Potential for adaptation in response to thermal stress in an intertidal macroalga

Abstract

Understanding responses of marine algae to changing ocean temperatures requires knowledge of the impacts of elevated temperatures and the likelihood of adaptation to thermal stress. The potential for rapid evolution of thermal tolerance is dependent on the levels of heritable genetic variation in response to thermal stress within a population. Here, we use a quantitative genetic breeding design to establish whether there is a heritable variation in thermal sensitivity in two populations of a habitat-forming intertidal macroalga, Hormosira banksii (Turner) Descaisne. Gametes from multiple parents were mixed and growth and photosynthetic performance were measured in the resulting embryos, which were incubated under control and elevated temperature (20°C and 28°C). Embryo growth was reduced at 28°C, but significant interactions between male genotype and temperature in one population indicated the presence of genetic variation in thermal sensitivity. Selection for more tolerant genotypes thus has the ability to result in the evolution of increased thermal tolerance. Furthermore, genetic correlations between embryos grown in the two temperatures were positive, indicating that those genotypes that performed well in elevated temperature also performed well in control temperature. Chlorophyll a fluorescence measurements showed a marked decrease in maximum quantum yield of photosystem II (PSII) under elevated temperature. There was an increase in the proportion of energy directed to photoinhibition (nonregulated nonphotochemical quenching) and a concomitant decrease in energy used to drive photochemistry and xanthophyll cycling (regulated nonphotochemical quenching). However, PSII performance between genotypes was similar, suggesting that thermal sensitivity is related to processes other than photosynthesis.

Family‐level variation in early life‐cycle traits of kelp

“…), and intertidal seaweed (growth, F v / F m ; Clark et al. ). These strong family‐level effects occurred across development stages, suggesting a genetic basis for these traits and the potential for selection against deleterious alleles in the free‐living haploid stage (Barner et al.…”

“…Dioecious species without alternation of generations such as Hormosira banksii provide better opportunities for these kinds of tests in seaweed (Clark et al. ).…”

“…), while the growth and photosystem traits of the brown alga Hormosira banksii show heritable genetic variation to temperature which was identified through partitioning variance to sire effects, which is free from maternal effects (Clark et al. ). Moreover, because climate change is characterized by changes in multiple factors concurrently, understanding the response of species to multiple stressors is important in understanding adaptive capacity in habitat‐forming seaweeds.…”

Thermal plasticity is independent of environmental history in an intertidal seaweed

“…However, not only does individual variability exist in climate change responses, it may affect ecological function under climate stress (CaraDonna et al, ; McCoy & Kamenos, ; McCoy, Kamenos, Chung, Wootton, & Pfister, ). Trait variability, as a trait in itself, can have a genetic basis (Clark et al, ; Pistevos, Calosi, Widdicombe, & Bishop, ), affecting species specialization and adaptation potential to new or changing environments (Kawecki, ; Wiens & Graham, ). Such variation in temperature response could influence spatial patterns of temperature susceptibility if populations are not genetically well mixed, or between populations, though apparently not on the pool‐by‐pool scale of the experiments conducted in this study.…”

“…As revealed in our dataset, high variability in climate change responses between individuals may indicate the potential for resilience to future conditions and, thus, may play a compensatory role at the population or species level. Within other intertidal macroalgal species, individuals belonging to the same genotype perform consistently, and those that are more productive at elevated temperatures are also more productive in control temperatures (Clark et al, ).…”