An examination of the plasticity of gonad development in sea lampreys, Petromyzon marinus: Observations through gonadal biopsies

Observations of larvae with atypical gonads led to this study to determine the extent of the plasticity of gonad development in larval, metamorphosing, and juvenile sea lampreys. Larval and early metamorphosing, sea lampreys underwent microsurgery to remove a biopsy of gonadal tissue. These biopsies were examined quantitatively and were categorized as ovaries, presumptive testes, or as atypical gonads. After a period of approximately 8 to 10 months, the larvae and subsequent juveniles were killed and the gonads were re-examined, again quantitatively, for any changes in gonad development. There was no significant change in the number of larvae with typical ovaries as a direct result of sex reversals and oocyte atresia. None of the metamorphosing lampreys initially biopsied had atypical gonads and no sex reversals were observed in this group. Oocyte number in typical ovaries of the larvae and metamorphosing lampreys did not change over the course of the study; however germ cell number increased significantly in typical testes of both larvae and metamorphosing lampreys. The results of the study confirm that the lability of sex in larval sea lampreys is much greater than previously thought; however, it is clear that sex is defined and does not appear to change once the lampreys have entered the juvenile period.