Effects of predation risk on mating behavior of the Kanzawa spider mite

In the Kanzawa spider mite, Tetranychus kanzawai, adult males locate pre-reproductive quiescent females and engage in precopulatory mate guarding. We found that re-reproductive quiescent females preferred to be near veins, rather than other leaf parts, and moreover, adult males spent more time along the vein than on other parts. Consequently, T. kanzawai males found more quiescent females along veins than those on other parts. However, the predatory mite Neoseiulus womersleyi also found more quiescent T. kanzawai females along veins than those on other parts. Moreover, N. womersleyi found more guarding males than solitary males of T. kanzawai. Thus, we experimentally examined the effects of predation risk on the mating behavior of T. kanzawai. The presence of N. womersleyi reduced T. kanzawai female preference for vein vicinity as a quiescent site. Although the predation risk of guarding T. kanzawai males was lower than that of solitary males after detection by predators, the presence of N. womersleyi also reduced the proportion of guarding T. kanzawai males. These results suggest that the possible benefits of preferring vein vicinity as quiescent sites by T. kanzawai females is outweighed by predation risk in the presence of predators, and that the risk of detection by predators would be more important for T. kanzawai males than the risk of being preyed upon.     

Elevated predation risk changes mating behaviour and courtship in a fiddler crab

The fiddler crab, Uca beebei, lives in individually defended burrows, in mixed-sex colonies on intertidal mud flats. Avian predation is common, especially of crabs unable to escape into burrows. Mating pairs form in two ways. Females either mate on the surface at their burrow entrance (''surface mating'') or leave their own burrow and sequentially enter and leave (''sample'') courting males'' burrows, before staying in one to mate underground (''burrow mating''). We tested whether perceived predation risk affects the relative frequency of these mating modes. We first observed mating under natural levels of predation during one biweekly, semi-lunar cycle. We then experimentally increased the perceived predation risk by attracting grackles (Quiscalus mexicanus) to each half of the study site in two successive biweekly cycles. In each experimental cycle, crabs were significantly less likely to mate on the side with more birds. Moreover, on the side with elevated predation risk, the number of females leaving burrows to sample was greatly reduced relative to the number of females that surface-mated. Males waved less and built fewer mud pillars, which attract females, when birds were present. We discuss several plausible proximate explanations for these results and the effect of changes in predation regime on sexual selection.     

Eutrophication and predation risk interact to affect sexual trait expression and mating success

Sexual traits are especially sensitive to low food resources. Other environmental parameters (e.g., predation) should also affect sexual trait expression by favoring investment in viability traits rather than sexual traits. We know surprisingly little about how predators alter investment in sexual traits, or how predator and resource environments interact to affect sexual trait investment. We explored how increasing phosphorous (P) availability, at a level mimicking cultural eutrophication, affects the development of sexual, nonsexual, and viability traits of amphipods in the presence and absence of predators. Sexual traits and growth were hypersensitive to low P compared to nonsexual traits. However, a key sexual trait responded to low P only when predator cues were absent. Furthermore, investment trade-offs between sexual traits and growth only occurred when P was low. The phenotypic changes caused by predator cues and increased P availability resulted in higher male mating success. Thus, eutrophication not only affects sexual trait expression but also masks the trade-off between traits with similar P demand. Sensitivity of sexually selected traits to changes in P, combined with the important roles these traits play in determining fitness and driving speciation, suggests that human-induced environmental change can greatly alter the evolutionary trajectories of populations.     

Trade-off between mating and predation risk in the marine snail, Littorina plena

Abstract. We investigated the hypothesis that predation risk affects mating decisions in the intertidal snail Littorina plena in Bamfield Inlet, Northeast Pacific. First, we conducted a field tethering experiment to test the assumption that mating pairs of snails are more susceptible to predation than solitary individuals, and then performed a laboratory experiment to quantify the effect of predation threat on the propensity of snails to form mating pairs. Our results support the hypothesis, in that "mating pairs" were more frequently killed than single snails in the field, and snails were less likely to form mating pairs in the laboratory when simulated predation risk was high (chemical cues from crushed conspecifics were added to the water) than when it was low (no risk cues were added to the water). In contrast to several earlier studies, we found no effect of individual size on snail susceptibility to predation, perhaps because our two size classes were contiguous and snails within them were not dissimilar enough. The results of the behavioral experiment were consistent with this lack of individual size effect on snail vulnerability; both size classes of snails showed a significant and similar tendency to decrease mating when predation risk was high. Taken together, the results of this and recent studies indicate that predators can considerably affect the behavior of littorinid snails, including their movement patterns, feeding, and reproduction. We argue that greater consideration should be given to how marine invertebrates trade off predation risk and activities related to reproduction.     

Yeast use translational control to compensate for extra copies of a ribosomal protein gene

The efficient assembly of ribosomes requires a balanced synthesis of ribosomal RNA and each ribosomal protein. In an attempt to establish the mechanisms responsible for such balanced synthesis we have altered the gene dosage for one of the components by introducing into yeast an autonomously replicating plasmid containing the gene tcm1, which codes for ribosomal protein L3. The plasmid is maintained at 5–10 copies per cell by selection for expression of its URA3 gene. The plasmid-containing cells transcribe 7.5 times as much L3 mRNA as control cells, maintain 3.5 times as much L3 mRNA as control cells and synthesize no more than 1.2 times as much L3 protein as control cells. We conclude that the balanced synthesis of ribosomal proteins is maintained by modulating both the efficiency of translation and the lifetime of their mRNAs.     

Consequences of mating and predation risk for longevity in a freshwater snail: abstinence makes the heart beat longer

Senescence is not a static property of an individual or population, but rather it is a dynamic process that may be influenced by environmental conditions. This can occur in at least two ways: in the long‐term across multiple generations, and in the short‐term via phenotypic plasticity. The former has attracted a lot of attention, both theoretically and empirically; the latter has lagged behind. To determine whether two important environmental variables (predation risk and mate availability) affect the pattern of actuarial senescence (i.e. the increase in mortality with age), we reared 30 full‐sib families of the simultaneously hermaphroditic freshwater snail Physa acuta under four different environmental conditions and tracked individuals until death. Individuals were reared in a 2×2 factorial experiment that manipulated the nonlethal presence of chemical cues from predatory crayfish (presence/absence) and the opportunity to mate with an unrelated partner (mated/not mated). Snails that receive a partner reproduce by outcrossing, whereas those that remain in isolation can reproduce by self‐fertilization. We compared the cumulative survival curves to test for an effect of predation risk and mating. The hazard ratio (HR) for the predation risk comparison was 1.042 indicating no significant difference between the curves. However, the HR for the mating comparison was 4.021, reflecting a significant reduction in survival probability for mated snails relative to isolated snails. As such, mating resulted in a much shorter lifespan, an outcome that we interpret in terms of shifting resource allocation.     

Balancing variable patch quality with predation risk

Patch choice is almost always under the influence of multiple factors. Patch quality and the threat of predation are two such factors that have been shown to influence the foraging decisions of animals. In addition, aspects of patch quality may also vary with time, and consequently animals should incorporate temporal information to reduce their uncertainty about current patch conditions. The temporal weighting rule (TWR), which has been validated in previous studies, describes how animals should choose among variable options with the passage of time. In this study, we varied an additional factor, predation risk, along with certainty about patch yields in a field experiment, utilizing individually marked, free-ranging least chipmunks, Tamias minimus. We gave the animals in each condition experience at our experimental patches and then recorded patch choices a few minutes or one to 2 days later. The results show that animals combined perceived predation risk with a progressively shifting assessment of patch quality to form estimates of overall patch value as modeled by TWR. Based on the information available, the animals' patch choices were, arguably, the most adaptive choices.     

Can multiple mating compensate for slower development and shorter adult life in a male dimorphic dwarf spider?

Oedothorax gibbosus (Blackwall, 1841) is a dwarf spider characterized by the occurrence of a male dimorphism: the tuberosus male does not show any remarkable differentiation at the dorsal side of the carapace; the gibbosus morph on the contrary has a hunch behind the eye region, with a transversal groove densely clothed with hairs. These structures play an important function in the gustatorial courtship, being the uptake of secretions by the female from a body part of the male during courtship. Based on standardized survival experiments we show that tuberosus has a greater overall survival strength for different humidity levels than gibbosus . The two male morphs of O. gibbosus also have a different mating strategy: tuberosus as well as gibbosus copulate with virgin females, but gibbosus copulates significantly more with already inseminated females. Because of this strategy gibbosus secures its offspring notwithstanding the faster development, the longer adult life and the greater overall survival strength of tuberosus. © 2004 The Linnean Society of London, Biological Journal of the Linnean Society , 2004, 82 , 269–273.     

Sexual conflict over mating in a spider: increased fecundity does not compensate for the costs of polyandry

Female multiple mating (polyandry) is a widespread but costly behavior that remains poorly understood. Polyandry may arise when whatever benefits females accrue from multiple mating outweigh the costs, or males manipulate females against the females' best interests. In a polyandrous spider Stegodyphus lineatus females may mate with up to five males, but behave aggressively toward additional males after the first mating. Female aggressiveness may act to select for better quality males. Alternatively, females may try to avoid superfluous matings. To test these alternatives, we allocated females into single-mating (SM) and double-mating treatments. Double-mated females either accepted (DM) or rejected (RE) the second male. DM females laid more eggs, but did not produce more offspring than SM and RE females. Offspring of DM females were smaller at dispersal than offspring of SM and RE females. Also, nest failure was significantly more common in DM females. Paternal variables did not influence female reproductive success, whereas maternal body condition explained much of the variation. We show that polyandry is costly for females despite the production of larger clutches and suggest that multiple mating results from male manipulation of female remating behavior.     

Standard YPD, even supplemented with extra nutrients, does not always compensate growth defects of Saccharomyces cerevisiae auxotrophic strains

Conventional complex media are routinely used to grow auxotrophic strains under the assumption that they can compensate the latter's nutritional deficiencies. We here demonstrate that this is not always true. This study compares the growth parameters of Saccharomyces cerevisiae (S288C) and its derived auxotrophic strains FY1679-14C and BY4741 in synthetic minimal medium (SD), standard YPD medium from two of the most commonly used suppliers, or modified YPD medium. Maximum specific growth rates of auxotrophic strains were slightly lower than the prototrophic case in all growth conditions tested. Also, the biomass production of auxotrophic strains in synthetic medium was slightly less than the prototrophic case. However in both of the two standard YPD media used, the biomass production of both auxotrophic strains was markedly lower than that of the prototrophic one. The extent of the differences depended on the medium used. Indeed in one of the two YPD media, the lower biomass production of auxotrophic strains was evident even at the diauxic shift. Uracil seems to be the main limiting growth factor for both auxotrophic strains growing in the two standard YPD medium tested. No YPD media or specific supplement was able to compensate for the effect of the auxotrophic mutations in the multiple auxotrophic marker strain BY4741. The fact that auxotrophic strains grew poorly on YPD when compared to their prototrophic counterpart indicates that standard YPD medium is not sufficient to overcome the effect of auxotrophic mutations.     

Female mating preferences for colourful males in a population of guppies subject to high predation

Female guppies Poecilia reticulata descended from the Tacarigua population in Trinidad subject to high predation exhibited strong preferences for males with relatively high levels of carotenoid colouration. The study, which controlled for differences in male courtship, revealed that mate choice in this population is based on the expression of orange pigmentation, irrespective of differences in male motivation.     

Understanding predation risk and individual variation in risk avoidance for threatened boreal caribou

Predation risk is a driver of species’ distributions. Animals can increase risk avoidance in response to fluctuations in predation risk, but questions remain regarding individual variability and the capacity to respond to changes in spatial risk across human‐altered landscapes. In northeast British Columbia, Canada, boreal caribou populations declined as roads and seismic lines have increased, which are theorized to increase gray wolf predation. Our goal was to model risk and to evaluate individual variability and the development of risk perception by examining individual risk avoidance in response to reproductive status and age. We used locations from collared caribou and wolves to identify landscape features associated with the risk of a potential wolf‐caribou encounter and risk of being killed given an encounter. We built resource selection functions to estimate individual responses to risk. We used general linear regressions to evaluate individual risk and linear feature avoidance as a function of age and reproductive status (calf or no calf). Linear features increased the risk of encounter. Older caribou and caribou with calves demonstrated stronger avoidance of the risk of encounter and roads, but weaker avoidance in late summer to the risk of being killed relative to younger and calf‐less individuals. Mechanisms explaining the inverse relationships between the risk of encounter and risk of being killed are uncertain, but it is conceivable that caribou learn to avoid the risk of encounter and roads. Responses by females with vulnerable calves to the risk of encounter and risk of being killed might be explained by a trade‐off between these two risk types and a prioritization on the risk of encounter. Despite the capacity to alter their responses to risk, the global decline in Rangifer populations (caribou and wild reindeer) suggests these behaviors are insufficient to mitigate the impacts of anthropogenic disturbances.     

Visual extrapolation under risk: human observers estimate and compensate for exogenous uncertainty

Humans commonly face choices between multiple options with uncertain outcomes. Such situations occur in many contexts, from purely financial decisions (which shares should I buy?) to perceptuo-motor decisions between different actions (where should I aim my shot at goal?). Regardless of context, successful decision-making requires that the uncertainty at the heart of the decision-making problem is taken into account. Here, we ask whether humans can recover an estimate of exogenous uncertainty and then use it to make good decisions. Observers viewed a small dot that moved erratically until it disappeared behind an occluder. We varied the size of the occluder and the unpredictability of the dot''s path. The observer attempted to capture the dot as it emerged from behind the occluded region by setting the location and extent of a ‘catcher’ along the edge of the occluder. The reward for successfully catching the dot was reduced as the size of the catcher increased. We compared human performance with that of an agent maximizing expected gain and found that observers consistently selected catcher size close to this theoretical solution. These results suggest that humans are finely tuned to exogenous uncertainty information and can exploit it to guide action.     

Enhancement of chromatic contrast increases predation risk for striped butterflies

Many prey species have evolved defensive colour patterns to avoid attacks. One type of camouflage, disruptive coloration, relies on contrasting patterns that hinder predators' ability to recognize an object. While high contrasts are used to facilitate detection in many visual communication systems, they are thought to provide misleading information about prey appearance in disruptive patterns. A fundamental tenet in disruptive coloration theory is the principle of 'maximum disruptive contrast', i.e. disruptive patterns are more effective when higher contrasts are involved. We tested this principle in highly contrasting stripes that have often been described as disruptive patterns. Varying the strength of chromatic contrast between stripes and adjacent pattern elements in artificial butterflies, we found a strong negative correlation between survival probability and chromatic contrast strength. We conclude that too high a contrast leads to increased conspicuousness rather than to effective camouflage. However, artificial butterflies that sported contrasts similar to those of the model species Limenitis camilla survived equally well as background-matching butterflies without these stripes. Contrasting stripes do thus not necessarily increase predation rates. This result may provide new insights into the design and characteristics of a range of colour patterns such as sexual, mimetic and aposematic signals.     

Search for species-specific mating signal in courtship songs of sympatric sibling species,Drosophila ananassae and D. pallidosa

Sexual isolation is one of the most important mechanisms that may lead to speciation. Drosophila ananassae and D. pallidosa are useful for the study of sexual isolation, because of their sympatric distribution and no postmating isolation between them. Courtship songs are considered to play a crucial role in sexual isolation between D. ananassae and D. pallidosa. We recorded and analyzed male courtship songs of D. ananassae and D. pallidosa for eight and four geographical strains, respectively. Courtship behaviors of the two species were consistent with those previously described, however, male's middle leg shaking, which had not before been described, was observed in both species. Males sing by wing vibration only during courtship. Their song oscillograms were distinct between species, but those of conspecific strains were very similar, in spite of their different geographical derivation. We found species-specificity in burst length, pulse length, cycle number in a pulse, and frequency spectra of bursts; these results suggest that these song parameters may play a role in mate recognition that enforces their sexual isolation. The specific values of interpulse interval, cycle number in a pulse and intrapulse frequency were involved with the determination of specificity in frequency spectra of bursts. We discussed the possibility that the specific frequency spectra of bursts are recognized by females as the species-specific signal rather than each parameter individually.     

Preferences for familiar fish do not vary with predation risk in the European minnow

In the near-natural conditions of a fluvarium in the River Frome, U.K., European minnows Phoxinus phoxinus displayed schooling preferences for familiar conspecifics. Schools were composed of 75% familiar fish. The minnows in this river co-occur with many piscivores, the most notable being the pike Esox Iucius . The preference for familiar shoalmates was not increased by the threat of predatory attack from a model pike, despite the antipredator benefits afforded to individual members of schools of familiar fish.     

Interacting effects of predation risk and male and female density on male/female conflicts and mating dynamics of stream water striders

We used a factorial experiment to examine interacting effectsof male density, female density, and sunfish (predation risk)on mating dynamics of the stream water strider (Aquarius remigis).Many of our results corroborated earlier studies on the isolatedeffects of each factor on mating behavior. The effect of eachfactor, however, depended on the other factors. For example,in low density pools, predation risk decreased male generalactivity, male/female harassment rates, mating activity, andmating duration and increased the large male mating advantage.At higher densities, however, water striders apparently enjoyed"safety in numbers" and did not alter their mating dynamicsin response to the presence of predators. Female activity showeda particularly complex response to male density and fish. Whenmales were scarce, fish caused females to reduce their activity.However, when males were abundant, fish increased female activity,probably because fish decreased male activity thus releasingfemales from harassment by males. The three treatment factorsalso had interacting effects on male mating success. In theabsence of fish, when females were scarce, increased male densityresulted in a decrease in mean male mating success; however,when females were abundant, increased male density enhancedmean male mating success. In contrast, in the presence of fish,male density had little effect on male mating success. Manyof the observed mating patterns can be explained by the effectsof ecological and social factors on male/female conflicts; thatis, on male harassment of females and female reluctance to mate.     

Freezing behaviour facilitates bioelectric crypsis in cuttlefish faced with predation risk

Cephalopods, and in particular the cuttlefish Sepia officinalis, are common models for studies of camouflage and predator avoidance behaviour. Preventing detection by predators is especially important to this group of animals, most of which are soft-bodied, lack physical defences, and are subject to both visually and non-visually mediated detection. Here, we report a novel cryptic mechanism in S. officinalis in which bioelectric cues are reduced via a behavioural freeze response to a predator stimulus. The reduction of bioelectric fields created by the freeze-simulating stimulus resulted in a possible decrease in shark predation risk by reducing detectability. The freeze response may also facilitate other non-visual cryptic mechanisms to lower predation risk from a wide range of predator types.     

Snake activity affects seasonal variation in nest predation risk for birds

Variation in predator behavior has been proposed, but not tested, as a mechanism producing seasonal declines in avian nest success. We test this hypothesis by documenting seasonal activity of Texas ratsnakes Elaphe obsoleta and nest failure of endangered black-capped vireos Vireo atricapilla and golden-cheeked warblers Dendroica chrysoparia on which the snakes prey. Nest survival analysis was based on 880 vireo and 228 warbler nests and 3,060 snake locations from 62 radio-tracked snakes. Although nest success varied with snake activity for both birds, specific patterns differed substantially. Vireo daily nest survival was negatively correlated with snake activity over the three-year study, despite substantial variation among years in weather, and the fact that these birds are almost certainly a minor prey species of the ratsnakes. Warblers exhibited less clear-cut seasonal variation in nest success, and the association between nest success and snake activity was less pronounced than for vireos. Increased activity at warmer temperatures explained some of the seasonal change in snake movements, although mating may have accounted for a mid-season peak in activity. These results indicate that variation in predator behavior can be associated with and potentially cause seasonal changes in nest success, but also that these relationships are species specific even within the same community and may depend on aspects of the nesting ecology of the prey such as nest site selection.