BACKGROUND:When males are selective, they can either reject low-quality females or adjust their reproductive investment in response to traits that indicate female quality (e.g., body size or condition). According to the differential allocation hypothesis, males increase their reproductive investment when paired with high-quality females (positive differential allocation) or increase their reproductive investment when paired with low-quality females (negative differential allocation). This hypothesis has been proposed for monogamous species with biparental care, and most empirical studies focus on birds. Here we used the polygamous spider Paratrechalea ornata, in which males offer prey wrapped in silk as nuptial gifts, to test whether males adjust their reproductive investment in gift size, pre-copulatory and copulatory courtship, and sperm transfer in response to female body condition.RESULTS:Males exposed to females in good body condition added more flies to the gift, stimulated these females longer with abdominal touches during pre-copulatory courtship, and had longer pedipalp insertions than males exposed to females in poor body condition. Female condition affected neither silk investment in nuptial gift wrapping nor the quantity of sperm transferred by males. Finally, females in good body condition oviposited faster after copulation and laid more eggs than females in poor body condition.CONCLUSIONS:We provide experimental evidence that males of a gift-giving spider exhibit positive differential allocation in three key aspects of their reproductive investment: the size of the nutritious gift, duration of pre-copulatory courtship, and duration of pedipalp insertions, which is regarded as a form of copulatory courtship in spiders. This positive differential allocation is likely associated with the benefits of copulating with females in good body condition. These females are more fecund and oviposit faster after copulation than females in poor body condition, which under natural field conditions probably reduces the risk of multiple matings and thus the level of sperm competition faced by the males. As a final remark, our findings indicate that the hypothesis of differential allocation also applies to species with a scramble competition mating system, in which males heavily invest in nuptial gift construction, but not in parental care.

Sexual communication in mate choice scenarios involves nonmutually exclusive functions: species recognition, mate location and mate assessment. Most studies on sexual communication in mate choice have focused on female assessment of conspicuous male traits, such as visual and acoustic signals. Only a few studies have addressed male assessment of female traits, especially those that are inconspicuous to the human sensory system, such as chemical signals. Although chemical signals are important in sexual communication of many arachnids, there is a gap in our knowledge about how male scorpions use these signals to evaluate potential partners. Here we studied sexual communication functions in two scorpion species (Urophonius brachycentrus and Urophonius achalensis) with sympatric populations and synchronic reproduction, where males are under a scramble competition mating system. We addressed the volatile pheromones role in each of the sexual communication functions. We used Y-mazes to test volatile pheromones, exposing males to different female stimulus arrays in single-signal (conspecific only) and mixed-signal (conspecific and heterospecific) contexts. Males located conspecific females through volatile pheromones, and the time spent in proximity to the female was proportional to males' perception of the female's quality, reinforcing the pheromones' function in mate location and assessment in single-signal environments. However, these sexually selected functions were overridden in mixed-signal contexts, in which males could not differentiate conspecific from heterospecific females, suggesting that pheromones do not allow species recognition. This interaction between sexual communication functions can lead to reproductive interference in this sympatric zone. Male indiscriminateness mediated by scramble competition could attenuate pheromones' species recognition function during mate choice. We provide a comprehensive study of the pheromones' role for mate and species recognition in different social contexts in scorpions. We found support for nonindependent and interacting functions of sexual communication, indicating that mate choice is a complex process in scorpions.

In scramble competition mating systems, males do not guard females and females usually mate polyandrously, leading to high levels of sperm competition. Mathematical models predict that males facing sperm competition can either decrease or increase their reproductive effort. To test how male reproductive responses vary according to sperm competition risk, we ran two experiments using the polyandrous gift-giving spider Paratrechalea ornata. First, we tested whether males prefer substrates containing silk of unmated females than substrates containing silk of once-mated females, competitor males or without silk. Males spent more time on substrates containing silk of females but showed no preference for unmated females, which indicates that males may optimize mate search by prioritizing substrates containing cues of potential mating partners. The lack of preference for unmated females suggests that males cannot detect female mating status from silk or that the costs of searching preferentially for unmated females are high in the field. Second, we tested whether males adjust prey-gift construction when facing sperm competition risk. Experimental groups (substrate containing silk of an unmated female and silk of another male vs. substrate containing only silk of an unmated female) did not differ in the frequency of gift construction, latency to gift construction and number of flies added to the gift. However, males facing sperm competition risk constructed gifts with less silk, suggesting the occurrence of a less evident form of male mate choice based on differential allocation of resources to prey-gift. Additionally, given the trade-off between investing in prey-gifts quantity or quality, a lower silk investment should enable males to increase the number of gifts constructed and the number of courted females. Taken together, our results indicate that males detect female and male pheromones on substrate and adjust the construction of prey-gifts in response to apparent sperm competition risk.

Abstract. Trophic subsidy is an ecological process consisting in the transference of nutrients between adjacent habitats, allowing the occupancy of less productive habitats by several species. We tested for the existence of trophic subsidy provided by aquatic plants of temporary ponds in maintaining individuals of the sand dune lizard Liolaemus occipitalis in southern Brazil. This lizard is a sit-and-wait predator restricted to coastal sand dunes. As these sand dunes occur in a mosaic of temporary ponds, we hypothesized the existence of a nutritional/energetic dependence of lizards from adjacent aquatic habitats. Our evaluation was based on carbon and nitrogen stable isotope analysis in association with gut content analysis of lizards sampled along an entire inundation cycle. Stomach contents revealed no seasonal variation in consumed prey item composition. Nevertheless, we detected changes in prey group composition. The volumetric contribution of Diptera increased over inundation classes (increase = 5%; peak = 61%). Carbon and nitrogen stable isotope ratios indicated that the L. occipitalis trophic web is mainly maintained by terrestrial sources. Isotope ratios also indicated the existence of aquatic contributions to tissue formation, but, despite its tendency to increase over the inundation process (10.7–13.3%), this trend lacks statistical support. We conclude that the studied population of L. occipitalis partially depends on trophic subsidy from aquatic sources and that any conservation plan for this endangered lizard species should take into account the preservation of non-habitats like temporary ponds.

The present study aims to describe the ontogenetic changes in the skull of the loggerhead turtle, Caretta caretta by focusing on the stages of development in the western South Atlantic Ocean. Our hypothesis is based on the premise that changes in feeding habits will reflect changes in the shape and/or size of the skull. The existence of changes in skull of the loggerhead turtle were analyzed using traditional and geometric morphometrics on skulls collected from stranded individuals in the southern Brazilian coast. As a general result, a transformation pattern was observed: from younger specimens with smaller, elongated and flattened skulls towards a larger, rounded and more robust skull in older specimens. It is suggested that these skull changes are associated with the diet shift of the loggerhead turtle specimens, providing the skull with greater mechanical resistance and enabling a change in feeding strategy from soft organisms to hard-shelled preys. This result highlights the importance of southern Brazilian coast for the life cycle of the loggerhead turtle. In this region, the individuals undergo the process of ontogenetic diet shift, changing their skull shape to adapt to the newly occupied niche and ensuring the ecological success of the species.

Females not only produce costly gametes, but also store the eggs until laying them, a period called gravidity. The volume that eggs occupy in the female abdomen may decrease female foraging ability by making them slower. Although females of all species are subjected to these potential costs, it remains an unexplored matter in invertebrates. Females of the spiderParatrechalea ornatacarry their egg sac after oviposition and thus represent a unique opportunity to evaluate gravidity costs because females carry an extra volume before and after laying eggs. We conducted foraging ability experiments usingP. ornatafemales on different treatments regarding gravidity and maternal care. We first hypothesized that internal egg load and egg sac carrying decrease female foraging ability. We also hypothesized that greater egg sac size decreases female foraging ability. We found that both internal egg load and egg sac carrying decreased female foraging ability, and females about to oviposit had a similar foraging ability to females carrying an egg sac. Egg sac size did not influence female foraging ability. Our results show that females' foraging ability changes before the maternal care period and therefore may influence their life-history evolution. The little support for our second hypothesis may also suggest that the decrease in foraging ability is not due to the volume being carried per se, but possibly an associated physiological state.

One remarkable reproductive feature in animals with internal fertilization is a reduction in sperm viability over time in females. Whether this reduction is driven by male–male competition and/or cryptic female choice is unclear. From the perspective of cryptic female choice, we postulated that sperm viability is affected by a particular male copulatory behaviour. In this study, we investigated the following aspects: (1) sperm viability in mated females vs. males; (2) whether sperm viability varies temporally after mating; and (3) whether male copulatory behaviour covaries positively with sperm viability within females. We used the spider Holocnemus pluchei, whose males use several copulatory behaviours to court females. We found that females that stored sperm for 4 or 15 days showed no difference in sperm viability but had lower sperm viability compared with males, and males that performed a longer post-insemination behaviour had higher sperm viability inside the female. It is unclear how sperm viability is reduced and how male post-insemination behaviour affects this. It is possible that extending copulation allows males to induce females to keep sperm alive for longer. This result is predicted by theory whereby males induce females to facilitate sperm to reach and fertilize eggs based on male postcopulatory behaviour.

The emergence of anti-predatory strategies for prey survival are ruled by the minimization of the encounters/interactions with potential predators, but at the same time by maximizing the access to limiting resources such as food or mating partners. Cues indicating predatory activity influence decision-making activities in the two-spotted spider mite Tetranychus urticae, such as dispersion, foraging activities, and reproductive effort. However, anti-predatory strategies studied in spider mites generally considers mainly the female perspective (e.g. oviposition), leaving a gap in how T. urticae couples deal with predatory risk. Here, through laboratory experiments, we observed that matured spider mite couples were only affected by predation risk during the pre-copulatory stages of the mating process, especially when deciding to proceed in a mating opportunity. The mating performance of individuals was independent of their exposure to predation risk, suggesting that couples would adopt full investment behavior after opting to proceed in a mating attempt. Though our working hypothesis predicted predation risk interference throughout the entire mating process, we conclude that decision-making activities by spider mite during pre-copulatory stages act independently from copulatory stages associated to insemination.

In the spider families Trechaleidae and Pisauridae, males offer nuptial gifts to females during courtship. Nutritive gifts contain recently caught prey wrapped in silk, while worthless gifts contain prey leftovers or plant parts. The presence of wrapped gifts is known in three out of 16 genera (Paratrechalea Carico, 2005, Trechalea Thorell, 1869 and Trechaleoides Carico, 2005) in Trechaleidae, suggesting that this sexual trait is of widespread occurrence in the family. Here, we report the presence of wrapped nuptial gifts in the genus Paradossenus F.O. Pickard-Cambridge, 1903. Males of P. longipes (Taczanowski, 1874) produce prey-gifts following the same sequence of behavioral units as described for other species of the family. More surprisingly, these males may also produce empty gifts consisting of a silken structure lacking contents. This is the first record of empty nuptial gifts in spiders. This novel male tactic may have evolved from worthless gifts as a further step in the evolution of deception in gift-giving spiders.

Females not only produce costly gametes, but also store the eggs until oviposition, a period called pregnancy. The volume that eggs occupy in the female abdomen may decrease female foraging ability by making females slow. Although females of all species are subjected to these potential costs, it remains an unexplored matter in invertebrates. Females of the spider Paratrechalea ornata carry their egg sac after oviposition and thus represent a unique opportunity to evaluate pregnancy costs because females carry an extra volume before and after laying eggs. We conducted foraging ability experiments using P. ornata females on different treatments regarding pregnancy and maternal care. We first hypothesized that internal egg load and egg sac carrying decrease female foraging ability. We also hypothesized that greater egg sac size decreases female foraging ability. We found that both internal egg load and egg sac carrying decreased female foraging ability, and females about to oviposit had a similar foraging ability to females carrying an egg sac. Egg sac size did not influence female foraging ability. Our results show that pregnancy can impose high costs to female foraging ability, likely increasing their mortality during this period. The little support for our second hypothesis may also suggest that the decrease in foraging ability is not due to the volume being carried per se, but possibly an associated physiological state.

Sexually dimorphic traits are the outcome of a network of selective pressures acting upon each sex. While male secondary sexual traits are frequently restricted to intrasexual competition, female ornaments or weapons are mostly associated to social interactions for the access to limited resources. Here we investigate a sexually dimorphic trait expressed within the female's sternum of the spider species Holocnemus pluchei (Pholcidae), and its adaptive maintenance under the three leading hypotheses: sexual receptivity signaling, mate choice and sexual conflict hypothesis. We provide fine-scaled behavioral descriptions of the copulatory behavior of Holocnemus pluchei, corroborating that mating interactions are mediated by the female's sternum projection. The single moment of contact between the female projection and male body occurs during sperm transfer, always followed by a reduction on the intensity of the male genital movement. Additionally, biometrical properties of the female sternum projection corroborate our functional interpretation for the trait as restricting the intensity of males' copulatory movements. We claim that female sternum projection is a sexually selected trait mediating sexual conflict, with several adaptive consequences upon the sexes.

Terrestrial diplopods are a diverse group of invertebrates with important ecosystem roles within soil communities, though information from the Neotropical Region is still scarce. The present study investigates the association between Diplopoda diversity and composition with vegetation structure, based on pitfall trap samples taken from three different successional vegetation formations in southern Brazil (primary forest, secondary forest, and Pinus monoculture). Samples were collected monthly from October 2000 to May 2002, resulting in 938 diplopod specimens, belonging to 5 families and 13 species. An emergent pattern of close connection between primary and secondary forests was represented by greater species richness and abundance than monoculture samples, a pattern not shared in terms of species composition. Two species, Oncoleptodesmus deflexus Schubart, 1958 and Catharosoma sp. were highly abundant among the sample areas, representing, respectively, 60 and 25% of the total abundance. By assuming a direct association between forest successional stages with habitat heterogeneity, we concluded that the diversity of millipedes is a reflection of habitat heterogeneity, species composition showed similar responses but independently from habitat heterogeneity and disturbance.

The handicap principle proposes that sexual signals must be costly to be honest. Honesty may be maintained by the costs paid by honest signallers or by the potential costs of cheating. In the latter, handicaps should emerge as a consequence of specific biological constraints, such as life-history trade-offs. Nuptial prey-giving arthropods are good systems to investigate the honesty of sexual signals taking into account trade-offs between self-maintenance and mating effort. We experimentally evaluated if prolonged food shortage during early adulthood imposes long-term negative effects on gift construction by males of the spider Paratrechalea ornata. We also evaluated whether a burst of food availability improved body condition of poorly fed males, increasing their frequency of gift construction. Poorly fed males hardly constructed gifts, even after a marked increase in feeding rate, which clearly improved their body condition. Moreover, initially poorly fed males that latter received high food intake constructed lighter gifts than continuously well fed males. The long-term effects of prolonged dietary restriction on male propensity to construct a gift and on the size of this gift may increase the honesty of this sexually selected signal. From the female's perspective the offer of a gift may bring information on male quality.

Environmental enrichment (EE) is a non-pharmacological manipulation that promotes diverse forms of benefits in the central nervous system of captive animals. It is thought that EE influences animal behavior in a specie-(strain)-specific manner. Since rodents in general present different behaviors during distinct periods of the day, in this study we aimed to investigate the influence of time-of-day on behavioral repertoire of Swiss mice that reared in EE. Forty male Swiss mice (21 days old) were housed in standard (SC) or enriched conditions (EC) for 60 days. Behavioral assessments were conducted during the light phase (in presence of light) or dark phase (in absence of light) in the following tasks: open field, object recognition and elevated plus maze. First, we observed that the locomotor and exploratory activities are distinct between SC and EC groups only during the light phase. Second, we observed that "self-protective behaviors" were increased in EC group only when mice were tested during the light phase. However, "less defensive behaviors" were not affected by both housing conditions and time-of-day. Third, we showed that the performance of EE animals in object recognition task was improved in both light and dark conditions. Our findings highlight that EE-induced alterations in exploratory and emotional behaviors are just evident during light conditions. However, EE-induced cognitive benefits are remarkable even during dark conditions, when exploratory and emotional behaviors were similar between groups.

Riparian forests bordering open terrestrial environments may have three microhabitats differing in structure and conditions: a grassland/pasture-forest edge (GE), a forest interior (FI) and a river–forest edge. The influence of such edge effects and vegetation characteristics on spider diversity of riparian forests was evaluated in Southern Brazil. Four different rivers were sampled on the tree–shrub strata with a beating tray, twice per season for 2 years. There were six transects per river, two per microhabitat. We compared spider abundance, species richness and composition. Vegetation variables sampled were vertical structure and (horizontal) density, canopy height and cover. Overall 42,057 spiders were sampled, 28 spider families and 440 species. The FI had higher spider abundance than the edges. Average species richness differed among rivers. Microhabitats did not differ in average richness, although overall richness (from sample-based rarefaction) was higher for GE than FI. High abundances in FI may result from lowered stress due to abiotic conditions, while higher GE richness may result from a faunal superposition between forest species and those from the grassland/pasture. Only canopy cover returns a positive relationship with spider diversity (richness and adult abundance). This might result from more spider species preferring to build webs or hunt under low-light environments. Rivers had spider faunas differing in composition but among microhabitats species composition was the same. Vegetation structure has been hypothesized to affect spiders, but this impact might be best seen in specific subgroups or guilds within spiders, not in the whole assemblage.

We investigated the possibility of reproductive interference between two sibling spider species, Paratrechalea azul and Paratrechalea ornata, which occur syntopically and reproduce synchronously. Males of both species offer a nuptial gift composed of prey wrapped in silk to females. Through laboratory experiments, we evaluated possible asymmetries in the outcome of heterospecific encounters between males and females, and investigated whether chemical signalling could function as a premating barrier between the two species. Males of P. azul were unable to discriminate conspecific from heterospecific female draglines, which resulted in wasted time and energy in nuptial gift construction. Males of P. ornata incurred a higher cost for discrimination mistakes because most of them were attacked by heterospecific females; 95% lost the nuptial gift upon the attack and 33% were preyed upon. This pattern is probably a consequence of differences in body size between males and females of each species. Both species showed erroneous female choice, but only P. ornata females courted heterospecific males, which are considerably larger than conspecific males and may resemble high-quality mating partners. Males of P. ornata also made discrimination mistakes, but at a much lower frequency compared to P. azul males. The selective pressure for precise recognition of conspecific female signs is probably stronger on P. ornata males because misdirected courtship may increase their chances of encountering predatory heterospecific females. This study provides the first detailed evidence of reproductive interference between two reproductively isolated spider species, showing that the costs paid by individuals of different sexes and different species are highly asymmetric. (C) 2012 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.

Nuptial gift offering is a courtship trait found among several insect orders and some spider families. Recent studies indicate that this gift-giving behavior in spiders represents the male mating effort acting on female receptivity through a mechanism of foraging motivation. However, little attention has been given to the sensory channels that are influencing female acceptance. To understand the role of these sensory channels in female perception of a nuptial gift, we focused on the nuptial gift of the neotropical spider Paratrechalea ornata (Araneae, Trechaleidae). The nuptial gift of this species is composed of a prey item wrapped in silk, and previous works suggest that visual and/or chemical cues may be involved in inducing female grasping behavior. We isolated sensory channels using mimetic nuptial gifts (artificial items) or by manipulating real nuptial gifts. Isolated visual signals were not responsible for female acceptance, whereas chemical signals found within the nuptial gift silk layer induced female acceptance. Our findings clearly indicate that a chemical signal located in the silk of the nuptial gift is the main attractant channel, and we formulated 2 hypotheses to explain the mechanisms of action in the female sensory system. We also discuss the consequences of such signaling over female acceptance.

For spiders, morphological differentiation within genitalic traits is the main diagnostic criterion of a species. Beside some well-described exceptions of genitalic polymorphism and crypticity, spider genitalic variation is seldom quantitatively analyzed. Using geometric morphometrics landmark analysis, we report clear evidence of quantitative interspecific divergence and intraspecific variation in the genital shape of three species of the genus Paratrechalea (P. azul, P. ornata and P. galianone). The genitalic species recognition was very consistent with our quantitative data for both sexes. Interspecific variation suggested a character displacement pattern between two syntopic populations of P. azul and P ornata, and also a possible case of species crypticity in P. maul that will involve splitting the Uruguayan populations from the Brazilian ones.