The Greatest Show from Darwin to Dawkins. 9-guppie

9. Experiments with guppies

With each new example, it seems that the task is much more difficult than it was supposed at the beginning of the journey. It is foolish to think that biology is not higher mathematics, and proving a theory is a trivial matter.
But we are not used to retreating. Maybe the next example will be easier than the previous ones, and it will finally be possible to put a winning point.
So, the example is again taken from the same book and concerns the research of Dr. John Endler, author of "Natural Selection in the Wild." Endler studied wild guppies (Poecilia reticulata) and noticed that the local populations were strikingly different from each other.

According to Endler's observations conducted in Venezuela and Trinidad, in reservoirs with a large number of predators, the guppies were less bright than in streams with weak predator activity, where male guppies were noticeably brighter colored, with large garish spots, and a large number of them. According to the author, "here the males could evolve a bright color more freely in order to please the females."

As proof of his assumptions, Endler conducted the following experiment with guppy. In his own greenhouse, he arranged ten reservoirs, overlaying five of them with large gravel, and the other five — a smaller, sandy one.
Released into all reservoirs, guppies were allowed to breed freely for six months without predators. Then Endler placed one "dangerous predator" in two reservoirs with large gravel and two reservoirs with small gravel, six "weak predators" in each of two reservoirs with large gravel and two reservoirs with small gravel, and left the remaining two reservoirs without predators.
"And what are the results? Dawkins asks. And he answers himself: - They were exciting, even after such a short time."

Before the "dangerous predators" were launched in the first four reservoirs, the spotting increased noticeably, and with their appearance fell sharply. In all other reservoirs, spotting continued to increase.

"In the presence of predators, no matter weak or strong, coarse gravel contributed to the appearance of relatively large spots, while fine gravel favored relatively small spots. This can easily be interpreted as an imitation of the size of the spots of the size of the stones.

Admirably, however, in reservoirs where there were no predators at all, Endler found exactly the opposite situation. Fine gravel contributed to the appearance of large spots on male guppies, and coarse gravel favored small spots."
Everything seems to be simple and clear. In the presence of predators, there is a tendency to natural selection of guppies with a color that merges with the bottom, and in reservoirs free of predators to color guppies in a different color from the background.

But this is only at first glance. If you look more broadly, there are two trends here: adaptation for survival and the desire for visibility, uniqueness.
Let's ask ourselves: what is evolution? Isn't its essence the search for new forms and overcoming the usual framework? Is the appearance of each new species a challenge to the species from which it evolved?
Any new look is a challenge to the surrounding background, a breakthrough from the familiar to the new and unusual. In fact, evolution is a search for something new.

Of course, coloring guppies in a different color from each other is not a significant evolutionary leap. However, there is a tendency to intraspecific difference.

Please note that this process was observed only in reservoirs free of predators. Where guppies had to survive, their coloring tended to merge not only with the background, but also with each other.

It turns out that the presence of a survival factor in this case led to uniformity, and the absence of such led to diversity. It can be said that, at least in this example, predatory selection was a stabilizing factor rather than an evolutionary one.

However, Endler was not satisfied with this. From a natural stream containing dangerous predators and in which male guppies were almost inconspicuous, he transplanted guppies of both sexes into a tributary of the same stream, where there were no guppies or dangerous predators before, but the small predator rivulus Harti lived.

After two years without one month, the male guppies acquired a brighter color "without a doubt, pushed by the females and walking freely along this path in the absence of dangerous predators."

Nine years later, it was discovered that the males were even more brightly colored. Here 's what Dockins reports about it:
"Differences in color are just the tip of the iceberg.
Guppies from streams with low predation reach sexual maturity later than guppies from streams with high predation, and they are larger when they reach adulthood; they produce young less frequently; and their broods have smaller numbers, and the fry themselves are larger.

When Resnick examined the descendants of Endler's guppy, his results were almost too good to be true... the evolutionary changes witnessed by Endler and Resnick, driven solely by natural selection (actually, including sexual selection), raced forward at a speed comparable to the achievements of artificial selection of domestic animals.

This is an exciting example of evolution right before our eyes."
Well, if such an authority as Professor Dawkins says that this is an example of evolution, then we will not argue.

Summarizing all the information given to them, we will see the following. In the absence of predators, there is a sharp spike in spotting, in the presence of a "weak predator" there is almost the same spike, but the size of the spots contributes to camouflage. And in those reservoirs in which "strong predators" were settled, the changes were suppressed.

There are also changes in the size, frequency of childbirth and the number of young animals in a reservoir with a "weak predator". Most likely, in a reservoir without predators, the results were even more noticeable.

If we are told about evolutionary changes, what should we look at? Of course, for the participation of natural selection in them. If natural selection influenced evolutionary changes, then the theory works.

Without a doubt, natural selection helped our poor guppies to disguise themselves in reservoirs with predators. However, in reservoirs where predators were completely absent or their influence was not so significant, the changes were much more significant.

It turns out that, at least in this particular example, such an important factor of natural selection as the pressure of a "strong predator" led to less changes, while significantly less predatory pressure or its complete absence led to such serious changes that Dockins himself called them evolutionary.
If not predators, then what instrument of natural selection influenced the evolution of guppies?

In the process of natural selection, mutations are fixed that increase the fitness of organisms to their environment. If the evolutionary changes took place in the absence of predators or their weak presence, then how did the guppies compete with each other in the struggle for survival?

Dockins tells us that the reason that evolutionary changes were rushing forward was "exclusively natural selection (actually, including sexual selection)."
Forgive me, Dockins, but there was a problem with sexual selection. Every slightly trained aquarist knows that a guppy is a harem fish, and, therefore, it is very unlikely that females could somehow influence the selection of males.
Well, there remains one more, but perhaps the most important factor of survival, which, from the point of view of theory, is able to influence evolutionary changes.

Competition for food resources! Unfortunately, our primary source did not leave any information about the abundance or lack of food. Most likely, a serious scientist like John Endler would have reported any significant factors that could affect evolution.

As a result, we should have put the final point, because in a visual experiment with guppies, it was clearly shown that evolutionary changes take place in conditions of fierce competition. However, at the same time, we are forced to state that in the absence of natural selection factors, "the evolutionary changes witnessed by Endler and Resnick ... are rushing forward at a speed comparable to the achievements in the artificial selection of domestic animals."
And it turns out that it's too early to put a point.

* - I apologizes for my English. I would be grateful for the corrections.

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