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Eggs of black widow spiders in the genus Latrodectus Walckenaer, 1805 (Theridiidae) are known to be toxic when injected into mammals. We surveyed eggs from 39 species of spiders in 21 families to determine if spider egg toxicity is a unique property of widow spiders, or if spider egg toxicity is associated with other spider taxa. Eggs from 13 species of spiders in three families were determined to be highly lethal to mice, eggs from four species in four families were moderately lethal, and eggs from 22 species in 17 families lacked detectable lethality. Egg lethality appears to have evolved multiple times in spiders within the Araneidae, Theridiidae, and Agelenidae, and possibly also within the Tetragnathidae, Pimoidae, and Linyphiidae. These toxins in the various spiders may have differing chemical structures and could represent new sources of toxins that may be of future research interest. [ABSTRACT FROM AUTHOR]

Web designs of young spiders are often less derived than those of older conspecific individuals. This study tested whether this "ontogeny repeats phylogeny" pattern occurs in two species of Latrodectus and two species of the closely related genus Steatoda. This pattern was assumed to occur in a recent study of a third Latrodectus species, L geometricus, which attempted to deduce a probable evolutionary derivation of gum-foot webs of theridiids on the basis of ontogenetic changes. We found the same basic ontogeny repeats phylogeny ontogenetic pattern in all four species, suggesting that the previous suppositions were justified. As expected, the webs of the young instars of the two Latrodectus species were more similar than those of the adults, and were more similar to those of young than to those of adults of L. geometricus. One apparently derived trait of L. mirabilis, attaching prey remains as camouflage for the spider in the central portion of the web, did not change during ontogeny, and was present in even the webs of first-instar spiderlings. Field observations of L. mirabilis suggest that the ontogenetic change from light to darker abdominal color patterns that occurs in many Latrodectus species may result from changes in selection for camouflage associated with ontogenetic changes in web designs and the spiders' resting sites. The webs of Steatoda also fit the ontogenetic pattern: at least some ontogenetic changes in both species involved younger spiders having less derived traits than those of adults. The webs of young Steatoda spiders were more derived in some respects than those of the early instars of Latrodectus [ABSTRACT FROM AUTHOR]

Spiders spin a variety of task-specific silk fibers, each composed of one or more unique proteins synthesized within specialized glands in the spider's abdomen. Tubuliform glands are the source of the large diameter silk fibers used by many species in the construction of egg cases. Unlike other silk glands that synthesize protein throughout a spider's lifetime, the tubuliform glands synthesize silk in association with the maturation of oocytes, culminating in the production of an egg case. In the Western black widow, Lactrodectus hesperus Chamberlin & lvie (1935), egg case fibers are composed of at least three proteins: tubuliform spidroin 1(TuSpl), egg case protein-1/ECP-1), and egg case protein-2 (ECP-2). Here, we present the first study to quantify the pattern of transcription for these three genes in a developmental series of tubuliform glands from L. hesperus. All three transcripts increase in abundance prior to the production of an egg case, but at different time points. After egg case production, silk transcripts are still detectable in the tubuliform glands. Relative abundance of TuSpl mRNA is several orders of magnitude higher than that of ECP-1 and ECP-2 at almost every stage. The relative abundance of silk transcripts across the reproductive life history of black widows suggests differential regulation of silk gene transcription within tubuliform glands. [ABSTRACT FROM AUTHOR]

We used experimental manipulations to test adaptive explanations for the courtship display of the male widow spider, Latrodectus pallidus O. Pickard-Cambridge 1872. Two hypotheses have been suggested to explain a long and complex male display: a) Cooperation of males and females in the effort to physically stimulate the female. As the time of male arrival is not predictable, females may delay sexual readiness until the appearance of a courting male, b) Conflict between males and females regarding the display cost. Females impose on the males an energetically costly display that may last several hours as a test of their quality. To test both hypotheses, we manipulated the previous experience of either the male or the female. We presented naive or experienced males (males that had courted and were accepted by females but were prevented from copulating) to females that were either naive or experienced (had been courted by a male but prevented from copulating). We also presented naive males to mated females. Following the stimulation hypothesis, courted females were presumed to have been stimulated to mate and thus were expected to accept non-courting males as mates. Both naive and mated females, however, were expected to await male stimulation before allowing copulation. In contrast, the conflict of interest hypothesis predicts that the female tests each male for quality indicators and therefore a non-courting male should not be accepted as a mate. Mated females, however, should apply a less stringent test to courting males. Our results show that 1) naive females prevented males that did not perform a full courtship display from entering the nest and mounting; 2) naive males courted virgin females with the full display, independent of the female previous courting history; and 3) naive males shortened their courtship when presented with mated females. The results are consistent with the conflict of interest hypothesis. [ABSTRACT FROM AUTHOR]

Quantifying primary sex ratios is necessary for studies in a wide range of areas including adaptive sex ratio modification, population demography, and sex-biased developmental mortality. Adult and penultimate male spiders are easy to sex, due to the great thickening of the male pedipalps, which are used for delivering sperm to the female reproductive tract. However, in many spider species, males and females are apparently monomorphic at hatching, are difficult to rear, and cannibalize their siblings, making assessment of primary sex ratios problematic. One technique for sexing spiders is karyotyping, but this can be challenging and time-consuming, particularly for species with high fecundity, and often requires destructive sampling. Here we report that, although apparently monomorphie, early-instar juveniles of two species of black widow spiders (Latrodectus hasselti Thorell 1870 and Latrodectus hesperus Chamberlin & Ivie 1935) can be sexed reliably. Palp width measurements are significantly different for males and females at the 3rd instar, with the palpi of juvenile females thinner than those of males. Moreover, sex identification with 89-100% accuracy can be achieved by an experienced observer visually inspecting the palpi of 3rd instar spiderlings under a dissecting microscope. Our results suggest that minimal investment in a pilot study can yield an accurate method for sexing juvenile spiders in the laboratory or field. The suitability of this method should be examined in other species with apparently monomorphic spiderlings, particularly those in which adult males have significantly enlarged palpi. [ABSTRACT FROM AUTHOR]