Experimentally testing the function of anal fins in the bluefin killifish, <em>Lucania goodei</em>

In this study, we investigated the effects of functional anal fins on male fitness components in bluefin killifish, Lucania goodei. To manipulate anal fin integrity, we placed a small cut in the anal fin perpendicular to the base and half the length between the edge and fin base in males. This altered the male anal fin from a continuous sheet of tissue to a partially torn tissue with two flopping pieces. We performed a sham manipulation on males of similar size and compared the two (cut and uncut males) in two experiments. In the first experiment, males were paired every other day for a month with a female. We measured female preference as the number of eggs laid with cut vs. uncut males. We also measured the proportion of eggs that survived to 4 days post-spawning and used this as our measure of fertilization success. We found that cut males had lower fertilization success than males with uncut females. Females also tended to lay more eggs with uncut males in comparison to cut males. In the second experiment, the fish were combined in a large aquarium, and behavioral observations were recorded. We recorded the number of times each male courted the female, followed the female, attacked the female, attacked the rival male, chased the rival male, and flared his fins. Uncut males were more likely to court and follow the female. They also tended to have higher numbers of attacks and chases of the competing males and more fin flares.