Fig. 1
When external salinity increases, euryhaline fish try to maintain constant internal osmotic pressures (homeostasis) by altering their osmoregulatory sub-PRN to intake more water and excrete excess ions. Above is a schematic highlighting some (not all) of this homeostatic response. Osmosensors in the gut, gills, and brain detect internal changes in osmotic pressure, which leads to a endocrine response. Highlighted here are two hormonal responses stemming from the Hypothalamus-Pituitary-Interrenal axis: (1) ACTH released from the pituitary stimulates the release of cortisol (CORT) from the interrenal into the bloodstream, and (2) GH is released into the bloodstream from the pituitary. CORT and GH then bind to receptors in the gill, which triggers the hypo-osmoregulatory function of the gills: the proliferation of saltwater type ionocytes. These ionocytes then sense osmotic changes and excrete excess ions via ion transporters (see text for specifics). Hence, although the gill, brain, and gut form their own trans-organ sub-PRN, each organ itself also contains a smaller sub-PRN, and communication between the tissues is facilitated by the neuroendocrine system (connection between the brain and gill). Depending on the severity of the (salinity) stress and the makeup of the individual’s sub-PRNs, which is determined by the individual’s genotype to phenotype map, the fish will enter one of 4 zones of stress: Optimal, Pejus, Pessium, Lethal. These zones are described in detail in Fig. 2, and the behavioral consequences are highlighted here. Depending on the zone, an individual will either engage in: fitness increasing tasks like reproduction (baby fish), behavioral regulation to reduce stress (circular arrows), or fleeing the environment (left pointing fish). Artwork by Emily Tarnawa.
ICB
"Historically, organismal #biologists have studied the organism’s response to #environmental variation from two complementary perspectives..."
Mauro et al
doi.org/10.1093/icb/...
#endocrine #neuroendocrine #osmoregulatory #osmotic #genotype #science #homeostatic #phenotype #fish