Branching Of Various Invertebrates

[Missourian]

A couple days ago, I asked about terminology on various characteristics of form and structure ( http://www.thefossilforum.com/index.php?/topic/43803-fossil-related-jargon-question/ ) that would include branching.

I guess the ultimate goal of my question is to understand why various organisms (coral, bryozoans, sponges, calcareous algae) branch. I'm talking about organisms that somehow respond to external stimuli, such as variations of environmental conditions. I'm not referring to things like crinoid arms or many vascular plants, which branch in a strict way due to genetics. I am especially interested in variability of branching within the same species, particularly at a single locality.

Any thoughts on this?

[Bullsnake]

Predation followed by regeneration?

[painshill]

Meusel (1935) describes growth form as the overall character of an organism [although he’s talking about plants] and that it’s a purely morphological term, as opposed to life form, which is more encompassing and describes the result of life conditions, including growth form, influence of environment, and assemblage of individuals (Warming 1896; Mägdefrau 1982). Life form embodies all the selection pressures that are brought to bear upon a species, or in the words of Mägdefrau (1969), “the organization in correspondence with its life conditions.” Hence, life forms are genetically determined whereas growth forms within that are influenced by the environment. [ref: Adaptive Strategies: Growth and Life Forms... linked below]

It would be reasonable to assume that when particular growth forms are observed in successful organisms then they have some adaptive significance that relates to an advantage – even if that advantage is small. The vast majority of such advantages relate to water (including oxygen/nutrient supply therein) or light; temperature to a lesser extent; things like pH and mineral availability in specialist organisms; occasionally also to things like anchorage and even camouflage. I don’t think you could speak in generalities about drivers which could be quite specific to particular organisms.

Jason Williams of Texas A&M University [writing about corals] says: In addition to growth… the colony shape and/or architecture can vary for the same species existing in different environments. Light and levels of exposure are considered to be the key drivers of colony morphology as well as growth, although across global spatial scales, temperature also plays a role. Despite such environmentally regulated variations in overall coral morphology, reef building corals are often functionally and not taxonomically classified by their dominant growth form. Such growth forms include:

a] massive corals

b] branching corals

c] submassive corals

d] foliose corals

e] tabulate corals

f] digitate corals and

g] encrusting corals.

These different growth forms can be readily identified across reefs world-wide and the contribution to overall reef complexity is varied with some growth forms providing long-term stable structures but low complexity (e.g. “massive” species) and other forms providing relatively short-term high complexity (e.g. “branching” species). Thus, the overall architecture of a reef and hence its physical complexity, topographic diversity and habitat availability is dependent on the composition and abundance of the different coral growth forms.

“Why do organisms branch?” is a slightly ambiguous question because it potentially embraces both the “why?” implied by “what is the driver?” and the why implied by “what is the mechanism?” Although this chapter: “Adaptive Strategies: Growth and Life Forms” is from a book about Bryophyte Ecology, it does nevertheless contain some interesting information relating to the drivers:

http://www.bryoecol.mtu.edu/chapters/4-5AdaptStratForm.pdf

As for the mechanisms, you might be interested in “Modelling genetic regulation of growth and form in a branching sponge” but I forewarn you its really heavy going:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2605804/

[PS: I made some further comments on your other thread about branching]

Edited February 1, 2014 by painshill

[Missourian]

Thanks painshill for the response. I had these in mind:

Incidentally, at one locality, I've been finding these that display various styles of branching. These tend to be segmented. Other forms at the same locality are smooth or otherwise irregularly rippled. I'm not even sure if they are all the same species or two or more. I think the unsegmented forms may be the red alga Archaeolithophyllum sp., which happen to be quite common in the Pennsylvanian strata in the area.

Edited February 2, 2014 by Missourian

[andreas]

My two cents

in case of coral, bryozoans, sponges, calcareous algae I think

they branch to enlarge their surface to gain more food, light, etc... always towards to the better conditions of life

[painshill]

My two cents

in case of coral, bryozoans, sponges, calcareous algae I think

they branch to enlarge their surface to gain more food, light, etc... always towards to the better conditions of life

Of course that's the short answer to "why branch at all?". It's a very efficient way of exploring new parts of the environment with potentially better conditions and it maintains a better surface area to volume ratio than say growth by general enlargement, and without the need to develop a complex set of internal organs and transport mechanisms to move nutrients and waste products around.

But I think the question Missourian is trying to address is what determines different morphologies of branching in the same organism? That subtle distinction between growth form and life form. And the drivers for growth form are environmental, but complex and span a wide set of stimuli.

For example, it has been established that the morphogenesis of branching, phototrophic corals such as Madracis mirabilis is determined by external gradients of dissolved inorganic carbon (DIC) in the surrounding water (Kaandorp et al. 2005). It's very much more complex than striving for food or light or whatever.

Edited February 3, 2014 by painshill

[Auspex]

"Striving", "Reacting", "Responding To"...these all imply sentience and purpose. In reality, we just get to see what worked, whether the growth-form was biologically hardwired to subtleties in the environment, or all available forms were initiated but only the best match for the conditions was all that succeeded. Nature is confoundingly intricate.

[xonenine]

A couple days ago, I asked about terminology on various characteristics of form and structure ( http://www.thefossilforum.com/index.php?/topic/43803-fossil-related-jargon-question/ ) that would include branching.

I guess the ultimate goal of my question is to understand why various organisms (coral, bryozoans, sponges, calcareous algae) branch. I'm talking about organisms that somehow respond to external stimuli, such as variations of environmental conditions. I'm not referring to things like crinoid arms or many vascular plants, which branch in a strict way due to genetics. I am especially interested in variability of branching within the same species, particularly at a single locality.

Any thoughts on this?

my only thoughts beyond downloading the PDFs to read and try and keep up, is that it's a fascinating thread you started and I hope it runs 10 more pages

reminds me of A.Clarkes "any technology sufficiently advanced is indistinguishable from magic" I'd enjoy knowing more 'bout both the mechanisms and drivers.

[Missourian]

Than

Meusel (1935) describes growth form as the overall character of an organism [although he’s talking about plants] and that it’s a purely morphological term, as opposed to life form, which is more encompassing and describes the result of life conditions, including growth form, influence of environment, and assemblage of individuals (Warming 1896; Mägdefrau 1982). Life form embodies all the selection pressures that are brought to bear upon a species, or in the words of Mägdefrau (1969), “the organization in correspondence with its life conditions.” Hence, life forms are genetically determined whereas growth forms within that are influenced by the environment. [ref: Adaptive Strategies: Growth and Life Forms... linked below]

-----

Although this chapter: “Adaptive Strategies: Growth and Life Forms” is from a book about Bryophyte Ecology, it does nevertheless contain some interesting information relating to the drivers:

http://www.bryoecol.mtu.edu/chapters/4-5AdaptStratForm.pdf

As for the mechanisms, you might be interested in “Modelling genetic regulation of growth and form in a branching sponge” but I forewarn you its really heavy going:

http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2605804/

Thanks again painshill for the PDFs. I'm still working my way through the first one.

And the concept of growth form vs. life forms is interesting. Sometimes having the proper terminology helps to clarify a concept.

[painshill]

A little more food for thought.

To put it in the simplest terms I can muster, “growth” arises from surface instabilities. Most typically, an interface or boundary moves as a result of fluxes of heat and/or mass or by some mechanical or other force that leads to a “pressure gradient”. Small movements result in unstable growth which may decay or collapse, such that – although the boundary moves (resulting in enlargement) - it recovers its original shape.

The geometry of the surface, its physical properties and the prevailing thermodynamics determine the degree of stability. If the instabilities are larger, a moving boundary in unstable growth will ultimately develop some kind of pattern which then determines the final morphology. Many of the patterns that can be observed in nature or created experimentally are the result of these kinds of instabilities and the growth models are potentially applicable to everything from the expansion of the universe all the way down to the formation of a snowflake.

If the temperature, concentration or pressure fields that control these processes satisfy the “Laplace equation” (from the 18^th/19^th Century French mathematician and astronomer Pierre-Simon Laplace – generally regarded as the Isaac Newton of France) then the growth is said to be “Laplacian” or a “Laplacian paradigm”. Laplacian growth is viewed these days as a fundamental model for pattern formation – whether arising from radial or directional growth. Increasingly, these kinds of models are being used to explain the growth patterns of living organisms, which is of course rather easier to study in simple organisms – especially those which grow by branching. Researchers such as Jaap Kaandorp, Roeland Merks and colleagues are the pioneers here, generally using corals (branched and unbranched) as the study area.

Here’s a few more links for anyone that’s interested:

Models of coral growth: spontaneous branching, compactification and the Laplacian growth assumption (Merks, Hoekstra, Kaandorp & Sloot 2003):

http://carnuk.org/library/Journal%20of%20Theorectical%20Biology/Merks%20et%20al.%202003.pdf

Polyp oriented modelling of coral growth (Merks, Hoekstra, Kaandorp & Sloot 2004):

http://www.researchgate.net/publication/234057061_J_Theor_Biol_2004_Roeland_M_H_Merks/file/9fcfd50eac32034ca0.pdf

(I made a brief mention of this one earlier, but provided no link) - Morphogenesis of the branching reef coral Madracis mirabilis (Kaandorp, Sloot, Merks, Bak, Vermeij & Maier 2005):

http://rspb.royalsocietypublishing.org/content/272/1559/127.full.pdf

You can also download a full copy of Merks’ 2003 dissertation - Branching growth in stony corals: a modelling approach (but be forewarned it’s a big file and runs to over 160 pages):

http://dare.uva.nl/document/31821

[Herb]

divergence results from some change in the environment of the organism. As long as we are not including genetic mutations.

[Missourian]

The sponge Coelocladia is part of the reason I been wondering about branching. All Coelocladia I've found have been slender, branching cylindrical forms like these:

But then I found images of funnel-shaped or even foliose forms of the same sponge:

Finks (1960: http://digitallibrary.amnh.org/dspace/handle/2246/1220 ) says this sponge may have taken on a funnel or sheet-like form in the presence of local constant currents.

Edited February 16, 2014 by Missourian

[xonenine]

sounds fascinating, thanks for the update

[xonenine]

_{I can't help now, the last few days, thinking of the TFF directory tree and threads as a fun analogy, as this "life form" responds to its environment, so I guess we are one mechanism for the growth form...}

[ashcraft]

On a different level, how they grow offers advantages and disadvantages. A branching coral is going to add a lot of polyps per gram of growth, while one the expands like a ball is going to get much fewer polyps per gram. Why don't they all grow as branches then? Simply put, (and maybe even correctly) branching is weak in structure compared to expansion, causing them to be less stable in a high energy environment. They don't last as long, they don't produce as many offspring, and as such are at a reproductive disadvantage in that environment to a more structurally stable form. In a more stable area, they will grow faster however, monopolize more of the food source, and have a decided advantage in that environment.

That is not to say that they different structures won't grow in areas where the other form may dominate, but they are at a disadvantage. They are good enough however to dominate the less desirable ecosystem if something should happen to the other form. If one form should be wiped out in an extinction event, the other form (assuming survival) will "gladly" move into that system due to lack of competition, potentially precluding any other species by sheer weight of number.

Cactus suck at what they do, but there isn't anything else better.

The Fossil Hunter Once Known as Ashcraft