Growth is an important factor in predicting an organism's overall success as an adult. Understanding how abiotic and biotic factors influence body size is key to predicting how environmental changes will impact organisms and predicting optimal behaviors under varying conditions. Food items can vary widely in nutrient content and this variation can affect growth. We tested how the quantity and macronutrient content of live prey affected the growth of juvenile jumping spiders, Phiddipus audax, using 420 spiderlings raised on one of 21 diets. In addition, we measured the nutrient content of prey from the field and compared average prey nutrient content with the diet at which spiders maximized growth. Our results show that the quantity and nutrient content of prey have significant and interacting effects on the growth of an actively hunting predator. In particular, spiders grew larger in body size (tibia/patella length and posterior lateral eye width) and were heavier on diets with higher lipid content. Yet, data on the nutrient content of prey from the field shows that most potential prey have high protein and low lipid content in their bodies. This apparent mismatch between spider nutritional requirements and prey nutrient availability likely presents a challenge to spiders seeking to maximize growth in the field. Several hypotheses for how these predators overcome this challenge to reach the large body sizes observed in the field are discussed.

No abstract

In nature, food is often variable in composition and availability. As a consequence, predators may need to seek non‐prey food sources. Some predators are known to feed on nectar when food is limited. Nectar and other carbohydrate resources could also be beneficial when prey are more abundant if it helps predators balance protein‐biased diets. We tested if an actively hunting predator, the jumping spider, Phidippus audax , benefited from liquid carbohydrates when prey were not limited. We also tested if the benefit of carbohydrates varied with the nutrient content of prey (i.e., from protein to lipid biased). Spiders were reared on one of six live prey, Drosophila melanogaster , treatments that ranged from high protein to high lipid. Half of the spiders were given access to a 20% sucrose solution. After 2 months, we measured spider mass, cephalothorax width, instar duration, percent body fat, survival, and estimated number of prey eaten. Spiders reared on high‐protein diets with carbohydrates were larger and heavier than spiders on other treatments. Access to carbohydrates also increased percent body fat and survival across prey treatments. Our results suggest that carbohydrates may be a valuable component of spider diets, especially when prey have high protein and low lipid content as is commonly observed in prey in the field. Our results highlight the importance of diet balancing for predators, and that liquid carbohydrates can be an important nutrient to supplement a diet of prey rather than just being an energy supplement during periods of starvation.

The risk-taking tendencies and addiction in small vertebrates are often used to understand the processes of larger vertebrates, such as humans. We set out to find whether certain risk-taking behaviors characteristic of addiction remain consistent between vertebrates and invertebrates. Different animals will gorge on sugar water, and addiction-like tendencies are often associated with the overconsumption of sucrose. The goal of my study was to evaluate those risk-taking behaviors and compare invertebrate risk-taking behaviors to vertebrate risk-taking behaviors. The risk-taking behavior we observed was the process of relieving cravings while the risk of predation was present. Through this study we document evidence of wolf spiders feeding on a 25% sucrose solution and explain the wolf spiders’ preference to a sugar water solution over filtered tap water. To evaluate if wolf spiders exhibit addiction like behaviors associated with sucrose, we placed a green-colored, sugar water-soaked cotton ball on the silk of a large, predatory Tigrosa helluo wolf spider and a regular, filtered water-soaked cotton ball on the “safe” side of a plastic trial arena and then evaluated the behaviors of the prey spiders. We used a mixture of Pardosa milvina and Rabidosa rabida as test spiders, with one group given a sugar-water treatment beforehand and the other group was given a green colored control cotton ball with filtered tap water (n=14 for both the sugar water treatment and control groups). The wolf spiders who were predisposed to the sugar water treatment were more likely to cross through their predator’s silk in order to gain access to the sugar water cotton ball than their counterparts who were not given a sugar water treatment prior. These results suggest the risk for predation of the wolf spider is not worth the benefits of the sugar water, unless a wolf spider has been allowed unlimited access to sugar water in advance. When a wolf spider who was allowed unlimited access to sugar water beforehand is presented with a risky situation, they will increase their risk-taking behaviors via crossing through a predator’s silk in order indulge in the sugar water. These results suggest the addictive properties of sugar spans across vertebrates and invertebrates, and potentially opens the door for a cost-efficient and ethically acceptable invertebrate model-organism for examining the risk-taking behaviors associated with addiction.

In nature, food is often variable in composition and availability. As a consequence, predators may need to seek non-prey food sources. Some predators are known to feed on nectar when food is limited. Nectar and other carbohydrate resources could also be beneficial when prey are more abundant if it helps predators balance protein-biased diets. We tested if an actively hunting predator, the jumping spider, Phidippus audax, benefited from liquid carbohydrates when prey were not limited. We also tested if the benefit of carbohydrates varied with the nutrient content of prey (i.e., from protein to lipid-biased). Spiders were reared on one of six live prey, Drosophila melanogaster, treatments that ranged from high protein to high lipid. Half of the spiders were given access to a 20% sucrose solution. After two months, we measured spider mass, cephalothorax width, instar duration, percent body fat, survival, and estimated number of prey eaten. Spiders reared on high protein diets with carbohydrates were larger and heavier than spiders on other treatments. Access to carbohydrates also increased percent body fat and survival across prey treatments. Our results suggest that carbohydrates may be a valuable component of spider diets, especially when prey have high protein and low lipid content as is commonly observed in prey in the field. Our results highlight the importance of diet balancing for predators, and that liquid carbohydrates can be an important nutrient to supplement a diet of prey rather than just being an energy supplement during periods of starvation.Significance statementProtein and lipid are thought to be the primary nutrients used by predators, including spiders. Yet, some spiders have been observed feeding on carbohydrate-rich nectar from flowers. We tested if the addition of carbohydrates to a high protein or high lipid diet affected the growth of the North American jumping spider, Phidippus audax. Spiders grew largest on high protein diets with carbohydrates, demonstrating that plant-based foods rich in carbohydrates can be important for some predators.