selection

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Limited evolutionary responses to harvesting regime in the intensive production of algae

Authors: Rebecca J Lawton, Nicholas A Paul, Dustin J Marshall and Keyne Monro

Published in: Journal of Applied Phycology, January 2017

Abstract

Plastic changes in the growth and productivity of algae in response to environment and stocking density are well established. In contrast, the capacity for such changes to persist once environmental differences cease, potentially signalling an evolutionary response, have rarely been tested for algae in intensive production systems.

We tested whether continuous differences in harvesting regime (a high stocking density/low-yield regime versus low stocking density/high-yield regime) generated changes in biomass productivity and other growth metrics within several strains of the clonal macroalga Oedogonium (Chlorophyta, Oedogoniales) and whether such changes persisted once differential harvesting yields ceased.

We found considerable plasticity in growth rate and biomass productivity over a 12-week period of active selection (i.e. repeated high-yield and low-yield harvesting of clonal lineages within strains) and that strains responded differently to this selection pressure over time.

While small, but significant, differences in growth rates of clonal lineages exposed to high-yield vs low-yield harvesting regimes were maintained after prolonged culture under a common selection regime (i.e. medium-yield harvesting), differences in biomass productivity were not. There was no evidence for positive or negative effects of maintaining multiple strains in polyculture on growth and biomass productivity.

Overall, we detected limited potential for evolutionary responses to harvesting regime in the main commercial trait of interest — biomass productivity. This outcome is important for commercial cultivation in intensive production systems, since it identifies a low risk that harvesting practices will impact negatively on biomass productivity in the longer term.

Citation

Lawton RJ, Paul NA, Marshall DJ, Monro K (2017) Limited evolutionary responses to harvesting regime in the intensive production of algae. Journal of Applied Phycology PDF 1 MB doi:10.1007/s10811-016-1044-8

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Metabolic rate covaries with fitness and the pace of the life history in the field

Authors: Amanda K Pettersen, Craig R White and Dustin J Marshall

Published in: Proceedings of the Royal Society B, volume 283, issue 1831 (May 2016)

Abstract

Metabolic rate reflects the ‘pace of life’ in every organism. Metabolic rate is related to an organism’s capacity for essential maintenance, growth and reproduction—all of which interact to affect fitness.

Although thousands of measurements of metabolic rate have been made, the microevolutionary forces that shape metabolic rate remain poorly resolved. The relationship between metabolic rate and components of fitness are often inconsistent, possibly because these fitness components incompletely map to actual fitness and often negatively covary with each other.

Here we measure metabolic rate across ontogeny and monitor its effects on actual fitness (lifetime reproductive output) for a marine bryozoan in the field. We also measure key components of fitness throughout the entire life history including growth rate, longevity and age at the onset of reproduction.

We found that correlational selection favours individuals with higher metabolic rates in one stage and lower metabolic rates in the other—individuals with similar metabolic rates in each developmental stage displayed the lowest fitness. Furthermore, individuals with the lowest metabolic rates lived for longer and reproduced more, but they also grew more slowly and took longer to reproduce initially.

That metabolic rate is related to the pace of the life history in nature has long been suggested by macroevolutionary patterns but this study reveals the microevolutionary processes that probably generated these patterns.

Citation

Pettersen A, White CF, Marshall DJ (2016) Metabolic rate covaries with fitness and the pace of the life history in the field, Proceedings of the Royal Society B, 283: 20160323
PDF 548 KB doi: 20160323. doi:10.1098/rspb.2016.0323