Lamprey adults may be parasitic or non-parasitic, but the genetic basis of life history type is unknown. Although external differences between types are not apparent until metamorphosis, previous studies have suggested histological differences during ovarian differentiation. This study examined potential differences between parasitic chestnut lamprey Ichthyomyzon castaneus and non-parasitic northern brook lamprey I. fossor before, during, and after ovarian differentiation, using histological examination of the gonad, quantitative reverse-transcriptase PCR, and RNA sequencing. There were no observable differences in the timing or nature of ovarian differentiation. However, there was evidence of differential expression of individual genes associated with growth, apoptosis, and fecundity and of sets of genes associated with energy and lipid metabolism. The sequence resources developed in this project will be useful for future examination of the genetic basis of lamprey life history type and of the genes controlling sex differentiation in these ancient vertebrates.

Lamprey adults may be parasitic or non-parasitic, but the genetic basis of life history type is unknown. Although external differences between types are not apparent until metamorphosis, previous studies have suggested histological differences during ovarian differentiation. This study examined potential differences between parasitic chestnut lamprey Ichthyomyzon castaneus and non-parasitic northern brook lamprey I. fossor before, during, and after ovarian differentiation, using histological examination of the gonad, quantitative reverse-transcriptase PCR, and RNA sequencing. There were no observable differences in the timing or nature of ovarian differentiation. However, there was evidence of differential expression of individual genes associated with growth, apoptosis, and fecundity and of sets of genes associated with energy and lipid metabolism. The sequence resources developed in this project will be useful for future examination of the genetic basis of lamprey life history type and of the genes controlling sex differentiation in these ancient vertebrates.