The curious case of the Satyrium neglectum complex: a taxonomic, ecological, and phylogenetic study.

Abstract

Classical herbarium taxonomy uses a combination of morphological features from pressed specimens and distribution information as data in species delimitation. Whilst morphology is critical to species delimitation, additional information on phylogenetic relationships and fieldbased studies of ecology can inform taxonomic decisions. Satyrium neglectum Schltr. is a highly variable taxon currently comprising two subspecies, ssp. neglectum (Schltr.) A.V. Hall and ssp. woodii (Schltr.) A.V. Hall both of which are widely distributed in subtropical southern and eastern Africa. Variation in morphology and differences in apparent pollination systems, both between the subspecies, and within ssp. neglectum suggests the presence of two taxa within the current concept of the latter. This information, as well the exclusive reliance on herbariumbased taxonomy in the most recent species revision, formed the background to this re-evaluation of the systematics of the complex. A combination of detailed morphometrics and molecular phylogenetics demonstrated that the current concept of S. neglectum ssp. neglectum is inaccurate. A principal components analysis using traits measured from herbarium records from across the range, and ethanol-preserved flowers from South Africa, confirmed the presence of two morphologically distinct clusters within ssp. neglectum. Representatives from these two forms are separated along an elevation gradient. Bayesian inference using a combination of plastid and nuclear DNA sequence data revealed incongruent topologies. The nuclear topology is not consistent with current taxonomic boundaries, and revealed a separation between the high-elevation form and the low-elevation form of S. neglectum ssp. neglectum as well as ssp. woodii. The plastid data set also confirmed the separation of the high-altitude form of ssp. neglectum, but otherwise the topology reflects geography, as southern African accessions are separate from eastern African accessions. Floral scent was investigated in combination with published and novel pollinator observations in the Satyrium neglectum species complex. Floral scent composition and emission rates are mostly representative of associated pollination syndromes in previously published pollination work, with the exception of the high-elevation form. Published observations of ssp. woodii indicate that the species is pollinated by amethyst and the greater-double-coloured sunbirds, and the scent composition and emission rate is largely reflective of this. In addition, published observations showed a system of butterfly pollination in the low-elevation form of ssp. neglectum and long-proboscid fly pollination in the high-elevation form. However, new night time observations revealed additional pollination by settling moths in the high elevation form. These observations make sense in the context of the scent profile, which is dominated by compounds typically associated with moth pollination, such as phenylethyl alcohol and eugenol. In addition, two settling moths showed electroantennographic responses to the two dominant compounds in the scent bouquet of the high-elevation form. The compounds that dominate the scent of the butterfly-pollinated low elevation form are hexan-1-ol, octan-1-ol and benzyl alcohol, while previously published work on ssp. woodii showed that it is virtually unscented, and has emission rates that are markedly lower than other taxa pollinated by insects. Based on the morphological, phylogenetic and scent chemistry analyses, a case was made for the high-altitude form to be considered a separate taxonomic entity. This is formally described under the new name Satyrium basutorum. The analyses suggest that ssp. neglectum and ssp. woodii should be retained as subspecies, but a further investigation is required to identify the status of the eastern African synonyms Satyrium sceptrum and S. neglectum var. brevicalcar.