98
Marine Mammal Physiology: Requisites for Ocean Living
of the hyoid and tongue. These two capture mechanisms are not necessarily exclusive,
and some toothed whale species can use these strategies either together or in sequence.
Suction appears to be an important mechanism for prey capture in odontocetes as demonstrated by the well-developed tongue musculature and increased surface area of the
hyoid for attachment of these muscles (Bloodworth and Marshall 2005, 2007; Werth
2007). The hyolingual apparatus exhibits a greater proportion of extrinsic muscle fibers
(connects the tongue to other structures), and a lower proportion of intrinsic muscle
fibers (connects the tongue to itself), as compared to both terrestrial mammals and other
aquatic mammals (Werth 2007).
In general, suction feeders produce negative intraoral pressures through the rapid
depression of the hyolingual apparatus (Werth 2000, 2007; Bloodworth and Marshall 2005;
Marshall et al. 2008, 2014, in press; Kane and Marshall 2009). This so-called gular depression
to generate suction during feeding has been experimentally demonstrated (Werth 2006a)
in odontocetes of varying head shape and bluntness of the rostrum ( common dolphin,
Delphinus delphis; Atlantic white-sided dolphin, Lagenorhychus acutus; and harbor porpoise,
Phocoena phocoena). The greatest suction capability in this study was found in harbor porpoises, which also possessed the bluntest rostrum in the study (Werth 2006b). In addition,
gular depression as a mechanism to produce suction has been empirically demonstrated in
several toothed whale species including pygmy sperm whale (Kogia sp.), long-finned pilot
whales (Globicephala melas), belugas (Delphinapterus leucas) (Werth 2000; Bloodworth and
Marshall 2005, 2007; Kane and Marshall 2009) as well as harbor porpoises (Kastelein et al.
1997). In addition to blunt rostra and wide jaws, odontocetes that can produce a more circular mouth aperture to enhance suction feeding performance (Bloodworth and Marshall
2005; Kane and Marshall 2009). This phenotype, termed amblygnathy (blunt, wide), is well
represented in most toothed whale families and is well developed in globicephaline delphinids (Werth 2006b). Toothed whales that exhibit amblygnathy tend to be larger, deep
divers, and many species have evolved reduced dentition. The two exceptions to this trend
are river dolphins (Platanistoidea) and sperm whales (Physeteridae), which have elongated
skulls with teeth. Comparative morphological data for skull and dental traits analyzed
in a phylogenetic context suggest that suction feeding evolved once early in evolutionary
history, thereby representing the ancestral condition of crown cetaceans, but intermediate
ancestral reconstructions may also indicate that many extant odontocetes exhibit secondarily derived suction feeding mechanisms (Werth 2006a,b; Johnston and Berta 2011).
The morphological design of the skull and hyoid bones alone do not completely determine nor limit feeding mode and performance. Therefore, the function of soft tissues must
also be considered to fully understand the integrative biology of feeding in cetaceans. For
example, beluga whales (D. leucas) often exhibit discrete ram and suction components during feeding, but the latter is greatly enhanced by pursing of the lips to occlude the lateral
gape (Kane and Marshall 2009). Lip pursing behaviors act to form a small circular aperture
to magnify negative intraoral pressures, a mechanism that is convergent with more basal
vertebrates (Kane and Marshall 2009). Other odontocetes, such as bottlenose and pacific
white-sided dolphins, have limited lip pursing abilities and instead use ram primarily to
capture prey, although suction may be used to manipulate prey within the mouth to facilitate deglutition (Bloodworth and Marshall 2005; Kane and Marshall 2009). In other species,
ram and suction may be more synchronized, as demonstrated in long-finned pilot whales,
where sub-maximal gape angles or soft tissue adaptations effectively occlude lateral gape
to enhance suction performance during raptorial capture events (Werth 2000; Bloodworth
and Marshall 2007; Kane and Marshall 2009).
Marine Mammal Physiology: Requisites for Ocean Living
of the hyoid and tongue. These two capture mechanisms are not necessarily exclusive,
and some toothed whale species can use these strategies either together or in sequence.
Suction appears to be an important mechanism for prey capture in odontocetes as demonstrated by the well-developed tongue musculature and increased surface area of the
hyoid for attachment of these muscles (Bloodworth and Marshall 2005, 2007; Werth
2007). The hyolingual apparatus exhibits a greater proportion of extrinsic muscle fibers
(connects the tongue to other structures), and a lower proportion of intrinsic muscle
fibers (connects the tongue to itself), as compared to both terrestrial mammals and other
aquatic mammals (Werth 2007).
In general, suction feeders produce negative intraoral pressures through the rapid
depression of the hyolingual apparatus (Werth 2000, 2007; Bloodworth and Marshall 2005;
Marshall et al. 2008, 2014, in press; Kane and Marshall 2009). This so-called gular depression
to generate suction during feeding has been experimentally demonstrated (Werth 2006a)
in odontocetes of varying head shape and bluntness of the rostrum ( common dolphin,
Delphinus delphis; Atlantic white-sided dolphin, Lagenorhychus acutus; and harbor porpoise,
Phocoena phocoena). The greatest suction capability in this study was found in harbor porpoises, which also possessed the bluntest rostrum in the study (Werth 2006b). In addition,
gular depression as a mechanism to produce suction has been empirically demonstrated in
several toothed whale species including pygmy sperm whale (Kogia sp.), long-finned pilot
whales (Globicephala melas), belugas (Delphinapterus leucas) (Werth 2000; Bloodworth and
Marshall 2005, 2007; Kane and Marshall 2009) as well as harbor porpoises (Kastelein et al.
1997). In addition to blunt rostra and wide jaws, odontocetes that can produce a more circular mouth aperture to enhance suction feeding performance (Bloodworth and Marshall
2005; Kane and Marshall 2009). This phenotype, termed amblygnathy (blunt, wide), is well
represented in most toothed whale families and is well developed in globicephaline delphinids (Werth 2006b). Toothed whales that exhibit amblygnathy tend to be larger, deep
divers, and many species have evolved reduced dentition. The two exceptions to this trend
are river dolphins (Platanistoidea) and sperm whales (Physeteridae), which have elongated
skulls with teeth. Comparative morphological data for skull and dental traits analyzed
in a phylogenetic context suggest that suction feeding evolved once early in evolutionary
history, thereby representing the ancestral condition of crown cetaceans, but intermediate
ancestral reconstructions may also indicate that many extant odontocetes exhibit secondarily derived suction feeding mechanisms (Werth 2006a,b; Johnston and Berta 2011).
The morphological design of the skull and hyoid bones alone do not completely determine nor limit feeding mode and performance. Therefore, the function of soft tissues must
also be considered to fully understand the integrative biology of feeding in cetaceans. For
example, beluga whales (D. leucas) often exhibit discrete ram and suction components during feeding, but the latter is greatly enhanced by pursing of the lips to occlude the lateral
gape (Kane and Marshall 2009). Lip pursing behaviors act to form a small circular aperture
to magnify negative intraoral pressures, a mechanism that is convergent with more basal
vertebrates (Kane and Marshall 2009). Other odontocetes, such as bottlenose and pacific
white-sided dolphins, have limited lip pursing abilities and instead use ram primarily to
capture prey, although suction may be used to manipulate prey within the mouth to facilitate deglutition (Bloodworth and Marshall 2005; Kane and Marshall 2009). In other species,
ram and suction may be more synchronized, as demonstrated in long-finned pilot whales,
where sub-maximal gape angles or soft tissue adaptations effectively occlude lateral gape
to enhance suction performance during raptorial capture events (Werth 2000; Bloodworth
and Marshall 2007; Kane and Marshall 2009).