Metamorphosis of a sesarmid river crab, Armases roberti: stimulation by adult odours versus inhibition by salinity stress

Abstract

In an experimental laboratory study with the megalopa stage of Armases roberti, a freshwater-inhabiting species of crab from the Caribbean region, we evaluated the combined, potentially antagonistic effects of odours from conspecific adults and of stepwise salinity reductions (simulating upstream migration, reaching within 1 week conditions of 2‰ or freshwater). Neither of these treatments affected the rate of survival, but the duration of development to metamorphosis was significantly (by about 25%) shortened, when odours from conspecific adult crabs were present, regardless of the salinity conditions. Our results indicate that the metamorphosis-stimulating effect of chemical cues from an adult population of A. roberti is far stronger than the potentially retarding effect of increasing hypoosmotic stress. This suggests that the final phase of larval development, including the processes of settlement and metamorphosis, occurs in this species in freshwater habitats, where conspecific populations live.

Keywords:

• Crustaceans
• larval biology
• metamorphosis
• ontogenetic migrations
• salinity tolerance
• chemical cues
• recruitment

Acknowledgements

We thank U. Nettelmann and K. Boos for help in the experiments and Dr A. Malzahn who helped using the micrograph imaging software. G. T. acknowledges the Deutscher Akademischer Austausch Dienst, DAAD (Bonn, Germany), for funding this study as a part of her doctoral dissertation, and LG the Alexander-von-Humboldt Foundation (Bonn, Germany) for a postdoctoral research grant. The experiments comply with the current German animal and manipulation laws.