The term “fitness” congers images of six-pack abs, yoga poses, and 90’s spandex leotards (for me, anyway). But those images can be misleading when it comes to understanding evolutionary fitness.
Good “fitness” in evolution means “a good fit.” Organisms that fit well in their environmental niche spend less energy just trying to survive; they have more energy left over for reproduction. So fitness is often measured by the number of offspring produced.
A sloth is well camouflaged with its slo-mo movement. Many predators detect prey by movement (if we stick with the 90’s imagery, remember the T.rex in Jurassic Park “can’t see us if we don’t move”). Low metabolism in sloths means very low food requirements. One study measured sloth metabolic rate at 174 kJ (kilajoules) per day. (1) Just for comparison, an average human requires 6000-7000 kJ per day.
Nagy, KA and GG Montgomery. 1980. Field metabolic rate, water flux, and food consumption in three-toed sloths (Bradypus variegatus). Journal of Mammalogy 61(3)465-472
Favorite flower? Daisy (an Aster, like these).
Not only is it humble and cute, it’s a bargain. For each daisy you buy, you get hundreds of flowers. The disk part of each “flower” is actually a composite of scores of tiny flowers. Look close – you’ll see.
And the “petals” of a daisy? Each one is actually a whole flower too! The single petal plucked for “loves me” or “loves me not” is actually 5 petals fused over evolutionary time. If you look at the tips, you can still see some divisions.
See that tiny bump on the branch? You’re looking at a mom protecting hundreds of babies. Well, actually, the mama Oak Scale insect (Parthenolecanium quercifex) is dead now, but her exoskeleton is still harboring those little eggs underneath. When those baby Scales hatch around the end of May, the tiny darlings will move out to the oak leaves and begin to SUCK THAT POOR TREE DRY. They sniff out the precious sugar-water flowing through veins in leaves, insert their straw-like mouth parts and drink up. As the year progresses, Scales grow and mate. Mama lays her eggs beneath her and dies, making way for next May’s new generation. (These are the eggs… um, on my kitchen table. Didn’t realize they’d pop out like that when I lifted the mama Scale off. Oops.)
In the insect’s defense, healthy trees can resist Scale infestations. Some leaves and twigs may fall off – that’s all. But trees that are weakened (by physical damage, drought, chemicals, etc.) can be killed by the insects.
Cool Climate Change research recently found that densities of Oak Scale are up to 13x higher in warm urban areas! (1) Since things are getting toastier here on Earth, we may want to get more familiar with the life & times of the Oak Scale.
Branches of the Live Oak (Quercus virginiana) loop and twist their way toward openings in the forest canopy. Many branches sag down to the ground before stretching back up again.
These low branches help the oak survive in the hurricane-prone regions of the Southeastern U.S. Short, wide trees resist strong winds better than tall, thin ones. Those curvy branches helped the USS Constitution stay afloat during the War of 1812 too. Live Oak limbs were frequently used in ship building due to their natural bends, strength and density.
Carnivores have ‘em. Rodents and bats have ‘em. Even many primates have ‘em. But not humans.
The baculum (penis bone) is one of the most variable bones in the mammalian skeleton – you can even ID an animal by the shape and size of that one bone. Just like with insect penises, the shapes of these reproductive structures can change quickly in evolutionary terms (Carl Zimmer writes a wonderful post looking at these shifts)
What’s its function?
Well, we’re not 100% sure yet. It may allow males to copulate before being fully, ahem, at attention. Or it may stimulate the female to ovulate. Some bacula grow spiny projections which may, like some insect penises, clear out other sperm before injecting one’s own.
Let’s not leave out the girls!
The penis and clitoris develop from the same structure. So, if the penis has a bone… does the clitoris? You bet! It’s called the os clitoridis (or baubellum).