Interesting Evolutionary Research

There are are couple of interesting pieces of research in the news. The first concerns tail shedding in island lizards. PhysOrg has the story:

The U-M-led team decided to test the long-held predator-pressure idea using a clever combination of laboratory experiments and field measurements made in mainland Greece and multiple offshore Aegean Sea islands inhabited by different combinations of predators.
Their conclusion? The predator-pressure hypothesis, while generally true, comes with an unexpected twist: Not all predators are created equal.
“The only predators that truly matter are vipers,” said U-M vertebrate ecologist Johannes Foufopoulos, co-author of a study published online this week in the journal Evolution.

This is how the study worked:

The U-M-led team looked for correlations between autotomy rates and the presence or absence of various types of lizard predators at the study’s 10 collecting sites. The autotomy rate is a measure of the ease with which lizards shed their tails. The higher the rate, the easier the tail separates from the body.
The only strong signal that emerged from the study was the link to vipers.
The team found that viper-free islands are home to lizards that have largely lost the ability to shed their tails. Conversely, all the locations where vipers have survived are inhabited by lizards with high autotomy rates.
The study involved more than 200 insect-eating lizards from 15 species, most measuring 5 to 8 inches from snout to tail-tip.
To measure autotomy rates, the researchers combined field observations and laboratory measurements. In the field, lizards that have shed their tails and grown new ones can be distinguished from lizards that retain their original tails.
In the laboratory, researchers used calipers to gently pinch lizards’ tails with a standardized level of pressure for 15 seconds. Laboratory autotomy rates for each species were expressed as the fraction of lizards that shed their tails during this procedure.

It can be found here
The second papaer is covered by Science Daily:

This new finding is consistent with an old theory, often discounted in science textbooks, that fins and (later) limbs evolved from the gills of an extinct vertebrate, Gillis added. “A dearth of fossils prevents us from definitely concluding that fins evolved from gills. Nevertheless, this research shows that the genetic architecture of gills, fins and limbs is the same.”
The research builds on the breakthrough discovery of the fossil Tiktaalik, a “fish with legs,” by Neil Shubin and his colleagues in 2006. “This is another example of how evolution uses common developmental programs to pattern different anatomical structures,” said Shubin, who is the senior author on the PNAS paper and Professor and Associate Dean of Organismal and Evolutionary Biology at the University of Chicago. “In this case, shared developmental mechanisms pattern the skeletons of vertebrate gill arches and paired fins.”

The paper can be found here. If some one with access could send them to me I would appreciate it. My email is afarensis@scienceblogs.com

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13 Responses

  1. The lizard paper seems very interesting, too bad about the pay wall. The thing that seems counter-intuitive to me is the association with vipers since autotomy seems like it would be a poor strategy against these predators. First of all, vipers are ambush predators so I would think that most of their attacks would be so sudden that the lizard would not have time to shed their tails before the attack. I suppose that the vipers likely miss a certain proportion of the time and perhaps sometimes they get the tail. If nothing else autotomy would be a good strategy if the tail has been envenomated. Still, it seems like autotomy would work better against a pursuing bird or other lizard. It would be interesting to know about actual observations of predatory interactions between lizards and vipers to see how this would actually work.
    About the second paper, I don’t see how Tiktaalik relates to the specific problem of gills->fins. That would have had to occur in a much earlier (gnathostome?) ancestor. I suppose that it provides another example of the same sort of phenomenon but referring to it makes it seem like the transition from fins to limbs wasn’t already demonstrated by many other fossils (Ichthyostega and Acanthostega for example) or inferred long ago from fossil and recent Sarcopterigian limb/fins.

  2. Shame on you, Afarensis, for titling this post “Interesting Evolutionary Research”. Are you really so stupid that you think there is evolutionary research that isn’t interesting?
    All the boring stuff we re-classify as “ID research” (see Jerry, UD, passim).
    P.S. I’ve sent the PNAS paper.

  3. Well, no, it’s just that some is more interesting than others. I did clear the title with Darwin Orthodoxy Central…

  4. Thanks for the paper Bob…

  5. I’ve only yet read the abstract of the Tiktaalik paper (pay wall), but my immediate reaction is that there’s really no way to distinguish between a developmental mechanism inherited from a common ancestor (in this case, inherited by fin/leg from an ancestral gill structure) and a developmental mechanism recruited by a new structure. This ambiguity, AFAIK, is one of the key fallacies of the Recapitulation theory. (Or rather, the Recapitulation Procrustean bed. A theory that says ontogeny often tends to recapitulate phylogeny is a different kettle of Tiktaalik.)

  6. So I totally missed the link at the top of the post which explains how vipers select for autotomy. I gotta say though, it does seem a bit of an post-hoc just-so sort of hypothesis.

  7. I don’t have the paper yet, so I couldn’t say…

  8. The PNAS paper doesn’t actually mention Tiktaalik, but see The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb by Neil H. Shubin, Edward B. Daeschler, & Farish A. Jenkins for more information.

  9. I’ve been playing around for years with theories (speculations, actually) regarding deuterostome origins. The primary problem is in explaining the mouth with pharyngeal slits which arises as a second opening to the gut some time after the original blastopore.
    My favorite option is that the pharyngeal slits began as a set of extensions from a primitive acoelomate without a pass-through gut. These extensions may have looked like fins with slits through them, and with cilia pushing water through those slits. Oxygen could have been retrieved from the moving water, both by the ciliated cells, and by other cells close to the surface.
    I’m talking about a time before any sort of formal circulatory system, when major access to oxygen required a cell to be very close to the surface of the creature. These “slitted fins” could have served as primitive gills, except that instead of capturing oxygen for the blood (or whatever) to move through the system, they used the oxygen right there to reconstitute glucose from lactic acid. The glucose would then diffuse throughout the creature, most of whose cells would use anaerobic processes for energy, yielding lactic acid which would diffuse back to the “gills”. This is known as the Cori cycle, and is still used in vertebrates (including humans) during intense exercise and for supplying energy to cartilage cells (IIRC, I couldn’t find any ref’s with a quick search).
    The connection with the digestive tract comes in with keeping these early gill slits clean. A system of coating the skin with mucous which is slowly moved by embedded cilia is very common among many types of animals, both a defense against micropredators and parasites, and for filter feeding. It would have been easy for what started as independent “slitted fins” with a flow of mucous along an external groove into the original single gut opening to develop into a closed system with a mouth, gill slits, and a new, independent opening into the gut.
    Originally, the new gut opening would have been for transporting the protective mucous with captured micropredators and parasites into the gut, while the original opening would have been used for primary feeding, as well as expelling wastes. However, what started as a protective mechanism would have certainly been modified for primary feeding (in some lineages, at least). This probably set off a major explosion of adaptive radiation of which the chordates are a major surviving branch.
    Where the Gillis et al paper comes into it is that the original “slitted fin” may have just been the forward part of a paired fin that continued all the way back past the original opening (once both mouth and anus, now anus). In this case, the developmental mechanisms shared by by tetrapod limbs and branchial rays may well have been inherited from an ancestor that had not yet developed a second opening to the gut (pass-through gut).
    (I’ll point out that many early vertebrates appear to have had very long paired flaps which extended from behind the anus to somewhere just short of the gills. It has generally been accepted that the paired fins are derived from these, although many detailed scenarios have been proposed. My suggestion is that the gill structures (and sides of the mouth) and these paired flaps were originally serially homologous.)

  10. Our 8 fingers & 2 thumbs derive from the same source as 4 crab legs and 2 claws and squid 8 regular tentacles and 2 unusual tentacles. If fish are not ancestral to crabs and squid, then they are too late in evo development to find the source, one has to find the last common ancestor of all of the above, with gills used for both respiration and food gathering (filter feeding).

  11. @DDeden: I’m going to assume your comment was aimed at my post.

    Our 8 fingers & 2 thumbs derive from the same source as 4 crab legs and 2 claws and squid 8 regular tentacles and 2 unusual tentacles. If fish are not ancestral to crabs and squid, then they are too late in evo development to find the source, one has to find the last common ancestor of all of the above, with gills used for both respiration and food gathering (filter feeding).

    I seriously doubt it. I’d have to see some peer-reviewed ref’s before I take this idea seriously.
    OTOH, the possibility that the various paired extensions as such of all bilaterals are homologous is not inconsistent with my speculation (or the conclusions in Gillis et al). The stem bilateral was probably somewhat similar to modern acoelomate, and may well have had some sort of paired fold flaps or fin-folds whose development was controlled by some of the same genes found in tetropod limbs and chondrichthyan branchial rays. Certainly there are similar genes used in similar ways in the development of birds’ wings and flys’.
    As for gills, I’m very skeptical. Some of the ancestors of the bilaterals probably had both cilia and mucus. Whether they used them for filter feeding is another question: I strongly suspect this process could arise by convergent evolution from earlier use as a protective mechanism.
    I would date the use of mucus (and cilia to drive it) all the way back to the first divergence of Eumetazoa from sponges. A sponge whose outer skin was protected in such a fashion could survive in much more hostile environments (micropredator and parasitewise) than one without. Most sponge lineages include members that posses multi-nucleated amoeboid cells, which could be used to deal with anything trapped in protective mucus. The first gastric invaginations might well have developed as redoubts for such, again with most of the feeding going on in the old way, using choanoflagelli. (Note that the process used with food captured by choanoflagelli is the same one used by amoeboid cells, whether mono- or multi-neucleated.)

  12. The evidence is not that fins and limbs evolved from gills but that similar genetic pathways are involved in paired appendages and gill rays. The paper mentions too that shared developmental gene expression exists between paired appendages and unpaired median fins, found earlier by another groep. The evidence therefore seems to be that a particulare gene expression patterns is found in all types of appendage.
    As to gill to limb, paired appendages are pectoral fins, pelvic fins and anal fins: last two from gills too? And an unpaired median fin from gills?
    In other words, the question is: hyped?

  13. @Gerdien de Jong:
    It’s generally thought that the paired fins of fish evolved from a single fin-fold or flap-fold that ran from somewhere just back of the gills to the area of the anus. It seems likely that the developmental gene expression pattern was present in this fin-fold, and carried over to all the paired appendages that evolved from it.
    Nothing in the paper(s) referenced suggests any question of this theory, so I suppose we can assume that the authors accept it.
    AFAIK all living fish have two sets of such paired fins, but there was at least one early lineage that had a number of them. For steering the body while swimming with an undulating mechanism, two pairs (front and back) would seem to be more efficient than a whole bunch, which may be why the lineage(s) with more than two became extinct.

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