Shell Morphological Variation of Littoraria angulifera among and within Mangroves in NE Brazil

Abstract

The shell morphological variation of the periwinkle Littoraria angulifera (Lamarck, 1822) was studied in tropical northeast Brazilian mangroves. This area was selected because mangroves in different stages of regeneration, and thus different tree heights can be found. We evaluated whether differences in solar radiation due to differences in tree height influenced the distribution and shell morphology of L. angulifera, and carried out an experiment to test if individuals collected from mangroves with different tree heights differed in their resistance to desiccation. We also analysed if there were differences in L. angulifera shell length and shape between tidal levels within a mangrove. Finally, we tested if increased habitat complexity due to the presence of oysters could influence L. angulifera shell length and shape in different-statured mangroves. We predicted that the oysters could reduce desiccation stress on periwinkles in small-statured mangroves but have no effect in taller ones. Shell length and shape varied among mangroves, although a large variation within mangroves was also recorded. Shell proportionality (shell length:width ratio) increased with shell length, and this relationship differed among mangroves; however, no differences were found in a subsequent year. Individuals from small-statured mangroves survived longer than those from taller mangroves in the desiccation experiment, with a weak correlation between shell proportionality and loss of mass. The presence of oysters had no apparent influence on shell morphology that could be correlated with reduced desiccation stress. The patterns found varied greatly both at small and large spatial scales, suggesting that future studies should evaluate phenotypic and genetic variation at the same time to properly understand variation in L. angulifera shell morphology.