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Volvox

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shvarz:
So, you want to make a multicellular bot?  Here is the simplest known multicellular organism with complete division of labor: Volvox!  
- It is a ball of cells consisting of two cell types.  
- It does not have a pre-determined body plan.
- Cells in volvox act together to achieve common goal.
- It protects offspring until it is big enough to duke it out on its own.
- It is a veggie.

Can we make Volvox in DBs?

Just some links for you to get more sense of what volvox is:

Some pictures and basic info

Some movies of Volvox in action

Finally, just some copy-paste for your reading and enjoyment:

What is Volvox? The name comes from the Latin volvere, to roll, and -ox, as in atrox, fierce. Volvox is a spherical multicellular green alga, which contains many small biflagellate somatic cells and a few large, non-motile reproductive cells called gonidia, and swims with a characteristic rolling motion.

Ever since van Leeuwenhoek first viewed these algal ‘fierce rollers’ with utter fascination in 1700, one biologist after another has pointed to Volvox as a model organism that could be used to support or refute some important biological concept of the day, such as spontaneous generation, preformation, epigenesis, the continuity of the germ plasm, and so on. All attempts to exploit Volvox as a laboratory model system failed, however, until the 1960s, when Richard Starr's group finally discovered a medium in which the organism would thrive and reproduce in captivity. Starr then circled the globe, bringing into culture all 18 known (and several previously unknown) Volvox species. By 1970, he concluded that a mating pair of isolates of V. carteri from Japan had the best combination of properties to serve as a genetic model system. Most studies of Volvox reported in the last 30 years have used those strains of V. carteri or their descendants, and so this guide will be similarly restricted in scope.

How does Volvox reproduce? Although V. carteri has a sexual cycle that can be induced and exploited for Mendelian analysis, the sexual cycle is not used for reproduction in nature; it is used to produce dormant, diploid zygotes that are able to survive adverse conditions. During all active phases, Volvox (like other green algae) is haploid and reproduces asexually.

In V. carteri, an asexual cycle begins when each mature gonidium initiates a rapid series of cleavage divisions, certain of which are visibly asymmetric and produce large gonidial initials and small somatic initials. The fully cleaved embryo contains all of the cells of both types that will be present in an adult, but it is inside out, and to achieve the adult configuration it must turn right-side-out in a gastrulation-like process called inversion. Cleavage and inversion together take about 8 hours, and the complete asexual cycle takes precisely two days when it is synchronized by a suitable light–dark cycle.

Following inversion, both the adult spheroid and the juvenile spheroids within it increase in size (without further cell division) by depositing large quantities of a glycoprotein-based extracellular matrix. Part way through the expansion phase, the juveniles digest their way out of the parental matrix and become free-swimming. By that time, the somatic cells of the parental spheroids, having fulfilled their function, are already moribund, and will soon be history.

Thus, whereas the gonidia are non-motile and potentially immortal, the somatic cells are specialized for motility, but destined to die when they are only about four days old. This difference raises with particular clarity a central question of developmental biology: how are cells with entirely different phenotypes produced from the descendants of a single cell?

What is the genetic program for germ–soma differentiation in Volvox? In most close relatives of Volvox, all cells first execute motility and other vegetative functions, and then they redifferentiate and engage in asexual reproduction. Mutational analysis has defined three types of gene that play the major roles in converting this ancestral program for biphasic development into a germ–soma dichotomy in V. carteri: first, the gls (ImageonidiaImageesImage) genes act during cleavage to permit asymmetric division and formation of large–small sister-cell pairs; then the regA (Imageenerator Image) gene acts in the small cells to prevent all aspects of reproductive development, while the lag (Imagete Imageonidia) genes act in the large cells to prevent formation of somatic features such as flagella and eyespots. Genetic and experimental analysis indicates that it is the difference in cell size at the end of cleavage that determines whether regA or the lag genes will be activated.

Numsgil:
I think this would be a fun project to undertake, but there are a couple of things I think DB would need before we could really start.  (Feel free to correct me where warranted)

1.  Outer coverings.  Volvox seems to have what's called a "mucilage coat that surrounds the sphere".  I noticed that they also use ties, which we of course already have.

If we could introduce a new cell connective mechanism that's like a big bag for the cells, we could really simulate them.  Inside the bag maybe the environmental grid is overriden, and it could apply a mild elasticity to keep cells together.

Kind of like a disc scooting ontop of a table.  What's on top of the disc can be taken with it, without necessarily disturbing what's underneath.

This would also allow other multibot contruction using more biologic methods.  Dump massive amounts of hormone A in front of you and massive amounts of hormone B behind you.  Reproduce.  If you have more of hormone A near you, become cell A, else if you have more of hormone B, become cell B.  The sac ensures no interference from other bots doing the same near you.

2.  Protruding Flagella.  We could simulate this with ties that have no connected bot.  We could then provide any wiggle mechanics we like or can imagine (I'm not sure how it'd work to be honest.  I know how real flagella work, though, so we could always base it off of the real thing).

I think that's it.

shvarz:
I actually think that these would be the minor problems.  There is no real need for mucilage in DBs, it is just something that keeps cells together.   Ties would work for that.

Flagella is just something that makes these cells move.  We don't have to simulate that - our bots move without no stinking flagella :)

The real problems are in coding the behaviour.  The program should go somthing like this:

1. Divide equally two-three times. (easy).
2. Divide non-equally a couple of times, making more small cells and just several big cells. (easy)
3. Organise into a circle. (that would be hard...).
4. Move together towards light (difficult but doable).
5. Once enough energy is accumulated by gonads (it should be easy for them - they don't do anything, just hitch a ride) - reproduce into "inside" of the circle giving most of the energy to the offspring.
6. Wait several cycles until babys "form" - die.

Organising into a circle would be quite hard and maintaining the circle if one of the cells in the cycle dies even harder.  Would require some complex detection mechanisms and cross-ties to keep the structure together.

Numsgil:
The circle forming is where I think some kind of sac would be useful.  Volvox use both ties and this mucilage.  The mucilage must serve some purpose ties alone can't.  If the cells just adhere to the mucilage, they will orient themselves in a spherical shape since the mucilage, like bubbles or other other similar things, tries to become as spherical as possible.

So if we have a circular sac the volvox wannabe bot would just divide alot inside it.  Then each cell, when it's done reproducing, moves in a random direction until it hits the edge of the circular sac, then sticks to the sac.  You should end up with a roughly spherical shape.

The flagella is just a fun idea I've been playing with, waiting for a good excuse to look into.

shvarz:
Hmm, the mucilage is essentially some gooey (sp?) stuff around cells that makes them stick to each other.  The easiest way to implement that is to pretend that there is an extra-layer of stuff around a bot (use slime?).  Can be defined by a slightly larger radius, like a circle around a circle.  Bots that touch each other in that radius stick together with certain force.  

But I guess it would eat CPU resources like pigs eat carrots, with all those extra collisions and forces....  But worth thinking about it anyway - all multicellular organisms create their own "matrix" for their cells.  Just a matter of time before we need it.

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