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Over the past decade, many skeletal matrix proteins that are possibly related to calcification have been reported in various calcifying animals. Molluscs are among the most diverse calcifying animals and some gastropods have adapted to terrestrial ecological niches. Although many shell matrix proteins (SMPs) have already been reported in molluscs, most reports have focused on marine molluscs, and the SMPs of terrestrial snails remain unclear. In addition, some terrestrial stylommatophoran snails have evolved an additional unique calcified character, called a “love dart,” used for mating behavior. We identified 54 SMPs in the terrestrial snail Euhadra quaesita, and found that they contain specific domains that are widely conserved in molluscan SMPs. However, our results also suggest that some of them possibly have evolved independently by domain shuffling, domain recruitment, or gene co-option. We then identified four dart matrix proteins, and found that two of them are the same proteins as those identified as SMPs. Our results suggest that some dart matrix proteins possibly have evolved by independent gene co-option from SMPs during dart evolution events. These results provide a new perspective on the evolution of SMPs and “love darts” in land snails.

Focus has been placed on the relative importance of environmental heterogeneity and biological interactions on community structure. For land snails, abiotic factors have commonly been assumed to be the most important factors for shaping communities because resources for land snails are commonly not limiting, and because interspecific resource competition would not be strong enough to promote ecological divergence. However, clear divergence in habitat use is often observed among sympatric land snail species. Such an ecological divergence would be promoted not by resource competition but by other interactions such as aggression. To test this hypothesis, laboratory experiments were designed to explore aggressive behaviour in the land snails Euhadra quaesita and E. peliomphala and field surveys were conducted to examine their habitat use. In the laboratory experiments, we examined how the presence of one species affects the growth of the other species by supplying sufficient amounts of food and calcium for both species. Experimental trials showed that adult E. quaesita decreased the growth of E. peliomphala under constant diet conditions. In contrast, E. peliomphala did not affect the growth of E. quaesita. Because E. peliomphala was often attacked by E. quaesita and its shell was often eroded by E. quaesita gnawing, aggression by E. quaesita appears to be the primary factor reducing the growth of E. peliomphala. When the two species coexist in nature, adults and juveniles of E. quaesita are terrestrial, while those of E. peliomphala are arboreal. When these species occurred alone, E. quaesita were still terrestrial, but E. peliomphala were more terrestrial than when they were in sympatry. Our results suggest that habitat use of these species in the natural communities is affected by interspecific interference. These findings further suggest that the divergence of habitat use between the species can occur by aggression even in environments with unlimited resources.