AQUATIC LOCOMOTION IN BIRDS – BIOMECHANICS, MORPHOMETRICS, AND EVOLUTION

The entire diversity of life on earth exists in air or water. Whether an organism lives in air or water provides the most fundamental description of its physical world and establishes an organism’s ecological niche on the most essential level. Because these two fluids are vastly different from one another, they also dictate, via the process of natural selection, the morphology and physiology of the organisms which call them home. By studying how organisms interact with these fluids – to locomote or obtain food, for example – we have the ability to not only link organism form and function, but also to study the process of evolution itself. These two goals have been the focus of my dissertation, using diving birds as a model system. Of the 40 extant orders of birds, 16 orders contain aquatic or semi-aquatic members – species which regularly locomote on or in water as part of their life-history. Birds constitute just over 30% of all terrestrial vertebrates; thus, the bird species which move in water are both substantial and diverse. Only 1 of 16 orders have lost the ability to fly. Species in the remaining 15 orders face simultaneous selection for effective and efficient locomotion in both air and water, despite the vast differences between these two fluids. In Chapter 1 of this dissertation, I review the biomechanics of aquatic locomotion in birds and test existing hypotheses surrounding their morphologies. In Chapter 2, I use geometric morphometrics to determine how the multifunctionality of semi-aquatic birds – specifically, the wings of wing-propelled diving birds – has constrained or facilitated their morphological diversity. In Chapters 3 and 4, I use kinematic analysis to test whether the pressures of retaining aerial flight mean that species which use their wings for locomotion in both air and water are less effective and less efficient in water than lineages which have lost aerial flight. Finally, in Chapter 5, I document submerged aquatic locomotion in non-aquatic birds, despite a lack of selection or experience for this behavior, altering current understanding of the evolution of aquatic lifestyles in vertebrates

Active touch sensing in pinnipeds

Active touch sensing in humans is characterised by making purposive movements with their fingertips. These movements are task-specific to maximise the relevant information gathered from an object. In whisker-touch sensing, previous research has suggested that whisker movements are purposive, but no one has ever examined task-specific whisker movements in any animal. Pinnipeds are whisker specialists, with long, mobile, sensitive whiskers and diverse whisker morphologies. The aim of this PhD is to investigate active touch sensing in Pinnipeds (seals, sea lions and walrus), by: i) describing whisker morphology; ii) comparing and quantifying whisker movements; and iii) characterising task-dependency of whisker movements during texture, size and luminance discrimination tasks. Pinnipeds with long, numerous whiskers, such as California sea lions (Zalophus californianus) and Stellar sea lions (Eumetopias jubatus) have larger infraorbital foramen (IOF) sizes and therefore, more sensitive whiskers. The IOF being a small hole in the skull, allowing the infraorbital nerve (ION) to pass through, which supplies sensation to the whiskers. Comparing whisker movements in Harbor seals (Phoca vitulina), California sea lions and Pacific walrus (Odobenidae rosmarus), showed these species all protracted their whiskers forwards and oriented their head towards a moving fish stimulus. However, California sea lions moved their whiskers more than the other species, and independently of the head. Due to the movement capabilities and sensitivity of whiskers in California sea lions, this species was used to investigate whether whiskers can be moved in a task-specific way. Results suggested that California sea lions make task-specific movements, by feeling around the edge of different-sized shapes, and focussing and spreading their whiskers on the centre of different-textured shapes. Therefore, California sea lion whiskers are controlled like a true active touch sensory system, similar to human fingertips. I suggest that active touch sensing is likely to efficiently guide foraging and prey capture in dark, murky waters in these animals. Moreover, the complexity of California sea lion whisker movements and their subsequent behaviours makes them a good candidate from which to further investigate animal decision-making, perception and cognition