Arrested Sexual Development in Queen Conch (Lobatus gigas) Linked to Abnormalities in the Cerebral Ganglia

In the Florida Keys, queen conchs (Lobatus gigas) occur in two spatially distinct regions: nearshore in habitats immediately adjacent to the shoreline and offshore in habitats along the reef tract south of the islands. Our previous research demonstrated that adult conchs nearshore are not reproductively active, showing deficiencies in their gonadal condition compared to their offshore counterparts. Because sexual development in gastropods is controlled by hormones secreted by the cerebral ganglia, we hypothesized that the reproductive deficiencies seen in nearshore queen conchs involved the cerebral ganglia. We collected nearshore and offshore adults and made histological comparisons of their gonads and cerebral ganglia. Our results confirmed that gonadal maturity was delayed and that gamete production was reduced in nearshore conchs compared to offshore animals. These gonadal deficiencies in nearshore conchs were associated with abnormal cerebral ganglion histology (i.e., significant hypertrophy of ganglion cells and significantly lower density of ganglion cells). In addition, the shells of nearshore conchs were significantly lighter, which is particularly consequential because shell formation in gastropods is also mediated by hormones secreted by the cerebral ganglia. Given these results, it is apparent that some yet unidentified factor(s) is interfering with hormone production in the cerebral ganglia, to the detriment of gonad development and shell formation.