How cichlids adapt to changing environmental conditions

[duanes]

I dropped this link in another post, but believe it to be important enough to get its own
PDFRapid morphological change in multiple cichlid ecotypes.pdf

 

[neutrino]

I read that paper recently. It's a worthwhile read for someone interested in genetics, environmental effects on cichlids, or just SA cichlids.

Many comments could be made. A simple one is Heros efasciatus (efasciatus are specifically mentioned in the paper, but I've yet to see anything different for other Heros species) are omnivores. As I've also read in other papers, they become fruit eaters in certain conditions. This is different from some common wisdom that they need a lot of "greens" in their diet. They enjoy them but do not require them in an otherwise quality diet.

Another, not as simple, is it doesn't take thousands or millions of years for genetic mechanisms to respond to habitat changes in certain ways, the time scale for some adaptations is much shorter than the model some of us understand and doesn't wait on gene transcription errors (mutations). Some have been demonstrated as repeatable responses, apparently built into genetic mechanisms. Some are essentially morphological or species oscillations that have been taking place for long periods, tens of millions of years for geophagines and haplochromines. That they can happen quickly better fits the environmental, geologic, or climate histories of some regions that have changed over shorter periods than we might assume. The big picture is this has been happening for very long periods within such groups, which gives some context. After 50 million years or so, geophagines are still geophagines. After 45-46 million years haplochromines are still haplochromines.

Major Low Levels of Lake Malawi and their Implications for Speciation Rates in Cichlid Fishes

http://rspb.royalsocietypublishing.org/content/240/1299/519

Excerpts regarding lake level changes:

Major recessions occurred (note: several such events are mentioned in this paper, I'm skipping to the most recent) ...within the period 1500-1850. The 1500-1850 lake recession-refilling cycle is documented by using a variety of techniques.

...Oral histories reflect a group memory of this low period...

...methods show that lacustrine sedimentation had resumed by about 1860. At this time, early explorers, such as Livingstone, were reporting evidence of rising lake levels. Hydrological modelling shows that the lake-level changes indicated are possible in the timespan available.

Regarding implications for and data regarding consequences for cichlids in the lake:

The species flock of rocky-shore dwelling Lake Malawi cichlids known as `Mbuna' contains about 200 species in Malawi's waters. Mitochondrial DNA differentiation shows that the flock as a whole is of extremely recent origin. Almost every rocky outcrop and island has a unique Mbuna fauna, with endemic colour forms and species. As many of these islands and outcrops were dry land within the last 200-300 years, the establishment of the faunas has taken place within that time.

Another paper:
Divergent selection during speciation of Lake Malawi cichlid fishes inferred from parallel radiations in nuptial coloration
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC283548/

Repeated evolution of the same phenotypic difference during independent episodes of speciation is strong evidence for selection during speciation.

...most color variation among the rapidly radiated Lake Victoria cichlids and Lake Malawi Mbuna appears highly repetitive and can be partitioned into a small number of core patterns that are similar between the lakes.

...Each of the four male nuptial and three X-linked color patterns arose or was lost repeatedly within the zebra complex and additional times between the other Mbuna.

DNA, mRNA, epigenetics, etc. The science is changing and so is our understanding of how some this may work.