Einum, S. | Search bioRxiv

bioRxiv2022

Evolution of Daphnia population dynamics following invasion by a non-native predator

O_LIPredators are frequently observed to cause evolutionary responses in prey phenotypes, which may, in turn, translate into evolutionary shifts in prey population dynamics. Although a link between predation and population growth has been demonstrated in experimental evolution studies, insights from natural populations are lacking. C_LIO_LIHere we tested for evolutionary changes in the population dynamics of the herbivorous water flea Daphnia pulicaria in response to the invasion of the predatory spiny water flea (Bythotrephes longimanus) in the Great Lakes region, USA. Using a resurrection ecological approach and a 3-month population growth experiment (in the absence of predation) we compared population dynamics in daphnia from pre- and post-invasion time periods. C_LIO_LIPost-invasion daphnia were able to maintain an overall higher population abundance throughout the growth experiment, both in terms of the number of individuals (28% higher) and total population biomass (33% higher). Estimation of population dynamics parameters from a theta-logistic model suggested that this was achieved through an increase in intrinsic population growth rate as well as increased carrying capacity. C_LIO_LIThe observed difference in intrinsic rate of increase could not be predicted based on previous measurements of life-history traits in these clones. This indicates that care should be taken when extrapolating from a few life history traits measured in isolated individuals under controlled conditions to population dynamics. C_LIO_LIWhereas previous experimental evolution studies of predator-prey interactions have demonstrated that genotypes that have evolved under predation have inferior population growth when the predator is absent, this was not the case for the Daphnia. We suggest that complexities in ecological interactions of natural ecosystems, such as the potential for spatial and temporal avoidance of predation, makes it challenging to provide general predictions about evolutionary responses in population dynamics to predators. C_LI

evolutionary biology↗

bioRxiv2019

Do genetic differences in growth thermal reaction norms maintain genetic variation in timing of diapause induction?

O_LIAn optimal timing for diapause induction through the sexual production of dormant propagules is expected in populations of annual organisms. Yet, experimental work typically finds high within-population genetic variation in the sexual production of such propagules. Thus, high genetic variation in timing for diapause induction should be a common feature of annual organisms. C_LIO_LIHere, we hypothesize that genetic variation in the propensity to produce diapause propagules, Pd, is maintained by a genotype-by-environment interaction in growth performance, where fast-growing genotypes within an environment should delay diapause relative to slow-growing genotypes. From this, we derive two predictions. First, if there is ecological crossover in growth performance, the genetic correlation of Pd between environments should be negative. Second, the correlation between absolute plasticities of growth and Pd should be negative. C_LIO_LIWe tested these predictions by quantifying ephippia production in genotypes of a population of the facultative sexual cladoceran Daphnia magna at two temperatures. The population biomass at the onset of ephippia production was used as a measure of Pd, whereas somatic growth rate was used to quantify growth. Plasticity for both measurements was derived from thermal reaction norms. C_LIO_LIOur results did not support either prediction, as neither the genetic correlation of Pd between environments, nor the correlation between absolute plasticity of growth and Pd were found to be significant. C_LIO_LIOur results suggest that genetic variation in the timing of diapause is not maintained by genetic differences in thermal growth reaction norms. We propose as an alternative hypothesis that if there is across year variation in how stochastically the environment deteriorates, fluctuating selection may favor genotypes with different Pd between years. C_LI

evolutionary biology↗