In the mating world of yellow dung flies, large, brawny males almost always get the girl.
However, a new study suggests that smaller males rule if presented with an opportunity
to woo females when they are not hanging out on cow dung. It is the first time alternative
male reproductive strategies have been observed in this species.
In a study published in the June 24 Proceedings of The Royal Society B, a group of
Syracuse University (N.Y.) undergraduate students found that small male dung flies,
which are traditionally unsuccessful at finding and keeping mates on dung pats,
successfully mated with females feeding on composting apple pomace. In fact, large
males were generally absent from the pomace mounds.
"This is a new chapter in the story of yellow dung flies," says
Scott Pitnick, professor of
biology in SU's
College of Arts and Sciences. "No one has carefully studied this species
off the dung. Small male dung flies can't compete with their larger counterparts on the
dung, so in this case, they developed a different tactic to successfully pass their genes to
the next generation."
Pitnick co-authored the study with the students. The students were enrolled in an
advanced biology course designed to teach them to conduct original scientific research.
Pitnick co-teaches the course with
J. Albert C. Uy. As part of the course, the students
were tasked with designing a study around the size and mating success of yellow dung
flies.
"After we made our initial field observations for the class assignment, we could tell from
our professors' reactions that our discovery was a piece of important information in the
field," says Stephen Maheux '09, a biology major who graduated in May. "The course
was designed to teach us how to be biologists; as such, we made a unique observation
that ultimately resulted in a publication."
Until now, it was thought that yellow dung flies mated almost exclusively on manure.
Females are drawn to the dung only when they are ready to mate. Little is known about
the feeding habits of females when they are not at the dung pats, Pitnick says. On the
other hand, males were thought to hang out almost exclusively around the manure,
awaiting the arrival of the females. Competition on the dung among males is fierce and
can result in injury or death to smaller males as well as females caught up in the struggle.
But, on Toad Hollow Farms in Nedrow, N.Y., the students noticed large numbers of
females feeding on apple pomace in a field adjacent to the cow pasture where they were
observing flies on dung pats. Much to the students' surprise, the females were frequently
mating on the pomace, and with males that were significantly smaller in size than those
found in the cow pasture. Furthermore, none of the sexually aggressive behaviors
normally observed on the dung pats occurred on the pomace.
Owned by Bill Guptill, Toad Hollow Farms produces natural compost made from
manure, leaf and yard waste, and fruit and vegetable waste from grocers in and around
Central New York. Apple pomace is the pressed pulp that remains after juicing. The
students' initial observations suggested that the availability of the pomace seemed to
provide male dung flies with alternative mating opportunities.
Maheux and biology major Kali Henn, who will be a senior in the fall, continued working
with Pitnick after the class concluded to collect and analyze additional data, re-confirm
the initial class results, and help write the manuscript that was submitted for publication
to The Royal Society.
"The class focuses on enabling students to experience the research process-from
formulating questions and making the observations to designing the experiments,
analyzing the data and writing the final manuscript," Pitnick says. "In this case, what
started as a class exercise ended up as a significant finding in this field."
