Species emergence ...

The following in another thread prompted a
'perhaps there should be a new topic' comment ...
so here it is If evolution is, by and large, a slow process (taking millions
of years) how would we notice a speciation event?If only we had some historical record of species change
that dated back over millions of years!!Hmm ... new species are being discovered at a very high rate ...
is that just because they were previously unobserved or
becuase they didn't exist previously ... just an idle thought
that ... not entirely serious.

This is a good article on the species concept, that tries to come up with a useful definition of species, essential for any discussion of speciation: Species

Hi Peter,Itz provided a pretty good article covering the "state of play" on the question of just what the hell constitutes a species, so I'd like to just hit a couple of other points. There are actually two problems here. In the first place, what biologists and paleontologists mean when they say "species", while mostly congruent, are really two different concepts. The trick is finding a way of merging the two. Paleontologists are obviously not going to be able to see reproductive isolation in the fossil record, like biologists talk about when they talk about speciation. Usually, paleontologists are talking about a morphological concept, while biolgists are dealing with a ecological AND morphological concept. In essence, it's really easy to see two species in the fossil record, but it's really hard to see when they diverged and why.The other problem is cladogenesis vs anagenesis (or punctuated speciation vs gradual change within a lineage). Anagenesis can occur by fiat - paleontologists looking at miniscule changes in a lineage over very long time frames can eventually come to the conclusion that there has arbitrarily been enough change to declare a new species. In other cases, possibly due to the incompleteness of the fossil record, there can be "abrupt" appearances of two new related species where there was only one before - a cladogenesis event.So what CAN be seen in the fossils? Basically it's a pretty complex mosaic. However, there are three very broad trends:a) gradual change without stasis. See, for example, the planktonic diatom Rhizosolenia - 2 million years of gradual change, based on highly detailed sediment cores with a distinct sympatric speciation event at 3.1 mya. Before 3.1 mya, R. bergonii is the only thing found in all samples, although biometric divergeance was noted starting just before the magic date, then after 3.1 mya, two populations R. bergonii and R. praebergonii appear together in the cores. Interestingly, the latter show up "abruptly" in the Indian Ocean somewhat later. Without the detailed cores from the Pacific, the appearance in the Indian Ocean might have been mistaken for a "punk eq" sudden speciation.b) stasis or gradual change with stasis. Look up the Lake Turkana mollusc studies - 19 lineages of bivalves and snails followed in fine gradation over a period of nearly 4 mya showing little or no morphological change beyond what might have been variation in ecophenotype.c) stasis and punctuated speciation. See, for example, the case of the bryozoan Metrarabdotos spp. from fine grained sedimentary cores in the Caribbean. Scientists were able to examine thousands of specimens in carefully dated sediments spanning 10 my. Sometime between 8-4 mya, Metrarabdotos speciated into 12 distinct species - nine of which appeared within a million years (8-7 mya).I guess the answer to "how fast does it happen?" can only be answered by saying, "it depends on the critter and its environment". At one end of the spectrum, you've got critters like the Rhizosolenia that have a huge population with few if any behavioral or other barriers to mixing, which probably change or speciate very gradually if at all, and at the other end you've got critters like freshwater fish that live in a constrained and possibly temporary (or at least transient) environment. These latter may speciate so rapidly that every single river or lake has its own distinct species. However, these guys may not last long - and may be indistinguishable in the fossil record. In between, you have a continuum of critters which exhibit stasis for the most part, and then rapidly speciate (or disappear, which can look like the same thing if their neighbors are still around) following some significant environmental change. My guess is that - for the most part - when someone discovers a "new" species it merely means no scientist documented it previously. After all, they're even discovering new phyla that no one ever saw before (c.f. Gnasthotomulids, discovered in the 1960's). However, there are a huge number of populations of organisms that we can observe in the wild that appear to be "captured at the moment of speciation". From Ozark collared lizards to Ensatina salamanders to Helliconid butterflies in Nicaragua. Speciation is occurring all the time - we just might not recognize it as such, since all we get to see is a brief snapshot - a freeze frame of evolution.This ought to start the ball rolling... Okay mark - your turn to tell me again I have no idea what cladists are talking about.

Wow! And we criticise creationists for not being able
to define 'kind' consistently In terms of sudden appearences in the fossil record, is that
not more likely to be concerned with the incompleteness of the
'data points'.In data processing it is known that in order to accurately
reconstruct an analogue signal from a digital version one
must sample at least twice as fast as the fastest frequency
in the signal. E.g. if sampled erratically a sine wave may
appear as a straight line with a sudden step. Doesn't mean
the change in the signal value wasn't smooth, but that we
don't have enough data points to fully reconstruct the progress.The fossil record is broadly similar to this, so sudden emergence
of species is not an accurate description of what is seen.I understand the difficulties though ...My question over 'new' species is still relevent here I think.What would be the difference between finding a species that
never existed before and one that hasn't been observed before?Until we have complete flora & fauna maps of the planet we won't
know, and can only guess (again not 100% serious, but the explanation
for 'new' finds kinda fits both ways ).It's a major problem with studying biodiversity ... unlike
physics, where there is a stated assumption that everything works
the way it has always worked ... studying biodiversity is
like studying a flowing river from a single vantage on the
bank.

Heh. Too true. The difference being that biologists are pretty comfortable with the idea that "species" is a squishy, ill-defined set of organisms - a more-or-less arbitrary classification whose borders are undefined and highly porous. Creationists, OTOH, insist that their "kinds" are immutable, constrained, and explicitly defined. Hence their inability to define what those constraints are calls into question the entire concept. Yeah, that's basically the counterargument to punk-eq. However, as I tried to point out above, the actual observations from those few organisms where we DO have nice, fine-grained, long-term series of "begats" in the fossil record (mostly with marine invertebrates, obviously) show that there's evidence for both gradual change (anagenesis) AND stasis/punk-eq. It all depends on the critters. IMO, the finer the grain in the fossil record we're able to come up with, the more weight seems to be loading on the idea that punk-eq really IS simply "faster gradualism". (Q prepares to be drawn and quartered by the dedicated PE types...) Yepper. However, I find the evidence for speciation occurring "now" to be pretty compelling. The sheer difficulty in being able to tell exactly where one species leaves off and another begins - especially when you consider things like staggered clines, species flocks, semi- and subspecies, etc - provides at least one indicator (to me, anyway), that the reason it's so difficult is that we're seeing incipient speciation occurring before our eyes. The fact that we don't really recognize it is probably due more to our limited understanding of how speciation occurs, rather than to it not occurring. When I read about the Culex pipiens vs C. molestus debate, I don't read about a dry argument over entomological taxonomy. I read it as an exciting example of exactly what we should expect to see when partial reproductive isolation arises between two divergeant populations: the moment of speciation. The fact that there are solid arguments on both sides of the Culex shows just how arbitrary is the line we draw between species. Yep. And there's the rub. Physicists deal with particles whose properties are defined - an electron will always be an electron; it's a member of a class of objects whose definition doesn't change with context. It'll always be an electron whether it's part of a wall or part of a star. A species or cline or population or... is mutable, changeable, and context-dependent. Funny that only creationists seem to have a problem separating the two...

Quetzal,OK, so how do the phylogeographical breaks occur then, if some of then aren't attributable to previous geographical barriers?Mark------------------
Occam's razor is not for shaving with.

Quetzal,

quote:

---

Yeah, that's basically the counterargument to punk-eq. However, as I tried to point out above, the actual observations from those few organisms where we DO have nice, fine-grained, long-term series of "begats" in the fossil record (mostly with marine invertebrates, obviously) show that there's evidence for both gradual change (anagenesis) AND stasis/punk-eq. It all depends on the critters. IMO, the finer the grain in the fossil record we're able to come up with, the more weight seems to be loading on the idea that punk-eq really IS simply "faster gradualism". (Q prepares to be drawn and quartered by the dedicated PE types...)

---

It seems that PE has almost zero evidential support. The problem is, in order to be evidence of PE you must be able to show three things. Cladogenesis, a relatively rapid change, & then stasis (or thereabouts). There are almost no examples of this (he says tentatively). Theres plenty of changing tempos of change, plenty of stasis, & even cladogenesis, but none where all three occur together. By contrast, that evolutionary tempo could vary anagenetically, rather than cladogenetically, has rafts of support. It does seem to me that Gould & Eldredge jumped the gun a tad, Mayr, Simpson et al. are better supported than Gould & Eldredge. Don't get me wrong, it seems theoretically sound as far as I can see, small populations, faster fixation of genes etc. But there's precious little to support it, or to be more accurate, precious little to make it stand out against dollops of evidence that the tempo of evolution is unrelated to cladogenesis. Furthermore, there's plenty of examples of morphologically identical (or nearly so), but sexually isolated populations, which seems to, if not refute, at least be unexpected by PE.Mark------------------
Occam's razor is not for shaving with.

IS it just that punk-eq and gradualism are both missing
the mark ... kind of suggesting that what has actually happened
is that evolutionary rates vary over time,species,geography,etc.
in such a baffling way that we don't really get it yet.The evidence points to evolution, but the exact step-by-step
link that creationists want to see just doesn't exist in the
first place.

Peter,

quote:

---

The evidence points to evolution, but the exact step-by-step
link that creationists want to see just doesn't exist in the
first place.

---

Where they can all, ALL, of course, show there geneaology back to Adam & Eve. Double standards.Mark------------------
Occam's razor is not for shaving with.

I probably wasn't clear. The default view, well-supported by innumerable genetic and population studies dating back to the 1930's and 40's with Dobzhansky and Muller, is that geographic separation - allopatry - is the key ingredient in the development of phylogeographic breaks (speciation). However, recently there have been a fair number of articles published that indicate whereas allopatry may still hold in the majority of cases, there are other mechanisms that can produce the same result.For example, the Irwin paper I cited before discusses how individual dispersal distance and low population size in a continuously distribted species can cause such a break. Remember that phylogenetic breaks are judged on mtDNA geneologies. The explanation makes sense when you consider how mtDNA is usually inherited. Look at it this way: two individuals are more likely to be closely related if they are geographically close to each other than if they are widely separated. However, since mtDNA is usually inherited from only one parent (i.e., there is no recombination), the geneology of an individual mtDNA lineage continuously splits. Individuals can belong to either of the two clades, but they cannot be genealogically intermediate. Under extreme conditions of low dispersal, one pair of adjacent sampling locations is likely to have individuals that belong entirely to different mtDNA clades, while other pairs of adjacent locations may have much higher relatedness.In non-continuously distributed species, hybrid genetic incompatibilities can arise in the contact zone between two adjacent populations. In addition, ecological differentiation even in closely spaced populations with low dispersal and pronounced habitat preference can lead to both behavioral and genetic isolation - incipient speciation (see, for example, Korol et al 2000, "Nonrandom mating in Drosophila melanogaster laboratory populations derived from closely adjacent ecologically contrasting slopes at Evolution Canyon", PNAS 97:12637—12642).Reproductive isolation of some type (whether physical geography or other) and time are the only requirements for the creation of even very deep phylogeographic breaks. I hope this answers your question.

I don't really disagree with you here. If you consider PE to simply be a way of describing the stasis-rapid speciation-stasis pattern observed in critters like Metrarabdotos, then there's really nothing to quibble about. I'm not a paleontologist, so I may be misinterpreting the idea, but I've always considered PE to be what ecological release would look like if we could see it in the fossil record. Since ecological release isn't the only way speciation occurs, calling PE the "only" - or even the dominant - pattern is stretching things. The fact that it isn't universal (i.e., not every lineage they examine shows the pattern), seems to me to indicate the observation is more-or-less simply a special case (or subordinate case) of neo-darwinian gradualism.

Heh. I certainly agree that there's a whole pile of stuff left to learn about speciation and evolution. And the more we figure out, the more complex and convoluted the process becomes. That's what makes it fun...I'm not sure that the exact step by step doesn't exist. There are a lot of studies - both lab and field - that show the patterns inferred for evolution hold true. The creationists simply refuse to admit it, and change the goal posts whenever they're confronted with undeniable facts. Look how the creationist mainstream has shifted in the last 25 years or so - from True YEC (tm) "evolution doesn't occur and all kinds are immutable" to microevolution within a kind is okay but no "macroevolution between kinds" is impossible. It's the old "no transitional fossil" shell game - every time some new observation is made, they change the rules to exclude the observation as "not REALLY a transitional".

Quetzal,Much clearer,Thanks,Mark------------------
Occam's razor is not for shaving with.

I'd like to continue the interesting, if off-topic, discussion of ring species that began on the Nature of Mutations thread. (See moose, even Percy does it... ).
I'll pick it up from this post by NoseyNed. There are a number (IIRC 23) of identified ring species, some global, some regional. The herring gull complex is probably the best known global ring, but there are others. For example, the tropical trumpetfish is another global ring species, with Alustomus maculatus in the West Atlantic, A. chinensis in the Indo-Pacific, and A. strigosus in the East Atlantic. The other most famous ring species is the Ensatina salamander complex in California. Wounded King's greenish warblers (Phylloscopus trochiloides) represents a continental ring in Asia. Even our very own house mouse may represent a ring species (Mus musculus in Europe, M. domesticus in Asia, M. castaneus in Southwest Asia, and a new one in Yemen). Other regional rings include the pocket mouse (Perognathus amplus and P. longimembrus) of the American southwest and west, etc.Phylogeography is a relatively new branch of biology that seeks to fuze molecular phylogeny and biogeography to explain and rationalize species distribution. It's been criticized a lot because some of its more vociferous proponents (e.g., Matt Ridley, for one), have advocated completely dumping the entire concept of species, instead substituting something they call "evolutionarily significant units" (ESUs). ESUs are basically populations or demes that can be separated by molecular (mostly mtDNA) phylogenies into distinct clades. As such, the phylogeographers tend to be firmly in the "splitter" camp. For example, they propose splitting the bushmaster (Lachesis muta) species into three, the California kingsnake (Lampropeltis zonata) into seven! distinct species (for lack of a better term), etc.I think the whole argument reinforces Percy's point in post 304 that:

Indeed!!