Gene flow, adaptation and speciation in Antarctic octopus: consequences of climate change

A project undertaken at the Department of Genetics, La Trobe University, and supervised by Jan Strugnell


Australian Antarctic Territory covers about 42% of Antarctica (which is nearly 80% of the total area of Australia itself).  The benthic marine fauna of this region of Antarctica are very poorly sampled and this area consistently represents a crucial sampling gap in our ability to understand the evolution of Antarctic fauna.   250 geo-referenced octopod samples have been sourced (from the Australian Antarctic Division) that have been collected from the waters off the Australian Antarctic Territory and therefore fill the sampling gap prevalent in studies of Antarctic benthos.  In conjunction with samples already collected from other Antarctic regions these samples provide unparalleled coverage of a single Antarctic taxon around Antarctica and therefore represent a timely and unique opportunity to understand the effect of climate-related processes on driving intra and inter-specific divergence around the Antarctic continent.

Octopods are an ideal and tangible taxon to determine the effects of climatic and oceanographic processes on the evolution of Antarctic fauna, with at least 7 genera and upwards of 30 species known to inhabit the Southern Ocean.  In particular, it is clear that the taxonomy and therefore the processes that drive speciation of Antarctic octopuses are complex, with the group certainly more diverse than presently appreciated.  Taxonomic research is essential to fully quantify patterns of octopus biodiversity: these data form the basis to test hypotheses concerning processes that drive adaptive divergence and speciation.
 
Molecular laboratory work (including DNA extraction and sequencing) for this project will be carried out in Jan Strugnell's laboratory at La Trobe University. Primers effective on mitochondrial and nuclear genes have already been developed and optimised for octopods (Strugnell et al. 2005). 
 
Cryptic species (i.e. reproductive barriers within sympatric 'populations') will be identified using a powerful combination of Bayesian clustering, re-evaluation of whole specimens and maximum likelihood and Bayesian analyses of gene sequences.  Throughout the Antarctic seascape, 'landscape' analyses will be used to identify genetic boundaries that will be mapped to determine the level of congruence among species.  The effect of the Antarctic Circumpolar current in driving the direction of dispersal (source-sink dynamics) will be determine from asymmetry in migration and differences in genetic diversity.  Other standard analyses will be used to determine, for example, levels of genetic divergence, models of population structure, spatial scale of genetic equilibrium and demographic history.

 

Jan Strugnell with octopus on a cruise in the Southern Ocean