Effects of experience on food-searching behavior in the antFormica schaufussi (Hymenoptera: Formicidae)

Foragers of the ant Formica schaufussitend to return to and search at a site of a previous food find. The search tactic employed by a forager on its return trip is related to the type of food previously encountered: search is more persistent in response to carbohydrate than to protein food. Using different reinforcement schedules with carbohydrate and protein food rewards, we show that, on a short-term as well as on a long-term basis, the basic pattern of search observed in naive foragers is only slightly modified through foraging experience. Foragers do not increase their search effort or adjust their search pattern when either type of food is systematically renewed on a fixed reward schedule and thus do not seem to be able to learn to assess the food predictability. Collective responses that could compensate for this lack of individual flexibility and increase foraging efficiency at the colony level are discussed.     

Adult experience modifies attraction of the leafminer parasitoidOpius dissitus (Hymenoptera: Braconidae) to volatile semiochemicals

Oviposition-experienced females of Opius dissitus Muesebeck, a braconid parasitoid of Liriomyza sativaeBlanchard, preferentially landed on leafminer-infested rather than uninfested lima bean (Phaseolus lunatus L.) plants in a flight tunnel assay. Both naive and oviposition-experiencedparasitoids responded strongly to odors of infested lima bean plants in a four-arm olfactometer in comparison with odors of uninfested plants, suggesting that volatile semiochemicals are used in host location. Parasitoids with an oviposition experience on lima bean (lima-experienced) spent significantly more time in the infested odor than naive individuals, however, eggplant-experienced wasps did not spend significantly more time in the infested odor field than naive wasps. When parasitoids reared on leafminers in lima bean were provided a choice between the odor of infested lima bean and the odor of infested eggplant or cotton, naive and lima-experienced wasps preferred infested lima odor. An oviposition experience on the other plant species resulted in a dramatic shift in preference. It was concluded that the experience effect was due, at least in part, to associative learning, as has been reported for other parasitoids. The parasitoids may perceive unconditioned stimuli during host contact and oviposition on an infested leaf and may associate those stimuli with volatile semiochemicals emanating from the leaf or host. Subsequently, the volatiles associated with the presence of hosts are used in directing the search for hosts.     

Experience-based food consumption by larvae of Pieris rapae: addiction to glucosinolates?

When newly hatched larvae of P. rapae were transferred to cowpea foliage, they readily accepted this non-host as food, whereas later instars that had fed on cabbage rejected cowpea. However, when cowpea leaf discs were treated with aqueous extracts of cabbage foliage, they were accepted by cabbage-reared larvae. Experiments were conducted to determine whether larvae reared on one host plant would be stimulated to feed by extracts of other hosts. Larvae reared on Brassica juncea, Cleome spinosa, Tropaeolum majus, Sinapis alba, Alliaria petiolata, Barbarea vulgaris and cabbage (Brassica oleracea) were offered extracts of each of the other host plants on cowpea discs in choice assays. Larvae were generally stimulated to feed by extracts of all the alternate hosts, but quantitative differences in consumption occurred. In most cases, levels of discrimination between treatment and control cowpea discs showed no significant preference for extracts of the previously experienced plant. Since the test plants (and their extracts) contain glucosinolates of widely different structures, a general addiction to glucosinolates was suggested. A single glucosinolate, sinigrin, was sufficient to elicit feeding by cabbage-reared larvae. The time required for individual neonates to become addicted to glucosinolates as they fed on cabbage, as measured by refusal of cowpea, varied from 6 to 30 hours. Bioassays of cowpea extracts failed to show any deterrent activity and, therefore, supported the conclusion that addiction to glucosinolates is responsible for the fixation of P. rapae larvae on their host plants.     

The influence of prior experience on preference and performance of a cryptoparasitoid Scleroderma guani (Hymenoptera: Bethylidae) on beetle hosts

1. Numerous studies have reported the effects of learning or experience on parasitoid host preference and location. However, the integration of pre‐imaginal and adult experiences on the subsequent host preference and adult/offspring performance has been rarely tested in host–parasite interactions. 2. We present direct evidence that theses two kinds of experiences affect host preference and related fitness in the polyphagous parasitoid, Scleroderma guani. Two colonies of parasitoids were reared on Monochamus alternatus and Saperda populnea (Cerambycidae: Lamiinae). Individuals from the two colonies were given host‐switching experience for one generation (pre‐imaginal experience) while other individuals were given prior ovipositing experience on the two species, respectively (adult experience). 3. Scleroderma guani females demonstrated that their experiences determined adult behavioural responses and their subsequent performance to hosts. Females maximised both adult fitness (fecundity and longevity) and offspring fitness (survival and sex ratio) when they encountered hosts similar to their maternal hosts. Behavioural plasticity in host choice was affected by adult experience, resulting in improved adult feeding and ovipositing behaviour and further modifying adult fecundity and the offspring sex ratio. There was a positive correlation between oviposition preference and adult fecundity. 4. The results indicated that S. guani exhibited positive preference–performance correlations. This is most likely due to an adaptation to maternal hosts over multiple generations. However, foraging potential of adults to available cues from hosts may be driven quickly by an experience‐induced learning process rather than by natural selection processes shaped over many generations.     

What Do Mexican Fruit Flies Learn When They Experience Fruit?

Mexican fruit flies learn fruit characteristics that enable them to distinguish familiar fruits from novel fruits. We investigated whether mature Mexican fruit flies learn fruit color, size or odor. We found no evidence that female flies learn fruit color or size after experience with host fruit, including oviposition. However, green fruit and fruit models were more attractive than yellow and red fruit and fruit models regardless of previous experience. Females with grapefruit experience were more attracted to fruit models with extract of either grapefruit peel or pulp, than to models without extract. Females with no experience with grapefruit were not attracted to models treated with grapefruit extract. These results indicate that females learned fruit odor during exposure to grapefruit.     

Genetic and environmental (inter)actions in male mouse lines selected for aggressive and nonaggressive behavior

The purpose of this study was to investigate the effects of genetic and environmental factors, as well as their interaction, in the etiology of aggressive behavior in two mouse lines bidirectionally selected for offensive aggression. To this end, we raised the Finnish TA (aggressive) and TNA (nonagressive) selection lines either in isolation or in cohabitation with a female after weaning. At the age of 3 months we determined their aggressive behavior in three paradigms (intruder resident, neutral cage, resident intruder) against a male standard opponent. We also determined the animals' aggressive behavior against a female mouse. The results show genetic and environmental effects, as well as gene–environment interaction. We see prominent genotype effects under all conditions but each test is sensitive to a specific combination of environmental effects. A particularly noteworthy result is that variation in the unusual behavior of aggression towards a female is largely explained by the interaction of genotype with isolation. We also examined whether test experience influenced the outcome of an encounter between an experimental animal and an opponent, and found that this factor should not be underestimated, its effect size and direction depending on the type of paradigm and way of housing. These data suggest that the identification of genes underlying aggressive behavior in mice is by no means straightforward and that the result of this search will depend on the environmental design of the study (type of paradigm, housing conditions). These data also suggest that the use of 'test battery' mice might produce different results than the use of test-naïve animals.     

Sexual experience interacts with steroid exposure to shape the partner preferences of rats

A three-phase experiment manipulated sexual experience and hormone exposure (perinatally and in adulthood) in female rats housed individually from weaning so as to limit peripubertal social and sexual experience. Noncontact partner preference for a male or estrous female rat was measured both before and after sexual experience, first while rats were under the influence of circulating testosterone propionate (TP) and later after priming them with ovarian hormones (estradiol benzoate and progesterone; EB & P). When implanted with TP capsules and tested while sexually naive, all groups of female rats preferred females to males without differing statistically. However, following three sexual experience sessions with estrous females, differences emerged between the masculinized and control groups in the magnitude of their female-directed preference, with masculinized females demonstrating a significantly greater preference for estrous females. Sexual experience with male rats under EB & P did not result in a significant shift in preference in any group. Histological assessment indicated that the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) was increased by exposure to TP postnatally, and SDN-POA volume correlated positively with partner preference scores but only when rats were both sexually experienced and exposed to circulating TP in adulthood. These results suggest that sexual experience interacts with steroid exposure to shape partner preference.     

Relationships between hormones and aggressive behavior in green anole lizards: an analysis using structural equation modeling

We investigated the relationship between aggressive behavior and circulating androgens in the context of agonistic social interaction and examined the effect of this interaction on the androgen-aggression relationship in response to a subsequent social challenge in male Anolis carolinensis lizards. Individuals comprising an aggressive encounter group were exposed to an aggressive conspecific male for 10 min per day during a 5-day encounter period, while controls were exposed to a neutral stimulus for the same period. On the sixth day, their responses to an intruder test were observed. At intervals, individuals were sacrificed to monitor plasma androgen levels. Structural equation modeling (SEM) was used to test three a priori interaction models of the relationship between social stimulus, aggressive behavior, and androgen. Model 1 posits that exposure to a social stimulus influences androgen and aggressive behavior independently. In Model 2, a social stimulus triggers aggressive behavior, which in turn increases circulating levels of androgen. In Model 3, exposure to a social stimulus influences circulating androgen levels, which in turn triggers aggressive behavior. During the 5 days of the encounter period, circulating testosterone (T) levels of the aggressive encounter group followed the same pattern as their aggressive behavioral responses, while the control group did not show significant changes in their aggressive behavior or T level. Our SEM results supported Model 2. A means analysis showed that during the intruder test, animals with 5 days of aggressive encounters showed more aggressive responses than did control animals, while their circulating androgen levels did not differ. This further supports Model 2, suggesting that an animal's own aggressive behavior may trigger increases in levels of plasma androgen.     

Attraction of a predator to chemical information related to nonprey: when can it be adaptive?

Information specificity can be important to animals in makingoptimal decisions. However, it is not always necessary to useevery level of specificity. We analyzed the response of thepredatory mite Phytoseiulus persimilis to plant-produced informationrelated to a nonprey herbivore. This predator is a specialistfeeding on spider mites in the genus Tetranychus. Caterpillarsof Spodoptera exigua cannot serve as prey. Plants respond toan infestation by herbivores with the emission of volatilesthat attract carnivorous enemies of the herbivores. Conspecific plants infested with different herbivore species can emit blendsthat are qualitatively identical, while differing in the ratiosof blend components. However, different plant species emitvolatile blends that differ qualitatively. We demonstratedthat the predator P. persimilis is attracted to volatiles frombean plants infested with S. exigua caterpillars, but thatthis attraction is affected by predator starvation and host-plantexperience. One-hour and 24-h starved predators were made to represent predators that just lost a prey patch versus predatorsthat have totally lost a prey patch. Predators reared on spidermites on bean were attracted to bean plants infested with caterpillarswhen starved for 1 h but not when starved for 24 h. Both predatorgroups were attracted to bean plants infested with prey (i.e.,spider mites). One-hour starved predators can use the odorto relocate the rewarding prey patch they just lost contactwith, and using a general olfactory representation of the blendis sufficient for relocation. In contrast, for 24-h starvedpredators, the perception of a plant's odor blend is unlikelyto represent the prey patch lost, and discriminating betweenan odor blend representing prey or nonprey will avoid investingtime in finding a nonprey herbivore. In contrast, predatorsthat had been reared on spider mites on cucumber and thus hadexperienced a qualitatively different odor blend were not attractedto volatiles from caterpillar-infested bean plants. They wereattracted to spider mite-infested bean plants, irrespectiveof starvation level. To cucumber-experienced predators, theperception of bean plant odor cannot represent the prey patch lost, but only a new prey patch. Being discriminative and onlyresponding to prey-infested plants is adaptive in this situation.Our results are discussed in the context of optimal informationprocessing.     

Effects of early experience on the behaviour of yearling rhesus monkeys (Macaca mulatta) in the presence of a strange object: classification and correlation approaches

Special techniques are needed to help us understand the long-term effects of infants' experiences of their relationships with their mothers, especially when direct experimental control of the interaction between mother and young is impossible, or could distort their relationship. A classification approach is developed to show how outcomes in individuals can be predicted from their earlier experiences and characteristics. Four-week-old rhesus monkey infants' characteristic levels of enterprise persisted through their first year, but could be reduced in certain individuals who had been kept off their mothers by high rates of early maternal rejection. Correlational approaches are difficult to interpret when they fail to confirm simple effects of experience or of individual characteristics, because they are based on groups not individuals, and because certain individuals can affect the values of correlation coefficients in ways that cannot be specified without using a classification approach. The possible effects on correlation coefficients of inconsistent individuals, and of being unable to specify which infants respond in which ways to relevant variables were discussed.