Adaptation to Life in Fresh Water by Decapod Crustaceans: Evolutionary Challenges in the Early Life-History Stages
The Decapoda evolved in the Palaeozoic as a marine group and have since then shown limited radiation in limnic and terrestrial environments. About 80 % of the extant decapod species still live in the sea. The colonization of non-marine environments requir
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Adaptation to Life in Fresh Water by Decapod Crustaceans: Evolutionary Challenges in the Early Life-History Stages Klaus Anger
Abstract The Decapoda evolved in the Palaeozoic as a marine group and have since then shown limited radiation in limnic and terrestrial environments. About 80 % of the extant decapod species still live in the sea. The colonization of non-marine environments required physiological adaptations such as hyper-osmoregulate (for fresh water) and hypo-osmoregulate (for terrestrial and hypersaline habitats). Osmoregulatory abilities are strong in juvenile and adult freshwater decapods, but are typically absent in larval stages. Diadromous breeding migrations to estuaries or the sea are part of an adaptive strategy that allows adult life in non-marine habitats in combination with a conservation of the ancestral life-history pattern (extended planktonic larval development in salt water). Phylogenetically old groups of hololimnetic decapods (crayfish, aeglids, primary freshwater crabs) have completely eliminated the larval phase, showing direct development and brood care. Recent colonisers generally show intermediate patterns with an abbreviated and partially or fully lecithotrophic larval phase. Macroevolutionary patterns support possible colonization routes from the sea to fresh water and land. It is suggested that ecologically transitional habitats such as brackish mangrove swamps, salt marshes, seasonally inundated wetlands, and anchialine caves have been the principal entrance portals, rather than direct invasion through estuaries and rivers. Keywords Diadromy late Brood care
Abbreviated development Larval ecology osmoregu-
K. Anger (&) Eichkamp 25, 23714 Malente, Germany e-mail: [email protected] © Springer International Publishing AG 2016 T. Kawai and N. Cumberlidge (eds.), A Global Overview of the Conservation of Freshwater Decapod Crustaceans, DOI 10.1007/978-3-319-42527-6_5
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Introduction
The Decapoda represent the largest order of crustaceans, comprising almost 15,000 known extant species plus about 3000 fossil species (de Grave et al. 2009; Martin et al. 2009). According to the fossil record, decapods originated in the oceans in the Late Devonian about 360 mya, which was followed by a rapid radiation during the Mesozoic (Schram et al. 1978; Schram 2009). Model-based analyses of phylogenetic divergence times suggest that decapods made an even earlier appearance in the Silurian (>437 mya) (Porter et al. 2005; Bracken et al. 2009). Today almost 80 % of all extant decapod species are still living in their ancestral environment, the oceans, while less than 20 % have successfully conquered brackish and freshwater environments, and less than 2 % are terrestrial (de Grave et al. 2009; Vogt 2013). The relatively small percentage of non-marine decapod species indicates that the transition from marine to a limnic or terrestrial life style presents serious challenges. The most dramatic change in environmental conditions in fresh water is that the concentrations of
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