December 2019, ScientificAmerican.com 21PONGSAK POLBUBPHA
Alamy
B I O L O G YSingle-Sex
Snail Fighters
“Superfemale” prawns could
help take on a deadly diseaseScientists are mobilizing an all-female
army to help stymie schistosomiasis, a
sometimes deadly parasitic disease that
affects millions of people every year.
Macrobrachium rosenbergii prawns “are
voracious predators of parasite-carrying
snails” that spread the illness, says Amir Sagi,
a biologist at Ben-Gurion University of the
Negev in Israel and principal investigator of a
new study on the subject. “The possibility of
nonreproducing monosex [prawn] popula-
tions, which will not become invasive, opens
the path for their use as biocontrol agents.”
Using crustaceans to control Schistoso-
ma-carrying snails is not a novel concept,
but developing a sizable population that
is all one sex and therefore cannot repro-
duce—and potentially ruin an ecosys-
tem—has proved challenging.
Like humans, prawns pass on specific
chromosomes that determine their off-
spring’s sex. But unlike humans, female
prawns usually have one male and one
female chromosome, whereas males have
two identical male chromosomes. Labora-
tory-bred “superfemales,” each with two
female chromosomes, can yield only female
offspring—making them extremely useful
in building a nonbreeding population.
Current methods to produce super-
females are inefficient. By implanting cells
from a male’s androgenic gland, Sagi and
his colleagues sparked the transformation
of superfemales physically into males, the
first instance of male M. rosenbergii thatcompletely lack male chromosomes.
These prawns can then easily contribute
their female chromosomes to new genera-
tions of superfemales. The process was
detailed in August in Scientific Reports.
All-female prawn populations are partic-
ularly useful, scientists say. “Female prawns
are more docile and less cannibalistic” than
males, says Susanne Sokolow, a disease
ecologist and veterinarian at Stanford Uni-
versity, who has worked with Sagi on related
research. “They grow more evenly, poten-
tially providing a more consistent product for
harvest”—meaning local communities could
use them for food, as well as snail control.
The snails that carry the schistosomiasis
parasite live in southern and sub-Saharan
Africa, parts of Southeast Asia, South Amer-
ica, the Middle East and some Caribbean
islands. Within hours of touching snail-inhab-
ited water, an infected person can suffer
symptoms, including fever, cough, abdomi-
nal pain and diarrhea. The disease can also
be come chronic and lead to liver and kidney
failure, bladder cancer and ectopic pregnan-
cies. The World Health Organization reports
that 220.8 million people required preven-
tive treatment for schistosomiasis in 2017.
Deploying all-female prawns in addition
to traditional disease treatment is an inter-
esting strategy, but rigorous testing is need-
ed, cautions David Rollinson, director of the
Global Schistosomiasis Alliance, who was
not involved in the study.
Rollinson says establishing the habitats
in which the prawns could survive and
determining how often more must be added
should be top concerns. Sokolow adds that
environmental ministries must coordinate
on which types of monosex population they
introduce. “Otherwise,” she says, “the envi-
ronmental benefits to prevent local invasive
establishment would be hard, if not impos-
sible, to maintain.” — Jillian KramerMacrobrachium rosenbergiiUntitled-891 1 10/10/2019 14:13Scientific American is a registered trademark of Springer
Nature America, Inc.Untitled-1 4Untitled-1 1 10/22/19 10:03 AM2/19/19 4:26 PM© 2019 Scientific American