Matricide and Infanticide in a Spider
When Babies Eat Their Mother and Second Mates Destroy Eggs
Oct 30, 2009
For many spiders, the act of mating occurs near the end of their lives. Male spiders are often eaten by their mates to provide a burst of nutrients to the female and allow her to produce larger eggs that produce larger young which will have a greater chance of survival than young from smaller eggs. Female resources are often depleted after egg laying and many die shortly after laying their clutches.
Some spiders, like the wolf spiders wrap their eggs in a silk cocoon and carry this cocoon with them until the eggs hatch. Then the mother provides food for her spiderlings for several days or weeks before her children move out on their own.
Other spiders lay their eggs and attach the egg cocoons to their webs. The mother may die shortly after or survive to assist her offspring as do the wolf spiders.
Matriphagy
Several species of Stegodyphus spiders goes even farther than these examples in raising their young. Females of S. lineatus carefully attach their egg cocoons to their webs and watch over them until the babies hatch. Once her children have hatched, the mother continues to eat, but regurgitates most of her meals as a nutrient soup for her offspring while the spiderlings stay in their mother's web. When the young are about three to four weeks old, she rolls over on her back allowing the spiderlings to clamber over her, kill her by injecting their venom and digestive enzymes into her body, and eat her. After she is consumed, the young turn on each other and cannibalize as many of their siblings that they can before leaving their mother's web.
Male Intervention and Infanticide
Male S. lineatus are almost as large as females and unmated males invade female webs – sometimes more than one per female. While cohabiting, the males eat prey captured in the female's web, but do not help maintain the web. This reduces the female's food intake and she often loses weight. As a result of the male's activities, the female stops repairing her web while males are present. This further reduces the number of prey captured in the web and the female's body condition is severely affected. The male, however, gains weight and becomes more aggressive.
Although males are not killed and consumed in this species, females have different responses to males depending on their own reproductive state. If the female is unmated, she tolerates the male to some degree. Once she has mated and produced eggs, she becomes quite aggressive to him and attempts to chase him from the web. She becomes even more aggressive to males that enter her web after eggs are laid because these males attempt to cut out the eggs fathered by other males. When a male destroys her eggs, the female's chances of producing offspring becomes nil unless she remates with the male interloper and produces a new batch of eggs. If he can not destroy the eggs within one or two weeks after invading the web, he leaves to find another female to harass.
Conflicts of Interest
There is a strong conflict of interest between the sexes. The male has everything to gain by the association: He enhances his condition by gaining weight at the female's expense. If successful in mating, he increases the probability that his genes will be passed to the next generation.
Because the female becomes further weakened by fighting with and losing prey to a second male, she does not produce as many eggs in a second clutch as in her first clutch. Additionally, the offspring have a lower survival rate because:
- the eggs are smaller and
- the female has less nutrition for her young when they feed on her.
The female's interests are best served by accepting a single male, mating with him, and having him move out of her web quickly with no replacement. Many females delay implantation of sperm, and the resulting development of eggs, until some time after their mate has left. This reduces the probability that an invading second male will reduce her reproductive efforts by destroying eggs.
There is also a conflict of interest between a first mate and a second mate. It does not matter to a cuckolding male that he fathers a second clutch. About half of the females are invaded by a second male, and some of these are successful in destroying her first egg mass before being evicted. On the event a second male mates with the female and causes a second egg mass to be produced, sperm of the second male fertilize between thirty and fifty percent of the new eggs. Thus, a cuckolding male reduces the fecundity of both the female and the first male.
Here are links to other articles describing unusual spider behaviors.
 |
