Single-gene speciation: Mating and gene flow between mirror-image snails

Abstract

Impact SummaryAlthough most snails have a right-handed spiraling shell, rare "mirror-image" individuals have a shell that coils to the left. This curious inherited condition has attracted attention because the genitals of mirror image snails are on different sides of the head, and so mating is difficult or impossible. If they are unable to mate, then does a change in the direction of the shell coil make a new species? In investigating a Japanese snail genus, Euhadra, we were surprised to find that different-coiling individuals can sometimes mate, against expectations, and that there is evidence for this in their genetic make-up. It turns out that the mating problem is mainly behavioral, rather than a physical incompatibility. This new work therefore suggests that the two types of Japanese snail should be considered a single species, and has implications for the classification of other snail species. As it is has previously been shown that the same sets of genes that make mirror image snails are also involved in making mirror image bodies in other animalsincluding humans-then further research using the natural variation snails could offer the chance to develop an understanding of how organs are placed in the body and why this process can sometimes go wrong.

Speciation across the Tree of Life

“…There is some evidence for postzygotic barriers (maladaptive hybrids) in Albinaria snails (Cameron, 2013). Although shifts between left and right‐handedness (chirality) in snail shells has been suggested as a possible mechanism for single‐gene speciation in gastropods, the classic case study (Ueshima & Asami, 2003) of this phenomenon in Japanese snails ( Euhadra ) has not been supported by recent analyses (Richards et al ., 2017).…”

The direction of genital asymmetry is expressed stochastically in internally fertilizing anablepid fishes

“…[12][13][14])-the structures that make direct contact with the sexual partner during copulation and that are involved in sperm transfer are structurally asymmetric (reviewed in [5]). Genital asymmetry is an unusual trait that is interesting at many different levels of biological organization and is particularly important for evolutionary biologists because of its potential to drive speciation if mating success is reduced between opposite asymmetric morphs and thereby contributes to population divergence [15,16] (but see [17]). Moreover, the simple leftright nature of asymmetries has the advantage of permitting comparisons, not only between sexes within a species, but also across species, thus allowing for generalization beyond individual cases [5,18].…”

Removing the bad apples: A simple bioinformatic method to improve loci‐recovery in de novo RADseq data for non‐model organisms

“…To test the suggested pipeline, we used four datasets including: (a) a ddRADseq dataset comprising populations of the meiofaunal annelid Stygocapitella zecae (J. Cerca et al, unpubl. data; 21 samples, six populations); (b) a single‐digest RADseq dataset comprising several species of Euhadra molluscs (Richards et al., 2017); 16 samples, four species); (c) a ddRADseq dataset comprising populations of the Antarctic sponge Dendrilla antarctica (Leiva et al., 2019; 62 samples, seven populations); and (d) a hyRADseq dataset of Anthochaera phrygia combining museum and modern samples (Crates et al., 2019; 230 samples, eight populations).…”

“…With the exception of the Stygocapitella dataset, all data used here were downloaded from public repositories. The Euhadra dataset was generated and first analysed by Richards et al, (2017); the Dendrilla antarctica dataset was generated and first analysed by Leiva et al, (2019); and Anthochaera phrygia was generated and first analysed by Crates et al, (2019). The Stygocapitella dataset has been made public in the European Nucleotide Archive (ENA) under the project id PRJEB40223.…”