"Freshwaterization" revisited - Abbreviated and lecithotrophic modes of larval development in freshwater-invading decapods


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Ute.Alexander [ at ] awi.de

Abstract

In a review of adaptive patterns in the life-histories of freshwater-invading shrimp (Macrobrachium spp.), Jalihal, Sankolli and Shenoy coined in 1993 the term “freshwaterization”. This concept denotes a gradual evolutionary process, including an abbreviation of the larval phase, enhanced endotrophic potential of the larval stages, increasing tolerance of low salt concentrations, and a trend towards brood protection. All these patterns have extensively been documented in the literature on freshwater-invading clades such as palaemonid and atyid shrimp. However, the hypothesis of gradual “freshwaterization” does not explain, (1) why intermediate stages between extended and abbreviated larval developments (ELD, ALD) are practically absent, suggesting abrupt rather than gradual transitions; (2) why ELD does occur also in hololimnetic shrimp. Moreover, ALD and lecithotrophy occur not only in freshwater but frequently also in the sea, especially at high latitudes, where planktonic food limitation or extreme habitat specialization (e.g. commensalism) rather than low osmotic pressure select for those traits. Tentative selective forces favouring either the persistance of ELD and planktotrophy, or a shift to ALD and lecithotrophy, are discussed in relation to freshwater invasions. For the evolution of hololimnetic (i.e., excluding amphidromous) life-cycles, I suggest that an expression of osmoregulatory capabilities early in ontogeny is compulsory, while ALD, larval lecithotrophy, and maternal brood care are not necessarily required. In highly productive lentic waters such as seasonal flood plains (e.g. Amazon, Pantanal), ELD should even be advantageous for dispersal and connectivity of fully limnic inland populations. ALD and lecithotrophy may have evolved as adaptations to oligotrophic or nutritionally unpredictable environments such as fast-flowing lotic waters, groundwater wells, blackwater, clearwater, and troglobitic habitats.



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Conference (Keynote)
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Not peer-reviewed
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Published
Event Details
International Crustacean Congress, Summer Meeting The Crustacean Society, 07 Jul 2013 - 11 Jul 2013, University of Costa Rica, San José, CR.
Eprint ID
34582
Cite as
Anger, K. (2013): "Freshwaterization" revisited - Abbreviated and lecithotrophic modes of larval development in freshwater-invading decapods , International Crustacean Congress, Summer Meeting The Crustacean Society, University of Costa Rica, San José, CR, 7 July 2013 - 11 July 2013 .


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