title: Isolation Driven Divergence in Osmoregulation in Galaxias maculatus (Jenyns, 1848) (Actinopterygii: Osmeriformes).
abstract: Marine species have colonized extreme environments during evolution such as freshwater habitats. The amphidromous teleost fish, Galaxias maculatus is found mainly migrating between estuaries and rivers, but some landlocked populations have been described in lakes formed during the last deglaciation process in the Andes. In the present study we use mtDNA sequences to reconstruct the historical scenario of colonization of such a lake and evaluated the osmoregulatory shift associated to changes in habitat and life cycle between amphidromous and landlocked populations.
  
  
  
  Standard diversity indices including the average number of nucleotide differences (Π) and the haplotype diversity index (H) indicated that both populations were, as expected, genetically distinctive, being the landlocked population less diverse than the diadromous one. Similarly, pairwise GST and NST comparison detected statistically significant differences between both populations, while genealogy of haplotypes evidenced a recent founder effect from the diadromous stock, followed by an expansion process in the lake. To test for physiological differences, individuals of both populations were challenged with a range of salinities from 0 to 30 ppt for 8 days following a period of progressive acclimation. The results showed that the landlocked population had a surprisingly wider tolerance to salinity, as landlocked fish survival was 100% from 0 to 20 ppt, whereas diadromous fish survival was 100% only from 10 to 15 ppt. The activity of ATPase enzymes, including Na+/K+-ATPase (NKA), and H+-ATPase (HA) was measured in gills and intestine. Activity differences were detected between the populations at the lowest salinities, including differences in ATPases other than NKA and HA. Population differences in mortality are not reflected in enzyme activity differences, suggesting divergence in other processes.
  
  
  
  These results clearly demonstrate the striking adaptive changes of G. maculatus osmoregulatory system, especially at hyposmotic environments, associated to a drastic shift in habitat and life cycle at a scale of a few thousand years.
authors.affiliation: Centre of Marine Sciences (CCMar), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: Ignacio
authors.initials: I
authors.lastname: Ruiz-Jarabo
authors.affiliation: GAIA Antártica, Universidad de Magallanes, Avenida Bulnes 01855, Punta Arenas, XII Región de Magallanes y la Antártica Chilena, Chile.|Laboratorio de Ecología Molecular, Instituto Milenio de Ecología y Biodiversidad (IEB), Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras #3425, Ñuñoa, Santiago, Chile.
authors.forename: Claudio A
authors.identifier: 0000-0003-0807-8032
authors.initials: CA
authors.lastname: González-Wevar
authors.affiliation: Instituto de Ciencias Marinas y Limnológicas, Facultad de Ciencias, Universidad Austral de Chile, casilla 567, Valdivia, Chile.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Oyarzún
authors.affiliation: Centre of Marine Sciences (CCMar), Universidade do Algarve, Campus de Gambelas, 8005-139 Faro, Portugal.
authors.forename: Juan
authors.initials: J
authors.lastname: Fuentes
authors.affiliation: Laboratorio de Ecología Molecular, Instituto Milenio de Ecología y Biodiversidad (IEB), Departamento de Ciencias Ecológicas, Facultad de Ciencias, Universidad de Chile, Las Palmeras #3425, Ñuñoa, Santiago, Chile.
authors.forename: Elie
authors.initials: E
authors.lastname: Poulin
authors.affiliation: Instituto de Ciencias Marinas y Limnológicas, Facultad de Ciencias, Universidad Austral de Chile, casilla 567, Valdivia, Chile.
authors.forename: Carlos
authors.initials: C
authors.lastname: Bertrán
authors.affiliation: Instituto de Ciencias Marinas y Limnológicas, Facultad de Ciencias, Universidad Austral de Chile, casilla 567, Valdivia, Chile.|Centro Fondap de Investigación de Altas Latitudes (IDEAL), Universidad Austral de Chile, casilla 567, Valdivia, Chile.
authors.forename: Luis
authors.initials: L
authors.lastname: Vargas-Chacoff
mesh_terms: D000064:Acclimatization / Q000187:drug effects / Q000502:physiology*; D025041:Animal Migration / Q000502:physiology; D000818:Animals; D001499:Bayes Theorem; D044822:Biodiversity; D005075:Biological Evolution; D006239:Haplotypes; D007413:Intestinal Mucosa / Q000378:metabolism; D007422:Intestines / Q000187:drug effects; D018942:Macrolides / Q000494:pharmacology; D036441:Osmeriformes / Q000502:physiology*; D064587:Osmoregulation / Q000187:drug effects / Q000502:physiology*; D010042:Ouabain / Q000494:pharmacology; D011157:Population Dynamics; D006180:Proton-Translocating ATPases / Q000378:metabolism; D000254:Sodium-Potassium-Exchanging ATPase / Q000378:metabolism; D016019:Survival Analysis
chemical_list: D018942:Macrolides; D010042:Ouabain; C040929:bafilomycin A1; D006180:Proton-Translocating ATPases; D000254:Sodium-Potassium-Exchanging ATPase