assisted gene flow

Using cryopreserved reproductive cells of elkhorn corals, researchers have crossbreed individuals from Florida and Puerto Rico with those of Curaçao in an important first step to creating more heat tolerant populations. The goal is to increase genetic diversity within at-risk populations of corals to help build resilience for future generations.

Genetic evolution allows entire populations to adapt, over many generations, to their local environments. However, environmental conditions are now changing at an accelerated rate, and in some cases, outpacing the ability of species to adapt. This is where Assisted Gene Flow (AGF) comes into play; this conservation intervention involves directly introducing genetic diversity into at-risk populations. In other words, researchers can now influence the reproductive process of threatened species in order to introduce new genetic diversity and thus facilitate faster evolution.

Elkhorn coral. Photo credit: Hans Leijnse

Elkhorn Coral

Corals are excellent candidates for the Assisted Gene Flow technique, especially the IUCN “critically endangered” elkhorn coral (Acropora palmata). Estimates place the decline in their populations around 95% since the 1980s. Further, they’ve struggled to keep up with changing water conditions and have documented reproductive issues. Mature corals are difficult to relocate for the purposes of AGF and coral gametes (reproductive cells) lose viability within a few hours. Researchers have therefore used cryopreservation to achieve AGF in this species.

Within the region, there are two distinct populations of elkhorn coral, one from the northwestern Atlantic and one from the Caribbean. A central, mixed zone exists near Puerto Rico. Over time, these populations have evolved to their unique thermal and oceanographic environments.

New Techniques

A recently published report highlighted the successful demonstration of using AGF to fertilize elkhorn corals. This research was a collaborative effort by CARMABI, Smithsonian Conservation Biology Institute, Penn State University, Florida Aquarium Center for Conservation, and Mote Marine Laboratory. Using cryopreserved sperm from eastern and central Caribbean (Florida and Puerto Rico) elkhorn corals, researchers were able to fertilize eggs from western Caribbean (Curaçao). By mixing these genetic pools, researchers may be able to accelerate region-wide adaptations to climate change.

Elkhorn coral. Photo credit: Duncan MacRae

Future of Conservation

In addition to achieving the highest ever survival rate for elkhorn coral juveniles, these researchers were able to generate the largest living wildlife population ever created from cryopreserved cells. This research proved the viability of using cryopreserved genetic material to increase genetic diversity. The future of coral conservation will require innovative techniques, such as AGF, to help keep pace with the accelerated changed due to climate change. By identifying and cryopreserving genetic material for threatened corals, crossbreeding with more tolerant populations may be the key to preserving these species in the future.

To read the full report, please use the DCBD link below.

https://www.dcbd.nl/document/assisted-gene-flow-using-cryopreserved-sper...

Article published in BioNews 48

Assisted gene flow (AGF) is a conservation intervention to accelerate
species adaptation to climate change by importing genetic
diversity into at-risk populations. Corals exemplify both the need for
AGF and its technical challenges; corals have declined in abundance,
suffered pervasive reproductive failures, and struggled to adapt to
climate change, yet mature corals cannot be easily moved for breeding,
and coral gametes lose viability within hours. Here, we report
the successful demonstration of AGF in corals using cryopreserved
sperm that was frozen for 2 to 10 y. We fertilized Acropora palmata
eggs from the western Caribbean (Curaçao) with cryopreserved
sperm from genetically distinct populations in the eastern and central
Caribbean (Florida and Puerto Rico, respectively). We then confirmed
interpopulation parentage in the Curaçao–Florida offspring
using 19,696 single-nucleotide polymorphism markers. Thus, we
provide evidence of reproductive compatibility of a Caribbean coral
across a recognized barrier to gene flow. The 6-mo survival of AGF
offspring was 42%, the highest ever achieved in this species, yielding
the largest wildlife population ever raised from cryopreserved
material. By breeding a critically endangered coral across its range
withoutmoving adults, we show that AGF using cryopreservation is
a viable conservation tool to increase genetic diversity in threatened
marine populations.