Trans-marine dispersal inferred from the saltwater tolerance of lizards from Taiwan

Dehydration and hypersalinity challenge non-marine organisms crossing the ocean. The rate of water loss and saltwater tolerance thus determine the ability to disperse over sea and further influence species distribution. Surprisingly, this association between physiology and ecology is rarely investigated in terrestrial vertebrates. Here we conducted immersion experiments to individuals and eggs of six lizard species differently distributed across Taiwan and the adjacent islands to understand if the physiological responses reflect the geographical distribution. We found that Plestiodon elegans had the highest rate of water loss and the lowest saltwater tolerance, whereas Eutropis longicaudata and E. multifasciata showed the lowest rate of water loss and the highest saltwater tolerance. Diploderma swinhonis, Hemidactylus frenatus, and Anolis sagrei had medium measurements. For the eggs, only the rigid-shelled eggs of H. frenatus were incubated successfully after treatments. While, the parchment-shelled eggs of E. longicaudata and D. swinhonis lost or gained water dramatically in the immersions without any successful incubation. Combined with the historical geology of the islands and the origin areas of each species, the inferences of the results largely explain the current distribution of these lizards across Taiwan and the adjacent islands, pioneerly showing the association between physiological capability and species distribution.

Over-ocean dispersal inferred from the saltwater tolerance of lizards from Taiwan

BackgroundFor non-marine organisms, crossing the sea requires the challenges of dehydration and hypersalinity to be faced. Thus, the rate of water loss and saltwater tolerance determine the ability of species to disperse over sea and further influence species distribution. However, this association between physiology and ecology has rarely been investigated in terrestrial vertebrates. In this study, we examined the lizard species differently distributed across Taiwan and the adjacent islands to determine whether these physiological responses reflect the geographical distribution. We performed immersion experiments on individuals and eggs to test the rate of water loss and the saltwater tolerance in the six chosen species, that is, four native species (Plestiodon elegans, Eutropis longicaudata, Diploderma swinhonis, and Hemidactylus frenatus) and two introduced species (E. multifasciata and Anolis sagrei). Results For the individuals, the results showed that P. elegans had the highest rate of water loss and the lowest saltwater tolerance, whereas E. longicaudata and E. multifasciata showed the lowest rate of water loss and the highest saltwater tolerance. D. swinhonis, H. frenatus, and A. sagrei had medium measurements compared with the aforementioned species. On the other hand, for the eggs, only the rigid-shelled eggs of H. frenatus were not influenced by the water immersion and were incubated successfully after experimental treatment. In contrast, the parchment-shelled eggs of E. longicaudata and D. swinhonis lost or gained water dramatically in the experiments, and none of them hatched after immersion. ConclusionsThese interspecies differences in water loss and saltwater tolerance strongly suggest the heterogeneity of over-ocean dispersal ability among these lizards. Combined with the historical geology and the origin areas of each species, the inferences of the results largely explain the current distribution of these lizards across Taiwan and the adjacent islands. Furthermore, this study also helps to elucidate the potential dispersal of two invasive species, E. multifasciata and A. sagrei, for conservation purposes.

Can Atlantic salmon smolt twice? Endocrine and biochemical changes during smolting

Smolting is characterized by morphological and physiological changes, some of which are reversible if fish remain in freshwater. Whether fish that smolt in the first year will repeat physiological changes associated with smolting a second time is not known. To assess whether Atlantic salmon (Salmo salar) can smolt more than once, we sampled hatchery-reared Atlantic salmon at monthly intervals for 2 years beginning the fall after hatching. Fish showed differences in rate of growth and were easily differentiated by size into upper mode (UM) and lower mode (LM) by the first fall. In the first spring, gill Na+,K+-ATPase activity of UM and LM fish increased six- and three-fold, respectively. Plasma growth hormone levels in spring were significantly elevated in UM fish but not in LM. Plasma cortisol levels changed little and gill corticosteroid receptor concentration did not differ between the groups. During the summer, gill Na+,K+-ATPase activity declined in both groups and remained low until the next spring. The second spring, growth hormone levels did not increase significantly and cortisol levels increased. The increase in gill Na+,K+-ATPase activity and cortisol and high saltwater tolerance indicate that UM Atlantic salmon can smolt in two consecutive years.

Differences in Measurements of Smolt Development Between Wild and Hatchery-Reared Juvenile Coho Salmon (Oncorhynchus kisutch) Before and After Saltwater Exposure

We compared the saltwater tolerance of coho salmon (Oncorhynchus kisutch) juveniles that were reared in different environments. The groups examined consisted of fish reared exclusively in the hatchery, a hatchery group transplanted into the upper watershed of the river (colonized), and wild fish from natural spawning broodstock in the river. Although hatchery fish were much larger than their wild or colonized counterparts, they consistently showed a reduced saltwater tolerance as assessed by a much greater perturbation in plasma sodium concentration following transfer to salt water. Within each group there was no relationship between size of the fish and saltwater tolerance. Following transfer to sea water, hatchery fish showed a significant decline in haematocrit and a significant increase in circulating plasma cortisol concentration. Neither of these changes was seen in wild smolts. Hatchery fish possessed fewer chloride cells, and lower specific activities of the enzymes Na+K+ATPase and citrate synthase. The weaker osmoregulatory ability of hatchery fish led to a greater mortality following abrupt transfer to 35‰ seawater. We believe that the differences in saltwater tolerance seen among the different groups of fish are due to rearing environment.

The effect of feeding thyroid hormones on saltwater tolerance and growth rate of Atlantic salmon

Two experiments, involving the addition of thyroid hormones to the diet of salmon parr (Salmo salar) were carried out. The prime purpose of these experiments was to study the effect of feeding thyroid hormones on saltwater tolerance. Saltwater tolerance is interrelated with size and therefore growth rate was investigated. In experiment I three different thyroid preparations were used: thyroid extract, 3,5,3′-triiodo-L-thyronine (T3), and thyroxine (T4). Each thyroid preparation was fed to two different sizes of fish with two different concentrations in the diet. T3 gave the best overall results, both for saltwater tolerance and growth rate. No interaction was found between fish size and concentration of thyroid hormone in the diet. In experiment II three different concentrations of T3 in the diet were fed to salmon parr of two different ages. Feeding T3 improved saltwater tolerance and growth rate of 7-month-old fish but had a negative effect upon growth for 19-month-old fish. For the 7-month-old fish 10 mg T3/kg dry food gave the best effect on saltwater tolerance, while 1 mg T3/kg dry food was enough to improve growth. It is concluded that it is possible to induce smoltification in underyearling Atlantic salmon out of season by feeding thyroid hormones.