Changing Tusks in Response to Poaching
Lions, bushbucks, warthogs, hippos, crocs, and elephants all run freely in Gorongosa National Park, Mozambique¹. Built on the aspirations of Nelson Mandala, the park is now an oasis for many endangered animals and is hailed as a “restoration story”; recently, declared as “one of the most “biodiverse habitats on Earth”¹. Though a modern-day refuge, some of these animals have faced extreme hardships. Dominique Demille, Research Fellow at the Gorongosa Restoration Project, stated in an interview about the elephant population: “The older ones still remember what happened in the past, the war, the soldiers that hunted elephants for their ivory.”² The Mozambique Civil War from 1992–1997 affected not only civilians and soldiers, but wildlife as well; elephants were poached and their ivory sold in order to pay for ammunition and arms. While poaching has ceased to exist at Gorongosa National Park, the war wounds are still there: tusklessness is a common trait among female elephants.
Tusklessness is a trait that has captured the attention of many conservationists and researchers. Joyce Poole, co-director of ElephantVoices, views the trait as an advantage². Tusks are elongated teeth that grow throughout an elephant’s life and serve many purposes, helping elephants dig for minerals and scratch bark off trees. Functionally speaking, tusks make sense. However, poaching creates a strong selective pressure for tusklessness. Those who do not have tusks are able to escape under poachers’ eyes; they offer little to no value when the market offers nearly $1,000 per kilogram of ivory³. Elephants without tusks are naturally very rare, making up 2–6% of the population². This percentage jumps, however, when looking at areas highly impacted by poaching (see Gorongosa National Park, Addo Elephant National Park in South Africa, Selous Game Reserve in Tanzania, and Queen Elizabeth National Park in Uganda). The effects are striking, as Poole notes in one of her first encounters at Gorongosa: “The first day I was here in 2011, I met a group of 50 elephants. Most of them were tuskless, so I knew kind of straight-away when I came here that there was a high proportion of tusklessness.”² After population surveys, the higher frequency was verified. Of Mozambique’s Civil War survivors, 50% of the female elephants had an absence of tusks. Of the younger elephants, aged 10–20 years, 33% of the females shared this same trait².
Though researchers are further investigating the genetics behind tusklessness, the trait appears to be sex-linked³. In the abovementioned field study, the 33% of female elephants aged 10–20 are presumably the offspring of tuskless mothers. No tuskless males were observed at Gorongosa². This is perhaps due to more selective pressure on males to have tusks; mate competition among males is violent and sometimes deadly. If a male does not have tusks, he may be severely injured and at a disadvantage in fights. Male elephants seem to have a two-front war: mating pressure to produce more offspring, and poaching pressure that targets the largest pair of tusks. Though tusklessness is a rare trait linked primarily to a minority of the female population, those with tusks (male and female) are also changing in response to poaching pressure: tusk size itself is on the decline.
Researchers Patrick Chiyo, Vincent Obanda, and David Korir were interested in this ‘changing tusks’ phenomenon (Chiyo et. al (2015). Though tusklessness is easily detectable among populations, detecting changes in tusk size over the years is laborious work. Chiyo and colleagues compared tusk sizes in southern Kenya from differing decades afflicted by poaching. They examined tusks dated between 1966–1968, right before the severe ivory hunting of the ’70s and ’80s that caused a reduction of 50–90% of the elephant population in East Africa, to tusks of elephants born in the ’90s, a period marked by population recovery⁴. Data were also obtained on age, sex, tusk, and body measurements from 500 culled elephants at Tsavo East and Mikomazi National Parks during the years 1966 and 1968. For the years 2005–2013, 205 elephants from several locations in southern Kenya and 188 recovered tusks from dead animals in Tsavo National Park were measured for tusk size, as well as 200 confiscated tusks from illegal trade in Kenya during 2013. It was determined that the mean tusk length for elephants born in the ’90s declined by 21% in males and by 27% in females, against the 1966–1968 average tusk length standard.
What we see occurring in nature is a drastic difference in two generations of elephants. Poaching hotspots in the ’70s and ’80s are now home to a growing population of elephants with shorter tusks than their ancestors or no tusks at all. Such rapid, phenotypic change, or “contemporary evolution”⁴ is outstripping natural selection; where before, elephants with larger tusks were selected for advantages in fighting, digging up nutrients, and reaching food in high-up places. Poaching, however, shifted the more advantageous trait to shorter tusks or even the extreme: the absence of tusks. In a cruel game played with humans of “I’ve Got Your Tusk”, elephants are adapting so that there is no tusk to take at all.
¹“Our story.” Gorongosa National Park, http://www.gorongosa.org/our-story. Accessed 8 Feb, 2019.
² Poole, Joyce. “Selection for tuskless elephants.” HHMI Biointeractive, 23 Sept. 2019, https://www.hhmi.org/biointeractive/selection-tuskless-elephants. Accessed 8 Feb, 2019.
³Nordland, Ron. “Where female elephants without tusks roam — and poachers stay away.” The New York Times, 16 June 2018, https://www.nytimes.com/2018/06/16/world/africa/south-africa-elephants-tusks.html.
⁴Chiyo, Patrick I., Vincent Obanda, and David K. Korir. “Illegal tusk harvest and the decline of tusk size in the African elephant.” Ecology and Evolution 5.22 (2015): 5216–5229.