Long-term dynamics of morphogenetic indicators of the terrestrial mollusk Cepaea vindobonensis (Gastropoda, Pulmonata, Helicidae) in the Bekaryukovsky Bor Natural Monument, Russia

Abstract

Cepaea vindobonensis (Gastropoda, Pulmonata, Helicidae) is a terrestrial mollusk, protected in the Belgorod Region (European Russia). In the Bekaryukovsky Bor Natural Monument, its peripheral population is known considering to be one of the most abundant in the north-eastern part of its range. In this paper, changes in the morphogenetic structure of C. vindobonensis population and its relationships with microclimatic environmental factors were analysed for the last 20 years. The results of the Kruskal-Wallis test of conchiometric features showed statistically significant (p < 0.05) differences between the studied years for all measurements. We found a statistically significant correlation between the parameters of the adult shell and some climatic characteristics, including both the average values for a four-year period and values recorded during the shell formation at the juvenile life cycle stage. This correlation apparently indicates the epigenetic nature of this population adaptation to the environment. The calculation of the average number of phenotypes (identified according to Zhivotovsky) showed the lowest level in 2020 (µ = 1.44 ± 0.20), and the highest level in 2002 (µ = 2.19 ± 0.21). To determine the population vitality degree, we analysed the genetic structure of the C. vindobonensis population on the basis of esterase izozyme loci. The highest changes in allele frequencies were observed in EST8 locus, where there was a statistically significant (p < 0.05) decrease in the EST8-2 allele frequency in 2006–2011, while being absent in the population in 2012–2020. At the same time, in 2020 the studied population became monomorphic for the EST8-3 allele. It is assumed that the transition to the homozygous state in this locus was caused not only by the genetically automatic process, but also by changes in habitats. In addition, there was a considerable lack of heterozygotes (inbreeding coefficient F = 0.517 ± 0.395) in 2020. The effective population size (Ne), calculated using the temporal method, was equal to 13.52. The forecast of the lifetime of the С. vindobonensis population based on genetic data demonstrated the value of about 100 years. The obtained results show a low vitality degree of the studied peripheral C. vindobonensis population. This may lead to its further extinction, especially in the case of changes in environmental parameters. However, the maintaining of nature conservation measures in the study area may allow avoiding this event.

Keywords

• conchiometric features
• effective population size
• genetic structure
• peripheral population
• population dynamics