Instances of sexual size dimorphism (SSD) provide the context for rigorous tests of biological rules of size evolution, such as Cope’s rule (phyletic size increase), Rensch’s rule (allometric patterns of male and female size), as well as male and female body size optima. In certain spider groups, such as the golden orbweavers (Nephilidae), extreme female-biased SSD (eSSD, female:male body length \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{upgreek} \usepackage{mathrsfs} \setlength{\oddsidemargin}{-69pt} \begin{document} }{}$\ge$\end{document} 2) is the norm. Nephilid genera construct webs of exaggerated proportions, which can be aerial, arboricolous, or intermediate (hybrid). First, we established the backbone phylogeny of Nephilidae using 367 anchored hybrid enrichment markers, then combined these data with classical markers for a reference species-level phylogeny. Second, we used the phylogeny to test Cope and Rensch’s rules, sex specific size optima, and the coevolution of web size, type, and features with female and male body size and their ratio, SSD. Male, but not female, size increases significantly over time, and refutes Cope’s rule. Allometric analyses reject the converse, Rensch’s rule. Male and female body sizes are uncorrelated. Female size evolution is random, but males evolve toward an optimum size (3.2–4.9 mm). Overall, female body size correlates positively with absolute web size. However, intermediate sized females build the largest webs (of the hybrid type), giant female Nephila and Trichonephila build smaller webs (of the aerial type), and the smallest females build the smallest webs (of the arboricolous type). We propose taxonomic changes based on the criteria of clade age, monophyly and exclusivity, classification information content, and diagnosability. Spider families, as currently defined, tend to be between 37 million years old and 98 million years old, and Nephilidae is estimated at 133 Ma (97–146), thus deserving family status. We, therefore, resurrect the family Nephilidae Simon 1894 that contains Clitaetra Simon 1889, the Cretaceous Geratonephila Poinar and Buckley (2012) , Herennia Thorell 1877, Indoetra Kuntner 2006 , new rank, Nephila Leach 1815, Nephilengys L. Koch 1872, Nephilingis Kuntner 2013, Palaeonephila Wunderlich 2004 from Tertiary Baltic amber, and Trichonephila Dahl 1911 , new rank. We propose the new clade Orbipurae to contain Araneidae Clerck 1757, Phonognathidae Simon 1894, new rank, and Nephilidae. Nephilid female gigantism is a phylogenetically ancient phenotype (over 100 Ma), as is eSSD, though their magnitudes vary by lineag...

Living fossils are lineages that have retained plesiomorphic traits through long time periods. It is expected that such lineages have both originated and diversified long ago. Such expectations have recently been challenged in some textbook examples of living fossils, notably in extant cycads and coelacanths. Using a phylogenetic approach, we tested the patterns of the origin and diversification of liphistiid spiders, a clade of spiders considered to be living fossils due to their retention of arachnid plesiomorphies and their exclusive grouping in Mesothelae, an ancient clade sister to all modern spiders. Facilitated by original sampling throughout their Asian range, we here provide the phylogenetic framework necessary for reconstructing liphistiid biogeographic history. All phylogenetic analyses support the monophyly of Liphistiidae and of eight genera. As the fossil evidence supports a Carboniferous Euramerican origin of Mesothelae, our dating analyses postulate a long eastward over-land dispersal towards the Asian origin of Liphistiidae during the Palaeogene (39-58 Ma). Contrary to expectations, diversification within extant liphistiid genera is relatively recent, in the Neogene and Late Palaeogene (4-24 Ma). While no over-water dispersal events are needed to explain their evolutionary history, the history of liphistiid spiders has the potential to play prominently in vicariant biogeographic studies.

BackgroundBiogeography models typically focus on explaining patterns through island properties, such as size, complexity, age, and isolation. Such models explain variation in the richness of island biotas. Properties of the organisms themselves, such as their size, age, and dispersal abilities, in turn may explain which organisms come to occupy, and diversify across island archipelagos. Here, we restate and test the intermediate dispersal model (IDM) predicting peak diversity in clades of relatively intermediate dispersers.MethodologyWe test the model through a review of terrestrial and freshwater organisms in the western Indian Ocean examining the correlation among species richness and three potential explanatory variables: dispersal ability quantified as the number of estimated dispersal events, average body size for animals, and clade age.ConclusionsOur study supports the IDM with dispersal ability being the best predictor of regional diversity among the explored variables. We find a weaker relationship between diversity and clade age, but not body size. Principally, we find that richness strongly and positively correlates with dispersal ability in poor to good dispersers while a prior study found a strong decrease in richness with increased dispersal ability among excellent dispersers. Both studies therefore support the intermediate dispersal model, especially when considered together. We note that many additional variables not here considered are at play. For example, some taxa may lose dispersal ability subsequent to island colonization and some poor dispersers have reached high diversity through within island radiations. Nevertheless, our findings highlight the fundamental importance of dispersal ability in explaining patterns of biodiversity generation across islands.

Many organisms convey false signals to mislead their prey or predators. Some orb-weaving spiders build conspicuous structures on webs called decorations. Web decorations and spider colorations are both suggested to be important signals involved in interactions between spiders and other organisms. There are several hypotheses about the functions of signaling by decorations, among which prey attraction had received much support, but empirical evidence regarding predator defense is controversial. In this study, we conducted field experiments to investigate the effects of spider decoration and coloration on insect interception rates of webs built by Argiope aemula and to evaluate whether presence of decorations may decrease predation risk of spiders. Decorated webs with spiders present had the highest prey interception rate, followed by undecorated webs with spiders, and then undecorated webs without spiders. Such results indicated that decorations of Argiope spiders functioned as visual lures, and so did spiders' bright body colorations. In the field, almost all wasp attack events occurred on medium-sized spiders rather than on large ones. Moreover, medium-sized Arg. aemula on decorated webs received far more attacks than those on undecorated webs. Results of this study thus show that the signals conveyed by decorations can visually lure prey but at the cost of an increased predation risk.