Porpoise Clicks From a Sperm Whale Nose—convergent Evolution of 130 KHZ Pulses in Toothed Whale Sonars?

Abstract

Small toothed whales of the family Phocoenidae and delphinid genus Cephalorhynchus produce long-duration, narrowband biosonar clicks above 100 kHz, that might be seen as an adaptation for short range echolocation in shallow water. This paper presents data showing that the distantly related, and larger pygmy sperm whale Kogia breviceps (Kogiidae), that is a deep-diving, cephalopod-eating toothed whale, produce narrow-banded high frequency (NBHF) clicks identical to those of Phocoena and Cephalorhynchus (f 0 = 130kHz, Q 3 ds>10, duration > 80 msec). Thus, NBHF biosonar signals have evolved on three independent occasions in the odontocete suborder, but the apparent functional convergence does not relate to anatomical or niche similarity. Rather, it is suggested that a biosonar strategy adapting to a minimum in ocean ambient noise above 100 kHz in concert with high Q auditory filters have led to convergent evolution of the NBHF biosonar clicks. Since these biosonar signals carry all their energy at frequencies above the upper hearing limit of the killer whale Orcinus orca, predator avoidance may also have been a evolutionary shaping factor of the sonar signals from these non-whistling odontocetes.

Shape analysis of odontocete mandibles: Functional and evolutionary implications

“…commersonii and P. phocoena produce very similar sounds (Madsen et al, 2005a;Kyhn et al, 2010), perhaps indicating that the two species hear similar sounds, or share prey capture or predator avoidance strategies. This might confirm that shapes associated with PC 3 are subject to environmental selective pressures more so than Jaw Flare and Symphysis Elongation.…”

Clicking for calamari: toothed whales can echolocate squid Loligo pealeii

“…Squid-eating toothed whale species produce a variety of echolocation clicks of durations from 20 to 300 μs in the frequency range from 15 to 130 kHz (Au 1993, Madsen et al 2005b. One hypothesis to account for the differences in duration of The order of removal of the pen, the eyes, and the beak was alternated between squid echolocation clicks is that species limited in peak power may compensate by producing longer clicks with a higher energy flux density for the same peak pressure (Au et al 1999.…”

Echolocation in sympatric Peale's dolphins (Lagenorhynchus australis) and Commerson's dolphins (Cephalorhynchus commersonii) producing narrow-band high-frequency clicks

“…The groups producing these strikingly similar NBHF clicks include the Phocoenidea family (Møhl and Andersen, 1973;Akamatsu et al, 1998;Villadsgaard et al, 2007), the Cephalorhynchus genus (Kamminga and Wiersma, 1982;Dawson and Thorpe, 1990;Kyhn et al, 2009) within the dolphin family [including the hourglass dolphin (Lagenorhynchus cruciger)] and the pygmy sperm whale (Madsen et al, 2005). Furthermore, the Francicana river dolphin (Pontoporia blainvillei) (von Fersen et al, 2000) is proposed to use NBHF clicks, but only the peak frequency and -3dB bandwidth was stated by the investigators (von Fersen et al, 2000).…”

“…All these species likely use the NBHF signal as a result of evolutionary convergence under the possibly shared selection forces of a small body size and predation from killer whales (Andersen and Amundin, 1976;Madsen et al, 2005;Morisaka and Connor, 2007) that hear frequencies above 100kHz very poorly (Szymanski et al, 1999). Not all small toothed whales, however, are NBHF species, and, as discussed by Morisaka and Connor (Morisaka and Connor, 2007), there are general differences in both behaviour and group size between NBHF species and non-NBHF species.…”