Dynamics of Sexual Selection in a Changing Ocean: Integrating Life History and Local Adaptation

The long Norwegian coastline, with a harsher climate in the north, serves as an excellent natural laboratory for studying climate effects on marine animals, including fishes. Studying how the life of animals varies along the North-to-South climatic gradient of Norway's coastline may help us predict the consequences of climate change. In the project DYNAMAR, we investigate how climate affects reproduction and life history in fishes, using the small two-spotted goby fish as a model organism. Two-spotted gobies are very common in kelp forests along the rocky coasts of Norway, and are unusually well suited for combining studies in the field and in the laboratory. Model organisms are useful because they help us understand how climate may affect a wider range of organisms. DYNAMAR is a collaboration between three partner institutions: The Norwegian University of Science and Technology (NTNU, the lead partner), the Norwegian Institute for Nature Research (NINA) and the Institute of Marine Science (IMR), and also involves collaborating scientists at a range of universities in Norway and abroad. We focus particularly on how climate affects reproduction and life history. This includes the length of the breeding season, how many times the fish can reproduce each year, and how these life history traits affect sexual and reproductive dynamics. Climate may affect males and females differently. This may have evolutionary consequences, through effects on the competition among males and females for the best and the most partners. Climatic variation and climate change may lead to differences in sex ratio as well as in the morphology of males and females. This, in turn, may have effects on the life history of the fishes. Variation in life history among populations along environmental gradients, like the Norwegian coastline, can either result from local evolutionary adaptation over long periods of time, or be because individuals are able to adjust to local conditions here and now. Which of these scenarios apply is important for how the fish will respond to climate change. If geographic variation in life history is due to evolutionary adaptation, they will have less potential for adapting to a rapidly changing climate. We will test the potential for the fish to respond adaptively to climate change. We do this by laboratory experiments and by state-of-the art genetic analyses. The covid has been considerably delayed for reasons of covid, which prevented field work in 2020 and 2021. However, in 2022 we succeeded in conducting full-scale field investigations in accordance with plan. These studies included 6 study locations from West Sweden to Northern Norway (Vesterålen), by three independent field teams each working on 2 of the locations, with three visits at each location during the breeding season. Data collected included population densities, sex ratio of adults, female maturation stages, size, weight and more. The data were collected by a combination of in-situ observations by snorkeling fixed transects along the islands, in the natural environment of the fish, and by collection of fish for recording size, weight and image-based data, and to obtain samples for genomics, age determination and other analyses. In addition to quantifying numbers, sex ratios and other population parameters on the transects, we also systematically recorded sexual behaviours by males and females on the same transect lines. Such behaviours included competition with the own sex, and courtship of the opposite sex. We also collected data on reproduction by putting out artificial nests at all locations and recording data on breeding individuals and their breeding success from these nests, including collection of males and clutches for detailed analyses. Finally, we recorded vegetation development and temperature trajectories by means of video recordings and temperature loggers. Taken together, we have collected an extensive data set that allows us to analyze relationships between temperature, time of season, sexual dynamics, life history, reproduction, and more. It is still early days analytically, but preliminary analyses clearly reveal patterns of variation in reproductive dynamics, behaviour and life history along the south to north latitudinal and temperature gradient. For instance, it appears that northern-population fish reproduce at an older age, and that the dynamics of sex role behaviours are significantly different between south and north. In close collaboration with the Institute of Marine Research, we have started genomics work to reveal whether this variation is linked to genetic variation among population, along the South-to-North Nordic coastline “natural laboratory” of our project. The DYNAMAR team has also been engaged in the EEA-funded network FishNet, and in DKNVS-funded explorations of northwards distribution expansion related to climate change.

The project represents a unique approach to analyse effects of climatic variation in marine ecosystems on spatiotemporal dynamics of sexual selection, life history, and local adaptation. Such interactive ecological and genetic effects are very little explored but essential to predict consequences of climate change for life history strategies. The aim is to make a major step in the understanding of sexual selection and its relationship with life history evolution. We use an excellently suited marine model system and a powerful combination of field studies, lab experiments and mathematical modelling. Sexual selection is a major force in evolution, shaping the morphology and behaviour of animals (including ornaments, body size and striking displays), and is tightly linked to life history. We focus on variation on spatial and temporal scales within species, which may help explain maintenance of genetic variation in life-history and sexually selected traits. Spatiotemporal variation has been little studied and interactions with life history dynamics are poorly understood. This project analyses a main driver of sexual selection, the operational sex ratio, a measure of the availability of potential mates for each sex at a given point in time and space. We analyse spatiotemporal dynamics of operational sex ratio, sexual selection and life history on an unprecedented scale by combining (1) analyses of variation in sexual selection and its drivers in the wild, (2) mathematical modelling of such dynamics and how they relate to life history, (3) studies linking spatial population genetic differentiation with spatiotemporal variation in life history strategies in the wild, and (4) tests of local adaptation using whole-genome sampling from wild populations, and by common-garden laboratory. Our team combines top international complementary expertise and a model system ideally suited for this unique exploration of life history and sexual selection responses to climate variation.