High Gene Flow Due to Pelagic Larval Dispersal Among South Pacific Archipelagos in Two Amphidromous Gastropods (Neritomorpha: Neritidae)

The freshwater stream fauna of tropical oceanic islands is dominated by amphidromous species, whose larvae are transported to the ocean and develop in the plankton before recruiting back to freshwater habitat as juveniles. Because stream habitat is relatively scarce and unstable on oceanic islands, this life history would seem to favor either the retention of larvae to their natal streams, or the ability to delay metamorphosis until new habitat is encountered. To distinguish between these hypotheses, we used population genetic methods to estimate larval dispersal among five South Pacific archipelagos in two amphidromous species of Neritid gastropod (Neritina canalis and Neripteron dilatatus). Sequence data from mitochondrial COI revealed that neither species is genetically structured throughout the Western Pacific, suggesting that their larvae have a pelagic larval duration of at least eight weeks, longer than many marine species. Additionally, the two species have recently colonized isolated Central Pacific archipelagos in three independent events. Since colonization, there has been little to no gene flow between the Western and Central Pacific archipelagos in Neritina canalis, and high levels of gene flow across the same region in Neripteron dilatatus. Both species show departures from neutrality and recent dates for colonization of the Central Pacific archipelagos consistent with frequent extinction and recolonization of stream populations in this area. Similar results from other amphidromous species suggest that unstable freshwater habitats promote long-distance dispersal capabilities

Gender Roles and Medical Progress

Maternal mortality was the second-leading cause of death for women in childbearing years up until the mid-1930s in the United States. For each death, twenty times as many mothers were estimated to suffer pregnancy-related conditions, often leading to severe and prolonged disablement. Poor maternal health made it particularly hard for mothers to engage in market work. Between 1930 and 1960, there was a remarkable reduction in maternal mortality and morbidity, thanks to medical advances. We argue that these medical advances, by enabling women to reconcile work and motherhood, were essential for the joint rise in married women's labor force participation and fertility over this period. We also show that the diffusion of infant formula played an important auxiliary role