Vibratory signalling during courtship in the rneadow katydid Conocephalus nigropleurum

Paul Anthony De Luca

A thesis submitted in conformity with the requirements for the Degree of Master of Science Graduate Department of Zoology University of Toronto

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Canada Vibratory signalling during courtship in the meadow katydid Conocephalus nigropleurum Master of Science, 1997 De Luca, Paul Anthony Department of Zoology University of Toronto

When a male Conocephalus nigropleurum encounters a conspecific female he initiates the interaction with a behaviour known as tremulation. The male lifts his body up from the substrate and then brings it back dom again a number of times in rapid succassion. This behaviour always precedes copulation. Four components of this signal wexe measuxed in a population of lab reared males: pulse duration, peak positive amplitude, the number of oscillations per pulse, and pulse interval. Of these, peak positive amplitude and pulse interval displayed high repeatability. Correlations between male weight and the four parameters revealed a strong negative relationship only to pulse interval. In playback experiments females preferred to move ont0 a dowel transmitting tremulation over one that did not. Furthemore, when offered simultaneous presentations of tremulation signals that differed in pulse intemal, females preferred to orient towards the signal with the shorter pulse interval reflecting a large male. ACKNOWLEDGMENTS

First and foremost 1 would like to thank my supervisor, Glenn orr ris, for his encouragement and guidance throughout the

duration of this study. 1 owe much to his contagious fascination with the behaviour of these slnging wonders. Darryl Gwynne, Robert Baker, and Rex Cocroft provided much assistance in designlng the playback experiments. Their advice and criticisms were greatly appreciated at several points along the way . I would also like to thank the graduate students of the Behaviour Group: Adrienne Rigler, Tanta Savin, Pat Lorch, Janice Ragsdale, Ché Elkin, and Merrylee McGuffin. Their support and camaraderie will not go unremernbered. The gentlemen of the Academic workshop, John, Dave, and Paul, were always ready to build another piece for my playback apparatus. Many thanks go to them.

Luc Bussière and Daryl LeBlanc never wavered in theix friendship. And finally I would like to thank my parents, Filornena and Anthony, without whose total support in al1 aspects of my life none of this would be possible. Grazie.

iii Acknowledgements ...... iii Table of contents...... -iv

List of figures ...... vi

Methods,...... --...... ,...... -...-.....d Collection and rearing of individuals...... 6 Recording and analysis of tremulation signals-... 7 Playback signals ...... 16 Acoustic Song used in playback trials,...*.* .... -20 Playback procedure ...... -...O.0.---.21 Playback experiments ....O...... -...---.25 Res~lt~....~~~~~.~..-..~...~....~~~~~~..-.~.~.-~~.~~.~26 Analysis of the male tremulation signal ...... 26 Relationship between tremulation and male size...28 Female response to tremulation...... , ....-..----.28 Discussion-...... -..-.*.-.---.-...... ,...0...... 39 Information content of tremulation signals., ..-..39 Females respond to the vibratory component of tremulation...... ,.-....-..--.-.--..--....-..42 Cues for mate selection in Conocephalus nigropleurum ...... O.-...44 Table Page

1 Physical characteristics of vibratory signals ...... 17 2 Repeatability in male tremulation ...... 27 3 Correlation matrix between male weight and tremulation parmeters ...... 29 1 Screen cage used to record tremulation ...... 9 2 Tremulation parameters measured ...... 12 3 Tremulation pulse of Conocephalus nigropleurum ...... 14 4 Artificial vibration stimulus ...... 19 5 T-maze apparatus used in playback experiments ...... 23 6 Relationship between male weight and pulse interval ...31 7 Response of female C . nigropleurun to tremulation .....33 8 Ability of female C . nigropleurum to distinguish tremulation from a synthetic vibration...... -35 9 Preference of female C . nigropleurum for tremulation signalç that differ in pulse interval ...... 38 Many use substrate-borne vibrational signals to communicate with members of their own species. Although this form of vibrational communication is widespread across several different taxa (reviewed in Ewing 1989), the different contexts in which such signals are given have been examined in only a few groups . groups that have received the most attention for their use of substrate-mediated communication include spiders (Araneae) (Barth 1982; Uetz and Stratton 1982), and several insect orders: Heteroptera (Claridge 1985a; Gogala

1985), Neuroptera (Henry 1979; Duelli and Johnson 1981), (Keuper et al. 1985; Belwood and Morris 1987) and Plecoptera (Rupprecht 1968; Ziegler and Stewart 1977). In these groups, substrate signals are produced by both sexes for mate attraction. The vibrations generated when calling for mates are thought to play a role primarily in species recognition .(Ziegler and Stewart 1986; DeWinter and Rollenhagen 1990; Henry and Wells 1990; Schmitt et al. 1994). Once a male and female have corne together, vibrational signals continue to be used by both sexes to initiate courtship and elicit copulation (Morris 1980; Claridge 1985b; Wells and Henry 1992; Hunt 1993). Few studies to date, however, have examined how intraspecific variation in male-produced vibratory signals might be important in female mate choice. In Orthoptera three methods for generating vibratory signals have been identified. First, when male crickets

1 (Gryllidae) and katydidç () stridulate they impart vibrations into the substrate through their legs and abdomen as a by-product of their singing. Presented alone, these vibrations could be detected by conspecifics up to 2 metres away (Latimer and Schatral 1983; Kalmring et al. 1983; Weidemann and Keuper 1987). Second, some species transmit vibratory signais through a behaviour known as drumming. This is accomplished when an individual strikes the substrate repeatedly with either its abdomen or hind legs in rapid succession (Sismondo 1980; Morris and Beier 1982; Morris et al. 1994). The third method, called tremulation, occurs when an individual, keeping al1 six legs firmly on the substrate, moves its body up away Erom the substrate and then brings it back down in quick oscillations without allowing body contact with the substrate (Bell 1980; Morris 1980). Vibrations are detected with the subgenual organs, each located at the tibial-femoral joint of al1 six legs. This organ is extremely sensitive to the range of low frequencies generated from al1 three types of substrate vibration (Kalmuing et al. 1994; 1997). Tremulation occurs throughout the Tettigoniidae. Busnel et al. (1955) were the first to describe tremulation in katydids. They performed a detailed analyçis of the temporal structure of the signal in two species, Ephippiger ephippiger, and E. bitterensis, and found that both sexes tremulate. Further work revealed that males tremulate vigorously when they have paired with a conspecific female, just prior to copulation (Busnel

1963 ) . Steidl and Kalmring (1989) performed playback experiments with E. ephippiger females to examine their ability to locate artificial tremulation signals on a multi-branched woody plant. Although females were able to orient to an artificially- generated tremulation signal when it was the only stimulus provided, the time required to locate the signal decreased significantly when it was broadcast simultaneously with conspecific airborne Song. Some species of Neoconocephalus also use vibratory signals during courtship (Whitesell 1969; Gwynne 1977; Meixner and Shaw 1986). When a female approaches a singing male, she begins to tremulate, possibly to advertise her presence. Once the male is aware of her, he also begins to tremulate and continues to do so until copulation begins (Gwynne 1977). Morris (1967) described tremulation behaviour by males in the meadow katydid, Conocephalus nigropleurum. In this species males establish singing territories within which they do not tolerate the presence of conspecific males. If a singing male is approached by another, they will fight by kicking each other with their legs until one combatant withdraws. When two males corne together to fight, they initiate the encounter with a series of tremulations (Morris 1971)- Males also tremulate in the presence of females, but its function is not well understood in this context. As in Ephippiger and Neoconocephalus, this behaviour occurs only when a male has made contact with a female just prior to copulation.

What role does tremufation play in courtship? During copulation male katydids typically provide females with a large proteinaceous gift, the spermatophylax, which is part of the spenn-containing spennatophore (Boldyrev 1915). Consuming the spermatophylax after mating increases female fecundity in some katydids (Gwynne 1984; 1988). Gwynne (1982) showed that the spermatophores produced by males in Conocephalus nigropleurm are positively correlated with body weight. In addition, when given the choice between two different sized singing males, females always mated with the larger male (Gwynne 1982). Although acoustic cues were hypothesized to be one mechanism by which females identified larger males, vibratory cues were equally likely to play a role: wood dowels were used in this study, which is a substrate that conducts tremulation signals very efficiently (Bell 1980; Michelsen et al. 1982; Keuper and Kühne 1983).

Tremulation may be a reliable indicatox of body size tg females in C. nigropleurum. Since larger males produce a more substantial nuptial gift, females benefit by choosing to mate with a bigger individual. Therefore, females should use some cue to discriminate among different sized males in order to maximize the size of the spennatophore received during copulation. In fact, Gwynne (1982) reported that in three of his twelve trials, a female moved first to the smaller male and interacted with him for a short time before moving towards the larger male and eventually mating with him. In those three cases, females may have rejected the smaller male because his tremulations indicated his small size, and therefore, his poor potential at oifering a significant nuptial gift. In order to understand the role of tremulation during courtship in Conocephalus nigropleum this study was conducted with the following objectives: 1) to describe the tremulation signal given by courting males, 2) to detennine whether females respond to tremulation by moving towards it, and 3) to determine if any feature of the tremulation signal is a reliable indicator of male size, and therefore might be used as a cue by females to assess male weight. Because females are known to select large males as mates 1 hypothesized that: 1) males of different sizes will differ in their ability to tremulate, and 2) females will discriminate in favour of a tremulation signal that reflects the bigger male. MATERIALS AND METHODS

Collection and rearing of individuals Clonocephalus nigropleurum oviposit in willow (Salix sp.) galls made by flies of the family Cecidomyidae (Wheeler 1890). Eggs of C, nigropleurum were obtained from the field from two locations. In November 1995 and February 1997 1 collected eggs from galls located along Black Creek at Caledon, Ontario and in

June and November 1996 £rom alongside the Credit River adjacent to the campus of Erindale College at Mississauga, Ontario. In the summer of 1997 I collected nymphs from an old field in Oswego, New York State, and the Caledon site in Ontario. Eggs were removed £rom the galls and placed in glass petri- dishes (approx. 70-80 eggs per dish) lined with moistened filter paper. They were incubated in an environmental chamber maintained at 26OC, 85% relative humidity, and a 12:12 photoperiod. The egos were sprayed with water every day and nymphs began hatching 15 days later. These nymphs were housed communally to a maximum of about 50 individuals in each of two wood cages (32 x 32 x 30 cm) that were fitted with a clear Plexiglass lid. They were fed a mixture of wheat seedlings, apple slices and canned dogfood while kept in the wooden containers. After six weeks the nymphs were isolated individually in 330 rnL cylindrical plexiglass containers fitted with screen tops. Nymphs collected from the field were also placed individually in plexiglass cylinders. Once isolated, nymphs were fed apple slices and pellets composed of fish flakes, pollen and seeds (JJkatydidcake") developed by Cynthia Thomas, With this rearing protocol adults emerged 7-8 weeks after being brought into the lab as eggs, and 2-3 weeks after being brought back as nymphs.

Recording and analysis of tremulation signals

Al1 recordings were made in a sound-attenuating room under constant light at temperatures between 25-30°C. A male and female (both virgins and at least 10 days beyond their final moult) were placed inside a 575 mL aluminum screen cage (wire thickness: 0.06 cm) which was secured to a foam base with insect pins and observed for 10 minutes, An accelerometer (Brüel & Kjær [B&K] #4393, Elat frequency response: 0-18 kHz]) was attached at the mid-point of the cage along the side to record substrate vibrations produced by the (Fig, 1). The accelerometer was connected to a B&K Sound Level meter (#2203) calibrated for vibration measurements which relayed signals to a Racal 4DS tape recorder, The recorder was set to Frequency modulation mode with a recording speed of 15Vsec (frequency response: 0-5 kHz). Each tirne a male tremulated 1 noted it on the voice channel on the Racal. This allowed me to discriminate tremulation signals from other vibrations (walking or jumping disturbances) when 1 replayed the tape and observed the signals on an oscilloscope (Tektronix #455),

Recordings were lowpass filtered at 5 kHz with a Krohn-Hite (#3380) filter befoxe being digitized through a signal acquisition board (DAS50, Keithley Metrabyte) connected to an Fig 1. Aluminum screen cage used to record the male tremulation signal of Conocephalus nigropleurum. The accelerometer is located at the mid-point of the cage with the Sound Level meter to the right of the foam base. The screen cage measures 15 cm in height and 7.5 cm in diameter.

IBM-compatible computer. Once digitized, the recordings were saved in ASCII file format and imported into analysis software (DADiSP 3.01, DSP Development Corporation). Twenty males from the Caledon site were used to measure the physical parameters of tremulation. In order to also assess intra-individual variation three tremulations from each male were examined, The following parameters were measured using DADiSP: 1) pulse duration, 2) number of oscillations within one distinct pulse, and 3) frequency bandwidth (Figs. 2 & 3). During recording 1 was unable to monitor tremulation intensity on the Sound Level meter, however, an alternative measure of intensity was obtained using DADiSP- 1 measured the peak positive amplitude of each pulse, which reflected the magnitude of the signal in the vertical plane (Fig- 2). Although the value obtained is unitless, it can be used to compare different pulses with one another. For example, a pulse with a peak amplitude of 2000 can be regarded as having twice the peak intensity as a pulse with a peak amplitude of 1000, However, accelerometers record signals properly only when the vibrations are propagated directly along their main sensitivity axis (Serridge and Licht 1986). Therefore, the vibrations generated £rom a tremulating male whose signal is being transmitted in a plane other than the accelerometer's most sensitive will not be recorded well. This will result in reduced peak amplitude values that are not indicative of a male's true signalling ability. This caveat must be kept in mind when 1 discuss the relevance of peak amplitude as an Fig. 2, ILLustration of a typical tremulation pulse of a C. nigropleurum male, indicating the parameters measured. A. 1- Peak postive amplitude, 2- Pulse duration, 3- Pulse A interval. 8. An enlarged tremulation pulse from (A) showing the sinusoidal pattern of four (i-iv) oscillations.

Fig 3. An example of a tremulation pulse from a C. nigropleurum male. A. Amplitude modulation pattern. 8. Power spectrum. Main frequecy band lies in the range 175-400 Hz (ms- milliseconds, Hz- Hertz). important parameter of the tremulation display. A fifth parameter, pulse interval, was calculated by replaying the recording made for each male and with a stopwatch measuring the time interval between two successive tremulations while observing them on an oscilloscope (Fig. 2). Except for the number of oscillations within a pulse (see below), descriptive statistics for these parameters are expressed as the mean + SE (n=20 males). Repeatability measures were calculated for the following parameters: peak positive amplitude, pulse duration, number of oscillations per pulse, and pulse interval. Three tremulations from each male were selected randomly from their 10-minute signalling bout and used to calculate the repeatability values. Repeatability describes the extent to which variation within individuals contributes to total inter- individual variation for a particular behaviour (Boake 1989). Perfect repeatability, denoted by a value of 1.0, indicates no intra-individual variation for a behaviour. Therefore, traits that display high repeatability serve as reliable indicators of individual performance, and thus rnay ultimately operate as indicators for female choice (Clark and Moore 1995). Pearson product-moment correlation analyses were performed between the tremulation parameters and male weight to determine if any component of the signal reflected body size. Values for the number of oscillations per pulse were non-normally distributed (Kolmogorov-Smironov, Lilliefors P=0.001) therefore Spearman rank correlation was used to examine its relationship to the other signal parameters and male weight. Males were killed by freezing and then stored in 70% ethanol. After storage, they were weighed on an electronic balance (Mettler PC-440) to the nearest 0.01 gram.

Playback signals Natural playback tremulation From the 60 tremulation signals analyzed, one was chosen as the primary playback stimulus. This signal, herein-after referred to as TREM-1, contained modal values for the parameters that were examined (Table 1, Fig. 3). It was used as a representative conspecific signal both for initial playback and to mode1 both small and large-male tremulation signals. Artificial "control" vibration

A synthetic vibration (CONTROL-1) was constructed using DADiSP following a procedure similar to that used by Wells and Henry (1992). The signal was designed to have the same pulse duration, peak amplitude, and pulse interval as TREM-1, but with a broader spectral band and without a specific amplitude pattern when compared to TREM-1 (Table 1, Fig. 4). Modified tremulation sisnals

Two stimuli were constructed using DADiSP that differed in two parameters. Both were based on TREM-1 but differed in the two parameters that displayed the largest repeatability values

(see Results). One signal (TREM-H) was constructed to have the same pulse interval as TREM-1 but only half its peak amplitude, while the other stimulus (TREM-2) had the same peak amplitude as Table 1. Physical characteristics of vibratory signals used in playback experiments. Values for pulse duration, peak positive amplitude and thi number of oscillations per pulse for TREM-1 reflect the mode for those signal components in the population of males examined (n=20).

L m

, Stimulus Pulse Peak Nurnber of Pulse Frequency duration positive oscillations interval range (sec) amplitude per pulse ( sec (Hz) TREM- 1 O. 190 1500 4 1 -175-400 CONTROL - 1 O. 190 1500 - 1 -0-4000 TMM-H O. 190 750 4 1 -175-400 TREM-2 O. 190 1500 4 2 -175-400 Fig 4. Artificial vibration stimulus (CONTROL-1) used in experiment 2. Amplitude modulation pattern. 8. Power spectrum. Frequency band is much broader than in a normal tremulation pulse, covering a range from 0-4000 Hz. Note the difference in scale of the x-axis compared to Fig. 3 (ms- milliseconds, Hz- Hertz).

TREM-1 but twice its pulse interval (Table 1). These manipulations ensured that both signals provided equal levels of total stimulus energy during playback (Gerhardt 1992). Al1 four stimuli were saved in binary file format on DADiSP and exported to another computer for the playback experiments.

Acoustic song used in playback trials The acoustic song of Conocephalus nigropleurum was broadcast simultaneously with vibratory stimuli during the playback trials. This was done to make the trials biologically realistic, since in the field females moving through the habitat would most often hear the Song of males well before encountering any courtship vibratory signals. Also, females were released 36 cm below the choice point in the T-maze (see page 21), and so conspecific song broadcast from above would motivate a receptive female to begin climbing up the central stick rather than moving in another direction. A Song sample from a C. nigropleurum male recosded in a previous study by Morris et al. (1978) was used as the acoustic stimulus. The temperature at which the Song was recorded (2g°C) fell within the temperature range used for the playback experiments. The song was played from an IBM-compatible computer through a digital to analog converter (PCIP-AWFG) using custom-made playback software developed by Wes Brozda. The Song was bandpass filtered (10-70 kHz) using an analog filtew (Krohn-

Hite #3202) before being input into an amplifier (B&K #2706 or Pioneer GM43A) and bxoadcast through a directional speaker (Technics Leaf tweeter). The speaker was positioned directly behind the choice point (see below) 52 cm away (Fig. 5). The

playback level was set at 70 dB SPL at 52 cm (re 20 pPa).

Playback procedure Playbacks were conducted with an IBM-compatible cornputer using custom-made playback software developed by Kim Yue. Vibratory stimuli were played through a digital to analog converter (Tucker-Davis Technologies) and then lowpass filtered

at I kHz. For the first experiment, the output from the filter was connected to a B&K Power Amplifier (#2706) and a B&K electrodynamic vibration exciter (#4810) which transmitted the signal to wood dowels in the playback arena. For the second and

third experiments outputs from the filter were connected directly to the vibration exciters, as the filter was used to amplify the signals directly. A T-maze apparatus was used to examine female response to one or two tremulation signals (Fig. 5). Two electrodynamic vibration exciters transmitted vibratory stimuli via a thin metal rod to 0.1 cm diameter birch dowels supported by 4 cm diameter birch dowels. The point of stimulus application was 20 cm £rom the choice point on the T-maze. The exciters were held

in position with metal clamps attached to the ceiling of the room. Virgin females were placed in the centre of the T-maze 36 cm below the choice point in a screen cage and allowed to

acclimate for 5 minutes. The top of the screen was then removed and the locomotion of the female observed. Most females Fig 5. T-maze apparatus used in the playback experiments. Females were released from the screen cage 36 cm below the choice point. Stimuli were applied to the dowels with a metal rod, attached to a vibration exciter located 15 cm below each am of the maze. The point of stimulus application was 20 cm from the choice point. The speaker used to broadcast the calling Song is visible in the background, directly behind the choice point where the two anns meet just above the central stick. eventually climbed up the centre stick and arrived at the choice point. Once there, a female had to place both front tarsi on the arms of the maze simultaneously. This ensured that females were in contact with both sides of the maze at once for a few seconds before making a decision to move. Females that did not remain at the choice point in the manner described were immediately removed from the arena and used again at a later date. For a trial to be included in my analysis, a female had to move at least as far as the point where the stimulus was applied by the electrodynamic shaker. Females that did not conform to these criteria by their third tirne through the arena were not used again. The T-maze was situated in a sound-attenuating room and al1 trials were conducted under constant light and temperatures usually near 28OC, but rarely varying between 25-30°C. Playback intensities for the stimuli used approximated that obtained for tremulations given by two males measured on one of the 0.1 cm birch dowels £rom the T-maze. One male at a time was placed on the dowel with a virgin fernale to stimulate the commencement of courtship behaviour. An accelerometer attached to the dowel relayed trernulation signals to a Sound Level meter calibrated to provide vibration intensity readings in decibeis. Tsemulation intensities for both males ranged from 35-40 dB

(-0.196 m/s2 re 1 g RMS) when measured 7-15 cm away from the accelerometer. Since the electxodynamic shakers were located 20 cm away from the choice point, the intensity for al1 four stimuli during playback was increased slightly to between 43-45 dB (-0.348 m/s2 re 1 g RMS) at the choice point.

Playback experiments Experiment 1 This experiment was performed to determine whether females respond with vibrotaxis to the tremulation signal of a conspecific male. One am of the T-maze received stimulation by TREM-1, while the other am received no stimulus. For each trial, the am that received stimulation was switched to control for any possible bias by females to move preferentially to a particular side of the maze. Ex~eriment2

This experiment was conducted to examine if females move preferentially to a conspecific tremulation signal over another vibratory stimulus. The arms of the maze received stimulation by either TREM-1 or CONTROL-1 which were applied simultaneously during the trials. The side to which a particular stimulus was applied was alternated for every trial to guard against bias. Experiment 3 This experiment was performed to investigate female preference for tremulation signals that differed in pulse interval and peak amplitude, two parameters that Vary arnong males. The procedure was identical to that followed in the previous experiment, except that the two stimuli used were

TmM-H and TREM-2. RESULTS

Analysis of the male tremulation signal A single tremulation pulse comprised a series of sinusoidal oscillations executed in rapid succession (Fig. 2B)- The amplitude modulation pattern of the signal is very consistent between males, The oscillations within a pulse increase in amplitude and reach a peak level by about the second or third oscillation, and then decrease in amplitude as the pulse concludes (Fig. 2B). A tremulation pulse has a mean duration of 0.190 i 0.006 sec and is cornposed of a median of 4 (range:3-6) oscillations

(Fig. 3A). Mean pulse interval is 2.11 2 0.64 sec. Mean peak positive amplitude is 1560 i 132 (range: 482-2724). The frecpency spectrum of a tremulation pulse is broadband, covering a range from about 175-400 Hz (Fig. 3B). Repeatability values for the tremulation parameters varied greatly (Table 2)- The value for pulse duration (0.250) and the number of oscillations within a pulse (-0.012) were low, indicating substantial intra-male variation. However, repeatabilities for peak amplitude (0.664) and pulse interval (0.592) were much stronger, thus the variation within males was much smaller than the variation between males. These parameters thus have the potential to provide females with information about individual performance, and therefore might be used for evaluating the quality of a potential mate. Table 2. ~epeatabilityin male tremulation (Psb- sequential Bonferroni- adjusted critical probability value).

Parameter Sample size Repeat- F Psb ability Within Number of males males Pulse duration 3 1 20 0.250 1.14 > 0.0125 Number of 3 20 -0.012 O. 96 > 0.0125 oscillations ------Peak amplitude 3 20 O. 664 6.93 < 0.0125 Pulse interval 3 20 0.592 5.35 < 0.0125 Relationship between tremulation and male size Mean body weight of males was 0.137 + 0.005 gras (range: 0.096-0.169). Pulse duration, the number of oscillations within a pulse, and peak amplitude were not significantly correlated with male weight or with each other (Table 3). Although peak amplitude displayed high repeatability, the correlation to male size was weak (r=0.269) and non-significant (Bonferroni-adjusted P=1.00). Pulse interval, however, was strongly negatively correlated with male weight (r=-0.924, Bonferroni-adjusted P<0.001). The regression of mean pulse interval on weight was strong

(r2=0.855) and significant (F=100.83, Pc0.001, n=19, Fig. 6).

Female response to tremulation Experiment 1 Thirty-nine females moved ont0 the dowel transmitting tremulation, while 22 moved to the opposing am containing no stimulus (Normal Approximation to the Binomial test (two- tailed): 2=2.144, 0.02

Pulse Of Peak Pulse duration 1 oscillations amplitude interval Weight 1 Pulse duration Number of oscillations 1 -0.114t 1 0.486t 1 1.000

- - -- Peak amplitude 1 0.269 1 -0.177 1 0.038t Pulse interval Fig 6. Relationship between male weight and mean tremulation pulse interval in C. nigropleurum. Regression equatlon: y= -30.212~ + 6.248 (r*=0.855, P<0.001, n=19),

Fig 7. Response of C. nigropleurum females to playback of male tremulation. Histograms show the number of females that moved ont0 the dowel transmitting tremulation, or ont0 the opposite am lacking the conspecific signal.

Fig 8. Ability of C. nigropleurum females to distinguish tremulation fwom an artificial vibration pulse. The bars represent the number of females that preferred conspecific tremulation (TREM-1) over the synthetic stimulus (CONTROL-1). vibrations.

Ex~eriment3 When given the choice between similar tremulation signals that differed in pulse interval and peak amplitude, 17 females preferred the signal containing the short pulse interval reflecting a large male. In contrast, 7 females moved to the other stimulus reflecting a srnaller individual (Normal Approximation to the Binomial test (one-tailed): 2=2.071,

0.01

DISCUSSION

Female C. nigropleurum respond to tremulation in the absence of a signalling male, demonstrating that the vibratory component of the signal is sufficient to elicit vibrotaxis. Fernales also distinguish tremulation £rom a control vibration, demonstrating the specificity of Eemale recognition to the vibrations generated by conspecific males. Finally 1 have shown that females prefer to orient towards the tremulation signal of a large male, one possessing a shorter pulse interval than the population mean.

Information content of tremulation signals The preference by females for a tremulation signal with a pulse interval shorter than the population mean indicates this parameter does not function in species recognition. When females show a preference for a parameter of a male signal that differs significantly £rom the mean value in the population this is a dynamic, not static parameter (Gerhardt 1991). Such a parameter is potentially more important in mate choice than other (static) signal parameters. The high repeatability of pulse interval indicates strong consistency in performance within a male for this parameter. However, because the measurements were taken within only one signalling bout, it is unknown if this behaviour would remain so repeatable over the course of a male's lifetime. Factors such as food availability, age and/or parasite infection may influence the ability of a male to sustain consistent performance over an extended period. The results here suggest though that reliable information regarding the consistency of tremulation for a male is adequately conveyed during an interaction with a female. Several authors have shown that certain parameters of acoustic courtship signals are highly repeatable, and also function as cues to females about a male's phenotype. For example, the repeatability of cal1 duration was 0.42 in the treefrog Hyla versicolor (Gerhardt 1991) and 0.56 for chirp length in the grasshopper Chorthippus brunneus (Butlin and Hewitt 1986). Aspi and Hoikkala (1993) calculated the repeatability of Song frequency in Drosophila montana and D. littoralis to be 0.45 and 0.86, respectively. In the tree- cricket Oecanthus nigricornis, the repeatability of Song frequency was 0.98 (Brown et al. 1996). Pulse interval strongly predicts the size of a male in C. nigropleurum. Since only heavier males tremulate at high rates, this signal is an honest indication of a male's size. Smaller males may not be able to sustain tremulation at the level of bigger individuals, probably because this behaviour is energetically expensive to maintain for extended periods (Mappes et al. 1996)- Therefore, a female interacting with a courting male will be able to accurately assess his size, and hence, his potential at offering a significant spermatophore during copulation. Large males may also provide "good genes" in addition to material benefits, thereby siring offspring of higher quality with increased survival rates (Andersson 1994). In contxast to pulse interval pulse peak amplitude is an unreliable cue for a male to use to relay information about himself. The amplitude and spectxum of vibrational waves is strongly dependent upon the distance of the signaller £rom the receiver, and on the physical composition of the substrate medium (Mark1 1983). C. nigropleurum inhabits a very heterogenous plant environment, thus the transmission properties of the tremulation signal will be different depending upon the particular plant filtering properties (Bell 1980; Michelsen et al. 1982)- Although only one type of substrate was used to record the tremulation signal (aluminum screen), the distance and orientation of each male when tremulating relative to the accelerometer varied. This resulted in vastly different peak amplitude values between males. However, since a male tended to remain in one position during a signalling bout, the amplitude of each tremulation pulse remained relatively consistent within a male. This was reflected in the large repeatability value for this parameter (0.664).

1 used peak positive amplitude as a measure of tremulation intensity but it did not correlate strongly with male weight. Although direct measurement of signal intensity was not possible during recording, larger males may well generate significantly more powerful tremulations than smaller individuals, Their increased mass should allow them to produce larger amplitude body oscillations that would propagate vibrational waves with more force along the substrate (Morris 1980). However, for females to use intensity as a gauge for weight, they would require information about the particular plant they are on, including its specific filtering characteristics, and the exact distance they are to the signalling male (Morris 1980; ~euper- and Khüne 1983; Mark1 1983). It is highly unlikely that females are able to integrate al1 this information into a reliable estimate of the tremulation intensity, and hence the weight of, a courting male.

Females respond to the vibratory component of tremulation

The ability of females to distinguish tremulation from the random noise vibration indicateç they recognized the vibrations generated by the conspecific signal. However, the precise feature of tremulation that is used for recognition by females is unclear. A normal tremulation pulse contains a characteristic spectral band of 175-400 Hz. The control vibration possessed a substantially broader spectrum which completely incorparated this frequency band. Therefore, the band itself could not have been the sole basis of the discrimination observed in experiment 2. If it was, females would have reacted to both signals in the same way since both vibrations contained the range of frequencies that exist in a trernulation pulse. However, the subgenual organs of katydids are sensitive to vibrations in a wide range from 100 Hz to 5 kHz (Kalmring et al. 1997). Therefore, females most likely detected the additional frequencies present in the control vibration. Since only tremulation was prefexred, these additional frequencies, coupled with the lack of a specific amplitude pattern, probably resulted in the females detecting, but not recognizing the control vibration. In , response to the specific amplitude features of a conspecific vibratory signal has been reported in Heteroptera (Cocroft 1996) and Neuroptera (Wells and Henry 1992). In both these groups, females responded more strongly to playback of conspecific vibratory signals than to alternative stimuli that contained a similar frequency range but an incorrect time-amplitude pattern. Although C. nigropleurum males are active diurnal singers and so probably utilize visual signals during close encounters with conspecifics, the positive response by females to playback of the conspecific signal indicates the importance of the vibratory component of tremulation. Alexander (1975) proposed that once a male succeeds in attracting a female with acoustic Song, switching to a silent mode of communication for courtship would help reduce the chance of cuckoldry from nearby rival males. In addition, silent signalling would also minimize eavesdropping from acoustically-orienting predators (Belwood and Morris 1987). Males of the tropical katydid Copiphora rhinoceros cease their acoustic calling when approached by a fernale, instead switching to vigorous bouts of tremulation (Morris 1980). Tremulation here, however, functions as much more than a behaviour simply reducing the conspicuousness and range of the male courtship display. Pulse interval is a reliable feature of the signalling ability of a male, and is also a good predictor of his size. Since females prefer tremulations with short pulse intervals, this signal may be the mechanism by which females discriminate in favour of larger males in this species. The only other example of the use of a vibratory signal by females for mate discrimination in arthropods occurs in the wolf spider Hygrolycosa rubrofasciata (Parri et al. 1997). Males drum on the substrate with their abdomen during courtship, with females preferring percussions that are both louder and given at a higher rate. Drurnming activity does not correlate strongly with male mass, however, more active signallers live significantly longer than males that signal less often, suggesting females prefer the signals of high quality males (Kotiaho et al. 1996).

Cues for mate selection in Conocephalus nigropleurum Airborne song in orthopteran insects has received the most attention with respect to its role in influencing female mate choice in this group of insects. Specific components of male Song known to operate as cues for female choice include intensity (Forrest 1983; Bailey 1985), frequency (Latimer and Sippel 1987; Brown et al. 1996), duty cycle (Hedrick 1986; Simmons 1988), and syllable number (Tuckerman et al. 1993). Only a few studies, however, have shown that preferred Song parameters are reliable predictors of male size. For example: in the katydid Requena sp.5 30% (r2=0.3) of the variation in male size is explained by Song carrier frequency (Wedefl and Sandberg 1995); in the cricket Gryllus bînzaculatus, syllable rate explains 26% (r2=0.26) (Simmons and Zuk 1992); in the katydid Scudderia curvicada the number of syllables per phrase explains 71% (r2=0.71) (Tuckerman et al. 1993). In C. nigropleurum, however, pulse interval explains much more of the variation (86%) in male size than these acoustic Song components, Such strong predictive value commends its role as a cue for mate assessment, Although certain parameters of airborne song are used for mate discrimination in several orthopteran species, it is unknown if Song is used for female choice in Ce nigropleurum, The acoustic song of C. nigropleurum is characterized by a broad-band frequency spectrum, with most of the signal energy occurring in the range from 28-60 kHz (Morris and Pipher 1967). In addition, song elements are repeated at a high rate, resulting in a very redundant cal1 pattern (Morris et al, 1978). These two Song features, broad-banded spectrum and high redundancy, are important in facilitating localization by conspecifics in habitats where signal degradation by vegetation is an important concern (Keuper and Kühne 1983; Romer and Lewald 1992). Since higher frequencies degrade more than lower frequencies at short distances, the distance to a singing male can be estirnated by comparing the relative amounts of high and low frequencies in the song, Studies have shown that a female will orient to calls containing frequencies in the upper part of the song's spectrum over calls broadcasting only the low frequency components (Latimer and Sippel 1987; Bailey et al.

1990 ) . Morris et al. (1978) demonstrated that female C. nigropleurum are able to make fine discriminations of simultaneous presentations of altered acoustic song. They found that females prefer to orient toward a speaker broadcasting the call. of two males over that of only one singing male. However, females readily moved to the speaker broadcasting lone male Song when the intensity was egual to that of the two-male stimulus. This indicates that an individual's intensity is an important Song parameter females use for phonotaxis in this species. However, no examination of the relationship between male size and song intensity was perfomed in that study. As a result, whether intensity acts as an indicator of male size, or simply as an indication of the distance to a signalling male is unknown .

What cue then, are females using to select mates in C. nigropleum? If the acoustic cal1 is used only to attract females and does not contain information about individual quality, then assessrnent must occur at close-range. Tremulation provides females with a signal that is both highly consistent within a male, and reliably reflects male weight. Morris (1967) calculated the density in late summer of adult singing males in a natural population of C. nigropleurun to be 0.42 males/m2. At this high density, a searching female will encounter many males over a small area. In other katydid species, the density of males is much lower. Feaver (1983) calculated the density of males in nigripes and 0. gladiator to be 0.02 males/m2 and 0.15 males/m2, respectively. Bailey and Thiele

(1983) found the peak density of males in Mygalopsis marki to be

0.02 males/m2. A.

It is unlikely that females are able to remember the exact location of al1 the males they encounter. This is due, in part, to the frequent displacement of males from their singing sites as a result of intra-sexual aggressive encounters (Morris 1967). Therefore, females probably choose to mate with the first male whose tremulations meet some interna1 threshold of acceptability. This strategy, tenned the "one-step decision" by Janetos (1980), provides the highest return in fitness for a female in situations where returning to a previously encountered male is not possible. When a male Conocephalus nigropleurum encounters a conspecific female he initiates the interaction with a behaviour known as tremulation. The male lifts his body up from the substrate and then brings it back dom again a number of tirnes in rapid succession, This action generates a series of sinusoidal waves that are propagated several centimetres away £rom the male. This behaviour always precedes copulation in this species. 1 quantified the physical structure of the tremulation signal from a population of 20 males, and then tested its effectivenesç at eliciting taxis by virgin females. Two parameters of the signal, pulse interval and peak positive amplitude, displayed large repeatability values. This indicated that the variation within males was much smaller than the variation between males, therefore these parameters might play a xole in female mate choice. Pulse interval was strongly negatively correlated to body weight. Larger males signal at higher rates than smaller individuals due to the short time interval between consecutive tremulation pulses. In dual presentation playback experiments female C. nigropleurum prefer tremulation vibration over its absence. When offered simultaneously with a synthetic vibration constructed to share several features with the conspecific signal, females still prefer to move towards tremulation. Finally, when simultaneous presentations are made of tremulation signals that differ in pulse interval, females choose to move in the direction broadcasting the stimulus with the shorter pulse interval reflecting a large male. Alexander, R.D. 1975. Natural selection and çpecialized chorusing behavior in acoustical insects. In: Pimental, D. (ed) Insects, science, and society. Academic Press, New York, pp 35-79

Andersson, M. 1994. Semial selection. Princeton Univ. Press, Princeton Aspi, J. and Hoikkala, A. 1993. Laboratory and natural heritabilities of male courtship Song characters in Drosophila montana and O-littoralis, Heredity 70:400-406 Bailey, W.J. 1985. Acoustic cues for female choice in bushcrickets (Tettigoniidae). In: Kalmring, K., Elsner, N, (eds) Acoustic and vibrational communication in insects. Paul Parey Verlag, Berlin, pp 101-110 Bailey, W.J. and Thiele, D.R. 1983. Male spacing behavior in the Tettigoniidae: an experimental approach, In: Gwynne, D.T., Morris, G.K. (eds) Orthopteran mating systems: sexual cornpetition in a diverse group of insects. Westview Press, Colorado, pp 163-184 Bailey, W.J., Cunningham, R.J., Lebel, L. 1990. Song power, spectral distribution and female phonotaxis in the bushcricket Requena verticalis (Tettigoniidae: Orthoptera): active fernale choice or passive attraction? Anim. Behav. 40: 33-42 Barth, F.G. 1982. Spiders and vibratory signals: sensory reception and behavioral significance. In: Witt, P.M., Rovner, J.S. (eds) Spider communication: mechanisms and ecological significance. Princeton University Press, Princeton, pp 67-122 Bell, P.D. 1980. Transmission of vibrations along plant stems: implications for insect communication, N. Y. Ent. Soc. 88~210-216

Belwood, 5.3. and Morris, G.K. 1987. Bat predation and its influence on calling behavior in neotropical katydids Science 238~64-67 Boake, C.R.B. 1989. Repeatability: its role in evolutionary studies of mating behavior . Evol. Eco1 . 3 :173-182 Boldyrev, B.T. 1915. Contributions a l'etude de la structure des spermatophores et des particularities de la copulation chez Locustodea et Gryllodea. Ho. Soc. Ent. Rossicae 41:l-245 Brown, W.D., Wideman, J., Andrade, M.C.B., Maçon, A.C., Gwynne, D.T. 1996. Female choice for an indicator of male size in the Song of the black-horned tree cricket, Oecanthus nisricornis (Orthoptera: Gryllidae: Oecanthinae). Evolution 50 :24OO-24ll Busnel, R.G. 1963. Examples of the application of electro- acoustic techniques to the measurement of certain behaviour patterns. In: Busnel, R.G. (ed) Acoustic Behaviour of animals, Elsevier, New York, pp 54-65 Busnel, R.G., Pasquinelly, F., Dumortier, B. 1955. La trémulation du corps et la transmission aux supports des vibrations en résultant comme moyen d'information a courte portee des Éphippigères mâle et femelle. Bull. Soc. Fr. 80~8-23 Butlin, R.K. and Hewitt, G.M. 1986. Heritability estimates for characters under sexual selection in the grasshopper, Chorthi~pusbrunneus. Anh. Behav. 34~1256-1261 Claridge, M. 1985a. Acoustic behavior of leafhoppers and planthoppers: species problems and speciation. In: Rodriquez, L.R., Nault, J.G. (eds) The leafhoppers and planthoppers. John Wiley & Sons, New York, pp 103-125 Claridge, M. 1985b. Acoustic signals in the Homoptera: behavior, , and evolution. Ann. Rev. Entomol. 30~297-317 Clark, D.C. and Moore, A.J. 1995. Variation and repeatability of male agonistic hiss characteristics and their relationship to social rank in Gromphadorhina ~ortentosa.Anh. Behav, 50:719-729 Cocroft, R.B. 1996. Insect vibrational defence signals. Nature 382:679-680 DeWinter, A.J. and Rollenhagen, T. 1990. The importance of male and female acoustic behaviour for reproductive isolation in Ribautodel~haxplanthoppers (Homoptera: Delphacidae). Biol. J. Linn. Soc. 40:191-206 Duelli, P. and Johnson, J.B. 1981. Behavioral origin of tremulation, and possible stridulation in green lacewings (Neuroptera: Chrysopidae). Psyche 88:375-381 Ewing, A.W. 1989. Arthropod bioacoustics: neurobiology and behaviour. Corne11 University Press, Ithaca Feavex, M.N. 1983. Pair formation in the katydid Orchelimum niqripes (Orthoptera: Tettigoniidae). In: Gwynne, D.T., Morris, G.K. (eds) Orthopteran mating systems: sexual cornpetition in a diverse group of insects. Westview Press, Colorado, pp 205-239 Forrest, T. G. 1983. Phonotaxis and calling in Puerto Rican mole crickets (Orthoptera: Gryllotalpidae). Ann, Entomol. Soc, Am. 76~797-799 Gerhardt, H. C. 1991. Female mate choice in treefrogs: static and dynamic acoustic criteria. Anim. Behav. 42:615-635 Gerhardt, H.C. 1992. Conducting playback experiments and interpreting their results. In: McGregor, P.K. (ed) Playback and studies of communication. Plenum Press, New York, pp 59-78 Gogala, M. 1985. Vibrational songs of land bugs and their production. In: Kalmring, K., Elsner, N (eds) Acoustic and vibrational communication in insects. Paul Parey Verlag, Berlin, pp 143-150 Gwynne, D.T. 1977. Mating behavior of Neoconoce~halusensiuer (Orthoptera: Tettigoniidae) with notes on the calling Song. Can. Ent. 109:237-242 Gwynne, D.T. 1982. Mate selection by female katydids (Orthoptera: Tettigoniidae, Conoce~halusnigro~leurum). Anim. Behav. 30:734-738 Gwynne, D.T. 1984. Courtship feeding increases female reproductive succeçs in bushcrickets. Nature 307~361-363 Gwynne, D.T. 1988. Courtship Eeeding and the fitness of female katydids (Orthoptera: Tettigoniidae). Evolution 42:545-555 Hedrick, A.V. 1986. Female preferences for male calling bout duration in a field cricket. Behav. EcoT. Sociobiol. 19: 73-77 Henry, C.S. 1979. Acoustic communication during courtship and mating in the green lacewing Chrvso~acarnea (Neuroptera: Chrysopidae). Ann. Entomol. Soc. Am. 72:68-79 Henry, C.S.and Wells, M.M. 1990. Geographical variation in the Song of Chrvsoperla plorabunda (Neuroptera: Chrysopidae) in North America. Anne Entomol. Soc. Am. 83:317-325

Hunt, R. E. 1993. Role of vibrational signals in mating behavior of Spissistilus festinus (Homoptera: Membracidae). Ann. Entomol. Soc. Am. 86~356-361 Kalmring, K., Kuhne, R., Lewis, B. 1983. The acoustic behaviour of the bushcricket, Tettiqonia cantans. III. Coprocessing of auditory and vibratory information in the CNS. Behav. Proc, 8~213-228 Kalmring, K., Rossler W., Unrast, Co 1994. Complex tibia1 organs in the forelegs, midlegs, and hindlegs of the bushcricket Gam~socleisaratiosa (Tettigoniidae): cornparision of the physiology of the organs. J. Exp. 2001. 270~155-161 Kalmring, K., Jatho, M., Rossler, W., Sickmann, T. 1997. Acousto-vibratory communication in bushcrickets (Orthoptera: Tettigoniidae). Entomol, Gener, 21:265-291 Keuper, A. and Kuhne, R. 1983. The acoustic behaviour of the bushcricket Tettisonia cantans II. Transmission of airborne-sound and vibration signals in the biotope. Behav. Proc . 8: 125-145

Keuper, A., Otto, Co,Latimer, W., Schatral, A. 1985. Airborne sound and vibration signals of bushcrickets and locusts; their importance for the behaviour in the biotope. In: Kalmring, K., Elsner, N. (eds) Acoustic and vibrational communication in insects. Paul Parey Verlag, Berlin, pp 135-142 Kotiaho, J., Alatalo, R.V., Mappes, JO,Parri, S. 1997. Sexual selection in a wolf spider: male drumming activity, body size, and viability. Evolution 50:1977-1981

Latimer, W, and Schatral, A, 1983, The acoustic behaviour of the bushcricket Tettisonia cantans Io Behavioural responses to sound and vibration. Behav. Proc- 8~113-124 Latimer, W. and Sippel, M. 1987. Acoustic cues for female choice and male cornpetition in Tettiqonia cantans. Anim. Behav. 35~887-900 Mappes, J,, Alatalo, R.V., Kotiaho, J., Parri, S. 1996. Viability costs of condition-dependent sexual male display in a drumming wolf spider. Proc. R. Soc, Lond. B. 263:785- 789 Markl, H. 1983. Vibrational communication. In: Markl, ForHuber, H. (eds) Neuroethology and behavioral physiology. Springer- Verlag, Berlin, pp 332-353

Meixner, AoJ, and Shaw, K,C. 1986, Acoustic and associated behavior of the coneheaded katydid, Neoconocephalus nebrascensis (0rthoptera:Tettigoniidae). Ann. Entomol, Soc, Am. 79 :554-565 Michelsen, A., Fink, F., Gogala, M., Traue, D, 1982, Plants as transmission channels for insect vibrational songs. Behav. Ecol. Sociobiol. 11:269-281 Morris, G.K. 1967. Song and aggression in Tettigoniidae. Ph.D Thesis. Corne11 University, Ithaca, New York. Morris, G.K. 1971. Aggression in male conocephaline grasshoppers (Tettigoniidae). nim m. Behav. 19:132-137 Morris, G.K. 1980. Calling display and mating behaviour of Copi~horarhinoceros Pictet (Orthoptera: Tettigoniidae), Anim. Behav. 28:42-51

Morris, G.K. and Pipher, R.E. 1967. Tegminal amplifiers and spectrum consistencies in Conoce~halusnisro~leurum (Bruner), ~ettigoniidae.J. Ins. Physiol. 13~1075-1085 Morris, G.K. and Beier, M. 1982. Song structure and description of some Costa Rican katydids (Orthoptera: Tettigoniidae). Trans. Am, Ent. Soc. 108:287-314

Morris, G.K., Kerr, G.E., Fullard, J.H. 1978. Phonotactic preferences of female meadow katydids (Orthoptera: Tettigoniidae: Conoce~halusnigro~leurum). an. J. 2001. 56: 1479-1487 Morris, G.K., Mason, A.C., Wall, P., Belwood, J.J. 1994. High ultrasonic and tremulation signals in neotropical katydids (Orthoptera: Tettigoniidae). J. 2001. Lond. 233~129-163

Parri, S., Alatalo, R-V,, Kotiaho, J., Mappes, J. 1997. Fernale choice for male drumming in the wolf spider Hvsrolvcosa rubrofasciata. Anim. Behav. 53:305-312 Romer, H. and Lewald, J. 1992. High-frequency sound transmission in natural habitats: implications for the evolution of insect acoustic information- Behav. Ecol. Sociobiol, 29: 437-444 Rupprecht, R. 1968. Das Trommeln der Plectopteren. Zeit. vergleich. Physiol. 59~38-71 Schmitt, A., Schuster, M., Barth, F,G. 1994, Vibratory communication in a wandering spider, Cu~ienniussetazi: female and male preferences for features of the conspecific male's releaser. Anim. Behav, 48~1155-1171 Serridge, M. and Licht, T.R. 1986. Piezoelectric accelerometers and vibration preamplifiers. Brüel & Kjzr Information Handbook, Denmark. Simmons, L.W. 1988. The calling song of the field cricket, Grvllus bimaculatus (De ~eer):-constraintson transmission and its role in intermale competition and female choice. Anim. Behav. 36:380-394

Simmons, L.W. and Zuk, M. 1992. Variability in cal1 structure and pairing success of male field crickets, Gryllus bimaculatus: the effects of age, size and parasite load. Anim Behav. 44~1145-1152 Sismondo, E. 1980. Physical characteristics of the drumming of Meconema thalassinum. J. Ins. Physiol. 26~209-212

Stiedl, 0. and Kalmring, K. 1989. The importance of song and vibratory signals in the behaviour of the bushcricket E~hi~~iserephimiaer Fiebig (0rthoptera:Tettigoniiaae): taxis by females. Oecologia 80:142-144 Tuckerman, J.F., Gwynne, D.T., Morris, G.K. 1993. Reliable acoustic cues for female mate preference in a katydid (Scudderia curvicauda, Orthoptera: Tettigoniidae). Behav. Eco~. 4: 106-113

Uetz, G,W. and Stratton, G.E. 1982. Acoustic communication and reproductive isolation in spiders. In: Witt, P.N., Rovner, J.S. Spider communication: mechanisms and ecological significance. Princeton University Press, Princeton, pp 123-159 Wedell, N, and Sandberg, T. 1995. Female preference for large males in the bushcricket R- sp. 5 (Orthoptera: Tettigoniidae), J. Ins. Behav. 8:513-522 Weidemann, S. and Keuper, A. 1987. Influence of vibratory signals on the phonotaxis of the gryllid Grvllus bimaculatus DeGeer (: Gryllidae). Oecologia 74:316- 318 Wells, M.M. and Henry, C.S. 1992. Behavioural responses of green lacewings (Neuroptera: Chrysopidae: Chrvsoperla) to synthetic mating songs. Anim, Behav, 44:641-652 Wheeler, W.M. 1890. Notes on the oviposition and embryologie development of Xiphidium ensife2um Scudder. 1nsect ~ife 2:222-225

Whitesell, J.J. 1969. Biology of United States cone-headed katydids of the genus Neoconoce~halus.M.S. Thesis. University of Florida, Gainesville, Florida Ziegler, D.D. and Stewart, K.W. 1977. Drumming behavior of eleven nearctic stonefly (Plecoptera) species. Ann. Entomol. Soc. Am. 70:495-505 Ziegler, D.D. and Stewart, K.W. 1986. Female response thresholds of two stonefly (Plecoptera) species to cornputer simulated and modified male drming calls. Anim. Behav. 34:929-931 APPLiEO -1 IMAGE, lnc -.-= 1653 East Main Street --, Rochester, NY 14609 USA ------Phone: 7161482-0300 ---- Fax: 71 61288-5989

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