'Paranoia' about rivals alters insect mating behavior

August 8, 2011

Scientists at the University of Liverpool have found that male fruitflies experience a type of 'paranoia' in the presence of another male, which doubles the length of time they mate with a female, despite the female of the species only ever mating with one male.

Females in many species of animal have multiple mates and males have evolved particular reproductive characteristics to ensure their sperm are successful when in competition with the sperm of other males. include that result in increased sperm count, as well as behavioural alterations such as mating with females for up to 21% longer than they normally would.

In types of fruitfly where the female only mates once, however, there is little need for competitive behaviour. The male is not expected to increase its reproductive efforts in response to competition, because it 'knows' that the female will be fertilised with its sperm only. Scientists at Liverpool, however, have found that once a male had been in contact with another male, it subsequently increased the length of time it mates with a female by 93%, even though the risk of the female being fertilised by another male was remote.

The study suggests a number of reasons for this apparent 'paranoid' behaviour. One possible explanation is that females do occasionally mate with more than one male, and the male responds to the possibility of this rare event by changing its . Another reason could be that the presence of a competitor prompts the 'fear' that a male is unlikely to obtain another mate and it therefore increases its reproductive efforts in order to keep the one female fertile with its sperm for the female's entire .

Dr Anne Lize, from the University's Institute of , explains: "We already knew, from previous studies, that male insects evolve physical and behavioural characteristics to make them a stronger reproductive competitor for females that mate with many males. Some , for example, have evolved disproportionately large testes so that males can deliver increased sperm numbers. Fruitflies have behavioural reactions to the presence of rival males that result in prolonged reproduction with females to ensure fertilisation before the female mates with other males.

"We wanted to understand how this compared to fruitfly species where females only mated once, to see whether drivers of evolutionary change are different in species where sperm competition is low. What we observed might be considered the evolutionary equivalent of male 'paranoia'. Males more than doubled the length of time they mated with a female after they had been in the presence of other males.

"There doesn't appear to be an immediate biological reason as to why they would do this, but it is perhaps to ensure that the female remains fertile with one male's for her lifespan, even though the chance of reproducing with another is remote.

"Our findings are significant because they demonstrate that particular behaviours, such as the response to males, can have diverse evolutionary drivers. This takes us a step closer to understanding the differences between males that have evolved within species where individual females mate with many males and those have just one partner."

The research is published in Biology Letters.

Explore further: Why the best things come to those who wait

Related Stories

Why the best things come to those who wait

October 20, 2006

Pushing to the front of the queue is not the best ploy for males who want to propagate their genes according to scientists from the University of Exeter.

Sex is thirst-quenching for female beetles

August 28, 2007

Female beetles mate to quench their thirst according to new research by a University of Exeter biologist. The males of some insect species, including certain types of beetles, moths and crickets, produce unusually large ejaculates, ...

Does promiscuity prevent extinction?

February 25, 2010

Promiscuous females may be the key to a species' survival, according to new research by the Universities of Exeter and Liverpool. Published today (25 February) in Current Biology, the study could solve the mystery of why ...

Hens' sperm ejection secrets

August 3, 2011

In reproductive warfare sperm is a male’s ultimate weapon to decide who fathers the next generation.

Recommended for you

Secrets of a heat-loving microbe unlocked

September 4, 2015

Scientists studying how a heat-loving microbe transfers its DNA from one generation to the next say it could further our understanding of an extraordinary superbug.

Plants also suffer from stress

September 4, 2015

High salt in soil dramatically stresses plant biology and reduces the growth and yield of crops. Now researchers have found specific proteins that allow plants to grow better under salt stress, and may help breed future generations ...

Ancient walnut forests linked to languages, trade routes

September 4, 2015

If Persian walnut trees could talk, they might tell of the numerous traders who moved along the Silk Roads' thousands of miles over thousands of years, carrying among their valuable merchandise the seeds that would turn into ...

Huddling rats behave as a 'super-organism'

September 3, 2015

Rodents huddle together when it is cold, they separate when it is warm, and at moderate temperatures they cycle between the warm center and the cold edges of the group. In a new study published in PLOS Computational Biology, ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.