Understanding the shining Ramshorn snail, Segmentina Nitida: morphology, genetics and breeding

The Shining Ramshorn Snail, Segmentina nitida, is a rare freshwater snail found predominantly in drainage ditches along field margins and in marshland. It is experiencing marked declines in distribution in the United Kingdom (UK) and mainland Europe. The species was included in the IUCN Red Data Book for Invertebrates before a guideline change in 1994 and is included on the UK Biodiversity Action Plan (BAP) as a priority species for conservation. The BAP for S. nitida states that further research on the species required to inform reintroduction and translocation for its conservation.

For this thesis, a modified sample evaluation method for Segmentina nitida was developed and evaluated. It increased sample assessment speed without significantly reducing accuracy in comparison to a traditional method of sample evaluation.

Captive breeding of S. nitida was explored with the aim of developing simple breeding protocols that could provide stock for potential reintroduction of the species into historical locations. Breeding proved challenging due to fluctuations in water chemistry and subsequent high mortality rates.

Geometric morphometric shape analyses were used to investigate variation in shell shape of the species across European populations from the UK, Germany, Poland and Sweden, and the Czech Republic. German and UK snails had similar shell morphologies, and Polish and Czech snails also clustered together morphologically, with the shape of Swedish snails being less distinct.

Analysis of the population genetics of German, UK, Polish and Swedish populations using nuclear (ITS, microsatellites) and mitochondrial markers (COI) revealed two distinct lineages of S. nitida in Europe. One comprised of populations from Poland and Sweden (East), and one represented UK populations and a Swedish population (West) with the two lineages coexisting in Germany. These two lineages show no evidence of genetic admixture and can be delimited by both genetic markers and geometric morphometrics, indicating two evolutionarily distinct units, possibly equating to species.

The genetic and shape differences between European populations has impacts the conservation of Segmentina nitida, especially in the UK, as previous descriptions of range may now be incorrect and the UK populations may be more significant globally than previously thought, if they are indeed S. nitida. Any future reintroduction plans in the UK and elsewhere would also need to take into account these genetic lineages, as they may result in the introduction of an invasive species or result in infertile offspring.