Fluorescent Pigment Distinguishes Between Sibling Snail Species

Abstract

Traditional taxonomy of shell-bearing molluscs does not generally use soft-body coloration. However, the land snails Bradybaena pellucida and B. similaris have been distinguished only on the basis of the color of the soft-body visible through the shell. Thus, the taxonomic status of the two species has traditionally been questionable. We found that dense spots of pigments embedded in the dorsal mantle are responsible for the yellow coloration of B. pellucida . Similar spots in B. similaris are white and less densely aggregated in whorls further from the apex, and the brown color of the hepatopancreas is visible through the shell. The yellow pigments of B. pellucida seep out with mucus from the body in natural and laboratory conditions. The two species became externally indistinguishable after 30 days of laboratory feeding, because the yellow spots disappeared in B. pellucida and the color of the hepatopancreas changed from dark brown to pale brown in both species. Irradiation with ultraviolet A demonstrated that the yellow pigment of B. pellucida fluoresces. Adult specimens of the two species were distinct in penial microsculpture, with F(1) hybrids intermediate in form. Populations of the two species differed significantly in allelic frequencies at four allozyme loci. Therefore, B. pellucida and B. similaris are morphologically and genetically distinct. The fluorescent yellow pigment distinguishes B. pellucida from B. similaris under natural conditions despite its environmental dependence.

Fitness Consequences of Reciprocally Asymmetric Hybridization between Simultaneous Hermaphrodites

“…However, there was little heterogeneity among the three cross types in clutch size or hatching success, and B. similaris produced no eggs during the two-month period, indicating that it neither outcrossed nor selfed (Table 1). These results imply that B. pellucida, in interspecific pairs as well as conspecific pairs, reproduced by outcrossing, as Seki et al (2008) demonstrated based on penial microsculpture, which in hybrids exhibits a form intermediate between the two species.…”

“…We conducted breeding experiments to examine postzygotic isolation between sibling species of terrestrial pulmonates, Bradybaena pellucida and B. similaris. These hermaphroditic snails copulate simultaneously and reciprocally (Asami et al, , 1997aSeki et al, 2008). Bradybaena pellucida is endemic to Japan, whereas B. similaris was introduced presumably several hundred years ago (Komai and Emura, 1955;Asami et al, 1997b).…”

Synchronous and Non-Synchronous Semelparity in Sibling Species of Pulmonates

“…Considering their close relatedness and affinities in morphology and other characteristics (Seki et al, 2008;Wiwegweaw et al, 2009a, b;Hirano et al, 2014), the present results suggest that their annual patterns of population dynamics have relatively recently diverged. Our study demonstrates that closely related sibling species of terrestrial pulmonates can exhibit distinct life histories that are nonetheless similarly adaptive in the same temperate ranges.…”

“…The shell of BP is thin and could be sufficiently fragile to break when picked up from the substrate in the field, while this is not the case in BS (Seki et al, 2008). This may make sense for a snail species in which adults do not normally overwinter in terms of reducing the allocation of limiting resources to thicken the shell in an equivalent manner to BS.…”

“…They can be clearly distinguished from each other by penile microsculpture or fluorescent mantle pigments, although the latter disappears depending on the environment (Seki et al, 2008). They share common genetic systems of shell banding (Asami et al, 1993) and color (Asami et al, 1997a;Asami and Asami, 2008).…”