A strange blood-sucking fly appears to have reduced visual sensitivity after finding a host and abandoning flight for good, according to a new study.
These stinging flies, known as deer flies, are found throughout Europe, Asia, Africa, and the Americas. As adults, they use both flight and vision to search for a suitable host, most often deer, but may also target humans and other mammals.
Once a deer lands on a host, its lifestyle changes dramatically. The insect permanently sheds its wings and spends the rest of its life moving through the fur and sucking blood.
Scientists from Aberystwyth University and the University of Florence discovered that this major behavioral change was accompanied by changes in the flies’ sensory systems.
Their findings suggest that after deer settle in a host, they reduce their investment in vision and direct their energy toward functions more important to life as permanent parasites.
From flying hunter to permanent parasite
Dr Roger Santer, from Aberystwyth University’s School of Life Sciences, who led the study, explained:
“Vision plays an important role in animal behavior, but it is also energetically expensive. Evolution favors sensory systems that efficiently adapt to the animal’s lifestyle. Some blood-feeding flies rely heavily on vision, while others live permanently on their hosts, but there is little need for it. Pique are particularly interesting because they switch between these two lifestyles.”
To investigate how insects adapt to this dramatic change, researchers studied different points in the deer’s life cycle. The researchers examined winged adults actively searching for a host and compared them to wingless adults taken from deer after they had begun their parasitic life.
Visual gene activity decreases
The research team focused on genes associated with visual sensitivity known as opsins. By comparing gene activity before and after flies shed their wings, the researchers were able to see how the insect’s visual system responds to sudden changes in lifestyle.
Dr. Santer said:
“We found that the visual system of the spotted deer ked is very similar to that of the tsetse fly, which is famous for hunting mammalian hosts in Africa. However, when the white deer ked lost its wings and became an ectoparasite, its opsin gene activity was reduced to about half its previous level. This suggests that the fly is not completely blind, but has reduced visual sensitivity. We suspect that this fly is sacrificing vision to save energy for things like digestion and reproduction. ”
The results show that deer do not go blind when they find a host. Instead, they seem to scale back their visual abilities once they no longer need to search for animals in the sky.
New insights into parasite adaptation
Published in Journal of Experimental BiologyThis study provides new insights into how parasites adjust their sensory systems when lifestyle changes dramatically.
Researchers say a better understanding of how deer and other biting flies use their senses could ultimately help improve monitoring and control strategies.
