Felipe Alonso

Dominance hierarchies and social status ascent opportunity: Anticipatory behavioral and physiological adjustments in a Neotropical cichlid fish

In this work we characterized the social hierarchy of non-reproductive individuals of Cichlasoma dimerus (Heckel, 1840), independently for both sexes, and its relationship to the opportunity for social status ascent. Female and male individuals who were located on the top rank of the social hierarchy, ascended in social status when the opportunity arose, therefore indicating that dominance is directly correlated with social ascent likelihood. Dominance was positively correlated with size in males but not in females, suggesting for the latter a relationship with intrinsic features such as aggressiveness or personality rather than to body and/or ovarian size. Physiological and morphometrical variables related to reproduction, stress and body color were measured in non-reproductive fish and correlated with dominance and social ascent likelihood. Dominance was negatively correlated with plasma cortisol levels for both sexes. No correlation with dominance was found for androgen plasma levels (testosterone and 11-ketotestosterone). No correlation was detected between dominance and the selected morphological and physiological variables measured in females, suggesting no reproductive inhibition in this sex at a physiological level and that all females seem to be ready for reproduction. In contrast, social hierarchy of non-reproductive males was found to be positively correlated with follicle stimulating hormone (FSH) pituitary content levels and gonadosomatic indexes. This suggests an adaptive mechanism of non reproductive males, adjusting their reproductive investment in relation to their likelihood for social status ascent, as perceived by their position in the social hierarchy. This likelihood is translated into a physiological signal through plasma cortisol levels that inhibit gonad investment through pituitary inhibition of FSH, representing an anticipatory response to the opportunity for social status ascent.

An endangered new species of seasonal killifish of the genus Austrolebias (Cyprinodontiformes: Aplocheiloidei) from the Bermejo river basin in the Western Chacoan Region

Austrolebias wichi, new species, is herein described from seasonal ponds of the Bermejo river basin in the Western Chacoan district in northwestern Argentina. This species was found in a single pond, a paleochannel of the Bermejo River, which is seriously disturbed by soybean plantations surrounding it. Despite intensive sampling in the area, this species was only registered in this pond where it was relatively scarce. Therefore, we consider this species as critically endangered. This species is the sister species of A. patriciae in our phylogenetic analyses and is similar, in a general external aspect, to A. varzeae and A. carvalhoi. It can be distinguished among the species of Austrolebias by its unique color pattern in males. Additionally, from A. varzeae by presenting a supraorbital band equal or longer than the infraorbital band (vs. shorter) and from A. patriciae by the convex dorsal profile of head (vs. concave). Further diagnostic characters and additional comments on its ecology and reproduction are provided.

Living in the waterfalls: A new species of Trichomycterus (Siluriformes: Trichomycteridae) from Tabay stream, Misiones, Argentina

A new species assigned to the genus Trichomycterus from the area of the waterfalls of Tabay stream, Paraná River basin, Misiones, Argentina, is described. Trichomycterus ytororo sp. nov. is distinguished from all other species in the genus by the presence of 31–35 dorsal procurrent caudal-fin rays and the combination of some external characters such as: coloration, number of pectoral–fin rays and pores of the laterosensory canals. The new taxon belongs to a presumably monophyletic group of species composed of T. crassicaudatus, T. igobi, and T. stawiarski based on the presence of 24 or more thickly ossified and rigid procurrent caudal-fin rays with a slender distal tip extending along the tips of at least ten neural spines.

Geographical distribution of Austrolebias monstrosus (Huber, 1995), A. elongatus (Steindachner, 1881) and A. vandenbergi (Huber, 1995) (Teleostei: Cyprinodontiformes), with comments on the biogeography and ecology of Rivulidae in Pampasic and Chaco floodplains

We present a new record for Austrolebias elongatus from Gualeguaychu, in Entre Rios province, Argentina, based on new fieldwork and a revision of material deposited in national ichthyological collections. We also give evidence on the erroneous records of Austrolebias monstrosus and A. vandenbergi from Ituzaingo, Corrientes province, as well as present additional records from Salta province for those species. Material previously determined as A. elongatus from Santiago del Estero is attributed to A. monstrosus . We restrict the distribution of these two species to Semi-arid Chaco Region in Argentina, Paraguay and Bolivia.

Gross anatomy and histology of the alimentary system of Characidae (Teleostei: Ostariophysi: Characiformes) and potential phylogenetic information

Un estudio comparado de la morfologia del tracto alimentario y el higado de siete especies seleccionadas correspondientes a los principales clados de la familia Characidae es presentada aqui. Tres nuevos conjuntos de caracteres correspondientes a 1) anatomia gruesa del tracto alimentario, 2) histologia del tracto alimentario y 3) anatomia gruesa del higado son evaluados aqui como potenciales fuentes de informacion para futuros estudios filogeneticos de los Characidae. No se observo una variacion intraespecifica considerable a nivel histologico y consecuentemente esta fuente no es considerada como informativa filogeneticamente al nivel taxonomico analizado. En contraste, la anatomia gruesa del higado y el tracto alimentario presentaron una variacion interespecifica importante mientras que una relativamente homogenea variacion intraespecifica fue observada. Estos caracteres son optimizados en topologias de arboles de analisis filogeneticos previos y su evolucion y potencial relacion con caracteristicas ecologicas son discutidas.

Two new species of the genus Corydoras (Ostariophysi: Siluriformes: Callichthyidae) from northwestern Argentina, and redescription of C. micracanthus Regan, 1912

The group herein denominated as the Corydoras micracanthus species-group is supported by presenting dorsal and pectoral spines length reduced; caudal fin slightly emarginated; low body depth; parieto-supraoccipital process and nuchal plate not in contact and small eyes for the genus. It comprises Corydoras micracanthus, herein redescribed, and two new species described in the present paper, all from northwestern Argentina. Corydoras gladysae, a new species from the Calchaqui river, is distinguished from other species of the genus by the caudal-fin shape, slightly emarginated and by presenting the shortest dorsal and pectoral spines length (mean = 9.2 % and 14.8 % of SL, respectively). Corydoras petracinii, a new species from the Las Costas river, is distinguished from its congeners by the following combination of characters: dorsal spine short (mean = 16.6 % of SL), pectoral spine short (mean = 18.3 % of SL), body moderately elongate (body depth 29.5 % SL mean), caudal fin slightly forked and trunk flanks with 5–7 subsquare differenced blotches in the middle region. Corydoras micracanthus, from the Mojotoro river basin, is defined by its higher number of dorsolateral body plates (24–26) and trunk color pattern, presenting 4 to 6 subsquare blotches well differentiated in the flanks. The inclusion of these species into the genus Corydoras is discussed.

Shape and size variation of Jenynsia lineata (Jenyns 1842) (Cyprinodontiformes: Anablepidae) from different coastal environments

A key question in ecological speciation is to understand the causes and consequences of phenotypic divergence among populations. In this work, we analyzed the body shape and size variation in Jenynsia lineata across different coastal habitats along the Atlantic coast of South America. We hypothesized that J. lineata presents morphological variations to inhabit contrasting environments and that these adaptations are sex specific. We analyzed 13 populations from five coastal habitats, using linear and geometric morphometry, and tested the correlation of body shape variation with environmental variables to understand which environmental factors may influence body shape and size variation. Jenynsia lineata showed differences in body shape and size among populations, and these differences are specific to each sex. While females showed a variation in the caudal peduncle correlated with water current, we did not find such trait variation and correlation in males. Alternatively, individuals from marine rocky pools have a convex body curvature along the dorsal profile and larger body sizes, in both sexes. With these results, we describe the shape and size morphological variation of J. lineata and discuss this uncommon habitat-dependent sexual dimorphism in a Neotropical livebearer fish.

First record of Hypostomus boulengeri (Siluriformes: 1 Loricariidae) from Río Bermejo basin.

Hypostomus boulengeri (Eigenmann y Kennedy 1903) es una especie poco conocida registrada de las cuencas de los Rios Paraguay Parana. En este trabajo reportamos por primera vez la presencia de esta especie en la cuenca del Rio Bermejo representado una ampliacion en la distribucion de mas de 600km.

The pineal complex: a morphological and immunohistochemical comparison between a tropical (Paracheirodon axelrodi) and a subtropical (Aphyocharax anisitsi) characid species

Cardinal neon Paracheirodon axelrodi and bloodfin tetra Aphyocharax anisitsi are two species of characids with high trade value as ornamental fish in South America. Although both species inhabit middle water layers, cardinal neon exhibits a tropical distribution and bloodfin tetra a subtropical one. In this work, we carried out an anatomical, histological and immunohistochemical study of the pineal complex of P. axelrodi and A. anisitsi. In both species, the pineal complex consisted of three components, the pineal and parapineal organs and the dorsal sac (DS). The pineal organ was composed of a short, thin pineal stalk (PS), vertically disposed with respect to the upper surface of the telencephalon, and a pineal vesicle (PV), located at the distal end of the PS and attached to the skull by connective tissue. The pineal window (PW), a site in the skull where the luminal information accesses the pineal organ, appeared just above the latter structures. In the epidermis of P. axelrodis PW, club cells were identified, but were not observed in the epidermis of A. anisitsis one. With respect to the DS, it appeared to be folded on itself, and was bigger and more folded in A. anisitsi than in P. axelrodi. Immunohistochemical assays revealed the presence of cone opsin‐like and rod opsin‐like photoreceptor cells in the PS and PV. These results provide a first insight into the morphological assembly of the pineal complex of both species, and contribute to a better understanding of the integration and transduction of light stimuli in characids. J. Morphol. 277:1355–1367, 2016.

Occurrence of Astyanax dissensus Lucena & Thofehrn, 2013 (Teleostei: Characidae) in Argentina

The occurrence of Astyanax dissensus in the Uruguay River, at Yapeyu, Corrientes, Argentina is reported for the first time in the country.