Sensory Bias Research Articles

Information processing biases among chronic pain patients and ankylosing spondylitis patients: the impact of diagnosis

The aim of this research was to explore the impact that diagnostic status has on information processing biases among chronic pain (CP) and ankylosing spondylitis (AS) patients. AS patients, CP patients, and healthy hospital staff controls, completed a questionnaire and short computer task. During the computer task participants endorsed sensory, depression, illness, and neutral adjectives, following a cue question (which facilitated encoding of the adjectives in relation to the self). They were then asked to recall the adjectives in a surprise memory task. Diagnosed CP patients demonstrated a recall bias away from depression related stimuli, whilst the non-diagnosed CP patients did not. The results also suggest an association between receipt of a diagnosis and better psychological outcome in terms of information processing biasing. It was questioned whether the presence of a diagnosis among CP patients who are not currently depressed may protect or ‘buffer’ them against cognitive biasing towards classic depression related stimuli. The diagnosed AS group showed a bias towards sensory stimuli, perhaps reflecting the presence of an enduring and over-riding pain schema. The non-pain control group also displayed a sensory bias, which was attributed to a frequency effect as a result of working in an environment where they were regularly exposed to sensory language. The results are discussed in relation to existing literature in this area and implications for clinical practice are provided.

Ultraviolet signals in birds are special.

Recent behavioural experiments have shown that birds use ultraviolet (UV)-reflective and fluorescent plumage as cues in mate choice. It remains controversial, however, whether such UV signals play a special role in sexual communication, or whether they are part of general plumage coloration. We use a comparative approach to test for a general association between sexual signalling and either UV-reflective or fluorescent plumage. Among the species surveyed, 72% have UV colours and there is a significant positive association between UV reflectance and courtship displays. Among parrots (Psittaciformes), 68% of surveyed species have fluorescent plumage, and again there is a strong positive association between courtship displays and fluorescence. These associations are not artefacts of the plumage used in courtship displays, being generally more 'colourful' because there is no association between display and colours lacking UV reflectance or fluorescence. Equally, these associations are not phylogenetic artefacts because all results remain unchanged when families or genera, rather than species, are used as independent data points. We also find that, in parrots, fluorescent plumage is usually found adjacent to UV-reflective plumage. Using a simple visual model to examine one parrot, the budgerigar Melopsittacus undulatus, we show that the juxtaposition of UV-reflective and fluorescent plumage leads to a 25-fold increase in chromatic contrast to the budgerigar's visual system. Taken together, these results suggest that signals based on UV contrast are of special importance in the context of active sexual displays. We review briefly six hypotheses on why this may be the case: suitability for short-range signalling; high contrast with backgrounds; invisibility to predators; exploitation of pre-existing sensory biases; advertisement of feather structure; and amplification of behavioural signals.

Sensory Trap as the Mechanism of Sexual Selection in a Damselfly Genitalic Trait (Insecta: Calopterygidae)

During copulation, males of some calopterygid damselfly species displace the sperm stored in the spermatheca: the male genital appendages enter into the spermathecal ducts and physically remove sperm. In Calopteryx haemorrhoidalis, the genital appendages are too wide to penetrate the spermathecae, but males use a different mechanism in which the aedeagus stimulates the vaginal sensilla that control spermathecal sperm release. Since these sensilla are used during egg fertilization and oviposition, it was hypothesized that this function evolved before the male stimulatory ability. I investigated this using Hetaerina cruentata, a species whose position in the Calopterygidae phylogeny is more basal than Calopteryx. Given this position and having determined that males of this species are not able to displace sperm of their conspecific females during copulation, it was expected that H. cruentata females would eject sperm when stimulated with the aedeagi of C. haemorrhoidalis but not when stimulated with the aedeagi of their conspecifics. This prediction was confirmed. In order to investigate the widespread nature of this result, some other Calopteryx species-Calopteryx xanthostoma and Calopteryx virgo-were investigated. The results were similar to those of H. cruentata: conspecific males were unable to stimulate their females, but females ejected sperm when stimulated with C. haemorrhoidalis aedeagi. Morphometric analysis suggests that the mechanistic explanation for the stimulatory ability of C. haemorrhoidalis genitalia is that the aedeagal region that makes contact with the vaginal sensilla is wider in C. haemorrhoidalis than in the other species. These results suggest that the sensory "bias" shown and shared by H. cruentata, Calopteryx splendens, C. virgo, and C. haemorrhoidalis females represents an ancestral condition and that the male stimulatory ability is absent in the evolutionary history of the clade. These pieces of evidence as well as another one presented elsewhere, which indicates that C. haemorrhoidalis males vary in their stimulatory ability, constitute the three criteria for a case of sexual selection via exploitation of a female sensory bias. These results also provide support to the sensory trap hypothesis that indicates that the female bias-in this case, egg fertilization and oviposition-evolved in a context different from sexual selection. Considering that the male genital appendages responsible for physically removing spermathecal sperm in other calopterygids are present in C. haemorrhoidalis, I suggest that males were once able to displace spermathecal sperm physically. Such ability may have been later impeded by a reduction in size of the spermathecal ducts. Possibly, one of the latest events in this sequence is the male's stimulatory ability. This hypothetical series of events suggests a coevolutionary scenario in which the central actor is the sperm stored in the spermathecae.

No pre-existing biases for heterospecific call traits in the frog Physalaemus enesefae

Previous phonotaxis studies with two species of the Physalaemuspustulosus species group indicated that female preferences for several heterospecific call traits resulted from sensory biases inherited from a common ancestor. In phonotaxis experiments, we determined whether Physalaemus enesefae, a distant relative of the P. pustulosus group, showed similar preferences for call traits not present in conspecific males. We presented females with a choice between the typical conspecific advertisement call and the same call to which we digitally appended a chuck from P. pustulosus, a squawk from P. freibergi, and an amplitude-modulated prefix from P. pustulatus. In addition we presented the advertisement call in doublets, a trait peculiar to P. coloradorum. We also analysed male vocal behaviour evoked in response to the same suite of stimuli. Physalaemus enesefae females did not prefer the calls of their own males with appended heterospecific traits over unmodified calls, nor conspecific calls in doublets over single calls. The lack of preference among females was not the result of a behavioural polymorphism. Female responses to repeated presentations of the same stimulus pair were not consistent. Males also did not show an enhanced vocal response to altered calls relative to the typical conspecific call. Consequently, there are no pre-existing biases for these heterospecific call traits in P. enesefae; pre-existing preferences in the P. pustulosus group could have been inherited from an ancestor not shared with P. enesefae, but data from other closely related species are needed to confirm this conclusion. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Are human female preferences for symmetrical male faces enhanced when conception is likely?

Human females show a preference for the scent of symmetrical male bodies and appearance of masculine male faces only when conception is likely. These traits are thought to be signs of male quality. We examined whether females show an enhanced visual preference for another putative sign of mate quality, facial symmetry, when conception is likely. Twenty-nine females not taking oral contraceptives (nonpill users) rated the attractiveness of male faces varying in symmetry level (low, normal, high and perfect) for a short-term sexual partner at two phases of the menstrual cycle (low and high conception risk). They also rated the attractiveness of male faces for a long-term sexual partner and female faces for general attractiveness. We also tested a control group of 27 pill users. An overall preference for symmetry was found in all participants. However, the hypothesized enhanced cyclic preference for symmetrical male faces in nonpill users was not found. Nor was there an effect of relationship context. These results may be more consistent with a direct benefit or sensory bias model for preference evolution than with an indirect genetic benefit model. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.

Field bioassays show heterospecific mating preference asymmetry between hybridizing North American Papilio butterfly species (Lepidoptera: Papilionidae)

Few studies of interspecific mating preferences of naturally hybridizing species have been done in the field. Yet this is the only way potentially critical habitat-specific factors can be included in mating behavior evaluations. We conducted mate selection (male preference) studies using tethered pairs of heterospecific, size-matched virgin yellow females of Papilio glaucus and P. canadensis with free-flying male P. glaucus populations in south-central Florida, and with free-flying male P. canadensis populations in northern Michigan. Florida males clearly preferred the conspecific P. glaucus females of the pairs, as indicated by the touches/attempted matings and by the actual copulations observed. In 1997, 66.7% of the total attempts (n=168) and 94.2% of all copulations (n=69) were with the conspecific. In 1998 the same pattern of conspecific male preference was observed, with 67.3% of the touches/attempts (n=49) and 100% of the copulations (n=30) being with the P. glaucus females. In contrast, the natural populations of P. canadensis males did not show the expected conspecific preference. In fact, with wild P. canadensis males in 1997 a very strong preference was observed for the heterospecific P. glaucus females of the pairs, accounting for 75.8% of all touches/attempted matings (n=483) and 81.7% of all copulations (n=476). The strong asymmetry in interspecific mating preferences among these hybridizing Papilio species may reflect an ancestral trait in P. glaucus females that elicits strong preference in P. canadensis males, due perhaps to previously possessed male sensory bias or "good genes" indicators in the females. However, reinforcement of reproductive isolation in or near the hybrid zone of species overlap (sympatry) cannot be ruled out.

Contralateral inhibition as a sensory bias: the neural basis for a female preference in a synchronously calling bushcricket, Mecopoda elongata.

Imperfect synchrony between male calls occurs widely in acoustically courting crickets and bushcrickets. Males which are able to establish the temporal leadership usually attract more females in choice experiments but the proximate mechanism for this precedence effect is unknown. Here we show that contralateral inhibition, the neural basis for lateral contrast enhancement in the auditory pathways of insects and vertebrates, is also the probable proximate neural mechanism for this female preference. We recorded simultaneously from a pair of identified auditory interneurons in the synchronizing bushcricket Mecopoda elongata. When two identical acoustic stimuli are presented from opposite directions, one preceding the other by 120 ms, the neural representation within the receiver is far stronger for the leader signal. This results from a suppression of the neural response to the follower chirp by reciprocal contralateral inhibition. The advantage of the representation of the leader is 2-3-fold with time delays between 70 and 130 ms; the most clear-cut female preferences have also been found with such delays in previous behavioural experiments. In time-intensity trading experiments, a lead by 120 ms could only be compensated for by increasing the amplitude of the follower signal by 7-11 dB. We discuss contralateral inhibition in auditory systems as a sensory bias that results in female preference for leading signals, with important evolutionary consequences for male calling strategies.

A possible non-sexual origin of mate preference: are male guppies mimicking fruit?

In most animals, the origins of mating preferences are not clear. The "sensory-bias" hypothesis proposes that biases in female sensory or neural systems are important in triggering sexual selection and in determining which male traits will become elaborated into sexual ornaments. Subsequently, other mechanisms can evolve for discriminating between high- and low-quality mates. Female guppies (Poecilia reticulata) generally show a preference for males with larger, more chromatic orange spots. It has been proposed that this preference originated because it enabled females to obtain high-quality mates. We present evidence for an alternative hypothesis, that the origin of the preference is a pleiotropic effect of a sensory bias for the colour orange, which might have arisen in the context of food detection. In field and laboratory experiments, adult guppies of both sexes were more responsive to orange-coloured objects than to objects of other colours, even outside a mating context. Across populations, variation in attraction to orange objects explained 94% of the inter-population variation in female mate preference for orange coloration on males. This is one of the first studies to show both an association between a potential trigger of a mate-choice preference and a sexually selected trait, and also that an innate attraction to a coloured inanimate object explains almost all of the observed variation in female mate choice. These results support the "sensory-bias" hypothesis for the evolution of mating preferences.

Sensory Trap as the Mechanism of Sexual Selection in a Damselfly Genitalic Trait (Insecta: Calopterygidae)

During copulation, males of some calopterygid damselfly species displace the sperm stored in the spermatheca: the male genital appendages enter into the spermathecal ducts and physically remove sperm. In Calopteryx haemorrhoidalis, the genital appendages are too wide to penetrate the spermathecae, but males use a different mechanism in which the aedeagus stimulates the vaginal sensilla that control spermathecal sperm release. Since these sensilla are used during egg fertilization and oviposition, it was hypothesized that this function evolved before the male stimulatory ability. I investigated this using Hetaerina cruentata, a species whose position in the Calopterygidae phylogeny is more basal than Calopteryx. Given this position and having determined that males of this species are not able to displace sperm of their conspecific females during copulation, it was expected that H. cruentata females would eject sperm when stimulated with the aedeagi of C. haemorrhoidalis but not when stimulated with the aedeagi of their conspecifics. This prediction was confirmed. In order to investigate the widespread nature of this result, some other Calopteryx species—Calopteryx xanthostoma and Calopteryx virgo—were investigated. The results were similar to those of H. cruentata: conspecific males were unable to stimulate their females, but females ejected sperm when stimulated with C. haemorrhoidalis aedeagi. Morphometric analysis suggests that the mechanistic explanation for the stimulatory ability of C. haemorrhoidalis genitalia is that the aedeagal region that makes contact with the vaginal sensilla is wider in C. haemorrhoidalis than in the other species. These results suggest that the sensory “bias” shown and shared by H. cruentata, Calopteryx splendens, C. virgo, and C. haemorrhoidalis females represents an ancestral condition and that the male stimulatory ability is absent in the evolutionary history of the clade. These pieces of evidence as well as another one presented elsewhere, which indicates that C. haemorrhoidalis males vary in their stimulatory ability, constitute the three criteria for a case of sexual selection via exploitation of a female sensory bias. These results also provide support to the sensory trap hypothesis that indicates that the female bias—in this case, egg fertilization and oviposition—evolved in a context different from sexual selection. Considering that the male genital appendages responsible for physically removing spermathecal sperm in other calopterygids are present in C. haemorrhoidalis, I suggest that males were once able to displace spermathecal sperm physically. Such ability may have been later impeded by a reduction in size of the spermathecal ducts. Possibly, one of the latest events in this sequence is the male’s stimulatory ability. This hypothetical series of events suggests a coevolutionary scenario in which the central actor is the sperm stored in the spermathecae.

Out on a limb, or a new branch of signalling theory?

Could it be that one of nature's most dazzling displays is just a ‘keep out’ sign to insects? According to Hamilton and Brown's recent analysis 1xAutumn tree colours as a handicap signal. Hamilton, W.D. and Brown, S.P. Proc. R. Soc. London B Biol. Sci. 2001; 268: 1489–1493Crossref | Scopus (120)See all References1 of published data, the autumnal change in leaf colour of temperate deciduous trees is a handicap signal to their insect pests, revealing the commitment of the trees to defence. This is the first costly handicap signal to be proposed in plants 2xThe origin of autumn colours by coevolution. Archetti, M. J. Theor. Biol. 2000; 205: 625–630Crossref | PubMed | Scopus (90)See all References2. In animals, handicap signals are often behavioural: stotting in Thompson's gazelles being the most commonly cited example. The scope for handicap signals in plants is perhaps more limited, at least to our current view, but the area of plant–herbivore interactions is one in which they could evolve.Several conditions for a handicap signalling system between deciduous trees and their insect pests appear to be met. First, leaf colour change is costly. Greater percentages of chlorophylls than of carotenoids are resorbed before abscission, and, combined with the early cessation of photosynthesis and the production of other pigments in autumn leaves, it is difficult to view this process as a mere side effect of senescence. Second, the signal must be received. Some aphid species display a sensory bias towards yellow-green light, apparently preferring a dilute hue of the most attractive colour, which might provide a mechanism for host choice based on relative display intensity. Third, the signal should ultimately confer differential reproductive success. Pre-emptive antixenotic signalling, exploiting a pre-existing sensory bias, should protect the tree from both the effects of herbivory and any potentially damaging pathogens that their insect pests might be carrying.For the signal to remain honest, there must be a link between it and the quality (here defensive commitment) being signalled. In this case, there are two ways in which this might be true. Chemical changes in the leaf that result in the autumn colour display could be associated with the production of inhibitors that prevent germination of seedlings through the leaf litter. Aphids could therefore use leaf brightness as a means of assessing the overall energetic investment of the plant in defence. Alternatively, the colour change could be a visual call to arms: systems in which insect-damaged plants produce signals to attract other predatory insects are known 3xExperimental evidence that plants under attack may benefit from parasitoids. Fritzsche-Hoballah, M.E. and Turlings, T.C.J. Evol. Ecol. Res. 2001; 3: 553–565See all References3. Either way, the fact that a tree can produce a vivid display would provide useful information to insects seeking a host.The key, as always, lies in variation. The authors readily point out that only empirical tests will reveal the truth of their hypothesis, and suggest several potential veins of research at both the intra- and interspecific levels. In addition, some of their assumptions must be validated, particularly that specialist pests are more damaging to hosts than are generalist ones, and that the energetically costly autumn display is produced at the expense of some other function. However, this does not detract from a tantalizing idea that will no doubt spark an explosion of new research. Autumn will never be the same again.

Beyond reinforcement: the evolution of premating isolation by direct selection on preferences and postmating, prezygotic incompatibilities.

The evolution of premating isolation after secondary contact is primarily considered in the guise of reinforcement, which relies on low hybrid fitness as the driving force for mating preference divergence. Here I consider two additional forces that may play a substantial role in the adaptive evolution of premating isolation, direct selection on preferences and indirect selection against postmating, prezygotic incompatibilities. First, I argue that a combination of ecological character displacement and sensory bias can cause direct selection on preferences that results in the pattern of reproductive character displacement. Both analytical and numerical methods are then used to demonstrate that, as expected from work in single populations, such direct selection will easily overwhelm indirect selection due to low hybrid fitness as the primary determinant of preference evolution. Second, postmating, prezygotic incompatibilities are presented as a driving force in the evolution of premating isolation. Two classes of these mechanisms, those increasing female mortality after mating but before producing offspring and those reducing female fertility, are shown to be identical in their effects on preference divergence. Analytical and numerical techniques are then used to demonstrate that postmating, prezygotic factors may place strong selection on preference divergence. These selective forces are shown to be comparable if not greater than those produced by the low fitness of hybrids.

Signalling conflict between prey and predator attraction

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.

BEYOND REINFORCEMENT: THE EVOLUTION OF PREMATING ISOLATION BY DIRECT SELECTION ON PREFERENCES AND POSTMATING, PREZYGOTIC INCOMPATIBILITIES

The evolution of premating isolation after secondary contact is primarily considered in the guise of reinforcement, which relies on low hybrid fitness as the driving force for mating preference divergence. Here I consider two additional forces that may play a substantial role in the adaptive evolution of premating isolation, direct selection on preferences and indirect selection against postmating, prezygotic incompatibilities. First, I argue that a combination of ecological character displacement and sensory bias can cause direct selection on preferences that results in the pattern of reproductive character displacement. Both analytical and numerical methods are then used to demonstrate that, as expected from work in single populations, such direct selection will easily overwhelm indirect selection due to low hybrid fitness as the primary determinant of preference evolution. Second, postmating, prezygotic incompatibilities are presented as a driving force in the evolution of premating isolation. Two classes of these mechanisms, those increasing female mortality after mating but before producing offspring and those reducing female fertility, are shown to be identical in their effects on preference divergence. Analytical and numerical techniques are then used to demonstrate that postmating, prezygotic factors may place strong selection on preference divergence. These selective forces are shown to be comparable if not greater than those produced by the low fitness of hybrids.Corresponding Editor: M. Whitlock

Inferring the Origins of State‐Dependent Courtship Traits

We examine a simple model of state-dependent (indicator) traits that focuses on their evolutionary origins as courtship signals. A necessary condition for the initial evolution of signals was found: the marginal female preference for minimal traits must exceed a certain threshold, where that threshold is proportional to the marginal male fitness costs for minimal traits. We interpret a positive threshold as implying a need for preexisting sensory bias in order to overcome the threshold if indicator signals are to start to evolve. We extend the model to allow for the possibility that signal costs and female preferences may vary over evolutionary time. If there is independent information on the way that signaling costs have evolved, then one may use measurements of contemporary female preferences to make inferences concerning the presence of the ancestral threshold. It is the marginal female preferences for minimal male traits that are important, whereas reconstructing ancestral origins from measurement of average size signals is not informative. Our analyses suggest two foci for future studies: measurement of the marginal response of contemporary females to minimal male signals and reconstruction of how signaling costs have changed over evolutionary time.

Auditory symmetry analysis.

The study of biological symmetry continues to be an important and active area of research, yet in the hearing sciences there are no established quantitative methods for measuring auditory asymmetries and dissimilarities in threshold tuning curves (i.e. audiograms). Using a paired design and adopting methods from the analysis of fluctuating asymmetry, we describe methods for auditory researchers interested in delineating auditory asymmetries and comparing tuning curves, behavioral or neural. We illustrate the methods using audiograms of the prothoracic T-cell interneuron in a nocturnal katydid (Neoconocephalus ensiger). The results show that 87-92 % of T-cells had right-minus-left threshold asymmetries no larger than expected from measurement error alone. Thus, apart from small random fluctuating asymmetries, T-cell pairs in N. ensiger showed no sensory bias and were bilaterally symmetrical from 5 to 100 kHz. The sensitivity of the methods for detecting tuning curve dissimilarities was confirmed in a sound lateralization paradigm by comparing the 'symmetry' (i.e. similarity) of T-cell tuning curves measured at 0 degrees stimulation with tuning curves measured at 90 degrees stimulation for the same T-cell. The results show that T-cell thresholds measured frontally (0 degrees ) were significantly higher than those measured laterally (90 degrees ), particularly for ultrasonic frequencies. Statistically, the directional shift (increase) in auditory thresholds was detected as a directional asymmetry in T-cell tuning, whose origin and functional significance to an insect behaving normally are discussed. The paper discusses practical considerations for detecting auditory asymmetries and tuning curve dissimilarities in general, and closes by questioning the relevance of auditory symmetry for sound localization in both vertebrates and insects.

Call Structure Variability and Field Survival among Bushcrickets Exposed to Phonotactic Parasitoids

Calling adult males of the univoltine bushcricket Sciarasaga quadrata are subject to significant mortality from the phonotactic parasitoid fly Homotrixa alleni. These flies kill their host within 14d and act as a constant ‘filter’ on the survival of male bushcrickets. In this study, I investigate both short-term and lifetime variability in male call structure and compare the call properties of collections of males made over a 3-mo calling season to establish whether there are any significant differences in the call properties of males surviving the length of the calling season. Call frequency, chirp length, interchirp length, chirp rate, file teeth used to make a chirp and duty cycle all showed good differentiation among males and significant repeatability: (1) within a calling bout (0.57–0.88), (2) between successive nights (0.27–0.83), and (3) over a male's lifetime (0.15–0.43). Frequency and to a lesser extent chirp length showed low variability within and among males whereas interchirp length was the most flexible and dynamic call property. As males aged, chirp length, which is produced by one wing closure, and its correlate, teeth per chirp, significantly increased and chirp rate significantly decreased. Over the calling season chirp length and teeth per chirp showed strong directional shifts. Shorter chirp males were lost from the calling population, indicating that flies may use chirp length as a cue in host location. The implications of this result are discussed in relation to the reproductive fitness of male S. quadrata and within the context of host location and sensory bias in phontotactic parasitoids.

Trade-off in short- and long-distance communication in tungara (Physalaemus pustulosus) and cricket (Acris crepitans) frogs

Female phonotaxis in tungara (Physalaemus pustulosus) and cricket (Acris crepitans) frogs is biased toward male advertisement calls or call components of lower frequency. This behavioral bias might result in part from a mismatch between the spectral characteristics of the advertisement call and the most sensitive frequency of the peripheral end organ implicated in reception of these sounds. In both species, females are tuned to frequencies lower than average for the calls in their population. This mismatch, however, represents the situation during short-distance communication. Female frogs can also use the call to detect choruses at long distances, and the spectral distribution of call energy can vary with transmission distance. We used computer simulations to test the hypothesis that there is a better match between tuning and call spectral energy at long distances from the calling male than at short distances by comparing the performance (sound energy received) of the natural tuning curve relative to an optimal tuning curve (i.e., one centered at the call's dominant frequency). The relative performance of the natural tuning curve increased with distance in tungara frogs. For the two subspecies of cricket frogs, however, the relative performance decreased at longer distances. The performance did not equal the optimal tuning curve at the distances tested. The results indicate that the relationship between calls and auditory tuning cannot be optimal for both long and short distance reception. The relationship between female tuning and call dominant frequency may represent a compromise between short and long distance communication, and the bias toward short or long distances may vary among species. Key words: Acris crepitans, auditory system, communication, cricket frogs, Physalaemus pustulosus, sensory biases, sexual selection, tungara frogs. (Behav Ecol 11:102-109 (2000))

Is female preference for male repertoires due to sensory bias?

There are several possible explanations for the female preference for male repertoires in birds. These males are older, and have better territories; thus there are functional reasons for females to prefer these males. However, there is an alternative explanation; females may habituate less quickly to song repertoires than single songs. I tested whether females have a non-functional, sensory bias for male song repertoires, by testing female preference for a repertoire in zebra finches (Taenopygia guttata), a species in which males possess a single stereotyped song. Females chose between a male repertoire of four different phrases created from the song phrase of one individual and that of one of those phrases repeated four times (natural zebra finch song). Females were also given a choice between the above repertoire and a song made from the phrases of four related males ('family' stimulus). I tested female preference by training females to press a button for presentation of a song stimulus, and counting the number of button presses. Females preferred the song repertoire to a single phrase song, and did not differentiate between the repertoire and song phrases from four males. Evidence from the Estrildidae indicates that having a single song is the ancestral state for zebra finches, so the preference is not ancestral.

Performance Tradeoffs for Two Hosts within and between Populations of the Oligophagous Grasshopper Hesperotettix viridis (Acrididae)

Diet selection by insect herbivores often varies among sites in response to combined ecological and evolutionary factors. The oligophagous grasshopper Hesperotettix viridis feeds almost exclusively on composites (Asteraceae) in the tribe Astereae. While host lists compiled from throughout the species' geographic range are extensive, restricted diets within populations suggest local adaptation by H. viridis to specific but different host plants. We evaluated population differentiation in performance (developmental rate, individual weight gain, and survivorship) by H. viridis to two host plant species (Solidago mollis and Gutierrezia sarothrae) using reciprocal transplant experiments in the field. Even though out experiments included a conditioning treatment, individuals from all populations generally performed better on host plant species from which they were collected than on alternate hosts. Physiological tradeoffs in performance on alternate host plants best explain this result, a result expected if population differentiation in host plant use exists. Grasshoppers originally collected from G. sarothrae developed faster, survived longer, and gained more weight when fed G. sarothrae. Similarly, individuals originally collected from S. mollis developed faster and gained more weight on S. mollis compared with G. sarothrae although survivorship did not differ. Consumption of host species in paired choice tests revealed overwhelming preference for host species from which the grasshopper was collected, regardless of the host conditioning. Differentiation in performance on the two host species including negative tradeoffs also occurred at a single site, coupled to sensory biases in host selection reinforce the evolution of diet specialization in H. viridis.

Male copulatory sensory stimulation induces female ejection of rival sperm in a damselfly

Male damselflies possess very specialized genitalia. Females mate multiply and store sperm in two sperm storage organs, the bursa copulatrix and the spermatheca. During copulation, males physically remove the sperm stored in these organs using their genitalia. I document a novel mechanism by which males gain access to the spermatheca in Calopteryx haemorrhoidalis asturica . The mechanism is based on male stimulation of the female sensory system that controls egg fertilization and laying. During copulation, the aedeagus (a male genitalic structure indirectly involved in sperm transfer) distorts the cuticular plates in the female genital tract that bear mechanoreceptive sensilla. This stimulation results in sperm ejection from the spermatheca. Aedeagus width is positively correlated with the amount of sperm ejected. I propose that males have exploited a pre–existing female sensory bias to gain access to otherwise physically unreachable sperm. These results shed light on the issue of the origin of female preferences in current models of sexual selection and on the evolution of genitalia via sexual selection. It is postulated that females might use this process as a form of post–copulatory sexual selection on the basis of males9 genitalia.