REPEATED EVOLUTION OF MALE SACRIFICE BEHAVIOR IN SPIDERS CORRELATED WITH GENITAL MUTILATION

According to sexual cannibalism theory, male complicity in terminal mating can be adaptive when the male's future reproductive value is low relative to the benefits of self sacrifice. Spiders and insects that exhibit male sacrifice behavior (either complicity in cannibalism or spontaneous death associated with copulation) often also have male genitalia that stereotypically become broken or disfigured the first time they are used for copulation, potentially lowering his future reproductive value. Theoretical work on monogamy has identified male bias in the effective sex ratio as a precursor to the evolution of monogamy (including male sacrifice) as an adaptive form of paternity protection. Using phylogeny-based statistics and drawing on several phylogenetic studies of araneoid spiders, I investigate relationships between male sacrifice behavior, genital mutilation, extreme sexual size dimorphism, and the accumulation of multiple males in the female web (as an indicator of a male-based effective sex ratio). This investigation focuses on araneoid spiders because several independent origins of sacrifice behavior are known for this group and the phylogenetic structure of the lineage is relatively well studied. I report that male genital mutilation is significantly correlated with sacrifice behavior and argue that this finding is consistent with sexual cannibalism theory. Male sacrifice behavior is also correlated with male accumulation, a result that is consistent with theoretical work on the evolution of monogamy. Male accumulation and extreme sexual size dimorphism are correlated suggesting that sex-based differences in maturation time can lead to a male biased effective sex ratio. Similar patterns of correlated characters may hold for some insect taxa. Studying traits that have appeared independently in multiple lineages is a powerful method for developing general theories about the evolution of biological phenomena.

Ultrastructure of the major ampullate gland of the black widow spider, Latrodectus hesperus

Silk production in the spider occurs within specialized glands that are capable of the synthesis of large fibrous proteins and the post-translational processing of those proteins to form an insoluble fiber. The major ampullate gland of Latrodectus hesperus (black widow) is similar in morphology to those found in the Araneid spiders. The tail domain of this gland is highly protein synthetic, giving rise to a core, fibrous protein product. In addition to a storage function, the ampulla region also synthesizes and exports an electron dense material that appears to form a 'coat' surrounding the silk generated within the tail. The duct of the gland consists of at least two distinct cell types: one type contains 'honeycomb' vesicles of unknown function, while the other possesses elaborate apical microvilli that may be involved in the reabsorption of water and subsequent dehydration of the silk. As the silk product transits through these various stages of assembly, it can been seen to undergo a condensation or concentration, possibly reflecting the influence of both the shear forces induced by movement into the duct and the dehydration that is thought to occur there.

Black widow spider Latrodectus cinctus (Araneae: Theridiidae) new to Liberia--savanna species in the forest zone

The first record of the African black widow spider, Latrodectus cinctus Blackwall, 1865 (= L. indistinctus Pickard-Cambridge, 1904) from Liberia is presented. It is a further record of a savanna species in the forest zone of West Africa. Increasing deforestation may cause expansion of the ranges of savanna-inhabiting animal species into the forest zone.

Black and brown widow spider bites in South Africa. A series of 45 cases

Cases of black widow (Latrodectus indistinctus) and brown widow (L. geometricus) spider bites referred to the Tygerberg Pharmacology and Toxicology Consultation Centre from the summer of 1987/88 to the summer of 1991/92 were entered into this series. Of a total of 45 patients, 30 had been bitten by black and 15 by brown widow spiders. It was evident that black widow spider bites caused a more severe form of envenomation than brown widow bites, characterised by generalised muscle pain and cramps, abdominal muscle rigidity, profuse sweating, raised blood pressure and tachycardia. The symptoms and signs of brown widow bites were mild and tended to be restricted to the bite site and surrounding tissues. Conditions which should be considered in the differential diagnosis include cytotoxic spider bite, scorpion sting, snakebite, acute abdominal conditions, myocardial infarction, alcohol withdrawal and organophosphate poisoning. To prevent the development of complications, the administration of black widow spider antivenom is recommended in severe cases because untreated latrodectism could become protracted, without improvement, for several days.

Structure of the cuticle of the common house cricket with reference to the location of lipids

Cuticle segments from the thorax, abdomen, and jumping legs of the house cricket, Acheta domesticus, were examined using histological techniques for light microscopy, scanning and transmission electron microscopy, and direct examination of frozen-fractured cuticle. The surface of untreated cuticle is covered by a lipid film which obscures fine surface detail. Standard EM preparative procedures, as well as washing the cuticle with ethanol before examination, remove this film exposing previously covered openings to dermal gland ducts and wax canals. An epicuticle, exocuticle, mesocuticle, endocuticle, and a deposition layer were present in all transverse sections of cuticle. Light microscopy showed that the exocuticle and mesocuticle are heavily impregnated with lipids, whereas there is little lipid associated with the endocuticle. Frozen-fractured cuticle clearly shows the 'plywood' structure of the meso- and endocuticle, while the exocuticle fractures as if it were a solid sheet. The epicuticle is composed of a dense homogeneous layer, cuticulin, outer epicuticle, and the outer membrane. Superficial wax was detected only in cuticle samples prepared using vinylcyclohexane dioxide as a polar dehydrant. The results were used to construct a comprehensive model of the cuticle of A. domesticus.

Black widow spider bites

Black widow spiders (Latrodectus species) are found worldwide. Envenomation of humans usually occurs as the result of chance intrusion into the spider's domain by the human. The venom is regarded as one of the most potent biologic toxins. The venom acts by destabilization of cell membranes and degranulation of nerve terminals resulting in the release of neurotransmitters. The clinical picture is characterized by painful muscle spasm and hypertension. The very young, the elderly or enfeebled, and those with cardiovascular disease are at greatest risk. While not always necessary, the most effective treatment is specific antiserum. Muscle relaxants, analgesics and intravenous calcium are useful adjuvant treatment.

Review of the medically important spiders in Southern Africa

Known and suspected medically important Southern African spiders are reviewed in terms of their distribution, identification, action of the venom and treatment of the bite. Simple diagnostic characteristics of each species are provided to assist the non-specialist in identifications.