Evolution of time-control mechanisms in subterranean organisms: cave fishes under light-dark cycles (Teleostei: Siluriformes, Characiformes)

Subterranean organisms are excellent models for chronobiological studies, yet relatively few taxa have been investigated with this focus. Former results were interpreted as a pattern of regression of circadian locomotor activity rhythms in troglobitic (exclusively subterranean) species. In this paper we report results of experiments with cave fishes showing variable degrees of troglomorphism (reduction of eyes, melanic pigmentation and other specializations related to the hypogean life) submitted to light-dark cycles, preceded and followed by several days in constant darkness. Samples from seven species have been monitored in our laboratory for the detection of significant circadian rhythms in locomotor activity: S. typhlops, an extremely troglomophic species, presented the lowest number of significant components in the circadian range (only one individual out of eight in DD1 and three other fish in LD), all weak (low values of spectral power). Higher incidence of circadian components was observed for P. kronei - only one among six studied catfish without significant circadian rhythms under DD1 and DD2; spectral powers were generally high. Intermediate situations were observed for the remaining species, however all of them presented relatively strong significant rhythms under LD. Residual oscillations (circadian rhythms in DD2) were detected in at least part of the studied individuals of all species but S. typhlops, without a correlation with spectral powers of LD rhythms, i.e., individuals exhibiting residual oscillations were not necessarily those with the strongest LD rhythms. In conclusion, the accumulated evidence for troglobitic fishes strongly supports the hypothesis of external, environmental selection for circadian locomotor rhythms.

Nutrients removed by Kappaphycus alvarezii (Rhodophyta, Solieriaceae) in integrated cultivation with fishes in re-circulating water

The potential of the red alga Kappaphycus alvarezii to remove nutrients was tested to treat effluents of Trachinotus carolinus fish cultivation, and the production of carrageenan in this condition was analyzed. Experiments were conducted in four tanks of 8000 L with approximately 1200 fishes of 30 g each integrated with three tanks of 100 L with 700 g of K. alvarezii, as initial biomass per tank. Seawater was re-circulated between tanks with seaweed and with fish. As a control, three tanks with seawater circulating in an open system were utilized. Seawater samples were collected daily for 10 days and concentrations of nitrate, nitrite, ammonium and phosphate were determined in the inflow and outflow water of the tanks. Significant differences between both collecting points were considered as nutrient removal by the seaweed. Growth rates and carrageenan yields were also analyzed in seaweed cultivated in seawater and in effluents. Growth rates of seaweed cultivated in tanks were lower than those obtained in open sea and in laboratory cultivation. Effluents had concentrations of nitrate and nitrite ca. 100 times higher than in the control. Maximum values of nutrient removal on effluents were: nitrate= 18.2%; nitrite =50.8%; ammonium =70.5% and phosphate =26.8%. All plants survived throughout the experimental period, but some developed ""ice-ice"", a disease associated with physiological stress. After the experimental period, some plants selected and cultivated in open sea presented higher growth rates in 40 days, indicating nutrient storage. No significant differences between carrageenan yields of K alvarezii cultivated in seawater and in the effluents were observed. Our results show that K. alvarezii can be utilized as a biofilter for fish cultivation effluents, reducing the eutrophication process and can also be processed for carrageenan production, which provides an additional benefit to the fisheries. (C) 2008 Elsevier B.V. All rights reserved.

Threatened fishes of the world: Brycon nattereri Gunther, 1864 (Characidae)

Brycon nattereri (Ostariophysi: Characiformes: Characidae), a threatened South American freshwater fish, occurs in the Parana, Tocantins and Sao Francisco river basins in central Brazil. It is a middle-sized (up to 50 cm SL), omnivorous species, which occurs in swift, clear-water rivers with well-preserved riparian vegetation. Main threats to the species are water pollution, dam building, and deforestation.

The contrasting role of heterochromatin in the differentiation of sex chromosomes: an overview from Neotropical fishes

During the evolutionary process of the sex chromosomes, a general principle that arises is that cessation or a partial restriction of recombination between the sex chromosome pair is necessary. Data from phylogenetically distinct organisms reveal that this phenomenon is frequently associated with the accumulation of heterochromatin in the sex chromosomes. Fish species emerge as excellent models to study this phenomenon because they have much younger sex chromosomes compared to higher vertebrates and many other organisms making it possible to follow their steps of differentiation. In several Neotropical fish species, the heterochromatinization, accompanied by amplification of tandem repeats, represents an important step in the morphological differentiation of simple sex chromosome systems, especially in the ZZ/ZW sex systems. In contrast, multiple sex chromosome systems have no additional increase of heterochromatin in the chromosomes. Thus, the initial stage of differentiation of the multiple sex chromosome systems seems to be associated with proper chromosomal rearrangements, whereas the simple sex chromosome systems have an accumulation of heterochromatin. In this review, attention has been drawn to this contrasting role of heterochromatin in the differentiation of simple and multiple sex chromosomes of Neotropical fishes, highlighting their surprising evolutionary dynamism.

Anatomy and evolution of the mandibular, hyopalatine, and opercular muscles in characiform fishes (Teleostei: Ostariophysi)

The Characiformes are distributed throughout large portions of the freshwaters of Africa and America. About 90% of the almost 2000 characiform species inhabit the American rivers, with their greatest diversity occurring in the Neotropical region. As in most other groups of fishes, the current knowledge about characiform myology is extremely poor. This study presents the results of a survey of the mandibular, hyopalatine, and opercular musculature of 65 species representing all the 18 traditionally recognized characiform families, including the 14 subfamilies and several genera incertae sedis of the Characidae, the most speciose family of the order. The morphological variation of these muscles across the order is documented in detail and the homologies of the characiform adductor mandibulae divisions are clarified. Accordingly, the mistaken nomenclature previously applied to these divisions in some characiform taxa is herein corrected. Contradicting some previous studies, we found that none of the examined characiforms lacks an A3 section of the adductor mandibulae, but instead some taxa have an A3 continuous with A2. Derived myological features are identified as new putative synapomorphies for: the Characoidei; the clade composed of the Alestidae, Characidae, Gasteropelecidae, Cynodontoidea, and Erythrinoidea; the clade Cynodontoidea plus Erythrinoidea; the clade formed by Ctenoluciidae and Erythrinidae; the Serrasalminae; and the Triportheinae. Additionally, new myological data seems to indicate that the Agoniatinae might be more closely related to cynodontoids and erythrinoids than to other characids. (C) 2012 Elsevier GmbH. All rights reserved.

Considerations for Assessing Maximum Critical Temperatures in Small Ectothermic Animals: Insights from Leaf-Cutting Ants

The thermal limits of individual animals were originally proposed as a link between animal physiology and thermal ecology. Although this link is valid in theory, the evaluation of physiological tolerances involves some problems that are the focus of this study. One rationale was that heating rates shall influence upper critical limits, so that ecological thermal limits need to consider experimental heating rates. In addition, if thermal limits are not surpassed in experiments, subsequent tests of the same individual should yield similar results or produce evidence of hardening. Finally, several non-controlled variables such as time under experimental conditions and procedures may affect results. To analyze these issues we conducted an integrative study of upper critical temperatures in a single species, the ant Atta sexdens rubropiosa, an animal model providing large numbers of individuals of diverse sizes but similar genetic makeup. Our specific aims were to test the 1) influence of heating rates in the experimental evaluation of upper critical temperature, 2) assumptions of absence of physical damage and reproducibility, and 3) sources of variance often overlooked in the thermal-limits literature; and 4) to introduce some experimental approaches that may help researchers to separate physiological and methodological issues. The upper thermal limits were influenced by both heating rates and body mass. In the latter case, the effect was physiological rather than methodological. The critical temperature decreased during subsequent tests performed on the same individual ants, even one week after the initial test. Accordingly, upper thermal limits may have been overestimated by our (and typical) protocols. Heating rates, body mass, procedures independent of temperature and other variables may affect the estimation of upper critical temperatures. Therefore, based on our data, we offer suggestions to enhance the quality of measurements, and offer recommendations to authors aiming to compile and analyze databases from the literature.

Fishes of Paranagua Estuarine Complex, South West Atlantic

The objective of this work was to present an updated checklist of the currently known fishes in the Paranagua Estuarine Complex (PEC) and provides comments on conservation status for the treated species. We used a large dataset derived from a pool of studies which have been conducted within there along the last 30 years. Each study was based on monthly samplings and conducted in several estuarine habitat; thus, the pool covers practically all estuarine habitats and takes into account the seasonal cycle in the system. The PEC ichthyofauna represents a mixture between that fauna typical from the tropical Brazilian coast and that with affinities of temperate Argentinean and Uruguayan zones. The PEC harbors a rich fish fauna of 213 species, inserted in the families that are common along the Brazilian coast. Only a minor part (8%) of the PEC fish fauna was evaluated as regards the conservation status, mostly because of the lack of basic biological and ecological information for most species. Despite part of the among-estuaries differences are due to different and incomplete sampling efforts, the richness in the PEC is surprisingly higher than other systems in Brazil and around world, which emphasize the importance of the region for global biodiversity conservation.

Fishes of Paranaguá Estuarine Complex, South West Atlantic

The objective of this work was to present an updated checklist of the currently known fishes in the Paranaguá Estuarine Complex (PEC) and provides comments on conservation status for the treated species. We used a large dataset derived from a pool of studies which have been conducted within there along the last 30 years. Each study was based on monthly samplings and conducted in several estuarine habitat; thus, the pool covers practically all estuarine habitats and takes into account the seasonal cycle in the system. The PEC ichthyofauna represents a mixture between that fauna typical from the tropical Brazilian coast and that with affinities of temperate Argentinean and Uruguayan zones. The PEC harbors a rich fish fauna of 213 species, inserted in the families that are common along the Brazilian coast. Only a minor part (8%) of the PEC fish fauna was evaluated as regards the conservation status, mostly because of the lack of basic biological and ecological information for most species. Despite part of the among-estuaries differences are due to different and incomplete sampling efforts, the richness in the PEC is surprisingly higher than other systems in Brazil and around world, which emphasize the importance of the region for global biodiversity conservation.

Dynamics of mother-pup interactions: tradeoff between environment and physiology

The emergence and maintenance of maternal behavior are under the influence of environmental cues such as light and dark periods. This article discusses the characteristic neurobiology of the behavioral patterns of lactating rats. Specifically, the hormonal basis and neurocircuits that determine whether mother rats show typical sequential patterns of behavioral responses are discussed. During lactation, rats express a sequential pattern of behavioral parameters that may be determined by hormonal variations. Sensorial signals emitted by pups, as well as environmental cues, are suggested to serve as conditioned stimuli for these animals. Finally, the expression of maternal behavior is discussed under neuroeconomic and evolutionary perspectives.