Abstract: Behavioral flexibility allows individuals to react to environmental changes, but changing established behavior carries costs, with unknown benefits. Individuals may thus modify their behavioral flexibility according to the prevailing circumstances. Social information provided by the performance level of others provides one possible cue to assess the potential benefits of changing behavior, since out-performance in similar circumstances indicates that novel behaviors (innovations) are potentially useful. We demonstrate that social performance cues, in the form of previous playersâ scores in a problem-solving computer game, influence behavioral flexibility. Participants viewed only performance indicators, not the innovative behavior of others. While performance cues (high, low, or no scores) had little effect on innovation discovery rates, participants that viewed high scores increased their utilization of innovations, allowing them to exploit the virtual environment more effectively than players viewing low or no scores. Perceived conspecific performance can thus shape human decisions to adopt novel traits, even when the traits employed cannot be copied. This simple mechanism, social performance feedback, could be a driver of both the facultative adoption of innovations and cumulative cultural evolution, processes critical to human success.
Abstract: Conformist social learning, the tendency to acquire the most common trait in a group, allows individuals to rapidly acquire established beneficial traits from a multitude of options. However, conformist strategies hinder acquisition of novel advantageous behavior patterns, because such innovations are by definition uncommon. This raises the possibility that proxy cues of the success of novel traits may be utilized to identify and acquire advantageous innovations and disregard failing options. We show that humans use changes in trait frequency over time as such a cue in an economic game. Participants played a three-alternative forced choice game (i.e., a multi-armed bandit), using social information to attempt to locate a high reward that could change location. Participants viewed temporal changes in how many players chose each option in two successive rounds. Participants supplemented conformist strategies with a âcopy-increasing-traitsâ strategy. That is, regardless of the traits absolute population frequencies, participants' choices were guided by changes in trait frequencies. Thus, humans can detect advantageous innovations by monitoring how many individuals adopt these over time, adopting traits increasing in frequency, and abandoning traits decreasing in frequency. Copying rapidly increasing traits allows identification and acquisition of advantageous innovations, and is thus potentially key in facilitating their early diffusion and cultural evolution.
Abstract: Individuals can use information gathered personally (individual information) or from others (social information) to track environmental change. Established mathematical models predict the rates of environmental change at which a social versus individual information gathering strategy would be adaptive, but the assumptions of these models, particularly the issue of individual flexibility in the strategy employed, have not been subject to rigorous empirical test. Participants (62 adult male and female humans) explored a virtual three-dimensional computer maze, with a forced choice between four reward locations. There were three low-value and one high-value reward, and monetary earnings were proportional to the total rewards located. The three experimental treatments were low, intermediate and high environmental variability, represented by the probability that the high-reward location moved between rounds. On the first 20 rounds, participants explored the maze alone. On the subsequent 80 rounds, participants could view a virtual player exploring the maze while exploring themselves. Participants exposed to the low environmental variability treatment tended to use social information, from the virtual player, more than players in the higher environmental variability treatments. These results are in line with the predictions of evolutionary models. Moreover, they suggest flexibility in information gathering strategies. Humans appear to assess current environmental variability and bias their reliance on social versus personal information accordingly.
Abstract: Adaptive developmental plasticity has been demonstrated across a number of taxa in response to variables such as photoperiod, resource abundance, and predator presence. Demographics also vary temporally and spatially within populations, but few studies have examined the possibility that developmental plasticity in response to changes in these variables can alter phenotypic distributions. Plastic responses to variable population density and sex ratio may play an important role in explaining phenotypic variation in nature. In this study, we examine two species of spiders (Nephila plumipes and Argiope keyserlingi) to examine whether there is evidence that males alter their development in response to demographics in natural populations. We studied spiders in which developing males can use pheromones as a cue of the density of conspecific males and females. We used published information about the mating systems and life history of each species to make predictions about expected patterns of plasticity in development time and correlated changes in adult body size in response to demographic variation. Within each species, male size and mass were positively correlated with the density of males but negatively correlated with the density of females, and as predicted, this was true only when calculated at spatial scales relevant to selection in each species. In contrast, seasonal variation in photoperiod could not explain measured variance in male size. Our results support the idea that developmental plasticity in response to demographics has a significant effect on phenotypic distributions in natural populations. Our results suggest that a proportion of variation in male phenotypes could be explained as a plasticity-mediated evolutionary response to variation in population demographics rather than as a physiological response to resource abundance and/or photoperiod.
Abstract: Copulation in many sexually cannibalistic spiders is associated with a loss of function of the male reproductive organs and, as a consequence, males that survive sexual cannibalism may nevertheless be unable to subsequently copulate successfully. Sexual cannibalism is common in the Australian golden orb-web spider (Nephila plumipes), in which the tip of the conductor typically breaks during copulation. Thus, male mating frequency may be physiologically limited to two females, irrespective of the maleâs ability to avoid cannibalism or the opportunity to locate and court additional, receptive females. Laboratory experiments revealed that the likelihood of the conductor breaking depends upon the copulatory history of the female insemination duct: males were more likely to break their conductor if they inseminated a âvirginâ rather than âmatedâ insemination duct. However, the choice of insemination duct did not influence the duration of copulation or quantity of sperm transferred. In field populations, the proportion of males with both conductors broken increased during the course of the mating season, but while males with broken conductors did not copulate successfully with virgin females, they were nevertheless observed on the webs of immature females. We suggest that male N. plumipes with broken conductors on the webs of females are most likely mate guarding, as this appears to be the most effective mechanism of securing paternity.
Abstract: Non-human animals can acquire novel route preferences by following knowledgeable individuals. Such socially learned route preferences can be stably maintained over multiple transmission episodes, sometimes forming long-lived traditions. In humans, preferences for familiar routes or heavily used worn trails over unfamiliar ones have been described in various contexts. However, social learning of route preferences has not been experimentally demonstrated in humans. Here, we demonstrate that social learning and tradition influence route choice. We led adult male and female participants into a room by one of two routes. Participants followed the demonstrated route choices, and later remembered and preferred this choice even when determinably suboptimal (i.e. longer and not preferred by control participants) or when the choice was indicated as arbitrary (the demonstrator took one route to retrieve a poster that had ostensibly fallen). Moreover, route preferences were stably maintained over multiple transmission episodes. We suggest that simple social learning processes, often neglected in human and primate research, can result in long-lived route preferences that may influence a range of additional behaviour patterns.
Abstract: Mate searching is a risky behavior that decreases survival by increasing predation risk and the risk of energy depletion. However, few studies have quantified actual mortality during mate search, making it difficult to predict mate searching and mating strategies. Using a mark and recapture study, we examined mate-searching success in a highly sexually dimorphic species, the golden orb-web spider (Nephila plumipes). We show that despite the high-density aggregations of this species, male survival during mate searching is extremely low (36%) and is phenotype independent. Surprisingly, males that survived mate search were in better condition after recapture than prior to release, most likely due to kleptoparasitism on females' webs. In a complementary release experiment in a field enclosure, we show that males are choosy and adjust their choice of female depending on their own condition and weight. Thus, the high mortality rate of searching males in the field may be a cost of choosiness because released males traveled further than necessary to settle on females. Although males were choosy about female phenotypes, they did not avoid webs with rival males already present. This suggests that the cost of continued searching outweighs the cost of competition but not the cost of mating with certain females. Further examinations of mate-searching risk in other species in reference to their mating system and environmental conditions are necessary to determine the occurrence and effects of high mortality rates during searching.
Abstract: Animals are expected to alter their foraging behaviour depending on the risk of predation. We tested this idea using the orb-web spider Argiope keyserlingi. We measured the foraging investment of spiders in terms of web size and size of silk decorations in the presence of a predatory praying mantid, Pseudomantis albofimbriata. However, no limited evidence that A. keyserlingi alters its decorating behaviour and no evidence that this spider alters its web architecture in response to the presence of a mantid predator. We suggest that these spiders may use multiple cues to assess predation pressure and that they respond differently to predators based on past experience.
Abstract: Although the occurrence of silk decorations has been noted in scientific literature for over 100 years, there is still little consensus as to their function. This is despite the proliferation of studies examining the five major hypotheses: (1) protection against predators, (2) increasing foraging success, (3) prevention of damage to the web, (4) providing shade and (5) mechanical support for the web. The first three of these hypotheses have received the most attention, and thus generated the most evidence (for and against) suggesting that web decorations are a type of visual signal. However, the effect of this signal on prey and predator receivers is unclear as the evidence is contradictory. Thus, the function of silk decorations may be context specific, depending on factors such as predators, prey, background colour and ambient light. A better understanding of how predators and prey see and process visual information from silk decorations, coupled with experiments examining the mechanisms behind the various hypotheses, are crucial in illuminating their function and resolving the controversy.
Abstract: Spiders in the genus Argiope commonly include curious silk structures, termed web decorations or stabilimenta in their webs. Whilst interesting ontogenetic and interspecific variation in both the form and frequency of web decorations has been documented, to our knowledge this is the first study to compare this variation across a number of decorating species. Here we show that two sympatric species A. picta and A. aetherea construct different forms of web decorations as adults and that A. picta decorates at a higher frequency than A. aetherea. Furthermore, this difference in decoration frequency may be related to the different decoration forms (linear or cruciate) across this genus. We also show that native bees responded significantly more quickly to cruciate decorations than to linear decorations. Here we argue that consideration of the different decoration forms and the frequency at which spiders adorn their webs may help illuminate possible context-dependent functions for these curious structures.
Abstract: We are becoming increasingly aware of animal communication outside the range of human sensitivity. Web decorations are silk, structures used by orb-web spiders to deceive prey and predators. However, despite the level of interest in these structures, their visibility to prey and predators has never, to our knowledge, been objectively assessed. Here, we use spectrophotometric analyses to show that the decorations of all five tested spider species are visible to honey bees and birds over short and long distances. Furthermore, the discoid decorations of one species may provide some protection against arthropod predators. However, these decorations are inefficient at camouflaging the spider against birds, despite the overlap between the spider's body and web decoration.
Abstract: Visual signals are commonly used by animals to manipulate both their prey and predators. The conspicuous silk structures included in the webs of many orb-web spiders, termed web decorations or stabilimenta, could be an example of this. The function of these curious structures remains controversial with some authors suggesting that they attract insect prey, while others suggesting that they camouflage the spider or deter predators. Here we test the hypothesis that web decorations increase the foraging success of 'Araneus' eburnus by attracting prey to the web. Using field correlations and field manipulations we show that decorated webs capture more prey per web area than undecorated webs under certain conditions.
Abstract: Studies that investigate patterns of paternity in polyandrous species typically employ double-mating trials, in which the paternity share of each male is established by either the sterile male technique or using genetic markers. However, polyandrous females may mate with more than two males and, in some species, triple-mating trials produce different patterns of paternity from double-mating trials. We investigated patterns of paternity share in triple-mating trials of the sexually cannibalistic orb-web spider Nephila plumipes. These experiments reveal little quantitative changes to paternity share when more than two males mate with the female; the third male apparently diluted the fertilisation success of the second male but not of the first male. Sexual cannibalism had little impact on the fertilisation success of the first male, but greatly increased the fertilisation success of the third male. When offered a choice, males did not prefer to mate with virgin over mated females, but males that chose virgin females were significantly heavier than those that chose mated females.
Abstract: Predators may utilize signals to exploit the sensory biases of their prey or their predators. The inclusion of conspicuous silk structures called decorations or stabilimenta in the webs of some orb-web spiders (Araneae: Araneidae, Tetragnathidae, Uloboridae) appears to be an example of a sensory exploitation system. The function of these structures is controversial but they may signal to attract prey and/or deter predators. Here, we test these predictions, using a combination of field manipulations and laboratory experiments. In the field, decorations influenced the foraging success of adult female St. Andrew's Cross spiders, Argiope keyserlingi: inclusion of decorations increased prey capture rates as the available prey also increased. In contrast, when decorations were removed, prey capture rates were low and unrelated to the amount of available prey. Laboratory choice experiments showed that significantly more flies (Chrysomya varipes, Diptera: Calliphoridae) were attracted to decorated webs. However, decorations also attracted predators (adult and juvenile praying mantids, Archimantis latistylus; Mantodea: Mantidae) to the web. St. Andrew's Cross spiders apparently resolve the conflicting nature of a prey- and predator-attracting signal by varying their decorating behaviour according to the risk of predation: spiders spun fewer decorations if their webs were located in dense vegetation where predators had greater access, than if the webs were located in sparse vegetation.
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