In America, human women wake up every day and decide whether they want to have sex or not. They know somewhere a man is willing to make that happen.
In bushcrickets, the male is in charge.
When bushcrickets mate, the male attaches a spermatophore to the female's abdomen. Alongside the sperm themselves, the spermatophore contains a protein-rich mass that the female eats after mating. It then takes several hours for the sperm to find their way into the female's reproductive tract.
Who decides when this 'bridal present' is delivered? A paper by Bielefeld biologists Professor Klaus Reinhold and Dr. Steven Ramm says the male determines the dynamics of this process, even long after he has 'hopped off' somewhere else.
In contrast to direct sperm transfer, the use of a spermatophore could grant the female more influence over the fertilization or non-fertilization of her eggs - but that assumption does not hold up.
For their study, Reinhold and Ramm paired males and females from two subspecies of the bushcricket Poecilimon veluchianus, in whom the time between pairing and sperm transfer differ. In Poecilimon veluchianus minor, sperm are transferred within the first three hours but the transfer in Poecilimon veluchianus veluchianus starts only after four hours. If the two subspecies are interbred, the researchers thought, then the number of transferred sperm after three hours would indicate whether it is the male or the female who determines how long this transfer takes.
The researchers mated nine to twelve pairs in each of the four possible combinations of Poecilimon veluchianus minor and Poecilimon veluchianus veluchianus. Three hours after mating, they examined how many sperm they could find in the female's reproductive tract.
The result: the sperm from the males of the 'faster' subspecies Poecilimon veluchianus minor could be found in the females of both subspecies. In contrast, the males in the 'slower' sub-species Poecilimon veluchianus veluchianus had transferred almost no sperm at all to either type of female.
The researchers conclude from this experiment that the males control the speed of transfer over the sperm package. However, this does not automatically lead to the conclusion that the female is powerless. Females can also influence whether sperms are transferred by how quickly they eat the spermatophore. In addition, the larger the male, the larger the size of the sperm package, and this influences how long the females need to consume the protein.
As a result, the sperm have more time to transfer to the female – and the female's eggs have a greater chance of being fertilized by a 'high-quality' male. Professor Reinhold stresses, 'Our findings show that the females do not determine the transfer – not that they could not do so.'
Published in Behavioural Ecology and Sociobiology.