Species chosen

I have chosen to study the marine snails Acanthina punctulata and A. spirata for my independent study.

A. punctulata  inhabits the high intertidal zone on rocky shores exposed to moderate but not strong surf, from Monterey Bay to Punta Santo Tomas (Baja California), is a drilling carnivore, and bears a very strong resemblance to A. spirata.

A. spirata inhabits the high to middle intertidal zone on protected rocks and pilings from Tomales Bay (Marin Co.) to Camalu (Baja California), and is also a drilling carnivore.

A. punctulata and A. spirata were long united under the name A. spirata and many studies supposedly done on one were probably actually performed upon the other or perhaps both.  Where their ranges overlap, they are said to have distinct distributions and are easily distinguishable one from the other.

Could this be an example of sympatric speciation in action?

Sympatric speciation has always been a mind-bender for me: how can gene flow become sufficiently restricted among members of a single population so as to allow genetic drift to the extent that an entirely new species will evolve?  As someone supposedly interested in ecology, I can acknowledge that this question verges into territory claimed already by the Anthropic Principle.  It doesn’t matter how it happened, because obviously it did… now how can we keep all marine ecosystems from collapsing before my kids are born?  But I just can’t shake the feeling that it would be so cool to understand sympatric speciation.  Almost even cooler than preventing widespread ecological catastrophe.  Is that wrong of me?  It doesn’t matter whether or not I’m callous… I can only study what interests me, and I’m hooked on sympatric speciation.

So, where do I go now?  Assuming it is possible for me to reverse-derive the parameters of growth according to the Rice (1998) model for the bio-geometry of mollusc shells, those equations aren’t going to include what else is at work making the two Acanthina species really different, like breeding or feeding or their preferred milieu.  Some of these characters I will be able to ascribe in the field, and they may be different depending on lattitude.  Is that phenotypic plasticity, or genotype variance exhibiting also the expected norm of reaction for a variety of environments?  Maybe I’m understanding this wrong, but Lewontin (2006) seems to have come up with an analysis of variance that can parce out these variety of causes.  He calls it an analysis of causes, and I don’t understand the math at all.

The problem is that I only have a superficial understanding of  norm of reaction, epistasis and the analysis of causes, all of which are going to play a very important role in figuring out this phenotypic plasticity/sympatric speciation thing.  So, back to the books… but which books?

Response to Rice, 1998

Rice (1998) made a model of molluscan shell growth whose parameters can be altered to create the shape of any gastropod species fossil or extant. Even better, his parameters are based on biological realities, as determined by all sorts of research teams all over the place, such as which cells where are producing cell tissue, where, and at what rates. The result is a tool that allows us to model an hypothesis for what developmental parameters must be changed in order to derive one shell form from a seemingly very different ancestral form. (Question: do we know or only hypothesize the ancestor-descendant relationship?)

I think that’s cool.

My favorite quote: “In a sense, this model describes the “natural logic” (cf. “natural history”) of shells. Natural logic here refers to the relationships that must hold between different developmental and physiological processes and between these and phenotype. when combined with natural history (the actual attributes of the animal and its environment), this describes the opportunities and constraints that evolution has to work with.”

What I really want to know: Can equations for the morphospaces of actual animals be reverse-derived from measurements taken in the field? And then if we can derive the equations of two closely-related species, will the parameter variations between them paired with what we know of their natural history illuminate a mechanism for their sympatric radiation?

Choosing a species for study

Now I am trying to choose a species of Pacific intertidal gastropod for my own study of phenotypic plasticity.  This will be my first independent field research project, and I only have the 15 weeks remaining in the semester to complete it, so it cannot aspire to anything beyond the cursory or preliminary.  Yet I do not under any circumstances want my research to be redundant, and therefore merely for the sake of field experience.

Do I want to pick an animal that we know a lot about already, or a little-studied animal whose habits either remain largely a mystery to science or are so banal as not to be thought to merit any study?  If I pick a species familiar to Science, then any observsations I make can be substantiated by the literature.  Any hypotheses I make can be either supported or shot down with further reading.  On the other hand, if I pick a species that has not been widely studied, I will have the opportunity to propose and follow up on deeper investigations tailored specifically to my observations and my research.

The biggest problem is that I am so unfamiliar with the field, and with field research, that I can barely even pretend to anticipate what sort of data I need to collect.  No, the biggest problem is that there are so so so many variables on both sides of the equation that even if I do choose a species, and appropriate characters for study, and I do collect good data, and I am able to find some kind of trend, the validity of any explanation I might possibly come up with for this hypothetical trend will be so frail and questionable as to be basically arbitrary and worthless.  But hey… that’s ecology!

Response to “Phenotypic Plasticity in the Interactions and Evolution of Species” by Anurag A. Agarwal _Science_, Vol 294, no. 5541. (Oct. 12, 2001), pp. 321-326

In this article, Agarwal addresses the possibility that phenotypic plasticity, itself being an evolved trait, may in turn be an important factor in enabling sympatric speciation and true genetic differentiation.  One obstacle to testing this hypothesis is that we do not know the mechanism of phenotypic plasticity: what physiological pathways are necessary for a gene to be expressed platicly?  To this I would add, are those pathways capable of fixing unique genotypes to express various traits that were previously expressed plasticly from a single genotype, or do they aid divergence merely by the ultimate effect they have on phenotypes of restricting gene flow?  In that case, will plasticity be lost once speciation has occured?  Lost or just unexpressed?

And, is the physiological machinery of plasticity a convergent or homologous trait? Perhaps more importantly, is plasticity an accidental (and self-organized?) by-product of the dynamic genetic system that was selected for and “pressed into the service of adaptive function” (Smith, 1998) or were those pathways evolved entirely through selective pressures?

Smith, Maynard.  _Shaping life: genes, embryos, and evolution_.  London, Weidenfeld & Nicholson, 1998.