Abstract

In the Florida Keys, queen conch (Strombus gigas) occur in two spatially distinct regions: nearshore in habitats immediately adjacent to the shoreline and offshore in habitats along the reef tract. Our previous research has demonstrated that nearshore queen conch are not reproductively active, showing deficiencies in their gonadal condition compared to their offshore counterparts. Since, sexual development in gastropods is controlled by hormones secreted by the cerebral ganglia, we hypothesized that the reproductive deficiencies found in nearshore queen conch may involve the cerebral ganglia. We collected nearshore and offshore conch and made histological comparisons of their gonads and cerebral ganglia. Our results confirmed that nearshore conch exhibited delayed gonadal maturity and reduced gametogenic output compared to offshore animals. These gonadal deficiencies were significantly correlated with abnormal cerebral ganglia histology (e.g., reduced number of ganglia cells, hypertrophy). In addition, we observed that nearshore conch had significantly lighter shells. This finding is particularly consequential since shell formation in gastropods is also mediated by hormones secreted by the cerebral ganglia. Given these results, it is apparent that the unidentified causative factor(s) behind the developmental and morphological anomalies in nearshore queen conch is targeting the cerebral ganglia and the effects cascade through the neuroendocrine system to gonad development and shell formation.

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