Simulated Predation Risk Influences Female Choice in Túngara Frogs,Physalaemus pustulosus

While the presence of predators can influence female mate choice, few studies have investigated how females respond to quantitative variation in predation risk. In addition, we know little of how females respond to multiple, independent cues of risk. In this study, we investigated the effects of simulated predation risk on mate choice in túngara frogs, Physalaemus pustulosus, using the advertisement calls of predatory frogs, variation in ambient light, and simulated distance. Females showed aversion to conspecific calls associated with the calls of predators, and females were significantly less likely to travel perceived longer distances while the calls of predatory frogs were broadcast. In both the laboratory and field, females chose among potential mates significantly faster under higher light levels. Female responses to acoustic cues of predation risk were significantly influenced by light level, but decisions about travel distances were not. These results demonstrate that female choice is strongly influenced by perceived predation risk and that females can simultaneously evaluate quantitative variation in different cues of predation risk. The changes in search behavior and mate evaluation we demonstrate indicate that predation plays a strong role in limiting signal evolution and possibly reproductive isolation.     

Dynamic mate-searching tactic allows female satin bowerbirds Ptilonorhynchus violaceus to reduce searching

Females can maximize the benefits of mate choice by finding high-quality mates while using search tactics that limit the costs of searching for mates. Mate-searching models indicate that specific search tactics would best optimize this trade-off under different conditions. These models do not, however, consider that females may use information from previous years to improve mate searching and reduce search costs in subsequent years. We followed female satin bowerbirds Ptilonorhynchus violaceus during mate searching and reconstructed their search patterns. We found that females who chose very attractive males typically mated with the same male in the following year, resulting in these females sampling fewer males than those who switched mates. In contrast, females who mated with less attractive males typically rejected their previous mates and searched longer for more attractive mates in the following mating season. A potential cost to mate searching is suggested by the observed increase in the likelihood of force-copulation attempts from marauding males with increased searching. Our results suggest that by using past experiences to adjust their search tactics, females may obtain high-quality mates while limiting search costs. These results emphasize the need to consider historical effects in studies of sexual selection, especially for long-lived species with stable display sites.     

Male golden hamsters (<Emphasis Type="Italic">Mesocricetus auratus</Emphasis>) are more reactive than females to a visual predator cue

In most species of small mammals, males are exposed to higher levels of risk than females because they compete for mates, travel greater distances to find and procure mates, and/or defend a territory. This suggests that males and females might have different responses to risky situations, such as the presence of a predator. We tested responses to a visual predator cue (an owl silhouette) in male and female golden hamsters (Mesocricetus auratus). In a laboratory arena, there was no significant sex difference in the latency to enter the burrow or time spent in the burrow immediately after exposure to the owl silhouette. Males, however, were less likely to be active during the 3-min period following the animal’s exposure to the silhouette, indicating that male golden hamsters are more wary after exposure to an aerial predator cue than females. Most studies of responses to predators or predator cues have not considered sex differences, but our results show that males and females may have quite different responses to predator cues. Further work should be done to characterize and quantify sex differences in response to predators or predator cues.     

Predator experience overrides learned aversion to heterospecifics in stickleback species pairs

Predation risk can alter female mating decisions because the costs of mate searching and selecting attractive mates increase when predators are present. In response to predators, females have been found to plastically adjust mate preference within species, but little is known about how predators alter sexual isolation and hybridization among species. We tested the effects of predator exposure on sexual isolation between benthic and limnetic threespine sticklebacks (Gasterosteus spp.). Female discrimination against heterospecific mates was measured before and after females experienced a simulated attack by a trout predator or a control exposure to a harmless object. In the absence of predators, females showed increased aversion to heterospecifics over time. We found that predator exposure made females less discriminating and precluded this learned aversion to heterospecifics. Benthic and limnetic males differ in coloration, and predator exposure also affected sexual isolation by weakening female preferences for colourful males. Predator effects on sexual selection were also tested but predators had few effects on female choosiness among conspecific mates. Our results suggest that predation risk may disrupt the cognitive processes associated with mate choice and lead to fluctuations in the strength of sexual isolation between species.     

Increased predation risk while mate guarding as a cost of reproduction for male broad-headed skinks (Eumeces laticeps)

We investigated antipredatory costs associated with mate guarding as potential costs of reproduction for male broad-headed skinks. Mate guarding by male lizards may increase fitness by preventing loss of fertilizations of the guarded female's eggs to other males, but it may have several costs. In addition to lost opportunities to search for additional females, risk of injury while fighting other males, and energetic expenditures while following females and fighting, guarding males might suffer increased risk of predation and reduction of opportunities to forage. We studied potential antipredatory costs of mate guarding by simulating predators searching for and approaching pairs of lizards in the field. Among pairs of lizards in close proximity to each other, males were detected before females 10 times more frequently than females were detected before males, and females fled before males much more frequently than males fled before females when pairs were approached, leaving the males exposed to the predator. After one or both lizards fled, males frequently followed females by scanning visually and scent trailing, exposing themselves to the predator while the female hid. Females never followed males. The implications of these findings for antipredatory costs of mate guarding are discussed. Electronic Publication     

Female Field Crickets Incur Increased Parasitism Risk When Near Preferred Song

Female animals often prefer males with conspicuous traits because these males provide direct or indirect benefits. Conspicuous male traits, however, can attract predators. This not only increases the risk of predation for conspicuous males but also for the females that prefer them. In the variable field cricket, Gryllus lineaticeps, males that produce preferred song types provide females with greater material benefits, but they are also more likely to attract lethal parasitoid flies. First, we conducted a field experiment that tested the hypothesis that females have a greater risk of fly parasitism when in association with preferred high chirp rate males. Females were nearly twice as likely to be parasitized when caged with high chirp rate song than when caged with low chirp rate song. Females may thus be forced to trade off the quality of the benefits they receive from mating with preferred males and the risk of being killed by a predator when near these males. Second, we assessed female parasitism rates in a natural population. Up to 6% of the females were parasitized in field samples. Because the females we collected could have become parasitized had they not been collected, this provides a minimum estimate of the female parasitism rate in the field. In a laboratory study, we found no difference in the proportion of time parasitized and unparasitized females spent hiding under shelters; thus, differences in activity patterns do not appear to have biased our estimate of female parasitism rates. Overall, our results suggest that female association costs have the potential to shape the evolution of female mating preferences.     

Searching behavior and time budgets of the predator Podisus maculiventris

Searching behavior of the predaceous insect Podisus maculiventris (Say) (Heteroptera: Pentatomidae) was investigated in the laboratory to verify assumptions made in a predator search model. Female predators were placed into an arena containing 30 lima bean plants (Phaseolus lunatus L.), each having five numbered leaflets. Prey were third-instar larvae of Mexican bean beetle (Epilachna varivestis Mulsant) at two densities. Predators were observed for 4 h periods as they searched the plant canopy. Results showed that predators searched a greater area and for longer at low prey density than at high prey density. Predators apparently searched plants without using cues, did not search areas of the canopy repeatedly after attacks, and spent approximately 1 h handling prey. Predators spent more time resting than searching, and attack rates were negatively correlated with rest time, but were not correlated with search time. Long resting periods by predators may be a result of energy conservation. The implications for using predators such as P. maculiventris against pests in crops are (i) the predators' searching behavior limits the number of prey attacked, and (ii) the predator may be able to persist at low prey densities better than species with different searching behaviors.     

Cue hierarchy for host plant selection in Pieris rapae

During oviposition, female insects utilize a wide variety of cues to find an optimal host for their offspring. These cues may be encountered simultaneously or sequentially, and females must rely on a hierarchical categorization to rank cues for optimal ovipositional choice. During alighting, cues are often encountered at different distances, which may influence hierarchical order. Cues that are observed at longer distances and are experienced first may be more influential on oviposition choice than those experienced at shorter distances. We tested the effects of two long‐distance cues, plant size and habitat structure, and two short‐distance cues, plant nitrogen level and predator presence, on Pieris rapae L. (Lepidoptera: Pieridae) oviposition choice through a series of two‐ and four‐choice tests in both greenhouse and field settings. We found that the long‐distance cues of plant size and habitat structure had the largest impact on P. rapae oviposition in laboratory and field settings, with females preferring large plants without habitat structure. Plant nitrogen level had a smaller impact on oviposition, and the presence of predators did not affect oviposition choice. However, plant size and plant nitrogen level had a synergistic relationship, with more eggs laid on large high‐nitrogen plants compared to large low‐nitrogen or small high‐nitrogen plants, suggesting that optimal cues throughout the entire searching process may be important for P. rapae in choosing a host plant.     

Seasonal Variation in Female Response to Male Calling Song in the Field Cricket, Gryllus rubens

Conspicuous traits that make males attractive to females may make them vulnerable to predators. Females that approach conspicuous males may increase their risk of predation. This means that selection for reduced male conspicuousness in the presence of predators may be due to sexual selection resulting from altered female behavior in the face of increased predator risk. We examine this hypothesis in the field cricket, Gryllus rubens, in which male calling song attracts both conspecific females for mating and parasitoid flies (Ormia ochracea) which kill their hosts within a week. Female crickets are also parasitized by these flies as a result of associating with calling males. In northern Florida crickets that emerge in the spring are not subject to fly parasitism whereas autumn crickets encounter large numbers of flies. We predicted that autumn females should be less attracted to male song than spring females. We tested female response to male calls in a rectangular arena in which male calling song was broadcast from a speaker. Spring females readily approached the speaker but autumn females were less likely to approach and remain in the vicinity of the speaker. These results emphasize the importance of considering how risk affects the evolution of conspicuous male behavior both directly through its effect on the male and indirectly through its effect on female responses to males.     

The searching behaviour of Anthocoris confusus (Reuter) in relation to prey density and plant surface topography

• 1 The searching behaviour of A.confusus females was investigated in an artificial arena.
• 2 Females showed an increase in the frequency of turning movements following feeding and this concentrated search in a small area. As a result more prey were found in areas where prey distribution was clumped.
• 3 If no prey was encountered within 5–8 min the search track straightened out.
• 4 First and second instar nymphs searching on broad bean plants moved faster on the undersides of leaves which were the sites most likely to support aphid populations. A considerable proportion of available time was wasted in periods of inactivity.
• 5 It was concluded that while plant topography strongly influences search pattern, the underlying trend demonstrated in these experiments was of advantage to predators searching for colonial prey.

     

High costs of female choice in a lekking lizard

Although the cost of mate choice is an essential component of the evolution and maintenance of sexual selection, the energetic cost of female choice has not previously been assessed directly. Here we report that females can incur high energetic costs as a result of discriminating among potential mates. We used heart rate biologging to quantify energetic expenditure in lek-mating female Galápagos marine iguanas (Amblyrhynchus cristatus). Receptive females spent 78.9+/-23.2 kJ of energy on mate choice over a 30-day period, which is equivalent to approximately (3/4) of one day's energy budget. Females that spent more time on the territories of high-quality, high-activity males displayed greater energetic expenditure on mate choice, lost more mass, and showed a trend towards producing smaller follicles. Choosy females also appear to face a reduced probability of survival if El Ni?o conditions occur in the year following breeding. These findings indicate that female choice can carry significant costs, and suggest that the benefits that lek-mating females gain through mating with a preferred male may be higher than previously predicted.     

Searching behaviour and mate recognition by males of the two-spot ladybird beetle, Adalia bipunctata

Abstract. 1. Adult males of the two-spot ladybird beetle, Adalia bipunctata , did not show a functional response to increase in aphid abundance and consumed markedly fewer aphids than do the females.
2. At high densities of prey, females spent more time in area-restricted search than when prey was scarce. Males were always less active than females and they did not respond to an increase in prey abundance by a change in searching behaviour.
3. After a brief encounter with a female, a male showed area-restricted searching behaviour. This behaviour occurred in response to encountering a female's elytra and in particular to a chloroform-soluble component (sex pheromone) present on or in the elytra.
4. Males needed to encounter a female in order to respond to her presence, which indicated the pheromone is a contact pheromone.
5. The searching behaviour of males appeared to be mainly directed towards locating females; that of females towards locating aphids. This difference between the sexes should be taken into account when quantifying the predatory response of ladybirds to aphid abundance in the field.     

Sex Biased State Dependence in Natal Dispersal in Desert Isoponds, Hemilepistus reaumuri

Differences in the emergence, movement, and settling patterns of individuals during natal dispersal can provide testable hypotheses about the costs and functions of movement. Emergence, movement, and settling patterns were studied in desert isopods, Hemilepistus reaumuri. The young of this semelparous, monogamous, crustacean emerge from their natal burrows each spring and search for sites to establish new burrows or gain acceptance as mates in occupied burrows. Dispersal was measured in a long, narrow corridor into which individuals marked after emergence were monitored. Females emerged slightly earlier than males with substantial overlap. Size or condition varied with time before settling differently in males and females. Isopods in good or poor condition did not differ in distance traveled, but males in good condition took more time before settling. Small males were more likely to start new burrows and took less time before settling, suggesting they might be acting in anticipation of losing contests for female-initiated burrows. Larger females and those in higher condition were more likely to start new burrows and took less time before settling. The pattern in females could reflect male choice or constraints or costs associated with burrow establishment in females, which should be tested. Measures of dispersal based on recaptures of traveling or recently settled individuals may differ from the distribution of successful reproduction. In this study travelers were observed at shorter average distances than settlers, but successful settlers traveled less far than unsuccessful ones.     

The Outcome of a Previous Social Interaction with a Same‐sex Conspecific Affects the Behavior of Meadow Voles,Microtus pennsylvanicus

In species where conspecifics compete for resources such as territories, remembering where a neighbor was previously encountered and the outcome of that interaction may give individuals advantages over nearby conspecifics. We used a two‐phase experiment to test the hypothesis that female meadow voles, Microtus pennsylvanicus, who during the breeding season are territorial and agonistic toward one another, can use details of an encounter with another female in one location to later navigate nearby areas. During the encounter phase, pairs of females interacted for two minutes in one isolated section of a Y‐maze; control females were placed in alone. Females were scored as either winners or losers. Winners displayed twice as many agonistic acts against their opponent. The test phase took place after a retention interval of one hour, 1 d, or 1 wk. Single females were returned to a clean and empty Y‐maze and allowed to explore the entire apparatus for 15 min. We recorded the amount of time spent in each section of the maze. After retention intervals of one hour and 7 d winners, losers, and controls spent similar amounts of time in each section. However, after 24 h, winners spent more time in the encounter section; losers and control females spent similar amounts of time in each section. The results suggest that meadow voles' memory of the details of a single encounter is influenced by the emotional valence attached to that event. The duration of memory may be associated with the establishment of territories by female meadow voles.     

Predation risk and the opportunity for female mate choice in a coral reef fish

The influence of predation risk on the opportunity for female mate choice was investigated in the tailspot wrasse Halichoeres melanurus at two sites on a coral reef in Okinawa, Japan. Females mated repeatedly with the nearest males, but they also changed mates frequently at both sites. Mate changes were seen not only in the context of spatiosocial changes (mate disappearance or shifts in male territories) but were also probably the result of actual mate choice by females. Females at one site (site A) changed mates more often and conducted longer spawning trips from their home ranges to male territories than at the other site (site B). Fish at site A were faced with a higher frequency of predators than that of site B. However, fish of site A suffered fewer attacks from predators because they had more shelter, suggesting lower predation risk in that site. These results suggest that females under higher predation risk had less opportunity to choose preferable mates and that they had to mate with the same, nearest males in most cases.     

Female-female social relationships in wild white-faced capuchin monkeys,Cebus capucinus

A single social group of wild white-faced capuchin monkeys was studied for a period of 26 months at Lomas Barbudal Biological Reserve, Costa Rica. A total of 604 hr of focal animal data was collected on six adult females in a group of 21 monkeys. Females could be ranked in a stable, linear dominance hierarchy. Adult females spent much more time in proximity to other adult females than to adult males. Females groomed other females twice as often as they groomed males, and about 55 times more often than males groomed males. Females tended to groom up the dominance hierarchy, and dyads with smaller rank distances groomed more often. Higher-ranking females nursed infants other than their own at lower rates than did lower-ranking females; however, females nursed infants of females ranked both above and below them. Although lower-ranking females were more likely than higher-ranking females to be the victims of aggression, higher-ranking females were not necessarily more aggressive than lower-ranking females. In 96% of female-female coalitions vs. a female, the victim was lower-ranking than both coalition partners; in the remaining 4%, the victim was intermediate in rank between the two coalition partners. Higher-ranking female-female dyads formed coalitions more often than did lower-ranking dyads. Those female-female dyads that groomed more frequently also formed coalitions more frequently. The patterning of social interactions indicates that Cebus capucinus at Lomas Barbudal are female bonded. © 1996 Wiley-Liss, Inc.     

Intrinsic Factors Affecting Female Choice in House Crickets: Time Cost, Female Age, Nutritional Condition, Body Size, and Size-Relative Reproductive Investment

Few studies have examined potential costs of female choice and factors intrinsic to females that affect choice. To examine these factors, female house crickets, Acheta domesticus, were presented with a simultaneous choice between tapes of a priori attractive and unattractive male chirps. Females varied in age, nutritional condition, body size (potential fecundity), and size-relative reproductive investment. Female age had a significant effect on female choosiness: young females were selective, whereas older females were not selective. Nutritional condition, body size, and size-relative reproductive investment did not affect female choice. Females that chose the call of the attractive male spent approximately twice as long choosing as females that chose the unattractive male call.     

The advantage of alternative tactics of prey and predators depends on the spatial pattern of prey and social interactions among predators

Individual variation in behavioral strategies is ubiquitous in nature. Yet, explaining how this variation is being maintained remains a challenging task. We use a spatially-explicit individual-based simulation model to evaluate the extent to which the efficiency of an alternative spacing tactic of prey and an alternative search tactic of predators are influenced by the spatial pattern of prey, social interactions among predators (i.e., interference and information sharing) and predator density. In response to predation risk, prey individuals can either spread out or aggregate. We demonstrate that if prey is extremely clumped, spreading out may help when predators share information regarding prey locations and when predators shift to area-restricted search following an encounter with prey. However, dispersion is counter-selected when predators interact by interference, especially under high predator density. When predators search for more randomly distributed prey, interference and information sharing similarly affect the relative advantage of spreading out. Under a clumped prey spatial pattern, predators benefit from shifting their search tactic to an area-restricted search following an encounter with prey. This advantage is moderated as predator density increases and when predators interact either by interference or information sharing. Under a more random prey pattern, information sharing may deteriorate the inferior search tactic even more, compared to interference or no interaction among predators. Our simulation clarifies how interactions among searching predators may affect aggregation behavior of prey, the relative success of alternative search tactics and their potential to invade established populations using some other search or spacing tactics.     

Time allocation to the reproductive and feeding behaviors in the male cabbage butterfly

Individually marked males of Pieris rapae crucivora, were observed to determine how they allocate time to reproduction and feeding. Males were found to alternately feed and search for females. This manner of time allocation persisted throughout the day. The total times that males allocated to the two behaviors were positively correlated, i.e. those males that spent longer searching for females, also feed for longer periods. Males, however, tended to allocate more time to the female-searching in the morning than in the afternoon, while time allocated to feeding throughout the day. Older males spent more time searching for females in the morning. The body weight of male butterflies also changed as they aged. The results are discussed in terms of both proximal and ultimate aspects of female-search.     

Allocating time between feeding, resting and moving by the two-spotted spider mite, Tetranychus urticae and its predator Phytoseiulus persimilis

This study characterizes the timing of feeding, moving and resting for the two-spotted spider mite, Tetranychus urticae Koch and a phytoseiid predator, Phytoseiulus persimilis Athias-Henriot. Feeding is the interaction between T. urticae and plants, and between P. persimilis and T. urticae. Movement plays a key role in locating new food resources. Both activities are closely related to survival and reproduction. We measured the time allocated to these behaviours at four ages of the spider mite (juveniles, adult females immediately after moult and adult females 1 and 3 days after moult) and two ages of the predatory mite (juveniles and adult females). We also examined the effect of previous spider mite-inflicted leaf damage on the spider mite behaviour. Juveniles of both the spider mite and the predatory mite moved around less than their adult counterparts. Newly emerged adult female spider mites spent most of their time moving, stopping only to feed. This represents the teneral phase, during which adult female spider mites are most likely to disperse. With the exception of this age group, spider mites moved more and fed less on previously damaged than on clean leaves. Because of this, the spider mite behaviour was initially more variable on damaged leaves. Phytoseiulus persimilis rested at all stages for a much larger percentage of the time and spent less time feeding than did T. urticae; the predators invariably rested in close proximity to the prey. Compared to adult predators, juveniles spent approximately four times as long handling a prey egg. The predator-prey interaction is dependent upon the local movement of both the predators and prey. These details of individual behaviours in a multispecies environment can provide an understanding of population dynamics.