Posts Tagged ‘Extentded Phenotype’

The Cuckoo and the Trout.

August 31, 2013

The Cuckoo Head

I have recently been reading “The Selfish Gene” by Richard Dawkins, a fascinating look at the way genes control us and every other living thing for that matter. But one portion of the book fascinated me in particular, a discussion on Cuckoo’s and their foster parents. As no doubt we all know Cuckoo’s lay their eggs in the nests of other species and then let the hapless birds work day and night to feed their babies. It can get a little macabre, the baby cuckoo will turf the other eggs or baby birds out of the nest so that it gets all the attention and more to the point all of the food. Frequently the cuckoo fledgling is huge compared to its hapless adoptive mater and pater who work tirelessly to feed their grossly oversized intruder; they may even need to stand on the baby to be able to reach its mouth to feed it.

The Selfish Gene Cover

The question that interested me in particular was “why don’t the hijacked foster parents notice the fraud and simply stop feeding the baby cuckoo?” Apparently the bright red gape of the begging bird is a stimulus to the parents, an almost irresistible urge to put food into the open mouth. The larger than average and brighter coloured gape of the baby cuckoo is essentially a “super stimulus”.

It appears that the trigger is so strong that even other birds have been known to “stop by on the way home and feed the cuckoo” giving away hard won food that was destined for their own offspring.

CatchadragonOne would logically think that the fraud would be obvious.

Another interesting if somewhat more risqué example is the fact that simple images can stimulate sexual response in people. That one knows that you are looking at an airbrushed and two dimensional image of a man or woman that you will never meet and who quite evidently isn’t available to you, the mating response can still be switched on.  It doesn’t seem to matter that the subject is well aware that it is a fiction.

It seems that there are key triggers in nature, stimuli which are so powerful that they become, according to Dawkins, near addictive in their allure and that got me to wondering, are there such key triggers in feeding behaviour too? In particular are there such triggers in terms of the feeding behaviour of trout?

To my mind the art of fly tying is about caricature, there are those who will say “this is what the trout think” or “this is what the trout see”, actually I don’t have a damned idea what trout think or see but I do figure that, as anglers we cannot possibly actually imitate an insect, we can only represent it in some recognisable form. So we pick on key indicators, essential elements of real insects which we believe are representative.

Perhaps this is the key to why fish don’t seem to be overly bothered by the hook, after all, much like the oversized cuckoo, the hook sticking out of the rear of your delicately fashioned fraud should be a dead giveaway, but thousands if not millions of captured fish seem to show that it matters not a jot.

Trout and FlyDecision time.

I suspect then that if key triggers can be imitated or emphasised they can “overpower” what one might imagine to be an obvious flaw in the design.

Put simply then if a dragon fly nymph imitation is the same shape as the real thing, moves much like the real thing, is the colour of the real thing then the fact that it has a hook sticking out of one and nylon tippet sticking out of the other doesn’t affect the response of the fish to what they see as food.

Equally a mayfly pattern if it moves (or more likely doesn’t move), creates a similar pattern on the water surface to the real thing, is the right colour and size (perhaps larger could even result in a more pronounced response), the fish will eat it. It could very well be the reason for the success of cripple type patterns, it would be simple to imagine that the fish instantly recognises the struggle of a stillborn fly as a easy meal and can’t resist.

It seems to me that the idea adds credence to much that we already know about trout feeding behaviour, and offers explanation to much that we witness when on the water.

In tying and fishing flies then it would behove us to think in terms of key stimuli, the pattern the hackle makes on the water, the eyes of a dragonfly nymph, perhaps the pronounced tails on a spinner pattern, the classical segmentation of an ant pattern, the erratic movement of a corixa or the manipulated “escape” of a nymph pattern fished to create and induced take. Could it be that they are all “key triggers”?

We know that we cannot create an exact copy in much the same way that a baby cuckoo cannot, at least for long, look exactly like a baby wren, but we can, as does the cuckoo, overcome that apparent flaw by carefully designing our flies and fishing them in a manner to override the obvious in favour of key stimuli which will trigger we hope the required response.

TroutandHopperHow much of the feeding response is pre-programmed into the fish?

It could be that we can use the fish’s own genetic makeup to help us deceive it. In effect causing the pre-programmed genetic makeup (what Dawkins refers to as the extended phenotype) not so much to allow us to deceive the fish but to afford the fish the chance to deceive itself..  Perhaps that is what the wrens are thinking, “jeez look what good parents we are, look how big our baby is and how wide his mouth gets when he is hungry”.. ?

It has been long recognised that deliberate overemphasis of some elements in the way we tie and fish flies can be effective and Dawkins discussions on the extended phenotype (that is the effect that genes have on the world around us and our interactions with it) might offer a clue as to why such machinations work on the water.  If the fish’s genetic makeup program it to grab anything that looks like food, and furthermore determines what criteria it uses to recognise such food, then we can exploit that in very much the same manner as the baby cuckoo exploits the wren’s response to gaping beaks. It’s still a con, but perhaps a con now with a scientific basis.