PT Journal
AU Skaloud, P
   Skaloudova, M
   Knotek, P
   Jadrna, I
   Pusztai, M
TI Mallomonas intermedia: A case study of speciation and evolutionary dynamics of protists
SO Fottea
PY 2025
DI 10.5507/fot.2025.008
DE Chrysophyceae; evolution; microfossils; morphology; silica scales; speciation; Synurales
AB A total of 81 strains morphologically corresponding to the circumscription of Mallomonas intermedia were isolated from 27 freshwater localities across Europe and North America. Molecular genetic analyses revealed two distinct lineages with a strict geographical pattern, which diverged approximately 8 million years ago. According to comparative morphological analyses, we concluded that European populations corresponded to M. intermedia, whereas North American populations were described as a new species, M. retimedia sp. nov. The most notable morphological difference between the species is in the number of pores enclosed in the mesh formed on the siliceous scales. While in M. intermedia the mesh typically surrounds only one pore, meshes of M. retimedia usually encircle 3-4 pores. By incorporating fossil evidence into our time-calibrated phylogeny, we propose that the ancestor of M. intermedia and six related species likely lacked a thick secondary layer but had a distinct transverse rib, present in extant M. galeiformis, M. intermedia and M. retimedia species. The evolutionary history of this group further reveals that parallel ribs on the siliceous scales have evolved independently at least three times during the Miocene epoch, suggesting an adaptive significance, although their exact function remains unclear.
ER