Sorry I haven't blogged for a bit - I've been on the road, err, sky for a while.
So it turns out that Texas, which seems to be the source of much antiscience reaction these days, has yet another problem, and it turns on what a species is. Texas named the Guadalupe bass its state fish in 1989. Now it seems that overfishing, and restocking waterways with another species, has led to the probable extinction by interbreeding of the state icon.
kxan is reporting that the restocked fish, the small mouthed bass, was assumed to be infertile with the Guadalupe bass because it was a different species and dogma asserts that species do not interbreed. However, that turns out to be a very unfounded assumption. The small mouthed bass intrebred with the Guadalupe, leaving almost, possibly no, pure bred Guadalupes left.
It turns out, as Jim Mallett pointed out in a recent survey article, that hybridisation is a major process in the evolution of species. Botanists have known this for a long time, but it turns out that it is equally relevant in animals as well. So some real issues turn on what is a species. And here, unthinking assumptions based on the undergraduate definition of species as reproductively isolated populations have resulted in a species disappearing.
While we are on taxonomy, Christopher Taylor at Catalogue of Organisms takes on the arguments of those who claim that molecular data is all we need to describe species. It's a nice knockdown of the molecular hegemony in taxonomy. Organisms are more than their DNA.
In an unrelated matter, the Journal of Cell Biology has a nice critique of the use of Thompson ISI's citation data for impact indices of papers. Mike Rossner, Heather Van Epps, and Emma Hill show that Thompson's data is inaccurate, and their methods opaque, and yet these days even being hired depends crucially and rigidly on their indices. Update: some further critiques here, here, here, here, and here.
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Situations like this bring up interesting questions from a conservation perspective. Is the species extinct? Is its genetic lineage is still alive and well? But has the ecology changed? And round and round we go. Unfortunately, as we've seen in the past, legislation often doesn't cope well with such uncertainty.
Thanks for the link! I wasn't solely targeting DNA barcoding, though that is one subject that tends to make me start breaking things. I just dislike it when people try to tell me to do things that don't work so well in practice.
John, as you avoided a game of Mornington Crescent by not announcing your travel, I'll get my revenge by publically striking you with a blog meme.
Ha!
Bob
I can't access the review article mentioned. Could you give us a precis? At this point I am still sceptical about hybridization being very important in animal speciation (except for all female species).
I caught largemouth and Guadalupe bass together on a couple of occasions (previous to the stocking of smallmouths.) So they are syntopic (routinely encounter each other). I'm not aware of any reports of hybrids between the two species (google meanmouth bass). So the isolating mechanisms between these two sister species are well developed. Bring in the more distantly related, exotic smallmouth and and the Guadalupe mechanisms became ineffective.
Hybridization between similar species is promoted by habitat modification and introduction of exotic relatives. I think most of this today is human mediated and would guess that interspecies hybridization is an order or two of magnitude more common than the geological average. One needs to keep this in mind when thinking about the importance of hybridization
As I understand it, cladistics does not deal well with hyrid origin species. I think this is a major reason botanists were much slower than zoologists to accept cladistics.
There is there is disagreement on if hybrid studies shed light on relationships in a broad sense. Does the relative success of hybrid attempts give a general measure of DNA similarity, or is it that ability to interbreed is a plesiomorphous character and thus uninformative as to relationship? I have only done hybrid experiments to ask more mundane questions: will these two populations hybridize if given the chance, and, if so, what do the hybrids look like? Are there premating isolating mechanisms, postmating isolating mechanisms, both, or neither?
IIRC, Fred Allendorf and some of his students (Rob Leary and Kathy Knudsen, now that I've checked) did quite a lot of work on hybridisation in introduced trout populations in the eighties and early nineties. Similar things happen, and you end up with a population that can't be called anything other than "hybrid", but hale and hearty and true-breeding.
Sort of reminds me of 3 "species" of Rosella (green, eastern and some other I think) here in Aus. In some places they don't intermingle, have different breeding times, and are easily distinguishable. In other locations they intermingle in the biblical sense and thus would have to be the same species as they produce fertile offspring.
Cladistics handles hybridisation fine - as an unresolved polytomy (that is, a number of branches all from the same root node). But you can do hybrid studies at the gene level and resolve the tree for those genes. Herb Wagner wrote a lot about this before he died.
Mallet's paper reviews the evidence for hybrid speciation in animals, and concludes
I recommend the paper if you can get it.
Had a long discussion with one of my colleagues about empty niches. Based on his work on introduced species, he thinks there are none. I think there are some, but if they become occupied it affects the whole ecosystem. One argument as to why hybridization is so rare is that no nich exists for the hybrid; that the somewhat intermediate hybrid is outcompeted on either side by its parent species. However if there is habitat disruption, this may well break down, and parent niches lost, while hybrid nich(s) are formed. Also, if an exotic is involved in the hybridization (as is often the case) then who knows what the hybrid will be like in relation to available niches. The hybrid may well be better adapted than one or both of the parent species, and hybrid swamping will occur.
In managed species we are dealing with an inept semi-intelligent designer, thus catastrophes and unexpected outcomes. Generally speaking, hybrid sunfishes are more agressive feeders than their parent species, and thus more catchable. There was an experiment in Illinois where a pond was stocked with a large number of green sunfish x bluegill hybrids and straight bluegills. The pond was opened to intense public fishing, and all the hybrids were caught before a single bluegill was caught. See also the reference to meanmouth bass. If fishing regulations were such that no bass was returned to the water, the Guadalupe x smallmouth hybrids might well have reduced fitness compared to either parent species.
Went back and reread some of the source material. I would expect rod and reel sampling to produce a sample hugely biased toward hybrids.
"I recommend the paper if you can get it."
If? So you don't know Mallet's pages?
http://www.ucl.ac.uk/taxome/jim/
http://www.ucl.ac.uk/taxome/jim/jimpubs.html
http://www.ucl.ac.uk/taxome/jim/pap/mallet07_hybspn_Nature.pdf