Paraustrosimulium

The relationships of Paraustrosimulium and biogeographic considerations

Evidence presented here and in accordance with most previous studies is that Paraustrosimulium, Cnesiamima, Austrosimulium and “ Cnephia ” pilfreyi all share an immediate common ancestry (e.g., Wygodzinsky & Coscarón, 1972, Gil-Azevedo & Maia-Herzog 2007, Craig et al. 2012). This is somewhat at odds with Moulton’s (2003) comprehensive analysis of molecular data, in which Austrosimulium was placed as the sister group of all other simuliine genera analyzed—distantly removed from a strongly supported monophyletic lineage including “ Cnephia ” pilfreyi, Paraustrosimulium and “ Austrosimulium colboi ” (note that Cnesiamima was not among the taxa sampled in Moulton’s analysis). Whether the unexpected position of Austrosimulium was a product of long- branch attraction—as suggested by Gil-Azevedo & Maia-Herzog (2007), remains an open question. Monophyly of this clade of austral simuliids is supported by up to 4 synamporphies: viz. reduced abdominal armature in the pupa, hypostoma with ventral wall extended anteriorly to obscure teeth, larval antenna with distal antennomere markedly longer than the two proximal antennomeres combined (condition reversed in members of A. Novaustrosimulium) and presence of interarm struts in anal sclerite (yet to be definitely confirmed in “ Cnephia ” pilfreyi.

Monophyly of Paraustrosimulium, as currently defined, is supported by just one synapomorphy: namely, presence of markedly expressed cervical sclerites in the adults. Wygodzinsky & Coscarón (1973) established the monotypic genus Cnesiamima based solely on adults, but acknowledged the overall similarity of that segregate with Paraustrosimulium. Had the immature stages of Cnesiamima been known to those authors, as they are now, we wonder whether they would have described it as a separate genus. Nonetheless, the phylogenetic analysis of Gil-Azevedo & Maia-Herzog (2007) has Cnesiamima as the sister group of Paraustrosimulium + Austrosimulium —a reasonable placement based on available evidence. “ Cnephia ” pilfreyi wasn’t included in Gil- Azevedo & Maia-Herzog’s (2007) analysis, but Moulton’s (2003) molecular analysis placed that species in a trichotomy with Paraustrosimulium (as here defined) plus a cluster of northern Holarctic genera. More freshly collected material of “ C ” pilfreyi is needed to better understand its relationships with other members of this austral clade.

In terms of relationships within Paraustrosimulium, it seems likely that P. anthracinum is the sister of P. obcidens and P. colboi together, supported, in part, by geography and shared pupal gill structure in the latter two species (cf. Figs 26, 70, 112).

Paraustrosimulium, Cnesiamima, Austrosimulium and “ Cnephia ” pilfreyi exhibit marked structural heterogeneity, and the relictual distribution of their members bespeaks a relatively early origin for their common ancestor. Separation of southern Western Australia and Antarctica was complete ca. 95 Mya (Rix et al. 2015). Given the morphological similarities between P. anthracinum and P. obcidens, plus a predilection for cooler water, a reasonable assumption is that that tectonic movement was the vicariant event separating their precursor. The last connection between South America and Antarctica was at 41–35 Mya, with formation of the Drake Passage. Final separation of Australia and Antarctica was ca. 32 Mya, well to the east, when Tasmania separated and the Antarctic Circum–Polar Current was established. A secondary vicariant event that probably separated the precursor of P. obcidens and P. colboi was the inundation of the Nullarbor Plain region by the Eromanga Sea at ca. 25 Mya. The Nullabor marine incursion did not end until ca. 14 Mya (Toussaint et al. 2016), followed by a mid–Miocene climatic optimum. We consider P. colboi to be the more derived taxon of the two Australian species.