Phenotypic but no genetic adaptation in zooplankton 24 years after an abrupt +10 degrees C climate change

Abstract

The climate is currently warming fast, threatening biodiversity all over the globe. Populations often adapt rapidly to environmentalchange, but for climate warming very little evidence is available. Here, we investigate the pattern of adaptation to an extreme+10°C climate change in the wild, following the introduction of brine shrimpArtemia franciscanafrom San Francisco Bay, USA, toVinh Chau saltern in Vietnam. We use a resurrection ecology approach, hatching diapause eggs from the ancestral population andthe introduced population after 13 and 24 years (∼54 and∼100 generations, respectively). In a series of coordinated experiments,we determined whether the introducedArtemiashow increased tolerance to higher temperatures, and the extent to which geneticadaptation, developmental plasticity, transgenerational effects, and local microbiome differences contributed to this tolerance. Wefind that introduced brine shrimp do show increased phenotypic tolerance to warming. Yet strikingly, these changes do not havea detectable additive genetic component, are not caused by mitochondrial genetic variation, and do not seem to be caused byepigenetic marks set by adult parents exposed to warming. Further, we do not find any developmental plasticity that would helpcope with warming, nor any protective effect of heat-tolerant local microbiota. The evolved thermal tolerance might therefore beentirely due to transgenerational (great)grandparental effects, possibly epigenetic marks set by parents who were exposed to hightemperatures as juveniles. This study is a striking example of “missing heritability,” where a large adaptive phenotypic change isnot accompanied by additive genetic effects.