A complete record from colonization to extinction reveals density dependence and the importance of winter conditions for a population of the silvery blue, Glaucopsyche lygdamus.

Butterflies in the family Lycaenidac are often the focus of conservation efforts. However, our understanding of lycaenid population dynamics has been limited to relatively few examples of long-term monitoring data that have been reported. Here, factors associated with population regulation are investigated using a complete record of a single population of the silvery blue, Glaucopsyche lygdamus Doubleday (Lepidoptera: Lycaenidae). Adults of G. lygdamus were first observed in an annual grassland near Davis, California, in 1982 and were last seen in 2003. Relationships between inter-annual variation in abundance and climatic variables were examined, accounting for density dependent effects. Significant effects of both negative density dependence and climatic variation were detected, particularly precipitation and temperature during winter months. Variation in precipitation, the strongest predictor of abundance, was associated directly and positively with butterfly abundance in the same year. Winter temperatures had a negative effect in the same year, but had a lagged, positive effect on abundance in the subsequent year. Mechanistic hypotheses are posed that include climatic effects mediated through both larval and adult plant resources

Cone-specific mediation of rod sensitivity in trichromatic observers

PURPOSE. The slope of the rod threshold versus the illuminance (TVI) function changes with the wavelength of the background light. This study was conducted to determine whether the changes in slope are due to the stimulation of specific cone classes. METHODS. An eight-channel optical system was used to generate lights that differed in cone and rod photoreceptor illuminance. Rod flicker TVI functions were measured in normal trichromatic observers at mesopic light levels. The independent variables were (1) the relative contribution of the short (S)-and long (L)-wavelength cones to the background light (i.e., the background lights varied along S-only and L-only lines), and (2) the temporal frequency of the flickering lights (4, 7.5, and 15 Hz). RESULTS. The 4-Hz rod flicker TVI function had a slope of 0.87 when measured near W (MacLeod-Boynton chromaticity of 0.66, 1.0). At 4 and 7.5 Hz, an increase in the relative L-cone illuminance steepened the slope of the rod-only TVI curve, but an increase in the relative S-cone illuminance had no effect. The slope of the 7.5-Hz TVI function decreased at higher illuminance levels. At 15 Hz, the thresholds could be measured over only a limited range. CONCLUSIONS. The L-cone system contributes to the desensitization of the rod system at mesopic light levels, whereas, in the range of lights used in these experiments, the S-cone system apparently does not. The possibility that S-cone stimulation desensitizes the response to rod signals at higher levels of S-cone illumination cannot be eliminated. (Invest Ophthalmol Vis Sci. 2002;43:898 -905) T he primate visual system operates over a range of 10 log units. This ability is due in part to the duplex retina in which scotopic (i.e., rod-dominated) vision operates at low light levels and photopic (i.e., cone-dominated) vision operates at high light levels. In several early studies, researchers proposed that these two systems behave independently of each other under many conditions, 1-4 but there is now clear evidence of the rods' influence on the cone systems and the cones' influence on the rod system. Visual signals originating in the rod photoreceptors do not have their own pathway to the brain but instead combine with neural signals originating in the cone photoreceptors. Signals originating with the rod photoreceptors are transmitted to the retinal ganglion cells through at least two anatomic pathways. One pathway combines through second-order cells. Rod photoreceptors connect to rod bipolar cells, which in turn connect to rod (AII) amacrine cells. The rod amacrine cells have gap junction connections with on-center ganglion cells in sublamina b of the inner plexiform layer, and have inhibitory synapses with off-center ganglion cells in sublamina a. Rod signals may also enter the cone circuit through gap junctions between rod spherules and cone pedicles (see Refs. 5-7). There is also recent evidence in rodents of a third pathway connecting the rod photoreceptors directly to OFF cone bipolar cells. 8,9 The general perceptual consequences of interaction between rods and cones have been documented extensively. We know, for instance, that the rod photoreceptor system influences cone-mediated sensitivity 10 -13 and vice versa 14 -18 ; that interaction between the rod and cone systems is more evident with flashed lights than with steady lights 19 ; and that location, spatial extent, and temporal frequency play an important role in determining the magnitude of rod and cone interaction. 17,20 -24 Rod-cone interaction (how rods influence cones) and cone-rod interaction (how cones influence rods) have become umbrella terms that characterize many classes of visual processing. One historical difficulty with experiments that investigate rod-cone (and cone-rod) interaction is that the narrowbandwidth lights (i.e., lights of a few spectral wavelengths) used as experimental stimuli often stimulate more than one class of photoreceptor. These experiments therefore do not lend themselves as easily to physiological interpretation. Many previous researchers have addressed such topics by measuring rod sensitivity to lights to which the rod system is much more sensitive than the cone systems (e.g., Ref. 25) or by investigating the responses of monochromatic and dichromatic observers. 26 -28 To investigate questions concerned with cone-rod interaction, I used an approach based on the cone-rod photoreceptor space defined by Shapiro et al. For this article, I examined rod TVI functions for 4-Hz flickering lights. Aguilar and Stiles 25 measured a rod TVI function by optimizing experimental parameters to isolate the rod system. One of these optimizations was to desensitize the cone systems with a long-wavelength adaptation light. They found that the slope of a major portion of the curve (i.e., when the adaptation light is between Ϫ2 and 2.2 log scotopic trolands [td]) is approximately 1.0. However, Sharpe et al

Cone-specific mediation of rod sensitivity in trichromatic observers

PURPOSE. The slope of the rod threshold versus the illuminance (TVI) function changes with the wavelength of the background light. This study was conducted to determine whether the changes in slope are due to the stimulation of specific cone classes. METHODS. An eight-channel optical system was used to generate lights that differed in cone and rod photoreceptor illuminance. Rod flicker TVI functions were measured in normal trichromatic observers at mesopic light levels. The independent variables were (1) the relative contribution of the short (S)-and long (L)-wavelength cones to the background light (i.e., the background lights varied along S-only and L-only lines), and (2) the temporal frequency of the flickering lights (4, 7.5, and 15 Hz). RESULTS. The 4-Hz rod flicker TVI function had a slope of 0.87 when measured near W (MacLeod-Boynton chromaticity of 0.66, 1.0). At 4 and 7.5 Hz, an increase in the relative L-cone illuminance steepened the slope of the rod-only TVI curve, but an increase in the relative S-cone illuminance had no effect. The slope of the 7.5-Hz TVI function decreased at higher illuminance levels. At 15 Hz, the thresholds could be measured over only a limited range. CONCLUSIONS. The L-cone system contributes to the desensitization of the rod system at mesopic light levels, whereas, in the range of lights used in these experiments, the S-cone system apparently does not. The possibility that S-cone stimulation desensitizes the response to rod signals at higher levels of S-cone illumination cannot be eliminated. (Invest Ophthalmol Vis Sci. 2002;43:898 -905) T he primate visual system operates over a range of 10 log units. This ability is due in part to the duplex retina in which scotopic (i.e., rod-dominated) vision operates at low light levels and photopic (i.e., cone-dominated) vision operates at high light levels. In several early studies, researchers proposed that these two systems behave independently of each other under many conditions, 1-4 but there is now clear evidence of the rods' influence on the cone systems and the cones' influence on the rod system. Visual signals originating in the rod photoreceptors do not have their own pathway to the brain but instead combine with neural signals originating in the cone photoreceptors. Signals originating with the rod photoreceptors are transmitted to the retinal ganglion cells through at least two anatomic pathways. One pathway combines through second-order cells. Rod photoreceptors connect to rod bipolar cells, which in turn connect to rod (AII) amacrine cells. The rod amacrine cells have gap junction connections with on-center ganglion cells in sublamina b of the inner plexiform layer, and have inhibitory synapses with off-center ganglion cells in sublamina a. Rod signals may also enter the cone circuit through gap junctions between rod spherules and cone pedicles (see Refs. 5-7). There is also recent evidence in rodents of a third pathway connecting the rod photoreceptors directly to OFF cone bipolar cells. 8,9 The general perceptual consequences of interaction between rods and cones have been documented extensively. We know, for instance, that the rod photoreceptor system influences cone-mediated sensitivity 10 -13 and vice versa 14 -18 ; that interaction between the rod and cone systems is more evident with flashed lights than with steady lights 19 ; and that location, spatial extent, and temporal frequency play an important role in determining the magnitude of rod and cone interaction. 17,20 -24 Rod-cone interaction (how rods influence cones) and cone-rod interaction (how cones influence rods) have become umbrella terms that characterize many classes of visual processing. One historical difficulty with experiments that investigate rod-cone (and cone-rod) interaction is that the narrowbandwidth lights (i.e., lights of a few spectral wavelengths) used as experimental stimuli often stimulate more than one class of photoreceptor. These experiments therefore do not lend themselves as easily to physiological interpretation. Many previous researchers have addressed such topics by measuring rod sensitivity to lights to which the rod system is much more sensitive than the cone systems (e.g., Ref. 25) or by investigating the responses of monochromatic and dichromatic observers. 26 -28 To investigate questions concerned with cone-rod interaction, I used an approach based on the cone-rod photoreceptor space defined by Shapiro et al. For this article, I examined rod TVI functions for 4-Hz flickering lights. Aguilar and Stiles 25 measured a rod TVI function by optimizing experimental parameters to isolate the rod system. One of these optimizations was to desensitize the cone systems with a long-wavelength adaptation light. They found that the slope of a major portion of the curve (i.e., when the adaptation light is between Ϫ2 and 2.2 log scotopic trolands [td]) is approximately 1.0. However, Sharpe et al

The separation of monocular and binocular contrast

AbstractThe contrast asynchrony is a stimulus configuration that illustrates the visual system’s separable responses to luminance and luminance contrast information (Shapiro, 2008; Shapiro et al., 2004). When two disks, whose luminances modulate in phase with each other, are each surrounded by a disk, one light and one dark, observers can see both the in-phase brightness signals and the antiphase contrast signals and can separate the two. Here we present the results of experiments in which observers viewed a similar stimulus dichoptically. We report that no asynchrony is perceived when one eye is presented with modulating disks and the other eye is presented with the black and white surround rings, nor is an asynchrony perceived in gradient versions of the contrast asynchrony. We also explore the “window shade illusion” (Shapiro, Charles, & Shear-Heyman, 2005) dichoptically and find that when a modulating disk is presented to one eye and a horizontally split black/white annulus is presented to the other, observers perceive a “shading” motion up and down the disk. This shading can be seen in either direction in the binocular condition, but it is almost always seen as moving towards low contrast in the monocular condition. These findings indicate the presence of separable retinal and cortical networks for contrast processing at different temporal and spatial scales

Induction of NF-κB by the Akt/PKB kinase

AbstractThe serine/threonine kinase Akt (also known as protein kinase B, PKB) is activated by numerous growth-factor and immune receptors through lipid products of phosphatidylinositol (PI) 3-kinase. Akt can couple to pathways that regulate glucose metabolism or cell survival [1]. Akt can also regulate several transcription factors, including E2F, CREB, and the Forkhead family member Daf-16 [2–4]. Here, we show that Akt can regulate signaling pathways that lead to induction of the NF-κB family of transcription factors in the Jurkat T-cell line. This induction occurs, at least in part, at the level of degradation of the NF-κB inhibitor IκB, and is specific for NF-κB, as other inducible transcription factors are not affected by Akt overexpression. Furthermore, the effect requires the kinase activity and pleckstrin homology (PH) domain of Akt. Also, Akt does not act alone to induce cytokine promoters and NF-κB reporters, because signals from other pathways are required to observe the effect. These studies uncover a previously unappreciated connection between Akt and NF-κB induction that could have implications for the control of T-cell growth and survival

Relatedness and Population Differentiation in a Colonial Butterfly, Eucheira socialis (Lepidoptera: Pieridae)

Eucheira socialis (Westwood) occurs above 1,800 m in mountains throughout Mexico and has a remarkable suite of autapomorphies, including communal larval nests and a mean primary sex ratio of 70% males. We gathered allozyme data for 31 loci from individuals within nests within populations and used hierarchical F statistics to assess population structure and relatedness at these levels. Allozyme variation was far lower than reported in most Lepidoptera, and was absent from the populations sampled from southern Mexico. Among 5 sample sites distributed throughout Mexico, differentiation was high (FST = 0.54), which is consistent with a history of interrupted gene flow. At lower hierarchical levels in the variable populations, we found significant excess heterozygotes within nests (FIN = −0.15) and evidence for structuring within subpopulations (FIS =0.015, significantly greater than FIN). Average relatedness among nestmates was rNS = 0.28, which is significantly less than r = 0.5. This is probably caused largely by interchange among nests on multinest trees. ADAM H. PORTE