Macarena González

Reversed cannibalism, foraging, and surface activities of Allocosa alticeps and Allocosa brasiliensis: two wolf spiders from coastal sand dunes

Abstract Environments where prey availability is scarce or highly variable have been reported as potential settings for the occurrence of paternal investment and sex-role reversal (choosy males and competitive, courting females). Allocosa brasiliensis (Petrunkevitch 1910) and Allocosa alticeps (Mello-Leitão 1944) are two sand-dwelling wolf spiders that construct burrows along the Uruguayan coastline. Both species present a reversal in typical sex roles and size dimorphism. In the present study, we investigated foraging behavior and population density of both species by performing monthly samplings at the field during one year. Both Allocosa are general and highly opportunistic predators, varying their diet according to prey availability. The three most represented common prey belonged to Araneae, Diptera, and Hymenoptera (Formicidae). There were high levels of cannibalism in A. brasiliensis and, furthermore, males were observed frequently preying on conspecific adult females. Our discussion of the results based on hypotheses about food limitation and sex-role reversal contributes to our understanding of Allocosa species and establishes them as models for future evolutionary, behavioral, and ecological studies.

Sexual dimorphism in chelicerae, forelegs and palpal traits in two burrowing wolf spiders (Araneae: Lycosidae) with sex-role reversal

Allocosa alticeps and Allocosa brasiliensis are two sex-role-reversed spiders. Females locate males and initiate courtship. Copulation occurs inside male burrows and after copulation the males deliver their burrows to the females. We explored the occurrence of differences in morphological traits related to sex roles in both Allocosa species and compared the results with two non-burrowing wolf spiders with typical sex roles. We measured the length of the forelegs tibia-patella and the chelicerae. Scanning electron micrographs of palpal tarsus distal sections were taken. Males showed higher values than females in all the traits considered. Adult and penultimate males lacked true claws compared with juveniles and females, but showed modified spines. The palpal organ was more proximal to the tibia compared with the non-burrowing lycosids considered in this study. Spines and palpal organ location could be associated with more effective digging. We discuss how natural and sexual selection could interact on morphology in this scenario.

Behavioural evidence of male volatile pheromones in the sex-role reversed wolf spiders Allocosa brasiliensis and Allocosa alticeps.

The use of chemical signals in a sexual context is widespread in the animal kingdom. Most studies in spiders report the use of female pheromones that attract potential sexual partners. Allocosa brasiliensis and Allocosa alticeps are two burrowing wolf spiders that show sex-role reversal. Females locate male burrows and initiate courtship before males perform any detectable visual or vibratory signal. So, females of these species would be detecting chemical or mechanical cues left by males. Our objective was to explore the potential for male pheromones to play a role in mate detection in A. brasiliensis and A. alticeps. We designed two experiments. In Experiment 1, we tested the occurrence of male contact pheromones by evaluating female courtship when exposed to empty burrows constructed by males or females (control). In Experiment 2, we tested the existence of male volatile pheromones by evaluating female behaviour when exposed to artificial burrows connected to tubes containing males, females or empty tubes (control). Our results suggest the occurrence of male volatile pheromones that trigger female courtship in both Allocosa species. The sex-role reversal postulated for these wolf spiders could be driving the consequent reversal in typical pheromone-emitter and detector roles expected for spiders.

Spatial distribution, burrow depth and temperature: implications for the sexual strategies in two Allocosa wolf spiders

Allocosa brasiliensis and Allocosa alticeps are two burrowing wolf spiders that inhabit Uruguayan sandy coasts. Male efficient digging is necessary because copulation and oviposition occur inside their burrows. We examined burrow distribution, density and temperature variation according to burrow depth. Adult burrows were more frequent at the slope of sand-dunes in A. alticeps and at the base in A. brasiliensis. The base provides better digging conditions, whereas A. alticeps adults could prefer the slope to avoid intra-guild predation. Temperature buffering increased with depth, providing thermal stability in such a harsh environment as coastal dunes.

Differences in sexual behavior of two distant populations of the funnel-web wolf spider Aglaoctenus lagotis

Generally, sexual repertoire within a species is conserved, but frequencies of occurrence of sexual behavioral acts often vary, and wide geographic distributions may favor these variations. Aglaoctenus lagotis is distributed along South America and belongs to Sosippinae, a subfamily of wolf spiders that builds funnel webs. Previous reports, based on different populations, suggested variations in sexual behavior and life cycle. Our objective was to describe and compare the sexual behavior of two populations of A. lagotis: ‘Southern Uruguay’ (SU) and ‘Central Argentina’ (CA). We carried out intrapopulation trials, in the laboratory, with 15 female–male pair matings. The most representative courtship acts in SU were web-stretching, striding-forward and forelegs-elevating, whereas in CA they were alternate-waving, web-stretching and leg-tapping. Juddering, forelegs-elevating and striding-forward were exclusive for SU, while alternate-waving and simultaneous-waving were exclusive for CA. We also found differences in copulatory characteristics such as frequencies of insertions and ejaculations. We documented body-shaking during copulation for the first time. Some sexual acts were exclusive of each population, while the shared ones differed in pattern and frequencies of occurrence. In addition to variations in sexual periods, these differences may favor divergence processes or an exceptional high level of flexibility in the sexual behavior of A. lagotis.

Strong phenological differences between two populations of a Neotropical funnel-web wolf spider

Comparisons of phenological patterns among populations within a species are uncommon in arachnids. Aglaoctenus lagotis is a wolf spider that lives in funnel-webs across South America. The aim of this study was to describe the phenological patterns of two distant populations of A. lagotis (central Argentina, CA, and southern Uruguay, SU). Individuals of each population were sighted along transects, every month for two years. The CA and SU populations differed in their phenological patterns (Wald χ2 = 966.94, df = 66; p <0.001). The CA population showed a spring–summer unified reproductive season and immature individuals overwintered. SU showed the sexual period during autumn, the maternal period during spring–summer and the females, mostly mated, overwintered. These strong differences imply temporal isolation in mating possibilities between both populations. The differences encountered could be due to phenotypic plasticity or have a phylogenetic basis. Interpopulation studies of other features of A. lagotis would show whether they also vary, suggesting speciation.

Timing of female sexual unreceptivity and male adjustment of copulatory behaviour under competition risk in the wolf spider Schizocosa malitiosa

Males can change their copulatory or sperm transfer patterns in response to sperm competition risk. Schizocosa malitiosa performs long copulations, which include two consecutive patterns (Patterns 1 and 2). Virgin females are very sexually receptive, but mated females diminish their receptiveness. Female unreceptivity has been attributed to the action of receptivity-inhibiting substances, mainly transferred during Pattern 1. We tested: (1) if females who mated only with Pattern 1 were immediately unreceptive; (2) male and female behaviours when the copulating couple was exposed to another male. For (1), we interrupted mating when Pattern 1 finished and immediately exposed the female to a second male. For (2), we introduced a second male when the couple was starting (Ei) or finishing copulation (Li). Females were unreceptive immediately after finishing Pattern 1. Males from Ei and Li dismounted and approached the second males. Ei males diminished the frequencies of insertion after perceiving the presence of a second male and dismounted less frequently when copulating with heavy females. The study provides insights about the timing of sexual unreceptivity in S. malitiosa under possibilities of sperm competition, discussing male adjustment of copulatory behaviour in the presence of rival males.

Funnel-web construction and estimated immune costs in Aglaoctenus lagotis (Araneae: Lycosidae)

Abstract Constructing webs for survival is rare in wolf spiders. However, some species, postulated as basal in the family, live in funnel-webs. Aglaoctenus lagotis (Holmberg 1876), a South American lycosid, lives permanently in webs. It is virtually unknown how web construction occurs for this species and the few other lycosid weavers. Also, costs associated with construction have not been studied, although funnels are suggested to be particularly costly webs. This study describes the funnel-web construction behavior of A. lagotis (Lycosidae: Sosippinae) and measures its costs in subadult and adult individuals. We recorded web construction, effects of sealing spinnerets in weaving activity, and immune costs of weaving (measuring melanization of an implant) in individuals allowed to weave and prevented from weaving. Construction consisted of three alternating behaviors: deposition of thick threads with a radial orientation and prolonged attachments (mainly involving the anterior spinnerets); deposition of swaths of fine threads without consistent orientation and with short attachments (mainly involving the posterior spinnerets); and motionlessness. No sticky threads are present in the web. The thick threads have a supporting function and the fine threads have a filling function. Subadults and males allowed to weave reduced their immune response compared with those prevented from weaving; no such relationship was observed for females. Males presented the weakest immune response, followed by subadults and females. The web construction process showed greater similarity with agelenid spiders than with the only other lycosid studied, Sosippus janus Brady 1972, and appears to be a costly activity, especially for males.

Silk release by copulating Schizocosa malitiosa males (Araneae, Lycosidae): a bridal veil

Abstract We report release of silk threads by males of Schizocosa malitiosa (Tullgren 1905) during copulation. The silk is deposited over the females front legs and near her mouthparts. Possible functions for this behavior could be inhibiting female aggressiveness through chemicals deposited on the silk, inducing female catalepsy during copulation or repelling other males. We propose future studies manipulating male silk release to test these hypotheses.

Are multiple copulations harmful? Damage to male pedipalps in the funnel-web wolf spider Aglaoctenus lagotis (Araneae: Lycosidae)

Abstract Damage to genital structures during copulation has been reported in about twenty spider families, but never in Lycosidae. Aglaoctenus lagotis (Holmberg, 1876), a South American wolf spider, is one of the few that live their whole lives in funnel-webs. This work reports on the damage to pedipalpal bulbs observed in males of the “southern Uruguay” form of A. lagotis with multiple copulations. Observed damage consists of the irreversible expansion of the hematodocha and even its explosion. A high copulation cost resulting from multiple and long-lasting copulations could be causing this damage, affecting the mechanism of sperm transference in a definitive way. This is the first report of pedipalp damage in lycosids, and also the first report of damage involving the hematodocha in spiders.