October 8, 2012 | SCIENTIFIC AMERICAN
Ok, I know it’s not Friday Weird Science time, but this paper is both interesting science AND somewhat odd. And who can’t use extra weird in their day, right?
I know that Ed has already been here before me, but I can’t let this one go. I like studies on sleep, and I like studies on sex, and this has both!
Lesku et al. “Adaptive Sleep Loss in Polygynous Pectoral Sandpipers” Science, 2012.
This paper is not actually about gettin’ laid. Though it IS about getting laid…but what it’s really about is the purpose of sleep.
What is the purpose of sleep? After all, 8 hours a night (ish, for humans) is an awfully long time to spend unconscious and relatively defenseless. But almost all animals (all mammals and birds, definitely) that have more than a rudimentary brain do it. This leads us to think that it must really be an important thing to do. But why?
There are several hypotheses as to why we need to sleep. The one I see most often is that our brains need that relatively inactive time (though there is still a lot of activity) to perform restorative processes and promote the best brain performance. But we don’t know, exactly, what the restorative processes are. We just know that animals and humans perform very badly on tasks when sleep deprived.
But there is another hypothesis. This is the hypothesis that sleep is not really all that necessary for optimal performance. Instead, sleep is a way to preserve energy when it’s a better idea to be inactive. So, for example, humans might sleep at night because we’re at a disadvantage in the dark and would waste energy attempting activities. Support for this hypothesis comes from the fact that sleep needs vary massively across the animal kingdom. Some animals need 14 hours (see cats), while others need just 2-3.
If this hypothesis were correct, it would stand to reason that some species would be able to dispense with sleep when their lifestyle demanded constant activity. And this is where we bring in the pectoral sandpiper.
These particular pectoral sandpipers live in the Arctic, and this means that their breeding season has an interesting peculiarity: the sun never sets. The females are most fertile during the summer, when the sun never actually sets for weeks. And while the females are fertile, the males are hard at work. They don’t have anything to do with parenting, but during mating season they are defending territory, displaying to females with an inflatable chest sac, fighting off other males, and gettin’ some while the gettin’ is good. And this means…they don’t sleep.
The authors of this study looked at the sleeping patterns in the male sandpipers, and found that while the females slept about 30% of the time, during mating season, the males reduced their sleeping to a mere 10%!
You can see there the activity levels of the birds. During mating season (yellow dates) the males birds barely slept, but post-mating (when the females were incubating eggs), their sleep increased.
So the males are going sleepless…but are they making up for it? It turns out, somewhat.
Not all males completely reduced sleep, the laziest slept about 7.7 hours, while the most up and at ‘em had a mere 2.4! But as you can see above, those getting less sleep made up for it, a little, by sleeping deeper. The above figure shows EEG and EMG recordings, and shows that though the sleep was in shorter patches (blue), it was deeper (see the EMG line on the bottom).
And those males that slept the least definitely did the best in terms of mating. Those males who slept least fathered the most chicks, so it’s definitely a good thing to stay awake.
All this going without sleep is one thing. But if sleep serves an important purpose, shouldn’t the sleep deficit begin to be a major problem? Maybe the male birds who sleep the least are dying sooner? To look at this, the authors looked at how many birds returned the next year. The general number is very low (only 13 out of 640 males…in six years), but those who were the most reproductively successful had a higher return rate (about 10% higher). And the successful males were also the short sleeping ones. So it appears that the decreased sleep doesn’t make for decreased lifespan.
The authors believe that their study promotes the hypothesis that sleep is not really serving an essential function, instead, it is a way to save energy when further activity wouldn’t serve a purpose. While I see their point, I’m not sure that I agree with the hypothesis. The other hypothesis is that sleep serves an essential function, restoring certain functions for optimal performance. Given the major possibility of being attacked and killed in your sleep, of missing out on foraging opportunities, etc, and the major deficits in behavior that many species suffer when forced to go without it, I’m inclined to think this second hypothesis more likely. Also, while the birds observed here might support the idea that sleep is an adaptation to when you don’t need to be out and about, they don’t disprove the idea of sleep restoring function. These birds could be extremely unusual and specially adapted to their mating period, when the sun never sets in the Arctic, and have adaptive advantages that allow them to get away with so little sleep. And it would be really interesting to see what those advantages are! Unless of course, the birds are secretly drinking some coffee on the sly.
Lesku JA, Rattenborg NC, Valcu M, Vyssotski AL, Kuhn S, Kuemmeth F, Heidrich W, & Kempenaers B (2012). Adaptive sleep loss in polygynous pectoral sandpipers.Science (New York, N.Y.), 337 (6102), 1654-8 PMID: 22878501