Pardosa pseudoannulata
Pardosa pseudoannulata, a member of a group of species referred to as wolf-spiders, is a non-web-building spider belonging to the family Lycosidae. P. pseudoannulata are wandering spiders that track and ambush prey and display sexual cannibalism. They are commonly encountered in farmlands across China and other East Asian countries. Their venom has properties that helps it function as an effective insecticide, and it is, therefore, a crucial pesticide control agent.
Description
Pardosa pseudoannulata exhibits significant sexual dimorphism in terms of size. Females are, on average, 1.3 times larger than the males. This spider can be recognized by the ring markings on its legs and the dark bands on its carapace. The underside of these spiders is characterized by six black dots. Female P. pseudoannulata are easy to detect, as most will have an egg sac attached to their spinnerets. P. pseudoannulata have three rows of eyes with the front row having four eyes and the other rows having two eyes each.Habitat and distribution
Distribution
Pardosa pseudoannulata is widely spread across China, India, Korea, Japan and other countries in East Asia. It is most commonly found in farm fields throughout China. These spiders are commonly seen in rice fields and are the dominant predator.Habitat
Pardosa pseudoannulata commonly inhabits arable farm fields and similar open habitats. It is one of the most common surface-dwelling spider species in Central China and plays an important role as a control agent against pests and insects within the crop fields. The spider is also found near fields with ponds and has the ability to move swiftly over bodies of water. Due to the nature of agriculture, the fields will remain fallow for several months, decreasing the density of prey that migrate into the field to take advantage of nutrients in the crops. This causes P. pseudoannulata to starve for multiple months at times, explaining why they are well adapted to survive in environments with insufficient resources.In order to produce the maximum number of eggs and the highest rate of successful hatchings, Pardosa pseudoannulata prefers temperatures between 20 and 30°C, the optimal temperature being 25°C. If the temperature is lower than 10°C, the spiders will stop eating and, as a result, will not grow or develop. In temperatures above 40°C, the spiders will move slowly and remain hidden in burrows.
Diet
Pardosa pseudoannulata commonly starve and have a hard time foraging for sufficient nutrients. Therefore, the occurrence of sexual cannibalism provides an adaptive strategy for female survival as well as reproductive benefits. Pre-copulation cannibalism in which the male spider is used solely as food is commonly observed in females who have already mated. The consumption of conspecifics makes up a quarter of the female's diet. Male spiders are an especially good source of nutrition because of their large size when compared to natural prey, which are insects that are several times smaller than the females.The natural prey of Pardosa pseudoannulata are rice field pests, with the rice brown planthopper, Nilaparvata lugens, as the most common. N. lugens are abundant in rice fields and detrimental to the growth of rice plants. Pardosa pseudoannulata prefers the rice brown planthopper over other pests, with the planthopper making up around 30% percent of an average spider's diet.
Abdomen size
Pardosa pseudoannulata’s abdomen width is an important indicator of its hunting abilities and starvation resistance. There is a trade-off between the hunting abilities and the period of time the spider can withstand hunger. Spiders with larger abdomens are seen to withstand starvation for longer periods of time, whereas spiders with smaller abdomens are seen to be better and more agile hunters.Seasonal Changes in Resource Allocation
Pardosa pseudoannulataReproduction
Pardosa pseudoannulata males and females differ in terms of sexual behavior. Females are monandrous, meaning that they only mate with one male at a time. This motivates the evolution of sexual cannibalism for males, as the male will parent all of the female's offspring, making the paternal investment worthwhile. On the other hand, males are polygynous if not cannibalized.Females are able to store sperm from a copulation and use it produce multiple egg sacs. This prevents them from being motivated to mate again. The result is higher aggression rates in female spiders who have previously mated.
Females will carry their sac filled with eggs connected to their spinnerets. This will detach when it is time for the offspring to be born. The new offspring will crawl onto the mother's abdomen and stay there for 5 days. During this time, they will feed off of the remains of their yolk from the mother's eggs. After this period, they will move into the leaf litter and detach live from the mother.
Copulation duration for Pardosa pseudoannulata ranges from 19 to 93 minutes. The duration of copulation is significantly higher with males that are cannibalized. Copulation duration is independent of the sperm count of the male. Male spiders will need up to seven days in order to replenish their sperm count. For females, reproducing with a male that has recently mated and has a low sperm count will lead to a lower chance of reproductive success. The sperm count of the male has no impact on copulation duration or intensity, so it is believed that females are unable to distinguish males with high sperm counts from males with low sperm counts.
Life cycle
Pardosa pseudoannulata will have on average two and a half generations per year. Similar to other Pardosa species, sub-adults and adults overwinter in order to conserve energy and survive the cold winter months. Overwintering adults will be inactive from November to March as they save up body mass. They will burrow into the soil or use litter in their natural habitat as shelter. They will reach their reproductive peak in early May, and this peak is usually consists of the overwintering generation. A second reproductive peak is observed in early July with the second generation. A third one can be seen in late September with the following generation.Behavior
Sexual cannibalism
Pardosa pseudoannulata engages in sexual cannibalism as a foraging strategy. Conspecific prey can make up 25% of the female's diet. The female spider uses sexual cannibalism as a way to attain nutrition and increase offspring survival. There are instances where the female spider will attack and cannibalize the male before or after copulation, the latter being observed more frequently. The rate at which females attack males is dependent on the female's hunger level and mating history. Spiders that are well-fed and virgins are less likely to attack males and perform pre-copulative cannibalism. The reason why starved females are more aggressive is because they have more motivation to acquire nutrition. Interestingly, the rate of cannibalization occurring did not change with the female's sexual history or hunger state. Aside from this, male size is also a significant factor in cannibalization rates. As mate size dimorphism, the difference between the sizes of mates, increases, sexual cannibalism occurs more frequently.Sexual cannibalism increases offspring survival in Pardosa pseudoannulata. This is mainly due to the mother's ability to care for offspring as a result of nutrition derived through cannibalism. The presence of sexual cannibalism does not have any influence on fecundity, as cannibalistic and non-cannibalistic females produce the same amount of offspring. Another benefit of sexual cannibalism to the female is the increase in body mass through the nutrients in the male body.