Terrestrial Biodiversity

Evolution and dispersal of algae along a latitudinal gradient

Principle Investigator: Phil Novis
Organisation: Landcare Research

What we do: The most conspicuous "plants" in the Ross Sea region are actually algae, particularly cyanobacteria.  Marine algae can attain very large sizes; however, it is the much smaller microalgae that dominate the land in this part of continental Antarctica.  Although the individuals are small, very conspicuous populations of algae can appear in lakes, ponds, and streams, on irrigated soil, and on rock surfaces given sufficient time and conditions for proliferation.  This project aims to identify the organisms making up these populations, by examining them using light and electron microscopy and subjecting them to molecular genetic analysis (a suite of techniques including fingerprinting and sequencing DNA).  The Latitudinal Gradient Project makes it possible to compare these organisms over large distances within Antarctica (currently between 72 and 79 degrees south).  Because this span of latitude corresponds to a gradient of temperature and daylength, change in biodiversity can be correlated with environmental conditions, leading to hypotheses concerning evolution and dispersal of the algae and possible future changes in biodiversity resulting from changes in the environment.
 
Why we do it:  In many ways Antarctica provides a remarkable opportunity to undertake scientific research, in the absence of some key problems that complicate the interpreation of results in warmer regions.  Non-marine ecosystems in Antarctica are relatively simple: algae frequently dominate habitats without strong influence from other organisms, and the controls on growth and distribution are likely to be very predictable.  Non-marine habitats between 72 and 79 degrees south often support superficially similar populations of algae.  Are these populations really composed of the same organisms?  And if so, how have they travelled between sites?  And how often?  Do they exist now in isolation, or is genetic material still occasionally exchanged between them?  Such questions have become increasingly important to algologists in recent years.  "Cosmopolitanism" - the idea that relatively few species exist all over the globe - has been a prevailing view.  However, more and more exceptions (locally distributed, endemic algae) are being discovered, particularly in Oceania.  The latitudinal gradient mentioned above provides a potentially strong selective agent to help interpret results.  Therefore, Antarctica provides us with the best opportunity to examine the evolution, distribution and dispersal of structurally simple organisms at the molecular genetic level. 
 
Some things we've found out so far: Research to date has involved collecting samples of algae from the Garwood area (78 degrees south) and Cape Hallett (72 degrees south).  These represent the two ends of the latitudinal gradient, and algae from intermediate points have been obtained from other collectors.  Twenty of these collections, of the cyanobacterium Nostoc commune, are now being subjected to DNA sequencing and fingerprinting.  Sequence of part of the region known as tRNA(leu) shows that all these collections correspond to form species N. commune as defined by Wright et al. (2001, Int. J. Syst. Evol. Micro. 51:1839-1852), with very few differences between collections from different sites.  However, Amplified Fragment Length Polymorphism (AFLP), a fingerprinting technique that samples variation in sites recognised by certain DNA-cutting enzymes throughout the genome, detects significant genetic variation within these taxa.  Results to date indicate that the type of habitat (e.g., ponds versus terrestrial) corresponds with this variation more than latitude does.  However, not all samples have yet been examined.

This research contributes to the Latitudinal Gradient Project (LGP)