Influence of lighting environment on social preferences in sticklebacks from two different photic habitats. II. Shoaling and mate preferences of lab-bred fishes.

Different environmental conditions may lead to diverse morphological, behavioral, and physiological adaptations of different populations of the same species. Lighting conditions, for example, vary vastly especially between aquatic habitats, and have been shown to elicit adaptations. The availability of short-wave ultraviolet (UV) light is especially fluctuating, as UV wavelengths are attenuated strongly depending on water properties. The island of North Uist, Scotland, comprises 2 differential habitat types, tea-stained and clear-water lakes, varying considerably in UV transmission. In previous studies, wild-caught 3-spined stickleback Gasterosteus aculeatus populations (3 populations of each habitat type) were tested with respect to their shoaling and mate preferences for fish viewed under UV-present and UV-absent conditions. The results revealed a habitat-dependent preference of UV cues during shoal choice (tea-stained populations: preference for UV-absent condition in tea-stained water; clear-water populations: no preference in clear-water) but an overall preference for UV-present conditions during mate choice. To assess genetic influences on these behavioral patterns, similar experiments were conducted with lab-bred F1-generations of the same stickleback populations that were raised in a common environment (i.e. standardized clear-water conditions). Offspring of sticklebacks from tea-stained lakes tended to prefer shoals viewed under UV-absent conditions (only in tea-stained water), while sticklebacks from clear-water lakes showed a significant preference for the shoal viewed under UV-present conditions in clear-water but not in tea-stained water. Mate-preference experiments demonstrated that females from the tea-stained lakes significantly preferred and females from the clear-water lakes preferred by trend the male viewed under UV-present conditions in the clear-water treatment. The results for both shoaling- and mate-preference tests were largely similar for wild-caught and lab-bred sticklebacks, thus hinting at a genetic basis for the preference patterns.

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+) 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+ 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.

The dynamics of color signals in male threespine sticklebacks Gasterosteus aculeatus.

Body coloration and color patterns are ubiquitous throughout the animal kingdom and vary between 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-dependent. 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 ultraviolet (UV) waveband (300-400 nm) have rarely been studied. Threespine stickleback Gasterosteus aculeatus males develop conspicuous orange-red breeding coloration combined with UV reflectance 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.

Context-dependent dynamic UV signaling in female threespine sticklebacks.

Color signals, including ultraviolet (UV) signals, are widespread throughout the animal kingdom and color changes can be influenced by reproductive and motivational state. However, studies on dynamic changes of UV signals are scarce. Three spine sticklebacks (Gasterosteus aculeatus) that show intraspecific UV communication were used to study dynamic UV signaling in females. Reflectance measurements were taken from the distended abdomen, which serves as signal of female fecundity and readiness to spawn for courting males, and the melanized dorsal region. Scans were taken during egg maturation as well as before and after stimulation with a male to investigate context-dependent color changes. We used a physiological model of vision to determine how females might be perceived by conspecifics and quantified chromatic contrasts among both body regions and between body regions and the background for all stages. Females showed a significant increase in abdominal UV intensity during egg maturation and in response to a courting male. Measures of chromatic contrast among body regions (abdomen vs. dorsal region) and against the background (abdomen vs. background) were also increased during egg maturation and in response to the male stimulus (abdomen vs. background). Our results provide evidence for dynamic UV signaling in females in a reproductive context.

Habitat-dependent olfactory discrimination in three-spined sticklebacks (Gasterosteus aculeatus).

The ability to recognize conspecifics is indispensible for differential treatment of particular individuals in social contexts like grouping behavior. The advantages of grouping are multifarious, and there exist numerous additional benefits of joining aggregations of conspecifics. Recognition is based on different signals and transmitted via multiple channels, among others the olfactory channel. The sensory system or the combination of sensory modalities used in recognition processes is highly dependent on the availability and effectiveness of modalities, which are a function of the environmental conditions. Using F1-generations of six three-spined stickleback (Gasterosteus aculeatus) populations from two habitat types (tea-stained and clear-water lakes) from the Outer Hebrides, Scotland, we investigated whether individuals are able to recognize members of their own population solely based on olfactory cues and whether the habitat type an individual originated from had an influence on its recognition abilities. When given the choice (own vs. foreign population) sticklebacks from tea-stained lakes significantly preferred the odor of their own population, whereas fish from clear-water habitats did not show any preference. Moreover, fish from the two habitat types differed significantly in their recognition abilities, indicating that olfactory communication is better developed when visual signaling is disturbed. Thus, the observed odor preferences appear to be the consequence of different selective constraints and adaptations as a result of the differences in environmental conditions that have acted on the parental generations. These adaptations are likely genetically based as the differences are present in the F1-generation that had been reared under identical laboratory conditions.