Shell shape of the land snail Cornu aspersum in North Africa: unexpected evidence of a phylogeographical splitting

Impact of contamination on biology, biochemical, and histology of Eobania vermiculata and Monacha obstructa during different seasons in Ismailia, Egypt.. [DOI: 10.1101/2021.12.14.472665] [Citation(s) in RCA: 0] [Impact Index Per Article: 0]

Land snails are found to be an appropriate sentinel organism, and the biomarkers chosen are effective for terrestrial heavy metal biomonitoring. The study aimed to compare the biological, biochemistry, and histology of two land snails in the Ismailia governorate, Egypt during different seasons. Random snails were collected from January 2015 to December 2015 from two sites in the Ismailia Governorate, on wet days during each season’s middle month. Soft tissues were taken from the dissected snails. It was noticed that most of the morphometric parameters measured shell height (ShH), last whorl width (LWW), maximum diameter (MaxD), aperture height (AH), and aperture width (AW) were higher in Eobania vermiculata (Sp. 1) than those measured in Monacha obstructa (Sp. 2), except for shell height measurement, which was the same in both species. The growth rate of Sp. 1 and Sp. 2 changed seasonally. In the more polluted areas with heavy metals, lipid peroxidation (LPO) was higher in snails and total protein content than in the snails collected from the less polluted areas for all seasons. However, the snails displayed lower levels of glutathione (GSH) as compared to snails at a less polluted site. GSH and LPO levels, on the other hand, have a negative relationship between them. Histopathological alterations in the digestive gland were more obvious in the general architecture of the digestive gland that had lost its tubular appearance. The excretory cells showed an increase in their excretory granules’ number and size while calcium cells decreased. Also, gonad follicles have lost their normal architecture with the degeneration of some stages of spermatogenesis and oogenesis. In conclusion, There was a strong correlation between GSH levels and total protein content in the same soft tissues. GSH and LPO levels, on the other hand, have a negative relationship. The overall results display the usefulness of E. vermiculata and M. obstructa land snails as bioindicator organisms and support the application of this ecotoxicological approach for evaluating the biologic impact of toxins. E. vermiculata is more abundant than M. obstructa. The density, morphometric, biochemical, and histology of E. vermiculata and M. obstructa were different at different seasons.

Anthropogenic load іs a leading factor in the morphological variability of Chondrula tridens (Gastropoda, Enidae) in the northwestern Azov Sea region

Morphometric data are widely used in biology to assess intraspecific and inter-population variability and for bioindication and environmental condition assessment. The following hypotheses have been experimentally tested in the paper: 1) the vegetation type affects the change in the shell shape of Chondrula tridens martynovi Gural-Sverlova & Gural, 2010; 2) the change in the shell shape of this species is influenced by the biotope moisture regime; 3) the shell shape changes depending on the anthropogenic load level. The material in the form of empty, fully formed Ch. tridens shells was collected in 2019 in the north-western Azov region within the basin of the Molochna River. The collection points were located in settlements and outside them and differed in vegetation, moisture regime and level of anthropogenic load. The vegetation has been expertly attributed to two alternative types: herbaceous vegetation and tree plantations. By moisture level, the locations have been assessed as xerophytic and mesoxerophytic. The anthropogenic load levels have been assessed as low, medium and high. The study revealed that the morphological characteristics of Ch. tridens demonstrate a significant component of variability, which is due to the shell size. The shell size depends on the anthropogenic impact level. Under conditions of high anthropogenic impact, the shell size increases. Mollusks from locations with low and medium anthropogenic impact levels did not differ in shell size. After extraction of the size component, morphological properties develop three main trends of variability. The mouth apparatus development of mollusks does not depend on the vegetation type, but depends on the biotope moisture level and the anthropogenic transformation level. The mollusk shell elongation was observed to have the opposite dynamics of the height parameters in relation to the width and depended on the level of anthropogenic load. Rearrangement in the mouth apparatus depended on the biotope moisture level and the anthropogenic load level. There were distinguished four clusters, the quantitative morphological features of which allowed us to identify them as morphotypes. Each location was characterized by a combination of different morphotypes, according to which the sampling points may be classified. Morphotype 1 corresponds to biotopes with low level of anthropogenic load, morphotype 4 corresponded to biotopes with high anthropogenic load. Morphotypes 2 and 3 corresponded to moderate level of anthropogenic load. Vegetation type is not an important factor in determining the morphotypic diversity of populations. Under xerophytic conditions, morphotypes 2 and 3 are more common, and under mesoxerophytic conditions, morphotypes 1 and 4 are more common. The range of molluscs in different habitats needs to be expanded in the future to clarify climatic and other patterns.

From bioavailability to risk assessment of polluted soil using snails: link between excess transfer and inhibition of sexual maturation

An accurate assessment of the environmental risk of soils contaminated by metal(loid)s (MEs) requires quantifying exposure and knowing the toxicity of contaminants transferred to biota. For this purpose, two indices have been developed with the bioindicator Cantareus aspersus to assess exposure (SET: sum of the excess of transfer) and risk (ERITME: evaluation of the risk of the transferred metal elements) of multi-contaminated soils. If the SET and ERITME indices allow characterization of exposure and risk based on unspecific toxicity points, then the link between these indices and real effects on some toxicological endpoints, such as growth or sexual maturation, remains to be demonstrated. For this purpose, sub-adult snails were exposed for 28 days to 38 ME-contaminated soils. Relationships between the SET and/or ERITME indices and health alterations in C. aspersus were determined using Spearman correlations, linear regressions, univariate regression trees, and kinetic models. Relationships were determined between the values of the SET and ERITME indices, bioaccumulation as an indicator of ME bioavailability, and the alteration in physiological endpoints, such as the shell development used as a non-invasive indicator of sexual maturation. The results enabled the determination of three levels of risk according to the differences in reaching sexual maturity: no risk, uncertain, and proven risk depended on whether the value of ERITME was below, in, or beyond the interval [2574-22720], respectively. This study provides the first benchmarks with the SET and ERITME indices to interpret the risk of contaminated soils to snails and to relate the environmental and toxicological bioavailability of ME mixtures.

Responses of Leptinaria unilamellata (Gastropoda: Subulinidae) to Novel Micro-Environmental Conditions: Shift in Shell Morphology and the Balance between Protection against Desiccation and Reproductive Success

In the present study, we observed that Leptinaria unilamellata responds to changes in microclimatic conditions through shifts in shell morphology. Over three laboratory generations, shell differences between two populations, representing distinct morphotypes, became less evident. Only F1 generations from both populations showed shell morphometry very similar to the field parental snails, suggesting maternal effect. Snails from the locality with higher values of rainfall, relative humidity and evaporation index and smaller values of temperature and insolation produced more and larger hatchlings. Snails from the locality with less favorable climatic conditions presented shells traits that offer protection against desiccation, but reduce reproductive success. These snails showed smaller offspring production and faster response to a desiccation regime, through changes in conchiometrics. In addition, the results of the present study suggest that the spire index plays a less important role in determining protective properties of the shell of L. unilamellata, in response to desiccation risk, compared to aperture dimension. As shell aperture dimension is an important trait related to resistance to desiccation, and at the same time to reproduction, plastic responses to environmental conditions promoting the balance between survival and reproductive success are critical for the species adaptive success.

Exploring Monacha cantiana (Montagu, 1803) phylogeography: cryptic lineages and new insights into the origin of the English populations (Eupulmonata, Stylommatophora, Hygromiidae)

Molecular analysis of nucleotide sequences of mitochondrial cytochrome oxidase subunit 1 (COI) and 16S ribosomal DNA (16SrDNA) as well as nuclear histone 3 (H3) and internal transcribed spacer 2 of rDNA (ITS2) gene fragments together with morphological analysis of shell and genitalia features showed that English, French and Italian populations usually assigned to Monacha cantiana consist of four distinct lineages (CAN-1, CAN-2, CAN-3, CAN-4). One of these lineages (CAN-1) included most of the UK (five sites) and Italian (five sites) populations examined. Three other lineages represented populations from two sites in northern Italy (CAN-2), three sites in northern Italy and Austria (CAN-3), and two sites in south-eastern France (CAN-4). The taxonomic and nomenclatural setting is only currently available for lineages CAN-1 and CAN-4; a definitive frame for the other two requires much more research. The lineage CAN-1 corresponds to the true M. cantiana (Montagu, 1803) because it is the only one that includes topotypical English populations. The relationships and genetic distances support the hypothesis of the Italian origin of this lineage which was probably introduced to England by the Romans. The lineage CAN-4 is attributed to M. cemenelea (Risso, 1826), for which a neotype has been designated and deposited. Its diagnostic sequences of COI, 16SrDNA, H3 and ITS2 genes have also been deposited in GenBank. Molecular and morphological (shell and genitalia) features showed that M. parumcincta (Rossmässler, 1834) is a distinct taxon from the M. cantiana lineages.

Variation in thermal sensitivity and thermal tolerances in an invasive species across a climatic gradient: lessons from the land snail Cornu aspersum

The ability of organisms to perform at different temperatures could be described by a continuous nonlinear reaction norm (i.e., thermal performance curve, TPC), in which the phenotypic trait value varies as a function of temperature. Almost any shift in the parameters of this performance curve could highlight the direct effect of temperature on organism fitness, providing a powerful framework for testing thermal adaptation hypotheses. Inter-and intraspecific differences in this performance curve are also reflected in thermal tolerances limits (e.g., critical and lethal limits), influencing the biogeographic patterns of species' distribution. Within this context, here we investigated the intraspecific variation in thermal sensitivities and thermal tolerances in three populations of the invasive snail Cornu aspersum across a geographical gradient, characterized by different climatic conditions. Thus, we examined population differentiation in the TPCs, thermal-coma recovery times, expression of heat-shock proteins and standard metabolic rate (i.e., energetic costs of physiological differentiation). We tested two competing hypotheses regarding thermal adaptation (the "hotter is better" and the generalist-specialist trade-offs). Our results show that the differences in thermal sensitivity among populations of C. aspersum follow a latitudinal pattern, which is likely the result of a combination of thermodynamic constraints ("hotter is better") and thermal adaptations to their local environments (generalist-specialist trade-offs). This finding is also consistent with some thermal tolerance indices such as the Heat-Shock Protein Response and the recovery time from chill-coma. However, mixed responses in the evaluated traits suggest that thermal adaptation in this species is not complete, as we were not able to detect any differences in neither energetic costs of physiological differentiation among populations, nor in the heat-coma recovery.

Exploring species level taxonomy and species delimitation methods in the facultatively self-fertilizing land snail genus Rumina (gastropoda: pulmonata)

Delimiting species in facultatively selfing taxa is a challenging problem of which the terrestrial pulmonate snail genus Rumina is a good example. These snails have a mixed breeding system and show a high degree of shell and color variation. Three nominal species (R. decollata, R. saharica and R. paivae) and two color morphs within R. decollata (dark and light) are currently recognized. The present study aims at evaluating to what extent these entities reflect evolutionary diverging taxonomic units, rather than fixed polymorphisms due to sustained selfing. Therefore, a phylogenetic analysis of nuclear (ITS1, ITS2) and mitochondrial DNA (COI, CytB, 12S rDNA, 16S rDNA) sequences was performed. Putative species in Rumina, inferred from the mitochondrial DNA phylogeny, were compared with those proposed on the basis of the COI gene by (1) DNA barcoding gap analysis, (2) Automatic Barcode Gap Discovery, (3) the species delimitation plug-in of the Geneious software, (4) the Genealogical Sorting Index, and (5) the General Mixed Yule Coalescent model. It is shown that these methods produce a variety of different species hypotheses and as such one may wonder to what extent species delimitation methods are really useful. With respect to Rumina, the data suggest at least seven species, one corresponding to R. saharica and six that are currently grouped under the name R. decollata. The species-level status of R. paivae is rejected.

Linking immune patterns and life history shows two distinct defense strategies in land snails (gastropoda, pulmonata)

Life history integration of the defense response was investigated at intra- and interspecific levels in land snails of the family Helicidae. Two hypotheses were tested: (i) fitness consequences of defense responses are closely related to life history traits such as size at maturity and life span; (ii) different pathways of the immune response based on "nonspecific" versus "specific" responses may reflect different defense options. Relevant immune responses to a challenge with E. coli were measured using the following variables: blood cell density, cellular or plasma antibacterial activity via reactive oxygen species (ROS) level, and bacterial growth inhibition. The results revealed that the largest snails did not exhibit the strongest immune response. Instead, body mass influenced the type of response in determining the appropriate strategy. Snails with a higher body mass at maturity had more robust plasma immune responses than snails with a lower mass, which had greater cell-mediated immune responses with a higher hemocyte density. In addition, ROS appeared also to be a stress mediator as attested by differences between sites and generations for the same species.

Tracing the invasion of the mediterranean land snail Cornu aspersum aspersum becoming an agricultural and garden pest in areas recently introduced

This study is the first on the genetics of invasive populations of one of the most widely spread land mollusc species known in the world, the "Brown Snail" Cornu aspersum aspersum. Deliberately or accidentally imported, the species has become recently a notorious pest outside its native Mediterranean range. We compared the spatial structure and genetic variability of invasive (America, Oceania, South Africa) versus native populations using five microsatellite loci and mitochondrial (Cyt b and 16S rRNA) genes as a first step towards (i) the detection of potential source populations, and (ii) a better understanding of mechanisms governing evolutionary changes involved in the invasion process. Results based on multivariate analysis (Discriminant Analysis of Principal Components), Bayesian statistical inference (Clustering, Approximate Bayesian Computation) and demographic tests allowed a construction of the introduction pathways of the species over recent centuries. While emigrants originated from only one of the two native lineages, the West one, the most likely scenario involved several introduction events and "source switching" comprising (i) an early stage (around 1660) of simultaneous introductions from Europe (France, Spain) towards Oceania (New Zealand) and California, (ii) from the early 18(th) century, a second colonization wave from bridgehead populations successfully established in California, (iii) genetic admixture in invasive areas where highly divergent populations came into contact as in New Zealand. Although these man-made pathways are consistent with historical data, introduction time estimates suggest that the two putative waves of invasion would have occurred long before the first field observations recorded, both in America and in Oceania. A prolonged lag period as the use of an incorrect generation time could explain such 100-150 years discrepancy. Lastly, the contrasting patterns of neutral genetic signal left in invasive populations are discussed in light of possible ways of facing novel environments (standing genetic variation versus new mutation).

Bioaccumulative and conchological assessment of heavy metal transfer in a soil-plant-snail food chain

BACKGROUND

Copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) can pose serious threats to environmental health because they tend to bioaccumulate in terrestrial ecosystems. We investigated under field conditions the transfer of these heavy metals in a soil-plant-snail food chain in Banat area, Romania. The main goal of this paper was to assess the Roman snail (Helix pomatia) usefulness in environmental monitoring as bioindicator of heavy metal accumulation. Eight sampling sites, selected by different history of heavy metal (HM) exposure, were chosen to be sampled for soil, nettle leaves, and newly matured snails. This study also aimed to identify the putative effects of HM accumulation in the environment on phenotypic variability in selected shell features, which included shell height (SH), relative shell height (RSH), and whorl number (WN).

RESULTS

Significantly higher amounts of HMs were accumulated in snail hepatopancreas and not in foot. Cu, Zn, and Cd have biomagnified in the snail body, particularly in the hepatopancreas. In contrast, Pb decreased when going up into the food chain. Zn, Cd, and Pb correlated highly with each other at all levels of the investigated food chain. Zn and Pb exhibited an effective soil-plant transfer, whereas in the snail body only foot Cu concentration was correlated with that in soil. There were significant differences among sampling sites for WN, SH, and RSH when compared with reference snails. WN was strongly correlated with Cd and Pb concentrations in nettle leaves but not with Cu and Zn. SH was independent of HM concentrations in soil, snail hepatopancreas, and foot. However, SH correlated negatively with nettle leaves concentrations for each HM except Cu. In contrast, RSH correlated significantly only with Pb concentration in hepatopancreas.

CONCLUSIONS

The snail hepatopancreas accumulates high amounts of HMs, and therefore, this organ can function as a reliable biomarker for tracking HM bioavailability in soil. Long-term exposure to HMs via contaminated food might influence the variability of shell traits in snail populations. Therefore, our results highlight the Roman snail (Helix pomatia) potential to be used in environmental monitoring studies as bioindicator of HM pollution.

Historical biogeography of the land snail Cornu aspersum: a new scenario inferred from haplotype distribution in the Western Mediterranean basin

Background

Despite its key location between the rest of the continent and Europe, research on the phylogeography of north African species remains very limited compared to European and North American taxa. The Mediterranean land mollusc Cornu aspersum (= Helix aspersa) is part of the few species widely sampled in north Africa for biogeographical analysis. It then provides an excellent biological model to understand phylogeographical patterns across the Mediterranean basin, and to evaluate hypotheses of population differentiation. We investigated here the phylogeography of this land snail to reassess the evolutionary scenario we previously considered for explaining its scattered distribution in the western Mediterranean, and to help to resolve the question of the direction of its range expansion (from north Africa to Europe or vice versa). By analysing simultaneously individuals from 73 sites sampled in its putative native range, the present work provides the first broad-scale screening of mitochondrial variation (cyt b and 16S rRNA genes) of C. aspersum.

Results

Phylogeographical structure mirrored previous patterns inferred from anatomy and nuclear data, since all haplotypes could be ascribed to a B (West) or a C (East) lineage. Alternative migration models tested confirmed that C. aspersum most likely spread from north Africa to Europe. In addition to Kabylia in Algeria, which would have been successively a centre of dispersal and a zone of secondary contacts, we identified an area in Galicia where genetically distinct west and east type populations would have regained contact.

Conclusions

Vicariant and dispersal processes are reviewed and discussed in the light of signatures left in the geographical distribution of the genetic variation. In referring to Mediterranean taxa which show similar phylogeographical patterns, we proposed a parsimonious scenario to account for the "east-west" genetic splitting and the northward expansion of the western (B) clade which roughly involves (i) the dispersal of ancestral (eastern) types through Oligocene terranes in the Western Mediterranean (ii) the Tell Atlas orogenesis as gene flow barrier between future west and east populations, (iii) the impact of recurrent climatic fluctuations from mid-Pliocene to the last ice age, (iv) the loss of the eastern lineage during Pleistocene northwards expansion phases.

Spatial mosaic evolution of snail defensive traits

BACKGROUND

Recent models suggest that escalating reciprocal selection among antagonistically interacting species is predicted to occur in areas of higher resource productivity. In a putatively coevolved interaction between a freshwater snail (Mexipyrgus churinceanus) and a molluscivorous cichlid (Herichthys minckleyi), we examined three components of this interaction: 1) spatial variation in two putative defensive traits, crushing resistance and shell pigmentation; 2) whether abiotic variables or frequency of molariform cichlids are associated with spatial patterns of crushing resistance and shell pigmentation and 3) whether variation in primary productivity accounted for small-scale variation in these defensive traits.

RESULTS

Using spatial autocorrelation to account for genetic and geographic divergence among populations, we found no autocorrelation among populations at small geographic and genetic distances for the two defensive traits. There was also no correlation between abiotic variables (temperature and conductivity) and snail defensive traits. However, crushing resistance and frequency of pigmented shells were negatively correlated with molariform frequency. Crushing resistance and levels of pigmentation were significantly higher in habitats dominated by aquatic macrophytes, and both traits are phenotypically correlated.

CONCLUSION

Crushing resistance and pigmentation of M. churinceanus exhibit striking variation at small spatial scales often associated with differences in primary productivity, substrate coloration and the frequency of molariform cichlids. These local geographic differences may result from among-habitat variation in how resource productivity interacts to promote escalation in prey defenses.