Amphidromy and Migrations of Freshwater Shrimps. I. Costs, Benefits, Evolutionary Origins, and an Unusual Case of Amphidromy

Many freshwater shrimps (Decapoda, Caridea) have amphidromous life histories, with extended planktonic larval development in the sea. Larvae either are hatched upstream to drift down to the sea or are carried and released there by females. After development, postlarvae (juveniles) must migrate back up to their adult freshwater habitat. An amphidromous life cycle thus involves long distance migrations between marine and fresh waters. Other freshwater shrimps have abbreviated (or direct) larval development (ALD) with a completely freshwater life cycle and without such migrations. The question of which life history pattern (amphidromy versus ALD) is ancestral in freshwater shrimps is discussed in terms of costs, benefits, and phylogeny. Competing hypotheses are presented to explain the unusual distribution of Macrobrachium ohione, an amphidromous shrimp with recently abundant populations located very far (>1500 km) from the sea.