The dynamics of color signals in male threespine sticklebacks Gasterosteus aculeatus

Body coloration and color patterns are ubiquitous throughout the animal kingdom and vary be- tween and within species. Recent studies have dealt with individual dynamics of various aspects of coloration, as it is in many cases a flexible trait and changes in color expression may be context-de- pendent. During the reproductive phase, temporal changes of coloration in the visible spectral range （400-700 nm） have been shown for many animals but corresponding changes in the ultravio- let （UV） waveband （300-400 nm） have rarely been studied. Threespine stickleback Gasterosteus aculeatus males develop conspicuous orange-red breeding coloration combined with UV reflect- ance in the cheek region. We investigated dynamics of color patterns including UV throughout a male breeding cycle, as well as short-term changes in coloration in response to a computer- animated rival using reflectance spectrophotometry and visual modeling, to estimate how colors would be perceived by conspecifics. We found the orange-red component of coloration to vary during the breeding cycle with respect to hue （theta/R50） and intensity （achieved chroma/red chroma）. Furthermore, color intensity in the orange-red spectral part （achieved chroma） tended to be increased after the presentation of an artificial rival. Dynamic changes in specific measures of hue and intensity in the UV waveband were not found. In general, the orange-red component of the signal seems to be dynamic with respect to color intensity and hue. This accounts in particular for color changes during the breeding cycle, presumably to signal reproductive status, and with limitations as well in the intrasexual context, most likely to signal dominance or inferiority.

Visual ＂playback＂ of colorful signals in the field supports sensory drive for signal detectability

Colorful visual signals are important systems for investigating the effects of signaling environ ments and receiver physiology on signal evolution as predicted by the sensory drive hypothesis. Support for the sensory drive hypothesis on color signal evolution is mostly based on document ing correlations between the properties of signals and habitat conditions under which the signals are given （i.e., a correlational approach） and less commonly on the use of mathematical models that integrate representations of visual environments, signal properties, and sensory systems （i.e., a functional approach）. Here, we used an experimental approach in the field to evaluate signal efficacy of colorful lizard throat fans called dewlaps that show geographic variation in the lizard Anolis cristatellus. We used a remote controlled apparatus to display ＂fake dewlaps＂ to wild lizards to test for adaptive divergence in dewlap brightness （i.e., perceived intensity） among populations in situ. We found evidence of local adaptation in dewlap brightness consistent with the sensory drive hypothesis. Specifically, dewlaps that had the brightness characteristics of local lizards were more likely to be detected than those with the brightness characteristics of nonlocal lizards. Our findings indicate that simplified mathematical representations of visual environments may allow robust estimates of relative detectability or conspicuousness in natural habitats. We have shown the feasibility of evaluating color signal efficacy experimentally under natural conditions and dem onstrate the potential advantages of presenting isolated components of signals to an intended re ceiver to measure their contribution to signal function.

STUDY OF MISMATCHED FILTERING OF PASSIVE RADAR USING TV SIGNAL

This letter delnonstrates the structure of the passive radar using TV signals. Because the TV signal is a kind of pseudoperiodic signal, the matched filtering of color TV signals would yield high sidelobes which cause the range ambiguity. To overcome this problem, the mismatched filter is proposed to suppress the correlation sidelobcs of matched filtering of TV signals. By utilizing the iteration process, this method could achieve the required peak sidclobc level. The impacts of the noise and target movement on mismatched filtering are also analysed, Simulation results are included to demonstrate the effectiveness of the proposed technique.

Hormonal control of seasonal color change in female spiny-footed lizards:an observational and experimental approach

Breeding coloration of females often signals aspects of their reproductive status,suggesting a link between color and sex steroid hormones.In this study,we examined the relationships between 2 sex steroid hormones(progesterone and p-estradiol)and reproductive coloration in female spinyfooted lizards Acanthodactylus erythrurus.We first explored natural variation in female plasma hormone levels and coloration during their reproductive cycle,p-estradiol was negatively related to brightness and positively related to red saturation,whereas progesterone was not significantly related to coloration.After identifying key relationships,plasma hormone concentrations were manipulated by creating 3 experimental female groups(p-estradiol-treated,progesterone-treated,and control),and the effects on coloration were monitored,p-estradiol-treated females,in which there was a rise in both p-estradiol and progesterone levels,lost their red coloration earlier than females in the other 2 experimental groups,whereas progesterone treatment had no significant effect on female coloration.Our results suggest that high levels of either p-estradiol alone or(3-estradiol together with progesterone trigger the loss of red coloration in female spiny-footed lizards,and that progesterone alone does not affect coloration.We hypothesize that changes in female breeding color might be regulated by(3-estradiol in species in which conspicuous coloration is displayed before ovulation,and by progesterone in species in which this color is displayed during gravidity.

Influence of lighting environment on social preferences in sticklebacks from two different photic habitats.I.mate preferences of wild-caught females

Ultraviolet(UV)A signals(320-400 nm)are important in mate choice in numerous species.The sensitivity for UV signals is not only assumed to be costly,but also expected to be a function of the prevailing ecological conditions.Generally,those signals are favored by selection that efficiently reach the receiver.A decisive factor for color signaling is the lighting environment,especially in aquatic habitats,as the visibility of signals,and thus costs and benefits,are instantaneously influenced by it.Although ecological aspects of color signal evolution are relatively well-studied,there is little data on specific effects of environmental UV-light conditions on signaling at these shorter wavelengths.We studied wild-caught gravid female 3-spined sticklebacks Gasterosteus aculeatus of 2 photic habitat types(tea-stained and clear-water lakes),possessing great variation in their UV transmission.In 2 treatments,tea-stained and clear-water,preferences for males viewed under UV-present(UV-1-)and UV-absent(UV-)conditions were tested.A preference for males under UV+conditions was found for females from both habitat types,thus stressing the significance of UV signals in stickleback's mate choice decisions.However,females from both habitat types showed the most pronounced preferences for males under UV-h conditions under clear-water test conditions.Moreover,reflectance measurements revealed that the carotenoid-based orange-red breeding coloration in wild-caught males of both habitat types differed significantly in color intensity(higher in clear-water males)and hue(more red shifted in clear-water males)while no significant differences in UV coloration were found.The differential reflection patterns in longer wavelengths suggest that sticklebacks of both habitat types have adapted to the respective water conditions.Adaptations of UV signals in a sexual context to ambient light conditions in both behavior and coloration seem less evident.