How light, a predator, and experience influence bluegill use of shade and schooling

Bluegills, Lepomis macrochirus, form schools and use shade to avoid predators. How light intensity, predators, and experience might affect antipredator behavior of bluegill are not well understood. Hence, we evaluated use of shade and schooling by naive (hatchery) and experienced (wild) bluegills (50–60 mm total length) at four light levels (1.5, 85, 169, 340 lux) in the presence and absence of a model predator in experimental pools. Naive bluegills used shade extensively at all light levels, even when the predator was in the shade. They rarely schooled, preferring to shoal in the shade. Experienced bluegill used shade when the predator was in the open and avoided shade when the predator was there. Schooling was more prevalent at low light levels when shade was less intense. Use of shade became an increasingly important behavior at higher light levels, unless the predator was in the shade. A shaded predator caused experienced bluegills to shoal tightly in the opposite, open area. These data suggest naive bluegills may not have considered the model predator a threat. Their behavior suggests avian predator avoidance, a possibility given that avian predators were present at the hatchery. Experienced bluegill employed behaviors that would be useful in avoiding piscine predators.     

Ontogenic diet shifts and scale-eating in Roeboides dayi, a Neotropical characid

Scale feeding (lepidophagy) has been documented for a variety of Neotropical fish taxa, including the characid genus Roeboides. Ontogenetic differentiation of jaws and snout teeth allow larger Roeboides to remove scales, however, the less specialized tooth/jaw structure in Roeboides dayi, indicates that it may be a facultative scale feeder. Population dynamics and diets of R. dayi in a Venezuelan lowland swamp/creek and a piedmont stream were compared over an annual cycle. Juvenile R. dayi consumed aquatic insect larvae and microcrustacea, and although spawning was year-round at both sites, most reproduction occurred during the wet season when the availability of these resources was greatest for juveniles. At both sites, larger R. dayi fed on a combination of invertebrate prey and fish scales, the former being more important at the piedmont site, and the latter being especially important during initial low water conditions at both sites. In the lowland stream, the reduction of aquatic habitat during the early dry season created higher fish densities and a more profitable environment for scale-feeders. Insectivory probably was less profitable during this early low water period due to interspecific competition for reduced aquatic insect stocks.     

Morphological differences between an artificial lentic and adjacent lotic environments in a characid species

Dam constructions cause fundamental changes in the natural landscape, creating new ecological and evolutionary challenges for aquatic organisms. In some cases, such water impoundments have been related with morphological changes in organisms. Understanding how populations respond to rapid environmental changes imposed by dams is the first step to elucidate the consequences that disturbed habitats may have on species evolution. In this work, we analyzed shape and size variation in Bryconamericus iheringii Boulenger 1887 from the Chasqueiro stream basin, south of Brazil, which was recently dammed. We used linear measurements and geometric morphometrics to identify morphological differences among specimens from the reservoir (lentic habitat) compared to the habitat upstream and downstream of the dam (lotic habitats). We also tested for size- and shape-related sexual dimorphism to determine whether variations observed were the same for both sexes. We found that B. iheringii from the artificial reservoir were distinct in shape and size to those from their natural habitat in the stream. The size variation between environments was the same for both sexes, but the shape variation differed between males and females. Regarding the linear measurements, lotic populations were larger (greater body length, width, pectoral fin base length and caudal peduncle length), probably in response to increased swimming activity. Regarding body shape, we found that both sexes have a more fusiform body in lotic habitats than in the reservoir. In addition, females showed an altered mouth position that was distinct between these environments. This work indicates that the water reservoir seems to be an important factor influencing morphological variation in B. iheringii, a species with sexual shape dimorphism.

     

A light intensity threshold for schooling in the Atlantic mackerel, Scomber scombrus

The schooling behaviour of Atlantic mackerel was studied in a large tank at different light intensities in the range 12.6–1.8 × 10⁻¹⁰μEs⁻¹ m⁻². Variable light intensity was produced by accurately controlling the current to a green light-emitting diode (LED) 3 m above the experimental tank. Under high light levels (1.8 × 10⁻⁶μEs⁻¹ m⁻²) mackerel always formed a single school, whereas at lower levels (1.8 × 10⁻⁸μEs⁻¹ m⁻²) they swam as individuals. At light levels down to 1.0 × 10⁻⁶μEs⁻¹ m⁻² the mean nearest neighbour distance in a school remained relatively constant (0.3–0.9 body lengths), and individual mackerel swam along a path which deviated from the position of their nearest neighbours by less than 14°. As light dropped below 1.8 × 10⁻⁷μEs⁻¹ m⁻², both nearest neighbour distance and heading angle between nearest neighbours increased, with mean values of 1–1.8 body lengths and 23–92°, respectively, at 1.8 × 10⁻⁹μEs⁻¹ m⁻². The results are discussed in terms of ambient light conditions in the sea.     

Age at menarche, schooling, and sexual debut in northern Malawi

Background

Age at sexual debut is a key behavioural indicator used in HIV behavioural surveillance. Early age at menarche may precipitate early sex through perceived readiness for sex, or through school drop-out, but this is rarely studied. We investigated trends and circumstances of sexual debut in relation to schooling and age at menarche.

Methods and Findings

A cross-sectional sexual behaviour survey was conducted on all individuals age 15–59 within a demographic surveillance site in Karonga District, Malawi. Time trends were assessed using birth cohorts. Survival analysis was used to estimate the median age at menarche, sexual debut and first marriage. The 25^th centile was used to define “early” sex, and analyses of risk factors for early sex were restricted to those who had reached that age, and were done using logistic regression. Of the 8232 women and 7338 men resident in the area, 88% and 78%, respectively, were seen, and, 94% and 92% of these were interviewed. The median reported age at first sex was 17.5 for women and 18.8 for men. For women, ages at menarche, sexual debut and first marriage did not differ by birth cohort. For men, age at sexual debut and first marriage decreased slightly in later birth cohorts. For both men and women increased schooling was associated with later sexual debut and a longer delay between sexual debut and first marriage, but the associations were stronger for women. Earlier age at menarche was strongly associated with earlier sexual debut and marriage and lower schooling levels. In women early sexual debut (<16 years) was less likely in those with menarche at age 14–15 (odds ratio (OR) 0.31, 95%CI 0.26–0.36), and ≥16 (OR 0.04, 95%CI 0.02–0.05) compared to those with menarche at <14. The proportion of women who completed primary school was 46% in those with menarche at <14, 60% in those with menarche at 14–15 and 70% in those with menarche at ≥16. The association between age at menarche and schooling was partly explained by age at sexual debut. The association between age at menarche and early sex was not altered by adjusting for schooling.

Conclusions

Women with early menarche start sex and marry early, leading to school drop-out. It is important to find ways to support those who reach menarche early to access the same opportunities as other young women.     

Simultaneous separate detection of low angle and large angle light scattering in an arc lamp-based flow cytometer

A device is described for simultaneous separate detection of the light scattering of cells at low and large scattering angles in an arc lamp-based flow cytometer with epi-illumination through an oil immersion microscope objective. Light scattering was measured in a dark field configuration that allows separate detection of light scattering greater than 2 degrees and 15 degrees, respectively. Dual parameter light scattering histograms of a blood cell suspension containing various types of leukocytes were closely similar to that obtained with a commercial laser-based instrument with light scattering detection at forward and right angles. The sensitivity of the device was sufficient to measure polystyrene particles with 0.25-micron diameter. A potential application may be differentiation of bacteria.     

Sensitization and habituation of the swimming behavior in ascidian larvae to light

Ascidian larvae of Ciona intestinalis change their photic behavior during the course of development. Newly hatched larvae show no response to a light stimulus at any intensity. At 4 hr after hatching, larvae were induced to start to swimming upon the cessation of illumination, and to stop swimming upon the onset of illumination. At a weaker light intensity (5.0 x 10(-3) J/m (2).s), the larvae showed similar responses to either a single stimulus or repeated stimuli of onset and cessation of light until 10 hr after hatching. At a stronger light intensity (3.2 x 10(-1) J/m(2).s), when the stimulus was repeated, they showed sensitization and habituation of the swimming response. At 3 hr after hatching the larvae failed to show any response to an initial stimulus at any intensity of light, but after several repeated stimuli (sensitization) they showed a swimming response at light intensities above 4.0 x 10(-2) J/m (2).s. At 5 hr and with intensity above 1.0 x 10 (-2) J/m(2).s, the larvae showed photoresponses to the first stimulus, but after several repetitions the larvae failed to stop swimming upon the onset of light (habituation). A repeated series of stimuli at stronger intensities of light caused greater habituation; this habituation was retained for about 1 min. Since the larval central nervous system in Ciona is comprised of only about 100 neurons, learning behavior in ascidian larvae should provide insights for a minimal mechanism of memory in vertebrates.     

Leg coordination and swimming in an ant, Camponotus americanus

ABSTRACT. Leg movements of Camponotus americanus workers during straight swimming and turning are described herein. Thrust is generated through the different speeds and drag control between power v. return strokes in the forelegs. During the power stroke, femur, tibia and tarsus are straightened and thereby increase resistance; they bend backward during the return stroke. These thrusting legs move in a vertical plane which is similar to their position during walking. The backward stretching mesothoracic and metathoracic legs act, in conjunction with the gaster, as a rudder. Swimming in ants can be derived from walking; the major transformation being a suppression of the rhythmic movements of the middle and hind legs.     

Translational regulation of protein synthesis, in response to light, at a critical stage of Volvox development

In Volvox cultures synchronized by a light-dark cycle, juveniles containing presumptive somatic and reproductive cells are produced during the dark, but their cells do not differentiate until after the lights come on. The pattern of protein synthesis changes rapidly after the lights come on. Action spectra and effects of photosynthesis inhibitors indicate that this protein synthetic change is not simply a consequence of renewed flow of energy from illuminated chloroplasts. Actinomycin, at a level adequate to block the response to heat shock, has virtually no effect on the response of the same cells to light; furthermore, RNAs isolated from unilluminated and illuminated juveniles yield indistinguishable in vitro translation products. We conclude, therefore, that this effect of light is exerted almost exclusively at the translational level, generating one of the most striking examples of translational regulation yet described.     

Agonistic behavior in a schooling fish: form,function and ontogeny

Synopsis Although juvenile chum salmon,Oncorhynchus keta, are generally regarded as a schooling fish, when presented with a defensible point-source of food, some individuals abandon schooling, aggressively subordinate competitors, and monopolize food. When food is removed, fish gradually abandon solitary agonistic behaviors and return to schooling behavior. Agonism increases in frequency and intensity as juveniles age. The ability to alternate facultatively between schooling and solitary agonistic behavior may enable juvenile chum to respond to local patterns of food distribution and predation risk. The ontogenetic increase in agonism may result in school dispersal as fish move from the estuary into coastal waters, and may well reflect a shift in the costs versus the benefits of schooling as fish mature and become less vulnerable to predation.     

Individual swimming behavior of Daphnia: effects of food, light and container size in four clones

Different species of Daphnia show differences in their swimmingbehavior under different environmental conditions. We measuredthe three-dimensional swimming behavior of individual adultfemale Daphnia in the mesocosm-scale Plön plankton towers(6400 1) and in small (183 ml) observation chambers. Speed,sinking rate and turning angle were chosen as optimal variablesfor describing the free-swimming animals of four species. Speed,sinking rate and turning angle show uniformity of variance amongtreatments, and they are relatively independent. Light leveland food level strongly affected swimming behavior. Light andfood effects tended to be independent, although there were twoinstances of synergism (out of 12 possible interactions). Eachof the four species (one clone per species) showed a uniqueresponse to food and light, which may reflect the diverse environmentalorigin of each clone. Swimming behavior was consistently differentbetween the small-scale (183 ml) observation chamber and themesocosm-scale (6400 1) plankton tower, suggesting that containersize affects swimming behavior: in the smaller chamber, Daphnia,regardless of species, swam slower, sank slower and tended tomove in straighter paths.     

Developing a methodology for estimating the drag in front-crawl swimming at various velocities

We aimed to develop a new method for evaluating the drag in front-crawl swimming at various velocities and at full stroke. In this study, we introduce the basic principle and apparatus for the new method, which estimates the drag in swimming using measured values of residual thrust (MRT). Furthermore, we applied the MRT to evaluate the active drag (Da) and compared it with the passive drag (Dp) measured for the same swimmers. Da was estimated in five-stages for velocities ranging from 1.0 to 1.4 m s⁻¹; Dp was measured at flow velocities ranging from 0.9 to 1.5 m s⁻¹ at intervals of 0.1 m s⁻¹. The variability in the values of Da at MRT was also investigated for two swimmers. According to the results, Da (Da = 32.3 v^3.3, N = 30, R² = 0.90) was larger than Dp (Dp = 23.5 v^2.0, N = 42, R² = 0.89) and the variability in Da for the two swimmers was 6.5% and 3.0%. MRT can be used to evaluate Da at various velocities and is special in that it can be applied to various swimming styles. Therefore, the evaluation of drag in swimming using MRT is expected to play a role in establishing the fundamental data for swimming.     

Growth towards light as an adaptation to high light conditions in Chara branches

Growth of plants or plant organs towards more light is commonly interpreted as an adaptation to low light conditions. Here, we show for the first time, in a study of charophyte branches, a growth-based orientation towards light functioning as a mechanism to protect the plant from excessive light. Two Chara species were exposed to five different intensities of photosynthetically active radiation and species traits and pigmentation were measured. Branches of plants exposed to higher light intensities were convergent and pointed steeply upwards, whereas those exposed to lower light intensities grew nearly straight and were less inclined. Only branches that increased in length during the experiments reacted to differences in light intensity. This indicates that branch orientation is determined by a light-dependent growth reaction. Orientation of charophyte branches towards light is accompanied by a decrease in chlorophyll a (Chla) content and a lower Chla : carotenoid ratio, which clearly indicates that the plant is taking protective measures against potentially damaging excess light conditions. We suggest that the growth-based orientation of Chara branches towards light may protect sexual organs, which grow on adaxial branch sides, from light damage. In addition, the upward orientation of branches might lead to increased light transmission within dense charophyte beds, thus enabling an enhanced gross production.     

Effect of larval ontogeny, turbulence and light on prey attack rate and swimming activity in herring larvae

The effects of ontogeny (larval size), light and turbulence on the attack rate and swimming activity (proportion of time swimming and duration of swimming bout) of herring larvae (15-28 mm TL) have been investigated. Emphasis was put on the experimental design in order to create a set-up where the turbulence intensity distribution could be accurately measured as well as controlled in the entire experimental tank.Both larval size (ontogeny) and light had a significant positive effect on prey attack rate. Likewise, an intermediate increase in turbulence had a positive effect on prey attack rate, but this effect was dependent of light intensity and larval size.At low light (1.5 μE m² s⁻¹) intermediate turbulence increased the prey attack rate significantly for larger larvae (26 and 28 mm), while at high light (18 μE m² s⁻¹) intermediate turbulence had only a significant positive effect on the attack rate of smaller larvae 20 and 23 mm.In general, our data show a dome-shaped response of turbulence on attack rate and a U-shaped response of turbulence on swimming activity.For herring larvae >20 mm, the maximum (attack rate) and minimum (swimming activity) response of turbulence were found at intermediate turbulence intensities (energy dissipation rates between 7∗10⁻⁸ and 1∗10⁻⁶ W/kg). The highest turbulence level tested (8∗10⁻⁶ W/kg) showed only negative effects, as attack rates where at the lowest and swimming activity at the highest.Swimming activity increased with larval size or light, and decreased at intermediate turbulence. Compared to turbulent intensities under natural conditions this implies that larger herring larvae at 10 m depth have to be exposed to wind speeds of more than 17 m/s before negative effects on attack rate and swimming activity occurs.     

Pre-embedding immunohistochemistry as an approach to high resolution antigen localization at the light microscopic level

Summary Pre-embedding immunohistochemistry with subsequent embedding in hydroxypropyl methacrylate enables one to obtain high resolution staining of antigens in 1 tissue sections. A routine method using formaldehyde fixation, methanol permeation, and an indirect method with fluoresceinlabeled second antibody is described. This method is compared with other pre-embedding staining procedures. To illustrate the method the mouse small intestine was chosen as a model and stained with antibodies to tubulin, actin, and fibronectin. Some anticipated and some unusual staining patterns were found.     

Intensity of light diffraction from striated muscle as a function of incident angle.

In a recently developed theory of light diffraction by single striated muscle fibers, we considered only the case of normal beam incidence. The present investigation represents both an experimental and theoretical extension of the previous work to arbitrary incident angle. Angle scan profiles over a 50 degrees range of incident angle (+25 degrees to -25 degrees) were obtained at different sarcomere lengths. Left and right first-order scan peak separations were found to be a function of sarcomere length (separation angle = 2 theta B), and good agreement was found between theory and experiment. Our theoretical analysis further showed that a myofibrillar population with a single common skew angle can yield an angle scan profile containing many peaks. Thus, it is not necessary to associate each peak with a different skew population. Finally, we have found that symmetry angle, theta s, also varies with sarcomere length, but not in a regular manner. Its value at a given sarcomere length is a function of a particular region of a given fiber and represents the average skew angle of all the myofibril populations illuminated. The intensity of a diffraction order line is considered to be principally the resultant of two interference phenomena. The first is a volume-grating phenomenon which results from the periodic A-I band structure of the fiber (with some contribution from Z bands and H zones). The second is Bragg reflection from skew planes, if the correct relation between incident angle and skew angle is met. This may result in intensity asymmetry between the left and right first order lines.     

From the light to the darkness: thriving at the light extremes in the oceans

Light-acclimation processes are central to allowing photosynthesis in aquatic ecosystems to span from high light conditions, that are 10-fold higher than the light levels required to saturate photosynthesis, to the deep sea with extremely low light levels. In dim light systems, nutrient levels are often high, and cells maximize the absorption of light by increasing the cellular pool of pigments. The upper limits of light absorption are constrained by the package effect, which ultimately restricts the benefit of the light absorption associated with an increase in cellular pigmentation, thus decreasing the cost/benefit ratio relative to the metabolic cost of manufacturing cellular light-harvesting pigments. At extremely low light levels in the deep sea, chloroplasts are sequestered in numerous organisms; however, these species are not obligate autotrophs and supplement a heterotrophic/mixotrophic existence with opportunistic autotrophy. While low light acclimation is based on maximizing light absorption, photosynthetic systems under high light, in addition to decreased light-harvesting cross sections, rely on energy-dissipation processes to avoid light-induced damage to the photosynthetic apparatus and other free radical susceptible cell structures. Dissipation of excess light energy represents the largest sink of the absorbed light in high light environments; however, these processes remain largely unstudied and are rarely quantified. Cells supplement their energy-dissipation processes through increasing the capacity to remove high-light-generated radicals and/or inducing vertical movement. Improved understanding of strategies remains central for the understanding of algal distributions in nature and has broad industrial implications.