Salmon and Industrial Selection

Thursday

A few days ago in Longevity and Selection I developed the theme of the selective effect of industrialized society on human beings — call it industrial selection, if you will — and suggested in passing that other species closely related to our own would come under similar selection pressures. I had in mind economically significant species, but I did not at that time think of salmon. I was thus interested to see an illustration of the industrial selection of Columbia River salmon was on the front page of today’s Oregonian.

It has been suggested that salmon are evolving such that certain species may accommodate the dams that regularly interrupt the flow of the Columbia to the Pacific Ocean. Of course, nothing definitive can be proved in both the (biologically) short period of time that dams have been in the Columbia River or the even shorter period of time during which salmon have been scientifically studied and their populations documented. Recent research reported in today’s Oregonian, however, suggests that those reservoir-type fall chinook salmon that are delaying migration downstream to the ocean until they are a year older and a year larger are surviving and thus reproducing in numbers disproportionate to those salmon that continue to follow the established life cycle of migrating to ocean waters in the first year of life. The larger, older fish are more robust and therefore more readily survive the rigors of the dam passage. It is insufficiently appreciated how often that an adaptation comes about as a result of a behavioral mutation rather than a structural mutation in the body of an organism.

The Columbia River is one of the largest rivers in North America. I have lived near the Columbia my entire life, so it seems like an ordinary river to me, but subsequently seeing other rivers elsewhere in the world I came to an appreciation of the magnitude of the Columbia. The Columbia is also one of the most industrialized rivers in the world. Not only is it interrupted by a series of dams, but the uppermost watershed of the Columbia hosts of the Handford Nuclear Reservation, which produced the plutonium for the first atomic bombs. Agriculture throughout the region has also contributed its contaminants to the river. Thus we are not talking about a pristine river system.

The Industrialized Columbia is something of a petri dish for industrial selection, and it would not surprise me at all to see the adaptation of some species indigenous to the Columbia River to the conditions of industrialization. While strong selection pressures will likely bring about the extinction of many species, some few species will make a transition parallel to the transition of the environment in which they find themselves. Previously in the natural history of earth, environmental changes in habitats like freshwater lotic biomes (i.e., rivers) had natural causes. Now environmental changes can come about anthropogenically. Regardless of the genesis of the change, however, the same principle of descent with modification holds good in all cases.

A selection event is usually not a pretty sight. The selection event that ended the dominance of the dinosaurs, for example, came in the form of a mass extinction event, and the history of life on earth has been punctuated by repeated mass extinction events. A species under environmental pressure, subject to strong selection forces, may adapt or it may become extinct. If a given species under selection pressure does not become extinct simpliciter, it may experience adaptive radiation so that no successor species is identical to its predecessor species, but the genetic heritage of the predecessor species lives on in the successor species.

The preservation of genetic heritage in successor species is one of the quantitative measures of biological success that I proposed in Quantifying Biological Success. Extinction, thus, is not always the absolute that it is usually assumed to be. extinction is only the end of the line for genetic material when no successor species incorporates this material into itself. And certainly this does happen with alarming frequency, but it also happens that some species become extinct because they are succeeded by progeny that are its adaptive radiation.

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