Sexual behavior, cannibalism, and mating plugs as sticky traps in the orb weaver spider Leucauge argyra (Tetragnathidae)

Molecular phylogeny of the orb-weaving spider genus Leucauge and the intergeneric relationships of Leucauginae (Araneae, Tetragnathidae)

The tetragnathid genus Leucauge includes some of the most common orb-weaving spiders in the tropics. Although some species in this genus have attained relevance as model systems for several aspects of spider biology, our understanding of the generic diversity and evolutionary relationships among the species is poor. In this study we present the first attempt to determine the phylogenetic structure within Leucauge and the relationship of this genus with other genera of Leucauginae. This is based on DNA sequences from the five loci commonly used and Histone H4, used for the first time in spider phylogenetics. We also assess the informativeness of the standard markers and test for base composition biases in the dataset. Our results suggest that Leucauge is not monophyletic since species of the genera Opas, Opadometa, Mecynometa and Alcimosphenus are included within the current circumscription of the genus. Based on a phylogenetic re-circumscription of the genus to fulfil the requirement for monophyly of taxa, Leucauge White, 1841 is deemed to be a senior synonym of the genera Opas Pickard-Cambridge, 1896 revalidated synonymy, Mecynometa Simon, 1894 revalidated synonymy, Opadometa Archer, 1951 new synonymy and Alcimosphenus Simon, 1895 new synonymy. We identify groups of taxa critical for resolving relationships within Leucauginae and describe the limitations of the standard loci for accomplishing these resolutions.

Specificity of the female's local cellular immune response in genital plug producing scorpion species

Immune defense is a key feature in the life history of organisms, expensive to maintain, highly regulated by individuals and exposed to physiological and evolutionary trade-offs. In chelicerates, relatively scarce are the studies that relate postcopulatory mechanisms and immune response parameters. This work makes an approximation to the female’s immunological consequences produced after the placement of a foreign body in the genitalia of three scorpions species, two species that normally receive genital plugs during mating (Urophonius brachycentrus and U. achalensis) and one that does not (Zabius fuscus). Here we performed the first morphological description of the natural plugs of the two Urophonius species. We described complex three zoned structure anchored to the female genital atrium and based on this information we placed implants in the genitalia (for eliciting the local immune response) of virgin females of the three species and measured the immune encapsulation response to this foreign body. We found a greater and heterogeneous response in different zones of the implants in the plug producing species. To corroborate the specificity of this immune response, we compared the local genital reaction with the triggered response at a systemic level by inserting implants into the female body cavity of U. brachycentrus and Zabius fuscus. We found that the systemic response did not differ between species and that only in the plug producing species the local response in the genitalia was higher than the systemic one. We also compared the total hemocyte load before and after the genital implantation to see if this parameter was compromised by the immunological challenge. We confirmed that in Urophonius species the presence of a strange body in the genitalia caused a decrease in the hemocyte load. Besides, we find correlations between the body weight and the immunological parameters, as well as between different immunological parameters with each other. Complementarily, we characterized the hemocytes of the three scorpion species for the first time. This comparative study can help to provide a wider framework of the immunological characteristics of the species, their differences and their relationship with the particular postcopulatory mechanism such as the genital plugs.

Communication during copulation in the sex-role reversed wolf spider Allocosa brasiliensis: Female shakes for soliciting new ejaculations?

Traditional studies on sexual communication have focused on the exchange of signals during courtship. However, communication between the sexes can also occur during or after copulation. Allocosa brasiliensis is a wolf spider that shows a reversal in typical sex roles and of the usual sexual size dimorphism expected for spiders. Females are smaller than males and they are the roving sex that initiates courtship. Occasional previous observations suggested that females performed body shaking behaviors during copulation. Our objective was to analyze if female body shaking is associated with male copulatory behavior in A. brasiliensis, and determine if this female behavior has a communicatory function in this species. For that purpose, we performed fine-scaled analysis of fifteen copulations under laboratory conditions. We video-recorded all the trials and looked for associations between female and male copulatory behaviors. The significant difference between the time before and after female shaking, in favor of the subsequent ejaculation is analyzed. We discuss if shaking could be acting as a signal to accelerate and motivate palpal insertion and ejaculation, and/or inhibiting male cannibalistic tendencies in this species.

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

Background

Males usually produce mating plugs to reduce sperm competition. However, females can conceivably also produce mating plugs in order to prevent unwanted, superfluous and energetically costly matings. In spiders–appropriate models for testing plugging biology hypotheses–mating plugs may consist of male genital parts and/or of amorphous covers consisting of glandular or sperm secretions. In the giant wood spider Nephila pilipes, a highly sexually dimorphic and polygamous species, males are known to produce ineffective embolic plugs through genital damage, but nothing is known about the origin and function of additional conspicuous amorphous plugs (AP) covering female genitals.

Methodology

We tested alternative hypotheses of the nature and function of AP in N. pilipes by staging mating trials with varying degrees of polyandry. No APs were ever formed during mating trials, which rules out the possibility of male AP formation. Instead, those females that oviposited produced the AP from a liquid secreted during egg sac formation. Polyandrous females were more likely to lay eggs and to produce the AP, as were those that mated longer and with more total insertions. Our further tests revealed that, in spite of being a side product of egg sac production, AP, when hardened, prevented any subsequent copulation.

Conclusions

We conclude that in the giant wood spider (Nephila pilipes), the amorphous mating plugs are not produced by the males, that repeated copulations (most likely polyandrous) are necessary for egg fertilization and AP formation, and that the AP represents a female adaptation to sexual conflict through prevention of unwanted, excessive copulations. Considering the largely unknown origin of amorphous plugs in spiders, we predict that a similar pattern might be detected in other clades, which would help elucidate the evolutionary interplay of various selection pressures responsible for the origin and maintenance of mating plugs.