Resumen:
|
The main goal of this thesis is to study the function, evolution and maintenance of the multiple sexual signals that Lacerta schreiberi lizards use in sexual selection processes, and how the natural selection pressure on these signals affects antipredator strategies of lizards. Conspicuous sexual signals, mate searching and mate guarding can greatly enhance the predation risk on males of sexually dichromatic species. Therefore, we investigated how sex, reproductive condition/mating season and the environment affect preventive risk-taking behavior (distance from the refuge), and active escape decisions in an emergency situation (flight initiation distance) of lizards (Chapter I). We found that males do not apply behavioral compensation for higher risk of mate searching and conspicuous sexual signals. In contrast, antipredator strategies of L. schreiberi only depend on the physical environment and the relative location of the predator and the refuge. The elaboration of conspicuous sexual signals may have trade-offs with essential metabolic processes. We investigated the relationships among antioxidants, the immune system and multiple sexual signals of males (Chapter II-IV). We found that a carotenoid dietary supplementation is able to increase both carotenoid-based and structural visual signals. However, carotenoid supplementation does not increase the PHA-induced immune response, and, furthermore, an LPS-induced immune challenge neither has effects on carotenoid-based coloration. So, it seems that carotenoids do not boost immune system in this species. However, LPS and PHA-induced immune response do not cover the whole immune system. Nevertheless, carotenoids may have relation with health by increasing body condition (as fat stores). Carotenoid supplementation increases body condition, while a negative effect on body condition decreases carotenoid chroma in chest and back, suggesting that carotenoid signals indicate different types of quality than other types of visual signals. Surprisingly, immune challenged males increase intensity of some visual signal components, especially when combined with supplementary dietary vitamin E, which can boost sexual signals, increasing vitamin E content of femoral secretion and acting as an effective antioxidant to substitute glutathione in melanin-based signals. Males with an immune activation suffer a relevant challenge for the body and might be trying to maximize future fitness by increasing current signal intensity in a situation where long term expectative of survival and future reproduction are low. In contrast, the price of the higher throat color intensity seems to be the carotenoid decreasing in other body parts that, nevertheless, seems to be less important as sexual signals in these lizards. Furthermore, we found that vitamin E supplementation enhances PHA-induced immune response, shows a consistent increase in vitamin E content in femoral secretion in all treatments. However, we found conspicuous differences when comparing vitamin E supplementation effects on visual signals in two different experiments on the same population made in different years. Differences might be caused by different weather conditions with different challenges of males when developing sexual signals, which might be, however, the base of flexible female choice. Therefore, multimodal signals of L. schreiberi can be part of a special back-up signal system. Vitamin E content of femoral secretion may be a stable signal about the antioxidant status, while simultaneously health status might be related to one or more environmentally influenced visual signals. Which signal indicates male quality would depend on which visual trait is more reliable showing quality under each given environmental conditions. This alteration in male sexual signals would suppose the existence of flexible female mate choice that can also be the base of evolution and maintenance of multiple signals of L. schreiberi...
|