In prior interviews with Dr. Michael Hutchins, we discussed the impact of threats such as emerging infectious diseases and invasive species on extant wildlife populations. In recent times, many species have not fared well in the face of such threats, and in some cases have been rendered extinct in the wild merely since the industrial revolution. These include species that have been around much longer than humans and the advent of associated anthropogenic stressors that have had a negative impact on faunal diversity in a relatively short period.
Extinct species have succumbed to threats that have acted either independently or synergistically or both. A “new” threat—contemporary climate change will undoubtedly exacerbate or expedite the demise of a diversity of wildlife species that have already fallen victim to preexisting anthropogenic factors.
Will the polar bear adapt in time or “re-adapt” to life on land. Will these iconic, Arctic predators essentially evolve to negotiate unprecedented warming trends? It is highly doubtful. To preserve imperiled wildlife like the polar bear, humans may need to intervene on a number of fronts, not the least being the management of evolution? We will explore this topic and related aspects of conservation in the context of evolutionary biology with Dr. Hutchins in our eighth interview for National Geographic News.
Jordan: Before introducing the topic further let’s provide some perspective on what is at stake. Speaking of polar bears, what do you predict will be the future for the polar bear if we fail to significantly reduce global carbon emissions?
Michael: There is no doubt that global climate change is having a significant impact on polar bears. The Arctic sea ice, which has now shrunk to historical lows (http://www.washingtonpost.com/blogs/capital-weather-gang/wp/2013/03/26/arctic-sea-ice-reaches-maximum-6th-lowest-on-record/; http://www.climatecentral.org/news/study-arctic-summers-warmest-in-600-years-15873), is making it more difficult for the bears to move from one place to another. Consequently, one very warm year could leave hundreds of polar bears stranded on land for extended periods of time. In 2008, scientists started observing more bears swimming in open water long distances from land, an indication that, as the sea ice on which they live and hunt continues to melt, adult polar bears and their cubs are being forced to swim farther to locate sufficient food and habitat to survive (http://www.sciencedaily.com/releases/2008/08/080825210415.htm). Polar bears are highly specialized to hunt seals on sea ice, and it is unlikely that rapid climate change will give them the necessary time to adapt to a more terrestrial existence. Some species will be able to adapt in response to climate change (http://www.scientificamerican.com/article.cfm?id=sea-urchin-evolution-to-cope-with-climate-change-ocean-acidification&WT.mc_id=SA_Facebook), while others will not. Increased time spent on dry land also means that polar bears are coming into more frequent contact with their cousin, the brown bear and humans. It is estimated that polar and brown bears diverged from a common ancestor around 600,000 years ago (http://www.sciencedaily.com/releases/2012/04/120420105332.htm), but the genetic distance is not that great and interspecies breeding has been known to produce fertile offspring (http://www.slate.com/articles/news_and_politics/explainer/2010/05/pizzly_bears.html). Even though this is likely to have happened before during past bouts of climate change, frequent interbreeding could change the genetic makeup of both populations and thus alter the course of evolution, resulting in a hybrid species (http://www.natureworldnews.com/articles/13/20120728/climate-change-may-push-polar-bears-to-interbreed-with-brown-bears.htm). Shrinking ice is also bringing polar bears into more frequent conflict with humans, which is ironic given the fact that their population is decreasing (http://missoulian.com/news/local/warming-causing-polar-bear-human-conflicts-alberta-professor-says/article_54f1348a-748f-11e1-9fd7-0019bb2963f4.html). This could also cause long-term problems for the bears, unless new methods can be developed to try to mitigate human-bear conflicts.
The situation for polar bears has triggered alarm among conservationists, who have suggested that immediate action is necessary to curb climate change and to plan for the species’ uncertain future (http://www.sciencedaily.com/releases/2013/02/130204184716.htm). One option for polar bear management and conservation is a “wild bear park model.” This would involve provisioning the bears in temporary captivity and then releasing them when freeze-ups allow the animals to travel to their traditional hunting grounds. But this option could cost millions of dollars and have long-term impacts on the animals’ behavior. As serious as climate change is, we must not lose sight of the equally devastating effects of human population pressure and its subsidiary consequences. Human population has tripled since 1945 (http://en.wikipedia.org/wiki/World_population).
Of course, the dire predictions for polar bears and other Arctic species are not universal and much uncertainty exists. Some scientists have suggested that warmer conditions will be beneficial for many species and that widespread extinction will be unlikely, except for the most cold-adapted species (and except where human activity, such as high arctic shipping and oil development, occurs) (http://www.forbes.com/sites/jamestaylor/2013/01/02/news-alert-to-climate-alarmists-most-arctic-species-will-benefit-from-global-warming/). Recent studies have suggested that Antarctic’s Adelie penguins are actually benefiting from warmer temperatures, rather than being harmed by them (http://www.scientificamerican.com/podcast/episode.cfm?id=penguin-species-could-be-climate-wi-13-04-08).
Jordan: This is a fairly sophisticated topic so let’s provide some background and perhaps define some terms. Can you briefly explain how evolution works on small and large scales?
Michael: As you say, this is a complicated topic, especially when one gets into the details. I do not have time to get into all of the details here; however, the principles behind the modern synthetic theory of evolution through natural selection are quite simple and straightforward. Any population of living organisms displays variation in phenotype (i.e., physical and behavioral characteristics, such as height, arm length, etc.). To the extent that these phenotypic differences reflect differences in genotype (the genetic make-up of an individual), then natural selection can work on them. When a given trait confers a survival, and even more importantly, a reproductive advantage, then that trait will eventually come to dominate the entire population. At the genetic (micro) level, this involves a change in allelic frequencies, as genes control the expression of physical traits (i.e., the blueprint for development). Alleles are different forms of the same gene that result in different phenotypic outcomes that can be produced through mutation (a change in the DNA sequence).
As environments change, individuals with particular traits are favored, while those with other traits or some variation of them are not. In the terminology of evolutionary biology, some individuals are more “fit” than others. The result is a gradual evolutionary change in a species over long periods of geological time. One example might be the length of giraffes’ necks. If a population of ancestral giraffes had variation in the length of their necks, then we could easily see longer necks being selected for, as individuals that can reach leaves on the highest of branches would have access to enhanced nutrition and less competition, therefore allowing them to invest more energy in reproduction than their less-endowed counterparts. The longer neck, in this case, provided a selective advantage and thus came to characterize the entire population.
We’ve talked about evolutionary change within species, but how does speciation (the creation of new species) occur? Across an entire species’ range, there can be considerable variation in environmental characteristics, with some populations evolving to adapt to specific ecological circumstances. If these populations diverge and interact infrequently (e.g. through geographic isolation), they may eventually get to the point where they cannot interbreed and produce viable offspring due to behavioral or physical differences. At that point a new species has been created, and given enough time, further divergence may occur. Isolation does not have to be complete, but must allow evolutionary significant differences to accumulate. Speciation can also be driven by competition for resources. A classic example of divergent evolution is the Galapagos finches (Petren, K. 2011. Galapagos finches. In: Hutchins, M., Geist, V. and Pianka, E. Grzimek’s Animal Life Encyclopedia. Evolution. 2nd. Edition. Farmington Hills, MI: Gale). Thought to have a common mainland ancestor, the finches diverged into numerous species, each having a particular dietary niche, reflected primarily by differences in beak size and shape. There are other ways that speciation may occur; see Guy Bush’s essay “Speciation: The origin of diversity” (2011 in Hutchins, M., Geist, V. and Pianka, E. Grzimek’s Animal Life Encyclopedia. Evolution. 2nd. Edition. Farmington Hills, MI: Gale) for more details.
Two relatively recent discoveries have altered our view of classic Darwinian (i.e., gradual) evolution. The concept of punctuated equilibrium showed that, under the right circumstances, rapid evolutionary change can occur (http://en.wikipedia.org/wiki/Punctuated_equilibrium). In addition, the concept of kin selection showed that evolutionary change can occur when a particular trait is detrimental to individual fitness (a phenomenon known as “altruism”), but benefits relatives, which share those genes, thus perpetuating those genes within the population (http://en.wikipedia.org/wiki/Inclusive_fitness). The classic example of the latter are the social insects, such as termites, bees and ants, wherein the workers (all females) help the queen, produce offspring, but do not reproduce themselves, a phenomena that would not be predicted by individual natural selection (Goodsman, M.A.D. Kin selection. In: Hutchins, M., Geist, V. and Pianka, E. Grzimek’s Animal Life Encyclopedia. Evolution. 2nd. Edition. Farmington Hills, MI: Gale). These insects’ unusual genetic system, known as haplodiplody, leads to unusual genetic relationships among kin. In normal sexual reproduction, female offspring share 50% of their genes with both brothers and sisters on average. In haplodiploid systems, females are related to their sisters by 75% and to their brothers by only 25%, which suggests that workers “inclusive fitness” will be enhanced by helping the queen reproduce rather than reproducing themselves. Another way that individuals sharing alleles might interact is if they stay in one place, instead of dispersing far from the natal site. This explains the evolution of alarm calling behavior by animals, such as social marmots that warn their relatives about approaching predators, but increase the probability that they, themselves, will become prey (Barash, D.P. 1989. Marmots: Social Behavior and Ecology. Stanford, CA; Stanford University Press).
Jordan: Domestication is one way we have managed the evolution of other species for our own sake. Perhaps we should first talk a little bit about domestication because this concept tends to confuse people.
Michael: Yes, the process of domestication occurs through artificial, not natural selection (Clutton-Brock, J. 2011. Artificial selection. In: Hutchins, M., Geist, V. and Pianka, E. Grzimek’s Animal Life Encyclopedia. Evolution. 2nd. Edition. Farmington Hills, MI: Gale). Domestication essentially involves breeding animals for particular desirable traits. The process is the same as directional natural selection, except it is humans deciding (consciously or unconsciously), which individuals will survive and reproduce and which will not. All of the many dog breeds we see today—from the diminutive Chihuahua to the massive Great Dane were produced through artificial selection from wolf ancestors (Serpell, J.A. 2011. Canid evolution: From wolf to dog. In: Hutchins, M., Geist, V. and Pianka, E. Grzimek’s Animal Life Encyclopedia. Evolution. 2nd. Edition. Farmington Hills, MI: Gale). The many breeds of cattle, horses, goldfish, cats, chickens—some of them quite fantastic– were all produced through artificial selection. It should be noted that artificial selection (domestication) not only results in desired physical traits, it is also used to modify behavior. In general, dogs, particularly companion dogs, have been bred to suppress their aggressive behavior towards humans (i.e., to become more neotenous or juvenile in their behavioral and physical characteristics). However, dogs that are bred for protection (German shepherds, Rottweiler’s) are comparatively more aggressive, as are dogs that are bred for fighting (Pit bulls). Some dogs have been bred for very specific purposes: Newfoundlands are water rescue dogs that have been known to drag people out of their swimming pools, whether they are drowning or not. The otter dog was bred to hunt otters and has an incredible sense of smell, even detecting the presence of otters in water. Because dogs can learn, at least some of these instinctual behavioral traits can be modified through training. However, the underlying behavioral tendencies are still there and can express themselves under the right circumstances.
Jordan: We have talked about domestication of animals for our own purposes. How can we manage evolution of wildlife species for their own sake? How could disrupting or interrupting evolutionary trajectories serve to conserve wildlife, especially in the face of climate change and other anthropogenic factors?
Michael: Instead of consciously modifying evolutionary trajectories ourselves (an experiment that would involve much uncertainty), it might be better for us to maintain as much genetic diversity as possible in species’ populations. This would make it possible for some species to adapt to changing circumstances when they occur. This is precisely what is done in scientifically-managed captive breeding programs. Planned breeding seeks to maintain as much genetic variation as possible in a given population, thus preserving the potential for future evolutionary change (see below). Of course, the problems many species are experiencing today are largely anthropogenic (human-caused) and occur comparatively rapidly. In some cases, species will not be able to adapt to such changes quickly enough and will have an increased probability of extinction. This is especially true for “specialist” species—those that are closely adapted to very specific environmental requirements. If those specific ecological characteristics no longer exist, then the specialist species is in trouble. For example, the thorny devil—a lizard endemic to Australia survives almost entirely on a diet of ants. Similarly, North America’s black-footed ferret specializes in hunting prairie dogs. Another Australian native, the koala, subsists exclusively on eucalyptus leaves. If the ants, prairie dogs or eucalyptus trees become rare or disappear altogether, then the species that depend on them would go extinct as well. “Generalist” species, such as raccoons, coyotes or chimpanzees, that can subsist in a variety of different habitats and have wide-ranging diets, are less susceptible to environmental change. Scientists are now considering which species are more likely to be able to adapt to climate change and which not based on a variety of factors (http://bio.research.ucsc.edu/~barrylab/classes/climate_change/Hoffmann_Sgro_nature_2011_adaptation.pdf; http://www.sciencedaily.com/releases/2012/08/120816075403.htm). Perhaps this will provide us with guidance concerning which animals we should be expending our limited resources on trying to conserve and which not. This is clearly a form of triage, which may ultimately decide the fates of both species and ecosystems. Clearly, there is much that can be done to help some species adapt to climate change, including managing ecosystems for greater resilience, opening corridors that allow the movement of animals as habitats change, and restoring habitats when feasible. Such plans are being developed in the U.S. through the National Fish, Wildlife and Plants Climate Adaptation Plan (http://www.fws.gov/home/climatechange/adaptation.html) and Landscape Conservation Cooperatives or LCCs (http://www.fws.gov/landscape-conservation/lcc.html). One possible intervention strategy to conserve selected endangered species is the concept of meta-population management, which involves the active management of discrete populations (as in those existing in fragmented habitats) to maintain genetic diversity (http://life.bio.sunysb.edu/ee/akcakayalab/KeyTopicsChapter5.pdf). This could also involve a greater interaction between captive populations (held as an insurance policy) and wild populations (http://www.canids.org/PUBLICAT/EWACTPLN/EWAP%20Chapter%209%20Metapopulation%20Conservation.PDF). Thus, one way to prevent the extinction of selected species will be to actively move individuals between wild and captive populations to maintain genetic diversity and species viability. Of course, the drawback to this approach is that it involves intensive management and is likely to be very costly. The main question then becomes: Who is going to pay for it?
Jordan: Through captive breeding programs, zoos are in some ways managing evolution. Can you elaborate on this?
Michael: In scientifically-managed captive breeding programs, the goal is actually to reduce the probability that long-term captivity will result in unintended artificial selection. In fact, through planned breeding of animals of known ancestry, it is possible to retain as much genetic variation in the population as possible and to mitigate the potential damaging effects of unconscious artificial selection. Modern zoo breeding programs are based on computer databases that record the origin of given animals and their genetic relationships to others in the captive population. Zoos do not want to produce animals that have traits (e.g., docility) that would make them easier to manage in captivity, but which might be detrimental in nature. If the eventual goal is reintroduction, then they would not want to produce domesticated versions of their wild counterparts. Of course, because captive populations are relatively small, they are in danger of losing genetic variation rapidly through inbreeding. This would reduce viability of the population regardless of the zoo community’s primary goal for maintaining it (e.g., education, reintroduction, fund-raising to support in situ conservation, research). However, this can be mitigated by the occasional introduction of new founders into the population.
Jordan: The emerging interdisciplinary field known as Conservation Medicine draws from the disciplines of human and veterinary medicine and environmental science to examine and help protect human and animal health, and preserve biodiversity. As a veterinary parasitologist, I realize the importance of conserving parasites and parasite-host relationships to ecosystems and their organization. Parasitic agents can have a profound effect on shaping ecosystem ecology. Can you address some of these mechanisms as they influence the abundance of vertebrate species and perhaps how other disease agents like viruses and bacteria influence the diversity of wildlife and even plant communities?
Michael: I find it interesting the many people, especially many Americans, think that evolution is exclusively about the past—that it has no relevance to our contemporary world or to our individual lives. However, they are dead wrong. The utility of evolutionary thought is perhaps most evident when it comes to human and animal medicine. How, for instance, do people think that disease-causing bacteria and viruses, attain immunity against antibiotics and antivirals? This is a classic case of directional natural selection. There is variation in the population as to individual susceptibility to antibiotics and antivirals, and when subjected to them, some individuals survive and reproduce and some do not. Over time (in the case of rapidly reproducing microorganisms, which have many generations in a short time), the population comes to be composed of individuals that are immune to the treatments, thus necessitating constant efforts to discover new antibiotic and antiviral agents. That is precisely why the overuse of antibiotics and antivirals is not a good idea. Our understanding of other medical challenges would be impossible without knowledge of evolutionary biology. For example, take sickle cell anemia, which is found only in people of African or Mediterranean origin. As it turns out, having sickle cell anemia, which is an inherited trait, confers a survival and reproductive advantage in areas where malaria is prevalent, as those with the trait are less susceptible to the malaria parasite (http://suite101.com/article/the-connection-between-sickle-cell-anemia-and-malaria-a255511). Unfortunately, the trait is no longer beneficial when individuals move to other continents where malaria is rare or nonexistent. In such circumstances, the trait can become a medical problem, rather than a selective benefit.
Parasites and diseases are a natural part of our world and have had a profound impact on the evolution of both plants and animals. There has been more of an effort recently to think about parasites and diseases as a component of biological diversity (http://green.blogs.nytimes.com/2012/06/18/in-defense-of-parasites/). However, this poses some interesting philosophical questions (http://royalsociety.org/exhibitions/2009/extinction/). For example, humans have purposely caused the extinction of at least two disease-causing organisms—the small pox virus and rinderpest (http://en.wikipedia.org/wiki/Smallpox; http://www.theworld.org/2011/06/eradication-rinderpest/). There are many others we would like to eliminate (e.g. chief among them, the protozoan parasite that causes malaria), but, at best, have only been able to control. In some cases, rare parasites are getting in the way of our conserving species, such as the highly endangered Iberian lynx, which is infected by Felicola (Lorisicola) isodoroi, a louse exclusively parasitic on the lynx. Ironically, the louse is even more highly endangered than its host and current management activities devoted to the conservation of the Iberian lynx, such as captive breeding for reintroduction, could compromise the survival of the louse species. This poses an interesting conundrum for conservationists. (http://onlinelibrary.wiley.com/doi/10.1111/icad.12021/abstract ).
Jordan: Can you talk about the discipline of Conservation Genetics and describe how molecular technology is increasingly used to aid in the conservation management of wildlife species. Can you elaborate on this notion?
Michael: Yes, the relatively new field of conservation genetics is a critical tool in the battle for biological diversity (http://en.wikipedia.org/wiki/Conservation_genetics). Conservation genetics is a mixture of ecology, molecular biology, population genetics, mathematical modeling and evolutionary systematics (the construction of family relationships). It is both a basic and an applied science and employs modern techniques, such as mitochondrial DNA analysis and DNA fingerprinting (http://en.wikipedia.org/wiki/DNA_fingerprinting; http://en.wikipedia.org/wiki/Mitochondrial_DNA). Key among these applied roles are: (1) defining phylogenetic relationships among groups of animals and evolutionarily significant units for conservation (http://en.wikipedia.org/wiki/Evolutionarily_Significant_Unit), (2) assessing genetic variation in populations, (3) helping to develop management options to address species endangerment. Before conservationists can determine which taxa should be the focus of their concerns, they must know if it is an “evolutionary significant unit” (ESU) for conservation. Is it truly a separate species or subspecies? How it is related to other species within its Family or Order? How unique is it? All of these questions can be answered through modern genetic analysis. One of the most important tasks for conservation geneticists is in assessing the genetic viability of extant populations of endangered species, both in nature and captivity. The smaller a population is the more susceptible it is to losing genetic diversity through inbreeding or genetic drift (http://www.encyclopedia.com/topic/Genetic_Drift.aspx; http://www.encyclopedia.com/topic/inbreeding.aspx). Why is genetic variation so important? I’ve touched on this previously, but to reiterate, without genetic variation, individuals within a population are essentially clones of themselves (http://www.nps.gov/plants/restore/pubs/restgene/1.htm). If all the individuals in a population are identical, natural selection has nothing to work with. If the environment changes, the population will not be able to adapt through evolutionary change, and the probability of extinction would be considerably higher or even inevitable. Conservation geneticists can help to determine a Minimum Viable Population (MVP) size for a species to be able to maintain sufficient genetic diversity to survive in the wild (http://en.wikipedia.org/wiki/Minimum_viable_population). This is often useful for conservation planning. Conservation geneticists are also important for helping to determine what kinds of interactions will be necessary between populations to maintain genetic diversity and population viability (http://www.maths.uq.edu.au/~pkp/papers/modsim09/RossPollett.pdf). In conclusion, conservation genetics is an increasingly important discipline in conservation biology.