Bee Trypanosomatids: First Steps in the Analysis of the Genetic Variation and Population Structure of Lotmaria passim, Crithidia bombi and Crithidia mellificae

Abstract

Trypanosomatids are among the most prevalent parasites in bees but, despite the fact that their impact on the colonies can be quite important and that their infectivity may potentially depend on their genotypes, little is known about the population diversity of these pathogens. Here we cloned and sequenced three non-repetitive single copy loci (DNA topoisomerase II, glyceraldehyde-3-phosphate dehydrogenase and RNA polymerase II large subunit, RPB1) to produce new genetic data from Crithidia bombi, C. mellificae and Lotmaria passim isolated from honeybees and bumblebees. These were analysed by applying population genetic tools in order to quantify and compare their variability within and between species, and to obtain information on their demography and population structure. The general pattern for the three species was that (1) they were subject to the action of purifying selection on nonsynonymous variants, (2) the levels of within species diversity were similar irrespective of the host, (3) there was evidence of recombination among haplotypes and (4) they showed no haplotype structuring according to the host. C. bombi exhibited the lowest levels of synonymous variation (πS= 0.06 ± 0.04 %) — and a mutation frequency distribution compatible with a population expansion after a bottleneck — that contrasted with the extensive polymorphism displayed by C. mellificae (πS= 2.24 ± 1.00 %), which likely has a more ancient origin. L. passim showed intermediate values (πS= 0.40 ± 0.28 %) and an excess of variants a low frequencies probably linked to the spread of this species to new geographical areas.

Detection of Lotmaria passim and Crithidia mellificae in Selected Bumblebee Species

“…In the present study L. passim, the most prevalent honeybee trypanosomatid, was identified in bumblebees. Similar observations were made by Bartolome et al [37] who confirmed the simultaneous presence of L. passim and C. mellificae in two B. terrestris individuals.…”

The Haptomonad Stage of Crithidia acanthocephali in Apis mellifera Hindgut

“…It was detected in honey bee colonies throughout the year, at all seasons, and no differences were found between interior and forager bees, indicating it is a common organism in bee colonies. Together with the apparent absence of haplotype differentiation in L. passim, C. mellificae, or C. bombi between their hosts [38], these data suggest that insect trypanosomatids may infect a wider range of species than was previously thought.…”