Freshwater Biology - How I would teach it

Figure 1. The  beauty of amphibians, here an unnamed frog.

 

As a young man in Africa and later in the UK, I taught freshwater biology at both second and final year levels. My 1966 PhD and postdoc work were undertaken over a period of some eight years at such wonderful places as Lake Kariba ( 4 years) and lake Chilwa (4 years), in tropical Africa and I remained active in freshwater research and publication until the mid 1980s. I was thus presumably qualified to carry out teaching responsibilities in freshwater biology. My aim here is to produce an outline plan for a hypothetical course in freshwater biology which I would teach today, given the chance. From the perspective of nearly 40 years I have been looking back on those early years and wondering why freshwater biology seemed such an intellectually unrewarding subject and how it might be improved. A large part of this failing, I believe, is the absence of a unifying theme in undergraduate courses. This applies as much to my own earlier teaching as to the efforts of others. It  applies to freshwater biology specifically and not so much to ecology in general. Furthermore, freshwater biology, as it its taught today, has tended to be about the nature of the habitat rather than about the biota. It is this emphasis on habitat that may be responsible for the absence of a strong theme. A greater role for freshwater fauna could readily lead to a unifying theme. The theory of evolution custom made for the role. We freshwater biologists should continuously reminded ourselves of Theodore Dobzhansky's famous maxim . ... "Nothing in biology makes sense except in the light of evolution" (Dobzhansky 1973).

With this in mind I thought a way forward  might be to create a list of key literature sources. Under the umbrella of evolution I would emphasise three things. First, weight would be placed on  the waters of Africa. Africa has an exceptional diversity of freshwater habitats and faunas and was the cradle of mankind and, to quote Richard Dawkins, p265, ..." this alone makes African ecosystems an object of singular fascination" (Dawkins 2004). For that reason field courses in Africa would be desirable and a realistic possibility, at least in the financial climate prevailing before I retired in 2004. Second, in contrast to most courses I know of, I  would make vertebrates the principal study organism. This melds well with an emphasis on Africa with its wonderful world of fish and amphibians (Fig. 1). The study of amphibians leads naturally to the adaptive laboratories of ephemeral waters such as rain pools. Amphibians illustrate beautifully two things; phenotypic plasticity, that is the facultative response of which an organism is capable in the face of environmental challenges. An example of phenotypic plasticity is the development of  calluses on the hands of gardeners. Most amphibians have a larval stage dependent on standing water. It is these immature stages that show an astonishing range of adaptations to typically ephemeral and unpredictable water on which they depend. The larval stages are amenable to experimental manipulation, for example, the addition of iodine to the water, to alter developmental rate (Spaul 1928). Such manipulation opens the possibility of exploring mechanisms of plasticity and developmental adaptation. I can think of no finer laboratory to engage the interests of students.

Turning to fish (and I expressly do not meant commercial fisheries): fish tend to dominate permanent waters to the virtual exclusion of amphibians. The fish faun of the great lakes of Africa; Malawi, Tanganyika, and Victoria,  have captured the interest of biologists for many years. Here there is an outstanding demonstration of the wonders of adaptive speciation. I refer to the  indigenous cichlid flocks inhabiting these waters (Kocker 2004).

I give little attention to rivers and streams only because I am here attempting a  hypothetical exercise with myself as sole teacher and my research experience does no fit me for advanced teaching in those habitats. 

Core literature sources appear below:

  1). Two books to provide the ecological background. Begon et al (Begon, Townsend et al. 2006)/Corze and Reader (Croze and J. 2000).

Townsend et al. are here intended to provide access to the general principles of ecology. They provide the ecological setting for freshwater biology and set ecology within the evolutionary landscape. Croze and Reader offer a good general ecology text set in Africa and hence an appropriate accompaniment for Beadle (below).  Croze and Reader provide a fine introduction to the rich mammalian ecology of Africa. *

2).  The inland waters of tropical Africa.  Leonard  Beadle (Beadle 1974).

Leonard has the knack of exciting in his reader a sense of adventure and wonder at the wilderness and the adaptive challenges encountered by freshwater dwelling animals in  the  waters of Africa. This is just the text, I believe, to attract students to a research career in the subject.  Here both an introduction to both phenotypic plasticity (traditionally called 'adaptation' by physiologists), and changes in gene frequency within a population. i.e. evolution, can be found.

3). The Biology of Lakes and Ponds. Brönmark and Hanson (Bronmark and Hansson 2005).

To broaden an African emphasis and to introduce small and ephemeral water bodies, I would  include this excellent book. Research effort in Europe and America has favoured large lakes. By contrast these authors emphasise biotic adaptations in smaller waters. These, after all must be many orders of magnitude more abundant than larger lakes and because they are small tend to be ephemeral - drying out or freezing in unpredictable patterns which raise fascinating questions about adaptation.

4) The evolutionary ecology of rain pools

To build on the biology of temporary waters there are the ubiquitous rain pool. These are the ultimate in small bodies of water. They are the  most ephemeral and numerous waters, sometimes holding only a few ml of water. They lend themselves well to experimental manipulation. In view of their abundance rain pools may be where adaptive changes in the evolution of freshwater faunas principally take place - and even where life on earth may have originated, see Charles Darwin famous,  'Warm Little Pond' (Darwin 1Feb 1871). Some fine work on the biogeography of rain pool dwelling crustacea is being undertaken  by Brian Tims, Vanshoenwinkel  and colleagues in Africa and Australia (Pinceel, Brendonck et al. 2013). My own research in Africa focused on the extraordinary insects breeding exclusively in rain pools on rock surfaces (McLachlan and Ladle 2001). A recent explosion of research on rain pool faunas include some interesting adaptations among amphibians and even fish. 

References

Strother, P.K., Battison, L., Brasier, M. D. and Wellman, C. H. (2011). Earth's earliest non-marine eukaryotes. Nature 473, 505-509.

Beadle, L. C. (1974). The Inland Waters of Tropical Africa. London, Longman.

           

Begon, M., C. R. Townsend, et al. (2006). Ecology. From Individuals to Ecosystems., Blackwell Publishing 

           

Bronmark, C. and L.-A. Hansson (2005). The Biology of Lakes and Ponds. Oxford, Oxford University Press.

           

Croze, H. and R. J. (2000). Pyramids of Life. London, Harvill Press.

           

Darwin, C. (1Feb 1871). Warm Little Pond.

           

Dawkins, R. (2004). A devil's chaplain. London, Phoenix.

           

Dobzhansky, T. G. (1973). "Nothing in Biology makes sense except in the Light of Evolution." The American Biology Teacher 35: 125-129.

           

Kocker, T. D. (2004). "Adaptive Evolution and Explosive Spciation: The Cichlid Fish Model." Nature Reviews Genetics 5: 288-298.

           

McLachlan, A. J. and R. Ladle (2001). "Life in the puddle: behavioural and life-cycle adaptations in the Diptera of tropical rain pools." Biological Reviews 76: 377-388.

           

Pinceel, T., L. Brendonck, et al. (2013). "Environnmental change as a driver of diversification in temporary aquatic habitats: does the genetic structure of extant fairy shrimp populations reflect historic aridification?" Freshwater Biology 58: 1556-1572.

           

Spaul, E. A. (1928). "Comparative Studies of Accelarated Amphibian Metamorphosis. ." Journal of Experimental Biology 5: 212-232.

* On reflection, and with an eye to the evolutionary theme, I cannot avoid adding the highly effective text book by Scott Freeman and Jon Herron (1988). I wish this fine book had been available when I was an undergraduate.

Freeman , S. and Herron, J. (1998). Evolutionary analysis. Prentis Hall, New Jersey.