Trade-offs in osmoregulation and parallel shifts in molecular function follow ecological transitions to freshwater in the Alewife

Abstract

Adaptation to freshwater may be expected to reduce performance in seawater because these environments represent opposing selective regimes. We tested for such a trade-off in populations of the Alewife (Alosa pseudoharengus). Alewives are ancestrally anadromous, and multiple populations have been independently restricted to freshwater (landlocked). We conducted salinity challenge experiments, whereby juvenile Alewives from one anadromous and multiple landlocked populations were exposed to freshwater and seawater on acute and acclimation timescales. In response to acute salinity challenge trials, independently derived landlocked populations varied in the degree to which seawater tolerance has been lost. In laboratory-acclimation experiments, landlocked Alewives exhibited improved freshwater tolerance, which was correlated with reductions in seawater tolerance and hypo-osmotic balance, suggesting that trade-offs in osmoregulation may be associated with local adaptation to freshwater. We detected differentiation between life-history forms in the expression of an ion-uptake gene (NHE3), and in gill Na(+) /K(+) -ATPase activity. Trade-offs in osmoregulation, therefore, may be mediated by differentiation in ion-uptake and salt-secreting pathways.

Understanding the molecular basis of adaptation to freshwater environments by prawns in the genus Macrobrachium

“…PCR conditions were maintained at: 95˚C for 2 minutes for polymerase activation and 40 cycles (denaturation at 95˚C for 5 seconds, annealing at 58-62˚C for 20 seconds and an extension step at 72˚C for 20 seconds). Relative gene expression values were then obtained using a delta-delta method following standard protocols (Pfaffli, 2001;Velotta et al, 2015). Relative gene expression values were analyzed in SPSS (version 22) at 5% level of significance.…”

“…To date however, little work has been directed at identifying and characterizing genes and pathways that facilitated crustacean adaptation to freshwater environments. A number of studies of fish have concluded that changes to expression of osmoregulatory genes have played the principal roles in driving this process (DeFaveri et al, 2011;DeFaveri and Merila, 2014;Brennan et al, 2015;Velotta et al, 2015;Velotta et al, 2017). Crustaceans unlike most vertebrates often possess complex life cycles that involve many developmental stages in different habitats.…”

“…Multicellular organisms have evolved an array of sophisticated mechanisms to deal efficiently with different environmental stressors including: sensing stress and signal transduction; activating signaling pathways; and modifying expression of underlying genes that allow individuals to control most aspects of physiology (Nadal et al, 2011;Stern, 2013;Brennan et al, 2015). So, multicellular organisms are often able to minimize any potential negative physiological changes by maintaining their internal homeostasis and by buffering extracellular changes efficiently via regulation of gene expression (Velotta et al, 2015).…”

“…In a novel environment with different salinity level, efficient adaptation via osmoregulation depends on a combination of plastic morphological, physiological and genomic/genetic responses (Havird et al, 2014;Brennan et al, 2015;Velotta et al, 2015).…”

“…In parallel, changes may occur in many other organismal attributes including food habits, energy budgets, stress tolerance, and metabolic and behavioral processes directed at coping with newly invaded environments (Velotta et al, 2015).…”