Tonight Dr. Chris Carbone (IoZ) will be giving a talk entitled:
Everyone is welcome and the event is free!
If you’re in London, I can’t think of anything better to do!
Info:
Date: Wednesday 4th May 2011, 18.30
Location: Gustave Tuck Lecture Theatre (Wilkins Building, University College London, Gower Street, London WC1E 6BT)
More info at http://londonevolution.net/
See you there.
Well, first of all, a big BIG I’M SORRY to all the readers that might have come by during the last couple of weeks in search of a new post. I am in your debt. The truth is not very apologetic though…I’ve just been busy…erm…yeah, sorry. If you have been reading this, you might have read the About page (here) when I said that “very soon I should be starting some kind of semi-voluntary internship in a very prestigious society”. That’s exactly what happened. I am now based at the Institute of Zoology (The Zoological Society of London) working on a study about the evolution of specialized carnivore ecomorphs and the scaling relationship between their adapted morphological traits and body size. Let’s all hope you can read all about it when it gets published in a recognized scientific magazine and in this very blog right after it.
But reading about fierce carnivore predators has gotten me thinking of the topic for this new post: COMPETITION.
Let’s make one thing clear first: this is a post about terrestrial carnivorous carnivorans with body mass equal or larger than 7kg – i.e. terrestrial mammalian predators of the order Carnivora that feed on vertebrate prey in different levels of exclusivity. And no, saying carnivorous carnivorans is not a pleonasm since there are at least a few Carnivora species which have evolved towards different degrees of omnivory, insectivory and herbivory (to make it simple: think cute PANDA).
One (if not the most important) of the Carnivora’s synapomorphies is presence of carnassials: a pair of teeth in the upper and lower teeth rows modified for shearing meat (usually upper forth premolar – P4 and lower first molar – m1). Those teeth can easily tell you of an animal’s diet since animals who feed on plant material or are more omnivores will need a griding tooth surface while the ones who feed only on meat have greatly reduced or lost the griding portion of those teeth while enlarging and sharpening the shearing blades.
It might seem odd at first that all meat-eaters have converged to having a very similar feeding apparatus but it makes perfect sense if you realize that they are all feeding on the same thing and there is an optimum morphology for using this resource. Vertebrate prey do no change much in consistency. Honestly, it’s mostly either meat or bones, you pick. The thing that is going to change is the actual chosen prey (i.e. prey species and their morphological and ecological ranges: body mass, habitat, etc) and how the predator kills its prey. And that is going to rule how many other things vary, like the other teeth, for example (e.g. canines, incisives).
But prey is a limiting resource. For a bunch of reasons that out-limit this post, there isn’t an unlimited number of available prey and its availability might control the predators numbers. Also, there isn’t an unlimited number of strategies mammalian carnivores use to consume their food and although there is some partitioning of prey between them, there is also some overlap. The rules driving the degree of overlap or the established partitioning are derived from the competition dynamics between co-existing predator species.
Co-existing mammalian predators form a local ‘guild‘: “a group of species that exploit the same class of environmental resources in a similar way” (Root, 1967). Inside a guild, there may be different ‘hunting sets‘: ”a group of species with similar body build and hunting strategy” (Rosenzweig, 1966). I.e. The Serengheti mammalian carnivores form a guild that included species of felids, canids and hyaenids, while the felids present in this guild form a hunting set.
Competition between those predators is intense. Their prey are shared, difficult (and often dangerous) to kill and even the carcasses might be overtaken (kleptoparasitism). But how can different carnivoran predators co-exist for a long period of time with a dominant species simply extirpating the others and keeping the resources all to itself? There lies the beauty of it. Morphological and behavioural differences have evolved between them that allow for the co-existence of some species by minimizing interspecific competition.
Morphological traits differing in sympatric carnivores usually include body size, dental morphology (e.g. size and proportion of carnassial blade length) or skeletal anatomy. Body size usually determines the dominant species (the larger ones) in the guild. Prey size is usually correlated with predator size, which already causes some ecological separation but also mean that medium-sized prey will be the mainstream since more predators are capable of hunting them and still getting a positive energetic budget. Prey size is also reflected in canine size (e.g. feline canines, Dayan et al, 1990) and body sizes or canine sizes of closely related species living in sympatry (overlapping geographical distributions) are more different than in areas where the species live in allopatry (separate geographical distributions). This observation is the key to the theory of ‘character displacement’ (Brown and Wilson, 1956): “equal size ratios between species, spreading co-existing species across the size spectrum, thereby reducing dietary overlap” (Farlow and Pianka, 2003) since size is correlated to prey specialization. It also allows for the calculation of the critical value of Hutchinsonian ratio (Hutchinson, 1959) of 1.3. Hutchinsoninan ratio (larger/smaller trait) values lower than 1.3 mean the two species compared are too similar to co-exist once their prey spectrum would be entirely overlapping and the outcome result would be one of the species locally extirpating the other, or both suffering huge declines in numbers due to resource depletion.
Prey partitioning might instead be acquired by behavioural traits like different hunting methods (ambush or pursue, and prey handling techniques) and hunting times (smaller species are usually diurnal or crepuscular, while larger carnivorans are nocturnal). Intraguild predation is also a variable here and smaller species avoid the larger ones by seeking areas of low prey density or placing their home range along the margins of their larger competitor’s. It’s best to be somewhere with fewer prey than constantly having your meal stolen by someone bigger or even worse, turning into this someone-bigger’s meal.
Survival is tough for carnivores. So next time you’re watching an animal life documentary, stop feeling sorry for the lonely wildebeest who got too far from the big group or the baby gazelle who couldn’t run as fast as mommy and give that poor carnivore a big round of applause if it actually manages to outrun, kill and finally consume most of their prey without having to start it all over again.
Just thought some of you might be interested in reading this recent interview with the biologist nobelist Christian de Duve that was published today on New Scientist issue 2801.
It’s a bit controversial saying that “Natural Selection will destroy us” but I guess I need to read his book (Genetics of Original Sin, click here)first before making a real judgement (you might read a post on it very soon). I can see his point though…
Interview by Clint Witchalls:
We have evolved traits that will lead to humanity’s extinction, says Christian de Duve – so we must learn to overcome them
We are the most successful species on the planet, but you think we will ultimately pay the price for this success. Why?
The cost of our success is the exhaustion of natural resources, leading to energy crises, climate change, pollution and the destruction of our habitat. If you exhaust natural resources there will be nothing left for your children. If we continue in the same direction, humankind is headed for some frightful ordeals, if not extinction.
You think that natural selection has worked against us. How?
Because it has no foresight. Natural selection has resulted in traits such as group selfishness being coded in our genes. These were useful to our ancestors under the conditions in which they lived, but have become noxious to us today. What would help us preserve our natural resources are genetic traits that let us sacrifice the present for the sake of the future. You need wisdom to sacrifice something that is immediately useful or advantageous for the sake of something that will be important in the future. Natural selection doesn’t do that; it looks only at what is happening today. It doesn’t care about your grandchildren or grandchildren’s grandchildren.
You call this short-sightedness “original sin”. Why did you pick this terminology?
I believe that the writers of Genesis had detected the inherent selfishness in human nature that I propose is in our genes, and invented the myth of original sin to account for it. It’s an image. I am not acting as an exegete – I don’t interpret scripture.
How can humanity overcome this “original sin”?
We must act against natural selection and actively oppose some of our key genetic traits.
One solution you propose is population control, but isn’t this ethically dubious?
It is a simple matter of figures. If you want this planet to continue being habitable for everyone that lives here, you have to limit the number of inhabitants. Hunters do it by killing off the old or sick animals in a herd, but I don’t think that’s a very ethical way of limiting the population. So what remains? Birth control. We have access to practical, ethical and scientifically established methods of birth control. So I think that is the most ethical way to reduce our population.
You also advocate giving more power to women. Why?
Speaking as a biologist, I think women are less aggressive than men, and they play a larger role in the early education of the young and helping them overcome their genetic heirloom.
Are you optimistic about humankind’s future?
I’m cautiously optimistic – very cautiously. I try to be optimistic because I prefer to give a message of hope to young people, to say: you can do something about it. But in the present, there is not much evidence that this is happening.
Christian de Duve is professor emeritus at the Catholic University of Louvain (UCL), Belgium and Rockefeller University, New York. In 1974 he co-won a Nobel prize for his work on cellular structure. His latest book, Genetics of original sin, is published by Yale University Press
I went yesterday to the Natural History Museum (NHM) in London to see their new Sexual Nature exhibition and it stirred the first motivations and greatly inspired me to write this blog entry. 
The exhibition will be on till Oct 2nd 2011 but I would strongly recommend anyone who has the chance to visit it to do it asap. It is quite interesting and very well done for anyone from any age. Although it’s said to be aimed at adults and children over the age of 16, I honestly didn’t see any bits that would shock the faintest of hearts (must even say I was expecting something spicier…). The exhibition is full with interesting facts and curiosities (did you know that spinner dolphins mate in orgies called wuzzles or that lionesses mate up to 157 times in 3 days when they’re in oestrous?) of the love and sex lives of animals, portrayed in intelligent and easy to read panels, videos (with the beautiful Isabella Rossellini) and taxidermied specimens. There were a few things that could have been different in my point of view though… Where were the playbacks of sexual callings that could have created a sexy tropical forest atmosphere? Why were the visitors’ paper notes’ wall constantly checked (censured?) for ‘unsuitable’ messages if the exhibition was primarily for adults?
But anyway, the exhibition is well worth a visit and clearly fulfilled its purpose and got me thinking about SEX (and a quote in one of their panels is acting like the title on this post). Just having a quick look through an array of scientific papers on the topic is enough to come across a variety of hypothesis on how sex could have originated and why it’s still maintained and spread across a huge number of species. Apparently (now hold on to the edges of your seats) sex is not entirely adaptive. Wait…what?! Yes, you read it right. There are two main problems with the understanding of the widespread sexual reproduction. First, because of recombination, sex has the great potential to destroy favourable gene combinations that would easily and most likely be preserved in the next generation if only it was generated but cloning of parentals. Second, sexual females will potentially only produce half the number of daughters than asexual females (‘cost of males’).
That’s fine, we get that, don’t we? But isn’t it a bit too simplistic? Maintenance of exact copies of adaptive sets of genes would sound perfect in an unchangeable world but looking at the history of Earth, there weren’t many times when the environment was kept entirely biotically or abiotically constant. And when in an changing environment variability is what provides the capability of adaptation to the new conditions and having that possibility to cope with still unknown variables must be worth having some less adaptive sets of genes in a population. After all, the truly maladaptive genes should be purged from the population pool by means of natural selection while the current more adaptive ones are maintained and spread in the following generations.
Of course I am definitely not the only one who thinks sex is actually very much adaptive and there are a bunch of theories around trying to demonstrate exactly how that is. One is the environmentally biased Red Queen hypothesis, by which sex is adaptive in a world full with pathogens, another is the mutational approach, by which recombination would prevent the loss of temporally bad alleles by mixing them with the temporally good ones, maintaining the variability and potential for future adaptation in a changing environment. Or even a more ‘pluralist approach’ by adding both mechanisms to the model. Hey, they make sense, right? World full with pathogens? CHECK! Need to maintain different alleles for potential future adaptation? CHECK again!
I myself am convinced of all of sex adaptive characteristics. Although asexual reproduction is clearly widespread and functioning quite well for unicelular organisms (prokariotes or eukariotes such as yeasts, or the protists with their facultative rounds of sex), multicelular organisms are not able to cope with the “supersonic” velocity by which bacteria (for example) reproduce and would need a much longer time frame to come up with a sufficient number of generations that would statistically be enough for the right mutations to occur if those mutations would be the only source of variability on which sexual selection could act. Do not get me wrong, mutations do occur and they are hugely responsible for the evolution of species but Darwin pinpointed the importance of variation within species and sex and recombination are key mechanisms in keeping that.
Now, it’s not only because sex is adaptive and necessary for species of animals and plants that it is less of a war. Focusing on animals, females are a limiting resource for males (or the other way around for species where there is sex role reversal) and reproduction has a much higher cost for females, who need to make sure they choose the best candidates for fathering their babies once that’s a commitment that results in them carrying and nurturing the offspring during their embryonic stages and very often for a long time after birth (species where there is parental care). It’s all about passing your genes to the next generation and making sure that the better ones do.
So males (again, just usually) fight between themselves in order to have access to females (see picture on the left for examples of weapons) or they try to show females how superior they are by their flashy colourful spots, feathers, big muscular bodies or the beautiful songs and callings they perform (did anyone say PEACOCK? Point for you). All these cost a lot of energy and all this happens in an environment that is normally constantly changing, with limiting food resources, crowded with pathogens and predators just waiting for their next meal. So only the best ones, only the ones with the most adaptive or at least adaptive enough get to survive and mate, passing their selected genes and making sure the species prevails.
Sex indeed feeds evolution. And I am glad it does for some of the most beautiful behaviours and morphologies have originated to please and woo our patners.
Quoting but inverting another sentence present at the panels of the NHM Sexual Nature exhibition, asexual reproduction might even be twice as efficient as sexual reproduction, but is not half as fun.
Suggested readings:
Birky Jr C W (1999). An even broader perspective on sex and recombination. Journal of Evolutionary Biology 12, 1013.
Crow, J F (1999). The omnipresent process of sex. Journal of Evolutionary Biology 12, 1023.
Futuyma D J (1998). The evolution of genetic systems In: Evolutionary Biology. Sinauer Associates: Massachusetts.
Otto S P and Nuismer S L (2004). Species interactions and the evolution of sex. Science 304, 1018.
A big hello from a room in south-east London to the world!
If you haven’t read the About section, please do so because it should make everything a bit clearer.
This is evo-punk and in essence it is a blog about evolution. But saying so is at the same time incredibly presumptuous and not very clarifying. Here I intend to wander about and sometimes even explain some of the most exciting theories and facts about how evolutionary processes rule, shape and entwine all the organisms present in this world, no matter how big or small they are or if we as observers are aware of them at all or not. And that’s where the ‘evo‘ bit of the name came from. But most of all, this is a blog about my understanding of those processes, my views and opinions, maybe even more frequently about my doubts or pure amazement about how they truly work. The posts here will not conform to any journal’s guidelines for authors, they are not essays or papers. And that makes it punk, breaking the conformities of scientific publication, spreading the evolutionary knowledge in a crude, often mistaken as violent, but always true, direct and beautiful way. But do not fool yourself. They are intended to be as scientific as can be. Behind them will be a list of reading and long hours of thinking. This is my love dedication to biology and evolution and I have every intention to make it right.
As I said before in the About page, let me know what you think of it, of every piece of writing I share here. I welcome you to share your views in my little corner.
At first, my intentions are to post something new at least every week but I’ll try to make it much more frequent whenever possible. Sometimes there will be music references embedded in the posts (or in their titles, like this one’s, a reference to Swallow it by Brandon Flowers) when I believe they can be enriching or help sending a message but they are not the focus here. Today’s reference is a message to myself. I am, let’s say, in-between jobs or studies. Unfortunately finding funding for overseas biology students in the UK has proved to be much more difficult than I had foreseen and my so desired PhD degree might still take some time. Nevertheless, I continue to improve myself in other less expensive ways. Maybe a few rough edges need to be smoothed.
Anyway, the first true post is the next one. That’s an introduction and a welcoming to you.
Hope to see you around here. Make yourself noticed.
x
