Releasing a steady stream of urine to attract a mate and then fighting off anyone who still dares to approach you doesn’t seem like a great idea for getting sex. But this bizarre strategy is all part of the mating ritual of the signal crayfish. A female’s urine, strange as it sounds, is a powerful aphrodisiac to a male.
Fiona Berry and Thomas Breithaupt studied these courtship chemicals by organising blind speed-dates between male and female crayfish, whose eyes had been covered with tape. They also injected a fluorescent dye into the animals’ bodies, which accumulated in their bladders. Every time they urinated, a plume of green dispersed through the water.
If the duo blocked the female’s nephropores (her urine-producing glands), the males never showed her any interest. If they met, they did so aggressively. But when the duo injected female urine into the water, things took a more lustful turn, and the males quickly seized the females in an amorous grip. Female urine is clearly a turn-on for males.
But the female doesn’t want just any male – she’s after the best, and she makes her suitors prove their mettle by besting her in a test of strength. As he draws near, she responds aggressively, even though it was her who attracted him in the first place. No quarter is given in these fights. The female only stops resisting if the male can flip her over so that he can deposit his sperm on her underside.
To our ears, the buzz of a mosquito is intensely irritating and a sign of itchiness to come, but to theirs, it’s a lover’s serenade. The high-pitched drone of a female is a siren’s song that attracts male mosquitoes. And a new study shows that when the two love-bugs meet, they perform a duet, matching each other’s buzzing frequency with careful precision.
The female Aedes aegypti mosquito (the carrier of both dengue and yellow fever) beats her wings with a fundamental frequency of about 400Hz, producing a pitch just slightly lower than concert A. Males on the other hand, have a fundamental frequency of around 600Hz, about one D above middle C.
Lauren Cator and colleagues from Cornell University discovered the sonic secrets of courting mosquitoes by tethering individuals to pins and moving the females past the males. On two-thirds of these fly-bys, the amorous mosquitoes harmonised. Neither took the lead – instead, both buzzers shifted their flight tones so that the male’s second harmonic (the second multiple of his fundamental frequency) and the female’s third had a mutual frequency of about 1,200 Hz. They synchronised in this way for about 10 seconds.
You might not be that impressed to receive a clump of grass or branches on a first date, but a boto dolphin might think differently. A new study suggests that these Amazonian dolphins wave bits of flotsam to attract mates.
The boto is a freshwater river dolphin that swims through the currents of the Amazon and the Orinoco. They are elusive creatures that are difficult to study, so very little is known about their social lives.
Tony Martin from the University of St Andrews spent three years in the Amazonian Mamiraua reserve studying the behaviour of botos. During this time, he spotted over 200 groups of dolphins playing with objects, a behaviour that other scientists have noted throughout the animals’ range and was recently filmed in the “Fresh Water” episode of Planet Earth.
The botos pick up branches, sticks, vegetations and lumps of clay in their mouths, often thrashing them against the water surface or throwing them with jerks of the head. None of the objects are edible and the carriers often swim in a ritualised way, spinning slowly with their head above the water.