Molecular evidence for long-distance dispersal in the New Zealand pteridophyte flora
To examine the relative importance of long-distance dispersal in shaping the New Zealand pteridophyte (ferns and lycophytes) flora and its relationships with other floras, with the null hypothesis that the extant New Zealand pteridophyte flora has been isolated since New Zealand’s separation from Gondwana. Location
New Zealand. Methods
rbcL DNA sequences were assembled for 31 New Zealand pteridophyte genera, with each genus represented by one New Zealand species and the most closely related non-New Zealand species for which data were available. Maximum-likelihood, maximum-parsimony, and Bayesian analysis phylograms were constructed and used as input forr8smolecular dating, along with 23 fossil calibrations. Divergence estimates less than conservatively recent ages for New Zealand’s geological isolation, namely Ho > 30 Ma for pairs involving New Caledonian and Norfolk Island species and Ho > 55 Ma for all others, were taken as rejection of the null hypothesis. Results
The null hypothesis was rejected for all pairs except, under some parameter conditions, for those involving the New Zealand species Cardiomanes reniforme, Lindsaea trichomanoides, Loxsoma cunninghamii, Lygodium articulatum, Marattia salicina, and Pteris comans. However, the Lindsaea and Pteris results probably reflect the absence in the analyses of closely related non-New Zealand samples, while the Marattia divergence was highly contingent on which fossil calibrations were used. Main conclusions
Rejection of the null hypothesis for the majority of pairs implies that the extant New Zealand lineage has undergone long-distance dispersal either into or out of New Zealand. The notion of a long isolation since geological separation can, therefore, be dismissed for much of New Zealand’s pteridophyte flora. The analyses do not identify the direction of the long-distance dispersal, and these New Zealand lineages could have had vicariant origins with subsequent long-distance emigration. However, the alternative that many extant New Zealand pteridophyte lineages only arrived by long-distance immigration after geological isolation seems likely.