Evolution and behavioural responses to human-induced rapid environmental change

Behavioural changes and the adaptive diversification of pigeons and doves

What factors determine the extent of evolutionary diversification remains a major question in evolutionary biology. Behavioural changes have long been suggested to be a major driver of phenotypic diversification by exposing animals to new selective pressures. Nevertheless, the role of behaviour in evolution remains controversial because behavioural changes can also retard evolutionary change by hiding genetic variation from selection. In the present study, we apply recently implemented Ornstein-Uhlenbeck evolutionary models to show that behavioural changes led to associated evolutionary responses in functionally relevant morphological traits of pigeons and doves (Columbiformes). Specifically, changes from terrestrial to arboreal foraging behaviour reconstructed in a set of phylogenies brought associated shorter tarsi and longer tails, consistent with functional predictions. Interestingly, the transition to arboreality accelerated the rates of evolutionary divergence, leading to an increased morphological specialization that seems to have subsequently constrained reversals to terrestrial foraging. Altogether, our results support the view that behaviour may drive evolutionary diversification, but they also highlight that its evolutionary consequences largely depend on the limits imposed by the functional demands of the adaptive zone.

Can individual and social patterns of resource use buffer animal populations against resource decline?

Species in many ecosystems are facing declines of key resources. If we are to understand and predict the effects of resource loss on natural populations, we need to understand whether and how the way animals use resources changes under resource decline. We investigated how the abundance of arboreal marsupials varies in response to a critical resource, hollow-bearing trees. Principally, we asked what mechanisms mediate the relationship between resources and abundance? Do animals use a greater or smaller proportion of the remaining resource, and is there a change in cooperative resource use (den sharing), as the availability of hollow trees declines? Analyses of data from 160 sites surveyed from 1997 to 2007 showed that hollow tree availability was positively associated with abundance of the mountain brushtail possum, the agile antechinus and the greater glider. The abundance of Leadbeater’s possum was primarily influenced by forest age. Notably, the relationship between abundance and hollow tree availability was significantly less than 1∶1 for all species. This was due primarily to a significant increase by all species in the proportional use of hollow-bearing trees where the abundance of this resource was low. The resource-sharing response was weaker and inconsistent among species. Two species, the mountain brushtail possum and the agile antechinus, showed significant but contrasting relationships between the number of animals per occupied tree and hollow tree abundance. The discrepancies between the species can be explained partly by differences in several aspects of the species’ biology, including body size, types of hollows used and social behaviour as it relates to hollow use. Our results show that individual and social aspects of resource use are not always static in response to resource availability and support the need to account for dynamic resource use patterns in predictive models of animal distribution and abundance.

How the informational environment shapes how prey estimate predation risk and the resulting indirect effects of predators

Prey often behaviorally respond to changes in the intensity of predation risk, and these responses can often significantly shape community dynamics, but flexible responses to changes in predation risk require that prey have accurate and timely estimates of predation risk. We present a model of how a prey's environment should shape the cognitive rules they use to assess predation risk and present how these rules shape the effects predators have on prey and the prey's resources. In the model, prey can rely on a combination of a fixed estimate of predation risk and a flexible estimate of predation risk shaped by their recent experience. Prey relied more on their experience to estimate predation risk when predator cues were more reliable and when predator densities were lower. In addition, when the prey cognitive rules favored a greater use of their experience to estimate predation risk, the presence of predators caused larger nonconsumptive effects and generally smaller consumptive effects on prey and the prey's resources. These differences in prey cognition also altered the effects that alterations of cue reliability and predator densities had on prey and their resources.

Rapid responses of soil microorganisms improve plant fitness in novel environments

Global change is challenging plant and animal populations with novel environmental conditions, including increased atmospheric CO(2) concentrations, warmer temperatures, and altered precipitation regimes. In some cases, contemporary or "rapid" evolution can ameliorate the effects of global change. However, the direction and magnitude of evolutionary responses may be contingent upon interactions with other community members that also are experiencing novel environmental conditions. Here, we examine plant adaptation to drought stress in a multigeneration experiment that manipulated aboveground-belowground feedbacks between plants and soil microbial communities. Although drought stress reduced plant growth and accelerated plant phenologies, surprisingly, plant evolutionary responses to drought were relatively weak. In contrast, plant fitness in both drought and nondrought environments was linked strongly to the rapid responses of soil microbial community structure to moisture manipulations. Specifically, plants were most fit when their contemporary environmental conditions (wet vs. dry soil) matched the historical environmental conditions (wet vs. dry soil) of their associated microbial community. Together, our findings suggest that, when faced with environmental change, plants may not be limited to "adapt or migrate" strategies; instead, they also may benefit from association with interacting species, especially diverse soil microbial communities, that respond rapidly to environmental change.

High CO₂ and marine animal behaviour: potential mechanisms and ecological consequences

Exposure to pollution and environmental change can alter the behaviour of aquatic animals and here we review recent evidence that exposure to elevated CO₂ and reduced sea water pH alters the behaviour of tropical reef fish and hermit crabs. Three main routes through which behaviour might be altered are discussed; elevated metabolic load, 'info-disruption' and avoidance behaviour away from polluted locations. There is clear experimental evidence that exposure to high CO₂ disrupts the ability to find settlement sites and shelters, the ability to detect predators and the ability to detect prey and food. In marine vertebrates and marine crustaceans behavioural change appears to occur via info-disruption. In hermit crabs and other crustaceans impairment of performance capacities might also play a role. We discuss the implications for such behavioural changes in terms of potential impacts at the levels of population health and ecosystem services, and consider future directions for research.

Effects of ocean acidification on learning in coral reef fishes

Ocean acidification has the potential to cause dramatic changes in marine ecosystems. Larval damselfish exposed to concentrations of CO₂ predicted to occur in the mid- to late-century show maladaptive responses to predator cues. However, there is considerable variation both within and between species in CO₂ effects, whereby some individuals are unaffected at particular CO₂ concentrations while others show maladaptive responses to predator odour. Our goal was to test whether learning via chemical or visual information would be impaired by ocean acidification and ultimately, whether learning can mitigate the effects of ocean acidification by restoring the appropriate responses of prey to predators. Using two highly efficient and widespread mechanisms for predator learning, we compared the behaviour of pre-settlement damselfish Pomacentrus amboinensis that were exposed to 440 µatm CO₂ (current day levels) or 850 µatm CO₂, a concentration predicted to occur in the ocean before the end of this century. We found that, regardless of the method of learning, damselfish exposed to elevated CO₂ failed to learn to respond appropriately to a common predator, the dottyback, Pseudochromis fuscus. To determine whether the lack of response was due to a failure in learning or rather a short-term shift in trade-offs preventing the fish from displaying overt antipredator responses, we conditioned 440 or 700 µatm-CO₂ fish to learn to recognize a dottyback as a predator using injured conspecific cues, as in Experiment 1. When tested one day post-conditioning, CO₂ exposed fish failed to respond to predator odour. When tested 5 days post-conditioning, CO₂ exposed fish still failed to show an antipredator response to the dottyback odour, despite the fact that both control and CO₂-treated fish responded to a general risk cue (injured conspecific cues). These results indicate that exposure to CO₂ may alter the cognitive ability of juvenile fish and render learning ineffective.

Changing organisms in rapidly changing anthropogenic landscapes: the significance of the 'Umwelt'-concept and functional habitat for animal conservation

There is a growing recognition for the significance of evolutionary thinking in ecology and conservation biology. However, ecology and conservation studies often work with species-specific, fixed traits that ignore intraspecific variation. The way the habitat of a species is considered is an example of typological thinking biased by human perception. Structural habitat units (e.g., land cover types) as perceived by humans may not represent functional habitat units for other organisms. Human activity may also interfere with the environmental information used by organisms. Therefore, the Umwelt-concept from ethology needs to be integrated in the way we think about habitat and habitat selection. It states that different organisms live in different perceptual worlds dealing with specific subsamples of the environment as a result of their evolutionary and developmental history. The resource-based habitat concept is a functional habitat model based on resource distributions (consumables and conditions) and individual movements. This behavioural approach takes into account aspects that relate to the perceptual world of organisms. This approach may offer new opportunities for conservation and may help avoid failures with habitat restoration. Perceptual ability may be subject to adaptive change, but it may also constrain organisms from showing adaptive behaviours in rapidly changing environments.

Neural plasticity is affected by stress and heritable variation in stress coping style

Here we use a comparative model to investigate how behavioral and physiological traits correlate with neural plasticity. Selection for divergent post-stress cortisol levels in rainbow trout (Oncorhynchus mykiss) has yielded low- (LR) and high responsive (HR) lines. Recent reports show low behavioral flexibility in LR compared to HR fish and we hypothesize that this divergence is caused by differences in neural plasticity. Genes involved in neural plasticity and neurogenesis were investigated by quantitative PCR in brains of LR and HR fish at baseline conditions and in response to two different stress paradigms: short-term confinement (STC) and long-term social (LTS) stress. Expression of proliferating cell nuclear antigen (PCNA), neurogenic differentiation factor (NeuroD) and doublecortin (DCX) was generally higher in HR compared to LR fish. STC stress led to increased expression of PCNA and brain-derived neurotrophic factor (BDNF) in both lines, whereas LTS stress generally suppressed PCNA and NeuroD expression while leaving BDNF expression unaltered. These results indicate that the transcription of neuroplasticity-related genes is associated with variation in coping style, while also being affected by STC - and LTS stress in a biphasic manner. A higher degree of neural plasticity in HR fish may provide the substrate for enhanced behavioral flexibility.

Effects of ocean acidification on learning in coral reef fishes

Ocean acidification has the potential to cause dramatic changes in marine ecosystems. Larval damselfish exposed to concentrations of CO(2) predicted to occur in the mid- to late-century show maladaptive responses to predator cues. However, there is considerable variation both within and between species in CO(2) effects, whereby some individuals are unaffected at particular CO(2) concentrations while others show maladaptive responses to predator odour. Our goal was to test whether learning via chemical or visual information would be impaired by ocean acidification and ultimately, whether learning can mitigate the effects of ocean acidification by restoring the appropriate responses of prey to predators. Using two highly efficient and widespread mechanisms for predator learning, we compared the behaviour of pre-settlement damselfish Pomacentrus amboinensis that were exposed to 440 µatm CO(2) (current day levels) or 850 µatm CO(2), a concentration predicted to occur in the ocean before the end of this century. We found that, regardless of the method of learning, damselfish exposed to elevated CO(2) failed to learn to respond appropriately to a common predator, the dottyback, Pseudochromis fuscus. To determine whether the lack of response was due to a failure in learning or rather a short-term shift in trade-offs preventing the fish from displaying overt antipredator responses, we conditioned 440 or 700 µatm-CO(2) fish to learn to recognize a dottyback as a predator using injured conspecific cues, as in Experiment 1. When tested one day post-conditioning, CO(2) exposed fish failed to respond to predator odour. When tested 5 days post-conditioning, CO(2) exposed fish still failed to show an antipredator response to the dottyback odour, despite the fact that both control and CO(2)-treated fish responded to a general risk cue (injured conspecific cues). These results indicate that exposure to CO(2) may alter the cognitive ability of juvenile fish and render learning ineffective.

Cues and the optimal timing of activities under environmental changes

Organisms time activities by using environmental cues to forecast the future availability of important resources. Presently, there is limited understanding of the relationships between cues and optimal timing, and especially about how this relationship will be affected by environmental changes. We develop a general model to explore the relation between a cue and the optimal timing of an important life history activity. The model quantifies the fitness loss for organisms failing to time behaviours optimally. We decompose the immediate change in fitness resulting from environmental changes into a component that is due to changes in the predictive power of the cue and a component that derives from the mismatch of the old response to the cue to the new environmental conditions. Our results show that consequences may range from negative, neutral to positive and are highly dependent on how cue and optimal timing and their relation are specifically affected by environmental changes.

Effects of early stress on behavioral syndromes: an integrated adaptive perspective

This paper presents a behavioral ecologist's view on adaptive responses to early stress. I first summarize two approaches to this topic drawn from other papers in this Special Issue: the 'inoculation model' and the 'adaptive calibration model'. I then describe three relevant modeling approaches from behavioral and evolutionary ecology: models of adaptive plasticity, models of adaptive prey behavior under uncertainty about risk, and models of state-dependent adaptive behavioral syndromes. These models generate some novel predictions on factors that explain variation in how organisms might respond adaptively to early stress. In particular, the state-dependent models of adaptive behavioral syndromes emphasize the importance of feedback loops between behavior and state variables in explaining the long-term persistence of effects of early experiences. State variables can include aspects of physiology, morphology or life history, differences among individuals in information state or skill, or even in social state (e.g., social rank). The feedbacks between behavior and individual state suggest a framework for an integrative approach to understanding responses to stress. The behavioral syndrome approach also emphasizes the importance of understanding stress carryovers - e.g., situations where effects of one kind of stressor (e.g., early social stress) carry over to influence other stress responses (e.g., response to danger) later in life. Finally, I discuss how responses to early stress might relate to variation in the ability of animals to cope well with novel conditions associated with human-induced rapid environmental change, a ubiquitous problem that animals face in the modern world.

Incorporating evolutionary principles into environmental management and policy

As policymakers and managers work to mitigate the effects of rapid anthropogenic environmental changes, they need to consider organisms' responses. In light of recent evidence that evolution can be quite rapid, this now includes evolutionary responses. Evolutionary principles have a long history in conservation biology, and the necessary next step for the field is to consider ways in which conservation policy makers and managers can proactively manipulate evolutionary processes to achieve their goals. In this review, we aim to illustrate the potential conservation benefits of an increased understanding of evolutionary history and prescriptive manipulation of three basic evolutionary factors: selection, variation, and gene flow. For each, we review and propose ways that policy makers and managers can use evolutionary thinking to preserve threatened species, combat pest species, or reduce undesirable evolutionary changes. Such evolution-based management has potential to be a highly efficient and consistent way to create greater ecological resilience to widespread, rapid, and multifaceted environmental change.

Evolutionary principles and their practical application

Evolutionary principles are now routinely incorporated into medicine and agriculture. Examples include the design of treatments that slow the evolution of resistance by weeds, pests, and pathogens, and the design of breeding programs that maximize crop yield or quality. Evolutionary principles are also increasingly incorporated into conservation biology, natural resource management, and environmental science. Examples include the protection of small and isolated populations from inbreeding depression, the identification of key traits involved in adaptation to climate change, the design of harvesting regimes that minimize unwanted life-history evolution, and the setting of conservation priorities based on populations, species, or communities that harbor the greatest evolutionary diversity and potential. The adoption of evolutionary principles has proceeded somewhat independently in these different fields, even though the underlying fundamental concepts are the same. We explore these fundamental concepts under four main themes: variation, selection, connectivity, and eco-evolutionary dynamics. Within each theme, we present several key evolutionary principles and illustrate their use in addressing applied problems. We hope that the resulting primer of evolutionary concepts and their practical utility helps to advance a unified multidisciplinary field of applied evolutionary biology.