. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Diameter (cm) Figure 6. Fed urchins (solid points and line) have significantly lighter skeletons for a given diameter than do unfed urchins (open circles and dashed line). This difference is interpreted as reflecting the larger sutural gaps and general looseness of the plates of fed urchins in compar- ison to unfed urchins. Regression lines shown have equal slopes but different intercepts. 00 TJ 0) TJ *- 'c cn ro E 0) o>. 2000 4000 6000 8000 10000 frequency Figure 7. Characteristic frequen
. The Biological bulletin. Biology; Zoology; Biology; Marine Biology. Diameter (cm) Figure 6. Fed urchins (solid points and line) have significantly lighter skeletons for a given diameter than do unfed urchins (open circles and dashed line). This difference is interpreted as reflecting the larger sutural gaps and general looseness of the plates of fed urchins in compar- ison to unfed urchins. Regression lines shown have equal slopes but different intercepts. 00 TJ 0) TJ *- 'c cn ro E 0) o>. 2000 4000 6000 8000 10000 frequency Figure 7. Characteristic frequency spectra of sounds emitted by vibrating, bleached urchin skeletons. Fed urchins ring or ping like a bell when struck; a skeleton-specific set of discrete frequencies of vibration are detectable (solid line). In contrast, unfed urchins emit a dull "thud"; no discrete frequencies are identifiable (dotted line). For bleached skeletons of unfed urchins, the frequency spectrum is similar to that typical of three-dimensional vibrating objects such as drums or rectangular blocks (Kinsler el al, 1982). The lowest of the identifiable fre- quency peaks is correlated with urchin diameter (P < correlation = r = , n =-- 100. fre- quency = -940 diameter + X 10J. with diameter in centimeters and frequency in hertz). The negative correla- tion between frequency and diameter indicates that the size of the urchin skeleton determines some of the modes of vibration, and thus that vibrations are transmitted across sutures and throughout the skeleton. In contrast, bleached skeletons of fed urchins had no identifiable fre- quency peaks, thus indicating that vibrational energy was lost at loose sutures and that the structure as a whole did not vibrate. Skeletal vibrations can be used as a measure of sutural looseness. The cross-correlation between the sound pro- duced by a bleached skeleton and the predicted ringing frequency is a measure of looseness. The predict
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Keywords: ., bookauthorlilliefrankrat, booksubjectbiology, booksubjectzoology
