Lettuce leaves closing up

[AquaTrox]

Six days ago I put some lettuce seed in my aquaponic growbed and my soil non-aquaponic growbed and now I have 5 (4 aquaponic, 1 soil) really small plants (one stem coming up with two leaves at the top.) The leaves on each plant had been together and vertically pointed but opened up horizontally a day or so ago. Tonight the leaves on all the plants, minus one of the aquaponic plants, have come back together and are now pointing vertical again.
I assumed that once the leaves opened up horizontally they would stay that way and more leaves would grow in as the plants gets bigger.
The temperature stays fairly constant at about 61 degrees Fahrenheit so I wouldn't think the temperature is the reason.
Is this thing with the leaves normal or is it a problem that I should look into?

[Jason Palenske]

Should be fine, it may be a little chilly most liking around 72 but sometimes they will pull together as they prepare to grow. I would only worry if they look like they are shriveling.