Resolution of a taxonomic conundrum: an ultrastructural and molecular description of the life cycle of Pleistophora mulleri (Pfeiffer 1895; Georgevitch 1929)

The classification of a microsporidian parasite observed in the abdominal muscles of amphipod hosts has been repeatedly revised but still remains inconclusive. This parasite has variable spore numbers within a sporophorous vesicle and has been assigned to the genera Glugea, Pleistophora, Stempellia, and Thelohania. We used electron microscopy and molecular evidence to resolve the previous taxonomic confusion and confirm its identification as Pleistophora mulleri. The life cycle of P. mulleri is described from the freshwater amphipod host Gammarus duebeni celticus. Infection appeared as white tubular masses within the abdominal muscle of the host. Light and transmission electron microscope examination revealed the presence of an active microsporidian infection that was diffuse within the muscle block with no evidence of xenoma formation. Paucinucleate merogonial plasmodia were surrounded by an amorphous coat immediately external to the plasmalemma. The amorphous coat developed into a merontogenetic sporophorous vesicle that was present throughout sporulation. Sporogony was polysporous resulting in uninucleate spores, with a bipartite polaroplast, an anisofilar polar filament and a large posterior vacuole. SSU rDNA analysis supported the ultrastructural evidence clearly placing this parasite within the genus Pleistophora. This paper indicates that Pleistophora species are not restricted to vertebrate hosts.

When did Britain industrialise? The sectoral distribution of the labour force and labour productivity in Britain, 1381-1851

Britain's labour force industrialised early. The industrial and service sectors already accounted for 40% of the labour force in 1381, and a substantial further shift of labour out of agriculture occurred between 1522 and 1700. From the early seventeenth century rising agricultural labour productivity underpinned steadily increasing employment in industry and services, so that by 1759 agriculture's share of the labour force had shrunk to 37% and industry's grown to 34%. Thereafter, industry's output acceleration during the Industrial Revolution owed more to gains in labour productivity consequent upon mechanisation than the expansion of employment.