In the world of stalk-eyed flies, it is the males with longer eyestalks that have an advantage in attracting females. Females are more inclined towards males with longer antennae and eye-stalks, and other males are less likely to engage in fights with these well-endowed flies.
However, some males always end up with short eyestalks due to a genetic mutation carried by a copy of the X chromosome. Despite generations of sexual selection, this mutation has not disappeared. A team of scientists discovered that these flies may compensate for their shorter eyestalks by displaying more aggression. The details of this study were published on October 21 in the journal Frontiers in Ethology.
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The stalk-eyed flies, belonging to the fly family Diopsidae and order Diptera, are typically found in low-lying vegetation near rivers and streams. These flies are about a centimeter long and feed on decaying plants and animals.
Gene drives and dueling flies
Stalk-eyed flies carry two types of X chromosomes. One of these X chromosomes carries a mutation for short eyestalks and is known as a driving X chromosome or a meiotic driver. This chromosome passes on alleles that are over-represented in a male’s sperm, increasing the likelihood of being passed on to the next generation.
Male stalk-eyed flies use physical displays and fighting to defend their mating opportunities. They display more aggression towards flies with similar eyestalk sizes.
The study compared populations of flies carrying different X chromosomes and observed their behavior in contests. Fighting behaviors were more common when flies had similar eyestalk sizes, with males carrying the driving X chromosome displaying more aggression and winning contests more frequently.
The study suggests that the aggressive behavior of flies with short eyestalks may explain their ability to mate. While longer eyestalks signal a larger body size and potential threat, flies with shorter eyestalks may engage in contests due to increased aggression, providing them access to mating opportunities.
Mating opportunities
The study indicates that the extra aggression displayed by flies with short eyestalks may give them access to mating opportunities but does not fully counteract sexual selection. The preference for males with longer eyestalks by females keeps the frequency of the variant low, preventing the shorter eyestalks from taking over.
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Further research is needed to understand the impact of the driving X chromosome on female flies and to validate the increase in high-intensity behavior observed in this study.
The study highlights the complex interplay between genetics, behavior, and sexual selection in stalk-eyed flies, shedding light on how different traits influence mating opportunities in this unique insect species.
