I started work on New Zealand’s Alpine grasshoppers in 2008 with my summer studentship. This group taxonomically suffers from over-splitting and I have shown how some described and putative species are not phenotypically or genetically distinct from a more widespread species. But most of my work is focusing on the hybridisation between a very locally distinct species that occurs only in and around Alexandra (Central Otago). This species, Siguas childi, is phenotypically distinctive but genetically shows intensive hybridisation with the more wide spread species, Sigaus australis (Trewick 2008). These two species are in complete sympatry with each other and the local species, S. childi, has become a conservation concern in recent years with fears that it may go extinct. We have found that although genetically S. childi often shares more similar DNA with an S. australis than an S. childi phenotypically the two species fall into two very distinct clusters with no phenotypic hybrids. This may be an example of speciation occurring in the presence of intensive gene flow.

Whilst researching the use of molecular evolution to study speciation and biogeographic patterns I have also become interested in the recent use of molecular evolution in studies examining the Latitudinal Biodiversity Gradient (LBG).  The LBG is on of the most striking global biogeographic patterns. Molecular data has been used to examine the ‘evolutionary speed hypothesis’, which suggests that species are evolving faster in the tropics (Rohde 1992). There is a well documented skew in rates of molecular evolution that favours faster rates in the tropics yet there is no consensus as to what drives this skew and whether or not this skew is enough to explain the gradient (Gillman, Keeling et al. 2009; Wright, Gillman et al. 2010). I have identified several problems with this hypothesis. Firstly there has been many different ideas as to what drives this difference in rate of molecular evolution: population size, metabolic rates, generation time and, UV exposure. Yet each of these drivers is plagued with challenges and differing opinions. However perhaps the largest problem with using molecular data to explain the increase in species diversity towards the tropics is in the inability to find conclusive evidence that changes in molecular evolution can in fact drive changes in speciation rates itself. There is evidence which has shown the reverse effect (termed punctuated evolution) (Venditti and Pagel 2010). Without this link any difference in molecular evolutionary rates will always fail to explain the gradient. I intend to use a large and comprehensive data set to examine some of these issues to try and shed more light on the subject. Research on the gradient involves comparison of species diversity, population biology and rates of molecular evolution in temperate and tropical sister lineages.

For part of this work we are using related taxa that occur in New Zealand and New Caledonia. Of particular interest are the giant land snails Placostylus.

Recent publication:

Dowle EJ, Morgan-Richards M, Trewick SA. 2013. Molecular evolution and the latitudinal biodiversity gradient. Heredity advance online publication doi: 10.1038/hdy.2013.4

Eddies blurb references

Gillman, L. N., D. J. Keeling, et al. (2009). "Latitude, elevation and the tempo of molecular evolution in mammals." Proceedings of the Royal Society B-Biological Sciences 276(1671): 3353-3359.
Rohde, K. (1992). "Latitudinal Gradients in Species-Diversity - the Search for the Primary Cause." Oikos 65(3): 514-527.
Trewick, S. A. (2008). "DNA Barcoding is not enough: mismatch of taxonomy and genealogy in New Zealand grasshoppers (Orthoptera: Acrididae)." Cladistics 24(2): 240-254.
Venditti, C. and M. Pagel (2010). "Speciation as an active force in promoting genetic evolution." TREE 25(1): 14-20.
Wright, S. D., L. N. Gillman, et al. (2010). "Energy and the tempo of evolution in amphibians." Global Ecology and Biogeography.