Dominance Cues Leading to Sex Change in Blue-Banded Gobies (Lythrypnus dalli)

by Daniel Hohler on Apr.15, 2010, under Writing

This is research authored by me conducted in 2007.

By Daniel Hohler
May 4, 2007

ABSTRACT:
Blue-banded gobies (Lythrypnus dalli) are small hermaphroditic fish found in a large range in the pacific. L. dalli exhibits intermediate hermaphroditism because it displays large sexual dimorphism and usually only changes sex once during a lifetime, as well as maintaining both male and female gonadal tissue at the same time. This study looked at cues that lead to establishing dominance in females. Dominance is important because sex change in L. dalli is based on the social hierarchy. In the wild if a male leaves the social group a female ascends to the top of the hierarchy and changes sex. The cues that were looked at in this study were visual cue and chemical cues. 34 gobies were collected and 32 females and 2 males were used in this study. Morphological traits of papillae ratio, length, dorsal fin length, and weight were recorded and used as the starting point. Two tanks were set up for each treatment each treatment tank containing 2 females. In the visual treatment the two tanks were placed next to each other so the fish could respond to visual stimuli. In the chemical treatment the tanks were placed out of visual sight but the water flow was connected so the fish can respond to any chemical cues in the water. Two controls were used as well. One control without a male and four females in the same tank to test sex change without restriction, and one with a male and four females to test for changes in morphology without sex change occurring. Each treatment was run for 14 days to see if females could establish and maintain dominance using just visual or chemical cues. Behaviors of displacement, solicitation, bites, and % time in nesting tube were recorded during the 14 day period to see if the fish displayed dominant behaviors. At the end of 14 days the morphological traits were found again to determine if sex change occurred. Sex change occurred in all the treatments and control without males. From the fact that only one female changed sex in each visual treatment it can be concluded that females can establish and maintain dominance through only visual cues. An increase in papillae ratio, dorsal fin, and weight were found for sex changed fish. The increase in papillae ratio and dorsal fin length were found to be statistically significant with p-values less than 0.05. The behavioral observations were then looked at for the sex changed individuals and compared to the non-sex changed individuals. It was found that the sex changed individual showed a greater amount of displacements than a non-sex changed individual in the visual treatment. It was also found that sex changed individuals in the visual treatment spent a greater amount of time in the nesting tube. So females were able to establish and maintain dominance through visual cues only. The results of the chemical cue were inconclusive as in one treatment only one female changed sex and in the other treatment one female in each tank changed sex. The result that L. dalli can establish dominance and change sex through only visual cues shows that the mechanisms the social hierarchy are more complex than originally thought, and has implications in the complex sexual selection model in hermaphrodites.