Biomechanical Consequences of Rapid Evolution in the Polar Bear Lineage

The polar bear is the only living ursid with a fully carnivorous diet. Despite a number of well-documented craniodental adaptations for a diet of seal flesh and blubber, molecular and paleontological data indicate that this morphologically distinct species evolved less than a million years ago from the omnivorous brown bear. To better understand the evolution of this dietary specialization, we used phylogenetic tests to estimate the rate of morphological specialization in polar bears. We then used finite element analysis (FEA) to compare the limits of feeding performance in the polar bear skull to that of the phylogenetically and geographically close brown bear. Results indicate that extremely rapid evolution of semi-aquatic adaptations and dietary specialization in the polar bear lineage produced a cranial morphology that is weaker than that of brown bears and less suited to processing tough omnivorous or herbivorous diets. Our results suggest that continuation of current climate trends could affect polar bears by not only eliminating their primary food source, but also through competition with northward advancing, generalized brown populations for resources that they are ill-equipped to utilize

Toxic blooms in Oregon waters

Published July 2009. Reviewed December 2013. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalogKeywords: public health, water quality, cyanobacteria, blue green algae, toxic bloom

COVID-19 stressors and health behaviors. A multilevel longitudinal study across 86 countries

Anxiety associated with the COVID-19 pandemic and home confinement has been associated with adverse health behaviors, such as unhealthy eating, smoking, and drinking. However, most studies have been limited by regional sampling, which precludes the examination of behavioral consequences associated with the pandemic at a global level. Further, few studies operationalized pandemic-related stressors to enable the investigation of the impact of different types of stressors on health outcomes. This study examined the association between perceived risk of COVID-19 infection and economic burden of COVID-19 with health-promoting and health-damaging behaviors using data from the PsyCorona Study: an international, longitudinal online study of psychological and behavioral correlates of COVID-19. Analyses utilized data from 7,402 participants from 86 countries across three waves of assessment between May 16 and June 13, 2020. Participants completed self-report measures of COVID-19 infection risk, COVID-19-related economic burden, physical exercise, diet quality, cigarette smoking, sleep quality, and binge drinking. Multilevel structural equation modeling analyses showed that across three time points, perceived economic burden was associated with reduced diet quality and sleep quality, as well as increased smoking. Diet quality and sleep quality were lowest among respondents who perceived high COVID-19 infection risk combined with high economic burden. Neither binge drinking nor exercise were associated with perceived COVID-19 infection risk, economic burden, or their interaction. Findings point to the value of developing interventions to address COVID-related stressors, which have an impact on health behaviors that, in turn, may 111 influence vulnerability to COVID-19 and other health outcomes

The Women's Trade Union League: Labor, Suffrage, and Sisterhood

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Avian Responses to Mechanical Stress: Morphology and Bone Structure During Hovering, Migration, and Egg-Laying

All organisms experience mechanical forces which shape their body size and morphology. However, mechanical forces vary between species within a given lineage, between populations of a given species, between different sexes, and even within an individual organism over time. Here, I explore how variable mechanical forces influence bird morphology across these different scales. First, I explore how the presence or absence of hovering behavior alters bone morphology across a lineage of birds. Second, I look at how remaining sedentary or migrating influences morphology within a single species. Third, I study how egg-laying behavior alters female bone morphology over time. By studying how mechanical forces influence morphology we can gain an understanding of the mechanisms that control organism shape.Chapter 1: Morphological Adaptations to Hovering in a Remarkable Radiation of Old World Nectar-Eating Birds: the Sunbirds (Nectariniidae)Hovering is a unique form of locomotion that allows an animal to remain stationary in the air. While hummingbirds hover almost exclusively to obtain nectar from flowers, other nectar-eating birds vary in whether and how often they hover. This tendency may be constrained by morphology. Hummingbirds have several morphological adaptations to hovering, including long wings, short tarsi, and shortened proximal wing bones. I hypothesized that the morphology of hovering birds converges on hummingbird morphology. Specifically, I predicted that hovering birds would be lower in mass and have longer wings, reduced tarsi, and longer tails. I also predicted that hovering birds would not vary in mass across elevations, but that higher elevation species would have relatively long wings. To test these predictions, I measured mass, elevation, wing length, tail length, and tarsus length in a group of birds that includes species that hover and species that do not hover: the sunbirds (Nectariniidae). In contrast to my predictions, hovering sunbird species were heavier than those that did not hover. Female hovering sunbirds did have relatively long wings, but males did not. Hovering sunbirds did not have relatively short tarsi or long tails. However, male sunbirds in general did have relatively short tarsi and long tails. Hovering species did not vary in mass across elevation, Females but not males had longer wings with increasing elevation. These results suggest that nectar-eating behavior, not hovering behavior, may select for hummingbird-like morphologies such as long wings and short tarsi. Additionally, hovering behavior seems to apply weaker selective forces on the morphology of most birds than it does in hummingbirds. A deeper understanding of the morphological requirements for hovering will aid in our understanding of the evolution of nectar-eating and its association with hovering behavior.Chapter 2: Influence of Migratory Behavior on Bone Morphology in the Dark-Eyed Junco (Junco hyemalis)Migratory behavior requires birds to expend increased energy as they spend a greater proportion of the day flying. To prepare, birds increase body mass by 20% or more, increase the masses of muscles associated with flight, and shrink organs that are not used during migration such as the stomach. This simultaneous increase in body mass, muscle mass, and the number of loads applied to the body each day has been associated with increased microcrack formation and risk of fatigue fracture in humans. Is migratory behavior in birds associated with any adaptations in bone structure? To answer this question, I compared bone morphology of resident (J. h. carolinensis, J. h. pontilis) and migrant (J. h. hyemalis, J. h. montanus, J. h. aikeni) subspecies of the Dark-Eyed Junco (Junco hyemalis). Specifically, I looked at trabecular and cortical bone morphology in the humerus and femur using micro-computed tomography and linear mixed effects models.I found that migratory birds had humeri that were thinner and wider, but these changes were not associated with a difference in geometric stiffness. In contrast, migratory femora were thinner, resulting in reduced geometric resistance to bending. Therefore, migrant femurs are less stiff under loading, but migrant and resident humeri have similar whole bone stiffness properties.Taken together, these results suggest that residents and migrants have similar demands on the humerus, but that migrants have reduced demands in the femur. This may be due to resorption of muscle mass during migration, relatively increased evolutionary pressures to reduce body mass in migrants, or other differences in selection between residents and migrants. Further research should be performed to explore what mechanisms drive differences between resident and migrant birds.Chapter 3: Microstructure and Mechanical Properties of Bird Bone During Egg-LayingIn the week prior to laying an egg, a female bird creates a unique calcified tissue inside her long bones: medullary bone. Medullary bone is primarily thought to function in calcium storage, as females draw heavily from it when producing an eggshell. However, it also increases overall bone mass and alters whole bone mechanical properties, and thus may influence avian energetics and behavior. What is the structural contribution of medullary bone to resisting forces during bending, and how might it influence behavior? To answer this question, I gave male zebra finches (Taeniopygia guttata) an estrogen-eluting implant in order to generate a predictable model of medullary bone. Using micro-computed tomography scans of the humerus and femur, I created models with and without medullary bone, and used finite element analyses to apply bending forces (resulting in 1% axial displacement) and measure the load held in each bone. I found that the addition of medullary bone resulted in a 36 – 41% increase in bone mass but an increase in whole bone stiffness of only 24 – 30%. It also had minimal influences on the load held in the cortex. I confirmed these results in similar models of female birds during egg-laying. My results align with those of previous studies, which showed that medullary bone increases whole bone strength, but that increases are not concomitant with its increase in volume. Medullary bone therefore represents an ideal compromise between the need to store calcium for use during egg-laying while maintaining bone loading and bone mechanical integrity.ConclusionIn summary, variations in mechanical forces influence morphology across varying scales. Specifically, the high forces experienced during hovering may select for longer wings, while the large energy expenditures during migration may select for reduced femur mass. In addition, these studies demonstrate that birds can be a useful system in which to understand how mechanical forces influence morphology. Future work should explore the nuances and potential mechanisms by which mechanical forces shape morphology

Avian Responses to Mechanical Stress: Morphology and Bone Structure During Hovering, Migration, and Egg-Laying

All organisms experience mechanical forces which shape their body size and morphology. However, mechanical forces vary between species within a given lineage, between populations of a given species, between different sexes, and even within an individual organism over time. Here, I explore how variable mechanical forces influence bird morphology across these different scales. First, I explore how the presence or absence of hovering behavior alters bone morphology across a lineage of birds. Second, I look at how remaining sedentary or migrating influences morphology within a single species. Third, I study how egg-laying behavior alters female bone morphology over time. By studying how mechanical forces influence morphology we can gain an understanding of the mechanisms that control organism shape.Chapter 1: Morphological Adaptations to Hovering in a Remarkable Radiation of Old World Nectar-Eating Birds: the Sunbirds (Nectariniidae)Hovering is a unique form of locomotion that allows an animal to remain stationary in the air. While hummingbirds hover almost exclusively to obtain nectar from flowers, other nectar-eating birds vary in whether and how often they hover. This tendency may be constrained by morphology. Hummingbirds have several morphological adaptations to hovering, including long wings, short tarsi, and shortened proximal wing bones. I hypothesized that the morphology of hovering birds converges on hummingbird morphology. Specifically, I predicted that hovering birds would be lower in mass and have longer wings, reduced tarsi, and longer tails. I also predicted that hovering birds would not vary in mass across elevations, but that higher elevation species would have relatively long wings. To test these predictions, I measured mass, elevation, wing length, tail length, and tarsus length in a group of birds that includes species that hover and species that do not hover: the sunbirds (Nectariniidae). In contrast to my predictions, hovering sunbird species were heavier than those that did not hover. Female hovering sunbirds did have relatively long wings, but males did not. Hovering sunbirds did not have relatively short tarsi or long tails. However, male sunbirds in general did have relatively short tarsi and long tails. Hovering species did not vary in mass across elevation, Females but not males had longer wings with increasing elevation. These results suggest that nectar-eating behavior, not hovering behavior, may select for hummingbird-like morphologies such as long wings and short tarsi. Additionally, hovering behavior seems to apply weaker selective forces on the morphology of most birds than it does in hummingbirds. A deeper understanding of the morphological requirements for hovering will aid in our understanding of the evolution of nectar-eating and its association with hovering behavior.Chapter 2: Influence of Migratory Behavior on Bone Morphology in the Dark-Eyed Junco (Junco hyemalis)Migratory behavior requires birds to expend increased energy as they spend a greater proportion of the day flying. To prepare, birds increase body mass by 20% or more, increase the masses of muscles associated with flight, and shrink organs that are not used during migration such as the stomach. This simultaneous increase in body mass, muscle mass, and the number of loads applied to the body each day has been associated with increased microcrack formation and risk of fatigue fracture in humans. Is migratory behavior in birds associated with any adaptations in bone structure? To answer this question, I compared bone morphology of resident (J. h. carolinensis, J. h. pontilis) and migrant (J. h. hyemalis, J. h. montanus, J. h. aikeni) subspecies of the Dark-Eyed Junco (Junco hyemalis). Specifically, I looked at trabecular and cortical bone morphology in the humerus and femur using micro-computed tomography and linear mixed effects models.I found that migratory birds had humeri that were thinner and wider, but these changes were not associated with a difference in geometric stiffness. In contrast, migratory femora were thinner, resulting in reduced geometric resistance to bending. Therefore, migrant femurs are less stiff under loading, but migrant and resident humeri have similar whole bone stiffness properties.Taken together, these results suggest that residents and migrants have similar demands on the humerus, but that migrants have reduced demands in the femur. This may be due to resorption of muscle mass during migration, relatively increased evolutionary pressures to reduce body mass in migrants, or other differences in selection between residents and migrants. Further research should be performed to explore what mechanisms drive differences between resident and migrant birds.Chapter 3: Microstructure and Mechanical Properties of Bird Bone During Egg-LayingIn the week prior to laying an egg, a female bird creates a unique calcified tissue inside her long bones: medullary bone. Medullary bone is primarily thought to function in calcium storage, as females draw heavily from it when producing an eggshell. However, it also increases overall bone mass and alters whole bone mechanical properties, and thus may influence avian energetics and behavior. What is the structural contribution of medullary bone to resisting forces during bending, and how might it influence behavior? To answer this question, I gave male zebra finches (Taeniopygia guttata) an estrogen-eluting implant in order to generate a predictable model of medullary bone. Using micro-computed tomography scans of the humerus and femur, I created models with and without medullary bone, and used finite element analyses to apply bending forces (resulting in 1% axial displacement) and measure the load held in each bone. I found that the addition of medullary bone resulted in a 36 – 41% increase in bone mass but an increase in whole bone stiffness of only 24 – 30%. It also had minimal influences on the load held in the cortex. I confirmed these results in similar models of female birds during egg-laying. My results align with those of previous studies, which showed that medullary bone increases whole bone strength, but that increases are not concomitant with its increase in volume. Medullary bone therefore represents an ideal compromise between the need to store calcium for use during egg-laying while maintaining bone loading and bone mechanical integrity.ConclusionIn summary, variations in mechanical forces influence morphology across varying scales. Specifically, the high forces experienced during hovering may select for longer wings, while the large energy expenditures during migration may select for reduced femur mass. In addition, these studies demonstrate that birds can be a useful system in which to understand how mechanical forces influence morphology. Future work should explore the nuances and potential mechanisms by which mechanical forces shape morphology

Quasi-steady state aerodynamics of the cheetah tail

During high-speed pursuit of prey, the cheetah (Acinonyx jubatus) has been observed to swing its tail while manoeuvring (e.g. turning or braking) but the effect of these complex motions is not well understood. This study demonstrates the potential of the cheetah's long, furry tail to impart torques and forces on the body as a result of aerodynamic effects, in addition to the well-known inertial effects. The first-order aerodynamic forces on the tail are quantified through wind tunnel testing and it is observed that the fur nearly doubles the effective frontal area of the tail without much mass penalty. Simple dynamic models provide insight into manoeuvrability via simulation of pitch, roll and yaw tail motion primitives. The inertial and quasi-steady state aerodynamic effects of tail actuation are quantified and compared by calculating the angular impulse imparted onto the cheetah's body and its shown aerodynamic effects contribute to the tail's angular impulse, especially at the highest forward velocities

Biomechanical consequences of rapid evolution in the polar bear lineage.

The polar bear is the only living ursid with a fully carnivorous diet. Despite a number of well-documented craniodental adaptations for a diet of seal flesh and blubber, molecular and paleontological data indicate that this morphologically distinct species evolved less than a million years ago from the omnivorous brown bear. To better understand the evolution of this dietary specialization, we used phylogenetic tests to estimate the rate of morphological specialization in polar bears. We then used finite element analysis (FEA) to compare the limits of feeding performance in the polar bear skull to that of the phylogenetically and geographically close brown bear. Results indicate that extremely rapid evolution of semi-aquatic adaptations and dietary specialization in the polar bear lineage produced a cranial morphology that is weaker than that of brown bears and less suited to processing tough omnivorous or herbivorous diets. Our results suggest that continuation of current climate trends could affect polar bears by not only eliminating their primary food source, but also through competition with northward advancing, generalized brown populations for resources that they are ill-equipped to utilize