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Nitrogen in Animals: Applications. Overview How are δ 15 N affected by the following processes:. Pregnancy Nutritional Stress Different diets & diet quality Nursing Fasting. Spoiler alert! They all have VERY similar results…. Pregnancy and Nutritional Stress. Studies investigate :

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Nitrogen in Animals: Applications

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Nitrogen in Animals: Applications

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OverviewHow are δ15N affected by the following processes:

  • Pregnancy

  • Nutritional Stress

  • Different diets & diet quality

  • Nursing

  • Fasting

Spoiler alert! They all have VERY similar results…

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Pregnancy and Nutritional Stress

Studies investigate:

δ15N & δ13C values in body of pregnant women with and without nutritional stress (Fuller et al. 2004, 2005)


Examine δ15N & δ13C isotopes in the body from pre-conception to delivery by:

  • Conducting dietary surveys

    2) Collect hair samples of mother post-delivery

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Happy Mommy

Fuller et al. 2004

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Sad Mommy

Fuller et al. 2005

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Negative nitrogen balance = increased fractionation

Sick b/w

10-16 weeks

Sick throughout

1st trimester

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Well…not completely understood

DECREASES IN δ15N due to maternal N conservation:

  • Assimilation of greater percentage of dietary N with lower δ15N values results in a reduction of steady state diet to body trophic fractionation (0.5-1‰)

  • Decreased urea synthesis and increased urea salvage in colon (peeing out heavy nitrogen)

  • Mother decreases in N and fetus increases = fetus literally eating mommy and increasing in trophic level

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Reasoning for INCREASE in δ15N:

As nutritional stress & weight loss continue, increase of muscle protein breakdown, lighter N is not replaced by dietary protein, & remaining tissues are enriched in heavier N (increased fractionation)

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Diet quality

2 Studies:

Oreochromis niloticus – “Nile tilapia” (Gaye-Siessegger 2004)

Paradosa lugubris – “Wolf spider”(Oelbermann and Scheu 2001)

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Nile tilapia

Study investigates:

Influence of different diets on δ15N & δ13C in fish bodies


  • 32 fish reared on same diet for 11 weeks to equilibrate on diet, then 7 were killed to estimate initial isotopic composition of body

  • Provide fish with 3 different protein diets in controlled lab for 8 weeks

  • Analyze all fish at end of experiment after 48 hour fast

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  • No significant decrease inδ15N & δ13C, body mass, b/w averages of feeding groups

  • Declining trophic shift for individuals in δ15N (6.5‰- 4‰) & δ13C (4‰-2.5‰) w/ increasing protein retention in individual fish

Experiment demonstrates high influence of individual protein

balance of δ15N & δ13C in animals – dietary protein was

conserved differently in tissue of individual fish = less fraction.

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Wolf spider

Study investigates:

Influence of diet quality on δ15N & δ13C in spiders on different quality diets


Changes in δ15N & δ13C w/ time:

- Adult females, hatchlings, spiderlings fed intermediate quality food for 3, 6, & 11 weeks

Changes in δ15N & δ13C w/ trophic level and starvation:

- Adult and juvenile spiders were fed single species diets (low, med, high quality), mixed (high & low), and starved

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- Since 14N is preferentially excreted during metabolism, the hatchling N would be

isotopically lighter.

- As individuals become larger, more isotopically like food item, then become enriched over food item by ≈3‰

Changes in δ15N & δ13C w/ time:

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Changes in δ15N & δ13C w/ trophic level:





Stepwise trophic level enrichment

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Spiders on high-quality diet were bigger and increased in size faster, & had higher δ15N & δ13C values

V. High quality

Low quality

High quality

Intermediate quality

V. Low quality

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Changes in δ15N & δ13C when starved:

Starvation leads to enrichment of δ15N due to recycling body nitrogen (i.e. “eating yourself”)

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Sea Lions


  • Teeth and bone collagen samples from two different species with different weaning behaviors

  • Using δN values to determine age of pup weaning/ trophic level

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Northern Fur Seal aka Zalophus (bone collagen)

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Tooth dentin

Northern Fur


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Isla Santa Margarita Seal aka Callorhinus (bone collagen)

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  • May lead to a method for investigating pregnancy and fertility patterns in populations of animals (past & present)

  • Pregnancy, nutritional stress, diet quality findings need to be considered in diet studies (ca not always assume ≈3‰ fractionation factor for δ15N)

  • Non-invasive monitoring of nitrogen balance in women during pregnancy – examine overall health

  • Applied to medical studies of protein stress & N balance: anorexia, bulimia, exercise, disease, weight loss, & burns

  • Do other tissues detect pregnancy, nutritional stress, changes in diet quality?

  • Determining feeding habits in animals.

  • More research to discover the biochemical reasons for δ15N increase and decrease in animals

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