Mysteries of science: Why are cichlids evolving at a superfast rate?

[mynah]

Lake Victoria, which has only been around for some 12 000 years, has about 300 species of cichlid. Other great African lakes (Malawi, Tanganyika) also sport a rich variety - as do lakes across the waters in Panama. It is estimated that a new species appears in Lake Victoria every 30 to 40 years. Why? What makes these fishes so special?

[Moontanman]

I think their isolation and abundance of ecological niches has a lot to do with it.

[mynah]

I agree that would be important factors - but the fact that it happened in several places at once to the same group of fishes suggests to me that there is some special genetic advantage at work as well. Could this be a present-day example of the bursts of speciation experienced by various groups of animals (e.g. mammals in the early Tertiary) in prehistoric times?

[mynah]

Here's a good article on the subject:

 

Mechanisms and molecular genetic bases of rapid

speciation in African cichlids

[sman]

Here's a good article on the subject:

 

Mechanisms and molecular genetic bases of rapid

speciation in African cichlids

 

Good Lord! I'll print it out & read a little at a time if you don't mind. :)

 

From what I understand, different ecological niches are not nessesary for speciation, just genetic isolation - and cichlids are the shinning example of this. Rapid speciation seems to happen during genetic isolation - but not total isolation, so there's a trickle of gene flow between populations, but just a trickle. It' fascinating stuff - thank you.

[HydrogenBond]

This rapid speciation appears to reflect the impact of environmental pressures on evolution. In a tight eco-system, each species is optimized within a bandwidth, because of pressures above, below and lateral. There is an advantage being in the center, balancing this triangle of pressures. It has to be prepare for predictors, take advantage of the food available, meet other environmental demands such as terrain and weather, and meet the social needs of its group. If you can meet all those needs you have an advantage, since all conditions are met for that environment.

 

Say we change the pressures above and below, in a continuous way over time, the center is moving. As soon as advantage reaches a center, that center has moved, creating an imbalance.

 

I often wondered why we don't see modern bacteria turning into multicellular precursors, since we assume that something along this line happened in the past. Way in the past, there was no ceiling pushing down, since this was the top of the food chain. Modern bacteria have a thick ceiling, so rising beyond this ceiling is not so easy.

 

This might be analogous to going from a senior in high school, to a freshman in college. If you are the first college freshman of all time, all your previous advantages remain plus some new ones. But if you are a lowly freshman moving into an established college of sophomores, juniors and seniors, you are chum for the sharks. Colleges have rules against hazing and harassment, but in nature, this is the way of the world. So the bacteria stay on center and evolve laterally.

 

The cichlids may be positioned in a triangle of pressures, where the center moves and steady state is hard to reach. Their own speciation is creating an unusual pressure at the lateral level. The young lake that is building up species combined with modern pollution that is sorting the field, would have the impact of altering the pressures above and below, relative to the cichlids.

[sman]

Natural selection does not find perfect or elegant or even optimal solutions, all that is required of it is to find satisfactory solutions.

Sydney Brenner

 

:lightning:)

[HydrogenBond]

Let me explain a simple lateral pressure that could theoretically cause this speciation. The easiest way to see this is to look at dogs. There are over a hundred breeds of dogs (150+), that are registered with international kennel clubs. The reason there are so many breeds, is because breeders looked for the odd ball specification, so they can create a new breed.

 

Normally in nature, the brain/sensory specifications for breeding are very specific, within respect to a given species. It may involve checks and balances with respect to visuals, sound, smells, behavioral patterns, etc. If the mating call is off, no go. These have the impact of keeping the species in much tighter tolerance than dog breeding, where breeder often mixes apples with oranges. Relative to dogs, if one liked German Shepherds, and wished to breed them, the criterion gets tight again, so they will breed true.

 

Relative to the cichlids, all that had to happen was the breeding criterion become laxer, with a narrower range of criteria. This, like dogs breeding, makes the odd ball variation more desirable. This is able to combine additional genetic combinations, beyond what would occur under tighter sensory tolerances.

 

If you look at humans, over the ages, races, economic classes, nationalities, etc., tried to breed true to given specifications. In modern times, these semi-natural restrictions, linger to some extent, being more open, genetic blend more than ever. Maybe the cichlid babes, instead of being by the book, like most critters, prefer variation. While the cichlid studs instead of being by the book, also prefer variations. Most species are by the book which may be why they stay similar, until there is entropy in the DNA. The cichlids may have more entropy in the brain and not have to wait for DNA entropy.

[maikeru]

If you look at humans, over the ages, races, economic classes, nationalities, etc., tried to breed true to given specifications. In modern times, these semi-natural restrictions, linger to some extent, being more open, genetic blend more than ever. Maybe the cichlid babes, instead of being by the book, like most critters, prefer variation. While the cichlid studs instead of being by the book, also prefer variations. Most species are by the book which may be why they stay similar, until there is entropy in the DNA. The cichlids may have more entropy in the brain and not have to wait for DNA entropy.

 

Hydrogen, I was reading it up until the point you mentioned "races" and you should know, if you're a biologist, that race doesn't exist in humans, except for the human race. There's variation and genetic diversity within ethnic groups to greater or lesser degrees, or most populations whether animal, plant, microbial, or some form of carbon creepy-crawly for that matter, and this is the raw material that natural selection and other selective forces act upon (including artificial selection you mentioned with humans breeding dogs).

[Moontanman]

I think it should be noted that the fish being discussed are reproductively much more active than most other fishes. They breed like crazy, this leads to speciation as the fishes fight over resources and living space. In most fish species breeding is a highly seasonal thing, salmon for instance breed only once in their lives. Every salmon goes to an individual stream often the stream is less than a meter across where these fish breed and the hatched eggs come back to this very place to breed when they mature. Each small stream is genetically distinct from every other stream (although a small amount of mixing might happen by chance) the salmon do not compete with each other they compete with a specific environment resulting in the overall shape and size of the population being close enough to be the same species due to the limited breeding and small over lap of each population.

 

Cichlids in general are far more diverse than salmon like fishes and breed for more profusely, successful individuals might breed hundreds of times instead of one time in their life times. Cichlids are also free to seek out optimum habitat niches and this produces competition between individuals over how and where to live and breed. Turn these fishes loose in a body of water with little competition other than themselves and speciation is inevitable.

 

A similar type of speciation in a group of fishes can be seen in live bearers such as guppies, mollies, platies, swordtails and other related fishes. They are even more plastic than cichlids and in captivity can be bred into an amazing number of types far surpassing cichlids in both natural and artificial environments. Live bearers do this by breeding profusely and competing between themselves for habitats other fish cannot exploit as well or not all giving rise to a similar profusion of species in many areas.

[sman]

Cichlids may be particularly apt to specialization and the young African lakes may be particularly rich in untapped eco niches - these two things alone may mean (relatively) rapid speciation, but that's boring. The really cool thing that's going on with African cichlids is sexual selection. Females are picky about whom they mate with. Since genes involved in mating behavior are inherited by both sexes, these changes can take off geometrically, compared with the slow, incremental work of habitat adaption.

 

BTW, can't you buy cichlids at the pet store? It might be interesting to compare domesticated forms with the African forms.