Field study suggests that sex determination in sea lamprey is directly influenced by larval growth rate

Abstract

Sex determination mechanisms in fishes lie along a genetic-environmental continuum and thereby offer opportunities to understand how physiology and environment interact to determine sex. Mechanisms and ecological consequences of sex determination in fishes are primarily garnered from teleosts, with little investigation into basal fishes. We tagged and released larval sea lamprey (Petromyzon marinus) into unproductive lake and productive stream environments. Sex ratios produced from these environments were quantified by recapturing tagged individuals as adults. Sex ratios from unproductive and productive environments were initially similar. However, sex ratios soon diverged, with unproductive environments becoming increasingly male-skewed and productive environments becoming less male-skewed with time. We hypothesize that slower growth in unproductive environments contributed to the sex ratio differences by directly influencing sex determination. To the best of our knowledge, this is the first study suggesting that growth rate in a fish species directly influences sex determination; other studies have suggested that the environmental variables to which sex determination is sensitive (e.g. density, temperature) act as cues for favourable or unfavourable growth conditions. Understanding mechanisms of sex determination in lampreys may provide unique insight into the underlying principles of sex determination in other vertebrates and provide innovative approaches for their management where valued and invasive.

Keywords: condition factor; growth; lamprey; sex determination; sex ratio; sex reversal.

Figure 1.

Predictions from the Bayesian hierarchical logistic model estimating per cent male of CWT adult sea lamprey according to where they were stocked (lentic versus stream) and the year after stocking in which metamorphosis occurred. The top panel shows population-average predictions whereas the lower panel shows predictions for individual locations. The horizontal line on each panel indicates per cent model of adult sea lamprey without CWT that were captured in the same traps from 2007 to 2014 as adults with tags.