skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Mechanisms of Na+ uptake from freshwater habitats in animals
Life in fresh water is osmotically and energetically challenging for living organisms, requiring increases in ion uptake from dilute environments. However, mechanisms of ion uptake from freshwater environments are still poorly understood and controversial, especially in arthropods, for which several hypothetical models have been proposed based on incomplete data. One compelling model involves the proton pump V-type H + ATPase (VHA), which energizes the apical membrane, enabling the uptake of Na + (and other cations) via an unknown Na + transporter (referred to as the “Wieczorek Exchanger” in insects). What evidence exists for this model of ion uptake and what is this mystery exchanger or channel that cooperates with VHA? We present results from studies that explore this question in crustaceans, insects, and teleost fish. We argue that the Na + /H + antiporter (NHA) is a likely candidate for the Wieczorek Exchanger in many crustaceans and insects; although, there is no evidence that this is the case for fish. NHA was discovered relatively recently in animals and its functions have not been well characterized. Teleost fish exhibit redundancy of Na + uptake pathways at the gill level, performed by different ion transporter paralogs in diverse cell types, apparently enabling tolerance of low environmental salinity and various pH levels. We argue that much more research is needed on overall mechanisms of ion uptake from freshwater habitats, especially on NHA and other potential Wieczorek Exchangers. Such insights gained would contribute greatly to our general understanding of ionic regulation in diverse species across habitats.  more » « less
Award ID(s):
2055356
PAR ID:
10461959
Author(s) / Creator(s):
; ;
Date Published:
Journal Name:
Frontiers in Physiology
Volume:
13
ISSN:
1664-042X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; (, Molecular Ecology)
    Abstract Saline migrants into freshwater habitats constitute among the most destructive invaders in aquatic ecosystems throughout the globe. However, the evolutionary and physiological mechanisms underlying such habitat transitions remain poorly understood. To explore the mechanisms of freshwater adaptation and distinguish between adaptive (evolutionary) and acclimatory (plastic) responses to salinity change, we examined genome‐wide patterns of gene expression between ancestral saline and derived freshwater populations of theEurytemora affinisspecies complex, reared under two different common‐garden conditions (0 versus 15 PSU). We found that evolutionary shifts in gene expression (between saline and freshwater inbred lines) showed far greater changes and were more widespread than acclimatory responses to salinity (0 versus 15 PSU). Most notably, 30–40 genes showing evolutionary shifts in gene expression across the salinity boundary were associated with ion transport function, withinorganic cation transmembrane transportforming the largest Gene Ontology category. Of particular interest was the sodium transporter, the Na+/H+antiporter (NHA) gene family, which was discovered in animals relatively recently. Thirty key ion regulatory genes, such as NHA paralogue #7, demonstrated concordant evolutionary and plastic shifts in gene expression, suggesting the evolution of ion transporter function and plasticity during rapid invasions into novel salinities. Moreover, freshwater invasions were associated with the evolution of reduced plasticity in the freshwater population, again for the same key ion transporters, consistent with the predicted evolution of canalization following adaptation to stressful conditions. Our results have important implications for understanding evolutionary and physiological mechanisms of range expansions by some of the most widespread invaders in aquatic habitats. 
    more » « less
  2. ; ; (, Journal of experimental biology)
    All freshwater organisms are challenged to control their internal balance of water and ions in strongly hypotonic environments. We compared the influence of external salinity on the oxygen consumption rates (M O2) of three species of freshwater insects, one snail and two crustaceans. Consistent with available literature, we found a clear decrease in M O2 with increasing salinity in the snail Elimia sp. and crustaceans Hyalella azteca and Gammarus pulex (r5=−0.90, P=0.03). However, we show here for the first time that metabolic rate was unchanged by salinity in the aquatic insects, whereas ion transport rates were positively correlated with higher salinities. In contrast, when we examined the ionic influx rates in the freshwater snail and crustaceans, we found that Ca uptake rates were highest under the most dilute conditions, while Na uptake rates increased with salinity. In G. pulex exposed to a serially diluted ion matrix, Ca uptake rates were positively associated with M O2 (r5=−0.93, P=0.02). This positive association between Ca uptake rate and M O2 was also observed when conductivity was held constant but Ca concentration was manipulated (1.7–17.3 mg Ca l−1) (r5=0.94, P=0.05). This finding potentially implicates the cost of calcium uptake as a driver of increased metabolic rate under dilute conditions in organisms with calcified exoskeletons and suggests major phyletic differences in osmoregulatory physiology. Freshwater insects may be energetically challenged by higher salinities, while lower salinities may be more challenging for other freshwater taxa. 
    more » « less
  3. ; ; ; ; ; ; ; ; (, iScience)
    While many freshwater invaders originate from saline habitats, the physiological mechanisms involved are poorly understood. We investigated the evolution of ion transporter Na+/K+-ATPase (NKA) protein expression between ancestral saline and freshwater invading populations of the copepod Eurytemora carolleae (Atlantic clade of the E. affinis complex). We compared in situ NKA expression between populations under common-garden conditions at three salinities in the maxillary glands. We found the evolution of reduced NKA expression in the freshwater population under freshwater conditions and reduced plasticity (canalization) across salinities, relative to the saline population. Our results support the hypothesis that maxillary glands are involved in ion reabsorption from excretory fluids at low-salinity conditions in the saline population. However, mechanisms of freshwater adaptation, such as increased ion uptake from the environment, might reduce the need for ion reabsorption in the freshwater population. These patterns of ion transporter expression contribute insights into the evolution of ionic regulation during habitat change. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, iScience)
    While many freshwater invaders originate from saline habitats, the physiological mechanisms involved are poorly understood. We investigated the evolution of ion transporter Na+/K+-ATPase (NKA) protein expression between ancestral saline and freshwater invading populations of the copepod Eurytemora carolleae (Atlantic clade of the E. affinis complex). We compared in situ NKA expression between populations under common-garden conditions at three salinities in the maxillary glands. We found the evolution of reduced NKA expression in the freshwater population under freshwater conditions and reduced plasticity (canalization) across salinities, relative to the saline population. Our results support the hypothesis that maxillary glands are involved in ion reabsorption from excretory fluids at low-salinity conditions in the saline population. However, mechanisms of freshwater adaptation, such as increased ion uptake from the environment, might reduce the need for ion reabsorption in the freshwater population. These patterns of ion transporter expression contribute insights into the evolution of ionic regulation during habitat change. 
    more » « less
  5. ; (, Aquatic toxicology)
    null (Ed.)
    Many freshwater ecosystems are becoming saltier and/or warmer, but our understanding of how these factors interact and affect the physiology and life history outcomes of most aquatic species remain unknown. We hypothesize that temperature modulates ion transport rates. Since ion transport is energetically expensive, increases in salinity and/or temperature may influence ion flux rates and ultimately, organismal performance. Radiotracer (22Na+, 35SO4−2, and 45Ca2+) experiments with lab-reared mayflies (N. triangulifer) and other field-collected insects showed that increasing temperature generally increased ion transport rates. For example, increasing temperature from 15 °C to 25 °C, increased 22Na+ uptake rates by two-fold (p < 0.0001) and 35SO4−2 uptake rates by four-fold (p < 0.0001) in the caddisfly, Hydropsyche sparna. Smaller changes in 22Na+ and 35SO4−2 uptake rates were observed in the mayflies, Isonychia sayi and Maccaffertium sp., suggesting species-specific differences in the thermal sensitivity of ion transport. Finally, we demonstrated that the toxicity of SO4 was influenced by temperature profoundly in a 96-h bioassay. Under the saltiest conditions (1500 mg L−1 SO4), mayfly survival was 78 % at 15 °C, but only 44 % at 25 °C (p < 0.0036). Conceivably, the energetic cost of osmoregulation in warmer, saltier environments may cause significant major ion toxicity in certain freshwater insects. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email