From “Landlubber’ Fish Leap for Love When Tide Is Right: Research Sheds Light On How Animal Life First Evolved to Colonize Land” (ScienceDaily, Aug. 31, 2011), we learn: about the “leaping blenny,” a marine fish that spends almost all its time on land (yes) around intertidal pools. To breath through its gills and skin, it need only stay moist, not submerged.
“Our study showed that life on land for a marine fish is heavily dependent on tide and temperature fluctuations, so much so that almost all activity is restricted to a brief period at mid-tide, the timing of which changes daily. During our field study on Guam we never saw one voluntary return to water. Indeed, they spend much of their time actively avoiding submersion by incoming waves, even when we tried to capture them for study.
So they actually have an aversion to water – thus are free from any temptation to return to the sea. That last part is illuminating, because in a real-world account of evolution, one must address the fact that most marine creatures would probably just chuck the new, terrestrial way of life when difficulties arose, and return to the old one – to which they are well adapted.
“I can tell you they are very hard to catch and are extremely agile on land. They move quickly over complex rocky surfaces using a unique tail-twisting behaviour combined with expanded pectoral and tail fins that let them cling to almost any firm surface. To reach higher ground in a hurry, they can also twist their bodies and flick their tails to leap many times their own body length.”
Not only do they not like water, in other words, but they get on fine on land.
“The Pacific leaping blenny offers a unique opportunity to discover in a living animal how a water-land transition has taken place,” says Dr Ord.
”We know that our ancient ancestors evolved originally from lobe-finned fish but, today, all such fish are fully aquatic. Within the blenny family, however, are species that are either highly terrestrial, amphibious or entirely aquatic. Remarkably, representatives of all these types can be found on or around Guam, making it a unique evolutionary laboratory.”
Not really the answer to a transition to land. The conundrum for that transition involves the development of lungs, for example – which the blennie never did. As a result, the fish is committed to a tidal pools environment, and is not really a model for true terrestrial life.
The blennie demonstrates that it loves water as much as the average house cat does:
See also: Lobbing a grenade into the tetrapod evolution picture
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This reminds me of this cartoon:
notes;
“Waiting for a beneficial mutation” indicates a huge misunderstanding of evolution.
Individuals are already biologically competent. They are not waiting for anything. Some alleles become more frequent in a population due to drift or due to conferring advantage. That’s pretty much it.
We know by observation of alleles that there are many functionally equivalent or nearly equivalent sequences. Otherwise there would be no genetic diversity. Every individual would be a clone of every other individual.
We also know from direct observation of bacterial populations that they manage to thrive despite so-called genetic entropy. We can calculate the average number of mutations per generation and note that populations do not die out from entropy, despite accumulating changes.
Axe published the following:
Proc. Natl. Acad. Sci. USA
Vol. 93, pp. 5590-5594, May 1996
Active barnase variants with completely random
hydrophobic cores
“ABSTRACT The central structural feature of natural
proteins is a tightly packed and highly ordered hydrophobic
core. If some measure of exquisite, native-like core packing is necessary for enzymatic function, this would constitute a
significant obstacle to the development of novel enzymes,
either by design or by natural or experimental evolution. To
test the minimum requirements for a core to provide sufficient structural integrity for enzymatic activity, we have produced mutants of the ribonuclease barnase in which 12 of the 13 core residues have together been randomly replaced by hydrophobic alternatives. Using a sensitive biological screen, we find that a strikingly high proportion of these mutants (23%) retain enzymatic activity in vivo. Further substitution at the 13th core position shows that a similar proportion of completely random hydrophobic cores supports enzyme function.
Of the active mutants produced, several have no wild-type core residues. These results imply that hydrophobicity is nearly a sufficient criterion for the construction of a functional core and, in conjunction with previous studies, that refinement of a crudely functional core entails more stringent sequence constraints than does the initial attainment of crude core function. Since attainment of crude function is the critical initial step in evolutionary innovation, the relatively scant requirements contributed by the hydrophobic core would greatly reduce the initial hurdle on the evolutionary pathway to novel enzymes. Similarly, experimental development of novel functional proteins might be simplified by limiting core design to mere specification of hydrophobicity and using iterative mutation-selection to optimize core structure.”
Here’s Douglas Axe’s latest on the subject: