Lasiopogon, Loew, 1847

Cocker, Scott L., Cannings, Robert A. & McKnight, Tristan A., 2025, A Pleistocene LASIOPOGON robber fly (Diptera: Asilidae) subfossil from the Yukon Territory, Canada, The Canadian Entomologist (e 14) 157, pp. 1-11 : 8

Beringia and Lasiopogon palaeoecology

As previously discussed, Lasiopogon species in the present-day Yukon Territory are typically found in dune habitats, on south-facing grassland slopes, in dry forest habitats, or along sandy streamsides ( Cannings 1997). Of particular interest are the species living on south-facing slopes, given the habitat similarity between these relict grasslands and the now-extinct steppe–tundra (“mammoth steppe”) ecosystem that was dominant during the Pleistocene in this region. Numerous studies have contributed to our understanding of Pleistocene steppe–tundra ecosystems for which the consensus of a grass- and forb-dominated landscape is widely accepted but without a modern analogue ( Guthrie 2001; Murchie et al. 2021). Arctic ground squirrel middens are important sources of data for reconstructions of Beringian environments ( Zazula et al. 2005, 2007, 2011; Lopatina and Zanina 2006; Zanina et al. 2011). Seminal research by Zazula established the role of Arctic ground squirrel middens as valuable archives of plant macrofossils spanning the last 80 000 years in the Yukon Territory ( Zazula et al. 2005, 2007, 2011). When combined with the preservation potential of permafrost, much of the material is so exquisitely preserved that identifications can be made with increased taxonomic resolution when compared to other biological proxies, such as pollen. This local record of Beringian ecosystems provides a unique perspective of steppe–tundra diversity throughout the Late Pleistocene.

The plant macrofossil assemblage from the midden (BJ11-LLII-63) generally aligns with the interpretation of a cold and dry landscape dominated by low-lying vegetation (S.C., unpublished data), similar to the south-facing slopes in the Yukon today ( Fig. 3 ). The midden is dominated by capsules of the forb, Phlox cf. hoodii , which has been reported to be a subdominant taxon on grassland slopes of the Aishihik–Sekulmun Lakes area of the Yukon Territory and a dominant taxon across grasslands of the northern Great Plains ( Vetter 2000). These regions are consistent with the habitats of some Lasiopogon species and similarly provide an appropriate interpretation of the palaeoecological data recovered from midden BJ11-LLII-63.

Given the lack of Quaternary data for asilid flies and for the genus Lasiopogon , the data can conservatively suggest habitat continuity in this genus for at least the last 16 500 years. However, given the considerable reduction in available habitat following the collapse of steppe–tundra ecosystems in Beringia associated with the Pleistocene–Holocene transition, it is interesting to postulate whether Lasiopogon may have been more or less widespread during the Pleistocene. Such a decline in population is recorded by other invertebrate taxa, specifically the Yukon endemic weevil, Connatichela artemisiae Anderson ( Coleoptera : Curculionidae ) ( Anderson 1984). Quaternary entomological data from the region suggests a considerable collapse in C. artemisiae populations associated with a decline in prairie sage, Artemisia frigida Willdenow ( Asteraceae ). These two taxa are linked: the larvae of C. artemisiae feed on the roots of A. frigida , and adults often use the plant during copulation ( Anderson 1984; Monteath et al. 2023). If the Pleistocene habitat was more fitting for Lasiopogon than modern conditions are and regional species were more common, that could help explain how the patchy distributions common to this group were first established. On the other hand, the Pleistocene habitat could have been submarginal, and Lasiopogon may have been merely one of the few asilids that could colonise parts of it. Lasiopogon spp. are one of the more cold-adapted genera of robber flies and are usually one of the earliest to emerge in the spring ( Cannings 2002; McKnight and Cannings 2020).

Biogeographically, the recovery of this Lasiopogon head presents compelling evidence to establish the presence of the genus at a time and place where Beringian exchange has been presumed. Probable Beringian splits are found at several levels of the Lasiopogon phylogeny – for example, populations within a species (e.g., L. hinei ), species within a group (e.g., L. prima and L. septentrionalis ), and species groups along the backbone (e.g., the canus group in the cinctus clade). As more evidence such as the discovery reported here comes to light, future phylogenetic and biogeographic work seeking to model likely histories that explain these patterns and improve our understanding of the impressive adaptive radiation of this genus may be possible.

Figures

Figure 3. South-facing grassland slopes at Stepping Stone, Pelly River, Yukon Territory (62.7996°, –137.3271°), a common habitat of Lasiopogon canus and L. hinei. The yellow flower is Yukon Goldenweed, Nestotus macleanii (Brandegee) R.P. Roberts et al. (Asteraceae), a Yukon endemic. Photo by Syd Cannings.