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Marine Mammal Physiology: Requisites for Ocean Living
odontocetes and behavioral responses of cetaceans to noise, but they have great potential
to increase our knowledge on post-partum reproductive effort and behavior in cetaceans. For example, it may be possible to hear when a calf is suckling if a tag is placed
near the head of the calf. If mothers/calf pairs are instrumented at different stages of
lactation, it will be possible to estimate how much time the calf spends suckling and how
this changes as lactation progresses.
10.3.5 Metabolism
The full scope of biomedical tools for the study of metabolism are available for the study
of lactation in marine mammals, although their applicability is currently limited to pinnipeds that are able to be chemical immobilized without substantial handling artifacts
(Champagne et al. 2012). The tools include the use of antibody-based techniques to measure protein expression in tissue and circulating levels of chemical messengers including
hormones and adipokines. Western blots, enzyme immunoassays (EIA), enzyme-linked
immunosorbent assays (ELISA), and radioimmunoassays are used to quantify the concentrations of proteins and chemical messengers. The use of omics tools including genomics,
transcriptomics, and proteomics can be used to understand the changes in gene expression in specific tissues of fasting and lactating pinnipeds, usually blubber and muscle.
The systemic impacts of these changes in gene expression can be studied using metabolomics, which attempts to measure as many of the metabolites in circulation or tissue
as p ossible (Champagne et al. 2013). Finally, metabolic tracers can be used to quantify
metabolite flux during lactation. A variety of techniques have been developed that use
turnover of radioisotope or stable isotope-labeled metabolites to investigate whole-body
metabolism. Several of these tracer methodologies that were developed for biomedical
studies have been used for the first time in wildlife systems in studies on lactating pinnipeds (Champagne et al. 2006).
10.3.6 Detection of weaning
One challenge for some marine mammal species that slowly transition offspring from
milk to nutritional independence is the ability to detect weaning. One method that can
be used to study this transition is to compare the stable isotope values of C and N in milk
and plasma between mothers and offspring. When milk is their only food source, stable
isotopes show that offspring are feeding at a higher trophic level than their mothers. As
offspring transition to other food sources these differences disappear. In this way, stable
isotopes can give insight into the timing of weaning transition to other food sources in
marine mammals (Polischuk et al. 2001).
10.4 Unsolved mysteries
The ability of the mother to rapidly produce such large quantities of high fat milk must
be matched by the digestive and assimilation capabilities of the pup to process and
use these nutrients. Maximum energy assimilation rates by the digestive and metabolic systems of animals have been theorized to constrain energy expenditure and
growth (Weiner 1992). A limit of 7× basal metabolic rate (BMR) has been hypothesized
as an upper limit to assimilation of dietary energy from free-ranging energy budgets
(Hammond and Diamond 1997) and a mammalian record of 7.7× BMR was reported
for mice under conditions of extreme cold exposure (Johnson and Speakman 2001).
Marine Mammal Physiology: Requisites for Ocean Living
odontocetes and behavioral responses of cetaceans to noise, but they have great potential
to increase our knowledge on post-partum reproductive effort and behavior in cetaceans. For example, it may be possible to hear when a calf is suckling if a tag is placed
near the head of the calf. If mothers/calf pairs are instrumented at different stages of
lactation, it will be possible to estimate how much time the calf spends suckling and how
this changes as lactation progresses.
10.3.5 Metabolism
The full scope of biomedical tools for the study of metabolism are available for the study
of lactation in marine mammals, although their applicability is currently limited to pinnipeds that are able to be chemical immobilized without substantial handling artifacts
(Champagne et al. 2012). The tools include the use of antibody-based techniques to measure protein expression in tissue and circulating levels of chemical messengers including
hormones and adipokines. Western blots, enzyme immunoassays (EIA), enzyme-linked
immunosorbent assays (ELISA), and radioimmunoassays are used to quantify the concentrations of proteins and chemical messengers. The use of omics tools including genomics,
transcriptomics, and proteomics can be used to understand the changes in gene expression in specific tissues of fasting and lactating pinnipeds, usually blubber and muscle.
The systemic impacts of these changes in gene expression can be studied using metabolomics, which attempts to measure as many of the metabolites in circulation or tissue
as p ossible (Champagne et al. 2013). Finally, metabolic tracers can be used to quantify
metabolite flux during lactation. A variety of techniques have been developed that use
turnover of radioisotope or stable isotope-labeled metabolites to investigate whole-body
metabolism. Several of these tracer methodologies that were developed for biomedical
studies have been used for the first time in wildlife systems in studies on lactating pinnipeds (Champagne et al. 2006).
10.3.6 Detection of weaning
One challenge for some marine mammal species that slowly transition offspring from
milk to nutritional independence is the ability to detect weaning. One method that can
be used to study this transition is to compare the stable isotope values of C and N in milk
and plasma between mothers and offspring. When milk is their only food source, stable
isotopes show that offspring are feeding at a higher trophic level than their mothers. As
offspring transition to other food sources these differences disappear. In this way, stable
isotopes can give insight into the timing of weaning transition to other food sources in
marine mammals (Polischuk et al. 2001).
10.4 Unsolved mysteries
The ability of the mother to rapidly produce such large quantities of high fat milk must
be matched by the digestive and assimilation capabilities of the pup to process and
use these nutrients. Maximum energy assimilation rates by the digestive and metabolic systems of animals have been theorized to constrain energy expenditure and
growth (Weiner 1992). A limit of 7× basal metabolic rate (BMR) has been hypothesized
as an upper limit to assimilation of dietary energy from free-ranging energy budgets
(Hammond and Diamond 1997) and a mammalian record of 7.7× BMR was reported
for mice under conditions of extreme cold exposure (Johnson and Speakman 2001).