4 June 2010, by Tamera Jones
Wild insects beware. New research reveals that it's now possible to follow individual insects' efforts to reproduce in the wild as well as in a traditional lab setting.
Field cricket (Gryllus campestris).
Before this, insect scientists had to be content with studying their subjects in the confines of a lab and were forever envious of colleagues who investigated charismatic creatures like meerkats, orangutans or tigers in the wild.
But this looks set to change, as the costs of the technology needed to study tiny creatures in the wild has dropped significantly in recent years.
'The results we got in the lab were really interesting, but we always wondered how relevant our studies were to real crickets in the wild,' says Dr Rolando Rodríguez-Muñoz a postdoctoral researcher at the University of Exeter and lead author of the research.
Rodríguez-Muñoz and his colleagues built a network of 96 motion-sensitive, infrared-equipped CCTV cameras to spy on a 152-strong field cricket population in a meadow in Asturias, northern Spain.
The cameras allowed the team to monitor the crickets (Gryllus campestris) 24 hours a day throughout the breeding season over two summers. They wanted to find out what behaviours led to more offspring for both males and females.
The meadow with various cameras visible. There are 96 cameras in total. They run 24/7 using infra-red at night.
The researchers describe in Science how they super-glued a minute numbered placard – big enough for the cameras to read – to every cricket's back. They also took a tiny piece of tissue from each one to create a DNA fingerprint of every member of the population.
The tags made it easy to analyse the crickets' lives and behaviours, including mating partners, how long males and females spent together, the time males spent singing to attract females and how many fights occurred between competing males.
They then combined over 250,000 hours' worth of video with the information revealed by the DNA fingerprints to work out how many offspring each individual left in the next generation.
'The biggest issue was the amount of video we had to watch - 2.1 kilometres' long worth of video tape,' explains Professor Tom Tregenza who led the research team.
Generally their results tied in nicely with lab studies, but there were some surprising exceptions.
'This represents a new frontier for biological science.'
Professor Tom Tregenza, University of Exeter
'In the lab people usually use the number of matings as a proxy for reproductive success. But no-one had actually measured this until now,' says Tregenza.
They found that dominant males had fewer mates than males that lost the most fights, but they left just as many offspring. Males that sang for longer had the most mates, but this was only important for small males. Smaller crickets had to sing to have offspring, while large males did better even if they didn't sing.
'It could be that large males don't need to sing, because they look good anyway, but small males have to sing to even attract the attention of females,' explains Tregenza.
While some predictions based on lab studies were confirmed, the researchers were surprised to find that females as well as males leave more offspring when they mate with more partners.
'It's easy to understand why males mate – every mate means potentially more offspring. In our crickets, it seems that females that mate with more males leave more descendants, suggesting that promiscuity can be a good thing for females too,' explains Dr Rodriguez-Munoz.
'I think the really exciting thing is that this represents a new frontier for biological science,' adds Tregenza.
