How did the tail of the swordtail fish evolveSolutionThe swo

How did the tail of the swordtail fish evolve?

Solution

The swordtail fish (Xiphophorous hellerii) has distinguishing features in male fishes and female fishes. The male fishes have a sword-like tail and an organ called gonopodium. This tail is an extension of the caudal fin and is ornamental. The female fishes do not have the characteristic tail and lack the gonopodium.

The evolution of tail in swordtail fishes is guided by sexual selection and not natural selection. It has been hypothesized that ancestrally the female fishes preferred to mate with swordtail bearing fishes rather that the swordless counterparts. Female preference drove the evolution of the tail in males and the tail-less trait eventually disappeared.