It’s spring in the Northeast. Up here we have long, cold winters and often mediocre summers. Last year we had so much rain the zucchinis rotted on the vine. Falls are nice but the foliage doesn’t last long and then it’s winter again.
But we really, really appreciate spring.
And, as always, when I see the flowers, a middle aged man’s thoughts turn to evolution.
It’s easy to look at the perfection of flowers and marvel. But it’s important to remember that we’re not seeing the fully developed and diversified product of something that’s been percolating in the ecosystems for a long, long time.
So where did those flowers come from, anyway?
Flowers show up like Athena from the head of Zeus about 125 million years ago. One minute we have conifers and ginkos. The next flowers show up. Evolutionary success? Forget dinosaurs and mammals. Flowering plants are where it’s at.
Most symbiotic relationships either disappear or descend into parasitism. The symbiosis between insects and flowering plants seemed to take on quickly and wave as first the dinosaurs, then the ultra large birds and mammals bit the dust.
Recent work (See here.) has suggested that flowering plants (or their ancestors) appeared much earlier, between 290 and 240 million years ago. Scientists found oleanane , a compound used by flowering as a defense against fungi and microbes but is absent in conifers and other non-flowering plants. This does not mean flowers existed back then. However, it does suggest their ancestors could have.
One interesting aspect of this is the range neatly encapsulates the Permian extinction. I haven’t seen this mentioned in the literature. It would be interesting of the extinction event either created a niche for already existing possible flowering plants or set the stage for flowering to be generated.
Flowers are modified leaves. This is an idea 200 years old (suggested by Johan Wolfgang Goethe) and confirmed in the 90s. However, the way that flowers generated their structures was a mystery. It turns out its a two factor system: one gene (LEAFY) makes flowers different from shoots and a second gene (WUSCHEL) makes the center differentiate from the end.
What makes this interesting is that WUSCHEL is already known to be essential in the patterning of shoots and leaves. Plants are reusing a gene that was already in place for the shoots and leaves.
The curious thing about flowers is not the structuring of the flowers but the co-evolution (and co-option) of insects along with it. One idea is that this started on an island– islands are wonderful places for innovations to get started. There’s a narrow range of competition. Often, predation is reduced. Evolutionary strategies can be explored in relative safety.
If this occurred, then sometime by the early Cretaceous the cat escaped the bag and roamed the earth. Adaptation of insects closely followed. Pollinator and pollinated walked down the path together. There’s been some interesting work how flower types and pollinators matched one another. (See here and here.) There’s some lovely work on the co-evolution of the corolla tubes of plants (the plants through which the pollinator must reach) and the tongue length of the pollinator. (See here.)
Flower evolution turns out to be a much greater source of divergence between species that fruit product. (See here.) This suggests that once flowering plants were established, they became an adaptive mechanism themselves, bootstrapping their own adaptive radiation. Flowers are all about sex. They could probably be the most dynamic sexual evolutionary mechanism on the planet.
This was all was going through my mind as we returned from lunch, walking over sidewalks carpeted by thousands of discarded petals.
“Plant fornication,” mutters Chris, walking next to me.
“Not at all,” says Erik, not to be outdone. “This is merely plant fornication’s soiled and discarded lingerie.”
Ah, I thought.
The blog for Sunday.