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Ecol Evol. 2017 Jun 7;7(14):5258-5268. doi: 10.1002/ece3.3133. eCollection 2017 Jul.

Transcriptomic differentiation underlying marine-to-freshwater transitions in the South American silversides Odontesthes argentinensis and O. bonariensis (Atheriniformes).

Author information

1
Department of Biological Sciences The George Washington University Washington DC USA.
2
Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomús (CONICET-UNSAM) Chascomús Argentina.
3
Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) Buenos Aires Argentina.
4
Computational Biology Institute The George Washington University Washington DC USA.
5
Institute for Biomedical Sciences The George Washington University Washington DC USA.
6
Grupo de Biotaxonomía Morfológica y molecular de peces IIMyC-CONICET Universidad Nacional de Mar del PlataMar del Plata Argentina.

Abstract

Salinity gradients are critical habitat determinants for freshwater organisms. Silverside fishes in the genus Odontesthes have recently and repeatedly transitioned from marine to freshwater habitats, overcoming a strong ecological barrier. Genomic and transcriptomic changes involved in this kind of transition are only known for a few model species. We present new data and analyses of gene expression and microbiome composition in the gills of two closely related silverside species, marine O. argentinensis and freshwater O. bonariensis and find more than three thousand transcripts differentially expressed, with osmoregulatory/ion transport genes and immune genes showing very different expression patterns across species. Interspecific differences also involve more than one thousand transcripts with nonsynonymous SNPs in the coding sequences, most of which were not differentially expressed. In addition to characterizing gill transcriptomes from wild-caught marine and freshwater fishes, we test experimentally the response to salinity increases by O. bonariensis collected from freshwater habitats. Patterns of expression in gill transcriptomes of O. bonariensis exposed to high salinity do not resemble O. argentinensis mRNA expression, suggesting lack of plasticity for adaptation to marine conditions in this species. The diversity of functions associated with both the differentially expressed set of transcripts and those with sequence divergence plus marked microbiome differences suggest that multiple abiotic and biotic factors in marine and freshwater habitats are driving transcriptomic differences between these species.

KEYWORDS:

ecological genetics; fish; speciation; transcriptomics

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