A Biochemical Genetic Evaluation of Taxonomy of Sophora Microphylla (Fabaceae Subfamily Papilionoideae)

Abstract

Sophora (sect. Edwardsia) microphylla has previously been circumscribed as a widespread and variable species found throughout New Zealand from the far north to the far south. The extensive morphological variation within S.microphylla has recently lead to the promotion to species level of three locally distributed forms which lack a distinctive juvenile phase: S.fulvida restricted to the coast west of Auckland, S. longicarinata in the Nelson/Takaka area, and S. chathamica found in the North Island and the Chatham Islands. Two new species have also been recognized: S. godleyi from the Wanganui/Rangitikei region in the central North Island and S. molloyi found in the southern North Island headlands and on either side of Cook Strait. The recognition of these species is largely based on morphological differences and the Ecological Species Concept. Information obtained from enzyme electrophoresis is used in this study to further test the genetic and phylogenetic relationships of these new Sophora species, and help determine the validity of their promotion to species level. The Phylogenetic Species Concept defines species as 'the smallest aggregation of populations diagnosable by a unique combination of character states'. Unique allozymes found fixed within any of these newly described Sophora may be considered evidence of their genetic uniqueness and supports their recent promotion to species level. Seed material was collected from thirty-nine different localities. Six different loci with two or three alternative alleles were successfully resolved and used in this study. An Unweighted Pair Group with Arithmetic Mean (UPGMA) phenogram comparing Nei's genetic distance between all populations in the S. microphylla complex does not show any particular subdivisions to support any of the new Sophora species. Unbiased estimates of Nei's distance between and within the new Sophora species are low and give higher infraspecific than interspecific values. Variation in gene diversity overall was low with a single allele comprising the majority of the variation across all loci and populations. A deficiency in heterozygotes according to the Hardy-Weinberg Equilibrium was observed across all populations and loci, contributing to an overall non-conformity to Hardy-Weinberg Equilibrium. The allozyme data do not support a 'unique combination of character states' within any of the new Sophora species as required by the phylogenetic species concept to delimit species. In contrast, S. japonica from Japan showed two fixed differences relative to the New Zealand native species. The evidence suggests that S. microphylla sensu lato is still undergoing adaptive radiation at the allozyme level. Furthermore, adaptive radiation may still be occurring throughout all New Zealand Sophora as there are relatively small allozyme differences distinguishing S. microphylla sensu lato from S. tetraptera. Even with pronounced morphological differences, the process of adaptive radiation is commonly observed still occurring at the molecular level in many island plant taxa.