Thursday, August 09, 2012

Priorities and sleep

BBC reports a study in Science asserting that among pectoral sandpipers
male pectoral sandpipers ... are able to maintain high neurobehavioral performance despite greatly reducing their time spent sleeping during a 3-week period of intense male-male competition for access to fertile females. Males that slept the least sired the most offspring. Our results challenge the view that decreased performance is an inescapable outcome of sleep loss.

Or to put it another way, males that slept as little as possible sired more chicks and didn't seem more unhealthy than the others. Which you'd think would tend to breed populations where the males didn't sleep much during the three week breeding season, but apparently some do anyway.

From the report I learn that the males do display flights and ground displays to impress reluctant females, sometimes chasing them in flight in competition with other males, and try to maintain territory in the breeding grounds. And they squabble and fight. Sounds pretty energetic. My first thought on reading the BBC story was: their courtship displays must be low-energy, but apparently it isn't so.

The team wired up bird so they could monitor them 24/7 in their breeding area in Alaska. The study lasted 6 years, and they found only 13 out of 640 males returned to the breeding site, but the more-successful low-sleep males weren't less likely to return (they said 10% more likely, but with numbers that low...). The number of female encounters (monitored by telemetry) was proportional to the time spent awake (moving): which doesn't seem unlikely. And they sired more chicks.

Yep, they thought of the sleep quality issue:

"Short-sleeping males should show greater SWE than long-sleeping males if they compensated completely for sleep loss by sleeping deeper; however, we did not find an inverse correlation between sleep duration and SWE (r=0.22, t9=0.70, P=0.50). Consequently, short-sleeping males still experienced a deficit in sleep."

So the birds don't sleep better, they sleep less, chase more females, sire more chicks and still seem healthy enough to return next year at the same rate as sleepy-heads.

Moreover, the increase in sleep intensity in shortsleeping
males suggests that sleep serves a restorative function. In this case, long-sleeping males may lack genetic traits that enable shortsleeping males to maintain high performance on little sleep. Indeed, inter-individual variation in neurobehavioral vulnerability to sleep loss was recently linked to genetic polymorphisms in humans V. Bachmann et al., Functional ADA polymorphism increases sleep depth and reduces vigilant attention in humans. Cereb. Cortex 22, 962 (2012).

Or in summary:
"Late to bed and late to rise and you rub your bloodshot eyes. Early to bed and early to rise and your girl goes out with other guys."

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