The curious case of the Satyrium neglectum complex: a taxonomic, ecological, and phylogenetic study.
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Date
2021
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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.
Description
Masters Degree. University of KwaZulu-Natal, Pietermaritzburg.