Climate change has an impact on all levels of biodiversity: genes, species, populations and ecosystems. This effect is expected to be dependent on the rate of change. When faced with unfavorable environmental conditions, individuals have three non-exclusive options by which they can mitigate these changes: temporal alterations in phenology, spatial tracking of optimal conditions or in situ adaptation. For the latter to occur requires the existence of variability among conspecifics with respect to traits that directly or indirectly influence individual performance and fitness. One such “functional” trait is thermal stress tolerance. We investigated the presence of intraspecific functional trait variability of isofemale lineages of the free-living marine nematode Litoditis marina in monoculture, double and quadruple mixtures under thermal stress, which was applied in a gradient and a sudden treatment over 20 days, corresponding to at least four generations. We found a high degree of intraspecific functional trait variability relevant to thermal tolerance. This type of variability has traditionally been considered negligible compared to interspecific variation, but our results demonstrate the importance of its inclusion within trait-based eco-evolutionary studies as this will confer increased accuracy when inputting physiological parameters to relevant models (e.g. species distribution models). Additionally, we found a significant effect of the temperature treatments. In accordance with the majority of experimental evidence, our populations showed a stronger response to a sudden versus a gradient increase in temperature. Contrary to our expectations, no significant differences were observed between monocultures, double and quadruple lineage mixtures suggesting that increased intraspecific trait variability did not lead to higher fitness in L. marina populations exposed to thermal stress. |
