Edward D. Burress

Functional diversification within a predatory species flock.

Ecological speciation is well-known from adaptive radiations in cichlid fishes inhabiting lentic ecosystems throughout the African rift valley and Central America. Here, we investigate the ecological and morphological diversification of a recently discovered lotic predatory Neotropical cichlid species flock in subtropical South America. We document morphological and functional diversification using geometric morphometrics, stable C and N isotopes, stomach contents and character evolution. This species flock displays species-specific diets and skull and pharyngeal jaw morphology. Moreover, this lineage appears to have independently evolved away from piscivory multiple times and derived forms are highly specialized morphologically and functionally relative to ancestral states. Ecological speciation played a fundamental role in this radiation and our data reveal novel conditions of ecological speciation including a species flock that evolved: 1) in a piscivorous lineage, 2) under lotic conditions and 3) with pronounced morphological novelties, including hypertrophied lips that appear to have evolved rapidly.

Species-specific ontogenetic diet shifts among Neotropical Crenicichla: using stable isotopes and tissue stoichiometry

Ontogenetic diet shifts were compared among five sympatric pike cichlids Crenicichla in a subtropical South American stream using stable C and N isotopes and tissue stoichiometry (C:N). Within species, stable N isotopes were positively related to body size while C:N showed negative relationships. Stable C isotopes, however, were not related to body size in any species. By modelling the switch to piscivory using gut content-isotope-body size relationships, diet shifts were shown to be species-specific with regard to both rate and degree of piscivory. Compared to other piscivorous lineages, Crenicichla appear to be unusually small-bodied (based on maximum body size). Because of their diversity, abundance and dynamic size-structured functional roles, Crenicichla may exert broad and complex predation pressures on the aquatic community.

Perciformes, Cichlidae, Crenicichla tendybaguassu Lucena and Kullander, 1992: first record for Uruguay

The present note is the first record of the pike cichlid Crenicichla tendybaguassu for Uruguay, extending its distribution about 400 km to the South. The presence of C. tendybaguassu and their co-occurrence with other priority species for conservation in Uruguay adds greater value to conservation of the Cuareim River (Middle Uruguay River). Coloration of live breeding females is described for first time.

Body size is negatively correlated with trophic position among cyprinids

Body size has many ecological and evolutionary implications that extend across multiple levels of organization. Body size is often positively correlated with species traits such as metabolism, prey size and trophic position (TP) due to physiological and mechanical constraints. We used stable isotope analysis to quantify TP among minnows across multiple assemblages that differed in their species composition, diversity and food web structure. Body size significantly predicted TP across different lineages and assemblages, and indicated a significant negative relationship. The observed negative relationship between body size and TP is contrary to conventional knowledge, and is likely to have arisen owing to highly clade-specific patterns, such that clades consist of either large benthic species or small pelagic species. Cyprinids probably subvert the physiological and mechanical constraints that generally produce a positive relationship between body size and TP using anatomical modifications and by consuming small-bodied prey, respectively. The need for herbivorous cyprinids to digest cellulose-rich foods probably selected for larger bodies to accommodate longer intestinal tracts and thereby to facilitate digestion of nutrient-poor resources, such as algae. Therefore, body size and TP are likely to have coevolved in cyprinids in association with specialization along the benthic to pelagic resource axis.

First report of four characiform fishes (Ostariophysi: Characiformes) for Uruguay

In this article the authors present the first report of four characiform fish species for Uruguay, extending their current distribution to the middle and lower Uruguay River basin: Astyanax saguazu Casciotta, Almiron and Azpelicueta, 2003; Hypobrycon poi Almiron, Casciotta, Azpelicueta and Cione, 2001; Leporinus amae Gody, 1980; Cyphocharax saladensis (Meinken, 1933). These species were previously recorded from either the upper Uruguay River, Patos-Merin lagoon system or Parana River. Color pattern in life for A. saguazu and H. poi are described for the first time.

Diet and body shape among populations of Bryconamericus iheringii (Otophysi: Characidae) across the Campos Sulinos ecosystem

Alterations in natural landscapes, mainly caused by anthropic pressures, have been threatening the worlds biomes, including aquatic environments and its biota. This study describes the diet of Bryconamericus iheringii, and how its body shape relates to environmental variables in populations of 22 streams. A wide array of food items were found, mainly composed of allochthonous plants (50.5%) and autochthonous invertebrates (25.2%). Even though food items remained almost the same, the predominant food group significantly differed among streams, mainly in relation to environmental characteristics. There was variation in body shape primarily associated with body depth and length of the pre-dorsal region; however, these differences did not correspond with streams. PLS-CA analyses indicated that environmental characteristics, such as substrate type, percentage of marginal vegetation have some influence over food items availability but not on body shape. This may be because B. iheringii is a non-specialist species capable of prey switching based on availability due to an intermediate body shape suited for generalist feeding habits.(AU)

Resource partitioning among syntopic Characidae corroborated by gut content and stable isotope analyses

We aim to test the hypothesis that an assemblage of characid fishes coexist by partitioning food resources. We calculated dietary niche overlap of four syntopic species of the Characidae using gut content analysis. Secondly, we used a carbon (13C) and nitrogen (15N) isotope Bayesian mixing model to estimate relative assimilation. All characids consumed large proportions of plant material and aquatic insects; however, Pianka’s index indicated low dietary overlap among species throughout most of the sampling period. The low degrees of dietary overlap were due to discrepancies in the relative consumption of Ephemeroptera and aquatic insect remains. Secondly, there was high correspondence between the gut content analyses and isotope mixing model estimates. Astyanax xiru and Bryconamericus iheringii were the only species that ingested and assimilated large fractions of aquatic plants and algae, respectively. Astyanax procerus consumed and assimilated large fractions of terrestrial invertebrates, whereas Bryconamericus sp. assimilated mainly aquatic invertebrates. Therefore, we demonstrate that the assimilated nutrients were consistent with the relative consumption of food items. These results are consistent with the hypothesis that this characid assemblage may coexist via resource partitioning.

Body shape variation within the Southern Cavefish, Typhlichthys subterraneus (Percopsiformes: Amblyopsidae)

The Southern Cavefish, Typhlichthys subterraneus Girard 1859, is one of the most fascinating stygobionts of the Amblyopsidae because of its undescribed diversity. Previous molecular analysis suggests the presence of at least ten distinct lineages in the Southeastern United States. Morphological variation for this group has not been quantified previous to this study. We quantified differences in body shape within the Southern Cavefish utilizing landmark-based geometric morphometrics. We found significant allometry of body shape (Relative Warps) across all putative lineages. We then performed an allometric correction to develop a size-independent morphospace. Principal components analysis indicated that the major axes of size-independent shape explained variation in relative head length to predorsal length, as well as head size and shape in both lateral and dorsal views. We examined if morphological variation corresponded to putative genetic lineages and three geographic variables (aquifer, HUC subregion, and ecoregion). We found shape differences among groups within some variables, but generally, body shape variation was not well explained by these variables. Instead, the dramatic body shape diversity among individuals was explained by ontogeny. Poor agreement between morphology and lineages, as well as multiple geographic variables may be explained by convergent evolution of cave-adapted morphologies or cryptic morphology (i.e., no morphological characters to define diversity).