Correspondence analysis of shell morphology in the African freshwater snail Biomphalaria pfeifferi (Kraus 1848) (Pulmonata: Gastropoda)

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.

Morphological and molecular characterization of invasive Biomphalaria straminea in southern China

BACKGROUND

Schistosomiasis is a common parasitic disease designated as a neglected tropical disease by the World Health Organization. Schistosomiasis mansoni is a form of the disease that is caused by the digenean trematode Schistosoma mansoni, transmitted through Biomphalaria spp. as an intermediate host. Biomphalaria was introduced to Hong Kong, China in aquatic plants shipments coming from Brazil and the snail rapidly established its habitats in southern China. Earlier studies of Biomphalaria spp. introduced to southern China identified the snails as Biomphalaria straminea, one of the susceptible species implicated in S. mansoni transmission in South America. However, recent molecular investigations also indicated the presence of another South American species, B. kuhniana, which is refractory to infection. As such, it is important to identify accurately the species currently distributed in southern China, especially with emerging reports of active S. mansoni infections in Chinese workers returning from Africa.

METHODS

We combined morphological and molecular taxonomy tools to precisely identify Biomphalaria spp. distributed in Guangdong Province, southern China. In order to clearly understand the molecular profile of the species, we constructed a phylogeny using mtDNA data (COI and 16S rRNA sequences) from six populations of Biomphalaria spp. from Shenzhen City in Guangdong Province. In addition, we examined the external morphology of the shell and internal anatomy of the reproductive organs.

RESULTS

Both morphological and molecular evidences indicated a close affinity between Biomphalaria spp. populations from Guangdong and B. straminea from Brazil. The shell morphology was roughly identical in all the populations collected with rounded whorls on one side and subangulated on the other, a smooth periphery, an egg-shaped aperture bowed to one side, and a deep umbilicus. The shape and number of prostate diverticula (ranged from 11.67 to 17.67) in Guangdong populations supports its close affinity to B. straminea rather than B. kuhniana. Molecular analysis did not conflict with morphological analysis. Little genetic differentiation was observed within Biomphalaria populations collected. Phylogenetic analysis of COI and 16S rRNA haplotypes from snails collected and B. straminea sequences from Brazil and China using Bayesian inference revealed that Guangdong populations were clustered in one clade with B. straminea from Hong Kong of China and B. straminea from Brazil indicating their close affinity to each other.

CONCLUSIONS

Data obtained in the current study clearly show that the populations of Biomphalaria spp. investigated are B. straminea, and we assume that those snails were either introduced via passive dispersal from Hong Kong of China or as a result of multiple introduction routes from Brazil.