AR-News: spiders remember

[Mary Finelli]

SPIDERS 'REMEMBER FIRST DATE'
BBC News Online, Julianna Kettlewell, Oct. 27, 2003
http://news.bbc.co.uk/go/pr/fr/-/2/hi/science/nature/3218509.stm


A male wolf spider who looks familiar to his mate is less likely to get 
eaten during courtship, say scientists. Female wolf spiders - schizocosa 
uetzi - prefer to mate with males which look similar to those they 
encountered before they were sexually mature. This suggests invertebrates 
have social recognition, which can be maintained and remembered throughout 
the different phases of their lives.

The findings appear in the Proceedings of the National Academy of Sciences.

Sexy Legs
In the wild male wolf spiders mature much faster than females. This means 
that while she is still unable to mate herself, a female wolf spider is 
exposed to plenty of sexually mature males. What she sees at this crucial 
time in her life determines her future sexual preference.

A male wolf spider will seduce a potential mate by waving his forelegs at 
her. These hairy front legs vary in colour from dark brown to jet black, 
according to the individual. That is how females tell their suitors apart - 
and they are very picky indeed.

Female wolf spiders prefer to mate with males who have similar leg 
colouration to that sported by males they saw when they were sexually 
immature adolescents. Strange suitors who do not fit the bill tend to end up 
as lunch before the pair can get better acquainted. In other words, females 
will avoid breeding with unfamiliar males altogether.

Social Recognition
These findings suggest invertebrates possess social recognition - something 
never before found.

Dr Eileen Hebets, from Cornell University in New York, US, who led the 
study, said: "Social experience influences mate choice.
"This shows that invertebrates have social recognition, and it can be 
remembered even through the moulting process.
"It is exciting because it shows that there is a level of complexity that 
has not been seen before."

In mammals social recognition is usually used to the opposite effect. 
Mammals often choose mates that are not too familiar to them - to avoid 
breeding with a relative. But wolf spiders - which can be found all over the 
world, in diverse ecosystems - are so thick on the ground that inbreeding is 
not a common hazard. Dr Hebets told BBC News Online: "We collected our 
specimens in Mississippi and the population was very dense. So running into 
a sibling would be rare."

Evolutionary Advantage
Usually behaviour such as this will have arisen because it provides some 
evolutionary advantage. Dr Hebets said: "We don't know exactly what the 
evolutionary advantage might be yet but it could be that fitter, stronger 
males tend to mature earlier and, because females want to choose the fittest 
males to father their young, they choose the ones they remembered were 
sexually mature when they were still juvenile."

Put another way, strange looking males might not have been strutting their 
stuff when the lady wolf spider was still a girl because they were the 
weakling late developers. Therefore she would do well to avoid them - or 
devour them before they have a chance to father her babies.

Since wolf spiders live amongst some other very similar species, choosing a 
familiar mate might also be a way of ensuring the male is from the right 
species, according to Dr Hebets.

Wolf spiders, which mature at about 20 days old, have had their social 
memories tested for up to three weeks. But since they live for about a year, 
there is much more scope for tests. Dr Hebets said: "I want to know just how 
long these spiders can remember for."

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