Trematode infection affects shell shape and size in Bulinus tropicus

Area of Science:

• Malacology
• Parasitology
• Evolutionary Biology

Background:

• Trematodes are known to induce phenotypic variation in their intermediate snail hosts.
• The precise extent and nature of these trematode-induced phenotypic changes in snails are not fully understood.
• Bulinus tropicus is a significant intermediate host for medically important trematodes.

Purpose of the Study:

• To investigate the influence of trematode infection on the shell morphology of Bulinus tropicus.
• To identify specific trematode species that cause significant alterations in snail shell size and shape.
• To examine the effect of infection developmental stage on shell morphology.

Main Methods:

• Sampling of Bulinus tropicus from a homogeneous habitat in Uganda to minimize environmental variation.
• Genotypic barcoding to document snail genetic variation.
• Rapid-diagnostic PCRs and high-throughput amplicon sequencing for trematode infection and species identification.
• Landmark-based geometric morphometrics to analyze shell phenotype.
• Regression analyses to assess the impact of infection status and developmental stage on shell morphology.

Main Results:

• Snails infected by Petasiger sp. 5, Echinoparyphium sp., or Austrodiplostomum sp. 2 exhibited larger shells compared to uninfected snails or those infected by Plagiorchiida sp.
• Shell shape in snails solely infected by Petasiger sp. 5 significantly differed from uninfected snails and those with other trematode infections (except Austrodiplostomum sp. 2).
• Observed shape alterations included a more protuberant apex, an inward-folded outer apertural lip, and a more adapically positioned umbilicus. Size differences were more pronounced in late-stage infections (>25 days).

Conclusions:

• Specific trematode species significantly impact Bulinus tropicus shell morphology, affecting both size and shape.
• The developmental stage of infection plays a role in the magnitude of observed morphological changes.
• No significant phenotypic differences were detected between single and co-infections, suggesting dominant effects of certain trematode species.