Unknown,Transcriptomics,Genomics,Proteomics

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Fundulus majalis-heteroclitus osmotic response

ABSTRACT: The goals of these studies are to explore the mechanisms that enable extreme physiological plasticity and that may account for evolutionary divergence of adaptive osmotic physiologies among taxa that occupy different osmotic niches. In a common-garden environment, we track physiological and genome expression responses to hypo-osmotic (freshwater) challenge during a time-course of acclimation, and contrast these responses within and between species. We seek to identify mechanisms that facilitate osmotic acclimation that are evolutionarily conserved between basal and derived physiologies, and identify mechanisms that are uniquely derived to enable the extreme osmotic plasticity exhibited by F. heteroclitus. Importantly, previous studies using a comparable experimental design have identified physiological changes and genome expression responses that are adaptive for populations of F. heteroclitus that live in fresh water. As such, this enables us to test whether mechanisms of adaptive micro-evolutionary divergence across osmotic gradients within F. heteroclitus are shared with the mechanisms that account for patterns of macro-evolutionary divergence between F. heteroclitus and F. majalis that we identify in this study. That is, are the targets of micro-evolutionary fine-tuning the same or different as the targets of macro-evolutionary divergence across osmotic boundaries? Population comparisons include between populations from Chesapeake Bay (CB), coastal Virginia (VA), and coastal Georgia (GA).

ORGANISM(S): Fundulus majalis

SUBMITTER: Andrew Whitehead

PROVIDER: E-MTAB-1551 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:Despite the progress achieved in elucidating the ecological mechanisms of adaptive radiation, there has been little focus on documenting the extent of adaptive differentiation in physiological functions during this process. Moreover, a thorough understanding of the genomic basis underlying phenotypic adaptive divergence is still in its infancy. One important evolutionary process for which causal genetic mechanisms are largely unknown pertains to life-history trade-offs. We analysed patterns of gene transcription in liver tissue of sympatric dwarf and normal whitefish from two natural lakes, as well as from populations reared in controlled environments, using a 16 006-gene cDNA microarray in order to: (i) document the extent of physiological adaptive divergence between sympatric dwarf and normal species pairs, and (ii) explore the molecular mechanisms of differential life history trade-offs between growth and survival potentially involved in their adaptive divergence. In the two natural lakes, 6.45% of significantly transcribed genes showed regulation either in parallel fashion (2.39%) or in different directions (4.06%). Among genes showing parallelism in regulation patterns, we observed a higher proportion of over-expressed genes in dwarf relative to normal whitefish (70.6%). Patterns observed in controlled conditions were also generally congruent with those observed in natural populations. Dwarf whitefish consistently showed significant over-expression of genes potentially associated with survival through enhanced activity (energy metabolism, iron homeostasis, lipid metabolism, detoxification), whereas more genes associated with growth (protein synthesis, cell cycle, cell growth) were generally down-regulated in dwarf relative to normal whitefish. Overall, parallelism in patterns of gene transcription, as well as patterns of interindividual variation across controlled and natural environments, provide strong indirect evidence for the role of selection in the evolution of differential regulation of genes involving a vast array of potentially adaptive physiological processes between dwarf and normal whitefish. Our results also provide a first mechanistic, genomic basis for the observed trade-off in life-history traits distinguishing dwarf and normal whitefish species pairs, wherein enhanced survival via more active swimming, necessary for increased foraging and predator avoidance, engages energetic costs that translate into slower growth rate and reduced fecundity in dwarf relative to normal whitefish.

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Fundulus majalis-heteroclitus osmotic response

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