Anger, K. Anger: Life-history adaptations of decapod crustaceans to non-marine conditions

The evolutionary transition from the sea to freshwater or terrestrial environments requires special life-history adaptations, which are exemplified with grapsid crabs from the island of Jamaica and palaemonid shrimps from the Amazon region. As a phylogenetic convergence, limnic and terrestrial species show a reduced planktonic larval phase, large egg size, low fecundity, and larval tolerance of low osmotic pressure. Similar adaptations have been observed in transitional (brackish and semiterrestrial) coastal habitats which are characterized by short duration, great variability in physico-chemical conditions, and unpredictable food production. Crabs that reproduce in temporal supratidal shore or mangrove pools show an ontogenetically early appearance of osmoregulatory functions, allowing for larval tolerance of variable salinities. Low or unreliable plankton production selects for an enhanced energy storage in the eggs, decreasing the nutritional vulnerability during larval development. Intraspecific variability in the endotrophic potential (facultative lecithotrophy) of the early larval stages, as well as cannibalism and benthic behaviour in late stages suggest a bet-hedging strategy. It allows resource exploitation and maximum larval growth when food is temporarily available, but also some survival when food is absent. Flexibility is found also in the reproduction of freshwater shrimps: populations living in eutrophic lakes and rivers or in leaf litter of oligotrophic streams produce eggs throughout the year, while those in seasonally inundated forests reproduce only during the period of increasing water, maximizing the dispersal and access of larvae to new food sources. Bet-hedging strategies in temporary habitats may play a significant role in the evolutionary transition from the sea to non-marine environments.