Skip to main content
Dryad

Positive and negative frequency dependent parasitism in naturally co-occurring lineages of diploid sexual and polyploid asexual Lumbriculus variegatus

Tardent, Nadine1; Tamara, Schlegel1; Jokela, Jukka2; Hartikainen, Hanna3

Published Mar 26, 2025; Updated Apr 21, 2025 on Dryad. https://doi.org/10.5061/dryad.18931zd76

Data files

Mar 26, 2025 version files 1.45 GB
Apr 21, 2025 version files 1.45 GB

Abstract

Polyploidisation is an important evolutionary force. It drives sympatric speciation through reproductive isolation of different cytotypes, and often leads to loss of sexual reproduction in polyploid lineages. Polyploidisation and asexuality can change how other species engage in ecological interactions with the polyploid lineage and may change coevolutionary dynamics. Here, we quantified the phenotypic divergence in the freshwater oligochaete worm Lumbriculus variegatus, the California blackworm, among its co-occurring sexual diploid (Lineage II) and asexual polyploid (Lineage I) lineages. We further investigated variation in parasite communities and infection prevalence among sympatric and allopatric diploid/polyploid populations. Ten out of 18 populations showed co-existence of both lineages, with 7 populations harbouring only the polyploid lineage. Both worm lineages hosted  endoparasitic nematodes, an ectoparasitic rotifer, and one potentially symbiotic gut ciliate. The parasite community similarity and overlapping size range of diploid and polyploid worms points to the ecological similarity of the worm lineages, despite the substantial ploidy and reproductive strategy differentiation. Although parasite prevalence varied independently of worm lineage, prevalence was associated with frequency of local cytotypes. Specifically, the rotifer prevalence was highest on the rare local cytotype, and nematode prevalence was highest on the common local cytotype. These results suggest the presence of both positive and negative frequency dependent parasitism, which may contribute to the co-existence in the L. variegatus species complex.