The term 'assisted evolution' (AE) refers to a range of approaches that involve active intervention to accelerate the rate of naturally occurring evolutionary processes. These approaches aim to enhance certain attributes such as temperature tolerance, growth or reproduction.
Our goal is to enhance the resilience of corals to predicted future ocean scenarios of elevated temperature and acidification on the Great Barrier Reef.
AIMS researchers investigate a number of assisted evolution processes.
Exposure to sublethal stress may result in physiological changes that increase the tolerance to future stress events and this is referred to as ‘conditioning’. Evidence that some changes are passed from parents to later generations exists for a number of plants and animals. Conditioning can be rapid, and potentially induced.
Our projects examine whether conditioning occurs in corals, and whether it can prepare offspring for further ocean warming and acidification. The experiments are carried out in the National Sea Simulator (SeaSim), where advanced capabilities allow multi-generational and spawning experiments on many reef organisms simultaneously.
Torda et al (2017) Rapid adaptive responses to climate change in corals Nature Climate Change 7 627–636
Assisted gene flow (AGF)
This approach aims to enhance the spread of naturally warm-adapted genes across the Great Barrier Reef to buffer populations on on cooler reefs against continued warming and bleaching. The success of this approach relies on pre-existing genes for local temperature adaptation and and parental transmission (“heritability”) of temperature tolerance
Research at AIMS is currently investigating the feasibility, benefits and risks of AGF in a branching coral. We are interbreeding colonies from warmer far northern and cooler central Great Barrier Reef reefs to test whether offspring with at least one parent from the warmer reef have a temperature advantage under warmer conditions and no fitness disadvantages under cooler conditions. We measure the growth, survival and temperature tolerance of their offspring across multiple life stages.
Dixon et al (2015) Genomic determinants of coral heat tolerance across latitudes Science Vol. 348, Issue 6242, pp. 1460-1462
Hybridisation is a process where egg and sperm from two different species can fertilise and produce viable young. In coral, this process occurs occasionally in nature. It increases genetic diversity and makes novel genetic combinations that may be beneficial for adaptation.
Our experiments hybridise multiple pairs of coral species during the annual coral spawning and grow their young under future predicted ocean conditions in the SeaSim to select for climate resilience. We test whether hybrid offspring have higher survival and growth rates under both ambient and elevated conditions.
van Oppen et al (2015) Building coral reef resilience through assisted evolution Proc. Nat. Ac. Sci. vol. 112, no. 8, 2307-23313
Modifications of algal symbiont communities
The microscopic organisms that live in and on an coral animal are vital for its survival. Coral bleaching is a result of a breakdown between the coral animal and its symbiont, tiny photosynthetic algae, living inside the coral tissue.
Scientists are examining the effectiveness of breeding tougher symbiotic microalgae. Generation upon generation of the algae can be cultured outside the coral host to resist higher levels of heat stress. When the symbionts are re-introduced to a waiting coral, some are able to increase coral bleaching resilience.
Buerger et al (2020) Heat-evolved microalgal symbionts increase coral bleaching tolerance Science Advances Vol. 6, no. 20
Chakravati et al (2017) Rapid thermal adaptation in photosymbionts of reef-building corals Glob. Chan. Biol. 2017; 1-14
Manipulations of other microbes such as bacteria
Coral colonies are associated with hundreds to thousands of bacterial species, many of which are critical to their health and functioning. Probiotics are live microorganisms that, when administered in adequate amounts, confer a health benefit to the host.
AIMS researchers are examining whether the use of probiotics can increase a coral’s tolerance to heat or can help it recover faster from bleaching.
Damjanovic et al (2017) The contribution of microbial biotechnology to mitigating coral reef degradation Microbial biotechnology 10 (5), 1236-1243
Studies of gene function using novel techniques
We test the function of key genes that are thought to have roles in coral key coral life-history events such as settlement and metamorphosis. We employ multiple methods including RNAi and CRISPR/Cas9 gene editing using transfection and microinjection. We primarily work on the coral species Acropora millepora in SeaSim but are increasingly examining other reef taxa.
Cleves et al (2020) Reduced thermal tolerance in a coral carrying CRISPR-induced mutations in the gene for a heat-shock transcription factor PNAS 117 (46) 28899-28905