Recipients: Below are a number of articles pertaining to the rise of tuskless female elephants in Mozambique. African Elephants Evolved Tusklessness Amazingly Fast--But At What Cost? Ed Yong, The Atlantic October 21, 2021 Shane Campbell-Staton never planned on traveling to Mozambique in search of tuskless elephants, but weird things can happen when you stay up ’til 3 a.m. binge-watching YouTube videos. (“Sometimes, a brother can’t get to sleep, Ed,” he told me.) Battling insomnia, Campbell-Staton watched a video about Gorongosa National Park. The park was once Edenic, but during Mozambique’s civil war, from 1977 to 1992, much of its wildlife was exterminated. Government troops and resistance fighters slaughtered 90 percent of Gorongosa’s elephants, selling their ivory to buy arms and supplies. Naturally tuskless females, which are normally rare, were more likely to survive the culls; after the war, their unusual trait was noticeably common. Campbell-Staton, a biologist at Princeton who studies rapid evolution, had questions. Was this a dramatic example of natural selection in action? Why only the females? Which genes were involved? He idly emailed his questions to a colleague who studies elephants, inadvertently setting off a chain of emails that recast his casual curiosity as serious intent, and soon found himself being introduced to a large group of Gorongosa researchers as “a guy who wants to study the genetic basis of tusklessness in elephants,” he told me. In response to which he thought: Wait a minute, I didn’t say that! I didn’t mean for this to be a whole thing. He had only ever worked with small anole lizards, but even so, when one of those researchers invited him to Gorongosa, he said yes. Once there, Campbell-Staton met Joyce Poole, a veteran elephant researcher and a co-founder of the conservation nonprofit ElephantVoices. Using historical video footage and modern sighting records, Poole estimated that the proportion of tuskless females had risen from 19 percent before the war to 51 percent after it. The team confirmed that this was an evolutionary response: During the years of intense ivory-poaching, females without tusks were five times more likely to survive than those with them. The elephants then passed on the genes behind that trait to their descendants: About 33 percent of the females born after the war were tuskless. To identify those genes, Campbell-Staton and his colleague Brian Arnold sequenced the genomes of 18 Gorongosa elephants and looked for stretches of DNA that differed between tusked and tuskless individuals. One region stood out—a small slice of the X chromosome that includes a gene called AMELX. In mammals, this gene influences the production of enamel and the growth of teeth. When it’s disrupted, teeth become abnormal and brittle. It made sense that some fault in AMELX might stop elephants from growing tusks (which, however distinctive, are just very big teeth). This discovery also explained why only female African elephants are tuskless. AMELX is a bit player rolling with A-listers: Its immediate neighbors include essential genes that animals can’t survive without. But all of these genes are so tightly packed that “it’s hard to mess with one and not the other,” Campbell-Staton told me. A mutation that affects teeth by disabling AMELX could potentially bring down the entire animal if the neighboring genes are affected. Female elephants can tolerate such risk because they have two X chromosomes: If genes are disrupted in one copy, they have a backup. Males have no such luxury: With just one X chromosome, they suffer the full fatal brunt of any change that disrupts AMELX and the genes around it. That’s why tuskless males have never been recorded (at least in Gorongosa). They just don’t survive. Other genes might also be partly involved in tusklessness, and the team isn’t clear on exactly what changes to AMELX have led to the trait. But evidence from humans suggests that they’re on the right track. In 2009, a team studied an 18-year-old woman who was missing the entire AMELX gene and parts of its essential neighbors. Among several developmental problems, the woman was missing one of her upper lateral incisors, while the other was extremely small. These are the exact same teeth that, in elephants, grow into tusks. Campbell-Staton’s team has “done a convincing job showing that the Gorongosa elephants have evolved in response to poaching,” Kiyoko Gotanda, an evolutionary biologist at Brock University, told me. Usually, evolution is a slow process, but it can proceed with blinding speed. Hawaiian crickets went from noisy to silent in just 20 generations to avoid a lethal parasitic fly that was eavesdropping on their calls. The anole lizards that Campbell-Staton usually studies ended up with bigger toes and a tighter grip after hurricanes Irma and Maria battered the Caribbean, and better tolerance for cold after a polar vortex hit Texas. But almost all of these examples involved small creatures that breed quickly. To see tusklessness evolving after just 15 years of war, in a “long-lived, slow-reproducing species like the elephant, is incredible,” John Poulsen, a tropical ecologist at Duke University, told me. Other countries have seen similar patterns. In Zambia’s South Luangwa National Park, the proportion of tuskless females rose from 10 to 38 percent from 1969 to 1989. In South Africa’s Addo National Park, 98 percent of females are now tuskless. These trends suggest that even big, slow-breeding creatures could rapidly adapt to the exceptional pressures exerted by humans, who have been billed as the “greatest evolutionary force” currently operating. But there’s a catch: The elephant’s chromosomal quirk stops males from easily reaching full tusklessness (although their tusks can shrink). And “ironically, fewer tusked females could focus poaching efforts on males even more than it already is, potentially nearly stopping reproduction,” Poulsen said. Even if the evolution of tusklessness somehow saved elephants from poaching, the loss of their mighty teeth could lead to other losses. Tusks aren’t there just for show. Elephants use them as tools to strip bark from trees and excavate minerals from soil. Rob Pringle, an ecologist at Princeton and one of Campbell-Staton’s colleagues, has shown that these behaviors sculpt the savannah. In damaging trees, elephants create homes for lizards; in toppling other trees, they open up spaces for understory plants. A population of tuskless elephants is better than having no elephants at all, but it’s not functionally the same as a population of tusked ones. They’d be changed, and so probably would the world around them, and “all because we want their teeth, which sounds just absurd when you say it,” Campbell-Staton told me. He and his team are now planning to study the consequences of tusklessness—and whether its rise has changed the elephants’ diet, the way they move nutrients across the land, and the other plants and animals in their environment. In doing so, they hope to complete the full story of Gorongosa’s tuskless elephants—a tale in which the economic forces that dictate the price of ivory and the political history that drives a country to war collide upon a handful of genes in a single charismatic species, in a way that could reshape an entire ecosystem in the space of a few decades. https://www.theatlantic.com/science/archive/2021/10/elephants-poaching-war-tusklessness/620447/ Of war, tusks, and genes Chris T. Darimont and Fanie Pelletier, Science October 22, 2021 Elephants have long been dragged into war. Referred to as “elephantry,” military units rode into battle atop these giants over millennia. On page 483 of this issue, Campbell-Staton et al. (1) describe the evolutionary aftermath of a different type of wartime elephant use. Seeking ivory to finance a civil war in Mozambique, poachers relentlessly targeted specific African elephants (Loxodonta africana), individuals with tusks, sending the population—and the frequency of this important trait—into decline. The study reveals the consequence of this intense selective killing on the persistence of tusks and the genes associated, as well as for population dynamics. Campbell-Staton et al. also identify the simple genetic architecture underlying the presence of tusks. The findings bring new evidence to inform debates on the roles of environmental and selective forces underlying trait variation in populations subject to harvest. Over and above the environmental variation to which populations are subject, selective killing of specific phenotypes can influence traits such as body or ornament (for example, horn, antler, or tusk) size. Through multiple analyses, Campbell-Staton et al. report how intensive selective killing of African elephants caused the rapid evolution of increased tusklessness in females. Field data revealed that the proportion of tuskless females increased by more than 30% as the population declined over 28 years, which included 15 years of civil war. The frequency of tuskless phenotypes among adult females born after the war was also higher than before the conflict, suggesting an evolutionary response. Simulations showed that the observed increase in tusklessness is extremely unlikely to have occurred without selective killing of tusked animals. Model outputs estimated that the survival of tuskless individuals was five times higher than that of tusked individuals. Campbell-Staton et al. also investigated whether these phenotypic changes were accompanied by a genetic signature. Analyses of whole-genome sequences from individuals with and without tusks supported the hypothesis of a more severe population decline among tusked compared with tuskless individuals. The authors then looked for a pattern of inheritance that could explain the variation in tusk morphology observed in the field. Using data on mother-offspring phenotypic associations, they found that for ∼9 out of 10 offspring, the phenotype of the offspring was consistent with a single-locus X-linked dominant model of inheritance. The observed sex bias in the offspring produced by tuskless mothers suggest that tuskless male offspring were nonviable. Using a candidate gene approach, they then identified two genes involved in tusk presence that explain a large amount of variation: AMELX (X-linked isoform of amelogenin) and MEP1a (meprin A subunit alpha), which are known to have functional associations with the development of mammalian teeth. Physical linkage between AMELX and male-lethal loci nearby on the X chromosome may explain lethality among males inheriting the trait. Campbell-Staton et al.’s elegant approach is among the rare studies to document a genetic response to harvest selection, informing debate about the potential for selective harvests to lead to evolutionary responses. Work on trophy hunting of bighorn sheep (Ovis canadensis) in Canada, for example, has shown that size-selective regulations with no harvest quotas can lead to the evolution of smaller horns (2), although the genetic mechanism remains to be elucidated. The lack of evidence linking observed phenotypic trends to changes in the genetic composition of harvested populations more broadly, however, has been used by wildlife and fisheries managers and scientists to argue against the likelihood or importance of potential evolutionary changes in harvest systems (3). The comprehensive work by Campbell-Staton et al. has clearly satisfied the burden of evidence, showing that selective killing can indeed leave a strong evolutionary signature. Restoration of the trait and its associated ecosystem function might therefore require longer time scales than those for phenotypic changes not associated with genetic changes, an important implication relevant to other systems. Generalization of the findings on African elephants is constrained by the relatively simple genetic basis underlying tusklessness. Although other studies have shown that ornament traits can be influenced by a single gene [such as horn size in Soay sheep, Ovis aries (4)], it is more commonly observed that traits involved in response to environmental changes, including selective mortality, are affected by both many small-effect genes and in some cases one or a few genes of major effect (5). Accordingly, a quantitative understanding of whether and how much the phenotypic changes observed in myriad animal populations subject to harvesting (6) are associated with genetic changes remains a complex challenge (7). More broadly, even perfect knowledge of underlying genetic contributions do not address social-evolutionary processes that influence nonhuman life in today’s world. An extreme social event (a war, in this case) that triggered intense, selective exploitation of elephants crisply illustrates the pronounced coupling between human societies and evolutionary processes in other life forms. Through humanity’s cultures, economies, medicines, built environments, and more, societies have set in motion selective landscapes never before experienced by the world’s biota (8). Moreover, and often related to ecological changes imposed by humans, societies must commonly respond to the evolution of other organisms, a reality brought into painful relief during this extended COVID-19 pandemic. Recently, such complex relationships among society, ecology, and evolution have been well examined in perhaps the most radically changed of all landscapes, cities (9). The conceptual advances gained in urban systems can inform work in other contexts in which humanity’s hand in, and response to, evolution will likely also be observed. Future work could also draw upon the well-developed theoretical basis for understanding sustainability in what has been referred to as “social-ecological systems” (10), which could be adapted to consider evolutionary interactions and outcomes. Progress in understanding these complex relationships will require more interdisciplinary research. Until recently, natural and social sciences have largely been independent enterprises. In the context of harvest selection, evolutionary ecologists could team up with social scientists. They may ask, for example, how hunters and fishers would trade-off, personally and economically, the ability to target the largest phenotypes now with the specter of losing those phenotypes in the future. As noted in the context of ecology (10), past and current societies and the institutions that govern them might have considered similar trade-offs and sought solutions from which researchers and managers can potentially learn. https://www.science.org/doi/10.1126/science.abm2980?_ga=2.20069048.1673127581.1634830950-689641651.1609118629 Poaching is altering the genetics of wild animals Benji Jones, Vox October 21, 2021 See link <https://www.vox.com/down-to-earth/22735163/elephant-tusks-genetics-evolution-adaptation-hunting> for photos. Sometime in the distant past, well before humans walked the Earth, the ancestors of modern-day elephants evolved their iconic tusks. Elephants use their bleach-white incisors — they’re technically giant teeth, like ours but longer — to dig, collect food, and protect themselves. Then Homo sapiens arrived, and elephant tusks became a liability. Poachers kill the massive animals for their tusks, which are worth about $330 a pound wholesale as of 2017. Hunters slaughter roughly 20,000 elephants a year to supply the global ivory trade, according to the World Wildlife Fund. But just as tusks evolved because they provide a number of benefits, a striking new study shows that some populations of African elephants have rapidly evolved to become tusk–less. Published in the journal Science, the paper’s authors found that many elephants in a park in Mozambique, which were heavily hunted for their ivory during a civil war a few decades ago, have lost their tusks — presumably because tuskless elephants are more likely to survive and pass the trait on to their offspring. While scientists have known about this trend for a while — it’s not uncommon to see tuskless elephants in places with lots of poaching — the study provides strong evidence that the trait is rooted in genetics, something previous research failed to do, said Andrew Hendry, an evolutionary biologist at McGill University who was not involved in the research. In other words, the study shows evolution in action. The results also offer a vivid example of how animals can quickly adapt under human pressures such as poaching and climate change. Past research has shown that creatures can evolve new colors, shapes, and even behaviors to better tolerate the increasingly inhospitable world we’ve created for them. The problem is that even rapid evolution has its limits — and many species are already on the brink. How a Civil War Caused Elephants to Lose Their Tusks Social conflict and the decline of wildlife are often closely linked, the authors of the Science study write. Few locations reveal a clearer picture of this than Gorongosa National Park, a protected area in central Mozambique where Shane Campbell-Staton, an evolutionary biologist at Princeton University, led the research. During a 16-year civil war that began in 1977, poachers on both sides of the conflict slaughtered a huge number of elephants in the park for their ivory, which they sold to finance their efforts, according to the study. Over that period, the number of large herbivores (like elephants) at Gorongosa fell by more than 90 percent. That’s not all that changed in the park. Between 1970 and 2000 — a period that encompassed much of the impact of the long-running war — the portion of female elephants without tusks nearly tripled. The researchers’ best guess was that it had something to do with genetics: A trait visible only in females suggests it might be associated with changes to genes on the X chromosome. (Female elephants have two X chromosomes, whereas males have an X and a Y chromosome.) This study all but proved it. The first bit of evidence was that female calves born from tuskless mothers were often themselves tuskless, indicating that the trait is passed on from one generation to the next. “A heritable trait is pretty strong evidence of a genetic basis,” said Robert Pringle, a biology professor at Princeton and a co-author of the study. The authors also identified a couple of regions in the animals’ DNA that appear to be associated with a lack of tusks. Sure enough, “There is strong evidence for mutations on a particular region of the X chromosome,” Pringle said. Mutations, or variations in an organism’s DNA, are an important engine of evolution. If they result in traits that are beneficial — such as tusklessness, for certain populations of female elephants — they’re more likely to get passed to the next generation and drive evolution. Remarkably, one of the genes associated with tusklessness is also present in humans, where it’s linked to a condition that limits the growth of our lateral incisors. These are essentially the same teeth that, in elephants, evolved into tusks millions of years ago. What makes this study so fascinating is that it offers evidence of rapid evolution in an animal that has a pretty long lifespan — 50 or 60 years — in the wild, said Hendry and Fred Allendorf, a professor emeritus at the University of Montana who was not involved in the research. Studies of elephants “rarely can say anything about the genetic basis” of tusklessness, Hendry said. For years, researchers assumed that rapid evolution was common only in small species with short life cycles. Given these results, “Nobody can argue that evolution isn’t occurring, even in the biggest and longest-lived species,” he added. Should All Elephants Ditch Their Tusks? In theory, it’s advantageous to be born without tusks in areas where poachers are active, Hendry said. But tusklessness also has its downsides. Elephants need their tusks to dig, lift objects, and defend themselves. The hulking incisors are not useless appendages. The genes that seem to make female elephants tuskless also appear to prevent mothers from giving birth to male calves — that’s why all the tuskless elephants in the park are female, Pringle said. (Some mothers did give birth to males with tusks, who likely didn’t inherit the gene.) Over time, a shift in the sex of elephants could have consequences for population growth. There are also potential costs to African grasslands, which are among the rarest and most biodiverse ecosystems on Earth, the study authors write. By turning over soil in search of food and minerals and gouging trees with their tusks, African savanna elephants prevent forests from growing too dense and help maintain grasslands. That’s why they’re considered “engineers” of the ecosystem. If they lose their tusks, a whole web of plants and animals may feel the impact. “This evolutionary change could have massive cascading ecological influences,” Hendry said. How Humans are Changing Animals Humans have shaped the environment around them for centuries, down to the very genetics of wild plants and animals. The tuskless elephants in this study are just one example in a long list of species that have adapted in response to the pressures we’ve placed on them. “Human-induced changes are creating conditions for fast biological evolution — so rapid that its effects can be seen in only a few years or even more quickly,” a team of scientists wrote in a landmark intergovernmental biodiversity report in 2019. One of the earliest and most famous examples is the peppered moth in the UK. Before the Industrial Revolution, most of the moths flitting about England were white with speckles of black, which helped them blend in with lichen and tree bark. Then, in the mid- to late-1800s, coal-fired power plants and mills started belching dark soot that blackened trees in parts of the country. White moths stood out against the newly dark background and were more likely to be eaten by birds, whereas the once-rare black ones were camouflaged and survived. In a matter of years, some populations of peppered moths inverted from white to mostly black. The phenomenon was deemed “industrial melanism.” Scientists have measured similar changes in recent decades. One study from 2003, for example, found that bighorn sheep in Alberta, Canada, evolved smaller horns in roughly 30 years. The reason? Trophy hunters tend to target rams with larger horns. Another study, published in November 2020, suggests that a type of lily found in the mountains of China is evolving less-colorful leaves so it doesn't stand out in regions where it’s harvested as a traditional herb. In regions where a kind of lily called Fritillaria delavayi is heavily harvested, the plant has adapted better camouflage (see images C and D). Niu et al./Current Biology Rising temperatures from climate change also appear to be making some animals, including birds and mammals, smaller, as I previously reported. Smaller bodies cool off more easily than larger ones, so shrinking could be an adaptive response in warming environments (though it’s not yet clear whether these particular changes are genetic). Then there are species changing in less conspicuous ways. In Japan, populations of mamushi snakes that are heavily hunted for their perceived medicinal and nutritional benefits seem to be better at evading predators, compared to snake populations that hunters have ignored. Many species, including plants and insects, have evolved resistance to pesticides, which is why farmers often use several at once and chemical companies must constantly develop new solutions. There’s something like hope behind the idea of rapid evolution. Humans are deforesting, polluting, and exploiting the Earth at an alarming pace, yet in some cases, animals are adapting to live another day. There’s even a term for this resilience, Hendry said: “evolutionary rescue.” Still, this evolution, as fast-tracked as it may be, still often isn’t quick enough to overcome the many threats species face. And because adaptations can also come with drawbacks, there are untold and unpredictable consequences for the ecosystem at large. Plus, not all species can adapt their way out of crisis. Consider rhinoceroses, which poachers kill for their horns. Three of the five rhino species have been hunted almost to extinction, yet none appear to have evolved hornlessness. In Gorongosa National Park, the ecosystem has largely recovered from the war, Pringle said. Poaching has subsided, but tusks haven’t bounced back. After the war, the park successfully rebuilt its infrastructure, ramped up law enforcement, and put social development programs into place. The presence of tuskless elephants is now akin to a scar from an injury that’s healed, Pringle said. So while evolution may have helped these creatures survive, the real remedy is putting an end to the underlying forces that triggered it in the first place. https://www.vox.com/down-to-earth/22735163/elephant-tusks-genetics-evolution-adaptation-hunting Some elephants are evolving to have no tusks as a response to brutal poaching Katie Hunt, CNN October 22, 2021 An elephant's tusks are among its defining features -- they help the animal lift heavy branches, topple trees, strip bark, fight, and dig holes for water and minerals. But an increasing proportion of female elephants in Mozambique's Gorongosa National Park have been born without these crucial tools, and scientists say it's an evolutionary response to the brutal killing of elephants for their ivory tusks during the country's 15-year civil war. Elephant experts working in the park had begun to notice the phenomenon after the war ended in 1992. Field data and analysis of old video footage from the park found that the proportion of tuskless female elephants increased more than threefold between 1972 and the year 2000. It was a period during which the elephant population plummeted from roughly 2,000 to about 250 individuals, said Ryan Long, an associate professor of wildlife sciences at the University of Idaho. "During the war, Gorongosa was essentially the geographic center of the conflict," Long said via email. "As a result there were large numbers of soldiers in the area and a lot of associated motivation... to kill elephants and sell the ivory to purchase arms and ammunition. The resulting level of poaching was very intense." Genetic Signature Scientists now have a better understanding of the genetic basis for this tusklessness and why it only appears to affect female elephants, according to a study that published in the journal Science on Thursday. The analysis showed that tuskless females were over five times more likely to survive during the 28-year period than their tusked female counterparts, hence the adaptation was very unlikely to be a chance occurrence. Tusklessness does occur naturally -- and only in females -- even in the absence of poaching, but usually only in a small minority of elephants. In Gorongosa in the 1970s, 18.5% of female elephants didn't have tusks, while three decades later 51% did. "Evolution is simply a change in heritable characteristics within a population over successive generations, and based on the results of our study, the shift toward tusklessness among female elephants at Gorongosa fits this definition perfectly," said Long, an author of the study. "The fact that it occurred so rapidly is rare indeed, and is a direct function of the strength of selection," he said via email. "In other words, it happened so quickly because tuskless females had a MUCH higher probability of surviving the war, and thus a MUCH greater potential for passing their genes on to the next generation." But what about the male elephants? After taking blood samples of 18 female elephants, with and without tusks, the researchers sequenced their genomes. They found that the females with no tusks had a genetic variation in a very specific region of the X-chromosome, which plays a role in tusk development. "Females have 2 X chromosomes. In tuskless females, one of those chromosomes is 'normal' and the other contains the deleted information," Long explained. "When a tuskless female conceives a male offspring, that male has a 50/50 shot of receiving the affected X-chromosome from its mother. If it receives the 'normal' chromosome then it will survive and be born with the necessary genetic information to produce tusks." However, if the male elephant fetus receives the chromosome with the genetic variant, it dies in the womb because the variant that produces tusklessness females is lethal to males, Long said. The exact genetic and developmental mechanism that leads to tusklessness in females and the loss of male elephants during an elephant's 22-month pregnancy was not yet understood, according to the study. Elephant numbers have rebounded at Gorongosa to around 800, Long said. Having no tusks doesn't appear to significantly hinder the female elephants, but this is something researchers want to study further. He said dietary analysis suggested that females without tusks eat a greater proportion of grasses. "The population is doing well and there's a lot of tuskless elephants. They've clearly adapted to life without tusks but there's a lot we don't know." https://www.cnn.com/2021/10/22/africa/elephants-tusks-poaching-evolution-scn/index.html Ivory poaching has triggered a surge in elephants born without tusks Kate Baggaley, Popular Science October 22, 2021 From 1977 to 1992, the southeastern African country of Mozambique was gripped by a civil war during which both sides financed their efforts by hunting African savanna elephants for their ivory. This intense poaching slashed the elephant population of Gorongosa National Park by 90 percent. It also had another unintended impact on the animals, scientists reported this week. Female elephants without any tusks became much more common after the conflict. When the researchers examined population records and genetic material from park-dwelling elephants, they found that this trait rose swiftly as a response to poaching, and they pinned down several genes that may cause it. “This study highlights the ubiquity of human influence across the tree of life,” says Shane Campbell-Staton, an evolutionary biologist at Princeton University, who published the findings on October 21 in Science. “Even the largest organisms on the planet are not just being affected by population decline…we’re literally changing the trajectory of their evolution moving forward.” There are numerous cases of animals evolving in response to human activities, from moths darkening amidst the smog of the Industrial Revolution to lizards upping their heat tolerance to survive in sweltering cities and insects becoming resistant to pesticides. “Most of what we know comes from relatively small animals that are very abundant and have very quick generation times,” Campbell-Staton says. These changes are harder to track in large, long-lived animals that reproduce slowly, such as elephants. After the Mozambican Civil War ended, people began to notice that tuskless elephants had become more common in Gorongosa National Park. However, Campbell-Staton realized, little was known about what genetic changes might have actually caused the phenomenon. To get to the bottom of this mystery, he and his team pored over photos and videos of elephants in the park from before the conflict, as well as more recent observations. Generally, it’s rare for elephants to be born without the ability to develop tusks, and the trait is only seen in females. The park’s elephant population already had an unusually high number of tuskless females before the war, perhaps as a consequence of past hunting practices. Afterwards, though, the proportion of females without tusks had nearly tripled to 50.9 percent. “The question is whether or not this is actually natural selection favoring tuskless females, or whether or not it’s just because of the entire population decline that you get this rise simply by chance,” Campbell-Staton says. He and his colleagues ran computer simulations of the waning population from 1972 to 2000. They concluded that the odds of winding up with a population in which half the females were missing tusks were very slim, unless this characteristic was giving the elephants a survival advantage. The researchers suspected that the mutations responsible for tusklessness would be dominant—meaning that only one copy of the abnormal genes would be needed to result in a lack of tusks—in female elephants, and lethal for males. Supporting this idea, they observed that tusked mother elephants didn’t have tuskless daughters. On the other hand, tuskless elephants should have one abnormal copy of the gene inherited from their own mothers, and one normal copy inherited from their fathers. This means that a tuskless mother has a 50 percent chance of passing the trait to her offspring. Sure enough, the researchers found that elephants born to tuskless mothers were more likely to be female (the gene is deadly in males), and about half of these daughters were tuskless. Campbell-Staton and his team next searched for differences in the genomes of tusked versus tuskless elephants. They identified two genes related to tooth development that might have contributed to the rise of tuskless females. One, called MEP1a, plays a role in forming dentin, the layer of tissue surrounding the tooth’s pulp. The other is known as AMELX and is involved in enamel production. In humans, abnormalities in this gene and several of its close neighbors collectively cause a syndrome that’s lethal to males and can prevent the maxillary lateral incisors, which correspond roughly to elephant tusks, from growing in females. The precise nature of the genetic underpinnings of tusklessness in the park’s female elephants have yet to be determined, Campbell-Staton says. Another open question is whether the same thing could happen in other elephant species that are also threatened by poaching, adds John Poulsen, an ecologist at Duke University who studies how African forest elephants are affected by human disturbances and was not involved with the new research. Still, he says, finding such quick evolution in the elephants of Mozambique “is remarkable.” “When I first read the paper, my first thought was, ‘Wow this inspires hope for biodiversity conservation; maybe species like the elephant that are really slow-reproducing can actually adapt quickly to human pressures,” Poulsen says. However, the evidence that males cannot develop this trait is troubling, particularly since male elephants are already targeted more by poachers because of their larger tusks. It’s possible that the abundance of tuskless females could focus more poaching pressure on male elephants. “That puts us in a real pickle,” Poulsen says. “It also means that we can’t sort of depend on evolution to get us out of this problem of unsustainable killing of elephants…we still need management and we still need policy efforts to try to conserve elephants.” The evolution of tusklessness among elephants may also have far-reaching consequences for other species. Tusks are a bit like a Swiss army knife for elephants, Campbell-Staton says. Elephants use their tusks for a variety of tasks, including stripping bark off of trees and digging for subterranean minerals and water sources. These activities can open up habitat for other animals, destroy trees, and allow other plant species to grow—and have a myriad of other complex ecological effects. “If elephants don’t have this key tool to provide these important services, then what happens to the rest of the ecosystem?” Campbell-Staton says. In recent years, the elephant population of Gorongosa National Park has grown and the prevalence of tusklessness has begun to drop. Still, the animals grow slowly and take nearly two years to gestate their young. The elephants may have evolved quickly in response to poaching, Campbell-Staton says, but it will take them much longer to rebuild their numbers and play the same role in the ecosystem as they did before the war. https://www.popsci.com/science/elephant-poaching-tuskless/ Tuskless Elephants Escape Poachers, but May Evolve New Problems Elizabeth Preston, The New York Times October 21, 2021 A deep enough wound will leave a scar, but a traumatic event in the history of an animal population may leave a mark on the genome itself. During the Mozambican Civil War from 1977 to 1992, humans killed so many elephants for their lucrative ivory that the animals seem to have evolved in the space of a generation. The result was that a large number are now naturally tuskless. A paper published Thursday in Science has revealed the tooth-building genes that are likely involved, and that in elephants, the mutation is lethal to males. Although evolving to be tuskless might spare some surviving elephants from poachers, there will likely be long-term consequences for the population. Normally, both male and female African elephants have tusks, which are really a pair of massive teeth. But a few are born without them. Under heavy poaching, those few elephants without ivory are more likely to pass on their genes. Researchers have seen this phenomenon in Mozambique’s Gorongosa National Park, where tuskless elephants are now a common sight. Female elephants, that is. What no one has seen in the park is a tuskless male. “We had an inkling,” said Shane Campbell-Staton, an evolutionary biologist at Princeton University, that whatever genetic mutation took away these elephants’ tusks was also killing males. To learn more, Dr. Campbell-Staton and his co-authors started with long-term data, including prewar video footage of Gorongosa’s elephants. They calculated that even before the war, nearly one in five females were tuskless. This might reflect earlier conflict and poaching pressure, Dr. Campbell-Staton said. In well-protected elephant populations, tusklessness can be as low as 2 percent. Today, half of Gorongosa’s females are tuskless. The females who survived the war are passing the trait to their daughters. Mathematical modeling showed this change was almost certainly because of natural selection, and not a random fluke. In the decades spanning the war, tuskless females had more than five times greater odds of survival. And the pattern of tusklessness in families confirmed the scientists’ hunch: it seems to be a dominant trait, carried by females, that’s lethal to males. That means a female with one copy of the tuskless mutation has no tusks. Half of her daughters will have tusks, and half will be tuskless. Among her sons, though, half will have tusks and the other half will die, perhaps before birth. The team sequenced the genomes of 11 tuskless females and seven with tusks, looking for differences between the groups. They also searched for places in the genome showing the signature of recent natural selection without the random DNA reshuffling that happens over time. They found two genes that seemed to be at play. Both genes help to build teeth. The one that best explains the patterns scientists saw in nature is called AMELX, and is on the X chromosome, as the team expected. That gene is also involved in a rare human syndrome that can cause tiny or malformed teeth. AMELX is adjacent to other crucial genes whose absence from the X chromosome can kill males. In the elephant genome, “We don’t know what the exact changes are causing this loss of tusks, in either one of those genes,” Dr. Campbell-Staton says. That’s one of the things the researchers hope to figure out next. They also want to learn what life is like for a tuskless elephant. Elephants normally use their tusks to strip tree bark for food, dig holes for water and defend themselves. “If you don’t have this key tool, how do you have to adjust your behavior in order to compensate?” Dr. Campbell-Staton said. And the rise of tusklessness may affect not just individual elephants, but the population as a whole, Dr. Campbell-Staton said, since fewer males are being born. “I think it’s a very elegant study,” said Fanie Pelletier, a population biologist at the Université de Sherbrooke in Quebec who was not involved in the research but wrote an accompanying article in Science. “It’s a very complete story as well. All the pieces are there,” she said. In her own research, Dr. Pelletier has studied bighorn sheep in Canada. As trophy hunters targeted the males with the biggest horns, the sheep evolved to have smaller horns. The change in sheep is subtle, she said, unlike the elephants’ total loss of tusks. And the elephants’ genetic change has actually compounded their problems, Dr. Pelletier said. Even if poaching stopped tomorrow, tusklessness would keep indirectly killing males, and it could take a long time for the frequency of this trait to drop to normal levels. Dr. Campbell-Staton agreed that although the elephants have evolved to be safer from poachers, this isn’t a success story. “I think it’s easy when you hear stories like this to come away thinking, ‘Oh everything’s fine, they evolved and now they’re better and they can deal with it,’” he said. But the truth is that species pay a price for rapid evolution. “Selection always comes at a cost,” he said, “and that cost is lives.” https://www.nytimes.com/2021/10/21/science/tuskless-elephants-evolution.html