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First published online March 31, 2005
Journal of Experimental Biology 208, 1495-1512 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01550

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Simultaneous measurement of metabolic and acoustic power and the efficiency of sound production in two mole cricket species (Orthoptera: Gryllotalpidae)

Kenneth N. Prestwich^* and Kristin O'Sullivan

Department of Biology, College of the Holy Cross, Worcester, MA 01610, USA

View larger version (37K): [in a new window]   Fig. 1. Two views of the calling burrow of Scapteriscus borellii with the approximate location of the gas sampling tube. The single, oval-shaped opening acts as an approximately 1/3-wavelength radiator set in an infinite baffle. The horn matches the radiation impedance of the insect's acoustic radiator (tegminal harps) with that of the opening of the burrow. Males sing as shown from the constricted region with their heads facing into the burrow and their elevated tegmina largely filling the space above the cricket. The bulb is a straight or curved blind-ended burrow 1/4-wavelength in length with an opening to the main burrow in its side wall. The insect's harps are doublet sources and sound broadcast from their dorsal (anterior) surface into the bulb is reflected and then returns to the harps in phase with the sound emitted being emitted into the horn. Thus, the dimensions of the burrow, calling position of the insect, and acoustical properties of the burrow walls are all crucial to the system's performance (Bennet-Clark 1970, 1987; Daws et al., 1996). Figure modified from Bennet-Clark (1989) and used with permission.

View larger version (60K): [in a new window]   Fig. 2. (A) Sound pulses of S. borellii and our conventions for deducing the number of driven cycles and the duration of the closing and opening phases. (B) Sound pulse of S. vicinus.

View larger version (17K): [in a new window]   Fig. 3. Cycle-to-cycle frequencies (fC) of single sound pulses for representative S. borellii and S. vicinus at 25° C. The fC is not constant and decreases by 5–10% late in the call (especially so in this S. vicinus individual). The instantaneous jumps in frequency late in the pulses (asterisks) are believed to be associated with the disengagement of file and plectrum. This is followed by a period of undriven vibration, during which the sound amplitude drops exponentially. Although the patterns given in this figure are typical, a number of individuals of both species showed different degrees of fC stability and sometimes lacked a noticeable change in frequency at the start of the sound amplitude's exponential decay.

View larger version (92K): [in a new window]   Fig. 4. Scanning electron micrographs in side view of the files of S. borellii (A) at 1000x magnification and S. vicinus (B) at 1500x magnification. Measurement of tooth depth is illustrated in A.

View larger version (30K): [in a new window]   Fig. 5. Mean tooth-to-tooth distances as a function of tooth number for the right files of S. borellii (squares) and S. vicinus (circles). Teeth are numbered starting with the most medial (plectrum end of file). Similar results are obtained for the files of the left forewings. Values are means ± 95% CI, N=6 for most points.

View larger version (33K): [in a new window]   Fig. 6. Mean file tooth depths as a function of tooth number for the right files of S. borellii (squares) and S. vicinus (circles). Teeth are numbered starting with the most medial. Similar results are obtained for the files of the left forewings. Values are means ± 95% CI, N=5 for most points.

View larger version (15K): [in a new window]   Fig. 7. Simultaneous measurements of CO2 and O2 in a calling S. borellii. The initial drop is associated with washout of gases in the burrow prior to the start of an airflow and sampling. The two dips coincide with brief periods when the cricket stopped calling. Average RQ0.91. This figure shows the most commonly observed respiratory measurement in both species – one or two minutes of equilibration followed by steady rates of metabolism at a constant RQ.

View larger version (18K): [in a new window]   Fig. 8. Simultaneous measurements of CO2 and O2 in a continuously calling S. borellii. Sampling was underway when the cricket began calling. This record shows that continuously calling crickets do not necessarily have constant metabolic rates. Note that O2 records sometimes can spike and drift independently of the more reliable CO2 data (see start and middle of record). Near the end of the record the sampling tube was removed from the burrow and both measures of metabolism fell to essentially zero.

View larger version (27K): [in a new window]   Fig. 9. CO2 in a S. borellii that frequently stopped and restarted calling. Air stream sampling was continuous. The metabolic rate decreased during each brief calling bout only to increase again when the cricket resumed calling. Overall, respiratory rate decreased by approximately 25%.

View larger version (13K): [in a new window]   Fig. 10. Mean acoustic and metabolic power for individuals of both species. There was no statistically significant relationship between Pac and Pcall in either species. Values are means ± 95% CI.

View larger version (14K): [in a new window]   Fig. 11. Mean efficiency of sound production E for individuals of each species. There were no statistically significant differences in E between individual S. borellii. One S. vicinus had a mean E significantly lower than the others. In both species the major cause of variation in E was that Pac was generally more variable than Pcall. Overall E was significantly greater in S. borellii than in its congener. Values are means ± 95% CI.