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Diadromy as a conditional strategy: patterns and drivers of eel movements in continental habitats

Abstract : Diadromy, the change of habitat salinity, is found in many fish species and is often facultative, i.e., not all individuals of a population are diadromous. In some Anguilla spp., Sr:Ca ratios on transects from core to periphery of otoliths have revealed that, within a river basin, some eels enter freshwaters as glass eels and remain there, some remain in coastal or estuarine waters, some move between the habitats after some years, and some move between habitats annually or irregularly. These various patterns of diadromy reflect two fundamentally different behaviors: migration of individuals arriving from the sea and settling at different levels of the watershed, and foraging that is initiated after settlement and may lead to habitat relocations. Migration is an internally-initiated process while foraging is environmentally-initiated. Diadromy is depicted as a conditional strategy, i.e., a threshold reaction norm responding to internal cues during migration and to environmental cues during foraging. During the migratory phase, internal cues for being a migrant vs. a settler are provided by individual energetic and ontogenetic status while, during foraging, environmental cues for dispersal are provided by agonistic interactions and resources availability. During both phases, the switchpoint for alternative movement decisions is underlaid by significant genetic variation so that the conditional strategy may evolve to an evolutionary stable state. We provide a speculative endocrine mechanism for proximate mediation of alternative migratory tactics, which is based on an antagonism between thyroid hormones and a growth hormone-cortisol group. Changes in selective pressures during the last decades (decreased densities in saltwater habitats and increased selection against upstream migrants) may have displaced the stable state of the conditional strategy and thus induced an adaptive drop in the proportion of diadromous individuals among populations.
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Contributor : Eric Edeline Connect in order to contact the contributor
Submitted on : Friday, November 13, 2009 - 11:14:15 PM
Last modification on : Friday, August 5, 2022 - 2:38:10 PM


  • HAL Id : bioemco-00432165, version 1
  • PRODINRA : 248790


James D. Mccleave, Eric Edeline. Diadromy as a conditional strategy: patterns and drivers of eel movements in continental habitats. Challenges for diadromous fishes in a dynamic global environment, American Fisheries Society, pp.97-119, 2009, American Fisheries Society symposium. ⟨bioemco-00432165⟩



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