The stickleback: evidence of evolution?

Photo by sam2cents, flickr.com

by David Catchpoole

“One of the most compelling case studies of evolution” is how one leading biologist labelled the stickleback fish (Gasterosteus spp.).¹ A Science journal writer termed it a “star” of evolutionary research.² Another science reporter went even further, dubbing it as a “superstar of evolutionary science”, adding that “Sticklebacks are so central to the new wave of evolutionary research that they may well eclipse Darwin’s finches in importance and earn the honorary title of ‘Darwin’s finches’.”³

Not to be outdone in this anniversary “Year of Darwin”, Nature journal has honoured the stickleback as one of “15 Evolutionary Gems”.⁴

But on what evidence do they base these grandiose claims?

Differences between saltwater and freshwater sticklebacks

Threespine sticklebacks can be found in oceans and coastal rivers and streams in north America, Japan and northern Asia and Europe.

The oceangoing sticklebacks spend most of their adult life in the sea, returning to freshwater to breed.⁵

The saltwater form is morphologically similar all around the Northern Hemisphere, with adults typically between 6–10 cm (2–4 in.) in length, with long dorsal and pelvic spines. Lacking scales, their bodies are covered by as many as 36 armour plates covering their sides⁶ —believed to protect sticklebacks against predatory fish. Certainly the spines seem to serve that purpose, because when a larger fish tries to eat a marine stickleback, the stickleback defends itself by extending the spines on its back and pelvis.

In contrast to the saltwater form, freshwater populations are extremely morphologically diverse, with great variation between sticklebacks from different streams or lakes.⁷ They also have generally shorter dorsal and pelvic spines and substantially fewer armour plates (normally 12 or less) than their marine counterparts. In fact, many freshwater sticklebacks have no pelvic spines or armour plates at all.

These differences between saltwater and freshwater forms of the stickleback are paraded as evidence of evolution, i.e. the marine form “evolved” into the freshwater form over evolutionary timescales:

“Sticklebacks were once a solely saltwater species that migrated from the sea to streams and lakes to breed; as the glaciers retreated up to 22,000 years ago, some settled in lakes. Although they evolved to look very different from their ancestors, they often came to resemble their counterparts who were evolving in a similar way in lakes that are geographically distant.”^2,8

It is certainly not unreasonable to conclude that the freshwater stickleback is descended from the saltwater form. After all, ocean-going sticklebacks migrate up streams to inland freshwater lakes to spawn, both freshwater and saltwater populations can interbreed, and, as we shall see, recent observations certainly support this. But are the changes in stickleback morphology really evolutionary? Is the stickleback’s “disappearing armour” truly evidence for the capacity of fish to have gradually evolved into philosophers over supposed hundreds of millions of years?

Somewhat ironically, thanks to evolutionary scientists’ eagerly directing their attention to the stickleback and various freshwater lakes as “natural laboratories for evolutionary studies”, these questions have been answered—by evolutionists themselves. As we shall see, stickleback changes have been acknowledged as not only providing no support for molecules-to-man evolution, but have also upset the “slow-and-gradual” long-age evolutionary mindset.

Recolonization of a freshwater lake by ocean sticklebacks, and subsequent adaptation

Loberg Lake is a small (~4.5 hectares) lake in Southern Alaska. In 1982 the Alaska Department of Fish and Game poisoned all the fish in Loberg Lake to improve the lake for recreational fishing (i.e. as preparation for restocking the lake with salmon and trout). Thus Loberg’s native freshwater stickleback population was exterminated.

However, eight years later, researchers sampling Lake Loberg found that the sticklebacks were back. But these new sticklebacks were strikingly different from the pre-1982 population, as they were heavily armoured, like ocean-going sticklebacks. The researchers surmised, quite reasonably, that saltwater sticklebacks had made their way upstream from Cook Inlet and colonized Lake Loberg sometime between 1983 and 1989.⁹

In the years since 1990, however, annual sampling of the lake’s sticklebacks revealed a progressive reduction in body armour. In 1990, fully-plated sticklebacks made up 96% of the population, but just three years later, only 39% had the full suite of bony body plates.¹⁰ Individuals with only the front plates first appeared in 1991, but by 2001 their numbers had increased to 75%.

Thus after just a few generations (sticklebacks take 1–3 years to reach maturity), the sticklebacks in Lake Loberg increasingly resembled the pre-1982 native stickleback population, and their freshwater counterparts in other Alaskan lakes and streams. So what had driven this rapid reduction of armour plating and pelvic spines?

Natural selection at work

Looking past the hype of researchers’ claims that this is “rapid evolution”,⁹ it is in fact a classic example of “strong natural selection acting on variation that was carried by the anadromous¹¹ fish that colonized the lake”.⁹ Notice that natural selection acted on existing variation in the colonizing stickleback population. In other words, the so-called “rapid evolution” did not result in the addition of any new features but rather the reduction or even complete loss of existing features—bony plates and pelvic spines.

The researchers have made several reasonable suggestions as to why the selection pressure should be so strong, i.e. favouring the fast loss of spines and plates in freshwater habitat:

• As a trade-off for the bulky armour, sticklebacks likely gain in speed and agility, so as lakes typically have places to hide, the fish can escape from any larger predators lurking, assuming the sticklebacks can dart into ‘hiding holes’ quickly enough.²
• As many lakes lack the large predatory fish typical of ocean waters, the selection pressure for armour no longer applies, hence fish lacking pelvic spines and/or with less bony plate covering survive. Also, because fresh water lacks the rich calcium reserves of sea water, bony armour could be “too costly to make”.² Supporting this, biologists have documented that sticklebacks with reduced armour are significantly larger in size. One of the researchers explained, “If the fish aren’t expending resources growing bones—which may be significantly more difficult in fresh water due to its lack of ions—they can devote more energy to increasing biomass. This in turn allows them to breed earlier and improves over-winter survival rate.”¹²

• On the lake bottom, in the absence of a threat from larger predators, pelvic spines not only lose their defensive value, but turn out to be a handicap when dragonfly larvae and other bottom-dwelling predator larvae are present. University of Utah biologist Michael Shapiro explained, “[D]ragonfly larvae can grab sticklebacks by the [belly] spines, reel them in and eat them. They wait for sticklebacks to swim by and grab them.”^13,14

A decline in armour in stickleback populations has also been reported in other freshwater locations.

For example, when researchers relocated 200 marine sticklebacks to freshwater ponds on the University of British Columbia’s Vancouver campus, they soon observed in the offspring that “natural selection favours reduced armour in freshwater”.¹² From that and other studies, geneticists have now identified that a mutated genetic switch is responsible for the loss of armour. Specifically, it affects expression of the Pitx gene. In the pelvic region, the corrupted genetic switch prevents spines forming in that area. Elsewhere, it can affect “a whole suite of bony characters”² not just the external bony plates but also jaw shape and bones associated with protecting the gills.

Hence this now gives us a better understanding of genetic factors undergirding the great morphological variation in freshwater sticklebacks,⁷ even such differences as jaw shape, upon which natural selection can act. (Note that studies have found that the genetic basis for low-platedness is present in populations of ocean-going sticklebacks, albeit at low frequencies.)¹⁵

Note that at root here is brokenness or corruption—right in line with the Bible’s account of the Creation being corrupted, in “bondage to decay” (Romans 8:19–22). It is certainly no support for fish-to-philosopher evolution, as there is no new genetic information here, rather the mutated (i.e. broken) genetic switch simply prevents expression of a gene.

That is in no way evolution but rather devolution—see The evolution train’s a-comin (Sorry, a-goin’—in the wrong direction) and Mutations: evolution’s engine becomes evolution’s end! Even leading evolutionary proponent Jerry Coyne (University of Chicago) has candidly admitted as much: “these examples represent the loss of traits, rather than the origin of evolutionary novelties.”¹⁶

Despite Coyne and other evolutionists recognizing this, they are not backing away from their belief in evolution. Prominent evolutionist Sean Carroll (with two colleagues), writing in Scientific American of the stickleback’s disappearing pelvic spine under the heading “A Beneficial Loss” (emphasis added), nevertheless claims it “offers another vivid example of adaptation through the evolution of a gene-regulating enhancer sequence.”¹⁷

Similar pro-evolution “spin” on the pelvic spine loss comes from Neil Shubin and Randall Dahn, writing in Nature: “Surprisingly, some of the most significant novelties in the history of life are associated not with the evolution of new structures but with the loss or reduction of primitive ones.”¹⁸ Incredibly, they (and other evolutionists)^17,19 refer to the stickback’s pelvic spine as being a limb, and therefore the observed “limb reduction” in freshwater stickleback populations can be equated with “hindlimb loss” in whales and manatees!²⁰ (Whales and manatees, aquatic mammals, are presumed over tens of millions of years of supposed earth history to have evolved from terrestrial quadrupeds. However, as we have written previously (see, e.g., Not at all like a whale), such creative storytelling (with, of necessity, it’s ever-changing storyline to fit each new discovery of contradicting evidence) is completely without credible foundation.)

“Slow-and-gradual” notions debunked

An article in Science journal explained, “Since the 1930s, the prevailing view has been that evolution moves in a slow shuffle, advancing in small increments, propelled by numerous, minor genetic changes.”² However, by evolutionists’ own admission, the stickleback findings represent a challenge to that view.

As we’ve seen, dramatic changes in the fish’s bony armour were traced to an already-existing corrupted form of just one gene switch. The article in Science conceded, “from an evolutionary perspective, this gene may change at lightning speeds.”² While evolutionists are describing this as “rapid evolution”, the reality, in their own words, is simply that “natural selection had taken its toll on the armored fish in just a few years”.²

As The Scientist put it, “when these marine fish move to a new freshwater environment, the low-plated phenotype has a selective advantage, and the low-plated fish can appear quickly through natural selection at a higher frequency of the preexisting genetic change.”²¹ (Emphasis added.)

Of course, this is right in line with a biblical perspective. (See Brisk biters—fast changes in mosquitoes astonish evolutionists, but delight creationists.) It’s most certainly not “rapid evolution” at work as there is nowhere in evidence any sort of processes that might have been able to change pond scum into people over billions of years. Rather, it is just natural selection operating on existing genetic information, acting to favour a corrupted gene switch,²² which thus becomes predominant in the stickleback population after just a few generations. Such rapid changes within the stickleback ought be no surprise.

Rapid reversal, too! (and it’s not evolution, either)

Despite the lessons evolutionary researchers learned from having observed rapid changes in saltwater sticklebacks colonizing freshwater lakes, they were in for another stickleback surprise. The ScienceDaily headline summed it up, “Rapid, dramatic ‘reverse evolution’ documented in tiny fish species”. The article went on to explain that “Evolution is supposed to inch forward over eons,” but in Lake Washington (near Seattle), stickleback researchers had observed that “the process can go in relative warp-speed reverse”.²³ (Emphasis added.)

Other reports used similar language. “While evolution is usually expected to creep along over eons, the stickleback has managed to evolve in full-speed reverse … ”, explained a newspaper article, citing it as “a rare example of animal reverting to an earlier evolutionary version to survive a rapid change in its environment.”²⁴ That report quoted one researcher as saying, “It was very surprising.”

So what actually happened? Five decades ago, when Lake Washington was so polluted that visibility was limited to about 75 cm (30 inches), only about 6% of the lake’s sticklebacks were fully plated (like the saltwater form)—the remainder having little or no armour. But since a pollution cleanup operation began in the mid-1960s, the researchers, “to their surprise”,²⁴ recorded that the proportion of fully-plated sticklebacks (i.e. from snout-to-tail) has increased to about 49% today, with an additional 35% having at least half of their bodies shielded in bony armour.

The researchers surmise that prior to the cleanup, the murky water provided sticklebacks with “an opaque blanket of security” against their primary predator in Lake Washington, cutthroat trout, so armour plating was of little advantage. But as visibility improved—by the early 1970s it was up to 3 metres (10 ft); today water clarity is approaching 7.5 metres (25 ft)—low-armour sticklebacks became more vulnerable to the cutthroat trout that suddenly could now see, and eat, them.

Of course, this has nothing to do with microbes-to-man evolution, ‘reverse’ or otherwise. It is simply yet another example of natural selection operating on existing genetic information—note that just prior to the cleanup, a small proportion (6%) of the stickleback population were fully-plated. With increased water transparency, there was now a stronger selection pressure against low-plating, and so natural selection favoured fish with more armour. In the researchers’ own words summing up their paper in Current Biology (when we look past their claims of “reverse evolution” and “rapid evolution”), we see natural selection for sure, but no evidence of any new genetic information of the sort needed to turn sticklebacks into scientists, whether over a short time or long:

“On the basis of our genetic studies and simulations, we propose that the most likely cause of reverse evolution is increased selection for the completely plated morph, which we suggest could result from higher levels of trout predation after a sudden increase in water transparency during the early 1970s. Rapid evolution was facilitated by the existence of standing allelic variation in Ectodysplasin (Eda), the gene that underlies the major plate-morph locus. The Lake Washington stickleback thus provides a novel example of reverse evolution, which is probably caused by a change in allele frequency at the major plate locus in response to a changing predation regime.”²⁵ (Emphasis added.)

This is not the first time that evolutionists have tried to claim shifting gene frequencies in a population as evidence for molecules-to-man evolution—see Goodbye, peppered moths and Don’t fall for the bait and switch. At the end of five decades of supposed “rapid, reverse evolution”, Lake Washington’s stickleback population is still a population of sticklebacks. No evolution has taken place.

Stickleback speciation is not evolution

As mentioned at the start of this article, Nature journal has this year decreed the stickleback to be one of “15 Evolutionary Gems”. (There were five “Gems from the Fossil Record”, four “Gems from Molecular Processes” with the stickleback being one of six “Gems from Habitats”; specifically tagged: “Natural selection in speciation”.)⁴ The journal cited its own 2004 paper by the University of Wisconsin’s Jeffrey McKinnon and his colleagues reporting that reproductive isolation in sticklebacks “can evolve as a by-product of selection on body size”.²⁶

Put simply, the basis for the claim that this is evidence of evolution can be summed up as follows:

1. Individual sticklebacks tend to mate with individuals like themselves, i.e. of similar size and occupying similar ecological niche.²⁷ E.g. the long and heavy-bodied benthic form (feeds on invertebrates at the lake bottom; has a relatively horizontal jaw and small eyes) usually prefers not to mate with the shorter, slimmer limnetic form (sticklebacks that live in the surface waters of lakes, feeding on plankton; they can have an upturned jaw and large eyes). Thus the different forms can be said to be reproductively isolated.
2. Having demonstrated that forms with distinctively different physical features are also reproductively isolated from each other, biologists can declare the different forms to be different species, i.e. there has been speciation.
3. Speciation is evidence of evolution.

The argument that speciation is evidence of evolution has been thoroughly rebutted in our earlier publications—see e.g. Chapter 4 of Refuting Evolution II. Rapid speciation is no surprise from a biblical perspective—see Speedy Species Surprise. In short, species are subsets of the originally created kinds, as can be readily seen by examples of inter-species hybridization (see, e.g. Ligers and wholphins? What next?)

In sticklebacks, although the benthic and limnetic forms in the wild are reproductively isolated, and therefore can technically be declared to be separate species, they can still mate with each other. E.g. benthic and limnetic sticklebacks in Lake Enos on Vancouver Island are now known to be interbreeding and are no longer two distinct species.²⁸ And of course, as already mentioned, freshwater sticklebacks can be readily crossed with ocean-going sticklebacks—in fact, it was through careful observation of such crosses that the Pitx gene was identified.

Conclusion

The stickleback provides us with great examples of natural selection, mutations, rapid adaptation and speciation. Claims that these are evidence for evolution are completely without foundation. The observed changes in stickleback populations today are in no way the sorts of changes needed to have changed fish into philosophers—ever.

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