Cost of life-history adaptations: Multiple-trait consequences of fisheries-induced evolution

There is no such thing as a free lunch. This applies also to animals adapting to new challenges in their environment. In practice, this means that if they get more "perfected" in one way, they will get slightly less perfected in some other ways. In wild animals, just how the costs of adaptation are paid is often difficult to demonstrate. In this project, we use guppies that have been selected to excel under different size-dependent fishing regimes to study how their characteristics have changed in ways that are not directly related to their performance under fishing. We have tested how different size-selection regimes affect the ability of fish to combat parasite infections. We have used Gyrodactylus turnbulli, an ectoparasite that is a common problem in aquarium trade. Our results show that fish adapted to different fishing regimes have different ability to cope with the parasite: fish coming from populations subject to harvesting of small fish develop higher parasite loads than fish from randomly harvested populations or from populations subject to harvesting of large fish. This finding is consistent with the ?pace of life syndrome?: when selection favors fast development to maturity (harvest of small fish), they have less energy available to invest in immune defenses and responses. Interestingly, fish from randomly harvested populations had initially high parasite loads, but were the only group that was consistently able to reduce parasite loads towards the experimental period.

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The central tenet of evolutionary biology is that adaptations are costly. Here we study the costs of adaptation to external mortality, as experienced by exploited fish populations and other organisms that are exposed to elevated external mortality. Such adaptation is traditionally understood in terms of evolving growth and maturation, reflecting an energetic trade-off between current and future reproduction. This view is overly simplistic as it ignores the many other ways organisms can allocate their resources to functions that are not required by immediate survival but impact their future survival and growth. This includes allocation to cognition, immune system, and body repair, and can be measured as changes in behavioural and physiological traits. Thus, we predict that adaptation to external mortality in a fish model system leads to fish that are less smart, more vulnerable to parasites, and have shorter lifespans. The work is divided into six scientific work packages (five for primary scientific tasks and one for synthesis) as well as one for dissemination. The planned experiments take advantage of selected lines of guppies at the University of Bergen that have adapted to different types of external mortality over a period of three years. We use an array of behavioural, physiological and biochemical tests to characterize how the selected lines differ in their individual performance, complemented by a longevity assessment. The project will help us to understand the many facets of fisheries-induced evolution. As fish continue to be an important source of nutrition, income, and recreation, fisheries-induced evolution and its impacts on population viability are also important societal challenges.