Friday, January 26, 2007

A Species Concept...How hard could it be??

People have thought about the origins of closely related species for decades. In fact, scientific research on speciation can be traced all the way back into the early 19th century. By looking at older literature, we can understand old arguments, as well as, provide us with ideas toward current problems.

The evolution of biology is a like a history of unanswered problems that have been worked on by some of the most original thinkers of our time. This is very different from a field like molecular biology, where much of the older literature may be irrelevant due to advancement of the field. One of the first things that you should know is that researchers cannot come up with one universal definition of a species.

Speciation is a process that can be looked at from many points of view, whether it be by Behaviorists, Phylogeneticists, Systematists or Evolutionary biologists. So, when trying to decide on a single definition, many conflicting ideas come into play depending on the angle you are examining it from. Most often, the definition for a species, depends on the specific criteria you have set for boundaries.

As you can see, this is not as easy to define as it initially seemed. So, how do we begin to understand speciation?

First and foremost, it is best to understand the current definitions that are accepted for a species.

Then, tackle the problem of understanding the difference between concepts to finally be able to choose a definition that works best for you.

Species Concepts for Speciation:

1. Biological Species Concept (Isolation Concept) (BSC)

"Groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups" (Mayr 1963)

"Systems of populations, the gene exchange between these systems is limited or prevented in nature by a reproduction isolating mechanism or by a combination of such mechanisms" (Dobzhansky 1970)

2. Recognition Species Concept
"The most inclusive population of individual biparental organisms which share a common fertilization system [specific mate recognition system]" (Paterson 1985)

3. Cohesion Species Concept
"The most inclusive population of individuals having the potential for phenotypic cohesion through intrinsic cohesion mechanisms [genetic and/or demographic exchangeability]" (Templeteton 1989)

4. Phylogenetic Species Concept (Character-based)
"An irreducible (basal) cluster of organisms, diagnosable distinct from other such clusters, and within which there is a parental pattern of ancestry and descent" (Cracaraft 1989)

5. Genealogical Species Concept
"exclusive' groups of organisms, where and exclusive group is one whose members are all more closely related to each other than to any organisms outside the group..." (Baum and Shaw 1995)

6. Evolutionary Species Concept
"A single lineage of ancestor-descendant populations which maintains its identity from other such lineages and which has its own evolutionary tendencies and historical fate" (Wiley 1978)

7. Genotypic Species Cluster Definition
"Distinguishable groups of individuals that have few or no intermediates when in contact..."

"...clusters are recognized by a deficit of intermediates, both at a single loci (heterozygote deficits) and at multiple loci (strong correlations or disequilibria between loci that are divergent between clusters)" (Mallet 1995)

From this list, 1-3 are process based, while 4-7 are pattern based. Many researchers are adamant that pattern not process should form the basis of any species definition while the others are just as adamant for the opposite.


A generally defined and consistently applied definition of species is vital for the study of diversity, as well as, phylogenetic investigations of diversification...which ultimately gives valuable insights into the study of speciation.


However, what previously seemed easy to define, is in fact a hot issue being debated to this day... with the science community still not using a single, general concept of what exactly defines a species.


I hope this opens up conversations as to what is a species, as well as, leads to interesting topics of speciation. I have given a foundation....so off you go now...

16 comments:

Revealed said...

I'm all for the genetic concept. It's the clearest and also the easiest method. It can be demarcated properly, without confusion. In fact I was working on speciation in yeast (Saccharomyces paradoxus), and we did some really interesting work with speciation. Using the conventional parameters, the Saccharomyces family tree has already been worked out. But the genetic information we obtained suggests that the lines are so much more blurred that it was earlier thought. It's a very interesting subject.

Sakshi said...

Defining the term species will remain a gray area for some time. But I like the fact that with genome sequencing we can attempt to address this in a more refined way. However, it does not still address whether speciation occures because of genetic changes first (say change in egg's receptor proteins) or behavior modifications (change in courtsip).
I think the whole biz is very fascinating - esp when you look at the intergenomic conflicts that exists within a species. Nice start, Sonya.

Revealed said...

Yeah but the awesome part about genomic speciation is that you can pick on the junk DNA instead of the ones with a purpose. So, you almost completely cut out the chicken or egg argument.

Revealed said...

And you can pinpoint translocations, recombinations etc. It's pretty accurate yknow.

Sakshi said...

I know it is pretty accurate but as behavior biologist will point out - the chicken or egg argument is something we would really like to solve.

Revealed said...

Yeah but if you're using junk DNA then it can't be a chicken or egg story cos it's DNA that serves no purpose. So the behavior aspect doesn't come into it, dont you think?

John Wilkins said...

I have a list of 26 species conceptions (not concepts - there is one concept, "species", of which there are 26 or so conceptions or definitions) here:

A list of 26 Species Concepts

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