Highlight: Genome Duplication in a New Zealand Snail Holds Clues for the Persistence of (A)sexual Reproduction

Why does sexual reproduction persist in so many species? This is a fundamental question in biology that, remarkably, remains a mystery. Sexual reproduction (i.e. the union of two gametes and their genomes; Lehtonen et al. 2012) is the most common form of reproduction in eukaryotes. Yet, in prokaryotes, asexual reproduction is vastly more common, and multiple eukaryotic lineages, including diverse lineages of animals, have evolved forms of asexual reproduction from ancestors that reproduced sexually.

Since most animal species reproduce either sexually or asexually, it is challenging to separate the mechanisms driving the evolution of reproductive modes from those associated with broader differences in biology. The rare species that exhibit variation in their basic form of reproduction thus provide an avenue into the study of the genomic mechanisms underlying the evolution of reproductive modes.

Joseph Jalinsky and Kyle E. McElroy, from the University of Iowa, are among the group of evolutionary biologists who took an interest in the small New Zealand snail Potamopyrgus antipodarum (Fig. 1). They explain that this species' uniqueness lies in the occurrence of “dozens, or more, of separately derived obligately asexual lineages that coexist with otherwise similar sexual counterparts.” In other words, asexual reproduction has not only evolved multiple times within this species, but in some populations, inter-individual variation in reproductive mode is maintained as a trait.

Fig. 1.

The snail P. antipodarum, native to freshwater and brackish habitats in Aotearoa New Zealand, has recently gained notoriety as a model species in evolutionary biology, ecology, and toxicology. Photo credit: Christian Böck.

As reported in an article just published in Genome Biology and Evolution (Jalinsky et al. 2025), Jalinsky and McElroy (Fig. 2) assembled the genome of P. antipodarum to investigate it for clues into the evolution of its distinctive reproductive biology. However, this task turned out to be far from trivial. “To our great surprise, we discovered that the P. antipodarum nuclear genome has been duplicated in its recent evolutionary history,” Jalinsky says, alluding to how a genome duplication made it challenging to assemble a reference sequence: “Imagine trying to complete a jigsaw puzzle, only to realize that you’re actually working with a mixture of pieces from several nearly identical puzzles.”

Fig. 2.

GBE author spotlight: Joseph Jalinsky (left) and Kyle E. McElroy. Dr. Joseph Jalinsky is currently a visiting assistant professor at the University of Iowa, where he also earned his PhD. Joe's research employs bioinformatic and comparative genomic approaches to explore a range of questions in evolutionary and molecular genomics, including the genomic consequences of asexual reproduction in lichenized fungi and snails, the evolution of immune genes in the snail hosts that transmit the parasite responsible for schistosomiasis, and the role R-loops play in DNA damage in C. elegans. Dr. Kyle E. McElroy is a postdoctoral researcher at Iowa State University in Dr. Jeanne Serb's lab. Kyle uses comparative genomics and molecular genetics to investigate the evolution of light-sensing systems in bivalve mollusks. He is broadly interested in exploring connections between organismal and genomic evolution. Studying P. antipodarum in Dr. Maurine Neiman's lab during graduate school introduced Kyle to comparative genomics, the wild world of mollusks, and the many great collaborators included in this paper.

The team carefully curated the data as they disentangled the species' evolutionary history. Most of the analyzed heterozygous sites in the P. antipodarum genome had sequencing depths and allele frequencies that suggested deviations from diploidy, supporting tetraploidy instead (hence, a whole-genome duplication). Analyses of the genomes of two closely related species (Potamopyrgus estuarinus and Potamopyrgus kaitunuparaoa), on the other hand, revealed that these were diploid. These patterns suggested to the researchers that the whole-genome duplication was a recent event, specific to the P. antipodarum lineage. Gene copy analysis corroborated this conclusion—duplicate genes in the P. antipodarum genome are much more closely related to each other than to their orthologues in either P. estuarinus or P. kaitunuparaoa. Analyses of transposable element abundance and gene order (i.e. synteny) in the P. antipodarum genome, compared to the other species, further revealed a dynamic recent genome history likely triggered by the duplication event.

Strikingly, and despite the recent duplication, not all sections of the genome conformed to the expectations of tetraploidy. Instead, nearly 20% of the genome showed allele frequency signatures consistent with either diploidy or triploidy. Jalinsky et al. (2025) interpret the pattern as evidence of rediploidization, i.e. the genome returning to diploidy, after the genome duplication established tetraploidy.

According to McElroy, catching an animal lineage undergoing rediploidization is rare and sheds a unique light on biological diversification: “the period of time when a lineage is rediploidizing may generate diversity because reciprocal gene loss in structured populations, like those of P. antipodarum, can drive reproductive incompatibilities within a species.” The authors note that these inter-population incompatibilities can create one of the few evolutionary scenarios in which asexuality might be favored, if frequent inter-population hybridization decreases the average fitness of sexually reproducing individuals.

Did this complex genome architecture create the evolutionary dynamics that explain the recurrent evolution of asexuality in P. antipodarum? The authors cautiously note that they have not demonstrated a causal link between whole-genome duplication and asexuality. They point, however, to the known role of whole-genome duplications in generating evolutionary novelty. Jalinsky explains that: “even if the rediploidizing genome per se does not drive the genetic transition to asexuality, it could produce an evolutionary scenario in which the long-term fitness stability afforded by asexual reproduction is favored over the evolutionary uncertainty of sex.”

Looking forward, the authors set their sights on leveraging the genomic data of P. antipodarum to explain the evolutionary success of sex: “We are interested in understanding whether lineages that transition to asexual reproduction are inevitably fated for extinction, as the almost complete absence of ancient asexual lineages demonstrates,” McElroy explains. Beyond the evolution of sex, the authors anticipate that the genome assembly will be useful to researchers working on a range of topics for which P. antipodarum can serve as a model system, including host–parasite coevolution, invasion biology, and ecotoxicology.

The future looks bright for research on this unassuming freshwater snail. Jalinsky and McElroy stress, however, that researchers across the globe should make efforts to include and give back the returns of the research to the local communities. The authors conclude, stating that: “were we to begin now, we would involve New Zealand collaborators and establish meaningful relationships with the local Māori community, who have guardianship of the animals and plants living in Lake Alexandrina (Whakatukumoana), the source of the snails we used to generate our genome assembly.” Expanding collaborations in science is the most powerful way to engender new hypotheses and accelerate the rate of knowledge discovery.

Want to learn more? Check out these other articles on the evolution of sexual reproduction recently published in Genome Biology and Evolution:

• Forni G, Mantovani B, Mikheyev AS, Luchetti A. Parthenogenetic stick insects exhibit signatures of preservation in the molecular architecture of male reproduction. Genome Biol Evol. 2024:16(5):evae073. https://doi.org/10.1093/gbe/evae073.

• Rimbault M, Legeai F, Peccoud J, Mieuzet L, Call E, Nouhaud P, Defendini H, Mahéo F, Marande W, Théron N, Tagu D. Contrasting evolutionary patterns between sexual and asexual lineages in a genomic region linked to reproductive mode variation in the pea aphid. Genome Biol Evol. 2023:15(9):evad168. https://doi.org/10.1093/gbe/evad168.

• Sandler G, Agrawal AF, Wright SI. Population genomics of the facultatively sexual liverwort Marchantia polymorpha. Genome Biol Evol. 2023:15(11):evad196. https://doi.org/10.1093/gbe/evad196.