Watering holes bring together wildlife, and their parasites

Date:
January 11, 2022
Source:
University of California - Santa Barbara
Summary:
The sun rises on the savannas of central Kenya. Grasses sway in
the wind as hoof-steps fall on the dusty ground. A menagerie of
Africa's iconic wildlife congregates around a watering hole to
quench their thirst during the region's dry season.



FULL STORY ==========================================================================
The sun rises on the savannas of central Kenya. Grasses sway in the wind
as hoof-steps fall on the dusty ground. A menagerie of Africa's iconic
wildlife congregates around a watering hole to quench their thirst during
the region's dry season.


==========================================================================
But it's not only the region's herbivores and carnivores that are
gathering at this waystation.

"We think about watering holes as being iconic centers of these majestic animals," said UC Santa Barbara biologist Georgia Titcomb, "but they are
also hotspots for the parasites that infect these animals." Resources
bring organisms together, so Titcomb was curious how watering holes might affect the distribution and density of the savanna's parasites. With help
from citizen scientists, she and an international team of researchers discovered that parasite density is far higher around water sources than elsewhere in the landscape. While the jump in exposure risk varied among different host species, the team found it was two orders of magnitude
greater for cattle and elephants in particular. The results, published in Nature Communications, provide ecological insights as well as potential applications in ranching and wildlife management.

Attracting both wildlife and livestock, such intensely shared resources
as watering holes foster the spread of pathogens and parasites. And while
they are often maligned, parasites can provide scientists with a wealth
of information about ecosystem health and interactions between species.

Titcomb and her co-authors investigated how watering holes affected
parasite transmission using gastrointestinal nematodes -- an economically important parasite group with a relatively simple lifecycle.



==========================================================================
To investigate the phenomenon, Titcomb conducted an experiment at
Ol Pejeta Conservancy, in central Kenya. The sanctuary fills 16-foot
wide concrete basins to provide wildlife and livestock with water. The scientists worked with Ol Pejeta staff to drain five basins for at least
a year to compare them with five permanently filled basins and five dry locations for a total of 15 sites. They surveyed each location multiple
times over the course of the experiment, visiting the basins before,
during and after the time in which they were drained.

The scientists sampled along transects running outward from the center
of each site, identifying dung density and species of origin. The team conducted fecal egg counts across different host species and contexts
to establish nematode egg density. They then synthesized their data with information from the literature to estimate parasite density at each site.

The scientists quickly discovered that parasite densities were far
higher around water and that altering water supply also altered parasite density. The parasite densities around the drained basins dropped to
one-third of the levels relative to the sites that remained filled. That
said, densities didn't fall to levels comparable to the sites with
no water at all. "[That's] probably due to a combination of animals
drinking rainwater and grazing on productive grasses that can spring up
around watering holes," Titcomb said, referencing her previous paper on watering hole plant communities.

The researchers also wanted to estimate potential parasite exposure,
not just density, and that required them to measure animal activity. So
they placed camera traps at all the sites, capturing images of animal visitations for two continuous years.

Using the online platform Zooniverse, they then enlisted the help of
citizen scientists to sort through the nearly 1 million photographs. The project attracted around 10,000 contributors and saw a huge uptick in participation during the pandemic. "We are very grateful to all of those volunteers who made our lives that much easier and the project a lot
more fun," Titcomb said.



========================================================================== Volunteers identified the number and species of animals in an image
and how many individuals were either eating or drinking. For each host
species, the scientists took the number of seconds spent feeding per day
and multiplied it by the parasite density to estimate a species' exposure.

Titcomb said she expected watering holes to aggregate parasites, leading
to higher exposure for hosts. "But we didn't expect quite the degree
of variation among different wildlife species," she explained. "The
animals that were most strongly affected, and that really followed
our expectations, were ones that are quite water dependent: elephants
and cattle." Potential parasite exposure for cattle and elephants was
143 and 67 times higher, respectively, near water than at dry sites at
Ol Pejeta Conservancy.

Zebra and impala also saw increased potential exposure rates near water:
20 and eight times higher.

Intrigued by the strong results, Titcomb calculated what proportion
of parasite exposure happens around water. "Assuming the exposure
densities from our study are roughly consistent across the landscape,
more than half of all elephant and cattle exposures to these parasites
happen within 500 feet of watering holes," she said. And this doesn't
include other important resources in the landscape - - like rivers,
salt licks or cattle corrals -- which likely function in a similar way.

These results inspired the researchers to examine how different aridity
might alter the degree to which water sources concentrated parasites. The researchers surveyed 17 different watering holes and 17 dry locations at
the Mpala Research Centre, in central Kenya, and another three paired
wet and dry sites at Ol Pejeta Conservancy. These locations varied
dramatically in rainfall received.

What's more, the sites experienced highly variable seasonal rainfall,
which the researchers could use to identify potential short-term parasite pulses. They found that in the driest areas and periods, parasite density around water sources was more than 150 times higher than in locations
without water.

In addition to illuminating ecological processes, the results have
management implications.

"If a cattle herder wants to reduce the chances that their cattle are
exposed to parasites, they may want to avoid grazing their animals within
150 meters of water," Titcomb said. And if a rancher knows their livestock share a watering hole with wildlife, they may want to treat for parasites
when more animals converge on the available sources of water.

Titcomb hopes to investigate how parasite infections in cattle might
affect wildlife. "Because cattle are so numerous, their infection
patterns have really strong potential to affect less numerous wildlife
in the area," she said.

She also wants to study parasite community composition and sharing
patterns between host species. Scientists still know relatively little
about the species that make up the savanna's parasite community, their
life histories and the hosts that they infect. Answering questions like
these used to involve dissecting animals, but now they can be addressed non-invasively using DNA meta-barcoding on animal dung.

Titcomb is also curious about the effect of aridity on parasite exposure.

"Water distribution, and its ensuing effects on vegetation, are
responsible for many of the huge movements of animals that we see across
the continent," she said.

In dry periods and locations, animals may change their water foraging
behaviors including how far they travel to find water and how long they
spend around watering holes. Additionally, the parasites themselves
may survive better in different environments. All these factors can significantly shape parasite dynamics.

========================================================================== Story Source: Materials provided by
University_of_California_-_Santa_Barbara. Original written by Harrison
Tasoff. Note: Content may be edited for style and length.


========================================================================== Journal Reference:
1. Georgia Titcomb, John Naisikie Mantas, Jenna Hulke, Ivan Rodriguez,
Douglas Branch, Hillary Young. Water sources aggregate parasites
with increasing effects in more arid conditions. Nature
Communications, 2021; 12 (1) DOI: 10.1038/s41467-021-27352-y ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2022/01/220111153631.htm

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