A comparison of adhesive performance among six cursorial spider species

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  A comparison of adhesive performance among six cursorial spider species Abstract The ability to adhere to surfaces is particularly relevant for cursorial predatory arthropods like hunting spiders, which often traverse relatively complex environments characterized by large variation in substrate properties. Here, we evaluated the adhesive performance of six hunting spider species that are common in eastern temperate North America and lack specialized tarsi for climbing smooth or inclined surfaces [Lycosidae: Pardosa lapidicina Emerton, 1885 and Rabidosa rabida (Walckenaer, 1837); Oxyopidae: Oxyopes salticus Hentz, 1845; Pisauridae: Pisaurina mira (Walckenaer, 1837); Dolomedidae: Dolomedes triton (Walckenaer, 1837), and Dolomedes scriptus Hentz, 1845]. We tested adhesion performance as shear load resistance (g) on a glass plate, and as the angle of failure (°) when the plate was gradually inclined relative to horizontal. Average angle of failure and shear resistance differed among ...

Development, Adult Body Mass and Extreme Sexual Size-Dimorphism in the Brown Widow Spider, Latrodectus Geometricus

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A brown widow spider, Latrodectus geometricus with the orange hourglass marking clearly visible. Captured and photographed in Los Angeles, California. The image is a 25 frame focus stack. 

Development, Adult Body Mass and Extreme Sexual Size-Dimorphism in the Brown Widow Spider, Latrodectus Geometricus

Abstract

Intraspecific differences in the growth rates and adult body sizes of male and female offspring are frequently observed in both vertebrate and invertebrate taxa. In some species, males are the larger sex, whereas in others females are larger, a process described as ‘sexual size dimorphism’ (SSD). Several hypotheses have been postulated to explain SSD, such as intra-sexual competition for access to mates, differences in the mass-scaling of gamete production costs (eggs, sperm), and sexual variation in mortality risks during early development. Among spiders, differences in the body masses of males and females at maturity are among the largest in the animal kingdom, with females sometimes attaining a body mass a 100-fold greater than that of males. Here, we tracked growth trajectories of brown widow spiders (Latrodectus geometricus) from neonate to adult. To assess whether prey availability affects sexual variation in adult body mass, we either fed spiderlings weekly (‘continuous-feeding treatment’) or once every three weeks (‘intermittent-feeding treatment’) on fruit flies and then crickets or blow flies. Approximately 60% of continuously-fed spiderlings survived to adulthood, compared to only 2 spiderlings in the intermittent-feeding treatment. Males molted on average 4 times, and reached maximum virgin body masses after around 100 days, whereas females molted 6-7 times, and reached maximum virgin body masses after around 170 days. Growth rate of males was consistent across different instars whereas it was highest in later female instars. Mature males were less than 1% as large as mature females, revealing extreme (SSD) in this species. We discuss different factors that may account for extreme sexual size dimorphism (ESSD) in widows and other spiders.


Harvey, Jeffrey and Gerosa, Francesco and Gols, Rieta and Verberk, Wilco C.E.P., Development, Adult Body Mass and Extreme Sexual Size-Dimorphism in the Brown Widow Spider, Latrodectus Geometricus. 

Available at SSRN: https://ssrn.com/abstract=4741608 or http://dx.doi.org/10.2139/ssrn.4741608