The Sexology of the Chirally Dimorphic Snail Species<i>Amphidromus inversus</i>(Gastropoda: Camaenidae)

Looijestijn, Sylvia

doi:10.4002/040.051.0210

Cited by 17 publications

(18 citation statements)

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“…Field and molecular studies have shown that the dimorphism may be maintained by sexual selection actually favouring mates of the opposite chirality (Schilthuizen et al , 2007; Schilthuizen & Looijestijn, 2009;), and that it is a phylogenetically old trait within the genus (Sutcharit, Asami & Panha, 2006). This would suggest that in Amphidromus , the long history of selection for chiral dimorphism should have purged populations from any ancestral disadvantageous pleiotropic effects of sinistrality (unlike P. suturalis , which shows chiral dimorphism only in a narrow zone flanked by large areas of fixed chirality where no such purging of deleterious effects would occur).…”

Section: Introductionmentioning

confidence: 99%

Disentangling true shape differences and experimenter bias: are dextral and sinistral snail shells exact mirror images?

Haase

2010

Journal of Zoology

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In theory, snails can come in two enantiomorphs: either dextral (coiling clockwise) or sinistral (coiling counter-clockwise). In snail species where both forms are actually present, coiling direction is determined by a single gene with delayed maternal inheritance; there is no predictable relationship between a snail's own coiling genotype and its actual coiling direction. Because of this genetic decoupling, it might be expected that dextral and sinistral individuals would be exact mirror images of one another. However, indications exist that there is a subtle but detectable shape difference between dextral and sinistral individuals that derive from the same gene pool. In this paper, we attempt to detect such differences in 50 dextral and 50 sinistral individuals of Amphidromus inversus, a species of land snail that is consistently chirally dimorphic. Four out of 18 volunteers who measured the shells with Vernier calipers found that sinistrals are stouter to a significant degree. A similar result was found by one out of five volunteers who measured the shells from photographs. These results do not allow distinguishing between real shape differences and a handling bias of sinistral as compared with dextral shells. However, when the same set of shells was subjected to a geometric morphometric analysis, we were able to show that sinistrals indeed exhibit a slight but significant widening and twisting of the shell near the palatal and parietal apertural areas. This result is surprising because species of the subgenus Amphidromus s. str. share a long history of chiral dimorphism, and the species would be expected to have been purged from disadvantageous interactions between direction of coil and general shell shape. We conclude that selection on the shape differences is either very weak or constrained by the fact that the pleiotropic effects of the chirality gene are of importance very early in development only.

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Section: Introductionmentioning

confidence: 99%

Disentangling true shape differences and experimenter bias: are dextral and sinistral snail shells exact mirror images?

Haase

2010

Journal of Zoology

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“…However, the data here suggest that the problem is mainly behavioral. As in Amphidromus , the only snail genus that routinely has interchiral mating (Schilthuizen et al ; Schilthuizen and Looijestijn ), it is likely that the long, thin, flexible genital organs are able to twist to match the partners chirality. Moreover, in high‐spired snails, it is already known that interchiral mating (by “shell‐mounting”) is less of an issue–‐and AFLP markers have recently been used to show that gene flow is extensive between the two types, as expected (Koch et al.…”

Section: Discussionmentioning

confidence: 80%

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

et al. 2017

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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.

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“…A possible solution for this evolutionary conundrum was found in sexual selection. Unlike the situation in other land snails, interchiral (SxD) copulation in Amphidromus is not impeded (Schilthuizen & Looijestijn, 2009). In fact, a slight preference appears to exist for dextrals to mate with sinistrals and vice versa.…”

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confidence: 89%

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confidence: 97%

“…2007; Schilthuizen & Looijestijn, 2009). Chiral dimorphism is present at all spatial scales (Schilthuizen et al, 2007), and S:D mixes are found even in individual trees (Schilthuizen & Looijestijn, 2009). No indication of niche differentiation can be observed (Schilthuizen et al, 2012), and dispersal is equal between both morphs and sufficient to assure the mixing of populations at a spatial scale larger than that of individual trees (Schilthuizen et al, , 2012.…”

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Supplemental Information 1: Supplementary File (Data and Model Details)

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One of the very few snail taxa that display genetic antisymmetry (that is, roughly equal mixes of genetically determined clockwise [D] and anticlockwise [S] coiled individuals within a single population) are the circa 35 species of the tropical tree snail subgenus Amphidromus. Previous work has shown that this may be due to a particular type of sexual selection, in which sperm transfer is improved in copulations between the two mirrorimage morphs. However, it is not yet clear why so often significant deviations from 50:50 proportions are found. Modelling studies show that population structure will affect the degree by which the dimorphism is skewed towards the morph associated with the recessive allele. In this study, we mapped the proportions of sinistrals (PropS) in 56 demes in A. inversus on the Malaysian island of Kapas. We also mapped population density, predation rates, and several measures of vegetation structure. Our results show that PropS amounts on average to 0.65, but across the island it varies from 0.30 to 0.85. Density and overall predation are inversely correlated. A general linear model selection procedure results in the proportion of sinistrals to be positively correlated with density and predation on dextrals. We find no overwhelming evidence for a role for drift in explaining the deviations from equal S:D proportions, but we do argue that further study of crab-snail interactions may be warranted.PeerJ reviewing PDF |

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The Sexology of the Chirally Dimorphic Snail SpeciesAmphidromus inversus(Gastropoda: Camaenidae)

Cited by 17 publications

References 1 publication

Disentangling true shape differences and experimenter bias: are dextral and sinistral snail shells exact mirror images?

Disentangling true shape differences and experimenter bias: are dextral and sinistral snail shells exact mirror images?

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

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