Polymorphism can arise across taxa due to various selection pressures and potentially lead to alternative mating or antipredator strategies. For male jumping spiders, sexual selection and predation risk are often intertwined when courting cannibalistic females and may be a driving factor in the polymorphism of the jumping spider, Maevia inclemens. The dimorphic males of M. inclemens differ dramatically in their complex courtship behavior and display traits that may function as alternative mating strategies to reduce female aggression and maximize mating success. We hypothesized that males of the Btufted^morph honestly communicate condition or body size to females with three conspicuous tufts of setae on their head and males of the Bstripedm orph reduce female aggression with coloration commonly found in aposematic animals (here, yellow-orange pedipalps and striped legs). We examined correlations between tuft length and symmetry and metrics of body size and condition in fieldcollected spiders and conducted prey color choice tests (with live color-manipulated prey) to determine if yellow-orange and striped prey are avoided. Tuft length was variable and correlated with male size (but not condition). All prey color types were attacked at equal rates, but spiders oriented to striped prey more often, suggesting that male stripes may attract female attention without increasing predation. This study provides insight into the potential functions of the different courtship and visual displays of M. inclemens males. Using jumping spiders to study polymorphism can provide new insight into how multiple morphs can evolve, as males use mating strategies not only to impress females but also avoid getting eaten by their potential mates. Significance statement Understanding the selection pressures that shape and maintain polymorphisms in natural populations is an active area of inquiry, yet most of what we know comes from a small handful of well-studied vertebrate taxa. The unique biology of jumping spiders and the fact that males have to avoid cannibalism during courtship, makes them well-suited to provide novel insights into the functions and maintenance of dimorphic male traits. The unusual male dimorphism of M. inclemens captured the attention of naturalists as early as the 1800s, yet we still do not understand why the two male morphs differ so dramatically in morphology and courtship behavior. Here, we propose and test a novel hypothesis that provides insight into the long-studied but still largely unexplained phenomenon of male dimorphism in this species.

The timing and nutritional value of a first meal is important for spiderlings, but little is known about what spiderlings specifically consume. For wandering spiders, nectar feeding is a common occurrence thought to be directly beneficial in providing nutrients and serving to fuel energy costly for foraging. Cannibalism is also prevalent among many spiders. We suspect in spiderlings of the cursorial species, Oxyopes salticus Hentz, 1845, nectar feeding could decrease cannibalism by causing satiation, or increase cannibalism by enhancing energy levels and rates of interaction. We conducted laboratory experiments to test the longevity of newly hatched O. salticus in the presence of different nutrient resources and the effect these resources had on cannibalism rates. Spiderlings were housed solitarily or in pairs and given access to different nutrient resources that reflect those available in the wild, including nectar and insect prey items (fructose, protein, and water). In a 14-day period, we recorded the number of days each spiderling was alive to determine survivorship. By the end of the experiment, 60% of spiderlings housed with fructose were still alive and 10% survived when housed with protein or water. Based on survivorship models, the predicted mean age at death differed between treatments (15.9 days for fructose, 11.2 days for protein, and 9.5 days for water). Spiderlings housed in pairs declined more rapidly in survivorship compared to solitary spiderlings, suggesting cannibalism occurred across all treatments. Fructose significantly increased longevity of spiderlings regardless of their housing and reduced cannibalism.

In sexually cannibalistic animals, the relative sizes of potential mates often predict the outcome of aggressive encounters. Mantidflies are spider egg predators as larvae and generalist predators as adults. Unlike most cannibalistic species, there is considerable individual variation in body size in both sexes. Using preserved collections of Dicromantispa sayi , we focused on three body size metrics that we found to be positively correlated and accurately measured across researchers. We found extreme size variation in both sexes: the largest 10% of females were 1.72× larger than the smallest 10%, and the largest 10% of males were 1.65× larger than the smallest 10%. On average, females were 7.94% larger than males. In exploring possible causes of this variation, we uncovered differences among populations. To explore the effect of spider egg sac size on adult mantidfly size, we reared mantidfly larvae on egg sacs from two jumping spider species with small or large egg sacs. Mantidfly larvae reared on small egg sacs were smaller than those reared on large egg sacs. This study provides the groundwork to design ecologically relevant experiments exploring the causes and consequences of extreme size variation in an understudied system with intriguing natural history.

Maevia inclemens is a common jumping spider found in vines and ivy along tree lines throughout eastern North America. Learn about this interesting and possibly agriculturally beneficial spider in this 3-page fact sheet written by Laurel Lietzenmayer and Lisa Taylor and published by the UF/IFAS Department of Entomology and Nematology. http://edis.ifas.ufl.edu/in1209 Also available on the Featured Creatures website: http://entnemdept.ufl.edu/creatures/URBAN/SPIDERS/dimorphic_jumper.html