Family Trees Revisited

Here's an interesting trio:

Edith's Checkerspot (Euphydryas editha), Flaming Gorge NRA, Daggett Co, UT 5/27/13

Steel-blue Cricket Hunter, (Chlorion aerarium), Illinois Beach SP, Lake Co, IL 8/2/2013

Red-bellied Snake (Storeria occipitomaculata), Lyons Woods FP, Lake Co, IL 3/5/2012

What's the link here? These are all illustrations of a common pattern in evolution. Not so many years ago, butterfly guides talked about 3 suborders of Lepidoptera -- moths, butterflies, and skippers. Similarly, Hymenopterans were split into three groups -- parasitic wasps, stinging wasps and bees, and sawflies. The squamate reptiles consisted of two -- the snakes, and the lizards. In each case, the assumption was that these groups had split apart early, and then each had diversified on its own.

Here's a rough cladogram, to give an idea:

Cladistic analysis, these days greatly enhanced by DNA analysis, has shown that this pattern doesn't often hold. Instead, what we see is early splits leading to "basal" groups that don't diversify much, (like several of the sawfly families and some "primitive" moths), a succession of further splits that don't do much, then one or two groups that split and apparently cross some sort of adaptive threshold, followed by an impressive radiation. So we find that the sawflies, for example, are actually not a natural group at all -- they're just those hymenopterans that didn't become wasps. Here's a more recent conception:

We find the same with Lepidopterans -- butterflies make up part of one suborder, along with most of our moths. Even within that suborder, most of the groups are moths, as are a large majority of the species. The old breakdown of moth, butterfly, skipper isn't tenable.

Even the snakes, clearly a natural group themselves, turn out to be nested within one of several suborders of lizards, long thought to be a separate group.

(A quick note on the use of scare quotes above -- these are two terms I cordially detest when used this way. A primitive species is one that died out a long time ago -- modern species have all been evolving since that early ur-ancestor. And a basal group, if you examine any cladogram that purports to show "the basal" species, is whichever lineage that emerged from that first split either without diversifying much, without becoming "interesting", or that has since lost most of its earlier diversity.)