April 15, 2005

Dinosaur Eggs & Trade-offs

The fossil of a female dinosaur with two unlaid eggs provides tremendous new insight into the dinosaur reproductive system. The find confirms that dinosaur anatomy shares certain features with bird anatomy.

The article notes that birds only have one ovary (and that isn't the only thing they've got a light complement of), while their dinosaur forebears appear to have had two. One of the many changes along the way that ended up being beneficial to flight.

What's even less well known is that one of the most common mutations in birds is flightlessness. It's a defect that gets sorted out by the behavior of pushing chicks out of the nest where the flightless ones will get eaten, or in the case of a few birds, muddling through to a point where they could live comfortably on the ground given favorable conditions. Because flight is an expensive mutation for which everything has to come together just right to work, there's plenty that can go wrong. And on the road to flight, a lot had to be paid and sacrificed.

This is the trade-off aspect of evolution. Any organism only has a finite amount of energy in their system, which is illustrated by the way your immune system can only has the juice to handle so many insults at the same time before throwing in the towel and letting you come down with all manner of unpleasantness. Whether a critter's genes are set up to spend their energy wisely or not will usually sort itself out with a quickness.

Which brings me to a study I read* where the researchers looked at two related species of rainforest tree that each stuck to a particular type of soil. One type grew in a richer soil, and tended to grow faster and taller. The other type grew in a sandy soil with few nutrients, and it was shorter and slower growing. The assumption was that the faster growing trees just couldn't handle the poor soil. But the experimental results showed that when protected from insects and competing organisms, the faster growing trees would do what they normally did and overshade their slower relations, preventing them from gaining a foothold.

The soil specialization was only indirectly related to the soil, and mainly had to do with the rate at which resources were used. The slow growing trees were slow because they put a lot of their energy into producing insect repelling chemicals, which meant that they didn't have to spend those resources regrowing eaten tissue. When the fast growing trees were put in poor soil, they didn't have enough energy to grow faster than they were being eaten, which is their strategy on more hospitable ground.

When dinosaurs and birds split off from each other, birds gradually gave up organ redundancy, bone density, clawed forelimbs, and generally, size. But after a global extinction event that likely changed the climate, the fluffy feather wrapping and ability to get off the ground proved mighty useful.

And so yet again, I would like to remind readers that natural selection isn't really about being the one with the nastiest claws. It's about being suited to your time and place, and then being able to survive when the battle changes. A clever adapter can outlast the snarliest of predators, which is why songbirds can whistle happy little come hither tunes at each other in the Spring over the multi-million year old bones of fearsome Velociraptors.

This has been a public service announcement from the Eastside chapter of the Darwinian Illuminati in partnership with Unitarian Jihad.

* If I can find the issue of the magazine where the study was published, I'll update this spot with a reference.

Posted by natasha at April 15, 2005 02:21 AM | Science | Technorati links |

What a marvelous post!

It reminds me of a small company I worked for in the late 1990s that made metrology quality control software to use with the really big auto/airplane CAD systems. Metrology is the science of measurement - I hadn't known there was a word for it! This little company had a poetry contest (of all things!), and I wrote a "beat" poem (complete with finger-snapping and choruses for the audience) that wound up at the conclusion that "it ain't the size that matters, it's the fit!"

Thanks for reminding me!

Posted by: CaliforniaDrySherry at April 15, 2005 03:21 PM

If you can find it, post it in the comments here. I'd love to read it :)

Posted by: natasha at April 17, 2005 03:54 PM