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In this issue |
Sealing Snake Skin
kathryn{at}biologists.com
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Snakes aren't the most maternal creatures, and many snakes abandon their young at birth. But some snake species stay with their young, curling up with their brood until the family unit disperses when the young snakes shed their first skin. Harvey Lillywhite wondered whether some species that stay with their young, do so to protect them from dehydration? If the mothers are waiting until their young's skins became more water tight, he wondered whether other snakes that are less well cared for, also have more waterproof second skins. When California king snakes emerge from their eggs, they have to survive by conserving water in a semi-arid climate, but they're already on their own. Lillywhite decided to measure the evaporation rate from recently hatched California king snakes to see whether their second skin gave them better protection from dehydration. Remarkably, the small reptile's water loss rates dropped by almost half after they shed their first skin, as the skin's waterproof layer doubled in thickness (p. 3019).
For creatures that live in arid environments, skin is their major barrier against dehydration. How reptiles seal their skin to preserve precious body fluid wasn't clear until the 1970s, when Lillywhite and his team discovered that lipid bilayers, sandwiched between layers of keratin-packed cells, form the essential waterproof layer that protects snakes from dehydration.
But snakes shed their skins at different stages in their lives, by a process known as ecdysis, and the first ecdysis occurs within a few days of hatching. Lillywhite wondered if the first ecdysis marked a point when the small snake's skin finally became more impermeable to water loss.
Lillywhite and his colleague Ming-Chung Tu decided to measure the evaporation rates from recently hatched California king snakes. The results were remarkably clear-cut; the small reptile's evaporation rate dropped to half of the rate it had been before the snake shed its skin.
Wondering how the snake's skin had changed to reduce the snake's water loss so dramatically, Lillywhite sent samples of both skin types to Jaishiri and Gopi Menon, to see how the lipid waterproof barrier had changed after ecdysis. Lillywhite explains that he was amazed when the analysis of the skin's microscopic structure came back from the Menons' Labs; the thickness of the keratin/lipid barrier had doubled. Lillywhite explains that he was surprised that the correlation between the resistance to water loss and the thickness of the lipid/keratin layer `was so clearly demonstrated'.
But did the snake's behaviour change after they'd acquired their new watertight skin? When Tu compared whether the hatchlings preferred dry or damp conditions, he discovered that recent hatchlings avoided dry moss, but after they gained their watertight second skin, the youngsters became more adventurous, exploring dry environments that they'd avoided before.
Having found this tight correlation between the lipid/keratin barrier's thickness and the evaporation rate across the young snake's skin, Lillywhite explains that he is keen to see if the correlation is as watertight in the maternal snakes that inspired him.
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