Invasive species are hurting fragile ecosystems around the world, and nowhere is this more prevalent than on the Hawaiian Islands. Biological invaders of all shapes and sizes can be found across the archipelago. Large populations of cats, rats, mosquitos and parasites—originating overseas—are thriving in Hawaii, and as a result, native bird populations are plummeting.
The Hawaiian honeycreeper has been hit especially hard. Invasive mosquitoes brought a highly virulent strain of avian malaria to Hawaii and a large proportion of the honeycreeper population has been infected. On the Hawaiian island of Kaua’i, the number of these small, colorful finches has declined by more than 50 percent over the last 15 years. At their current rate of decline, the species will likely go extinct within the next 30 years.
Stopping the spread of avian malaria across the Hawaiian Islands is no small feat. Scientists have tried and failed to eradicate Hawaii’s invasive mosquitoes. Traditional methods, such as culling, have proven ineffective.
Conservation biologist Robert Fleischer has been studying the evolutionary interactions between honeycreepers, mosquitos and the malaria parasite for many years. He thinks there is only one permanent solution to this unique conservation problem: genetic modification. Fleischer wants to use genetic modification to bolster the birds’ resistance to avian malaria and make mosquitoes incapable of transmitting the pathogen.
Fleischer heads the Center for Conservation Genomics at the Smithsonian Conservation Biology Institute. His research is focused on the use of genetics to study the evolutionary interactions between hosts, vectors and infectious disease.
At the annual meeting of the American Association for the Advancement of Science in Austin, Texas, in February, Fleischer sat down with SciCom’s Annie Roth to talk about using genetic methods to combat insect-borne diseases.
What is conservation genomics?
It's the use of genomic theory and genomics methods to help in conservation.
How can genomics be used conserve species?
We now have the means to identify genes—involved in some important aspect of an organism's life—that are causing it to be impacted by something humans have put into the system, like a disease or a particular pathogen. We can actually figure out why a species is being impacted and, with these new synthetic biology methods, we have the power to fix the problem.
When you say synthetic biology, what do you mean?
Genetic modification. I mean changing the genes, either by changing the gene expression or the actual genomic sequences.
It's exciting to me, but it's also fraught with difficulties in terms of policy, public opinion, cultural norms and those sorts of things. This is because you're talking about modifying something which will save it, but in the end, have you saved the same thing or is it something different? We have to be careful how we proceed on this.
Tell me about your latest conservation project.
Plasmodium relictum [avian malaria] is causing lots of problems for native birds in Hawaii, especially honeycreepers. Plasmodium relictum is a very benign parasite in Europe, Africa and Asia where it's native—but in Hawaii, where it was introduced, it has become a highly virulent parasite. On the island of Kauai, mosquitoes have spread malaria all over the island and birds are starting to go extinct.
We've been studying this for many years from the standpoint of the birds and how they can fight it, in terms of genetic-based immune response. We know from our previous work that one of the species, the amakihi, shows a mixed response to the parasite. So we're using that species to try to find the genetic and immunological factors that are allowing some birds to survive infections. We've also been studying the parasite to try to figure out where it came from, when it got there and why it's so virulent.
"You're talking about modifying something which will save it, but in the end, have you saved the same thing or is it something different?"
How can this information be used to save Hawaiian honeycreepers?
One thing that could be done, which is probably the cleanest way of dealing with this, would be to use genetic and genomic methods to make mosquitoes unable to transmit the malaria parasite. You could also [genetically] manipulate the birds to make them less susceptible in some way; that's something we've been working on.
How close are you to being able to genetically modify birds and mosquitos?
We haven't done anything with them yet. These [ideas] are all still up in the air, but we're probably closest to modifying mosquitoes.
Modifying birds hasn’t been as easy as people thought. In most birds, the egg develops in the oviduct, but there's some development before the egg is even laid. This makes it kind of difficult to get into the embryos.
I've heard recently that people have worked out that problem, at least in some domestic birds, but that’s not the real issue. The real issue is getting the genes incorporated into the genome to permanently modify the offspring. You can move genes into a developing embryo and have them expressed; scientists have been doing that for 20 or 30 years. But they haven't cracked the egg, so to speak, on getting things incorporated into the germ line.
What are the greatest threats to biodiversity in Hawaii right now?
Invasive species are probably the biggest threat [to biodiversity]. If you could get rid of the invasive species in Hawaii, which means mosquitoes, rats, mongoose, feral cats and coqui frogs, you would solve nearly all the conservation problems in Hawaii.
How serious is Hawaii’s avian malaria problem?
There are six native species of honeycreepers left on Kaua’i—and we're probably going to lose all of them in the next five years if we don't do something. Maui and the Big Island still have native birds at high elevations, but how rapidly is that going to fail over time? It's sort of a crisis situation, especially on Kaua’i. They're doing a captive breeding program for three of the [honeycreeper] species right now and will probably do another one or two soon. They're also looking heavily into mosquito eradication methods.
What do you think about controlling invasive species by introducing another non-native species to prey on it?
It's worked in some cases. They've been able to control some invasive plants with introduced insects, but you have to be very careful when you do these approaches to ensure that you're not going to have unintended consequences.
Do you think introducing genetically modified animals into natural populations carries the same risk of unintended consequences ?
In some cases, it certainly does. For example, we want to get rid of mosquitoes in Hawaii, but we don't necessarily want to impact mosquitoes where they're native. If a [modified] mosquito managed to make it back to a place where there are native mosquitoes, the modified genes could potentially get incorporated into natural populations. So that's a risk.
But making a mosquito that can't transmit the malaria parasite is probably something that's not going to have as many unintended consequences as, say, putting a gene drive mechanism in mosquitoes that kills them. If you did that and then the mosquitos escape to an area where they’re native, it can wipe out the native biodiversity.
There's other risks that people have come up with that I think are less likely or valid. Clearly there's a public perception out there that "franken-skeeters" are a potentially bad thing. There's this idea that modified mosquitoes could turn into monsters—and they could. The likelihood is very low, but these things have to be weighed and balanced against the risk.
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© 2018 Annie Roth. Annie continually modifies her online archive at www.rothreporting.com.
