# PolyQ Length of the Clock Gene Is Correlated With Pelagic Larval Duration in the Damselfishes (Pomacentridae), but Within a Species Habitat Availability Counts

## TL;DR

A part of the 'clock' gene influences how long coral reef fish larvae stay in the open ocean, but habitat availability can override this genetic effect.

## Contribution

The study shows that PolyQ length in the clock gene correlates with pelagic larval duration across species, but not within a single species.

## Key findings

- PolyQ and Qrich repeat lengths in the clock gene correlate with pelagic larval duration across 20 damselfish species.
- Within the neon damselfish, PLD is reduced when habitat availability increases, not due to PolyQ length.
- Ecological factors like habitat availability can override genetic influences on larval dispersal timing.

## Abstract

Immediately after hatching, larvae of coral reef fish leave their natal reef environment and begin their pelagic larval phase probably to avoid high predation on the reef. The time they spend in the open ocean (pelagic larval duration, PLD), before settlement varies from species to species and depends partly on developmental processes that eventually require re‐settlement to a reef. The polyglutamine region (PolyQ) as part of the clock gene has been suggested as a possible candidate that could control developmental processes and potentially the time until settlement, which can be determined by counting the rings of the otoliths. We studied the potential relationship between the number of glutamine repeats in 20 species of pomacentrids and their PLDs. Most pomacentrids came from similar locations, so we avoided the impact of latitudinal clines on PLD. Within the clock gene, we found two main distinguishable, variable glutamine‐rich regions (PolyQ and Qrich). Considering phylogenetic relationships, PolyQ/Qrich repeat length and pelagic larval duration were significantly positively correlated. However, when analyzing this relationship in a single species, the neon damselfish (
Pomacentrus coelestis
), we did not find a significant correlation between PolyQ length variation and PLD. Instead, we found a significant reduction of PLD in years with increased habitat availability. Our results show that glutamine‐rich regions can influence the timing of settlement on a broader scale, but that ecological factors—such as habitat availability—can also have a significant impact.

The length of a part of the ‘clock’ gene explains the duration of dispersal in coral reef fishes. However, ecological factors such as the availability of habitats can override this effect.