316
Marine Mammal Physiology: Requisites for Ocean Living
coats of hair throughout their life histories, and therefore cannot be easily implicated as
a direct adaptation of the developing fetus to excreting toxicants. However, it is interesting to speculate that the shedding of contaminants in utero via lanugo perhaps persists as
one of the selective pressures to protect from neurotoxicity in situations where mercury
exposure may be high.
14.2.1.2 Blubber and nursing
The term blubber is often misrepresented in both popular culture and occasionally scientific literature, so we will use the definition provided by Reeb et al. (2007) where blubber is integument layers below the epidermis (dermis and hypodermis). As sizeable
endotherms that make their living in the marine environment, many marine mammals
utilize extensive lipid-rich blubber tissue for thermal insulation and other needs (store
nutrients, enhance hydrodynamics, protection from predators, etc.). In migratory species, such as gray whales (Eschrichtius robustus), not only are individual animals often
subject to large changes in ambient water temperature, but migratory periods are often
marked by little or no foraging activity (fasting). The laying down and mobilization of
energy stored in adipose tissue is truly remarkable in marine mammals. While duration
of nursing is often radically different between marine mammal species (on scale of a few
weeks to several years), in some species with short nursing periods, such as the northern
elephant seal (Mirounga angustirostris), females can lose up to 42% of their initial body
mass during nursing (58% of adipose mass) (Costa et al. 1986). The energetics of nursing
is discussed in Chapters 8 and 10, however, the transfer of toxicants during lactation is
interesting to consider from the perspective of both the lactating female and the nursing
pup. While the nursing young is exposed to a milieu of potential toxicants during a sensitive developmental stage, it does represent a significant excretory route for reproductive
females (Addison and Brodie 1987; Debier et al. 2006; Frouin et al. 2012). A decrease in
maternal contaminant concentrations following parity has been described in sea otters
(Jessup et al. 2010). In particular, primiparous females (females giving birth to their first
offspring) often transfer a majority of their blubber (lipid store)-based contaminant load
to their firstborn. Indeed, Beckmen et al. (2003) found increased blood concentrations of
PCB congeners as well as p,p-DDE in pups born to young dams compared to pups born
to older, presumably multiparous dams. Similarly, Ylitalo et al. (2001) found higher concentrations of OCs in first-recruited resident male Alaskan killer whales as compared to
second or later recruitment.
14.3 Biotoxins and the evolutionary chemical arms race
Toxins that are produced by prey species either as defensive mechanisms or as secondary metabolites play a role in the predator–prey relationship. While examples exist of
specific adaptations to poisons in predator–prey relationships (i.e., the skin of the roughskinned newt Taricha granulosa produces tetradotoxin to which the common garter snake
Thamnophis sirtalis demonstrates resistance), it is often difficult to assign a quid-pro-quo
physiologic or behavioral adaptation of a species or taxonomic group as a result of exposure to a poisonous prey (Brodie and Brodie 1990).
A number of marine organisms have been identified that produce compounds that are
toxic to marine mammals such as dinoflagellates, diatoms, and prokaryotes (Valério et al.
2010) and there are a number of fish, mollusk, and cnidarian species that are poisonous
or venomous to marine mammals. These poisons are often encountered by marine mammals through diet. However, saxitoxin produced by the dinoflagellate Gonyaulax catenella
Marine Mammal Physiology: Requisites for Ocean Living
coats of hair throughout their life histories, and therefore cannot be easily implicated as
a direct adaptation of the developing fetus to excreting toxicants. However, it is interesting to speculate that the shedding of contaminants in utero via lanugo perhaps persists as
one of the selective pressures to protect from neurotoxicity in situations where mercury
exposure may be high.
14.2.1.2 Blubber and nursing
The term blubber is often misrepresented in both popular culture and occasionally scientific literature, so we will use the definition provided by Reeb et al. (2007) where blubber is integument layers below the epidermis (dermis and hypodermis). As sizeable
endotherms that make their living in the marine environment, many marine mammals
utilize extensive lipid-rich blubber tissue for thermal insulation and other needs (store
nutrients, enhance hydrodynamics, protection from predators, etc.). In migratory species, such as gray whales (Eschrichtius robustus), not only are individual animals often
subject to large changes in ambient water temperature, but migratory periods are often
marked by little or no foraging activity (fasting). The laying down and mobilization of
energy stored in adipose tissue is truly remarkable in marine mammals. While duration
of nursing is often radically different between marine mammal species (on scale of a few
weeks to several years), in some species with short nursing periods, such as the northern
elephant seal (Mirounga angustirostris), females can lose up to 42% of their initial body
mass during nursing (58% of adipose mass) (Costa et al. 1986). The energetics of nursing
is discussed in Chapters 8 and 10, however, the transfer of toxicants during lactation is
interesting to consider from the perspective of both the lactating female and the nursing
pup. While the nursing young is exposed to a milieu of potential toxicants during a sensitive developmental stage, it does represent a significant excretory route for reproductive
females (Addison and Brodie 1987; Debier et al. 2006; Frouin et al. 2012). A decrease in
maternal contaminant concentrations following parity has been described in sea otters
(Jessup et al. 2010). In particular, primiparous females (females giving birth to their first
offspring) often transfer a majority of their blubber (lipid store)-based contaminant load
to their firstborn. Indeed, Beckmen et al. (2003) found increased blood concentrations of
PCB congeners as well as p,p-DDE in pups born to young dams compared to pups born
to older, presumably multiparous dams. Similarly, Ylitalo et al. (2001) found higher concentrations of OCs in first-recruited resident male Alaskan killer whales as compared to
second or later recruitment.
14.3 Biotoxins and the evolutionary chemical arms race
Toxins that are produced by prey species either as defensive mechanisms or as secondary metabolites play a role in the predator–prey relationship. While examples exist of
specific adaptations to poisons in predator–prey relationships (i.e., the skin of the roughskinned newt Taricha granulosa produces tetradotoxin to which the common garter snake
Thamnophis sirtalis demonstrates resistance), it is often difficult to assign a quid-pro-quo
physiologic or behavioral adaptation of a species or taxonomic group as a result of exposure to a poisonous prey (Brodie and Brodie 1990).
A number of marine organisms have been identified that produce compounds that are
toxic to marine mammals such as dinoflagellates, diatoms, and prokaryotes (Valério et al.
2010) and there are a number of fish, mollusk, and cnidarian species that are poisonous
or venomous to marine mammals. These poisons are often encountered by marine mammals through diet. However, saxitoxin produced by the dinoflagellate Gonyaulax catenella