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

Published in: Evolutionary Applications

Abstract

Evolutionary responses to indirect selection pressures imposed by intensive harvesting are increasingly common. While artificial selection has shown that biochemical components can show rapid and dramatic evolution, it remains unclear as to whether intensive harvesting can inadvertently induce changes in the biochemistry of harvested populations. For applications such as algal culture, many of the desirable bioproducts could evolve in response to harvesting, reducing cost‐effectiveness, but experimental tests are lacking.

We used an experimental evolution approach where we imposed heavy and light harvesting regimes on multiple lines of an alga of commercial interest for twelve cycles of harvesting and then placed all lines in a common garden regime for four cycles. We have previously shown that lines in a heavy harvesting regime evolve a “live fast” phenotype with higher growth rates relative to light harvesting regimes. Here, we show that algal biochemistry also shows evolutionary responses, although they were temporarily masked by differences in density under the different harvesting regimes. Heavy harvesting regimes, relative to light harvesting regimes, had reduced productivity of desirable bioproducts, particularly fatty acids.

We suggest that commercial operators wishing to maximize productivity of desirable bioproducts should maintain mother cultures, kept at higher densities (which tend to select for desirable phenotypes), and periodically restart their intensively harvested cultures to minimize the negative consequences of biochemical evolution.

Our study shows that the burgeoning algal culture industry should pay careful attention to the role of evolution in intensively harvested crops as these effects are nontrivial if subtle.

Marshall DJ, Lawton RJ, Monro K, Paul NA (2018) Biochemical evolution in response to intensive harvesting in algae: evolution of quality and quantity. Evolutionary Applications, PDF 746 KB doi:10.1111/eva.12632

Authors: Giulia Ghedini, Craig R White, and Dustin J Marshall

Published in: Functional Ecology, volume 32, issue 6 (June 2018)

Abstract

A major goal of metabolic ecology is to make predictions across scales such that individual metabolic rates might be used to predict the metabolic rates of populations and communities, but the success of these predictions is unclear given the rarity of tests.

Given that older communities tend to have species with slower life histories and larger body sizes, we hypothesized that the metabolism of whole communities should scale allometrically with their mass across successional stages.

We created experimental chronosequences of sessile marine invertebrate communities in the field. We then:

1. determined the metabolic scaling of these whole communities across successional stages of different mass, and
2. tested whether the sum of individual metabolic rates for the dominant species could predict overall community metabolism.

Contrary to what we expected based on metabolic theory and succession theory, community metabolism scaled isometrically with mass across succession, despite the mean body size of dominant individuals within the communities increasing over time. We resolved this paradox by estimating community metabolism based on individual metabolic rates for the dominant species in the community. We show that non‐random changes in the membership of the species maintain mass‐specific metabolic rates of the whole community invariant across succession despite changes in size structure.

These results suggest that simple assumptions about how community‐level processes scale up from species are unlikely to be correct, because community turnover is non‐random with respect to metabolic rate. Nevertheless, with the appropriate parametrization, the sum of individual species rates can predict the function of the community as a whole.

Ghedini G, White CR, Marshall DJ (2018) Metabolic scaling across succession: Do individual rates predict community-level energy use?, Functional Ecology, PDF 909 KB doi:10.1111/1365-2435.13103