a delicious anomoly

Somebody's lame (but oh-so-comfy) shoes and socks

What is your reproductive strategy? Are you the jerk with the popped collar who hits on every girl ever, knowing that with an increased sample size comes increased odds of taking one home? Maybe you’re the sassy lady who dresses to the nines to increase visibility of your secondary sexual characteristics (sexual traits other than the obvious one- like boobs). Maybe you have good intentions to be attractive but find yourself wearing “active casual shoes” with striped socks and high-water jeans to work and wonder what happened to your self respect.

Well, let me just go ahead and answer the question for you. You, PUNY HUMAN, have an iteroparous reproductive strategy.

Iteroparity and semelparity are the two main approaches life can take to reproduction. Semelparous organisms are usually short-lived and “put all their eggs in one basket,” if you will. They pool all their bodily resources into a single reproductive event and then die. Think about those clouds of gnats that buzz around in your yard during the summer. Those little gnats are just a few days old and are already having a giant orgy. After their thousands of eggs are fertilized and laid, the bugs’ tiny bodies are so exhausted and depleted that they die. Then just days later, their offspring emerge and the cycle starts again. This is semelparity.

Iteroparity (latin for “to beget repetitively”) is characterized by multiple reproductive events before death- ones that usually occur over a much longer time span. Almost all vertebrates are iterparous and invest only part of their physical resources towards gravidity, allowing them to live past each reproductive event and have future ones. Subsequently, iteroparous organisms have longer lifespans and experience more growth.

Of course, each strategy has its pros and cons. Semelparous events are usually so large that a single gnat will have more offspring in a single event than you, as an iterparious critter, ever will. Iterparous organisms generally live longer, experience more parental care, and grow larger; therefore they have increased fitness and odds of surviving the elements (gnat vs. human in high winds or something of the like).

I’ve been living in Alaska for a few months now and have become well acquainted with one of the foremost exceptions to the semelparity/iteroparity trends. The Pacific Salmon is a relatively large vertebrate with a fascinating reproductive cycle. First off, a little salmonlet hatches in a freshwater stream. The newborns hang around in their stream anywhere from a few months to a few years, depending on the species. During this time, 90% of them will die. When they have grown into little silver fishies, they swim down the streams and into the salty ocean, where they will spend up to five years swimming around and eating. During this time, they grow in size and sequester the nutrients that the ocean has to offer. After five or so years, it is time to do the hanky panky.

These incredible fish find their way back to the same spot on the shore from which they emerged as little tiny salmon years ago, with their destination being the original stream in which they were hatched. There, females lay eggs and males fertilize them and are responsible for defending the nests. Their bodies, ravaged from the long journey from the ocean and reproduction are physiologically spent. At this point, the fish begin to die.

When this sexy journey begins, the physiology of the fish changes into reproductive mode. This means they completely quit eating, and their bodies begin to consume reserves and tissue for energy. Some species undergo a color change- males becoming bright red to attract the lay-des, and their mouths changing so dramatically as to become hooked with a ferocious set of teeth. Aside from their bodies being energetically depleted, this new morphology is completely unsuitable for life in back the ocean. Any way you slice it, it is the end of the road for these fish.

Top: Sockeye salmon before reproductive journey
Bottom: Sockeye salmon during reproductive jounrey
(adfg.alaska.gov)

And there you have it- a single reproductive event before death. Semelparity. But in a vertebrate that devotes five years and hundreds of miles to becoming a 4 pound hunk of impressive fish! It is an anomaly. But it is a successful enough strategy to cause the yearly Pacific Salmon runs to be stable, repetitive, and critical cornerstones of coastal ecosystems of the great Northwest.

It seems as though the odds are stacked against these guys. They must overcome so many treacherous obstacles- not being eaten as an egg and surviving larval-hood, dodging the hungry predators of their natal streams, enduring 5 years in the perilous ocean, and then making the arduous journey back (without being caught by a bear or fly fisherman). But nonetheless, it works. Millions of years of natural selection and random chance have whittled what we see as statistically unlikely into a highly refined, highly adapted system.

AND, they taste really good. Especially when fresh. And with butter.