Little Fern Provides Cryptic Proof of On Going New Zealand To Chatham Islands Plant Dispersal
In 2007 fern researchers at Te Papa Tongarewa Museum of New Zealand published a paper outlining their discovery of 25 haplotypes (meaning DNA polymorphisms that are inherited as a unit) in New Zealand (North and South Island) samples of Hooker’s spleenwort (Asplenium hookerianum) (Shepherd et al. 2007). As a result of that study people wondered what would be the situation on the Chathams Islands?Accordingly two fronds of Hooker’s spleenwort were collected in September 2007, one each from the Tuku-a-Tamatea Nature Reserve, Chatham Island and from the Ellen Elizabeth Preece Conservation Covenant (Caravan Bush), Pitt Island. Following DNA analysis it was found that the frond from the Tuku-a-Tamatea represented a unique “Chatham Island” haplotype, while the frond from Pitt Island matched haplotype Q of Shepherd et al. (2007) the most common and widespread haplotype in New Zealand proper. These results have just been published in the international Journal of Biogeography (Shepherd et al. 2009).
The haplotypes provide clear evidence that Hooker’s spleenwort has colonised the Chatham Islands at least twice. While this is hardly earth shattering news – it is after all common knowledge that plants and animals have naturally reached New Zealand from Australia, and also the Chatham Islands from New Zealand, e.g., spur winged plover and welcome swallow, very few published studies provide some insight into the frequency of long distance dispersal (LDD). For the Chatham Islands we now have published evidence for LDD in both Hooker’s spleenwort (Shepherd et al. 2007) and shield fern (Polystichum vestitium) (Perrie et al. 2003). From a flora perspective the Chathams has possibly as many as 50 endemic vascular plants, which is c.12% of a total indigenous Chatham flora of c.410 taxa. While this figure reveals the importance of the islands as a global hot spot of diversity one feature that is frequently overlooked is the status of the remaining 360 or so taxa which are shared with New Zealand and Australia. Many of these plants, like Hooker’s spleenwort are very uncommon on the islands. Is this because they were formerly more widespread and have declined as a result of habitat loss, or is it because they have only recently colonised from New Zealand or both? Currently we just don’t know. What also of weeds, plant and animal pests that are capable of LDD? The Chatham Islands may seem remote by world standards but if indigenous plants and animals are capable of naturally colonizing it so too can organisms that Chatham Islanders don’t want. Studies to ascertain the levels of natural LDD colonisation using many of the plants shared between New Zealand and the Chatham Islands (including weed species) would provide a very useful guide as to the levels of LDD and subsequent genetic divergence of both native and introduced plants.
Peter J. de Lange
References
Perrie, L.R.; Brownsey, P.J.; Lockhart, P.J.; Large, M.F. 2003): Morphological and genetic diversity in the New Zealand fern Polystichum vestitum (Dryopteridaceae), with special reference to the Chatham Islands. New Zealand Journal of Botany 41: 581–602.
Shepherd, L.D.; Perrie, L.R.; Brownsey, P.J. 2007: Fire and ice: volcanic and glacial impacts on the phylogeography of the New Zealand forest fern Asplenium hookerianum.
Molecular Ecology 16: 536–549.
Shepherd, L.D.; de Lange, P.J.; Perrie, L.R. 2009: Multiple colonizations of a remote oceanic archipelago by one species: how common is long distance dispersal? Journal of Biogeography 36: 1972–1977.
Posted: 21/09/2009