Variation in nuclear genome size in a freshwater snail model system featuring a recent whole-genome duplication

Conspecifics often share-or are assumed to share-nuclear genome characteristics like nucleotide composition and genome size. These fundamental aspects of the nuclear genome can themselves be the object of natural selection. We here provide the first high-quality direct measurements of nuclear genome DNA content in a representative diverse sample of Potamopyrgus antipodarum, an Aotearoa New Zealand freshwater snail that is a textbook example of the maintenance of sexual reproduction in nature and is invasive worldwide. We used propidium-iodide-based flow cytometry to characterize nuclear DNA content and its variation in nearly 100 P. antipodarum from multiple populations representing both sexual and asexual individuals. We also estimated nuclear DNA content in multiple P. estuarinus, a closely related obligately sexual species. These data confirmed and extended earlier lines of evidence for polyploidy and variable genome size within asexual P. antipodarum and provided the first direct demonstration of distinctly higher nuclear genome content in diploid (sexual) P. antipodarum relative to diploid sexual P. estuarinus. Together, these results are consistent with genomic evidence for a recent whole-genome duplication (WGD) and subsequent and in-process rediploidization in P. antipodarum, setting the stage for use of Potamopyrgus as a model for WGD and its consequences.