Speciation II: isolationism-ishy

Let's continue to think on and discuss this issue of speciation.  As opposed to the genetic concept, which we discussed last time, we're going to look at the other two popular versions of the biological concept and the ecological concept.  Hang tight!

The biological species concept is one of the more well known models and although it centers around several pieces of evidence, the core piece deals with reproductive isolation.  We've discussed this idea a little in the past when talking about the African Cichlid fish and again last time, in part, with the ring species example.  This isolation however, has many parts to it.  For the sake of simplicity, we'll talk about two general sections

1. Pre-zygotic isolation: Isolation that occurs before the completion of the zygote.  At the risk of over-generalizing and simplifying we'll refer to this as pre-mating.  These are the things most people think of-mate choice, mate and species recognition, behavior, etc.
2. Post-zygotic isolation: This isolation is a little less well known and can be a little more difficult to understand.  These are isolations that occur AFTER mating, basically penalties for poor mate choice.  Generally these refer future of the offspring.  This can be things like zygote mortality, sterile young (cannot produce offspring of their own like a mule), or a poor mix of adaptations (mom is adapted to one and dad is adapted to another and the middle ground isn't well adapted to anything).

The thing I want to reinforce here is that speciation is in fact a PROCESS by which species come about.  Usually you see these species first experience some post-zygotic isolation that will be reinforced by pre-zygotic isolation.  Generally a species isn't truly called until there is no survival of any young and that there is no choice mating between the different populations. 

Now the ecological concept seems a little more straight forward.  The idea here is that the species experience isolation based on their ecological niche, things like habitat choice, nesting, food choice, life-cycle and timing.  An example would be birds that choose marshier habitat and those that choose higher ground, dry habitat.  Different habitat and attracting different partners, thusly reducing the change of cross breeding.  Here you consider that the species are now filling (or starting to fill) different ecological roles.  

As you can imagine as straight forward as this can be (to breed or not to breed) there is a lot of space for haziness too.  With a shifting environment and climate you can be on the brink of isolation and suddenly end up with hybrids between the populations that are even more well adapted than either of their parents.  There are plenty of cases where, as with the ring species example, although you can identify clear separate species, they are not finite and have hazy zones in the long line that got them there.  So where do we draw the line?  If we are more strict we lose the potential to understand discrete ecological impacts and in some cases destroy chances of species or populations of receiving government protection because they they don't qualify under endangerment laws.  If we are more flexible with our definitions we get widespread confusion and, as some birders and avian biologists can tell you, infinite updates on what species are and which are mere groups.  And, as I mentioned in the last speciation post, you get some cranky extreme creationists that run with it like it's on fire.  So what do you think?  What is a species?

Feel free to post with your comments, this is a controversial and ever changing topic! I'm happy to discuss! I have the book I referenced and some additional sources from a class I took!

Until next time!

"It is by universal misunderstanding that all agree. For if, by ill luck, people understood each other, they would never agree." Charles Baudelaire

Speciation: What the and the why hows??

Speciation (process of species forming) seems simple enough on the surface.  Over time adaptation and evolution drive a divergence between two populations.  Let's take a population of birds.  The population splits as it colonizes around a large mountain range.  As each subset of the original population colonizes farther and farther around the mountain range, each subset is undergoing natural and sexual selection pressures.  Of course, these pressures are not the same on both sides of the mountain, you have different light, weather, environment, predators, nesting sites, etc. When the two subsets reach the other end of the mountain range and re-converge they no longer recognize each other as of the same species.  They choose different nest sites and even sing slightly different songs.  They are both different from each other and from the original source population.  This particular mechanism is referred to as "ring species."  The image below shows why.

As a side, when looking for an image to help show this I found a lot of creationism websites that use ring species and speciation as reason to show evolution does not exist.  They cite that such species are not stead fast and singular and thereby are not showing evolutionary process.  To this I say, by being fluctuating and changing they certainly aren't showing that they were put on this Earth in their perfect form then are they?  Ecology and evolution are messy, that's why they're so interesting.  If anyone actually knew the straight answer to everything, they'd get paid a lot more.

Now that aside, that issue of fluctuating species is the major point I actually want to talk about.  Apparently unbeknownst to our extreme creationist friends, it is not necessarily speciation that does the fluctuating, it is the way in which we define it.  Our example above shows speciation, up to three species total in the end.  The problem arises when we try to draw lines.  What about all of the colonies in the middle?  They're a little bit of everybody and would probably breed with more than one group.  What are they?  Hybrids may be the answer.  Mixes between two populations.  But that leads to all sorts of problems.  Let's take a step back first and look at why defining species is so hard in the first place.  Don't worry, we'll get back to this later.

Two guys named Coyne and Orr took time in their 2004 book on Speciation to figure out just how many different ways we had to identify species. Nine. Nine MAJOR ways with sub groups among them.  These range from change of habitat, to reproductive isolation, to genetic change, to biochemical effects and so on.  Now firstly I'd like to dispel the "genetics is the answer to all" idea.  I more than understand and respect using genetic code changes, especially since genetics of course is one of the necessary basic constructs for evolution to occur.  But bear with me and follow me through an example.

When I took my Phycology course (study of algae) I was confronted with a interesting and (at the time) frustrating situation.  We were in lab learning to identify different species of algae.  I was identifying one using the standard dichotomous key.  For those of you who are unfamiliar, a dichotomous key takes characteristics for a given specimen and splits them into 2 groups-Spines are present or absent.  You follow the pathway for your given sample and if you play your cards right you use these split characteristics to arrive at the proper identification.  See below for a very general example.


Now, when I had reached the end of the road I had two choices that led to two related but separate species.  The way to tell the difference was by color.  More specifically, I had to decide whether my specimen was "dark lime green" or "apple green".  Ooookay, so I was stumped, thinking what is the actual difference between these colors (since my 64 crayons box was at home) and was it distinct enough for the average person to get right, even with the correct illumination.  So I brought my professor, here on the Triggerfish, over and explained.  Hand on my heart, the conversation went thusly.  Triggerfish quickly told me the answer.  I was surprised and asked how it could tell.  Triggerfish responded that it just knew.  I asked if the coloration was useful, it replied no, there was almost no way to make a correct assessment based on that.  (Okay, so for you following along by in large these two species look the same).  When I asked how it knew, Triggerfish replied that it knew the genetic coding for the species in the area (Okay so the genes were different).  I then asked in the two species had any ecological differences, looking for habitat choice, temperature tolerance, nutrient requirements.  The answer? No. Bluntly.  (So functionally these species were identical).  Then angry Triggerfish walked away.  I promise you will hear about Triggerfish again, it was a particular thorn in my side and the side of my other grad student counterparts.  Facebook page dedication and all (of course not under Triggerfish, combined with a terminator spoof if I recall).  I'll discuss this in my teaching posts as well, "I just know" and "try harder" are things you never tell a student.



Anyway, I digress, my point is these two algae were separated into different species groups because they were genetically distinct somewhere in their lines of code.  This to this day seems completely pointless to me, different shades of green and a little obscene if you will.  Moreover it shows that what seems to be the most straightforward way of assigning species isn't any more irrefutable than some of the others.  There's always a dance of where to draw the line, and people will argue violently on where to draw the line.

Next time we'll hit on other popular ways to define species and where those have pitfalls as well.

Don't forget, questions or comments are welcome!


"In science the credit goes to the man who convinces the world, not the man to whom the idea first occurs."
Sir Francis Darwin