Discerning males remain faithful

Apr 24, 2012
This is a smaller male orb web spider (Argiope bruennichi) together with freshly molted female. Credit: K.W.Welke

Discerning males remain faithful ... if you are a spider. Sex for male orb web spiders (Argiope bruennichi) is a two shot affair since the act of mating destroys their genitalia. If they survive being eaten during their first encounter with a female, they have two choices – to mate again with the same female (monogynous) or try to find a new partner (bigynous). New research published in BioMed Central's open access journal Frontiers in Zoology shows that choice of mating behavior for A. bruennichi depends on the size and age of the first female they mate with.

Monogamous behavior, such as for life, is thought to evolve when paternal protection of the female increases fertilization success. For cannibalistic spiders, monogamy means that the life of the male can be very short indeed. However this can improve chances of fatherhood: of the black widow spider can increase the duration of mating, and hence the likelihood of successful fertilization, by allowing themselves to be eaten.

Monogamous spiders like A. bruennichi have evolved specialized pedipalps, which are used to transfer sperm into a female's reproductive organs. These specialized are usually damaged during mating, breaking off inside the female, and forming a plug to prevent subsequent fertilization by a different male. Each male can consequently only mate twice in their entire lives, but, if they survive the first encounter (a female will usually eat the male if mating continues to long) they can then chose to either mate with her again or to find a different female to mate with.

This shows a cannibalized male orb web spider (Argiope bruennichi) inside the female's web. Credit: S.M.Zimmer

Researchers from the Zoological Institute, University of Hamburg, discovered that the mating strategy of A. bruennichi was not random. Males made mating decisions based on females mating status (virgin or already mated) age, weight, availability of other females, and the time of day.

Klaas Welke explained, "Amongst spiders, regardless of age, heavier females are the most fertile. Males were more likely to mate twice with the same female if it was early in the day, she was heavy, and if the nearest other females were sub-adult. Males kept on searching for a second female if it was late in the day and the first female was light. We found that bigynous males preferred to 'trade up' to heavier females as second mates, but ran the risk of attempting to copulate with already mated females."

Two thirds of the monogamous males were eaten after their first mating. These males, which only managed to mate once, tended to mate with the oldest and heaviest females. Klaas Welke explained, "These are the ones which have the highest fecundity and which are most ready to lay their eggs. While these males do not have a second chance at mating their probability of reproductive success is high."

Based on paternity of lifetime reproductive success bigyny appeared to be the more successful strategy. Despite this about half of the males were monogamous and half bigynous demonstrating that males alter their behavior to make the best of the situation they find themselves in.

Explore further: Orchid named after UC Riverside researcher

More information: Conditional monogyny: female quality predicts male faithfulness Klaas W Welke, Stefanie M Zimmer and Jutta M Schneider, Frontiers in Zoology (in press)

Related Stories

'Paranoia' about rivals alters insect mating behavior

Aug 08, 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 ...

Mating that causes injuries

Feb 20, 2009

Researchers at Uppsala University can now show that what is good for one sex is not always good for the other sex. In fact, evolutionary conflicts between the two sexes cause characteristics and behaviors that are downright ...

Sex is thirst-quenching for female beetles

Aug 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, ...

Recommended for you

Orchid named after UC Riverside researcher

9 hours ago

One day about eight years ago, Katia Silvera, a postdoctoral scholar at the University of California, Riverside, and her father were on a field trip in a mountainous area in central Panama when they stumbled ...

In sex-reversed cave insects, females have the penises

12 hours ago

Researchers reporting in the Cell Press journal Current Biology on April 17 have discovered little-known cave insects with rather novel sex lives. The Brazilian insects, which represent four distinct but re ...

Fear of the cuckoo mafia

12 hours ago

If a restaurant owner fails to pay the protection money demanded of him, he can expect his premises to be trashed. Warnings like these are seldom required, however, as fear of the consequences is enough to ...

User comments : 0

More news stories

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...

Hackathon team's GoogolPlex gives Siri extra powers

(Phys.org) —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...