Ecological and biogeographic information for marine gastropods has lagged behind taxonomic, molecular and phylogenetic information, limiting understanding of evolutionary processes. We investigated niche separation and speciation in rapinine whelks that represent a rare deep estuarine penetration by muricid gastropods. We studied the genetic and ecological differentiation of four Indothais morphotypes, distributed along a salinity gradient in Brunei (Borneo, South East Asia). Our molecular analyses, based on three mitochondrial genes (COI, 12S rRNA and 16S rRNA) and one nuclear gene (28S rRNA), revealed three species having the following relationship [Indothais rufotincta (Tan & Sigurdsson, 1996), [I. javanica (Philippi, 1848), [I. gradata (Jonas, 1846)]]]. This pattern coincided with their salinity-related distributions, such that I. rufotincta occurred alone in the open coastal waters, and I. javanica and I. gradata extended into the upper estuary. This suggests speciation through divergent selection and local adaptation, specifically synapomorphic low salinity tolerance by I. javanica and I. gradata. The observed intertidal vertical separation where the species co-occur suggests competitive exclusion of the others by the most-recently evolved I. gradata. This species also showed greatest morphological and genetic variation, and unique niche expansion involving feeding on both hard surface and muddy sediment organisms. Our study presents a novel hypothesis for the speciation of these snails.

We compared, for the first time the foraging ecology of both sexes of the blue-eyed Crozet shag (Phalacrocorax melanogenis), using ventrally attached time depth recorders to investigate differences in time-budget and diving behaviour between the sexes during the chick-rearing. Males were the only ones to dive over 55 m. Females dived mostly between 15 and 35 m, a zone poorly used by males. Females foraged mostly in the morning and males in the afternoon. Females also spent one hour longer diving per day compared to males. There were differences in diving strategies and diet, indicating that both sexes targeted essentially the same prey, but of different sizes, males specializing in bigger fish. Although the relationship between sexual dimorphism and diving depth was positive (larger animals diving deeper), evidence suggests that body size (in terms of oxygen storage capacity) is not sufficient to explain so many differences in foraging ecology. Instead, we propose prey size (possibly driven by a limitation of prey handling ability in relation to beak size) could be an essential factor in shaping the male/female behavioural segregation in the Crozet shag; future studies should concentrate on this particular aspect.