Biogeography of temperate Australasian Polystichum ferns as inferred from chloroplast sequence and AFLP

Abstract

Aim and location New Zealand began to separate from Gondwana c. 85 Ma, and has been isolated from the nearest large landmass, Australia, by some 2000 km of the Tasman Sea since c. 60 Ma. Given New Zealand's long geographical isolation, there has been considerable interest in explaining the origins of its different biotic elements. Here we investigate the biogeography of the fern genus Polystichum from temperate Australasia. Six species are found in New Zealand, four in Australia, and two on Lord Howe Island. Methods The evolutionary relationships between the twelve Polystichum species found in temperate Australasia were inferred from phylogenetic analyses of two molecular data sets: DNA sequence from the chloroplast rps4–trnS spacer locus; and AFLP DNA‐fingerprinting. The timing of the separation between Australian and New Zealand Polystichum was estimated by using the fossil record to temporally calibrate the rbcL sequence differentiation between representative species from these regions. Results Species of Polystichum from New Zealand appear to comprise a monophyletic group. This suggests that Polystichum crossed the Tasman only once. Temporal calibration of the rbcL sequence differentiation between Australian and New Zealand Polystichum indicates that a vicariant explanation for their separation can be rejected in favour of trans‐oceanic dispersal. Main conclusions The extant diversity within New Zealand Polystichum appears to have been derived from a single, trans‐oceanic dispersal event (within the last c. 20 Myr), followed by a relatively extensive in situ ecological radiation.

A well-sampled phylogenetic analysis of the polystichoid ferns (Dryopteridaceae) suggests a complex biogeographical history involving both boreotropical migrations and recent transoceanic dispersals

“…For example, species of Clade A all belong to the section Xiphopolystichum (sensu Zhang and Barrington, 2013a) confirming this section monophyletic as reported by Driscoll and Barrington (2007), Li et al (2007Li et al ( , 2008, and Lu et al (2007). We failed to recover the monophyly of Australasian species, despite the fact that this group was recovered as monophyletic in two independent studies Perrie et al, 2003). Such uncertainties are likely related to the differences in the taxonomic sampling.…”

“…Such uncertainties are likely related to the differences in the taxonomic sampling. Perrie et al (2003) included only two species from outside of Australasia, whereas Li et al (2007) focused on the relationships between Asian and Australasia species and their sampling did not include taxa from outside these two areas. Therefore, the monophyly of Australasia species is equivocal and need further investigation.…”

“…The monophyly of polystichoid ferns is not in doubt (Driscoll and Barrington, 2007;Li et al, 2007;Little and Barrington, 2003;Lu et al, 2007;Schuettpelz and Pryer, 2008;McHenry and Barrington, 2014;Le Péchon et al, 2016) and unlike most other fern taxa, Polystichum has been a subject of several previous biogeographical analyses (e.g., Perrie et al, 2003;Li et al, 2004Li et al, , 2007Driscoll and Barrington, 2007;McHenry and Barrington, 2014). Polystichum may have originated in (i) Asia ca.…”

“…Polystichum may have originated in (i) Asia ca. 75 Ma ago (Li et al, 2008(Li et al, , 2004), (ii) may then have migrated to Australasia in the middle Miocene Perrie et al, 2003); (iii) and colonized Hawaii at least two times (Driscoll and Barrington, 2007). Recently, McHenry and Barrington (2014) showed that the exindusiate Andean Polystichum diverged from a Mexican lineage during the middle Miocene.…”

“…Recently, McHenry and Barrington (2014) showed that the exindusiate Andean Polystichum diverged from a Mexican lineage during the middle Miocene. However, all previous phylogenetic and biogeographical studies on the polystichoid ferns focused on specific geographical regions and were based on limited taxon and character samplings (Driscoll and Barrington, 2007;Li et al, 2008Li et al, , 2007Li et al, , 2004Lu et al, 2007;McHenry and Barrington, 2014;Perrie et al, 2003). Large-scale analyses using a worldwide time-calibrated phylogenetic framework to trace the biogeographical history of the polystichoid ferns are still lacking except a recent study by Le Péchon et al (2016) which focused on testing the morphology-based classifications.…”