Prosimulium, Adler & S & Irin, 2014

Adler, Peter H., S, Ümit & Irin, 2014, Cytotaxonomy of the Prosimulium (Diptera: Simuliidae) of Western Asia, Zoological Journal of the Linnean Society 171 (4), pp. 753-768 : 766

PROSIMULIUM SP. NOV.

The new species of Prosimulium discovered during our investigation bears a superficial resemblance to Prosimulium latimucro (Enderlein) and P. petrosum Rubtsov in the pupal stage by having a gill with three rather long, strongly divergent trunks that present an open, splayed appearance of the 16 filaments. A scattering of previous records of P. latimucro and P. petrosum (e.g. in Bulgaria), therefore, might be misidentifications of this new species. The larval hypostoma, however, is markedly different from that of the chromosomally unstudied P. petrosum . The chromosomes show no relation to P. latimucro , and instead demonstrate a trichotomous relationship with P. hirtipes and P. tomosvaryi , all three of which share IIS-3 and IIL-1.

PHYLOGENETIC RELATIONSHIPS ( FIG. 12 )

The five cytological segregates in our study share a transformed centromere region (CIt) that is fixed in the entire Palaearctic P. hirtipes group and distinguishes it from the Nearctic P. hirtipes group, which, with the exception of eight of 22 nominal species, has the standard CI region ( Rothfels, 1979; Adler et al., 2004). The presence of CIt in both Nearctic and Palaearctic species of the P. hirtipes group and some species of the P. magnum group implies that the transformed centromeric condition was polymorphic in a common ancestor ( Basrur, 1959). CIt is shown in our phylogeny as having become fixed in the Palaearctic P. hirtipes group, while remaining polymorphic in the ancestor of the P. magnum group. The Palaearctic P. hirtipes group, thus, is weakly defined; monophyly, based on chromosomal characters, rests on the assumption that CIt became lost in some species of the P. magnum group but became fixed in others independently of the ancestor of the Palaearctic P. hirtipes group. Several relationships in our phylogeny remain unresolved and are shown as trichotomies. Further study is needed to integrate unstudied Palaearctic species and the Nearctic species into a larger phylogeny of Prosimulium .

Three uniquely shared inversions, relative to the outgroups, indicate two clusters amongst our five taxa. Prosimulium tomosvaryi and P. sp. nov. share inversions IIS-3 and IIL-1. Prosimulium hirtipes (Fries) s.s., the only other species with these inversions ( Basrur, 1959), joins P. tomosvaryi and P. sp. nov. in an unresolved trichotomy. Prosimulium frontatum and P. rachiliense ‘A’ and ‘B’ share IS-20, which probably was present as a polymorphism in the ancestor of the three, becoming fixed in ‘A’ and P. frontatum while remaining polymorphic in ‘B.’ The available chromosomal evidence, however, does not resolve whether IS- 20 independently became fixed in P. frontatum and ‘A’ or became fixed in a common ancestor of the two, exclusive of ‘B’; we depict the latter topology on the basis of parsimony (one vs. two fixation events) and the geographical proximity of the taxa.

The chromosomal relationships belie the classic structural features of the pupal gill conventionally used in species diagnoses. Prosimulium hirtipes , P. tomosvaryi , and P. sp. nov. have some of the most disparate gill arrangements in the P. hirtipes group: 16 vs. 23–27 filaments, short vs. long trunks, and bunched vs. splayed filaments. Similarly, in the Nearctic P. hirtipes group, Prosimulium mixtum Syme & Davies and Prosimulium rhizophorum Stone & Jamnback have markedly different gill structures but chromosomally are two of the most similar species ( Rothfels & Freeman, 1977). Conversely, similarity of gill structure, such as the splayed filaments of P. sp. nov. and P. latimucro , is not always reflected in chromosomal relationships; these two species share no unique chromosomal rearrangements. Thus, as a caveat, structural differentiation in the P. hirtipes group is not necessarily associated with large macrogenomic (chromosomal) changes, nor does gill structure necessarily provide phylogenetic signal.

Figures

Figure 12. Phylogenetic relationships of nine taxa in the Palaearctic Prosimulium hirtipes group, which have been resolved chromosomally relative to the standard sequence of Basrur (1959). The genus Twinnia and the Prosimulium magnum group are outgroups. Chromosomal characters uniquely defining a lineage are shown to the right of the branch. Fixed rearrangements are italicized, polymorphic rearrangements are in parentheses, and Y-linked rearrangements are neither. Species lacking a unique chromosomal character, nonetheless, are structurally unique.