This study takes us to the Kalahari in northern South Africa, specifically to the Kuruman River Reserve. Nested alongside a dried-up riverbed, the area is monitored by the Kalahari Research Centre, which runs a variety of research projects focusing on the Kalahari ecosystem. Previously directed by Tim Clutton-Brock of Cambridge University and now led by Marta Manser of the University of Zurich, an international team of researchers study the region’s biodiversity, including semidesert-adapted bird species, Damaraland mole-rats, Cape ground squirrels, yellow mongooses and, most famously, Kalahari meerkats. To study meerkats, researchers must be early risers, setting out for the field before sunrise to reach the meerkats’ sleeping burrows before the meerkats emerge for the day. Once the meerkat group emerges to bask in the sun, socialise and prepare to set out in search of food, the researchers begin collecting data. The meerkat population has been under continuous observation for over 30 years. This long-term monitoring enables the researchers to track the life histories of individuals in detail. This includes information on when and where each meerkat was born or died, when and to which group they dispersed, and which individuals became the dominant breeding pair and reproduced. The contributions of individuals are key to the success of the group, including sentinel duty to guard against predators, babysitting pups, feeding the young and defending their home range against neighbouring rival groups. These contributions are, of course, also documented.
By closely following the meerkats, researchers discovered over 25 years ago that they can be affected by a devastating infection: Mycobacterium suricattae, a strain of tuberculosis (TB) specific to meerkats. Infected individuals can remain asymptomatic for extended periods, but once the disease reaches the clinical stage, i.e. visible symptoms appear, the effects are dramatic: Affected meerkats rapidly deteriorate, becoming skinny and lethargic. They also develop swellings around the head and inguinal lymph nodes, which can burst and ooze infectious pus in the late stages if the infection. Due to their highly social nature, infections can spread rapidly both within and between meerkat groups. TB is almost always fatal, with infected individuals typically dying within a few months of displaying symptoms of the disease, and entire groups have been known to be lost due to infection.
Despite these dire circumstances, we have observed striking variation in how individual meerkats respond to TB infection. Some individuals develop symptoms shortly after coming into contact with infected group members and die within weeks of developing visible signs of TB infection. Others live in affected groups without ever showing signs of the disease or survive for years despite displaying visible symptoms. The current record is held by a female who lived more than seven years after the onset of clinical TB. These observations prompted us to investigate potential explanations for the marked variation in disease resistance and progression. Could the strong selective pressure exerted by the pathogen be driving the evolution of traits that help individuals withstand infection better? One compelling candidate for further investigation is the Major Histocompatibilty Complex (MHC), which encodes immune genes that are crucial for recognizing pathogen, initiating and mediating immune responses. Could certain MHC gene variants provide individuals with an advantage against this deadly disease? And if so, do these advantages translate into higher reproductive success, enabling individuals to pass these beneficial gene variants on to the next generation?
In a collaborative effort involving researchers from Ulm University, the universities of Zürich, Cambridge, Salford, and Sydney, and drawing on over 20 years of TB data and biological samples collected through the Kalahari Meerkat Project, we could investigate the relationships between MHC immune genes and individual variation in TB susceptibility, resistance, survival, and reproduction. Our study encompassed data from over 1,500 meerkats, while also accounting for social factors and environmental influences. Our results clearly demonstrate that meerkat MHC gene variants influence how individuals cope with TB infections. One particular allele was associated with a higher initial risk of contracting TB, but also enabled infected individuals to survive the disease for longer and produce more offspring. Over the course of the study, this same allele shifted from being a risk factor to offering protection against TB, and its frequency increased within the population. These findings suggest a dynamic interaction between meerkat immune genes and the TB pathogen, implying a coevolutionary arms race. Despite the severe toll of the disease, the genetic diversity of immune genes enables some meerkats to survive long enough to reproduce and pass on advantageous genes, which contributes to the resilience of the population.
Zooming out to consider the broader Kalahari ecosystem, TB is not the only challenge that meerkats face. In recent years, rainfall patterns in the Kalahari have become more unpredictable, and average temperatures have increased more rapidly than the global average. These climate changes have a profoundly negative impact on the meerkats and many other species in the Kalahari. The threat intensifies when TB outbreaks coincide with harsh climate conditions, putting already vulnerable groups at an increased risk of collapse. The combined effects of climate change and infectious disease on wildlife populations are now well established. In the Kalahari, our ongoing research aims to reveal the exact ways in which climate change affects meerkats and other species. The Kalahari Research Centre is uniquely positioned to study these effects at multiple ecological levels - from how heat and drought affect invertebrate communities, a critical food source for small predators such as meerkats and yellow mongooses, to the broader consequences for animal biodiversity in this semi-desert environment.