Size matters—to livebearer fish, big fins are a big deal

Phys.org ^ | January 17, 2019 | University of California - Riverside

[ETL]

To female molly and Limia fish, nothing is hotter than a male with a large dorsal fin.

But these fins aren't just decorations to attract females. Males also use them to fight or intimidate rivals.

For scientists who study evolution, the fins present a chicken-and-egg dilemma. Which came first—ornamental fins for courtship displays, or fighting fins only later used in displays?

In a new paper, biologists from the University of California, Riverside, studied the evolution of 40 molly and Limia species, and concluded dorsal fin displays arose first for males to compete with other males, only later being used in courtship displays to females. These changes in fin function went hand in hand with enlargement of the male dorsal fin. The fins reached extreme sizes in a few species and appear to be associated with rapid evolution, especially in mollies.

When Charles Darwin proposed his theory of evolution, he noted that some features arise not from natural selection by outside pressures like predators and food sources, but from competition within a species to find mates and reproduce. He called this "sexual selection," and scientists have used it to explain why males from many species have elaborate ornamentation and are larger than females.

Simply put, the ornament can evolve either because females prefer to mate with ornamented males, or because the ornament helps males defeat rivals. The male peacock's tail, for example, probably evolved through female choice. Deer antlers, on the other hand, probably evolved to compete with other males.

[ETL]

[Dilbert San Diego]

It’s amusing, when describing mating rituals in the animal kingdom. I’m sure someone will then draw comparisons to humans.

[bgill]

The bigger the fin, the bigger the cheat.