RESUMEN

The neotropical fish genus Astyanax (Characidae) and its associated helminths migrated northward from South America following the Great American Biotic Interchange (GABI): ca. 150 Astyanax spp. are found throughout South and Central America, up to the Mexico-USA border. Most characids are distributed south of the Trans-Mexican Volcanic Belt (TMVB), which bisects the country and represents a major transition zone between the neotropical and nearctic realms. Here, we characterize parasites of the monogenean genus Gyrodactylus infecting Astyanax spp. in Mexico: Astyanax aeneus south of the TMBV, Astyanax mexicanus north of it. Based on morphological, phylogenetic (internal transcribed spacer (ITS) and cytochrome oxidase subunit II (cox 2)) and statistical analyses of morphometric data, we confirmed the validity of Gyrodactylus pakan and Gyrodactylus teken, and erected two new species, Gyrodactylus aphaa n. sp. and Gyrodactylus ricardoi n. sp. These four gyrodactylids are part of a complex of morphologically cryptic species, which are phylogenetically closely related to each other, and sister species to Gyrodactylus carolinae and Gyrodactylus heteracanthus, parasites of characins in Brazil. Four gyrodactylid lineages (G. pakan, G. ricardoi n. sp., G. teken, Gyrodactylus sp. A) are distributed north of the TMVB; G. pakan is also widely distributed south of the TMVB, together with G. aphaa n. sp. Based on the ITS phylogeny, Brazilian parasites form a sister clade to all Mexican gyrodactylids, whose derived clades are distributed in progressively more northerly latitudes in Mexico - the three most-derived species north of the TMVB. This would suggest that gyrodactylid species diverged gradually, presumably as their characid fish hosts colonized and adapted to new environments north of the TMVB.

RESUMEN

RESUMEN Pseudoxiphophorus bimaculatus es una especie invasora ampliamente propagada en los ecosistemas de agua dulce del centro de México, por eso se describe su estrategia trófica en un gradiente de calidad ambiental. Se muestrearon individuos de P. bimaculatus en ocho sitios localizados en las cuencas de los Ríos Lerma-Chapala y Pánuco durante la temporada de secas. Estas cuencas se han visto afectadas por los procesos de industrialización y urbanización, pero la Comisión Nacional del Agua las considera reservas de agua en México. Para evaluar las condiciones ambientales de las cuencas, aplicamos el Índice de Integridad Biótica basado y el Índice Biótico basado en Familias. Evaluamos el gremio trófico, la amplitud de la dieta y la selectividad de la dieta de P. bimaculatus en sitios con diferente calidad ambiental. Además, exploramos la relación de las estrategias tróficas con la condición del hábitat. Capturamos un total de 202 individuos de P. bimaculatus de 10 a 67 mm de LP, encontrando un total de 24 artículos alimenticios. La dieta de P. bimaculatus está compuesta de insectos terrestres y acuáticos y restos óseos de peces. Pseudoxiphophorus bimaculatus en algunos sitios puede alimentarse de diferentes niveles tróficos, en otros, es especialista y consumidor secundario. Encontramos que P. bimaculatus cambia su dieta acorde con alteraciones en la estructura del hábitat, la calidad del agua y la integridad biótica. Además, esta especie invasora puede tolerar cambios en la red trófica y la disponibilidad de alimento.

ABSTRACT Pseudoxiphophorus bimaculatus is an invasive species widely spread throughout freshwater ecosystems in central Mexico, for that reason we described its trophic strategy into a gradient of environmental quality. We sampled individuals of P. bimaculatus at eight sites located in the Lerma-Chapala and Pánuco River Basins during dry season. These basins have been impacted by industrialization and urbanization processes, but are considered as water reserves in México. To evaluate the environmental quality of the river, we applied the Visual-based Habitat Assessment, the Index of Biological Integrity and the Family-level Biotic Index. We assessed the trophic guild, the diet width, the omnivory level, and the diet selectivity. We also explored the relation of trophic strategies with the habitat condition. We captured a total of 202 individuals of P. bimaculatus from 10 to 67 mm of SL, finding a total of 24 food items. The diet of P. bimaculatus was composed of terrestrial, aquatic insects and bony fish. Pseudoxiphophorus bimaculatus in some sites can feed on different trophic levels, in other it is a specialist and secondary consumer. We found that P. bimaculatus changes its diet according the alterations in the habitat structure, water quality, and biotic integrity. Moreover, this invasive species can endure changes in the trophic web and food availability.

RESUMEN

Pseudoxiphophorus bimaculatus is an invasive species widely spread throughout freshwater ecosystems in central Mexico, for that reason we described its trophic strategy into a gradient of environmental quality. We sampled individuals of P. bimaculatus at eight sites located in the Lerma-Chapala and Pánuco River Basins during dry season. These basins have been impacted by industrialization and urbanization processes, but are considered as water reserves in México. To evaluate the environmental quality of the river, we applied the Visual-based Habitat Assessment, the Index of Biological Integrity and the Family-level Biotic Index. We assessed the trophic guild, the diet width, the omnivory level, and the diet selectivity. We also explored the relation of trophic strategies with the habitat condition. We captured a total of 202 individuals of P. bimaculatus from 10 to 67 mm of SL, finding a total of 24 food items. The diet of P. bimaculatus was composed of terrestrial, aquatic insects and bony fish. Pseudoxiphophorus bimaculatus in some sites can feed on different trophic levels, in other it is a specialist and secondary consumer. We found that P. bimaculatus changes its diet according the alterations in the habitat structure, water quality, and biotic integrity. Moreover, this invasive species can endure changes in the trophic web and food availability.(AU)

Pseudoxiphophorus bimaculatus es una especie invasora ampliamente propagada en los ecosistemas de agua dulce del centro de México, por eso se describe su estrategia trófica en un gradiente de calidad ambiental. Se muestrearon individuos de P. bimaculatus en ocho sitios localizados en las cuencas de los Ríos Lerma-Chapala y Pánuco durante la temporada de secas. Estas cuencas se han visto afectadas por los procesos de industrialización y urbanización, pero la Comisión Nacional del Agua las considera reservas de agua en México. Para evaluar las condiciones ambientales de las cuencas, aplicamos el Índice de Integridad Biótica basado y el Índice Biótico basado en Familias. Evaluamos el gremio trófico, la amplitud de la dieta y la selectividad de la dieta de P. bimaculatus en sitios con diferente calidad ambiental. Además, exploramos la relación de las estrategias tróficas con la condición del hábitat. Capturamos un total de 202 individuos de P. bimaculatus de 10 a 67 mm de LP, encontrando un total de 24 artículos alimenticios. La dieta de P. bimaculatus está compuesta de insectos terrestres y acuáticos y restos óseos de peces. Pseudoxiphophorus bimaculatus en algunos sitios puede alimentarse de diferentes niveles tróficos, en otros, es especialista y consumidor secundario. Encontramos que P. bimaculatus cambia su dieta acorde con alteraciones en la estructura del hábitat, la calidad del agua y la integridad biótica. Además, esta especie invasora puede tolerar cambios en la red trófica y la disponibilidad de alimento.(AU)

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RESUMEN

Efforts to halt freshwater ecosystem degradation in central Mexico can benefit from using bio-monitoring tools that reflect the condition of their biotic integrity. We analyzed the applicability of two fish-based indices of biotic integrity using data from lotic and lentic systems in the Angulo River subbasin (Lerma-Chapala basin). Both independent data from our own collections during two consecutive years, and existing information detailing the ecological attributes of each species, were used to calculate indices of biological integrity for 16 sites in lotic and lentic habitats. We assessed environmental quality by combining independent evaluations water and habitat quality for each site. We found sites with poor, regular and good biotic integrity. Our study did not find sites with good environmental quality. Fish-based IBI scores were strongly and significantly correlated with scores from independent environmental assessment techniques. IBI scores were adequate at representing environmental conditions in most study sites. These results expand the area where a lotic system fish-based IBI can be used, and constitute an initial validation of a lentic system fish-based IBI. Our results suggest that these bio-monitoring tools can be used in future conservation efforts in freshwater ecosystems in the Middle Lerma Basin.

Las acciones para detener el deterioro de los ecosistemas dulceacuícolas del centro del México requieren herramientas de biomonitoreo que permitan el análisis de su integridad biológica. En este trabajo se analizó la viabilidad del uso de dos índices biológicos de integridad (IBI) con base en las comunidades de peces en ambientes lóticos y lénticos en la subcuenca del Río Angulo (Cuenca del Lerma-Chapala). Utilizando datos provenientes de recolectas independientes durante dos años consecutivos e información sobre los atributos ecológicos para cada una de las especies, se calcularon los valores de dos IBI en 16 sistemas lénticos y lóticos. Se estimó también la calidad ambiental a través de la evaluación de la calidad del agua y del hábitat en cada sitio. Se encontró integridad biótica pobre, regular y buena. El estudio no mostró sitios con buena calidad ambiental. Los valores de los IBI presentaron correlaciones altas y significativas con aquellos derivados de metodologías independientes de evaluación ambiental. Los IBI reflejaron de forma fehaciente las condiciones ambientales en la mayoría de los sitios de estudio. Con este análisis se logró la expansión de área de uso del IBI para ambientes lóticos y una validación inicial del IBI para ambientes lénticos. Estos resultados sugieren que las herramientas pueden ser utilizadas en futuros esfuerzos de conservación en cuerpos dulceacuícolas en la cuenca del Medio Lerma.

Asunto(s)

RESUMEN

Efforts to halt freshwater ecosystem degradation in central Mexico can benefit from using bio-monitoring tools that reflect the condition of their biotic integrity. We analyzed the applicability of two fish-based indices of biotic integrity using data from lotic and lentic systems in the Angulo River subbasin (Lerma-Chapala basin). Both independent data from our own collections during two consecutive years, and existing information detailing the ecological attributes of each species, were used to calculate indices of biological integrity for 16 sites in lotic and lentic habitats. We assessed environmental quality by combining independent evaluations water and habitat quality for each site. We found sites with poor, regular and good biotic integrity. Our study did not find sites with good environmental quality. Fish-based IBI scores were strongly and significantly correlated with scores from independent environmental assessment techniques. IBI scores were adequate at representing environmental conditions in most study sites. These results expand the area where a lotic system fish-based IBI can be used, and constitute an initial validation of a lentic system fish-based IBI. Our results suggest that these bio-monitoring tools can be used in future conservation efforts in freshwater ecosystems in the Middle Lerma Basin.

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