Relative influences of catchment- and reach-scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica

Esselman PC, Allan JD. Relative influences of catchment- and reach-scale abiotic factors on freshwater fish communities in rivers of northeastern Mesoamerica. Ecology of Freshwater Fish 2010: 19: 439–454. © 2010 John Wiley & Sons A/SWhile the abiotic factors important to freshwater fish assemblages at a reach scale are well understood, studies of larger scale constraints have yielded variable conclusions, spurring a need for further studies in new biogeographic contexts. This study investigated the importance of catchment- and reach-scale abiotic factors to variation in freshwater fish assemblages in rivers of northeastern Mesoamerica. Abiotic variables and fish data from 72 sampling sites on main stem rivers of Belize were used with partial constrained ordination to determine the proportion of spatially structured and unstructured variation in fish presence and absence, relative abundance, and community metrics explained by catchment- and reach-scale environmental factors. Results showed that, combined, catchment and reach variables explained a large portion of the total variation in the fish assemblage data (54–75%), and that catchment environment explained a greater portion of variation (42–63%) than reach environment (34–50%). Variables representing landscape position (local elevation, watershed area) and their reach-level correlates (channel width, depth variation, and substrate) correlated strongly to the fish assemblage data. Our results suggest that landscape-scale factors have a stronger relative influence on assemblages than environmental conditions at the reach scale within our study area. These results contrast with past findings that showed greater local scale influence in landscapes with low anthropogenic disturbance levels. Our findings suggest that biodiversity conservation efforts should consider assemblage variation across a longitudinal gradient, and that a multi-catchment region is a biologically relevant scale for fish conservation planning and coordination in northeastern Mesoamerica.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/79336/1/j.1600-0633.2010.00430.x.pd

Mutations in Protein-Binding Hot-Spots on the Hub Protein Smad3 Differentially Affect Its Protein Interactions and Smad3-Regulated Gene Expression

Hub proteins are connected through binding interactions to many other proteins. Smad3, a mediator of signal transduction induced by transforming growth factor beta (TGF-β), serves as a hub protein for over 50 protein-protein interactions. Different cellular responses mediated by Smad3 are the product of cell-type and context dependent Smad3-nucleated protein complexes acting in concert. Our hypothesis is that perturbation of this spectrum of protein complexes by mutation of single protein-binding hot-spots on Smad3 will have distinct consequences on Smad3-mediated responses.We mutated 28 amino acids on the surface of the Smad3 MH2 domain and identified 22 Smad3 variants with reduced binding to subsets of 17 Smad3-binding proteins including Smad4, SARA, Ski, Smurf2 and SIP1. Mutations defective in binding to Smad4, e.g., D408H, or defective in nucleocytoplasmic shuttling, e.g., W406A, were compromised in modulating the expression levels of a Smad3-dependent reporter gene or six endogenous Smad3-responsive genes: Mmp9, IL11, Tnfaip6, Fermt1, Olfm2 and Wnt11. However, the Smad3 mutants Y226A, Y297A, W326A, K341A, and E267A had distinct differences on TGF-β signaling. For example, K341A and Y226A both reduced the Smad3-mediated activation of the reporter gene by ∼50% but K341A only reduced the TGF-β inducibilty of Olfm2 in contrast to Y226A which reduced the TGF-β inducibility of all six endogenous genes as severely as the W406A mutation. E267A had increased protein binding but reduced TGF-β inducibility because it caused higher basal levels of expression. Y297A had increased TGF-β inducibility because it caused lower Smad3-induced basal levels of gene expression.Mutations in protein binding hot-spots on Smad3 reduced the binding to different subsets of interacting proteins and caused a range of quantitative changes in the expression of genes induced by Smad3. This approach should be useful for unraveling which Smad3 protein complexes are critical for specific biological responses

New species of Eugerres from the Usumacinta Province, México and Guatemala with a redescription of E. mexicanus (Steindachner, 1863) (Teleostei: Gerreidae)

Eugerres castroaguirrei, new species is described from the río Grijalva-Usumacinta basin of southeastern Mexico and northern Guatemala. Eugerres castroaguirrei and E. mexicanus are distinguishable from their marine estuarine congeners by the dorsal-fin origin posterior to the insertion of the pectoral and pelvic fins, a shorter and broad based supraoccipital crest, and a distinct geographic distribution restricted to freshwater habitats. Eugerres castroaguirrei differs from E. mexicanus by diagnostic characters of the body skeleton: anterior process of supraoccipital convex, infraorbital 1 with foramen, premaxillary ascending process developed with margins curved, pharyngeal plate granular and not serially arranged, and dorsal and anal fin-rays reduced. Likewise, E. castroaguirrei is characterized by an oblong and laterally thicker body (37.6-58.5% HL); greater body depth (33.8-42.1% SL), and eye diameter (23.3-31.6% HL); in addition to 16 significant morphometric characters: length of the second dorsal-fin spine 23.2-34.2% SL; depressed second dorsal-fin spine (extending to base of third to fourth dorsal-fin rays); length of second anal-fin spine 11.1-20.6% SL, depressed second anal-fin spine extending to the base of third to fourth anal-fin rays not reaching the distal point of last anal-fin ray; pelvic-fin spine length 49.7-65.0% in the first pelvic-fin ray lengt

Morfometría de las especies de Vieja (Cichlidae) en ríos de la cuenca del Usumacinta, Chiapas, México

We evaluated and compared morphological characteristics among the 6 species of Vieja Fernández-Yépez, 1969 from Usumacinta River. We analyzed 20 adults by specie, obtaining 33 measurements, which were standardized and analyzed with a discriminant analysis. We also performed a comparison of body shape among species, using the geometric morphometric analysis from digitalized images. Traditional and geometric morphometrics allowed distinguishing each taxa. We found 10 discriminants measures, related with the head region and length of fins, only mouth position was different among more taxa. In both analyses, similarity relationships showed 2 groups, being V. bifasciata (Steindachner, 1864) and V. synspila (Hubbs, 1935) the most similar species. Thin plate spline showed greater variation in the cephalic region, specifically in eyes and mouth position. Morphometrics differences can be used for taxonomic identification in future works. The variation found in cephalic and trophic morphology can be a mechanism that promotes coexistence of species and explain the diversity of the group in this region.Se evaluaron y compararon diversas características morfológicas de 6 especies de Vieja Fernández-Yépez, 1969 del río Usumacinta. Se emplearon 20 organismos adultos por especie y 33 medidas corporales que fueron estandarizadas y examinadas con un análisis discriminante. Además se comparó la forma del cuerpo entre las especies, mediante el análisis de morfometría geométrica a partir de imágenes digitalizadas. El análisis con la morfometría tradicional y geométrica permitió diferenciar los seis taxones. Se encontraron 10 medidas discriminantes, que expresan diferencias significativas en la longitud de las aletas y la región cefálica, de las cuales la posición de la boca diferenció estadísticamente más taxones. Las relaciones de similitud con ambos análisis mostraron 2 grupos, siendo V. bifasciata (Steindachner, 1864) y V. synspila (Hubbs, 1935) las especies más parecidas. Las gradillas de deformación mostraron que la mayor variación está en la región cefálica, específicamente en la posición de la boca y los ojos. Las diferencias morfométricas encontradas pueden servir para la determinación taxonómica en trabajos futuros. La variación encontrada en la morfología cefálica y trófica puede ser un mecanismo que favorece la coexistencia de las especies y la diversidad del grupo en la región