To view the photo-rich magazine version, click here.

Originally appears in the Fall 2022 issue.

By Lisa Nichols

Education of children who are beginning to explore fields of interest and develop ideas about further educational studies can be critical for building a conservation base of future scientists, including citizen scientists. Painting these broad pictures of how human influences on evolution of species has an expansive impact on an ecosystem allows the field of science to encompass an even wider net of people who have an interest in environmental stewardship. A story of elephant poaching and the ivory trade brings in the child who loves elephants and wants to save them. A story that talks about elephants and their tusks’ evolution brings in the elephant supporters and the future genetics scientist. A tale of elephants, tusk evolution, reptile habitat, and changes in ecosystems due to the ivory trade can bring in people with law enforcement interests, herpetologists, ecologists, mammalogists, and more. 

 This article explores recent evolutionary changes in an iconic species, the African Elephant. We can help teachers of high school students find a story of ecosystem evolution that gives them an understanding of the all-encompassing impacts that humans have on an entire geographic environment by altering one single element. Included here is a lesson plan for 11^th– and 12^th-grade students which relates to other species and habitats and how certain environmental changes can have long-lasting impacts. This story is about the illegal ivory trade and how it does more than just remove a large mammal from a balanced ecosystem. It changes the dynamics of that ecosystem and influences the evolution of certain characteristics of elephants. This rapid evolution may initially appear to be an adaptation that might in one way save African Elephants from extinction (due to less poaching desirability because they have no ivory worth collecting), but it has a much broader impact on the evolution of other species.

Wildlife trade and species survival pressures

The demand for wildlife parts and products has created a pressure on species survival that is leading many of those targeted species down a road toward extinction. What would happen to the species’ chances of survival if this demand pressure created an evolutionary genetic trait that had the ability to help the species survive? Could these animals evolve to run faster and develop better camouflage to avoid capture by humans, or be smarter so they avoid contact with humans altogether? These are unlikely scenarios given the advancements in technology, the ingenuity of humans, and the financial incentives that exist due to the high demand for wildlife. So, what genetic changes have we seen that could help a species survive?

How fast is fast enough to save a species?

In general, the concept of species evolution is often thought of as being a long-term process, something that often takes centuries of mutations, adaptations, gene flow, genetic drift, and natural selection. All of these processes can work independently or interdependently with each other, but we often think about seeing these changes appearing after centuries and many generations. Multiple generations can occur in a shorter time period when we talk about species that have very short life spans, such as insects. Species with longer gestation periods, and low reproductive rates are placed in a category of higher risk for extinction because of the potential for slower turnover of genetic adaptations.¹ 

Wildlife species that are long-lived will most often take much longer time periods for those genetic changes to manifest in a population¹ — that is until lately, when human influences have begun to place extreme pressures on a species’ ability to adapt and change, either in phenotypic (observable) characteristics or behaviors which may also be controlled by genetic changes. This faster process of high-speed adaptation is known as evolutionary rescue.² We are seeing it more often and in more species, some due to climate change influences, some due to the volume of legal commercial collecting for the food industry, and some due to changes in their habitats and more human influences in their geographic home ranges. 

In the case of wildlife commonly seen in the trade industry, under both the legal international trade limits and on the illegal market, what appears to be the beginning of evolutionary rescue in terms of phenotypic characteristics may not be true rescue. In some cases, the changes may be the start of the species’ adaptation to human influence, but they may not create population fitness that is strong enough to overcome the speed of anthropogenic pressures.³ Those changes may also create a cascading effect that impacts other aspects of the species’ ecosystem. Scientists no longer think just in terms of ecology affecting the evolution of species through adaptation, but also in terms of how these individual species’ adaptations are impacting their ecosystems. This is where we see evolutionary dynamics having an impact on the ecology of an ecosystem.⁴

A new evolutionary phenomenon

One example of evolutionary dynamics is seen in African Elephants being born more frequently without tusks. This is raising additional questions about the impact these tuskless elephants might have on their ecosystems. It also leaves questions as to whether a tuskless elephant population has the potential to rescue elephants from extinction due to poaching by making them less desirable for the illegal ivory trade. 

As we will see in this discussion, so many other factors are influenced by the lack of tusks being produced in certain geographic populations of elephants. Changes in male-to-female ratios within some herds of elephants are part of what seems to be connected to the tuskless traits. Whether this “tusklessness” is an advantage which might make elephants no longer desirable for poachers or whether it is a disadvantage by unbalancing the female-to-male sex ratios in certain populations is yet to be determined. It could also be creating negative aspects of the overall ecology in elephants’ ecosystems. Which positive or negative impact is stronger is still unknown, as this phenomenon is relatively young from an evolutionary standpoint.

Increased percentage of female tuskless African Elephants

A study conducted on elephants in Gorongosa National Park (GNP) in Mozambique is now seeing about one third of the female elephants born without tusks, compared to past percentages which were around 2% to 4% of females born without tusks.⁵ Mozambique had an extremely high rate of poaching pressure placed on elephants during their civil war from 1977 to 1992, where elephant ivory was gathered and sold to fund the war.⁶ During that time period, the GNP elephant population showed a 90% decline in numbers and an even higher rate of 50% of tuskless females being born. 

Examples of tuskless elephant herds were seen in the past in another study⁷ in South Africa’s Addo Elephant National Park (AENP). In that park, 98% of the females are tuskless. Although that study did not attribute the tusklessness to selective poaching, it did discuss human/elephant conflicts and farmers shooting elephants during a time period between 1931 and 1954, when the elephant population in the area could not be properly protected by fencing. This created a bottleneck of low genetic diversity and a very small population size in the area resulting in a 50% tuskless female population in the AENP (in its original founder herd) in 1931. The initial population decline was due to indiscriminate killing of nuisance elephants, not poaching for large ivory tusks.

Although the example of tuskless elephants in AENP is not ascribed to selective hunting in the park, this paper⁷ referenced other parks in Tanzania, Zambia, and Uganda where significant tuskless female elephant populations grew in the heavily poached areas. The trend in tuskless elephants found in geographic regions that were prone to high incidents of poaching and selectivity for elephants with large tusks is supported by other research. One study⁸ reviewed information on 15 different elephant populations throughout Africa. They concluded that higher incidents of tusklessness in elephant populations was due to human selection for elephants bearing large tusks. It was also found that if the original population of elephants in a select geographic area is small, the likelihood of the selection for tusklessness is higher. Similarly, if the original population is larger, then the possibility of genetic changes towards tusklessness may decline.

Genetic cause for tusklessness

So why are females, and not males, being born without tusks, and why are those females passing on the tuskless gene only to their female offspring? The tuskless genome is an X-chromosome trait that is lethal in male elephants.⁶ The male offspring with the X-chromosome carrying the tuskless allele generally will not survive (Figure 1). 

The study⁶ referencing this detrimental genetic trait in male elephants simply labeled it “male-lethal,” but it appears that the researchers are referring to lethality at an embryonic level. Tusks appear in African Elephants at a very young age, between one and three years old.⁹ The study did not find tuskless male elephants in Gorongosa National Park, but the mechanism which causes tusklessness in male elephants or the nonviability of this trait in the males is still unknown.

Female-to-male ratio changes

Another possible detrimental impact of this tuskless evolution was that the ratio of female to male offspring of the tuskless mothers is not 50/50, but was instead a 65.75% birth rate of females versus males.⁶ The tusked females that reproduced showed no sex bias in the ratio of female to male offspring. The tuskless female breeding elephants carrying the tuskless chromosome were showing a higher percentage of lethality in their male offspring. This study indicates that the imbalance in sex ratios shown in offspring of tuskless female elephants is correlated with the genetic expression of the phenotype for tusklessness.⁶ If that sex-bias ratio were to continue in the future, this could ultimately jeopardize the survival of the species in GNP, Mozambique from the long-term imbalance of females over males. Because this is a relatively new phenomenon in terms of evolutionary adaptations, there are still many unanswered questions as to where this might lead.

Tusklessness impacts on the ecosystem

Tusks used to create habitat for ungulates

The decline in the percentage of African Elephants that have tusks results in changes in their environment. An elephant that does not have tusks cannot move trees and logs, or manipulate large, downed trees in the same manner as an elephant with tusks. Species that manipulate resources in their environment and alter or modify habitat (thereby impacting the sympatric species in their geographic ecosystems) are referred to as ecosystem engineers.¹⁰ In this respect, elephants are keystone species because if they were removed, the ecosystem would change drastically. Their ability to be useful engineers to their environment has been changed in some areas of Africa where the percentage of elephants with tusks is diminishing. This is particularly seen in studies done in Gorongosa National Park. In the past decade, many other species of large herbivores which were also impacted by the civil wars in Mozambique are beginning to show recovery.¹¹

 Elephant movement and migration also results in tramping down vegetation and uprooting smaller shrubs, creating open spaces where large herbivores potentially prefer to browse due to higher visibility of predators.¹² Elephants change the structure of an ecosystem from predominantly woodland areas to shrubland due to their movement of large trees and woody plants. Where the trees and bushes have been cropped by elephant movement, the shorter and smaller ungulates such as steenbok and impala also show a preference for plants in those areas.¹³ The elephants create this low shrub, less woody savannah structure through the use of their tusks. They use their tusks to strip bark from trees and break tree branches.¹⁴ Loss of this type of habitat could drastically change the population balances of other herbivores or alter the predator/prey relationship, should populations of elephants without tusks continue to increase.

Arboreal geckos’ habitat changes

Certain species of lizards prefer habitat of downed trees that are created by elephants.¹⁴ A species of arboreal gecko was found to prefer trees and debris that had been manipulated or engineered by elephants. Because the tusks of elephants are a necessary part of the damage created in the wooded tree environment, a future population of elephants that has fewer individuals with tusks could lead to reduced environments that are suitable for these geckos. This is just one more example of how this genetic transformation in elephant phenotypes can have lasting impacts on the evolution of an ecosystem. 

Potential for increased human/elephant conflicts

In a study conducted in South Africa, it was found that a large portion of the elephants’ diet (75%) was composed of Colophospermum mopane, a woody tree.¹⁵ It could be speculated that loss of useful tusks for elephants to forage for food may in turn increase their geographic ranges as they search farther abroad for other food sources. This in turn puts them in situations where there are likely to be more human/elephant conflicts over agriculture regions — another potential cause of African Elephant population decline. Not only do these conflicts result in the killing of some individual animals, but they can also lead to lack of concern for preservation of the species.¹⁶ It becomes much more difficult to gather support for protection of a species if the wildlife we are trying to protect is destroying the livelihood of the local communities. Anthropogenic influences, such as this tusklessness characteristic, that cause elephants to potentially come into contact with humans more often could be detrimental to elephants’ survival.

The bigger picture

It is too soon to know what evolutionary adaptations might develop in the lizards that need elephant-tusk-manipulated trees and logs. It is too soon to see if these changes in the lizards might impact species that would normally feed on those lizards. It is too soon to understand how these evolutionary genetic alterations in elephant populations might impact human/elephant conflicts by increasing elephant geographic ranges to include more human habitats and farmlands. 

What may have first appeared to be the ultimate genetic rescue of a species now might lead to a different need to reduce elephant populations because of these potential human/elephant conflicts. The relationship that these large herbivores have on their environment, which is now being guided by human activities, could have a cascading effect on the ecology of their ecosystems.¹⁴ Is it possible that if the poaching of elephants for their large and valuable tusks is curtailed, these evolutionary transformations may be slowed and possibly reversed? Only time will answer that question.

Lisa Nichols spent 33 years in federal law enforcement, first as a National Park Ranger, then as a U.S. Customs Inspector, with her final 20 years as a Special Agent for the U.S. Fish & Wildlife Service. Her undergraduate BS degree in Zoology was completed at San Diego State University. She is currently working on an MA in biology/conservation at Miami University, Oxford, OH, working on finding a solution to stop the demand for wildlife used in traditional medicines. She also volunteers as a conservation ambassador at the San Diego Zoo Wildlife Alliance Safari park.

Endnotes:

1. Purvis, Andy, John L. Gittleman, Guy Cowlishaw, and Georgina M. Mace. 2000. “Predicting Extinction Risk in Declining Species.” Proceedings of the Royal Society of London. Series B: Biological Sciences 267 (1456): 1947–52. https://doi.org/10.1098/rspb.2000.1234.

2. Carlson, Stephanie M., Curry J.Cunningham and Peter A.H.Westley. 2014. “Evolutionary Rescue in a Changing World.” Trends in Ecology & Evolution 29 (9): 521–30. https://doi.org/10.1016/j.tree.2014.06.005.

3. Bell, Graham. “Evolutionary Rescue and the Limits of Adaptation.” Philosophical Transactions of the Royal Society B: Biological Sciences, January 19, 2013. https://doi.org/10.1098/rstb.2012.0080.

4. Schoener, Thomas W. 2011. “The Newest Synthesis: Understanding the Interplay of Evolutionary and Ecological Dynamics.” n.d. Science. Accessed March 7, 2022. http://www.science.org/doi/abs/10.1126/science.1193954.

5. Maron, Dina Fine. 2018. “Under Poaching Pressure, Elephants Are Evolving to Lose Their Tusks.” 2018. Animals. November 9, 2018. https://www.nationalgeographic.com/animals/article/wildlife-watch-news-tuskless-elephants-behavior-change.

6. Campbell-Staton, Shane C., Brian J. Arnold, Dominique Gonçalves, Petter Granli, Joyce Poole, Ryan A. Long, and Robert M. Pringle. 2021. “Ivory Poaching and the Rapid Evolution of Tusklessness in African Elephants.” Science, October. https://doi.org/10.1126/science.abe7389.

7. Whitehouse, Anna M. 2002. “Tusklessness in the Elephant Population of the Addo Elephant National Park, South Africa.” Journal of Zoology 257 (2): 249–54. https://doi.org/10.1017/S0952836902000845.

8. Steenkamp, G., S. M. Ferreira, and M. N. Bester. 2007. “Tusklessness and Tusk Fractures in Free-Ranging African Savanna Elephants (Loxodonta Africana).” Journal of the South African Veterinary Association 78 (2): 75–80.

9. “Elephant Facts.” n.d. Elephant Aid International (blog). Accessed March 7, 2022. https://elephantaidinternational.org/elephant-facts/.

10. Crain, Caitlin Mullan, and Mark D. Bertness. 2006. “Ecosystem Engineering across Environmental Gradients: Implications for Conservation and Management.” BioScience 56 (3): 211–18. https://doi.org/10.1641/0006-3568(2006)056[0211:EEAEGI]2.0.CO;2.

11. Stalmans, Marc E., Tara J. Massad, Mike J.S. Peel, Corina E. Tarnita, and Robert M. Pringle. 2019. “War-Induced Collapse and Asymmetric Recovery of Large-Mammal Populations in Gorongosa National Park, Mozambique. https://journals-plos-org.proxy.lib.miamioh.edu/plosone/article?id=10.1371/journal.pone.0212864.

12. Fležar, Ursa, Elizabeth le Roux, Graham I.H. Kerley, Dries P.J. Kuijper, Mariska te Beest, Dave J. Druce, Dominique Prinsloo, and Joris P.G.M. Cromsigt. 2019. “Simulated Elephant-Induced Habitat Changes Can Create Dynamic Landscapes of Fear.” Biological Conservation 237 (September): 267–79. https://doi.org/10.1016/j.biocon.2019.07.012.

13. Valeix, Marion, Herve Fritz, Rodolphe Sabatier, Felix Murindagomo, David Cumming, and Patrick Duncan. 2011. “Elephant-Induced Structural Changes in the Vegetation and Habitat Selection by Large Herbivores in an African Savanna.” Biological Conservation 144 (2): 902–12. https://doi.org/10.1016/j.biocon.2010.10.029.

14. Pringle, Robert M. 2008. “Elephants as Agents of Habitat Creation for Small Vertebrates at the Path Scale.” Ecology 89 (1): 26–33. https://doi.org/10.1890/07-0776.1.

15. Pretorius, Y., J. D. Stigter, W. F. de Boer, S. E. van Wieren, C. B. de Jong, H. J. de Knegt, C. C. Grant, et al. 2012. “Diet Selection of African Elephant over Time Shows Changing Optimization Currency.” Oikos 121 (12): 2110–20. https://doi.org/10.1111/j.1600-0706.2012.19680.x.

16. Ngcobo, Jabulani Nkululeko, Tshimangadzo Lucky Nedambale, Khatutshelo Agree Nephawe, Ewa Sawosz, and Andre Chwalibog. 2018. “The Future Survival of African Elephants: Implications for Conservation.” International Journal of Avian & Wildlife Biology Volume 3 (Issue 5). https://doi.org/10.15406/ijawb.2018.03.00123.

17. “Wolf Reintroduction Changes Ecosystem in Yellowstone.” 2021. Yellowstone National Park (blog). June 30, 2021. https://www.yellowstonepark.com/things-to-do/wildlife/wolf-reintroduction-changes-ecosystem/.

Appendix A