Human body changes on the verge of adulthood can be awkward, but at least our eyes don't protrude from our heads on stalks longer than our legs.
The adult male Pelmatops fruit fly, on the other hand, has macho eyes. According to a new study, the eye-up transformation takes only about 50 minutes in one of the stalkier species, P. tangliangi. When the skinny eyestalks are stretched, they darken and harden, keeping the eyes stuck out like selfie sticks for the rest of the fly's life.
|A long skinny male fruit fly (Pelmatops tangling) prowls shrubbery after the swift and strange extension of its eyes, with eyeballs sticking out at the end of extravagant stalks on its head. WANG YONG|
Images from a lab video depict the somewhat awkward stages of male fruit fly eye extension (Pelmatops tangling). The eyes are still close to his head 16 minutes after emerging from the small capsule that transformed him from a fat wormy larva to a sleek adult (A). The gangly eyestalks grow and eventually darken over the next 34 minutes (B-H), stretching the eyes away from the body. The fully periscoped adult is ready to explore the next day. Annals of the Entomological Society of America 2022, N. Huangfu et al.
The first published photo sequence of P. tangliangi's ocular blossoming appears in the September Annals of the Entomological Society of America. Eyestalks evolved in eight different fly families, according to biologists. Despite this, Pelmatops flies have received so little scientific attention that much of their basic biology remains a mystery.
The eyestalks curl and rise irregularly in video images. Yet, according to Xiaolin Chen, an entomologist and evolutionary biologist at the Chinese Academy of Sciences in Beijing, "they are not flopping around while partially inflated." "They appear slightly stiff, but still flexible."
Females of the species may also produce shorter eyestalks if Chen and her colleagues find the right females. Chen suspects that the two species that have been named based on the few specimens available are actually two sexes of the same species. The new study shows a male P. tangliangi mating with a female of a different species. Her stalks aren't as impressive as his, but she does have some.
While headgear can be a hindrance to a flying insect, long eyestalks can give flies a swagger. Pelmatops and other stalk-eyed flies square off with arrogant intruders, eyestalk to eyestalk. In a fierce fly fight, however, there is no knocking and locking of stalks. Chen claims that any pushing and shoving is "done with other body parts."
Other advantages to having extreme eyes may exist. Chen discovers these fruit flies in the wild on long stems of Rubus berry brambles. The flies' eyes naturally periscope outward and upward, allowing them to spot danger while remaining hidden in the greenery.