Random notions of the evolutionary concept of “Adaptation” with an introduction to The Various Contrivances by Which Orchids are Fertilized by Insects. By Charles Darwin
Human Values Network
January 31, 2010
C. Michael Stahl
We will start by capturing the Oxford Reference, Dictionary of Biology and use that definition of the term “Adaptation”. Here goes: Any change in the structure or functioning of an organism that makes it better suited to its environment. Increasing adaptation of a species to a particular environment tends to diminish its ability to adapt to any change in that environment.
A trait is adaptive if it is maintained in a population by selection. It is non-adaptive if it reduces the fitness of individuals that consistently manifest it under environmental circumstances that are usual for the species. Traits are flexible and can change with different environmental conditions from adaptive to non-adaptive.
There is more to the definition but these two aspects will do for now. The point of this paper is to use Darwin’s The Various Contrivances by Which Orchids are Fertilized by Insects as a launch pad to discuss the concept of Adaptation; it is one of my favorite way of looking natural history and speciation. Let’s start with a brief look at Darwin’s book and then go into several examples of unique and interesting examples of tested versions of this concept. Lastly there will be a discussion on what it all means.
The Various Contrivances by Which Orchids are Fertilized by Insects. Charles Darwin,
London, John Murray 1877 306 pp. (2nd Edition). Internet access to this can be
found at (http://darwin-online.org.uk/content/frameset?itemID=F801&viewtype=text&pageseq=1)
This book was accessed on line and it was accessed by me twice and by others
110,231 times as of December 8, 2009. This suggests to me that after 132 years,
The Various Contrivances still has staying power.
Some 30 years ago I decided to plant Tomatillo plants using the citrus-like
fruits for salsas and salads. I asked around at the local Farmer’s Market for
advice and insight into this plant. What I received was rather amorphous and I
left unsure (though determined) as to what my results would be. Some weeks
later I selected the two best shoots and planted them side by side. They
appeared to be on steroids and grew to enormous plants nearly 6 feet high and
triangular in shape. The fruits could be counted in the several hundreds,
perhaps even a thousand.
I made my sauces and my salads. I froze many and gave more away. I enjoy a
Tomatillo on a hot summer evening but my bounty was a burden. The next year I
decided to grow one plant. I was able to reap no more than perhaps 10 fruits.
That was when I first gave serious thought to cross fertilization though not to
the “various contrivances” that Darwin discusses of the Orchid species of
flowers. Darwin was intrigued by “contrivance” or the many ways that creatures
make their living or disperse their seed.
Darwin knew that organisms did not really contrive to do anything
though the concept is intriguing. When we examine any flora or fauna closely it
will seem as if they are determined to “be the best” so to speak. It is
inherently human to imagine that as sentient and often brilliant beings, that
we are the superior life form. In fact we are only good at being humans.
Darwin contended that, “If nature ever showed her playfulness in the formation of plants this is visible in the most striking way among the orchids…Nature has formed orchids in such a way that, unless they make us laugh, they surely excite our greatest admiration”
Science fiction often presents a scenario where a human intellect is thrust into the form of another species. Like Kafka falling out of bed one morning, the stories remind us that we would not be very adept at anything except being human. Nor would chimps be adept at taking our roles although there are plenty of cinematic efforts to make it as if it could be so.
What Darwin came to understand (and has
been re-proven over the years) is that plants were actively responding to the
environment and how they move is an active response to their environment.
Plants respond to external stimuli.
Darwin’s efforts in this book are very particular to scientists in that the
detail and the terminology can be overwhelming. Those intricacies need not be
discussed in this short overview. He wanted to make a couple of interesting
points and that is where this is going.
Essentially Darwin is telling us that plants produce flowers and they encourage insects to settle on them and collect pollen. That pollen goes with the insect (or Hummingbird for that matter) to the next plane in which pollen is disseminated from the insects body to the new plant, thus fertilizing it. The genes get passed on; the insect gets its foodstuff. All is honky dory except for the “Red Queen” affect which reminds us that the faster we run, the faster we are chased.
Plants mutate as their insects do and
this creates a circumstance that often very finely tunes this symbiosis. The
plants that change little are fertilized by many insects and those that become
rare evolve into species that require unique species to fertilize them. This
makes the plant (in Darwin’s book he only discusses orchids) more rare and
valuable for breeders and collectors but it puts its future at risk. Any
environmental risk factor to either the plant or the fertilizer can doom them
both.
At some point in Darwin’s life he reflected on the poor health and early deaths
of some of his children (not a rarity during the mid 19th century) and wondered
about inbreeding. He married a first cousin which was not uncommon especially
amongst the wealthy. Plenty of his studies on natural selection and adaptation
suggested to him that cross fertilization produced the best chances of
survival. Perhaps this worried him about his own family.
This book was one of them. Darwin focused on two aspects of his grand theory
here. He accounted for the glory and success of cross fertilization and the
beautiful anomalies resulting from adaptation. He studied a large variety of
“tribes” (his term for species at that time) of Orchids. He examined the
methods that they were fertilized thus likely to propel another generation.
Those included evolving elaborate reproductive systems and thus feeding
systems. Ultimately the insects that collected pollen and transported
fertilization had to adapt to the conditions of the Orchid.
Amongst the many things this book brings
to mind is the value of sexual reproduction versus asexual reproduction. The
former requires more time and energy but it creates a more versatile gene pool
and it is genetic diversity that is one of the significant factors in species
health. There are simply a larger number of genes to share as well as a better
prophylactic against mutations that may be harmful.
Adaptation and survival required an elaborate set of conditions for the right
insect to fertilize the right flower. When one failed the other did as well. Ultimately
the most exotic of the Orchids depended on fewer fertilizers. This makes for
precarious symbioses. Should a condition such as weather, kill off too many of
the fertilizing insects then fertilizing the Orchid becomes limited. The “easy”
flowers provide more insects with the opportunity to collect pollen and to
assist in the fertilizing.
Darwin also recognized the difference in the quality of progeny distinguished
by cross fertilization as opposed to self fertilization. I discovered this with
my accidental Tomatillo experiment. His studies and those of his many cohorts
who aided in data collection, showed that the results of self-fertilization
produced few and weak offspring. The point being (Darwin did not know it at the
time) is that accumulation of a gene pool was far superior to regenerating the
same genes. It makes species stronger and survival improved.
He did provide some guarded subjectivity that I found interesting. He fully
realized that there was no guided plan that drove evolutionary improvement. It
was the chance of successful mutation. Yet he commented on what he considered
superiority in Orchids (with qualifications). The more common species produced
far more seeds and were easier to be fertilized. They became common and less
interesting (despite their survival superiority). The more exotic were more
beautiful and rare. They required a more sophisticated adaptation in the
fertilizer (often a single species). Yet they lived a more precarious
existence. Too many outside factors could doom the Orchid species as well as
its fertilizer who had adapted to find only one food source.
Often I hear scientists say that they understand that Darwin wrote beautifully
though they have not read his works. Well I am not a scientist and I enjoy
reading Darwin but I would say that in order to do scientific work reading the
progenitor of the brilliant theory is not necessary and Darwin can be
incredibly arcane. In my opinion we amateurs can read him because we are not
trying to prove anything unless it is to show how smart we are. Scientists
should read Darwin if they feel like it. His theories sparked about 170 years
of ideas that have advanced to the extent that his specific notions, not as
relevant in the lab as what those that have been amassed since his days.
For the complete Darwin works you can go to http://www.darwin-online.org.uk/
So Darwin did very minute observations of diverse orchids and how they attract pollinators. This includes “food trickery”-by appearing as if to be the provender some orchids fool insects of both sexes into landing for dinner only to be thwarted. They also use sex trickery-this time fooling males into imagining an amorous adventure where none exists. On the surface it would seem that the latter form of trickery would be less successful as a method of pollinating. Studies however, have shown that this method ensures that more pollen is taken and it is more secure in flight to the next orchid that appears to be offering favors.
Sexual reproduction survives because it provides variability, and is rapid enough for corrective DNA to counter various mutations and allow survival of the species. With the random genetics that provide the chromosomes from each parent to be dealt from the well shuffled deck to the new born provides for a grander gene pool and a better chance at species survival.
Competition is one constructive process leading to adaptation to the environment. Sexual competition promotes adaptation by breeding with “the best”. Normally it is assumed that females pick the males based on a variety of qualities; qualities that help define their fitness.
Geoff Parker defined “Sexual Conflict Theory” some 30 years. While studying dung flies he found a variation of that theory. He found that predominant male breeders actually proffered a negative impact on the female. The males that bred the most actually provided a detriment to the females by cutting their fecundity and lifespan shortened as a result of mating with these males.
The adaptation process here only works if the females breed with large number of males thereby discounting the breeding of the prominent males. This is the only way to prevent the obvious which would occur a few generations away. That would be extinction.
Orchids are not the only ones involved in this chicanery. In fact my ex-wife…oh that is for another paper. In fact in a recent study a particular daisy (Gorteria diffusia) had its “dark spots” examined thoroughly and several interesting things discovered. First of all these spots resemble the female of a particular beetle and like our orchid story it is a lure to enhance pollination. The more curious aspect of the study is that it found that the daisy evolved these spots by spreading them over several petals in essence having partial spots on several petals that form the image of the insect. At least I found this to be fascinating.
This is the Nieuw morphotype of Gorteria diffusa, which exhibits striking dark petal spots at the bases of some ray florets. Scale bar = 1 cm. (Credit: Courtesy Meredith Murphy Thomas.)
In the end it seems, we can understand that our flora and fauna at times develop very specified means of feeding, fertilizing, preying and protecting. They adapt to their environment. Humans themselves can adapt far better than other species to dramatic changes in the environment but so can many of our other sentient and otherwise brethren in this symbiotic world.
Many cannot make those changes and there lies the rub. The reason that they fail is because they have become so finely attuned to the specifics of their symbioses –The insect feeding and the plant fertilizing, that an imbalance can lead to the extinction of both. In better times (and I assume sometimes even now) those imbalances are subject to natural causes. A forest fire may deplete a feeding ground, so could a flood. One of the symbiotic species may mutate into a new adaptation leading its partner to new devices. For an understanding of the realm of adaptation, this point cannot be made often enough.
Nicotiana attentuata is the name for North American Wild Tobacco which is prey to the larva left by female Hawkmoths. As they hatch they become hungry and eat the flower. This is no way to survive and the plant lives on. That is because it has adapted to open its flower when the moth is dormant and it blasts off the sexy aromas that the moth falls for, when the moth is no longer feeding. Hummingbirds with their less noxious ways find this suitable and do their feasting and secondary pollination and everyone involved is happy.
Nothing of course impacts these many species and their too specific cooperation with each other as much as the intrusion of humans on their lifestyles. Whether it is the increasing carbon emissions that bring on obvious problems such as soil contamination or air pollution or the more complex issue of acid rain, humans have impacted the symbioses of approximately one trillion species (I purposefully am being hyperbolic here). As we cut through forests to expand our living and working spaces; as we top off mountains for coal; as we fertilize our golf courses and overwater them we are continuing to impact the delicacies of nature.
It is not a matter of being a simple “tree hugger” or a limp wristed “liberal” as our gainsayers would purport. It is a proven fact that symbioses is a real matter and that when we affect the lives of beasts and flowers we are ultimately impacting our own lives. Certainly all of us here are going to survive the ecological onslaught that is occurring but how will it affect our grandchildren? It is not just that they will have fewer species to understand, more importantly will they continue to be able to adapt to a world that has fewer species doing their life’s work?
Ladies and gentlemen, flora and fauna, we are all in this together!
Here are some examples that recently have come to mind:
Darwin was gripped, and troubled, by the mere existence of land snails. He explained his obsession: “One of the subjects on which I have been experimentising & which cost me much trouble is the means of distribution of all organic beings found on oceanic islands; & any facts on this subject would be most gratefully received: Land-Molluscs are a great perplexity to me.”
He understood that land snails were especially susceptible to salt and tried to assess how they migrated from one environment to another when only salt water lay between them. So he experimented by submerging snails and their eggs in seawater for weeks at a time. After some Roman snails survived his long “baths,” he found that the snails survived. Since his day we have learned a bit about snail anatomy and their bodies.
We have discovered one of their “contrivances” and that is in their protective shells. We can see that it is coiled and asymmetric. If we hold a shell with the opening facing us and the pointed tip facing up, the opening is usually on the right. These shells are referred to as dextral or right-handed. In rare cases the shells will have the opening on the left and are referred to as sinistral, or left-handed. Some entire species are sinistral.
Biologists have known for almost a century that a simple genetic basis is behind shell “handedness”, in some species, such that the mutation of a single gene can cause right-left reversal. Why are there variances in this left-right spiral condition? How is this adaptable to snail species?
Well it all has to do with mating as the genital opening is behind the right tentacle in right-handed snails. When land snails mate, they face each other, which brings their genital openings side by side. Snails with opposite handedness are misaligned, making it physically difficult for them to mate. A reversed snail would have a serious sexual problem and that is a problem for the continuation of a species. So those snails have to find mates with the same “sidedness”. This is one way that a new species comes about. Remember that if you can mate with a mate and can have progeny that can mate with a mate you are a species. If you cannot mate with a mate nor can your fellow species members mate with a mate you are living in the last generation of your species.
However if you have unique sexual traits and they can fertilize or be fertilized by another with unique traits you survive and all of your unique partners will as well. Your tribe as Darwin liked to call his orchid species, would be subject to a large number of threats. Weather, disease, predation or mutation could speed you towards extinction. As it stands however, the right handed and the left handed spirals of the snails have been a perfect match for their species generation (and on the other hand for their predators but that is another story).
A male club-winged manakin. (Credit: Image courtesy of Cornell University)
So…adaptation takes on many forms all directed toward the goal of species perpetuation. A bird in South America has sort of learned to play the violin for courtship displays. It is a special display (though I have not had the privilege of actually hearing it) and while falling short of Tchaikovsky’s Violin Concertos it is apparently quite alluring…especially if you are a female Club Winged Manakin. Your wooer will woo by rubbing specialized wing feathers -- more than 100 cycles per second -- to create a high hum, similar to a sustained violin note. It has been proven that the bird’s feathers resonate at a particular frequency to create the tone.
This species modified an essential body part for the purpose of attracting a mate. The sparrow-sized, bird has inner-wing feathers held adjacent by a ligament on each wing, but uniquely, the two innermost feathers, have enlarged and hollow shafts. Researchers found that when the enlarged feathers are excited at their resonant frequency -- an object's natural frequency of vibration -- all hollow feathers resonate as a unit at 1500 Hertz to create a note close to an F-sharp. The wing also produces a second harmonic tone and act as sort of a tuning fork.
All feathers naturally resonate at a frequency of 1500 Hz, but this weak resonance cannot be heard without such special adaptations (or a secondary contrivance as Darwins may have noted). The enlarged hollow feathers of the male bird create the audible tone that attracts females.
Now then, on to one of my favorites…this would be Hummingbirds. They have been found to have a very specialized ability to extract nectar (and to incidentally fertilize other flowers) by creating straws with their tongues to extract nectar, taking advantage of surface tensions –the same force that causes water to bead rather than spread infinitely. Some water birds use the same tension to draw water up their long beaks. Essentially they roll their tongues “just so” to perfect a straw and allowing them to suck nectar as we might our sodas. It’s the same principle and in doing so they gather pollen which they disseminate on other flowers keeping one species well fed and the other perpetuation.
Adaptation also has a darker side and that is the carnivorous species. We all know about lions and spiders and humans but perhaps spend less time imagining the stationary world of plants. To be sure these species have their share of “meat” eaters. Darwin was very interested in carnivorous species and maintained a rigorous correspondence with Joseph Hooker regarding them. He also wrote the book Insectivorous Plants which strongly suggested the idea that plants could eat animals and it was, early on generally accepted.
We are learning more about carnivorous plants (including sundews, Venus flytraps and pitcher plants) all of the time. These plants have adapted to luring prey into their very constricted environments and eating them. It doesn’t help to fertilize them but it makes for what I feel to be, and interesting sidelight.
Scientists at the National Evolutionary Synthesis Center (NESCent), Cornell Lab of Ornithology and McGill University have evidence that inconsistent climates play a role in Bird song. A more variable climate leads to a larger array of songs. This gives them the ability to lure more females. “Complexity of a song display-how many song types a bird sings, how hard the songs are-is a good predictor of the quality of the individual.” –Carlos Botero of NESCent.
Songs are a learned behavior for the oscines (and there is at least a bit of evidence for the suboscines. Better songs suggests a compensation for a difficult climate. Sounds were recorded creating 100 tracks from 29 Mockingbird species. Using sound technology sonograms were created to visualize the sounds.
We can use our avian population as the canary in the mine shaft. They tell us much about our environment and they have been studied and recorded since ancient times and so we have something like a pre-industrial baseline to work with.
Birds are continually attempting to shift to meet environmental demands for food and breeding grounds. Species like the Purple Finch have changed their wintering locations by 35 miles in the last 40 years in order to meet their diets and their locations for siring the next generation. During those 40 years the average January temperature has shifted upwards by five degrees. The standard for winter birds in California’s Sierra Nevada has found that 48/53 of them winter beyond the region to the north-some as far as 400 km. This is based on the marvelous “grinnellian niche. Named after the UC Berkeley ornithologist of 100 years ago this is a massive baseline of bird records kept by hundreds of students and researchers in the first two decades of the 19th century. That baseline has been re-surveyed beginning in 2008 and finds that the Sierra Nevada birds are both heading north for food and are heading higher up in the mountains. Of course they are running out of room.
Birds are shifting northward as the globe warms. There are 305 known species of birds in North America. Approximately half of them are spending winter about 35 miles farther north than they did 40 years ago. The Purple Finch used to winter south of Springfield, MO and now are routinely found in Milwaukee, WI. During that time the January average temperature has risen about 5 degrees. With milder winters the birds expend less energy traveling but more importantly, shivering. It takes a lot of eating to maintain a winter of shivering.
In the Sierra Nevada the birds are responding in a different way. They are apt to move to higher elevations. When the weather is not right, birds look for greener pastures. According to the results of the Grinnelian Resurvey Project, 48 of 53 species have sought higher elevations largely due to more water being found there. Curiously this pattern could easily hint at speciation due to adaptive radiation. Essentially a species moves to a new area and creates an eating and nesting niche which creates the conditions for allopatric speciation-they stop breeding with their ancestor species.
Species movement is being used to understand global climate effects and birds are the biggest movers.
I could go on with anecdotes forever but I will stop now.