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Two recent studies by environmentalists from the National University of Singapore (NUS) shed light on the relationship between the tiny pitcher and his "tenant", the spider-crab Thomisus nepenthiphilus, providing information on foraging behaviors little known to the spider.
Thomisus nepenthiphilus is only in the tiny plant Nepenthes gracilis, originally from Singapore, is also present in Indonesia, Borneo and Malaysia. Carnivorous that traps and devours insects to supplement its nutrient needs, the crab spider Thomisus nepenthiphilus is able to exploit the fragrant nectar of the pitcher's plant to catch its prey while providing additional nutrients to its host.
"Our two studies provide important insights into the circumstances that favor cooperation rather than parasitism, and the results are critical to achieving a better understanding of these interactions," said Associate Professor, Research Supervisor Hugh Tan. , from the Department of Biological Sciences at NUS. Faculty of Sciences.
The benefit of being "stolen"
In the first study, Dr. Tan, associated with the PhD student, Mr. Lam Weng Ngai, and the former undergraduate student, Ms. Robyn Lim, discovered that the crab-spider-free pitchers drew more from each prey than their prey, while those inhabited by traps more prey but receive less nutrients from each prey.
Their laboratory experiments revealed that the crab spider ambushes the flies that feed in the pitcher and sucks the body fluids out of the prey of the insect. The crab spider then drops the carcasses of the prey, which still contain nutrients, into the liquids contained in the pitcher in order to be digested. As such, although the crab spider "flies" from the pitcher's plant and has the first taste of prey, the net effect of this "burglary" can still be beneficial to the plant's Pitcher because it recovers the residual nutrients of the prey.
The results suggest that when resources are scarce, this partnership between the crab spider and the jar plant is beneficial. However, when resources are abundant, this partnership is not favorable. The results of the study were published in the journal Oecologia August 14, 2018.
"A trend observed in recent research on mutualism is that, under more stressful conditions, the frequency and intensity of mutualism between the different organisms is increasing, and our results corroborate this observation. the old adage "a friend in need" "It's a friend, it's true not only for humans, but also for plants and animals," said Professor Assoc.
Big prey, big gains
Professors Tan and Lam also conducted additional experiments in the natural habitat of plants. With the help of field investigations, researchers identified the most numerous prey among pitchers inhabited by spiders and those that were not.
Laboratory experiments were conducted to measure the nutrient content of these prey species in order to estimate the amount of nutrients that the pitchers would get if the prey had been trapped with and without the l '. help crab spiders.
"Our results confirm the conclusions of our previous study – the T. nepenthiphilus crab spider actually helps the N. gracilis Pitcher plant catch many species of prey. More importantly, the net contribution of T. nepenthiphilus at N. gracilis"Nutrition seems to be proportional to the size of the prey that T. nepenthiphilus taken, "said Lam.
He explained: "If the spider-crab catches only small prey, such as mosquitoes or lake flies, the net benefit to the pitcher's plant will be negative: it will be" theft "of However, when the crab spider catches large insects such as cockroaches or large insects, the pitcher will benefit, as the "service charge" paid to the insects will increase. crab spider are reduced in relation to the total amount of nutrients obtained through the interaction. receives carcasses rejected by the spider-crab is a good compromise. "
The results of this study were published in the Journal of Animal Ecology October 10, 2018.
Theoretical model to build
Based on the knowledge gained from these two studies, the research team is building a theoretical model on mutualism that involves the supply of nutrients from one species to another. Such a model will allow scientists to examine the stability factors of mutualism and to determine how environmental changes, such as global warming or habitat modification, will alter ecological outcomes.
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