Parental investment of male two-spotted goby, Gobiusculus flavescens (Fabricius)

The trade-off between parental care and feeding was studied in the male two -spotted goby (Gobiusculus flavescens F.). Two temperatures, 8.5 degreesC a nd 13.0 degreesC, were used, with five replicates at each temperature, in o rder to determine whether temperature influenced parental behaviour. In eac h replicate, two males acid four females were introduced to an aquarium, wh ere the males chose between two nests and courted the females. In each repl icate, one male spawned. After spawning, the males guarded the eggs until h atching. The guarding males' behaviour was recorded with a video camera twi ce a day (15 min each time), once before and once after they were fed. The male's condition (c-factor) was calculated at the start of the experiment a nd after egg hatching. The eggs were spawned in an artificial nest (half of a PVC tube), and attached to the nest in a single layer. The areas with eg gs (representing brood size) were marked after spawning and the fry counted after hatching (which was used to calculate area hatched). Numbers of prey eaten (plankton) and number of aggressive encounters between the guarding male and the other fishes were recorded. Time spent in the nest and time us ed on fertilisation, fanning and cleaning were estimated and related to egg age, brood size, hatching success, temperature and food availability (no f ood or fond). The results showed that feeding (expected to influence future reproduction) decreased and parental expenditure (current reproduction) increased, as th e eggs developed (became closer to independence). Parental expenditure was significantly higher at 13.0 degreesC than at 8.5 degreesC, presumably due to higher oxygen demands by the eggs, and a greater risk of egg-infections. The c-factor of the males guarding eggs decreased over time, in contrast t o the non-guarding males' c-factor. Guarding males' aggressiveness decrease d as the eggs got older, but increased just before hatching. A possible exp lanation for this could be the decreasing intrusion by the non-guarding mal e and females caused by high aggressive behaviour by the guarding male earl y in the brood cycle. The exploitation of the nest (percentage of total nes t area covered by eggs) seemed to determine the amount of parental expendit ure and loss of condition, while brood size (area of eggs) had no effect. ( C) 2001 Elsevier Science B.V. All rights reserved.