WR Osmoregulation

Question 1

Hyper-hypo osmoregulation in Crustacea

The study

Answer 1

Study 1: Hyper-Hypo osmoregulation crustacean – Capacity to osmoregulate varies with development

Ontogeny of osmoregulation and salinity tolerance in a mangrove crab, Sesarma curacaoense (Decapoda: Grapsidae) (Anger and Charmantier, 2000)

• Living in mangrove swamps with variable salinity conditions and showing semiterrestrial behaviour, S. curacaoense exhibits ecological adaptations to non-marine conditions
• In laboratory experiment
• Studying the ontogenetic changes in the capability of osmoregulation in S. curacaoense and the salinity tolerance during early-life stages
• Larvae released into stagnant, temporary water puddles within the adult habitat

Question 2

Study 1: Hyper-Hypo osmoregulation crustacean – Capacity to osmoregulate varies with development

The results

Answer 2

Results:

· Adult crabs were observed to be strong hyper–hypo-osmoregulators in a salinity range from at least 1 PSU to 44 PSU

· Zoeae are strong hyper-osmoregulators in moderately dilute media (10–17 PSU).

· Hypo-osmoregulation in concentrated media (≥32 PSU) becomes functional in the megalopa stage

· the capability of hyper-osmoregulation appears in S. curacaoense earlier and increases more rapidly than the function of hypo-osmoregulation

· Zoeal I, II stage is short (1-2 days) – reduction in saline can occur in pools through rainwater – therefore more important to hypo osmoregulate

· Megalopa (8-12 days) is longer – Hypersaline conditions can occur but at a slower rate – there import to be able to hypo osmoregulate

Question 3

Study 1: Hyper-Hypo osmoregulation crustacean – Capacity to osmoregulate varies with development

Critical analysis

Answer 3

Critical analysis:

· Larvae from eggs hatched at constant conditions – 24°C and 25 PSU – Not accurate of mangrove habitat – conditions fluctuate, especially salinity

· Laboratory experiment – only acclimation to salinity – not taking into account other factors such as variable temperature, so reaction to variable salinity may not be accurate

Question 4

Study 2: Hypo- regulation teleost

The study

Answer 4

The expression of gill Na, K-ATPase in milkfish, Chanos chanos, acclimated to seawater, brackish water and fresh water – (Lin et al., 2003)

· Resident marine species

· Study was to characterise the adaptive response of NKA in the gills of the milkfish acclimated to a range of salinities (35PSU Hyperosmotic environment – 0PSU Hypo osmotic environment)

· Na, K-ATPase (NKA) = a universal membrane-bound enzyme that actively transports Na+ out of and K+ into animal cells

Question 5

Study 2: Hypo- regulation teleost

The expression of gill Na, K-ATPase in milkfish, Chanos chanos, acclimated to seawater, brackish water and fresh water – (Lin et al., 2003)

The results

Answer 5

Results:

· Study confirms the capacity of juvenile milkfish to tolerate abrupt changes in salinity and the fish osmoregulate well over a wide range of salinities

· juvenile milkfish in various fixed salinities from full strength SW to FW maintained their plasma osmolality and ionic concentrations within very narrow limits

· Brackish water (BW)-adapted fish, a decline in salinity induces a substantial rise in NKA activity only due to the recruitment of latent pumps

· Freshwater (FW)-adapted individuals, elevated NKA activity as well as newly synthesized NKA protein amounts – to hypo osmoregulate to pump Na+ out of the cells – to maintain a constant level of plasma osmolality in FW

· Enable euryhaline ability

Question 6

Study 2: Hypo- regulation teleost

The expression of gill Na, K-ATPase in milkfish, Chanos chanos, acclimated to seawater, brackish water and fresh water – (Lin et al., 2003)

Critical analysis

Answer 6

Critical analysis:

• Seawater made from tap water and sea salt – doesn’t have other solutes found in seawater that may influence osmoregulation
• Water temperature was kept at a constant 27°C which is representative of the tropical environment in which they live

Question 7

Study 3: Hyper regulator bivalve

The study

Answer 7

Osmoregulation and salinity tolerance in two species of bivalve mollusc: Limnoperna fortunei and Mytilopsis leucophaeta – (Deaton et al., 1989)

· This paper reports on salinity tolerance and osmotic regulation in two bivalve molluscs: Mytilopsis leucophaeta, an oligohaline species and Limnoperna fortunei, a freshwater species.

· Acclimation to a range of salinities (osmotic concentration from 0 to 970 mOsm)

Question 8

Study 3: Hyper regulator bivalve

Osmoregulation and salinity tolerance in two species of bivalve mollusc: Limnoperna fortunei and Mytilopsis leucophaeta – (Deaton et al., 1989)

The results

Answer 8

Results:

· Similar responses to dilute media

· Both species are osmotic and ionic conformers in osmotic concentrations >70 mOsm (Osmolality)

· At lower ambient salinities both are hyperosmotic regulators

· Haemolymph in both are hyperosmotic to dilute external media and hyper-osmoregulation begins <approx.></approx.>

<p>· Higher acclimations to 210 osmolality demonstrated highest free amino acids content in mantle tissue in Limnoperna fortunei</p>

<p>· Limnoperna fortunei is a freshwater species but it also has considerable tolerance for high salinity and is common in estuarine habitats – due to amino acids serving as osmotic effectors for cellular volume</p>

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Question 9

Study 3: Hyper regulator bivalve

Osmoregulation and salinity tolerance in two species of bivalve mollusc: Limnoperna fortunei and Mytilopsis leucophaeta – (Deaton et al., 1989)

Critical analysis

Answer 9

Critical analysis:

· Did not undertake study at different points within the year – so some muscles may have been undertaking aestivation – decreasing metabolism and activity which may affect osmoregulation mechanisms

· In laboratory experiment – may not replicate true natural conditions

· Good because compared it to the ‘natural’ environment osmotic conditions

Question 10

Study 4: Oligochaetes osmoregulation:

The study

Answer 10

Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids – (Generlich and Giere, 1996)

· The osmoregulatory capacity of two oligochaete species: Enchytraeus albidus and Heterochaeta costata, was investigated by direct measurements of the osmolality of the coelomic fluid.

· Two E. albidus populations – one from under decaying seaweed on the shore of N. Sea (28-29 Salinity) – second from a compost heap in Hamburg – Terrestrial and coastal species

· Heterochaeta costata collected from western Baltic Sea (13-14 Salinity) – Truly marine species

· E. albidus were kept at 0, 10, 20, 30, 40 Salinities for at least two weeks (acclimation)

Question 11

Study 4: Oligochaetes osmoregulation:

Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids – (Generlich and Giere, 1996)

The results

Answer 11

Results:

· E. albidus maintained a hyperosmotic coelomic fluid over all salinities tested.

· In low salinities the osmolality of the coelomic fluid of the marine population was significantly higher than that of the terrestrial population

· The coelomic fluid of H. costata was hyperosmotic to medium at 15 PSU and isosmotic at 30 PSU (Higher salinities)

· Active transport of ions combined with a changeable permeability of the body wall play a major role in the regulation of body fluids

Question 12

Study 4: Oligochaetes osmoregulation:

Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids – (Generlich and Giere, 1996)

Answer 12

Critical analysis:

· Worms were kept at temperature of 16°C which may not be representative of the habitat – may affect the rate of ion transport = effecting osmoregulation

· Good because acclimation to range of salinities was done over 2-weeks which has been tested to be enough time for acclimation in previous studies

Question 13

Study 4: Oligochaetes osmoregulation:

Osmoregulation in two aquatic oligochaetes from habitats with different salinity and comparison to other annelids – (Generlich and Giere, 1996)

Critical analysis

Answer 13

Critical analysis:

· Worms were kept at temperature of 16°C which may not be representative of the habitat – may affect the rate of ion transport = effecting osmoregulation

· Good because acclimation to range of salinities was done over 2-weeks which has been tested to be enough time for acclimation in previous studies

Question 14

Elenas tuna study

Answer 14

Gill and intestinal Na+-K+ ATPase activity, and estimated maximal osmoregulatory costs, in three high-energy-demand teleosts: yellowfin tuna (Thunnus albacares), skipjack tuna (Katsuwonus pelamis), and dolphin fish (Coryphaena hippurus)

Brill et al., 2001: Tuna have high SMR, but do NOT have high osmoregulatory costs

Study:

Scientists hypothesis that the large and thin gills of tuna should result in high osmoregulatory costs (large SA = high water and ion influx across gills).

Method:

· Measure Na+-K+ ATPase activity in:

o Intestines and gills: Yellow fin, Skipjack, hybrid red tilapia (brackish sp).

o Gills only: Dolphin fish

· Hybrid red tilapia was measured as there has been numerous previous studies on tilapia metabolism and osmoregulation. Used to check procedures.

Results:

· No difference in Na+-K+ ATPase activity between the four species.

· Cost of osmoregulation:

o 9% SMR in Skipjack

o 13% SMR in Yellowfin

· HYPOTHESIS WAS WRONG. Tuna do not have exceptionally high osmoregulatory costs.

Critical Analysis:

· Results differ significantly to previous studies.

· Due to differences in procedure: pH/ ion concentration/ buffers.

· Cannot conduct direct comparisons with other studies. Can’t build up big picture.