces cerevisiae/metabolismo , Saccharomyces cerevisiae/enzimologia , Tebaína/metabolismo , Conformação Molecular , Proteínas de Saccharomyces cerevisiae/química , Tebaína/químicaRESUMO
We analyzed the infestation of the attached copepod species Lepeophtheirus sp on a wild population of Sciades herzbergii. The infestation and occurrence of attached copepods were related to body size, maturity and sex of host and the presence of lesions on fish skin were described. In 61 fish specimens (37 males and 24 females), total of 218 ectoparasitic copepods, including 204 mature and 14 immature stages were found. Copepods were attached to different regions of fish body without any regular pattern. The prevalence of infestation was 80.3% and intensity between 1 and 15 copepods/fish. No significant differences were found between sex or maturity and the presence of attached Lepeophtheirus sp. However, a contingency table including both sex and maturity status, and the total number of attached copepod per combined category showed a significant association. A positive correlation was found between body length of fish and intensity of infestation. Similarly, when comparing the infested fish according to group size, we found more copepods on larger individual. Attached copepods were associated with the presence of lesions visible to the naked eye. Histological analyses showed changes in cell architecture when sections of copepod-free tissues and attached copepods were compared.
RESUMO
We explore the trophic role that a diverse sympatric group of fishes in the genus Chirostoma play in a large, shallow lake in central Mexico, Lake Chapala. We use δ13C and δ15N stable isotope - based food web analyses to explore how they relate to other components of the Lake Chapala ecosystem. We find five Chirostoma species in top trophic levels of the Chapala food web compared to other fishes, relying on a combination of zooplankton, fish and benthic resources as energy sources. Food web metric analyses showed generally overlapping trophic niches for members of Chirostoma, especially in terms of δ13C. However, C. jordani had lower mean δ15N isotopic values than C. promelas. As a group, "pescados blancos" (C. sphyraena and C. promelas) also had higher δ15N signatures than "charales" (C. consocium, C. jordani and C. labarcae) reflecting greater piscivory, but these differences were not strong for all food web metrics used. Trophic overlap among species of Chirostoma in Lake Chapala raises questions about the forces that might have led to a morphologically diverse but functionally similar and monophyletic group of species.
Exploramos el papel trófico de un diverso grupo de peces (género Chirostoma) que habita en simpatría en el Lago Chapala, México central. Utilizamos isótopos estables de δ13C y δ15N para explorar la relación que guardan éstos peces con otros componentes del ecosistema. Encontramos a Chirostoma en niveles altos de la red trófica de Chapala, dependiendo energéticamente de zooplankton, peces y recursos del bentos. Análisis de parámetros de la red trófica demostraron traslape de nicho trófico para cinco miembros de Chirostoma, especialmente con relación a δ13C. Sin embargo, C. jordani tuvo un menor valor promedio de δ15N que C. promelas. Al ser analizados como grupo, los "pescados blancos" (C. sphyraena, C. promelas) tuvieron niveles promedio de δ15N mayores que los "charales" (C. consocium, C. jordani, C. labarcae), indicando mayor ictiofagia, pero las diferencias no fueron significativas para todos los parámetros de red trófica utilizados. El traslape trófico entre las especies de Chirostoma en Chapala da origen a cuestionamientos acerca de las fuerzas que pueden haber intervenido en el surgimiento de un morfológicamente diverso pero funcionalmente similar grupo monofilético de peces.
Assuntos
Animais , Isótopos/análise , Isótopos/química , Peixes/metabolismoRESUMO
Esta investigación realiza una evaluación ex-post de la sustentabilidad en espacios rurales relacionados con el ecoturismo, centrada en un estudio comparativo de tres empresas enclavadas en la Reserva de la Biosfera Montes Azules (REBIMA) y una empresa más ubicada fuera de ella, todas en el municipio de Ocosingo, Chiapas, México. 75% de los entrevistados son hombres con edad promedio de 36 años, siete años de escolaridad y 1,9 hectáreas. La principal fuente de ingresos es el ecoturismo, que presenta una relación beneficio-costo venida a menos de 2,7 a 1,7, entre 2007 y 2011, respectivamente. La evidencia indica un desequilibrio en el acceso a subsidios, donde la pertenencia étnica desempeña un rol trascendental.
This research performs an ex-post evaluation of the sustainability in rural spaces related to ecotourism, focused on a comparative study of three companies located in the Montes Azules Biosphere Reserve (MABR) and another company located outside, all of them in the town of Ocosingo, Chiapas, México. 75% of respondents are male with an average age of 36 years, seven years of schooling and 1,9 hectares. The main source of income is ecotourism, which presents a cost-benefit relationship that has ran down from 2,7 to 1,7 between 2007 and 2011, respectively. The evidence indicates an imbalance in the access to subsidies, where the ethnical ownership plays a transcendental role.
Assuntos
Humanos , Indicadores de Desenvolvimento Sustentável , Florestas , Reservas Naturais , BiosferaRESUMO
Non-native species are often major drivers of the deterioration of natural ecosystems. The common carp Cyprinus carpio are known to cause major changes in lentic systems, but may not be solely responsible for large scale changes in these ecosystems. We used data from extensive collection efforts to gain insight into the importance of carp as drivers of ecosystem change in Lake Patzcuaro, Mexico. We compared the structure (fish density, biomass, diversity, and evenness) of fish assemblages from six Lake Patzcuaro sites with different habitat characteristics. Intersite comparisons were carried out for both wet and dry seasons. We explored the relationships between non-carp species and carp; and studied multivariate interactions between fish abundance and habitat characteristics. From a biomass perspective, carp was dominant in only four of six sites. In terms of density, carp was not a dominant species in all sites. Further, carp density and biomass were not negatively related to native species density and biomass, even when carp density and biomass were positively correlated to water turbidity levels. Carp dominated fish assemblages in the shallowest sites with the highest water turbidity, plant detritus at the bottom, and floating macrophytes covering the lake surface. These results suggest that the effect of carp on fish assemblages may be highly dependent on habitat characteristics in Lake Patzcuaro. Watershed degradation, pollution, water level loss, and other sources of anthropogenic influence may be more important drivers of Lake Patzcuaro degradation than the abundance of carp.
Assuntos
Carpas/crescimento & desenvolvimento , Ecossistema , Eutrofização , Espécies Introduzidas , Lagos/química , Animais , Organismos Aquáticos/crescimento & desenvolvimento , Biomassa , México , Densidade Demográfica , Estações do Ano , Especificidade da EspécieRESUMO
In addition to the DNA contributed by sperm and oocytes, embryos receive parent-specific epigenetic information that can include histone variants, histone post-translational modifications (PTMs), and DNA methylation. However, a global view of how such marks are erased or retained during gamete formation and reprogrammed after fertilization is lacking. To focus on features conveyed by histones, we conducted a large-scale proteomic identification of histone variants and PTMs in sperm and mixed-stage embryo chromatin from C. elegans, a species that lacks conserved DNA methylation pathways. The fate of these histone marks was then tracked using immunostaining. Proteomic analysis found that sperm harbor â¼2.4 fold lower levels of histone PTMs than embryos and revealed differences in classes of PTMs between sperm and embryos. Sperm chromatin repackaging involves the incorporation of the sperm-specific histone H2A variant HTAS-1, a widespread erasure of histone acetylation, and the retention of histone methylation at sites that mark the transcriptional history of chromatin domains during spermatogenesis. After fertilization, we show HTAS-1 and 6 histone PTM marks distinguish sperm and oocyte chromatin in the new embryo and characterize distinct paternal and maternal histone remodeling events during the oocyte-to-embryo transition. These include the exchange of histone H2A that is marked by ubiquitination, retention of HTAS-1, removal of the H2A variant HTZ-1, and differential reprogramming of histone PTMs. This work identifies novel and conserved features of paternal chromatin that are specified during spermatogenesis and processed in the embryo. Furthermore, our results show that different species, even those with diverged DNA packaging and imprinting strategies, use conserved histone modification and removal mechanisms to reprogram epigenetic information.
Assuntos
Caenorhabditis elegans/embriologia , Caenorhabditis elegans/genética , Epigênese Genética , Histonas/metabolismo , Espermatozoides/fisiologia , Acetilação , Sequência de Aminoácidos , Animais , Proteínas de Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/metabolismo , Cromatina/metabolismo , Embrião não Mamífero , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Masculino , Metilação , Dados de Sequência Molecular , Oócitos/metabolismo , Processamento de Proteína Pós-Traducional , Espermatozoides/metabolismo , UbiquitinaçãoRESUMO
Exotic fish species has caused several impacts on aquatic biodiversity. The Lago de Pátzcuaro has some well-studied exotic species, except the Lerma livebearer Poeciliopsis infans. This fish species was introduced into the Lago de Pátzcuaro before 1997 and the aspects of its biology are still unknown. In this study we assessed aspects of the trophic ecology of this exotic fish, P infans, using gut content and stable isotope analysis to understand its capacity to tolerate anthropogenic environmental degradation in the Lago de Pátzcuaro. We also determined its trophic guild position (TP) using the TrophLab Program and stable isotope. Niche breadth was calculated by standardized Levins' Index (Bi). Fish was captured with a seine during wet and dry seasons at six environmentally different sites and gut contents were obtained. We analyzed a total of 239 gut contents of P. infans. The contribution of each food item in the diet was quantified using frequency of occurrence and area percentage. The importance of each prey item was determined according to the index of relative importance (IRI), and the omnivory index (OI) was used to assess the feeding behavior. Fish were categorized by size and the diet was compared between fish sizes and sites. Dorsal muscle tissue and water hyacinth tissue was obtained for nitrogen isotope signature he fish can behave as a specialist (Bi = 0.39) or generalist (Bi = 0.68) and as a primary consumer (TROPH = 2.2; TP = 2.3) with a feeding strategy that was the same at dif- f erent sizes, seasons and sites. None of the evaluated sites showed good environmental quality. We argue that P infans can tolerate changes in water quality and feeding items availability, because it can exploit resources in multiple trophic webs. However, this species could be dependent on habitat complexity, especially in the aquatic vegetation cover.
Assuntos
Ecossistema , Comportamento Alimentar/fisiologia , Poecilia/fisiologia , Animais , Conteúdo Gastrointestinal , Lagos , México , Poecilia/anatomia & histologia , Poecilia/classificação , Estações do AnoRESUMO
Exotic fish species has caused several impacts on aquatic biodiversity. The Lago de Pátzcuaro has some well-studied exotic species, except the Lerma livebearer Poeciliopsis infans. This fish species was introduced into the Lago de Pátzcuaro before 1997 and the aspects of its biology are still unknown. In this study we assessed aspects of the trophic ecology of this exotic fish, P. infans, using gut content and stable isotope analysis to understand its capacity to tolerate anthropogenic environmental degradation in the Lago de Pátzcuaro. We also determined its trophic guild position (TP) using the TrophLab Program and stable isotope. Niche breadth was calculated by standardized Levins’ Index (Bi). Fish was captured with a seine during wet and dry seasons at six environmentally different sites and gut contents were obtained. We analyzed a total of 239 gut contents of P. infans. The contribution of each food item in the diet was quantified using frequency of occurrence and area percentage. The importance of each prey item was determined according to the index of relative importance (IRI), and the omnivory index (OI) was used to assess the feeding behavior. Fish were categorized by size and the diet was compared between fish sizes and sites. Dorsal muscle tissue and water hyacinth tissue was obtained for nitrogen isotope signature (δ15N) analysis. Additionally, we measured water and habitat quality to evaluate environmental conditions at each site. We concluded that P. infans is an omnivore (OI=0.28) that consumes mainly detritus (44%), epiphytic diatoms (37%), and secondary on terrestrial insects (6%) and zooplankton (10%). The fish can behave as a specialist (Bi=0.39) or generalist (Bi=0.68) and as a primary consumer (TROPH=2.2; TP=2.3) with a feeding strategy that was the same at different sizes, seasons and sites. None of the evaluated sites showed good environmental quality. We argue that P. infans can tolerate changes in water quality and feeding items availability, because it can exploit resources in multiple trophic webs. However, this species could be dependent on habitat complexity, especially in the aquatic vegetation cover.
Las especies de peces exóticas han causado numerosos impactos sobre la biodiversidad acuática. El Lago de Pátzcuaro tiene especies exóticas bien estudiadas, excepto el Guatapote del Lerma, Poeciliopsis infans. Esta especie fue introducida en el Lago de Pátzcuaro antes de 1997 y los aspectos de su biología son aún desconocidos. Se estudiaron aspectos de la ecología trófica de este pez exótico, P. infans, mediante el uso de análisis de contenidos del tracto digestivo para entender su capacidad para tolerar la degradación ambiental antrópica en el Lago de Pátzcuaro. Lo que involucró la determinación del gremio y posición trófica (TP) con el programa TrophLab e isotopos estables. La amplitud de dieta fue calculada con el índice estandarizado de Levin (Bi). Un total de 239 tractos digestivos de P.infans fueron analizados. Los peces fueron capturados con una red tipo chinchorro durante la temporada de lluvias y estiaje en seis sitios ambientalmente distintos. La contribución de cada componente de la dieta fue cuantificada con la frecuencia de ocurrencia y el porcentaje de área. La importancia relativa de cada artículo alimentario fue determinada de acuerdo al índice de importancia relativa (IIR) y el índice de omnivoría (OI) fue usado para estimar la conducta en la forma de alimentarse. La dieta fue comparada entre tallas y entre sitios de estudio. El tejido de músculo dorsal y el tejido de lirio fueron obtenidos para determinar valores de δ15N. De manera adicional, la calidad del agua y del hábitat fue medida para evaluar la condición ambiental en cada sitio. P. infans es un omnívoro (OI=0.28) que consume principalmente detritus (44%), diatomeas epifíticas (37%) y de forma secundaria insectos terrestres (6%) y zooplancton (10%); puede comportarse como especialista (Bi=0.39) o generalista (Bi=0.68) y consumidor primario (TROPH=2.2; TP=2.3). La estrategia alimenticia fue similar entre tallas, temporadas y sitios. Ningún sitio mostró buena calidad ambiental. Los resultados del presente estudio permiten argumentar que P. infans puede tolerar cambios en la calidad del agua y en la disponibilidad de artículos alimenticios, porque puede usar recursos provenientes de múltiples redes tróficas. Sin embargo, esta especie podría ser dependiente de la complejidad del hábitat, especialmente de la cobertura de la vegetación acuática.
Assuntos
Animais , Ecossistema , Comportamento Alimentar/fisiologia , Poecilia/fisiologia , Conteúdo Gastrointestinal , Lagos , México , Poecilia/anatomia & histologia , Poecilia/classificação , Estações do AnoRESUMO
Significant reductions in the water volume of shallow lakes impose a restriction on species segregation promoting more interactions in the trophic relationships. The diets of three closely related zooplanktivorous silversides belonging to the Atherinopsidae species flock of lake Chapala, Mexico, were analyzed at two sites (Chirostoma jordani, C. labarcae, andC. consocium). Diets were described in critical shallow (August 2000) and volume recovery conditions (August 2005). Diets included mainly cladocerans (Bosmina, Ceriodaphnia, and Daphnia) and copepods (Cyclops). A significant difference in diets was detected when comparing years (MRPP analysis, A = 0.22, p < 0.0001) and sites at different years (MRPP analysis, A = 0.17, p = 0.004). According to niche breadth mean values, species were classified as specialized and intermediate feeders. In shallow conditions, the small range of niche breadth (1.72 to 3.64) and high diet overlap values (D = 0.64, L = 8.62) indicated a high potential for interspecific exploitative interaction. When the lake volume recovered, an increase in the niche breadth range (1.04 to 4.96) and low niche overlap values (D = 0.53, L = 2.32) indicated a reduction of the species interaction. The Mann- Whitney U-test supported this pattern by showing a significant difference between years for niche overlap (p = 0.006). The increased interaction during the low volume suggests alternative segregation in life-history variations and other niche dimensions such as spatial or temporal distribution.
La reducción significativa en el volumen de agua de los lagos someros impone una restricción en la segregación de las especies y promueve una mayor interacción en las relaciones tróficas. Se analizó la dieta de tres especies cercanamente emparentadas de zooplanctívoros pertenecientes al flock de Aterinópsidos del lago de Chapala en dos sitios (Chirostoma jordani, C. labarcae y C. consocium). Las dieta fue descrita en una condición somera crítica (Agosto 2000) y en una condición de recuperación del lago (Agosto 2005). En la dieta se incluyen principalmente cladóceros (Bosmina, Ceriodaphnia y Daphnia) y copépodos (Cyclops). Se detectó una diferencia significativa en la dieta cuando se comparan los años (análisis MRPP, A = 0.22, p < 0.0001) y los sitios en los diferentes años (análisis MRPP, A = 0.17, p = 0.004). De acuerdo a los valores promedio de amplitud de nicho, las especies fueron clasificadas como especialistas y consumidores intermediarios. En condiciones someras, el pequeño intervalo de la amplitud de nicho (1.72 a 3.64) y los altos valores del traslape de nicho (D = 0.64, L = 8.62) indicaron un alto potencial para una interacción explotativa inter-específica. Cuando el lago se recupera en su volumen, un incremento en el intervalo de amplitud de nicho (1.04 a 4.96) y los bajos valores del traslape de nicho (D = 0.53, L = 2.32) indicaron una reducción en la interacción de las especies. La prueba U de Mann-Whitney refuerza este patrón al mostrar una diferencia significativa entre los años para el traslape de nicho (p = 0.006). El incremento en la interacción de las especies durante condiciones de volumen bajo, sugiere una segregación alternativa con variaciones en la historia de vida y en otras dimensiones del nicho como en el caso de la distribución espacial y temporal.
Assuntos
Animais , Peixes/classificação , Níveis Tróficos , Dieta/estatística & dados numéricos , Medição de Níveis de Água , Zooplâncton/classificaçãoRESUMO
This study addresses the influence of water-level fluctuations on fish distribution at two temporal scales: seasonal (dry and rainy) and interannual (low and high volume conditions). The analysis of abundance relationships among three zooplanktivore Chirostoma species at fifteen sites in Lake Chapala, Mexico, revealed the significant influence of contrasting conditions (P=0.0002). Seasonally, segregation was more related to species dominance in the dry season and exclusively related to environmental characteristics in the rainy season. Interanually, biotic influence occurred in the shallowest and the deepest episodes of the lake. Environmental characteristics influenced species distribution when the lake reached 25 percent of its volume. Site, depth, temperature, and salinity were the leading factors influencing fish distribution. These results emphasize the necessity to implement different management strategies according to lake volume, particularly when a critical threshold is reached.
El presente estudio describe la influencia que tiene la fluctuación del nivel del agua en la distribución de los peces a dos diferentes escalas: estacional (estiaje y lluvias) e interanual (condiciones de bajo y alto volumen). El análisis de las relaciones de abundancia entre tres especies zooplanctófagas de Chirostoma en quince sitios del Lago de Chapala, México, reveló una influencia estadísticamente significativa en las condiciones contrastantes (P=0.0002). Estacionalmente, la segregación estuvo más relacionada a la dominancia de las especies en la época de estiaje y exclusivamente relacionada a las características ambientales en la época de lluvias. Interanualmente, la influencia biótica se presenta en los episodios más someros y más profundos del lago. Las características ambientales influenciaron la distribución de las especies cuando el lago alcanzó el 25 por ciento de su volumen. El sitio geográfico, profundidad, temperatura y salinidad fueron los principales factores que influenciaron la distribución de los peces. Estos resultados enfatizan la necesidad de implementar diferentes estrategias de manejo de acuerdo al volumen del lago, particularmente cuando se alcanza un umbral crítico.