My co-authors and I are pleased to announce the publication of our new paper in Ecology and Evolution on the correlated loss of olfactory anatomy with deeper, longer diving behavior in aquatic carnivorans.
Olfaction at depth: Cribriform plate size declines with dive depth and duration in aquatic arctoid carnivorans Deborah J. Bird, Iman Hamid, Lester Fox-Rosales, Blaire Van Valkenburgh Ecology and Evolution. 2020;00:1–15; https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.6343 Abstract It is widely accepted that obligate aquatic mammals, specifically toothed whales, rely relatively little on olfaction. There is less agreement about the importance of smell among aquatic mammals with residual ties to land, such as pinnipeds and sea otters. Field observations of marine carnivorans stress their keen use of smell while on land or pack ice. Yet, one dimension of olfactory ecology is often overlooked: while un- derwater, aquatic carnivorans forage “noseblind,” diving with nares closed, removed from airborne chemical cues. For this reason, we predicted marine carnivorans would have reduced olfactory anatomy relative to closely related terrestrial carnivorans. Moreover, because species that dive deeper and longer forage farther removed from surface scent cues, we predicted further reductions in their olfactory anatomy. To test these hypotheses, we looked to the cribriform plate (CP), a perforated bone in the posterior nasal chamber of mammals that serves as the only passageway for ol- factory nerves crossing from the periphery to the olfactory bulb and thus covaries in size with relative olfactory innervation. Using CT scans and digital quantification, we compared CP morphology across Arctoidea, a clade at the interface of terrestrial and aquatic ecologies. We found that aquatic carnivoran species from two lineages that independently reinvaded marine environments (Pinnipedia and Mustelidae), have significantly reduced relative CP than terrestrial species. Furthermore, within these aquatic lineages, diving depth and duration were strongly correlated with CP loss, and the most extreme divers, elephant seals, displayed the greatest reductions. These observations suggest that CP reduction in carnivorans is an adaptive response to shifting selection pressures during secondary invasion of marine environments, particularly to foraging at great depths. Because the CP is fairly well preserved in the fossil record, using methods presented here to quantify CP morphology in extinct species could further clarify evolutionary patterns of olfactory loss across aquatic mammal lineages that have independently committed to life in water. The publication can be found at: https://onlinelibrary.wiley.com/doi/full/10.1002/ece3.6343 PDF requests can be sent to dbirds...@gmail.com Deborah Bird Department of Ecology and Evolutionary Biology UCLA 610 Charles E. Young Dr. Los Angeles, CA 90095 Cell: 310-245-2003
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