The colorful history of fairy wrasses

Written By Danielle Moloney 

Introduction

A recent study from researchers at the University of Sydney provides exciting new insight into the evolutionary development of fairy wrasses. Wrasses are a family of marine fish which are well known for their brightly colored scales. Fairy wrasses are a subset of this group, consisting of 61 different species and accounting for 10% of all wrasses.  Despite the abundance of these colorful fish living around coral reefs, relatively little is known about the history of their evolution- until now! 

What’s so special about fairy wrasses?

  • Fairy wrasses were discovered in the 1800s but scientific research regarding their evolution has been more popular in recent decades, with a majority of scientific publications about the species published recently. 
  • They are small fish that grow only up to 15cm maximum.
  • This species usually lives in large groups near and around coral reefs, and usually between 10 and 250 meters depth. 
  • Fairy wrasses are sexual hermaphrodites, which allows females to change into functional males based on environmental conditions such as the distribution of males and females in the population that an individual lives in. This is especially true for wrasses living in aquariums, where the population is closed, and doesn’t mix with other outside individuals. Most often, females will transition to male as they get older in aquariums. 
  • As part of the mating courtship rituals that fairy wrasses partake in, males are larger, more colorful, and have ornamental fins. They use their bright colors along with mating “dances” to attract the attention of female fairy wrasses. 
  • Fairy wrasses are popular fish for people who keep home aquariums, as they are reef safe and generally get along in groups. 

Findings

Yi-Kai Tea, the lead author of the new paper, is an ichthyologist and PhD candidate at the University of Sydney. Ichthyologists are marine biologists who study bony, cartilaginous, and jawless fishes. Tea studies the evolution of fairy wrasses, specifically how and when they diverged from other wrasses to form their own distinct characteristics such as their colorful scales. His major finding is that fairy wrasses diverged rapidly over a short period of time, within the last two to five million years. He found that this divergence was driven by sea levels rising and falling during the last ice age, in a period of time known as the Pliocene/Pleistocene epoch. The conditions of the oceans during this time period ultimately led to fairy wrasses as we know them today: brightly colored and charismatic. 

According to Tea, “They developed distinct colours and forms in a sort of evolutionary arms race, putting on dazzling displays in an effort to court females and chase off rival males. Also, sea level changes caused groups to become isolated, and therefore evolve separately. The repeated rise and fall of sea levels acted like a ‘species pump’, propelling fish into the Indian Ocean and even as far as the Red Sea. Most of this movement, however, occurred in the Pacific Ocean, in particular, around the Indo-Australian Archipelago.”

A figure from Tea et. al showing different species of fairy wrasses. 
A panel from Tea et. al 2021 showing the most likely phylogenetic tree of fairy wrasse evolution. Phylogenetic trees are used by biologists to indicate relationships between species and how they have branched off from a common ancestor over time.

Conclusions 

This study’s new findings about how fairy wrasses have evolved over time tells an interesting story of how fairy wrasses have come to be. The way that sea levels impacted fairy wrasse evolution over a key period of time may provide insight into the evolutionary development of other species, both marine and terrestrial. Further analysis of the timing and characteristics that define the fairy wrasse evolutionary family tree will add to the value of this important research, and could even indicate how marine species may diverge in the future based on sea level rise. 

Read Tea’s publication here for more information about fairy wrasses and how they have evolved over time. 

See a male fairy wrasse in action during a courtship dance here

Please contact the author with any questions: dmoloney@fandm.edu.

Cover photo courtesy of Science News.

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