Overcoming the congenitally disadvantageous mutation through adaptation to environmental UV exposure in land snails.

Congenital fitness-disadvantageous mutations are not maintained in the population; they are purged from the population through processes such as purifying selection. However, these mutations could persist in the population as polymorphisms when it is advantageous for the individuals carrying them in adapting to a specific external environment. We tested this hypothesis using the dimorphic land snail in Japan; these snails have dark or bright coloured shells.

Shell colour diversification induced by ecological release: A shift in natural selection after a migration event.

Ecological release is often attributed to the rapid adaptive diversification of phenotypic traits. However, it is not well understood how natural selection changes its strength and direction through the process of ecological release. Herein, we demonstrated how shell colour of the Japanese land snail has diversified via a shift in natural selection due to ecological release after migration from the mainland to an island.

Morphological integration and pleiotropy in the adaptive body shape of the snail-feeding carabid beetle Damaster blaptoides.

The snail-feeding carabid beetle Damaster blaptoides exhibits diverse head and thorax morphologies, and these morphotypes are linked with two alternative feeding behaviours. Stout-shaped beetles feed on snails by crushing the shells, whereas slender-shaped beetles consume snails by inserting their heads into the shells. A trade-off exists between these feeding strategies.

A maladaptive intermediate form: a strong trade-off revealed by hybrids between two forms of a snail-feeding beetle.

Although trade-off curves between fitness components are essential in theoretical studies of ecological specialization, few empirical studies have actually determined these curves experimentally. Using the snail-feeding carabid beetle Damaster blaptoides, which is endemic to the Japanese archipelago, we estimated the trade-off curve for feeding success with alternative foraging behaviors that are linked to varying morphology. First, we crossed a stout-bodied and a slender-bodied subspecies and produced their F1 and backcross hybrids, which exhibited intermediate body shapes.

Factors determining the direction of ecological specialization in snail-feeding carabid beetles.

A stout-slender dimorphism in body shape is observed among carabid beetles of the subtribe Carabina, which feed on land snails. We hypothesized that this dimorphism has resulted from divergent ecological specialization for feeding on different-sized land snails. Therefore, we examined whether the geographic variation in the body shape of Damaster blaptoides, a representative snail-feeding species in Japan, is correlated with the size of Euhadra, a genus of land snails frequently consumed by D.

Ecological character displacement caused by reproductive interference.

We carried out a theoretical investigation of whether ecological character displacement can be caused by reproductive interference. Our model assumes that a quantitative character is associated with both resource use and species recognition, and that heterospecific mating incurs costs. The model shows that ecological character displacement can occur as a consequence of evolution of premating isolation; this conclusion is based on the premise that resource competition is less intense between species than within species and that the ecological character also contributes to premating isolation.