Graduate Thesis Defense

Name:Roxanne Beltran
Title:Bridging the gap between pupping and molting phenology: behavioral and ecological drivers in Weddell seals
Date:Thursday, 24 May 2018
Location:O'Neill Bldg, rm 201, Vera Alexander Learning Center
Major Professor:Greg Breed, Jenn Burns


In Antarctica, the narrow window of favorable conditions constrains the life history phenologies of female Weddell seals (Leptonychotes weddellii) such that pupping, breeding, foraging, and molting occur in quick succession during summer; however, little is known regarding the carry-over effects from one life history event to another. In this dissertation, I characterize the phenological links between molting and pupping, and evaluate the importance of feeding success and reproductive success to those links. I reviewed the contributions of natural and sexual selection to the evolution of molting strategies in the contexts of energetics, habitat, function, and physiology. Many polar birds and mammals adhere to a comparable biannual molting strategy wherein the thin, brown summer feathers/fur are replaced with thick, white winter feathers/fur. Pinnipeds are an exception to the biannual molting paradigm, relying on blubber for insulation and thus exhibiting a single molt per year.

Using survey data from over 4,000 individually identified Weddell seals, I found that successful reproduction delays the molt by approximately two weeks relative to non-reproductive individuals. By deploying time-depth recorders on 59 seals at the crucial time after pupping when they are initiating the annual molt, I discovered a striking mid-summer shallowing of seal dive depths that follows a vertical migration of fishes during the summer phytoplankton bloom. The seals experienced higher foraging success during this vertical shift in the marine ecosystem, which allows seals to gain mass prior to starting the molt. Across four years of study, late ice break-out resulted in later seal dive shallowing and later molt. In combination, the data presented in this dissertation suggest that molting, foraging, and pupping phenologies are linked in Weddell seals, and are driven by a combination of physiological and ecological factors. Characterizing these links is paramount to understanding the implications of phenological disruptions from global change.

Thesis Defenses

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