Genetic and morphological identification of a recurrent Dicksonia tree fern hybrid in New Zealand.

Lara D Shepherd,Leon R Perrie,Patrick J Brownsey,Claire Newell,Chris Stowe,Olga De Castro

doi:10.1371/journal.pone.0216903

Abstract

Hybridization is common in many ferns and has been a significant factor in fern evolution and speciation. However, hybrids are rare between the approximately 30 species of Dicksonia tree ferns world-wide, and none are well documented. In this study we examine the relationship of a newly-discovered Dicksonia tree fern from Whirinaki, New Zealand, which does not fit the current taxonomy of the three species currently recognized in New Zealand. Our microsatellite genotyping and ddRAD-seq data indicate these plants are F1 hybrids that have formed multiple times between D. fibrosa and D. lanata subsp. lanata. The Whirinaki plants have intermediate morphology between D. fibrosa and D. lanata subsp. lanata and their malformed spores are consistent with a hybrid origin. The Whirinaki plants–Dicksonia fibrosa × D. lanata subsp. lanata–are an example of hybridization between distantly related fern lineages, with the two parent species estimated to have diverged 55–25 mya. Our chloroplast sequencing indicates asymmetric chloroplast inheritance in the Whirinaki morphology with D. lanata subsp. lanata always contributing the chloroplast genome.

Highlights

Tree ferns (Cyatheales) are often a locally dominant feature of wet temperate Southern Hemisphere forests
Using morphological and genetic data we examine whether the Whirinaki morphology is: 1. the Australian species D. antarctica Labill., which is sometimes confused with D. fibrosa [2], including sometimes claimed to be present in New Zealand; 2. an undescribed species; 3. a homoploid hybrid between D. fibrosa and D. lanata subsp. lanata that has formed once and has spread vegetatively; 4. a recurrent homoploid hybrid between D. fibrosa and D. lanata subsp. lanata; 5. a fertile allopolyploid between D. fibrosa and D. lanata subsp. lanata
The haplotypes detected in D. antarctica and D. fibrosa differed from the D. lanata haplotypes by a 6 bp insertion plus at least 12 substitutions

Summary

Introduction

Tree ferns (Cyatheales) are often a locally dominant feature of wet temperate Southern Hemisphere forests. Within New Zealand’s forests tree ferns often represent a significant proportion of the forest community based on the number of individuals, biomass and basal area [1]. Two genera are represented in New Zealand’s tree ferns, Cyathea Sm. Dicksonia contains around 30 species that are found in Central and South America, Southeast Asia, eastern Australia, New Zealand and the Pacific [2,4]. Three indigenous Dicksonia species are recognized in New Zealand; all are endemic [2]. (whekī) have trunked rhizomes up to 6m tall and 7m tall, respectively. Both are found throughout the North Island in lowland to montane forest and are largely confined to lowland and coastal areas in the South Island [2].

Methods

Results

Conclusion