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Session Schedule & Abstracts




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Sunday 3rd July, 2016

AQU4
Symposium: Functional (secondary) adaptation to an aquatic life in vertebrates 4

Room: Salon A   4:30 pm–5:30 pm

Moderator(s): A. Houssaye & F. Fish
AQU4-1  4:30 pm  How to build a deep diver. Pabst D. A.*, UNC Wilmington; McLellan W.A., UNC Wilmington; Rommel S.A., UNC Wilmington   pabsta@uncw.edu
Abstract: Mesoplodonts are extreme divers, diving for over 45 minutes and to depths of over 800m (Tyack et al. 2006). These dives are of similar depth and duration to those of Physeter macrocephalus, whose body mass can be over 50 times greater (Watwood et al. 2006). Velten et al. (2103) suggested that the deep dives of mesoplodonts can remain aerobic if diving metabolic rate is low. We present body composition data that support the hypothesis of low metabolic rates in mesoplodonts. We utilized a mass dissection protocol to systematically dissect six mesoplodonts (one Mesoplodon bidens, one M. europaeus, two M. densirostris, and two M. mirus) into discrete anatomical compartments, including integument and individual muscles, organs, and bones. These component masses, as a percent total body mass (%TBM), were compared to those of shallow-diving species investigated using similar techniques - Phocoena phocoena (McLellan et al. 2001) and Tursiops truncatus (Mallette et al. 2016). The %TBM represented by integument (20-26%) and bone (9-11%) were similar across all species. Relative brain mass was smaller in mesoplodonts (0.2%) than in Tursiops (0.7%) or Phocoena (1%), as was combined thoracic and abdominal viscera (4-5% in mesoplodonts vs. 15% in Tursiops and 13% in Phocoena). In contrast, mesoplodonts invest a substantially larger %TBM (48-49%) in locomotor muscle than does Tursiops (31%) or Phocoena (26%). This locomotor muscle is composed of 80% large, fast-twitch glycolytic muscle fibers with low mitochondrial volume densities (Velten et al. 2013). This muscle fiber profile, apparently unique to beaked whales, suggests low rates of oxygen usage in this extremely large body compartment. The large investment in musculoskeletal tissues and small investment in brain and viscera likely contribute to low metabolic rates in diving mesoplodonts.

AQU4-2  5:00 pm  Aquatic habits in the ancestors of cetaceans: integrating stable isotopes and bone cross-sectional morphology. Cooper L.N.*, NEOMED; Clementz M.T., University of Wyoming; Usip S., NEOMED; Bajpai S., Birbal Sahni Institute of Palaeobotany; Hieronymus T.L., NEOMED; Hussain S.T., Howard University; Thewissen J.G.M., NEOMED   lcooper@neomed.edu
Abstract: The first 15 million years of cetacean evolution is one of the best case-studies in macroevolutionary transitions. The earliest cetaceans were interpreted as semi-aquatic based on the presence of thickened bones and stable oxygen isotope values in tooth enamel, relative to coeval, land-dwelling taxa. However, the origin of aquatic habits in cetacean ancestors remains unclear. This study reconstructed the origins of aquatic habits in this group based on CT scans of long bones of a large sample of extant and fossil cetartiodactylans. In agreement with isotopic evidence, the common ancestor of anthracotheres, hippopotamids, raoellids and cetaceans may have spent a great deal of time in the water. Some modern taxa (e.g., tragulids) are capable of submerging for long periods of time, but probably utilize a different, non-skeletal, solution to counteract body buoyancy. Results also showed bone cross-sectional phenotype is not a reliable stand-alone proxy for aquatic behaviors, and is best combined with other lines of information, like stable isotopes. Morphology was, however, an accurate indicator of a semi-aquatic lifestyle as taxa that spent the majority of their lives in water displayed extreme hyperostosis. This study extends our understanding of the progression of skeletal phenotypes associated with habitat shifts among mammals.



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