“Maladaptive shifts in life history in a changing environment”
Olivier Cotto, Linnea Sandell, Luis-Miguel Chevin, and Ophélie Ronce (Special Feature on Maladaptation)
Maladaptation can induce false-adaptive shifts in life history if different trait values maximize different vital rates
As climate warms, the performance of many organisms is affected, with negative effects on some aspects of their life cycle, but also of positive effects on others. Should we interpret such cases of improved performance as evidence for climate change facilitating the persistence of those populations? A model by researchers from CNRS, the University of Montpellier (France) and the University of British Columbia (Canada) suggests caution in doing so.
In some birds, breeding earlier in the season increases the number of chicks raised in that year, but compromises the parent prospects of survival. Similarly, in some plants, flowering early is associated with the production of a higher number of fruits, but increases the risk of being grazed. The seasonal timing of key events in the life cycle of many organisms has already been modified by the warming of temperatures. Further genetic evolution of populations will be necessary to adapt this timing to future climates. How will the conflicting consequences of altered timing on different aspects of the life cycle affect this adaptive race? The model predicts that even adapting populations will lag behind the climate. Such lags in adaptation however have unforeseen consequences for the life cycle of these organisms, with negative effects on some aspects of performance (e.g. on fecundity) and, more surprisingly, positive effects on others (e.g. on survival). Increased performance in some aspects of the life cycle under a changing climate may reflect the population inability to evolve fast enough and may be observed in populations on the verge of extinction. Lags in adaptation may also trigger drastic changes in the life cycle, with some populations evolving to reproduce only once during an individual’s lifetime. This study therefore suggests that consequences of climate change should be integrated over the whole life cycle to conclude about the persistence prospects of populations.
Many species facing climate change have complex life cycles, with individuals in different stages differing in their sensitivity to a changing climate and their contribution to population growth. We use a quantitative genetics model to predict the dynamics of adaptation in a stage-structured population confronted with a steadily changing environment. Our model assumes that different optimal phenotypic values maximize different fitness components, consistent with many empirical observations. In a constant environment, the population evolves towards an equilibrium phenotype, which represents the best compromise given the trade-off between vital rates. In a changing environment however, the mean phenotype in the population will lag behind this optimal compromise. We show that this lag may result in a shift along the trade-off between vital rates, with negative consequences for some fitness components, but, less intuitively, improvements in some others. Complex eco-evolutionary dynamics can emerge in our model due to feedbacks between population demography and adaptation. Because of such feedbacks loops, selection may favor further shifts in life history in the same direction as caused by maladaptive lags. These shifts in life history could be wrongly interpreted as adaptations to the new environment, while they only reflect the inability of the population to adapt fast enough.