Did you know caffeine does more than keep one awake? For Red Flour Beetles (Tribolium castaneum) caffeine affects mating behavior.

Yuhao et. al wrote “Effects of caffeine on mating behavior and sperm precedence in Tribolium castaneum”- https://onlinelibrary.wiley.com/doi/10.1111/eth.13094
PC: @Bertonemyia

/2 Their goal was to determine the effect of caffeine on the mating behavior of red flour beetles. The variables they observed were: time it took the male to a) initiate courtship b) mount the female c) protrude the penis d) separate and e) the number of copulation trials.

/3 Yuhao et. al's figure shows the contrast in variables amongst male beetles with and without exposure to caffeine. Caffeine exposure resulted in lower times to initiate copulation (a), mount the female (b), and protrude the penis (c), while increasing copulation trials (e).

/4 They tested sperm precedence through two variables, paternity success and the color of progeny. Black males were placed in a Petri dish with a female for 24 hours and replaced with a normal male, who either ingested caffeine or sucrose. Observed to see if copulation occurred.

/5 Yuhao et. al’s figure shows the insignificant effect of caffeine on sperm precedence. Differences in paternity success (proportion of offspring of normal color in all offspring) and the color of progeny between caffeine and sucrose groups were negligent.

/6 Other literature has shown caffeine to increase a beetle's walking distance which may improve a beetle's likelihood of finding a mate. That fact combined with this study's results may predict caffeine to improve a beetle's fitness, but more work needs to be done to be sure.

/7 Huge thanks goes to Ji Yuhao, Yuki Ryuji, Kentarou Matsumura, and Takahisa Miyatake for their work on red flour beetles!