The remarkable phenotypic diversity between and within species represents one of the most salient patterns across the Tree of Life. Why some clades exhibit low species diversity and morphological stasis for much of their evolutionary history whereas others have diversified into numerous species and morphological forms? And similarly, why do some populations exhibit greater intraspecific variation compared to other populations? In this dissertation, I used the carnivoran clade Musteloidea (badgers, minks, otters, raccoons, red panda, skunks, weasels) to examine how phenotypic variation between and within musteloid species contribute to their overall biological diversity. In my first two chapters (Chapters 1 and 2), I used a variety of phylogenetic comparative methods and osteological specimens to reveal that musteloids exhibited increased species richness due to evolutionary shifts to more elongate bodies. This morphological innovation potentially allowed these elongate musteloids to exploit novel habitats and prey associated with the climatic changes of the Mid-Miocone Climate Transition. In Chapter 3, I used 3D geometric morphometrics of musteloid crania and found that dietary divergence rather than sexual selection was a greater factor in maintaining cranial sexual dimorphism in musteloids. These results provide evidence that sexual selection is not always the primary force that maintains sexual dimorphism and demonstrate the importance of diet in reducing intraspecific competition for resources as an important mechanism that maintains the evolution of sexual dimorphism in extant musteloids. In my last two chapters (Chapters 4 and 5), I used 2D geometric morphometric and gross dissection approaches to quantify the size and shape of southern sea otter skulls and estimated their bite force. I found significant sexual dimorphism in adult sea otter skulls and bite force that arose through differences in developmental and growth rates and duration of the craniomandibular morphology. I postulate that males are selected to attain mature crania faster to presumably reach adult biting ability sooner, gaining a competitive advantage in obtaining food and in male–male agonistic interactions. Overall, my dissertation demonstrates how phenotypic variation can lead to increased diversification within certain clades as well as increases in potential competitive advantages within a single population.

Coleoid cephalopods (squids, octopuses, and cuttlefish) have been widely studied for a diversity of scientific inquiries. Despite their relevance as model organisms to fields such as cognitive psychology, neuroethology and physiology, there is still much to be learned about their own biology and how they interact with their environment. One group in particular, nearshore benthic octopuses, occupy an important ecological role as mid-level predators who are also a food resource to a myriad of other predators. Octopuses are generalist carnivores consuming a wide range of prey. They are also poikilotherms and are therefore physiologically sensitive to changes in their physical environment. However, little is known about how biotic and abiotic factors—such as prey type and water temperature—influence their complex suite of feeding behaviors. To investigate the effects of prey type and acute changes in water temperature on prey search, capture, and handling, I conducted controlled feeding trials with the California two-spot octopus (Octopus bimaculoides) and analyzed the videos to extract an integrative combination of behavioral measures and attack kinematics. In Chapter 1, I presented each octopus with either a live crab or live clam, to assess the behavioral variation associated with the characteristics of two distinct prey types. In clam trials, octopuses were less hesitant to approach or touch the prey, but conducted slower attacks, whereas while octopuses were more initially hesitant in crab trials their attacks on crab prey were more dynamic and deliberate. Prey type did not affect octopuses body orientation, arm usage, or eye choice. I also describe an interesting locomotion pattern for these octopuses where they move in a sinusoidal path along the bottom of the tank immediately prior to the attack of a crab, in an apparent corralling of the more mobile prey. For Chapter 2, I studied the effects of acute temperature change at three different treatment levels (baseline (14-17 °C), 20 °C, and 23 °C) on the feeding behavior of O. bimaculoides on live crab prey. I found that temperature had a significant negative effect on the probability that an octopus would attack their prey occurring in the feeding trial, and that warmer water produced longer latency to make an initial movement during the commencement of a trial, slower attack velocity and acceleration, and longer prey handling time. Finally, I discuss the ecological implications of my findings, and how these kinds of changes to octopus predator-prey dynamics could scale up to have system-level impacts.

Prey organisms have developed a variety of physiological and behavioral strategies to avoid, or mitigate, predation. Some are capable of regenerating tissue after sublethal predation, the non-fatal removal and consumption of a body part; however, the events leading up to arm loss in cryptic organisms such as octopuses are poorly understood. Octopuses have eight multifunctional, regenerative arms used to explore, handle objects, and presumably, defend against predators. In this dissertation, I explored the patterns of arm loss experienced by octopuses across species and ontogeny, as well as behaviors that put these arms at the highest risk. In Chapter 1, I observed injured arms, calculating scaling relationships specific to the arms of three sympatric Octopus species to calculate the proportion of arm truncation. Arm injuries in these species were frequent and asymmetrical, and that when injured, octopus on average lost about one-third of an arm. These injuries were biased to the anterior left arms, L1 and L2. However, different measures of injury supported very different conclusions. Therefore, in Chapter 2, I created and demonstrated the utility of an Injury Severity Index (ISI) to describe the magnitude of appendage injury in invertebrates, using counts and proportions of arm losses collected from octopuses in museums and the field. Museum specimens had most commonly lost part of one arm, with a mode ISI value of less than 2.00. Wild O. bimaculatus had a mean ISI value of 3.13, representing two to three arm injuries. I also calculated volume of lost tissue based on the shape of a cone to further enhance quantifications of arm loss. In Chapter 3, I describe the ways in which O. bimaculatus used their arms in self-defense against a common predator (Gymnothorax mordax). Octopuses and morays were observed interacting freely in tanks. Suites of antipredator strategies varied greatly by sex, leading to greater success for males avoiding an attack. Individual arm use was biased toward arm L1 and neighboring arms, and predatory bites were concentrated on L2 and its neighbors. This dissertation revealed octopus arm use and loss from high-risk contexts, with a bias toward anterior-left arms across species.

Studies have shown that ontogenetic shifts in ecology often drive adaptive changes in the scaling of musculoskeletal systems, resulting in differential performance. These support the idea that allometric changes in morphology often co-occur with changes in feeding strategies, locomotor behavior or habitat use. Fewer studies, however, have compared the ontogenetic trajectories of functional traits across closely related species to better understand the extent to which such patterns of scaling may be specifically adaptive during a particular life history stage. A confound, however, is that phylogenetic information is inherently present in development; phenotypic evolution occurs via modification of ancestral development patterns. Thus, a phylogenetically-informed approach that makes comparisons among species’ ontogenetic scaling patterns can make important contributions to our understanding of morphological diversity among species. Presently, studies using such an approach are absent in the literature. I use the evolution of cleaning behavior as a model system to understand how ontogenetic scaling patterns contribute to macroevolutionary patterns of morphological and ecological diversity. I first identify general head and body characteristics that were associated with the evolution of cleaning: an elongate body paired with an elongate head, and a terminal mouth that allows jaws with low mobility to bite rapidly on individually-targeted prey items. My “phylo-allometric” analyses then enable me to show evidence that the repeated evolution of facultative and obligate cleaning (in which taxa continue to clean as adults) is associated with the maintenance of characters over ontogeny that are conducive to cleaning in the juvenile phase. On the other hand, taxa that transition away from cleaning during ontogeny do not maintain such characters, and exhibit phenotypic trajectories that are distinct from those of other wrasses. This indicates that the recurring evolution of juvenile cleaning behavior in the Labridae has involved similar effects on developmental scaling patterns. The repeated evolution of each of these patterns shows that labrid scaling trajectories are fundamentally labile and appear to evolve adaptively to changing ecological pressures over ontogeny.

Consistent pressures from overfishing and extirpation have led to the study and conservation of many of the apex consumers within kelp forest ecosystems. Among kelp forests, those of Southern California have been described as the most diverse in the world. Yet, despite the large body of data on species interactions within these ecosystems, information on the ecology for many of the top predators is lacking. This paucity of information may be because of predator declines (e.g., giant sea bass) or simply the elusiveness of some species. One example of a large elusive predator about which little is known is the California moray (Gymnothorax mordax). The combination of a cryptic lifestyle and lack of a commercial fishery has enabled morays, in general, to have remained virtually undetected in standard species surveys. Moreover, basic biological information on morays is scarce. I use field methods, laboratory measurements, and metabolic experiments, to investigate the functional ecology of the California moray to answer questions pertaining to its dispersal, habitat preference, diet, and physiology. Data from my studies reveal that California moray dispersal is primarily driven by changes in oceanic currents caused by El Niño events. Larvae then settle to shallow Santa Catalina Island habitats consisting mainly of boulder and cobble substrates in densities ≤100x greater than previously estimated. The California moray is a piscivorous predator, consuming kelp bass, but also preying upon a wide range of fish and invertebrate species. Lastly, I discovered that the California moray has a relatively low standard metabolic rate (SMR) compared to non-anguilliform fish taxa of similar mass and that the SMRs of larger individuals do not respond to chronic changes in temperature as strongly as smaller individuals. The California moray has a subcutaneous adipose layer that increases in thickness as morays increase in mass. The adipose layer may be a physiological mechanism underlying the lower response in SMR of larger individuals at decreasing temperatures. Cumulatively, the results of this research suggest that the California moray is an apex consumer, with the potential to influence Southern California kelp forest community structure similar to patterns observed of morays in tropical communities.

The biodiversity of terrestrial and aquatic communities is driven by the ability of species to successfully disperse to and persist in different habitats. For many marine fishes, dispersal occurs via a planktonic larval form that resides in the surface layer of the ocean for a period of days to months before moving to juvenile habitats and metamorphosing. The period from hatching to soon after settlement is a critical period for fish, as it features high mortality rates. In this dissertation, I investigate selective factors that influence larval dispersal, biogeography, and population persistence in the Eastern Pacific. In Chapter 1, I examined whether morphology of larval eels (order Anguilliformes) can predict larval geographic range, and found that morphological traits of intermediate-stage larvae predicted larval latitudinal range, as leptocephali with larger relative predorsal lengths and snout-to-anus lengths exhibited larger larval ranges. In Chapter 2, I used RAD sequencing to examine genetic structure of California morays (Gymnothorax mordax) and found that California morays exhibit local adaptation in the face of high gene flow, with selection likely taking place primarily during the late larval or early juvenile period. In Chapter 3, I used highly quantitative methods to test if skin coloration of California morays around Catalina Island, CA were correlated with their habitats. I found that eels were yellower and lighter in sandy habitats and that countershading (surprising for a benthic, crevice-dwelling fish) was present on the head and tail. We hypothesize that selection on coloration is also occurring during the first few years after settlement. In Chapter 1, I used a long-term west coast ichthyoplankton dataset to examine what environmental factors are influencing larval distributions of five commercially-important taxa of fishes, as well as larval fish overall: Pacific sanddab (Citharichthys sordidus), California sheephead (Semicossyphus pulcher), cabezon (Scorpaenichthys marmoratus), rockfishes (Sebastes spp.) and sablefish (Anoplopoma fimbria). I found that Bayesian hierarchical modeling is an effect method to model larval fish abundance, and that sea surface height was the strongest environmental covariate.

Feeding is a complex process that is essential to an organism’s fitness. Individuals often show intraspecific variation when feeding, from utilizing different foraging habitats to targeting different prey. These individual differences in foraging strategies are important as they can directly affect fitness, population dynamics, behavioral flexibility, and ecosystem functioning. For several decades, intraspecific variation was largely ignored in biological studies, but, more recently, there has been a growing effort to understand the role of intraspecific variation in ecological and evolutionary processes. Phocids (true seals) are a widespread group of marine carnivores that exhibit a diversity of underwater foraging strategies. In this dissertation, I integrate field methods, bio-logging technologies, morphological and physiological sampling, and controlled feeding experiments to examine intraspecific variation and behavioral flexibility in the foraging strategies of seals. Specifically, I compare the at-sea foraging strategies of northern elephant seals (Mirounga angustirostris) across the species range and find that the species exhibits intraspecific variation across their range based on the interplay of life history, season, and geography. I also conduct a detailed analysis of the sex-specific foraging strategies of northern elephant seals, one of the most sexually dimorphic mammal species on the planet. My results reveal that male and female northern elephant seals have distinct foraging strategies and that intraspecific niche divergence helps maintain sexual dimorphism in this species. I then examine specific feeding (or prey capture) strategies used by seals and find that bearded (Erignathus barbatus), harbor (Phoca vitulina), Hawaiian monk (Neomonachus schauinslandi), ringed (Pusa hispida), and spotted seals (Phoca largha) have converged on two underwater strategies—biting and suction feeding, and these strategies are associated with different behaviors and kinematics. I also demonstrate that seals show intraspecific variation and behavioral flexibility in their use of these different strategies, with individuals switching behaviors and kinematics when targeting different prey. Cumulatively, the results of this dissertation reveal that intraspecific variation and behavioral flexibility are widespread in this group of marine carnivores, and this plasticity has likely contributed to the ability of seals to successfully occupy the role of top predators in marine ecosystems worldwide.