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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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overview how are 15 n affected by the following processes
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…


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





Happy Mommy

Fuller et al. 2004


Sad Mommy

Fuller et al. 2005


Negative nitrogen balance = increased fractionation

Sick b/w

10-16 weeks

Sick throughout

1st trimester


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

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)

diet quality
Diet quality

2 Studies:

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

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

nile tilapia
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
  • 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.

wolf spider
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


- 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:


Changes in δ15N & δ13C w/ trophic level:





Stepwise trophic level enrichment


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

changes in 15 n 13 c when starved
Changes in δ15N & δ13C when starved:

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

sea lions
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


Northern Fur Seal aka Zalophus (bone collagen)


Tooth dentin

Northern Fur


  • 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