The jumping spider Saitis barbipes lacks a red photoreceptor to see its own sexually dimorphic red coloration

Examining the role of color in mate choice without testing what colors the study animal is capable of seeing can lead to ill-posed hypotheses and erroneous conclusions. Here, we test the seemingly reasonable assumption that the sexually dimorphic red coloration of the male jumping spider Saitis barbipes is distinguishable, by females, from adjacent black color patches. Using microspectrophotometry, we find clear evidence for photoreceptor classes with maximal sensitivity in the UV (359 nm) and green (526 nm), inconclusive evidence for a photoreceptor maximally sensitive in the blue (451 nm), and no evidence for a red photoreceptor. No colored filters within the lens or retina could be found to shift green sensitivity to red. To quantify and visualize whether females may nevertheless be capable of discriminating red from black color patches, we take multispectral images of males and calculate photoreceptor excitations and color contrasts between color patches. Red patches would be, at best, barely discriminable from black, and not discriminable from a low-luminance green. Some color patches that appear achromatic to human eyes, such as beige and white, strongly absorb UV wavelengths and would appear as brighter “spider-greens” to S. barbipes than the red color patches. Unexpectedly, we discover an iridescent UV patch that contrasts strongly with the UV-absorbing surfaces dominating the rest of the spider. We propose that red and black coloration may serve identical purposes in sexual signaling, functioning to generate strong achromatic contrast with the visual background. The potential functional significance of red coloration outside of sexual signaling is discussed

How Did the Spider Cross the River? Behavioral Adaptations for River-Bridging Webs in Caerostris darwini (Araneae: Araneidae)

Interspecific coevolution is well described, but we know significantly less about how multiple traits coevolve within a species, particularly between behavioral traits and biomechanical properties of animals' "extended phenotypes". In orb weaving spiders, coevolution of spider behavior with ecological and physical traits of their webs is expected. Darwin's bark spider (Caerostris darwini) bridges large water bodies, building the largest known orb webs utilizing the toughest known silk. Here, we examine C. darwini web building behaviors to establish how bridge lines are formed over water. We also test the prediction that this spider's unique web ecology and architecture coevolved with new web building behaviors.We observed C. darwini in its natural habitat and filmed web building. We observed 90 web building events, and compared web building behaviors to other species of orb web spiders.Caerostris darwini uses a unique set of behaviors, some unknown in other spiders, to construct its enormous webs. First, the spiders release unusually large amounts of bridging silk into the air, which is then carried downwind, across the water body, establishing bridge lines. Second, the spiders perform almost no web site exploration. Third, they construct the orb capture area below the initial bridge line. In contrast to all known orb-weavers, the web hub is therefore not part of the initial bridge line but is instead built de novo. Fourth, the orb contains two types of radial threads, with those in the upper half of the web doubled. These unique behaviors result in a giant, yet rather simplified web. Our results continue to build evidence for the coevolution of behavioral (web building), ecological (web microhabitat) and biomaterial (silk biomechanics) traits that combined allow C. darwini to occupy a unique niche among spiders

Mating plugs in polyandrous giants: Which sex produces them, when, how and why?

10.1371/journal.pone.0040939PLoS ONE77

Vrstna diverziteta epigeične favne pajkov matičnega Krasa

The classical Karst (Kras in Slovenian) is a limestone karst plateau of south-western Slovenia and northeastern Italy surrounded by flysch or alluvial areas. We explored surface spider species richness in the Karst by conducting a season-long quantitative inventory of the epigean fauna. By examining three localities, each with three succession-stage sites (grassland, overgrowth, forest) we tested for differences in alpha and beta diversity among different successions based on species incidence data. A total of 90 ethylene glycol pitfall traps (10 traps per each of nine sites) operated between 24. V. 2005 and 20. VII. 2006. We recorded a total of 3681 adult spiders belonging to 136 species, 82 genera and 30 families. Of these 28 species are new records for Slovenia. The observed species richness and total adult spider abundances were highest in the spring and early summer, and among succession stages they were highest in grassland (95 species; 1563 individuals), followed by overgrowth (81 species; 1047 individuals) and forest (64 species; 1071 individuals). By comparing our results with previous pitfall samplings in the Dinaric karst, we conclude that the sampling effort needed for a meaningful estimation of epigean spider diversity was barely sufficient in our study when all data were combined, but completely inadequate in previous samplings. In our study the total species richness was estimated by nonparametric statistics to lie at 181, thus 25 % richer than observed. The spider fauna of Slovenia, including this contribution, currently standing at 615 species, continues to be inadequately known.Matični Kras je apnenčasta planota jugozahodne Slovenije in severovzhodne Italije, obdana večinoma z območji fliša. Z vsesezonskim, kvantitativnim vzorčenjem smo ugotavljali vrstno pestrost površinske favne pajkov na Krasu. Na treh lokalitetah, razdeljenih v tri sukcesijske stopnje (travnik, zaraščanje, gozd), smo na podlagi pojavljanja vrst ugotavljali razlike v alfa in beta diverziteti. Med 24. V. 2005 in 20. VII. 2006 je delovalo skupno 90 etilenglikolskih pasti (10 na vsakem vzorčnem mestu), v katere se je ujelo 3681 odraslih osebkov pajkov, ki pripadajo 136 vrstam, 82 rodovom in 30 družinam. Med temi je 28 vrst prvič zabeleženih v Sloveniji. Diverzitete in abundance so bile najvišje na travnikih (95 vrst; 1563 osebkov), nato na zaraščanjih (81 vrst; 1047 osebkov) in v gozdu (64 vrst; 1071 osebkov). V primerjavi s predhodnimi vzorčenji na Dinarskem krasu je intenziteta vzorčenja v naši raziskavi (vsi podatki združeni) komaj zadovoljiva za oceno vrstne pestrosti površinske favne pajkov, intenziteta v predhodnih vzorčenjih pa popolnoma neustrezna. V naši raziskavi je bilo skupno vrstno bogastvo z neparametrično statistiko ocenjeno na 181 vrst, kar je 25 % več, kot smo jih zabeležili. Favna pajkov Slovenije, ki vključno s to raziskavo šteje 615 vrst, ostaja še vedno nepopolno poznana

Phylogenetic position and composition of Zygiellinae and Caerostris, with new insight into orb-web evolution and gigantism

Gregorič, Matjaž, Agnarsson, Ingi, Blackledge, Todd A., Kuntner, Matjaž (2015): Phylogenetic position and composition of Zygiellinae and Caerostris, with new insight into orb-web evolution and gigantism. Zoological Journal of the Linnean Society 175 (2): 225-243, DOI: 10.1111/zoj.12281, URL: http://dx.doi.org/10.1111/zoj.1228

Orb web features as taxonomic characters in Zygiella s.l. (Araneae: Araneidae)

Volume: 38Start Page: 319End Page: 32

Nephilid spider eunuch phenomenon induced by female or rival male aggressiveness

Volume: 37Start Page: 266End Page: 27