Meeting Abstract
83.1 Sunday, Jan. 6 Novel muscle and connective tissue design controls engulfment volume in lunge-feeding whales SHADWICK, R.E.*; GOLDBOGEN, J.A.; POTVIN, J.; PYENSON, N.D.; VOGL, A.W.; Univ of British Columbia; Cascadia Res. Collective; St. Louis University; Smithsonian Inst.; Univ. of British Columbia shadwick@zoology.ubc.ca
Rorqual whales feed by engulfing and filtering large volumes of water containing schooling prey. The ability to engulf a mass of water on the order of the entire body mass is facilitated by highly compliant ventral groove blubber (VGB) and underlying muscle that make up the buccal cavity outer wall. Muscle fibres are in two strata, one is parallel to the body long axis (LS), the other is oblique (OS), at 45o to the LS. Based on a geometric model of engulfment we estimated the maximal circumferential VGB strain. For comparison we measured VGB strain from the relative separation of adjacent ridges seen in photos of lunging fin, blue, sei, Bryde’s and minke whales. In both cases we found that at full engulfment the VGB experiences circumferential strain of up to 160%. But how can the VGB muscles accommodate apparent strains as high as 160%? Histological examination showed that LS fibres are loosely connected and readily separate laterally with increasing VGB circumferential strain. OS fibres are embedded in a dense matrix of elastic tissue quite unlike other skeletal muscle. In the unloaded state we found that retraction of the elastin actually compresses the muscles by about 30%. The combination of re-orientation of the OS muscle fibres with VGB expansion, and their straightening as elastin is stretched, together allow for VGB strains of 160% to occur with only a 55% stretch in the muscle fibres. These results support the hypothesis that the VGB muscles play an active role in controlling the size and filling rate of the ventral cavity during engulfment feeding (J. Potvin et al. 2009, J. Royal Soc. Interface).
