Euryhalinity in An Evolutionary Context

Physiological mechanisms used by fish to cope with salinity stress

“…Although I am not aware of any direct evidence for this conjecture it is indirectly supported by osmotic permeability and water balance studies on teleosts acclimated to hyperhalinity (Motais et al, 1966(Motais et al, , 1969Gonzalez et al, 2005;Laverty and Skadhauge, 2012). Interestingly, many species of euryhaline fish have upper salinity tolerance thresholds of about 2× seawater (Schultz and McCormick, 2013), which suggests that only the most euryhaline species that tolerate salinities well above 2× seawater have evolved the capacity for qualitatively changing their osmoregulatory strategy when encountering extremely hyperhaline conditions. The highest upper salinity tolerance limits of euryhaline fishes have been recorded at 114 g kg −1 for Fundulus heteroclitus (Griffith, 1974), 120 g kg −1 for Oreochromis mossambicus (Stickney, 1986), 130 g kg −1 for Sarotherodon melanotheron (Panfili et al, 2004;Ouattara et al, 2009) and 110 g kg −1 for Craterocephalus eyresii (Glover and Sim, 1978).…”

“…The latter scenario is overwhelmingly supported by the pertinent literature. The physiological phenotype (trait) of euryhalinity is distributed in a mosaic pattern across different orders of fish (Nelson, 2006;Schultz and McCormick, 2013). This pattern could be a consequence of either selective loss or convergent evolution in multiple teleost orders, depending on whether euryhalinity represents an ancestral or derived condition.…”

“…This notion is supported by trait reconstructions from extant and fossil taxa (Vega and Wiens, 2012). Regardless of their habitat of origin, most fish orders include euryhaline species (Nelson, 2006;Schultz and McCormick, 2013). Moreover, the mosaic-like pattern of euryhalinity at the taxonomic level of orders is also apparent at lower taxonomic levels.…”

“…The highest upper salinity tolerance limits of euryhaline fishes have been recorded at 114 g kg −1 for Fundulus heteroclitus (Griffith, 1974), 120 g kg −1 for Oreochromis mossambicus (Stickney, 1986), 130 g kg −1 for Sarotherodon melanotheron (Panfili et al, 2004;Ouattara et al, 2009) and 110 g kg −1 for Craterocephalus eyresii (Glover and Sim, 1978). Additional salinity tolerance ranges for euryhaline fishes are provided in two excellent recent reviews (Brauner et al, 2012;Schultz and McCormick, 2013). The apparent existence of a finite upper salinity tolerance at approximately 120 g kg −1 suggests that an insurmountable physiological barrier prevents fish from conquering habitats of higher salinity, e.g.…”

Reciprocal osmotic challenges reveal mechanisms of divergence in phenotypic plasticity in the killifish Fundulus heteroclitus

“…It is thought that species from habitats characterized by variable salinities, such as estuaries, are those most able to invade novel osmotic niches (Lee and Bell, 1999). For fishes, this suggests that euryhalinity may enable the exploitation of diverse osmotic niches (Bamber and Henderson, 1988;Schultz and McCormick, 2013). We seek to identify the physiological and genetic mechanisms underlying euryhalinity, a plastic phenotype that enables exploitation of novel osmotic niches and serves to facilitate radiations across osmotic boundaries.…”