Reproductive diapause influences spermatogenesis and testes' size in the diplochronous wolf spider Allocosa senex (Lycosidae, Araneae) - A case study using a non-experimental approach.

Seasonality considerably impacts on the life of organisms and leads to numerous evolutionary adaptations. Some species face seasonal changes by entering a diapause during different life stages. During adulthood, a diapause in the non-reproductive period can affect male gametogenesis as, for example, it occurs in insects. Spiders are distributed worldwide and show a variety of life cycles. However, data on spiders' life cycles and seasonal adaptations are limited. Here, we explored the effect of reproductive diapause in a seasonal spider for the first time. We used the South American sand-dwelling spider Allocosa senex as a model as this species is diplochronous, meaning that individuals live two reproductive seasons, with juveniles and adults overwintering in burrows. It has been observed that individuals of this species reduce their metabolism during the non-reproductive season, diminishing prey consumption and locomotion to a minimum. This species is also well-known for exhibiting wandering and courting females and sedentary males. We analyzed spermatogenesis throughout the male's life cycle and described the male's reproductive system and spermiogenesis using light and transmission electron microscopy. We found that spermatogenesis in A. senex is asynchronous and continuous. However, when males face the non-reproductive season, the late spermatogenic stages and spermatozoa decline, causing an interruption but not a total arrest of this process. This seasonality is also reflected in smaller testes' size in males from the non-reproductive season than in other periods. The mechanisms and constraints are unknown, but they could be related to the metabolic depression during this life cycle period. Since sex-role reversal apparently sets a low-intensity sperm competition scenario compared with other wolf spiders, surviving two reproductive seasons may balance mating opportunities by distributing them between both periods. Thus, the partial interruption of spermatogenesis during diapause could allow new mating encounters during the second reproductive season.

Breaking the cliché: sex reversal in size dimorphism and mobility in South American Allocosinae (Lycosidae) spiders

Typically, females and males are expected to have characteristic sexual strategies and patterns of size dimorphism, but these generalizations are subject to exceptions. The occurrence of atypical cases has been related to species or populations from environments under strong physical, ecological and/or social constraints. Allocosa marindia and Allocosa senex are two coastal spiders (Lycosidae: Allocosinae) with reversal in sex roles and sexual size dimorphism. Males are larger than females, and females are the mobile sex that initiates courtship. It is unclear whether the occurrence of non-typical sexual traits in Allocosinae spiders is correlated with coastal habitats. Our aim was to study sexual size dimorphism and surface mobility in Allocosinae spiders from different habitats throughout South America. We revised specimens from scientific collections and performed 3-day samplings to collect individuals and determine nocturnal surface mobility. We analysed a total of 1071 Allocosinae adult individuals from 18 species and/or morphotypes. Our results revealed new species inhabiting coastal habitats with reversal in sexual size dimorphism and higher nocturnal surface activity in females; however, not all coastal species shared those characteristics. Future studies will focus on studying other ecological, physiological and/or phylogenetic factors that could be shaping the origin and maintenance of sex role reversal in Allocosinae.

Challenging monogamy in a spider with nontraditional sexual behavior.

Each species and sex can develop different reproductive strategies to optimize their fitness while assigning reproductive effort. Allocosa senex is a sex-role reversed spider whose males construct long burrows in the sand. They wait for wandering females to approach, assess their sexual partners and donate their constructions to females after copulation. Females stay in the burrow and lay their egg-sac. When offspring are ready for dispersion, females leave the burrow and gain access to new mating opportunities. Males are choosy during mate courtship, preferring to mate with virgin females over copulated ones, which can even be cannibalized if males reject them. This situation turns new mating opportunities dangerous for copulated females. We wondered whether a copulated female inside the previous mate's burrow responds to courtship from a new male and if this new male can copulate, avoiding burrow construction costs. We also explored whether courtship and copulation behaviors during the first sexual encounter affected the probability of occurrence of a second copulation. For that purposes we exposed copulated females inside male burrows to new males (non-donor males). Males could locate and court females inside the previous male's burrow, and females accepted a second copulation. Hence, A. senex females are not monogamous as was expected but increase their reproductive success by copulating with non-donor males. Also, males can develop opportunistic tactics, suggesting a more dynamic mating system for this sex-role reversed spider than assumed.

No pain, no gain: Male plasticity in burrow digging according to female rejection in a sand-dwelling wolf spider.

Behavioral plasticity allows individuals to reversibly respond to short-term variations in their ecological and social environment in order to maximize their fitness. Allocosa senex is a burrow-digging spider that inhabits the sandy coasts of South America. This species shows a reversal in typical sex roles expected in spiders: females are wanderers that visit males at their burrows and initiate courtship. They prefer males with long burrows for mating, and males prefer virgin over mated females. We tested whether female sexual rejection induced males to enlarge their burrows and if female reproductive status affected males' responses. We exposed males who had constructed burrows to: a) virgin females or b) mated females, (n=16 for each category). If female rejection occurred, we repeated the trial 48h later with the same female. As control, we maintained a group of males without female exposure (unexposed group, n=32). Rejected males enlarged their burrows more frequently and burrows were longer compared to unexposed males. However, frequency and length of enlargement did not differ according to female reproductive status. Males of A. senex showed plasticity in digging behavior in response to the availability of females, as a way to maximize the possibilities of future mating.

Geographical variation in sexual behavior and body traits in a sex role reversed wolf spider.

Mating partners need to recognize, assess each other, and exchange information through behavioral events that occur before, during, and after mating. Sexual signals, as well as life history traits, are influenced by selective pressures and environmental factors that can vary across distant geographical areas. Allocosa senex is a sand-dwelling wolf spider which constructs burrows along the sandy coasts of Argentina, Brazil, and Uruguay. Females are the mobile sex that searches for males and initiates courtship. They prefer males which construct longer burrows, and males prefer virgin females in good body condition. The objective of this study was to compare sexual behavior patterns, as well as body characteristics and burrow dimensions, between two geographically distant locations of A. senex, one in Uruguay (Uruguayan location) and the other from central Argentina (Argentinean location). We found differences in the number of male abdominal vibrations, male and female touches during mating, and number of erections of male leg spines, which all were higher in matings of Argentinean pairs. On the other hand, male body mass and female body condition were higher in Uruguayan individuals. The wide distribution of A. senex could be determining variations in the biotic and abiotic features that affect the species, generating differences in the strength of selective forces acting on individuals from the two studied locations.

Effect of gregarines (Apicomplexa: Sporozoa) on survival and weight loss of Victorwithius similis (Arachnida: Pseudoscorpiones).

Gregarines are common intestinal parasites of numerous invertebrate groups. Their effects on host viability and development have been a matter of debate. Although they may not be lethal to the host, they can be harmless commensals, by affecting adaptive traits, or have a beneficial relationship with the host. This study focused on determining prevalence, intensity, and change in infection intensity over time by septate gregarines, and monitoring the effects on survival and weight loss in the pseudoscorpion Victorwithius similis. Individuals (n=24 females, n=55 males and n=41 tritonymphs) were captured in the field, transported to the vivarium and bred under laboratory conditions. A high prevalence of infection was found, with 77.27% of females, 62.50% of males and 73.53% of tritonymphs harboring intense infections. Of the infected pseudoscorpions, 62% of females, 58% of males and 71% of tritonymphs did not show changes in infection intensity over time. The group that maintained intense infections survived longer than those with less intense infections (χ(2)=8.642; p=0.035). Most of the results obtained indicate that relationship studied between gregarines and the pseudoscorpion V. similis might be a case of commensalism. This would explain why the infection level and prevalence was very high, as well as the apparent lack of direct costs to highly infected individuals those with infections.