Research Article: Genetic structuring of the coastal herb Arthropodium cirratum (Asparagaceae) is shaped by low gene flow, hybridization and prehistoric translocation

Date Published: October 17, 2018

Publisher: Public Library of Science

Author(s): Lara D. Shepherd, Mariana Bulgarella, Peter J. de Lange, Tzen-Yuh Chiang.


We examined the genetic structuring of rengarenga (Arthropodium cirratum; Asparagaceae), an endemic New Zealand coastal herb, using nuclear microsatellite markers. This species was brought into cultivation by Māori within the last 700–800 years for its edible roots and was transplanted beyond its natural distribution as part of its cultivation. We found very high levels of genetic structuring in the natural populations (FST = 0.84), indicating low levels of gene flow. Reduced genetic diversity was found in the translocated populations, suggesting a large loss of genetic diversity early in the domestication process. The data indicates that rengarenga was brought into cultivation independently at least three times, with the sources of these introductions located within a narrow area encompassing about 250km of coastline. Hybridization was inferred between A. cirratum and the closely related A. bifurcatum, despite A. birfucatum not occurring in the vicinity.

Partial Text

New Zealand was the last substantial landmass to be colonised [1], about 700–800 years ago [2]. Pacific Islanders translocated and cultivated many food, medicinal and fibre plants as they colonised the Pacific [3]. Six of these were known to be cultivated in New Zealand by Māori at the time of European contact but their cultivation was marginal owing to New Zealand’s relatively cooler climate. Instead Māori began to cultivate several endemic New Zealand plant species for food, fibre and medicine [4]. These cultivated endemic plants are useful for studying the domestication process because their initial cultivation must have been no later than 800 years ago, and they therefore provide a window into the early stages of the domestication process.

Sampling included the specimens for which chloroplast loci had been sequenced [8], with additional samples for some populations. In total 279 A. cirratum samples from 54 populations were included with 1 to 22 individuals per population sampled (Table 1). Many populations were small so large numbers of individuals could not be sampled for these. Six samples of A. bifurcatum, from four sites, were also included; the samples of A. bifurcatum were pooled as one group for all analyses. Approval to collect samples from conservation land was provided by the Department of Conservation (permits WA-23814-FLO, BOP-23814-FLO, TT-23661-FLO and NO-233360-FLO). Permission to collect samples from the Otari Wilton’s Bush botanic gardens was provided under permit 145 and the permission of individual land owners was obtained prior to the collection of samples from private land.

Global population differentiation for A. cirratum was very high (FST = 0.84). Pairwise FST values for A. cirratum, calculated for populations with >5 individuals, were generally high and significant (Table 2). The only non-significant FST values were between the adjacent populations of Whanarua and Waikawa (populations 40 and 41) and the comparisons between the three cultivated South Island populations (populations 52, 54 and 55). Pairwise FST values between A. bifurcatum and the A. cirratum populations were also high and ranged from 0.14 to 0.93 (Table 2).




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