Latitudinal variation in the cold tolerance of the intertidal copepod Tigriopus californicus
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Broadly distributed species may adapt to local temperature conditions such that isolated populations have different thermal tolerance ranges than the species as a whole. Therefore, to accurately predict how species’ ranges will be affected by global climate change, bioclimate models would benefit from knowing the thermal tolerance of different populations within latitudinally distributed species. In this study, the intertidal copepod Tigriopus californicus was used as a model system to study how local adaptation influences the cold resistance of isolated populations. Among five populations spanning 18 degrees in latitude, two metrics were used to compare cold tolerance: post-freezing recovery and the temperature of chill coma onset (CTmin). Recovery rates following freezing were faster in copepods from colder northern latitudes. Likewise, northern populations exhibited lower chill coma onset temperatures. Importantly, both metrics showed a consistent latitudinal trend suggesting that any single metric could be used equivalently in future studies investigating latitudinal variation in cold tolerance. Our results provide evidence that populations within a single species can display strong local adaptation to spatially varying climatic conditions. Thus it would be valuable for bioclimate models to account for local adaptation when forecasting biological responses to climate change.