RISK-TAKING IN RELATION TO REPRODUCTIVE INVESTMENTS AND FUTURE REPRODUCTIVE OPPORTUNITIES - FIELD EXPERIMENTS ON NEST-GUARDING COMMON GOBIES, POMATOSCHISTUS-MICROPS

The common goby, Pomatoschistus microps, has parental care, with males building nests and guarding the fertilized eggs until hatching. We carried out field experiments to estimate the response of males to predation risk in relation to developmental stage of their brood and time of the season. Artificial nest substrates were placed in a shallow bay with soft substrate. After the nest had been built and eggs laid in it, a glass jar containing a potential predator (an eelpout, Zoarces viviparus) was placed 15 cm from the goby's nest. We subsequently chased the male goby away from the nest and measured his flight distance and time until return. This was repeated once a day in May, June, and August. Time away from the nest decreased in the course of one brood cycle, with a steeper slope in May compared to the other months, as a result of longer times away from the nest in the beginning of the experiment. Flight distance decreased slightly over one brood cycle and was longer in June than in May and August. In another experiment, a male P. microps was presented to the nest-guarding male, simulating a potential competitor for the nest. Again, we found a decrease in return time with advancement of the brood cycle, but the fish returned faster than when facing a predator, especially in the beginning of the brood cycle. No effect of habituation to the treatment was found, but there seemed to be a slight influence of development stage of the eggs. Thus, risk taking by nest-guarding male P. microps appears to be influenced by time already spent guarding one particular brood and the prospect for future reproductive opportunities.