Matt Skaggs had the audacity to ask, and follow up on, a paleobotany/evolution question involving the California flora, which I really should know more about than I do, instead of talking about stupid stuff like football. You can add to that discussion of course (copied below), one that ranges taxonomically from cypresses to sequoias to serpentine-tolerant mustards, and conceptually from Darwin to Wright to Goldschmidt, but I figured I’d better make a post allowing for questions/discussions on miscellaneous topics of interest, for putting up links to interesting articles, and so forth. The abrupt transition from bluegrass song lyrics to the evolutionary origins of serpentine endemics in California is well known to mess with peoples’ senses of flow and thus probably should be avoided. [Editor’s note: the term “bluegrass”, as used above, does not refer to Poa pratensis except in a very historically indirect way–apologies for any taxonomic confusion.]
In other thrilling news, I messed around with some other WordPress “Theme Options” to see if I could get the content and comments to span the screen better, but had no luck and figured I’d better leave well enough alone before I broke something. I was able to force replies to comments to nest to a max of one indentation level to aid the cause however.
Below is copied the discussion by Matt and I, for your literary pleasure. Note that this will likely bring a barrage of comments, so try to get yours in early.
I just read your background for the first time, and with your connections to California, thought I would offer up a paleobotany topic. I have always been fascinated by the distribution of Cupressus in California. Much of the global diversity resides there, but many of the species/subspecies are very rare. I’ve often thought that if one could truly understand the distribution and genetics of this group, the persistent mysteries of speciation- at least in plants – would be resolved. And if that were to happen, it would connect Darwin to Goldschmidt via the work of Sewall Wright. And there’s more: by the time we are in High School we know about the megafauna in the La Brea Tar Pits, but few are aware that the tar pits existed in a cypress forest that was once widespread but is now essentially gone. Understanding the change in forest composition could reveal what really happened to the megafauna. Paleobotany indicates that the Sierra also once had widespread cypress forests but of low diversity. My rather extensive research on Cupressus all occurred in the 1990s, and cladistics has improved our understanding a lot since then. Did you take in interest in these sorts of questions when you were in California?
Uh oh, I’m in trouble here!
The cypresses are indeed interesting, biogeographically, (and ecologically) like so many taxa in California. I’m no expert on them, that’s for sure, but their distribution exemplifies a familiar pattern across a number of important plant taxa. The one I have the most experience with is Arctostaphylos (the manzanitas) because I worked on one of the rare ones for a while. And there is the classic poster-child case–Giant Sequoia. And there are other examples of such disjunct distributions, like Ceanothus spp. (CA lilacs), and similar kinds of evidence even within individual species, such as (off the top of my head) Brewer spruce (Picea breweri), red fir (Abies magnifica), and foothill pine (Pinus sabiniana) all of which show major subspecies/race disjunctions, some of which are very hard to impossible to explain with existing data, although I’m unsure on how much genetic analysis has been done for each.
Arctotaphylos and Ceanothus are better analogues for the Cupressus situation, in terms of distribution pattern, as all involve many clearly different species scattered and disjunct over a large area. On the other hand, the sequoia and other tree examples mentioned above are better analogues, in the sense that they are wind-pollinated coniferous trees, like the cypresses (whereas the manzanitas and lilacs are smaller (i.e. shrubs), but more importantly, are insect pollinated). And these differences are likely reflected in the enormous numbers of species of both genera–where else will you find 40-60 species of shrubs in a single genus in an area about the size of California? And boatloads of similar examples can be found among the herbaceous species, especially the insect pollinated ones (e.g. Penstemon, Clarkia).
And then again, Cupressus and Arctostaphylos/Ceanothus share a distinguishing similarity, in that they originated from the “Madro-Tertiary geoflora”, so they share a long term ecological/environmental history, i.e. having originated in hot and dry, fire-adapted vegetation groups from the Mediterranean and similar xeric climates of North America, i.e. what are now Mexico and California. And certain life history traits that originated from that experience (e.g. latent bud sprouting after fire, long seed dormancies and cone closures broken only at heat thresholds), very likely influence their subsequent evolutionary history.
So, perhaps all that just to say that the cypresses really are an interesting case, as you state.
As for process, giant sequoia is probably the classic case of a taxon known to formerly have covered a much large area earlier in the Cenozoic which has since shrunk and split to its present scattered distribution. There is almost certainly an environmental tolerance component to this, since existing sequoia groves are restricted to +/- definable environmental ranges, and known, late Cenozoic geological events such as the rise of the Sierra Nevada (and consequent drying of the Great Basin) were very likely involved in the range reduction. But, how do we explain sequoia absence in the many Sierran locations currently having environmental conditions very similar to those in existing sequoia groves, but yet lacking sequoias?
But I’m pretty sure I’ve not answered your question about what Cupressus teaches us about plant evolution, or connected Darwin with Goldschmidt via Sewell Wright, much less in relating anything to megafaunal extinctions. Can you elaborate on what you were after there?
Thanks for taking the time to respond, you make some interesting points. I’m afraid I scattershot a few too many topics. Cypress distribution and diversity is interesting primarily because it challenges notions of genome plasticity.
My favorite hobby is an odd one, serpentine endemism and rarity, I have never been able to do much with the manzanitas because they are so darn hard to tell apart in the field. I did spend considerable time studying two oddball genus, Streptanthus and Hesperolinon, that are scattered on disjunct serpentine exposures in central California. Obligate self-fertilization is common in these groups, usually on serpentine and usually involving rarity. The central California serpentine/peridotite exposures are thought to all be young, almost certainly having been exhumed during the rise of the coast ranges and the Sierra Nevada. I like how that collapses the cause tree, these plants have had little time to diversify and so are almost certainly neo-endemics. The paradigm is that the rare serpentine plants evolved from more widespread and generalist species. It is really hard to imagine evolving selfing and serpentine tolerance sequentially for a single, rare, neo-endemic species; it is inconceivable that it would happen multiple times in the same genus.
A mutant seed plant that has developed serpentine tolerance faces a major hurdle. It is surrounded by closely related individuals that lack the tolerance, and the lineage is subject to loss of tolerance due to back-crossing. Borrowing ideas from Sewall Wright, the facilitation of speciation requires both the migration into a new niche (in this case serpentine) and reproductive isolation. These plants seem to have isolated in place by obligate selfing. So what do we have? We have multiple examples within a single genus in which the evidence strongly supports a simultaneous major metabolic change (immunity to heavy metal toxicity) and a major change in reproductive strategy. What plausible scenarios remain other than a Goldschmidtian homeotic mutation to a single founder plant? Heresy!