Biological Rhythms

Daily cycle and environmental factors influence fish assemblage structure in an Amazonian conservation unit

We investigated the influence of daily cycle cycleand local environmental factors on fish assemblages in a terra firme stream in southwestern Amazonia during the rainy season. We collected fish by using sieves and hand-nets over three days and local environmental variables were measured throughout the collection period as well. We employed Generalized Linear Models to examine the impact of daily cycle and local environmental variables on fish species richness and abundance. We used PERMANOVA to assess changes in fish assemblage composition and Redundancy Analysis to understand variations in fish species composition in response to daily cycle and local environmental factors. We collected 18 species and 271 individuals, 111 at night and 160 during the day. Dissolved oxygen (DO) had a positive influence on species richness and abundance and species composition differed between daily cycles. Redundancy Analysis revealed associations between fish species composition, environmental variables (temperature, pH and DO), and daily cycle. These findings underscore the significance of the local environment and daily cycle in predicting variations in fish assemblage structure in Amazonian streams. Understanding how stream fish assemblages are organized temporally is important for devising effective conservation strategies in a region facing increasing human pressures on aquatic ecosystems.

Ontogeny of daily rhythms in the expression of metabolic factors in Nile tilapia (Oreochromis niloticus) kept at two different temperature regimes: Thermocycle and constant temperature

The daily variations of temperature are one of the main synchronizers of the circadian rhythms. In addition, water temperature influences the embryonic and larval development of fish and directly affects their metabolic processes. The application of thermocycles to fish larvae has been reported to improve growth and the maturation of the digestive system, but their effects on metabolism are poorly understood. The aim of the present study was to evaluate the effect of two different temperature regimes, cycling versus constant, on the daily rhythms of metabolic factors of Nile tilapia (Oreochromis niloticus) larvae. For this purpose, fertilized eggs were divided into two groups: one reared in a 31 °C:25 °C day:night thermocycle (TCY) and another group maintained in a constant 28 °C temperature (CTE). The photoperiod was set to a 12:12 h light/dark cycle. Samples were collected every 4 h during a 24-h cycle on days 4, 8 and 13 post fertilization (dpf). The expression levels of alanine aminotransferase (alt), aspartate aminotransferase (ast), malic enzyme, glucose-6-phosphate dehydrogenase (g6pd), phosphofructokinase (pfk) and pyruvate kinase (pk) were analyzed by qPCR. Results showed that, in 13 dpf animals, most of the genes analyzed (alt, ast, malic, g6pd and pfk) showed daily rhythms in TCY, but not in the group kept at constant temperature, with most acrophases detected during the feeding period. An increase in nutrient metabolism around feeding time can improve food utilization and thus increase larval performance. Therefore, the use of thermocycles is recommended for tilapia larviculture.

A Spark in the Dark: Uncovering Natural Activity Patterns of Mormyrid Weakly Electric Fish

To understand animal ecology, observation of wildlife in the natural habitat is essential, but particularly challenging in the underwater realm. Weakly electric fishes provide an excellent opportunity to overcome some of these challenges because they generate electric organ discharges (EODs) to sense their environment and to communicate, which can be detected non-invasively. We tracked the EOD and swimming activity of two species of mormyrid weakly electric fishes (Marcusenius victoriae and Petrocephalus degeni) over diel cycles in the laboratory, and we recorded EODs and environmental dissolved oxygen (DO) concentration and temperature over several months in a naturally hypoxic habitat in Uganda. Under laboratory conditions, both species showed increases of activity and exploration behavior that were closely synchronized to the onset of the dark phase. In the wild, fish preferred structurally complex habitats during the day, but dispersed toward open areas at night, presumably to forage and interact. Nocturnal increase of movement range coincided with diel declines in DO concentration to extremely low levels. The fact that fish showed pronounced nocturnal activity patterns in the laboratory and in the open areas of their habitat, but not under floating vegetation, indicates that light intensity exerts a direct effect on their activity. We hypothesize that being dark-active and tolerant to hypoxia increases the resistance of these fish against predators. This study establishes a new technology to record EODs in the field and provides a window into the largely unknown behavior of mormyrids in their natural habitat.

Time does matter! Acute copper exposure abolishes rhythmicity of clock gene in Danio rerio

The circadian clock is a key cellular timing system that coordinates physiology and behavior. Light is a key regulator of the clock mechanism via its activation of Per and Cry clock gene expression. Evidence points to a key role of reactive oxygen species (ROS) in resetting this process. In this context, the aim of the present study was to explore copper as a ROS generator, using an innovative approach investigating its effects on circadian timing. Liver and brain from Danio rerio specimens exposed to 0, 5, 25 and 45 μg/L copper concentrations were obtained. Daily oscillations of superoxide dismutase (SOD) and catalase (CAT) enzymatic activity and their correlations both with clock genes (per1, per2, and cry1a) and with organism energy cost were determined. CAT expression correlates with per2 and cry1a and, thus, provides data to support the hypothesis of hydrogen peroxide production by a phototransducing flavin-containing oxidase. Higher SOD activity is correlated with higher intracellular ATP levels. Copper disturbed the daily oscillation of antioxidant enzymes and clock genes, with disturbed per1 rhythmicity in both the brain and liver, while cry1a rhythmicity was abolished in the liver at 25 μg/L copper. Coordination between the SOD and the CAT enzymes was lost when copper concentrations exceeded the limits established by international laws. These results indicate that organism synchronization with the environment may be impaired due to acute copper exposure.

Time-place learning and leader-follower relationships in Arctic charr Salvelinus alpinus

Feeding activity from a larger refuge site into two visually separated feeding sites with temporally restricted food availability, one in the morning and one in the evening was studied in duplicate groups of Arctic charr Salvelinus alpinus. A passive integrated transponder (PIT) system enabled continuous monitoring of individual movements between the sites. Both groups synchronized their diel pattern of visit activity to the two feeding sites when food was available. One group showed significant anticipatory visit activity into both feeding sites during the hours before the feed was available, suggesting a time and place learning of resource availability. The anticipatory activity of the other group was, however, less pronounced and only occurred into one of the feeding sites. Individual S. alpinus entered the feeding sites independently and no obvious patterns of leaders and followers were identified. All S. alpinus gained mass and moved between a refuge and the feeding sites. Different strategies of how individual S. alpinus utilized the feeding sites were not correlated with growth.

A case study: the effect of visitors on two captive pumas with respect to the time of the day

This study analyzed the effects of noise levels and number of visitors on the behaviors of a mother puma and her daughter in a zoo environment with respect to the time of day. The study monitored visitation (noise and number) over two 1-week periods (4 weeks between periods) and frequency of various puma behaviors (videorecorded). The study analyzed videotaped behavior of the pumas based on the time of day and visitors' number and noise levels. There was a direct association of puma behaviors with visitors' number and noise levels. The daughter puma was the most affected and behavioral changes of both pumas correlated more strongly with the noise level than the number of visitors. The noise level and number of visitors affected the behavior of the mother and her daughter only in the morning. The results of this study indicate that both noise level and number of visitors affected these pumas but revealed the noise as predominant. Moreover, the response of these pumas to visitors depended on the time of the day.

The blind catfish from the caves of Chapada Diamantina, Bahia, Brazil (Siluriformes: Heptapteridae): description, anatomy, phylogenetic relationships, natural history, and biogeography

Rhamdiopsis krugi, a new troglobitic heptapterid catfish, is described from the caves of Chapada Diamantina, State of Bahia, northeastern Brazil. This species, although frequently cited in the scientific literature along the last seventeen years, remained undescribed largely due to its uncertain phylogenetic affinities. The generic assignment of R. krugi was clouded largely by its high number of unusual morphological features (some related to cave life), for instance: absence of eyes and body pigmentation; presence of a widely exposed pseudotympanum; posterior border of the anterior branch and anterior margin of the arborescent portion of the posterior branch of the transverse process of fourth vertebra joined; dorsal hypural plate commonly with seven rays; ventral caudal plate usually with six rays; dorsal and ventral caudal-fin lobes typically with six branched fin rays each; 38-39 vertebrae; anal fin with 14-17 rays; and lateral line very short. Rhamdiopsis krugi can be easily distinguished from its congeners, R. microcephala and R. moreirai, by its troglomorphic features and by the presence of a shorter lateral line, fewer vertebrae and anal-fin rays, pattern of branching of caudal-fin rays, and several attributes of skeletal system. The affinities of this new species are discussed in light of current phylogenetic knowledge of the family Heptapteridae. Incongruent derived characters do not allow selection of a particular hypothesis of sister group relationships among species of Rhamdiopsis. The occurrence of R. krugi in the rio Paraguaçu basin is possibly due to an event of hydrological capture from a section of the middle portion of the rio São Francisco basin, caused by tectonic events. The semi-arid region where R. krugi presently lives was probably covered by a wide forested area during a humid cycle in Quaternary. A summary of natural history and ecology data of R. krugi, as well as notes on its conservation, are provided. We also offer comments on the morphological plasticity of R. krugi.