5 November 2007

Sexual frustration of the worst kind

The first reports always come from farms and small towns. Rural areas. Strange sounds in the forest at night. People call them cryptids. These creatures, presumed extinct, cast a delicious spell: we want to believe that they are out there, holding out against the odds. Survivors, after all. A flash of white on a black wing in an Arkansas swamp, and we desperately cling to the hope that the ivory-billed woodpecker has survived, that it is alive and well and breeding. Each frame of footage is cherished as grainy evidence that the thylacine still stalks the Eucalyptus forests of Australia. We want these creatures to have survived the ravages of hunting and habitat destruction. We are to blame for their disappearance. We need to ease our guilt, you see. Our desire to resurrect these species is so overwhelming that we end up ignoring all evidence to the contrary. We will not discover a live moa in a hidden valley in New Zealand. No amount of weeping will cause the cry violet to blossom in Bourgogne again. They are precious jewels lost down the drainpipe and no hook will ever be long enough to retrieve them.

Often we concentrate so much on what we have lost, that we don't notice the things we are about to lose, the findings on the other bracelets coming undone as we vainly poke around in the dark, chasing shadows in the plumbing. A small amount of organisms have indeed come back from the dead, as it were. These so-called Lazarus species, such as the painted frog and the Madagascar serpent-eagle, were reported as extinct for several years, until small populations are rediscovered. These are rare occurences, and dangerous ones for ecology in the end; they give us hope, which is so seldom of any practical use.

What a pitiful, sorrowful thing the very last wild thylacine must have been. All alone, without a mate. A population of top-end predators reduced to a single individual. The last thylacine would not even have been aware of it, of course, but it was doomed long ago. As soon as the number of individuals in a population drops below a certain threshold, the whole species collapses. Even though there are still individuals alive, the genetic diversity needed to sustain their next generation is already lost. You cannot fight natural selection with just a handful of alleles - you need the full arsenal. Imagine that last thylacine, gazing out over its dry scrubland habitat. A dead species walking. Functionally extinct.

The wonderful seaside city of Durban, South Africa, has an incredible botanic garden with a rich history. Planted in Victorian times, its mature tropical trees are a magnificent site to behold. On weekends, crowds of people enjoy a sunny afternoon picnic on its lawns. Its herbarium has collected and catalogued some of the most precious specimens of plants from all over the world and specifically the ravines and coastal forests of southern Africa. Music events, art installations and amateur astronomy nights bring people from all walks of life, not just plant lovers. Chiefly, it is indeed a plant lover's paradise: a whole avenue of Eucalyptus deglupta, the famous rainbow gum, leads to a carefully maintained Japanese garden. Tropical fruit trees grow outside, festooned with bromeliads and orchids, without the need of pampering under glass: jackfruit, cocoa, coffee, mangoes, they're all here. Ponds of waterlilies, formal rose gardens and arches dripping with purple Wisteria provide bridal couples and their photographers with many opportunities for gorgeous scenery. A Victorian orchid house gushes with colourful, heady blooms, a firm favourite with any visitor. And in the middle of it all stands a lonely looking Wood's cycad, Encephalartos woodii.

I've never been a big fan of cycads. They're big and spikey, grow exceedingly slowly, and produce no flowers. Still, the madness of cycad collectors probably exceeds that of the orchid folk. No other kind of rare plant has been as vehemently collected, illegally smuggled or heavily policed. In 1895, John Medley Wood came across a large cycad with four stems at the edge of the coastal forest of Ngoye in eastern South Africa. Luckily for the cycad, John had been curator of the Durban Botanic Gardens since 1882. In 1903, Wood sent James Wiley to collect some of the offsets growing at the base of the plant. In 1907, two of the larger trunks were collected and planted at the Botanic Gardens in Durban. However, Wood wasn't the only person interested in this cycad, apparently. By 1912, there was only a single trunk left. It is known that the indigenous people of the area sometimes use the starchy trunks as a food source, but it is doubtful that they were to blame. The plant seemed mutilated, diseased. In 1916, The Forestry Department sent this ailing trunk to the Government botanist in Pretoria. It died in 1964. All expeditions to find other specimens of Wood's cycad have returned empty-handed. It is very likely that the original plant collected one hundred years ago was the last of its kind.

Fortunately, the specimens growing in the Durban Botanic Garden thrived. Unfortunately, you need a mommy and a daddy cycad to make a baby cycad. The single specimen on the planet was a male, you see, and without a female Encephalartos woodii, no viable seed can ever be made. And yet, there are about 500 individual plants in the world now, in botanic gardens such as Kew and Kirstenbosch, and in private collections. How was this miracle accomplished? The plant regularly produces offsets at its base - all male, all genetically identical. Clones, with about as much chance of surviving in the wild as the original plant did. Functionally extinct. There has been much research and debate about using biotechnology to save Wood's cycad. It might be possible to induce one of the clones to change sex and become a female, whether chemically or using a genetic engineering approach. But even if this feat of gender reassignment surgery were possible, the genetic pool is still severely limited. Encephalartos woodii will remain in cultivation, of that there is no doubt. But genetically crippled, it could never survive in the wild.

The photograph above is of me hugging the trunk of the gigantic original cycad, first collected in 1907, still growing happily in the Durban Botanic Garden. A palaeontological relic, its chromosomes at a loss for something to do. A proud plant, but doomed like the thylacine. Its salvation through cultivation is a hollow victory. Lazarus was raised from the dead, only to die a second death. I recalled a lecture in population genetics, where the secrets of the gene were shared with me in darkened halls: "The only thing worse than somatic death, the death of the body, is genetic death, the failure to reproduce". I closed my eyes and grasped the trunk, cool and solid beneath my fingers.


morbidneko said...

i had a different idea around what this post was gonna be about.. ^_^

but, i can imagine the frustration of only having 1st cousins with whom to continue the human line.

that aside.

some of what you said really hit home - around searching for something, willing it to live, but losing what you have in the process.

that's deep.

a beautiful post. now.. if only that pic had better zoom..

arcadia said...

hierdie is 'n beautiful en fascinating post. ek het nooit geweet dat dit presies so werk nie. hoe oud was jy toe jou obsessie met die plantwereld begin het?

Unknown said...

morbidneko: that would shatter a lot of my mystique, I'm sure. ;-)

arcadia: dit was nog altyd vir my mooi op 'n casual manier, maar ek reken die obsessiewe neigings het eers in my eerste jaar op universiteit begin posvat.

Anonymous said...

I recognized the thylacine in the first picture. I think some folks believe they are still around, but your point is well taken. Any left are functionally extinct.

Funny how we hold on to the doomed species like the cycad. But then again, it's hard to bury a human body, even though its dead. There is a certain finality that we fight so hard against. The trees in the botanical gardens keep that loss at bay.

Hugely talented post.

Anonymous said...

I was bit worried thinking your title was of a personal nature. I should have known better.

I once saw a different looking tree at a conference I was attending. I asked and pursued different people until an old nun could give the full history of the tree. It is a Camperdown Elm. Do you know about it? I wouldn't want to bore you if you already do.

HopSkipJump said...

Wow... you sir, are a brilliant writer. Thank you for the passionate post.

singleton said...

Honestly, you need to have your own TV show......
Jacque Costeau of the land.....
Just incredible!
(Ok and I know I mispelled his name, but you know what I mean!)

SleekPelt said...

Can I change my vote? Amazing post, Teoh, really.

Aine said...

Hi, I've been lurking since Jason "met" you. This post is bringing me out in the open.

Fantastic writing. I love when science is made beautiful and readable.

I was a bio major (seems like it was back in the Pleistocene....) Sadly, I've forgotten so much since I don't use it now. Thanks for taking me back to my Evolution course-- loved that class... ah, the good old days ;)

Karen Little said...

d'you think the failure to reproduce is a tragedy for individuals, or only becomes a tragedy when it becomes a problem for the whole species?

I think humans have done far more than enough reproducing on an individual basis for now - i think the time has come for individuals to sacrifice their reproduction for the good of the species.

beautifully written post!

Unknown said...

jason: I wanted to illustrate how we need to be more concerned about critically endangered species, rather than with the ghosts of those already lost to us. Otherwise, the ghosts will soon outnumber the living.

wreckless: the Camperdown Elm is, of course, a mutant horticultural variety of weeping elm. This would not be classified as being of importance to conservation (it does not occur in nature). But what a gorgeous tree, nevertheless.

inarticulate fumblings: thank you - if the passion comes through, then I've achieved my goal with this blog.

singleton: thank you, but I do post about the ocean as well, now and again! Don't think I could be charismatic enough for television, though.

sleekpelt: thanks!

aine: welcome! Isn't it amazing how quickly we lose knowledge we don't use? I did physics back in the day, and cannot remember a single formula or principle. Bernoulli? What's that?

karen: the tragedy I'm referring to in this post is the loss of biodiversity. In essence, the extinction of a species is a tragedy for humankind (and a slap in the face of Mother Nature). On a personal level, the individual suffers genetic death if it leaves no offspring, so that's a tragedy of a personal nature. Of course, I doubt that Tasmanian tigers or cycads actually mourn their own downfall. They have no feelings - I'm anthropomorphizing. They are just beautiful vehicles for the transmission of specific DNA sequences.

Human overpopulation is the single biggest threat the stability of the planet faces today - our success as a species is truly the root of all evils.

Anonymous said...

Enjoyable writing style :)

Re your comment that once a population drops below a certain threshold point, the species is doomed to extinction - that's not a certainty.

There is almost no genetic diversity among the world's cheetah population and it's my understanding that this would only be possible if the species dropped to a single breeding pair in the not-too-distant past. It's amazing what life will do, of a necessity (and a little disturbing, also...)

Unknown said...

Dropping by before I go to work... will come back later to read this very article. How can I not... with this title!

Anyway, I want to say... hey, let's skype!

Sorry about the quickie :-)

Unknown said...

It depends on the environmental pressures felt by the population; as far as I know, most cheetah populations are carefully monitored by wildlife researchers and game wardens etc. Which makes your example just a little too artificial, in my opinion. Their survival has, in part, been contrived by human intervention in several habitats. A bottleneck in the recent past and stabilization after that is no guarantee that that is the global picture. Either way, we can't be certain.

I never suggested that extinction is a certainty for all species with little genetic variation, but the trend cannot be denied. It depends on the tempo of reproduction, the severity of the population drop, and is a function of environmental factors versus genetic robustness.

What I'm suggesting is that, were we to see a sudden change in the environment, it's doubtful that the cheetah would have sufficient allelic diversity to cope with that change than would, say, some antelope with masses of outcrossing, migration and large population numbers. For the moment, though, their environment is pretty stable, isn't it?

Aspens are clonal, and have very little genetic variation. We don't see those on the brink of extinction anytime soon, either. They've sacrificed adaptability for adaptedness. They are perfectly suited to their environment. And all virtually genetically identical.

Where does novel genetic variation come from? From random mutation, of course. This is the basis of evolution. But as beneficial mutations are the exception to the rule, rapid and successful adaptation is more statistically likely when you start off with a large population size.

You may also have noticed that I did mention the chromosomes of cycads. These are renowned for weird fusions, deletions, duplications and translocations. This makes them meiotically unstable, which contributes to the problem.

Conservation in the 21st century will be about more than just taking an individual organism and cloning it. The genetic diversity and the habitat needs to be conserved in parallel.

Even in horticulture: the genetic diversity of all the landraces of crops such as wheat and corn are being lost due to modern agriculture's insatiable appetite for monocultures of super varieties. Landraces which could potentially yield some interesting and worthwhile genes for use against pathogens and for increased nutrition.

Lastly, duneprincess, I'll leave you with this: saying "nature will find a way" was what cost us the dodo, the thylacine and the cry violet in the first place.

Anonymous said...

Ek geniet dit altyd om hier te lees, al skryf jy soms bietjie bo-oor my kop. Maar jy skryf wragtig goed.

En net so gaan ons perlemoen in Suid-Afrika ook binnekort uitsterf. Sad!

Unknown said...

Wow, that was a good read. Such a poignant ending.

Thank you dear blog friend.


Trundling Grunt said...

Great post. I guess I was musing on the last dodo who had seen it's relatives massacred without any thought. Occasionally these 'extinct' species are found which is always interesting.

Dead clade walking?

Anonymous said...

By recent past I mean evolutionarily speaking i.e. in the last 500-1000 years. A long time before the cheetah breeding programs and monitoring instigated by our species.

I don't deny the trend that low genetic diversity usually equals evolutionary death but it's not a certainty. It was your intimation that it WAS a certainty that struck me.

Unknown said...

missy: quickies are always welcome! ;)

sonkind: oeps, ek probeer om dit so maklik as moontlik te maak, maar soms raak dit maar 'n bietjie tegnies. As die regering net meer beheer kan uitoefen, sal dit al klaar 'n verskil maak vir die perlemoen.

trundling grunt: initially, I thought of doing the post mainly on Lazarus species. But then I remembered the E. woodii, and that sort of took over.

duneprincess: the genetic bottleneck in cheetahs has in fact been determined to have occured 10 000 years ago, an order of magnitude more than the time frame you provide (see Menotti-Raymond and SJ O'Brien [1993] Dating the Genetic Bottleneck of the African Cheetah PNAS 90: 3172-3176). It is reasonable to assume that this bottleneck was induced by climate change at the end of the Pleistocene - many large mammal species went extinct then. The cheetah just scraped by, but managed to keep ticking over with the genetic variation it had left for all these years. Now, with agricultural expansion, habitat loss and climate change, the new selective pressure is indeed caused by humans. It's unlikely that the cheetah gene pool could take another knock, which is why they are monitored in game reserves and transfrontier parks and bred in breeding programmes now.

Since my post talked about a critical threshold, that should leave it open-ended enough. The 'critical' threshold could vary from species to species: fifty individuals, ten individuals, two individuals. No two definitions of a 'small' population size will be identical - it's all relative. Perhaps the threshold is a single individual, unable to find a mate. There is inherent variability and uncertainty in natural systems. So no, I did not 'intimate', as you put it, that extinction is a biological certainty for an arbitrarily small number of individuals (ten? five?) for every species of organism that has ever existed. Re-read the post.

morbidneko said...


if the cheetah goes - what was the 2nd fastest mammal on earth?

Unknown said...

Oh, God, how should I know - probably its prey? Can we please, please, please let sleeping cheetahs lie now.

Chris Eldin said...

I read your beautiful entry on Jason's contest and now I come here and read another beautiful post!

I linked you on my blog as "Colorado Tree" if that's okay.

Colorado is my most favorite place on this planet!!