— A roundworm with a mix of male,
female and hermaphrodite offspring is offering researchers at UT Arlington a
look at a species in transition from one mode of reproduction to another.
A hermaphrodite (self-fertilizing) nematode
In a paper published online
Sept. 8 in Current Biology, Andre Pires da Silva, a UT Arlington
professor of biology, and his research team examined influences on the
reproductive activity of the Rhabditis, a nematode worm about 1 mm
long. They found that the worm’s reproductive characteristics
changed depending on environmental factors such as the availability of
The results add to the understanding
of evolutional biology. They could also shed light on the complex mating
systems of parasitic roundworms, some of which infect humans, livestock and
plants. More knowledge about roundworm reproduction could lead to better
methods of preventing and fighting infection.
The paper, “Regulation of Sexual Plasticity in a Nematode that
Produces Males, Females and Hermaphrodites,” is scheduled to be
published Sept. 8. Graduate students Jyotiska Chaudhuri and Vikas Kache
“Our question is very basic: We
know most roundworm species are male and female, but some are only
hermaphrodite. We want to know how that change occurs,” Pires da Silva said.
“Here we have a group of worms that seem to be at the transition state between
the two modes. They’re almost like a living fossil.”
Rhabditis feed on bacteria rich
environments such as compost heaps.
When reproducing in optimal
conditions, 45 percent of Rhabditis offspring are female, 10 percent are male
and 45 percent are self-fertilizing hermaphrodites. When conditions aren’t as
good, all of the offspring become hermaphrodites by going through a process
called a dauer stage, Pires da Silva said.
Pires da Silva’s research team
was able to manipulate the sex distribution of worm larvae by adding
cholesterol or removing cholesterol from the environment. Cholesterol is an important precursor for dafachronic
acid hormones, which are vital to worm development.
During the experiments, larvae that
began as females would enter a form in which their development slows and they
can withstand long periods of stressful conditions – called a dauer stage – if
they were deprived of cholesterol. When they emerged from the dauer stage, they
had transformed to hermaphrodites instead of females.
The study says dauer formation
likely helps the larvae to travel on a host to a more friendly location.
Developing as a hermaphrodite, rather than a female, means the worm “can
colonize and reproduce in new habitats in the absence of a mating partner,” it
Jon Campbell, chair of the biology department in UT Arlington’s
College of Science, said Pires da Silva’s work “is a good example of using
careful genetic sleuthing to uncover the unsuspected.”
"Learning about this species can tell us more about the changes
similar organisms may have undergone throughout their histories," he said.
The Current Biology publication
is the second important journal recognition for Pires da Silva’s laboratory this year.
In January, he was the coauthor of a paper published in the online journal
Nature Communications. That paper also dealt with reproduction modes of the
Recently, Pires da Silva and Diane C. Shakes, a professor at the College of William and Mary, won a three-year, $301,447 National Science Foundation grant to continue their research on the Rhabditis. As an outreach project included in the grant, Pires da Silva and Shakes also will work with prospective third-grade teachers to introduce discovery-based science modules into their classrooms.
Pires da Silva’s work is an example of the
cutting-edge research being conducted at UT Arlington, a comprehensive research
institution of nearly 34,000 students in the heart of North Texas. Visit www.uta.edu to learn more.