Conservation of the Eastern Black Rhinoceros

[MUSIC] Welcome to Science Sessions, the podcast of the proceedings of the National Academy of Sciences, where we connect you with Academy members, researchers, and policy makers. Join us as we explore the stories behind the science. I'm Paul Gabrelson. For managers of the critically endangered Eastern Black rhinoceros, individual safety is paramount. That's why they're kept in isolated, guarded populations. But preserving a healthy genetic diversity among the species is also important. In a recent PNAS study, Barbara Mabel of the University of Glasgow, Ronald Melia of Tanzania National Parks and Colleagues used whole genome studies of Eastern Black rhinos to assess the effects of rhino management strategies on genetic diversity. Their results have already led to changes in rhino management policies to cost effectively promote the rhino's genetic health. Barbara, why is genetic diversity important in managing small isolated populations? When populations come small and isolated, they eventually run out of mating partners that aren't related. So they lose genetic variation because they're breeding lists individuals that share genetic variants. Inbreeding, it increases homozygocity, so when you have two copies of the same variant at a genetic locus, some mutations that cause disease or are fatal are only expressed when there's two of the same copy. They can result in what's called inbreeding depression, which is a reduction in survival or reproductive fitness because of this exposure to these negative mutations. If there's not very much genetic variation in the population, then the theory predicts it's going to be less potential to adapt to changing environmental conditions or to things like pathogens, but we're starting to think more carefully about those theories. If there's been a long history of inbreeding, it means that only individuals that have survived exposure of these dilatirous mutations exist. You can get a purging of these negative variants, so paradoxically they may become more fit in the particular environment they're in even without a lot of genetic variation. On the other side, if a population has been what we would think of is genetically healthy, so there's lots of random mating and there's a lot of genetic variation, they can hide these negative mutations in the genome. This is called the genetic load, and so what we worry about for conservation is that we're getting the balance right in terms of having enough genetic variation, but without having a high genetic load. One of the strategies that people have used for conservation management is called genetic rescue, when they've brought in individuals from other populations to jumpstart the genetic variation, but if you bring back mutations that have been taken out of the population or if you introduce new genetic variants that they haven't seen before, those could actually be damaging in a long run. Ronald, you are a rhino warden in Tanzania. How did your first hand experience lead to this study? In East Africa, the management of rhinos has not considered genetics because the threat of the rhinos was security, so most of the management of the rhinos were consigned to protect them from poaching. This means rhinos were kept in intensive protection zone, known as IPZ. So in this area, the rhinos are further isolated from each other, where the individuals are not allowed to move in different areas because the areas are as a geofanst or with a physical face. Few attempts have been employed to increase variation in this management, such as using a supplement genetic variation from translocation, so most of this translocation was based from zoo animals. However, this long distance translocation are costly, both financially and in terms of stress that caused the animal. They have been a warden working with the Tanzania National Park for like 15 years, so the motivation for both my master studies and my PhD was too genetic to inform the Tanzania management on the best strategy to manage the eastern lacrano, which was one of the critical endangered species. So what I found in my masters, which I use metocondriary DNA sequence, was that keeping animals in episode strategies has meant that the population hasn't been a fit from the translocation because the animals were not moving around in areas like the serengetico system, where we have like four rhino population, so if we translocate animals in one of the episodes because they are not allowed to move, it's difficult to share genetic variation between the neighboring population. So also this had motivated to do a whole genome studies, which was intended to assess the impact of past management strategy. Tell us about the methods of your study. What were you looking for? Anubab Khan, he was a postdoc at the time. He did his PhD on genetic variation in Indian Tigers, but when he heard about the rhino work from Ronald, he got excited because he realized we could actually test the impacts of this past management. Most studies have focused at the population level, but we weren't focused on cohorts of individuals that had different ancestries. And this was only possible because Ronald was a rhino warden. He had access to a very unique set of samples. He was able to work with the Tanzanian park authorities and Tanzanian Wildlife Research Institute to collect samples from the majority of the remaining individuals. His work was also funded through the Zirag Zoo. It was actually a private philanthropist who unfortunately died before the study Rudy Shuddi, who funded it. It was through their generosity that we were able to bring together this international team to address this problem. So we used four different kinds of individuals. So we had offspring that had been maintained in the IPZ, so their parents were as well. We had individuals who had a parrot who had moved between these subpopulations naturally. And we had individuals who'd been translocated from captive or semi captive populations in South Africa or zoos. And then we had individuals who had one native and one translocated parent. And so then the whole genome sequencing data was used to compare genetic diversity levels of inbreeding and relative genetic load in these four cohorts. What were the results? What strategies were effective at improving genetic health? What we have found as expected that translocations had the intended benefits of increasing genetic variation and the reduced levels of inbreeding, we also found by looking at the whole genome sequences that they increased the potential risks if there's subsequent inbreeding. And this is because the cohorts with even one translocated parent had a higher proportion of these potentially damaged mutations than the cohorts that were from native individuals. We found that individuals that had moved between these subpopulations, they actually had a similar benefit in reducing inbreeding as these translocations, but without the cost of genetic load. And in fact, the genetic load was significantly lower, but our results also emphasize that this is really a transient effect. So if you let them inbreed in the future, even when you jump start the genetic variation, then there could be potential consequences. So the warning here is that sustainable management really requires frequent movement of individuals, not just occasional translocations. What are the takeaways for conservation managers of this and other endangered species? Our results suggest that we're exposed by opening up corridor to this path could be a most cost-effective and sustainable than a long distance location. It is important that if translocation do occur, which is the only strategy available for a first-decentuary strategy to reduce subsequent symbiode should also put in place. Also, monitoring genetic impact of various management strategy in real time is really critical. So in Tanzania, my research has heard the change the policy that did not allow a movement of individuals outside IPZ, rhinos have eventually natural from the new breeding group in Cerenaire region, or also in Masua, Gamedizel, which is the southern part of Assyringeti. Also, we've been having a rimer moving from southern Assyringeti, which is in more population as far as Masaymara in Kenya. My result have also been used to initiate cost-water management discussion between Tanzania and Kenya, on how to manage the cost-water population of rhinos between Masaymara, which is in Kenya, and Yamalumpa population, which is in the north part of Tanzania. What are the caveats or limitations of the study? As for many conservation studies, unfortunately, our sample sizes are small. Some of our cohorts arose from only a single father, who's mated with his offspring and his grand offspring, and so on. Part of the reality, these systems is there are no unrelated individuals left in some of these populations. But one of the main limitations for me is that so far we have a proxy for fitness. So we have this genetic load in the population, and we predict that these mutations are going to be negative and damaging, but it relates directly to the fitness of individuals and the viability of the populations. And so far, those data are lacking for most species. For rhinos, they live for a really long time, but they tend to produce one offspring every two years from the females. The reproductive rate is low, which means you need a lot of time to be able to assess reproductive fitness. Ronald has data on quite a few individuals where he's got indication on the population growth rates and the individual fitness, but not for enough individuals who have had their genome sequenced. Ronald's also working on a demographic analysis that makes predictions, but then having studies that can more directly relate fitness to genome variation would be useful. Even though the rhinos will be interesting, it might actually be more useful to test this inside something with a higher reproductive rate. Also, we had used the cohort system to assess the demographic and what we just found is that the native population have a very good growth rate when we compare to the other translocations. As Mahbrab said, we need a good dataset to relate this to their fitness. 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