Carmen Viera

Daring females, devoted males, and reversed sexual size dimorphism in the sand-dwelling spider Allocosa brasiliensis (Araneae, Lycosidae)

Sexual selection theory predicts that a higher investment in offspring will turn females into the selective sex, while males will compete for accessing and courting them. However, there are exceptions to the rule. When males present a high reproductive investment, sex roles can reverse from typical patterns, turning males into the choosy sex, while females locate males and initiate courtship. In many spiders, males are smaller than females, wandering in search of sedentary females and maximizing the number of copulations. In the present study, we present findings on the sand-dwelling wolf spider, Allocosa brasiliensis, evidencing a reversal in typical courtship roles reported for the first time in spiders. Males were bigger than females. Females located males and initiated courtship. Copulation always occurred in male burrows and took place mainly in long burrows. Males donated their burrows to the females after copulation, closing the entrance before leaving with female cooperation from inside. Males would provide females with a secure place for ovipositing, being exposed to predation and diminishing their future mating possibilities until constructing a new burrow. The cost of vacating the burrow and losing the refuge in an unpredictable habitat, such as sand dunes, would explain the courtship roles reversal in this spider species. Results turn A. brasiliensis as a promising model for discussing the determinants of sex roles and the pressures that drive their evolution and maintenance.

Pseudocopulation and male-male conflict elicited by subadult females of the subsocial spider Anelosimus cf. studiosus (Theridiidae)

In spider species with first male sperm priority, males guard subadult females as a tactic for improving their paternity. Preliminary observations in Anelosimus cf. studiosus , a subsocial species from Uruguay, showed that males court and guard subadult females. To elucidate the sexual tactics of this species, we placed two adult males with one adult female, and two other males with one subadult (penultimate) female under laboratory conditions (20 trials for each female status/group). Males courted both adult and subadult females, and subadult females were as receptive as adults, adopting the acceptance posture and pseudocopulating with males. Males performed conspicuous fights under both situations. Winner males copulated (or pseudocopulated), while the losers remained as satellites. Some females remated with satellite males. Subadult female behaviour simulating the adult receptive display could be a cheating tactic for retaining males and eliciting combats. Male-male fights and the guarding of subadult females suggest the occurrence of first male sperm priority, but the persistence of satellite males also suggests second males have some degree of paternity success. Competition could be caused by an asynchrony in female maturation at the beginning of the reproductive season, turning adult females in to the scarce resource.

REGURGITATION AMONG PENULTIMATE JUVENILES IN THE SUBSOCIAL SPIDER ANELOSIMUS CF. STUDIOSUS (THERIDIIDAE): ARE MALES FAVORED?

Abstract Regurgitation from adult females towards juveniles is a well known phenomenon in social spiders. However, occasional observations in Anelosimus cf. studiosus from Uruguay showed the occurrence of food transfer also between large juveniles. We experimentally tested if well fed penultimate females were capable of regurgitating fluids to starved males, and if well fed penultimate males were capable of regurgitating fluids to starved females. Other isolated and starved penultimate males and females were used as controls. Starved males and females of the experimental groups significantly increased their body weight, whereas body weight decreased in controls. Males increased their weight more than females. We conclude that both well fed penultimate males and females can feed other starved subadults, but when given access to members of the opposite sex, males benefit than females. This bias in the regurgitation exchange among subadults could contribute to accelerate the maturation of males.

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.

Progeny, development and phenology of the sub-social spider Anelosimus cf. studiosus (Araneae, Theridiidae) from Uruguay

We studied the life cycle of Anelosimus cf. studiosus under field and laboratory conditions. Nests were collected monthly from the field during a whole year for estimating the phenology of the species. Egg‐sac production, maternal care until spiderling emergence and instars of development until adulthood were recorded in the laboratory. This species showed an annual cycle. Each female built a mean of 2.7 egg‐sacs, averaging 32 spiderlings per egg‐sac. Mothers fed juveniles through regurgitations and shared whole captured prey. The sex‐ratio from reared penultimate individuals was biased towards females (1.9:1), and males reached adulthood earlier than females. According to our findings, only one clutch would develop per year in the field (univoltine strategy), with mothers focusing efforts on the first clutch allowing matriphagy. Resumen Se estudió el ciclo vital de Anelosimus cf. studiosus a campo y laboratorio. Los nidos fueron recolectados mensualmente a campo durante un año para determinar la fenología de la especie. En el laboratorio se registraron la producción de ootecas, el cuidado maternal hasta la emergencia de las arañitas y los estadios de desarrollo hasta la adultez. La especie mostró un ciclo anual. Cada hembra generó en el laboratorio una media de 2.7 ootecas, promediando 32 arañitas por ooteca. Las madres alimentaron a los juveniles mediante regurgitaciones y presas capturadas. La proporción sexual desde individuos penúltimos fue sesgada hacia las hembras (1.9:1), y los machos alcanzaron la adultez antes que las hembras. De acuerdo a nuestros resultados, se desarrollaría una única camada por año en el campo (estrategia univoltina) y la madre favorecería la primera puesta permitiendo la matrifagia.

Post-Embryonic Development of the Sub-Social Spider Anelosimus cf. Studiosus (Araneae, Theridiidae)

Summary Post-embryonic development has been studied exclusively in solitary spiders. Sociality could minimise development inside the egg-sac, because premature spiderlings would be cared for cooperatively. Here, we describe the postembryonic development of a Uruguayan sub-social spider, Anelosimus cf. studiosus. Fifteen egg-sacs were removed from their mothers, opened and the eggs raised in humid chambers. Nine females with their egg-sacs were kept as controls. Three consecutive instars were observed: prelarva, larva and nymph. Prelarvae were detected on average 16.58 days after oviposition, and moulted to larvae 1.38 days later. The larval period lasted 2.85 days before moulting to the first nymphal instar, giving a total of 20.73 days on average after oviposition. Spiderling emergence from the egg-sac in the control group took 20.77 days. The results suggest that the mother opens the egg-sac immediately when she perceives nymphal movements. No reduction in the number or duration of instars was observed compared with solitary theridiid spiders, but it is suggested that this might occur in other more social theridiid spiders.

Trophic Niches and Trophic Adaptations of Prey-Specialized Spiders from the Neotropics: A Guide

Spiders are the most diversified group of terrestrial predators. They employ a wide variety of feeding strategies, and exploit several prey types, from invertebrates up to small vertebrates. Many studies on the trophic ecology of spiders have focused on generalist and euryphagous species. Thus, our knowledge of prey specialist (and stenophagous) species is very limited despite the high number of endemic species occurring in the Neotropics, many of which are most probably specialized. In this chapter, we provide a guide on how to study the trophic niches of spiders in order to encourage other researchers to investigate prey-specialized species. At the beginning, we define the term trophic niche and identify its dimensions (prey type, size, and availability). We critically outline methodological approaches on how to study it. A narrow trophic niche is paralleled by the evolution of specific cognitive, behavioural, metabolic, morphological, and venomic adaptations used in prey capture. We provide an overview of these adaptations and focus on approaches to reveal them. On the basis of an extensive bibliographic review, we summarize the current state-of-the-art with respect to knowledge on the trophic ecology of Neotropical spiders, with particular emphasis on specialists. Finally, we provide recommendations for future research.

Diet composition and prey selectivity by the spider Oecobius concinnus (Araneae: Oecobiidae) from Colombia

Abstract The feeding ecology of most Oecobius species is poorly understood; nevertheless, the limited literature available suggests that obligate myrmecophagy is common in this genus. Recent evidence suggests that some species might do not share this trait, but could be locally specialized predators. We describe the diet and prey selectivity of the spider Oecobius concinnus (Simon 1893), a common pantropical species. Samplings of actual and potential prey for this species were made in the city of Ibagué, Colombia. Ants were the dominant prey. Other prey included in its diet were dipterans. These results suggest that O. concinnus is not an obligate myrmecophagous spider. Nevertheless, further studies will evaluate other aspects of the biology of this species to reveal its trophic strategy.

Comparison of the capture efficiency, prey processing, and nutrient extraction in a generalist and a specialist spider predator

Predators are traditionally classified as generalists and specialists based on the presence of adaptations that increase efficiency of prey capture and consumption and selection of particular prey types. Nevertheless, empirical evidence comparing foraging efficiency between generalist and specialist carnivores is scarce. We compared the prey-capture and feeding efficiency in a generalist and a specialist (araneophagous) spider predator. By using two related species, the generalist Harpactea rubicunda (Dysderidae) and the specialist Nops cf. variabilis (Caponiidae), we evaluated their fundamental trophic niche by studying the acceptance of different prey. Then, we compared their predatory behavior, efficiency in capturing prey of varying sizes, feeding efficiency, and nutrient extraction. Nops accepted only spiders as prey, while Harpactea accepted all offered prey, confirming that Nops is stenophagous, while Harpactea is euryphagous. Further, Nops displayed more specialized (stereotyped) capture behavior than Harpactea, suggesting that Nops is a specialist, while Harpactea is a generalist. The specialist immobilized prey faster, overcame much larger prey, and gained more mass (due to feeding on larger prey) than the generalist. Both the specialist and the generalist spider extracted more proteins than lipids, but the extraction of macronutrients in the specialist was achieved mainly by consuming the prosoma of the focal prey. We show that the specialist has more efficient foraging strategy than the generalist.

Loading the male pedipalps: sperm induction in a subsocial spider

Abstract Detailed descriptions of sperm induction are rare in the literature. Anelosimus vierae Agnarsson, 2012 (Theridiidae) is a Uruguayan subsocial spider that lives in communal nests. This paper describes the sperm induction of this species under laboratory conditions. We collected spiders in Montevideo, Uruguay, from different trees and placed them in thirty male and female pairs in Petri dishes to observe the occurrence of sperm induction. We witnessed twenty-two males performing sperm induction after copulation. Sperm web characteristics and description of the males behavior during sperm induction are described.