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Animal Nitrogen Overview of N cycling farm animals a few unfortunate songbirds road-kill down under. Nitrogen Isotopes in Mammalian Herbivores: Hair  15 N Values from a Controlled Feeding Study (Sponheimer et al., 2003)

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slide1

Animal Nitrogen

Overview of N cycling

farm animals

a few unfortunate songbirds

road-killdown under

Nitrogen Isotopes in Mammalian Herbivores: Hair 15N Values from a Controlled Feeding Study

(Sponheimer et al., 2003)

Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird

(Pearson et al., 2003)

Kangaroo metabolism does not cause the relationship between bone collagen δ15N and water availability

(Murphy et al., 2006)

n cycle human
N Cycle(human)
  • protein turnover
    • Some proteins turnover faster than others
    • some tagged (oxidized or other means)
  • amino acid pool
    • throughout body
    • significant mixing
n cycle human1
N Cycle(human)
  • Dietary protein
    • Low
      • deficiency of essential aa’s
  • High
    • conversion to fat/glucose
    • Ammonia/urea excretion
deamination
Deamination

First transfer amine group to carrier

Ketoglutarate → Glutamate

in liver or kidney

Then deaminate Glutamate

to produce ammonia

synthesis
Synthesis

First transfer amine group to carrier

Ketoglutarate → Glutamate

Then to amino acid

in liver or kidney

slide6

Deamination

Synthesis

  • *Direction of these reactions controlled by [ ] of
    • Glutamate
    • Ketoglutarate
    • Ammonia
    • ratio of oxidized to reduced enzymes
urea cycle

liver

kidney

Urea cycle

Urea cycle controlled by acetyl CoA and glutamate

increase in [ ] after protein rich meal

nitrogen excretion animals
Nitrogen excretion animals
  • Ammonia NH3
    • Simplest form, but toxic
    • fully aquatic animals
  • Urea (NH2)2CO
    • Still toxic more complex than ammonia
    • mammals some herps (frogs), cartilaginous fish
  • Uric Acid C5H4N4O3
    • Least toxic
    • egg layers (bird, reptiles, insects)
    • precipitates from egg
a few things
A few things
  • animals assimilate dietary components with varying efficiencies
  • animal tissues fractionate the isotopes in their diet
  • animals allocate nutrients in their diet differentially to specific tissues ‘isotopic routing’
  • animals retain δ15N, excreting δ14N (~6‰)
  • protein balance is a key to fractionation

low dietary protein = “protein sparing” reserve dietary protein for tissue maintenance rather than catabolizing it for energy (Castellini and Rea 1992).

high dietary protein = use diet protein for tissue synthesis and catabolize excess

slide10
Nitrogen Isotopes in Mammalian Herbivores: Hair 15N Values from a Controlled Feeding Study(Sponheimer et al., 2003)

Goals:

Determine the importance of

  • hindgut vs foregut fermentors
  • dietary protein levels

on herbivore δ15N values.

nitrogen uptake herbivores
Nitrogen uptake herbivores
  • Hindgut
    • Horses, rabbits, birds, iguanas, green turtle
    • Limited cycling of urea nitrogen
      • fermentation, N cycling, protein balance
  • Foregut
    • Ruminants (can synthesize proteins from inorganic nitrogen compounds)
    • multi compartmental stomachs
    • cows, llamas
    • Ruminant-like
    • kangaroos, wallabies, hoatzin
      • cycle/mix N from diet and self
      • deamination and de novo protein syntheses
slide12

Diet-Hair Fractionation

Same diet, fair bit of variation

rabbits and alpaca vary 3.6‰, > 1 trophic level!

Foregut fermenters are enriched vs hindgut fermenting rabbits

But not to horses…

slide13

High Protein vs Low Protein Herbivores

  • ↑ dietary protein (9-19%)
  • causes enrichment δ15N (1.5-2.8‰)
  • Not what they expected!
  • This refutes N cycling hypo
    • (states that low protein group ↑δ15N)
  • feces explanation poor
    • feces is δ15N enriched(0.5-3.0‰), low protein = less urine loss and greater relative (not absolute) %N loss via feces, ↑δ15N loss
slide14

Effects of elemental composition on the incorporation of dietary nitrogen and carbon isotopic signatures in an omnivorous songbird.

(Pearson et al., 2003)

  • Goals
  • Determine turnover rates of δ15N and
    • δ13C in whole blood and plasma.
  • δ15N and δ13C diet-tissue fractionation factors for plasma, whole blood, and feathers.
  • Influence of high protein (%N) and low protein (%C) concentrations on fractionation factors.

yellow-rumped warbler

slide15

Materials and methods

  • 32 captive wild-caught migratory birds
    • ‘controlled’ for age & sex
  • Acclimation diet 32% insect
  • Experimental diet
    • 20%,49%,73%, 97% insects
  • Sampled
    • 21 days, mass, blood (plasma, wb), feathers (entire)
  • Determined
    • C&N δvalues of different diets
    • turnover rates
    • Discrimination
    • Isotopic signatures of diet on different tissues
slide16

Diets: %Insect, Isotopes, & Concentrations

Attempted to created diets along a linear continuum of increasing

a) isotopic signature (didn’t quite work for 15N)

b) elemental concentration

by increasing the % insect protein in diet

slide17

Diets: %Insect, Isotopes, & Concentrations

Only 0.12‰ difference in δ15N values among diets.

Diet containing most insects did not have highest δ15Nvalue

(diet with lowest proportion of insects did not have the lowest δ15N value)

Banana Effect (δ15N0.5 - 5.3‰)

turnover rates
Turnover Rates

Isotope incorporation kinetics model

(O’Brien et. Al 2000)

Δdt = discrimination factor

r = fractional turnover rate

Half-life =

slide19

Turnover Rates: Half-life Plasma & Blood

Half-life estimates plasma: δ13C 0.4-0.7 days δ15N: 0.5-1.7 days

Half-life whole blood: δ13C~4-6 days (diet 1=33 days!) δ15N 7.45-27.7 days

Whole blood is variable!

slide20

Discrimination:Plasma, Feather, and Blood

15N values plasma & whole blood enriched 1.7 to 3.0‰

“Apparent” fractionation factor for feathers

15Nenriched (3.2-3.6‰)

Fractionation factors increased linearly with elemental concentration in diet for N

slide21

in

↑ %N

↑ tissue

δ15N

out

↑ urine w/ ↑14N

slide22

Importance of Elemental Concentrations

Both isotopic signature of diet and fractionation factors influence the ultimate isotopic signature of tissues (at least plasma).

Supports the importance of using concentration-dependent mixing models when reconstructing diet.

slide23

Results

  • Discrimination factors depend on diet and tissue
  • Fractionation factors to reconstruct diet requires an estimate of elemental concentrations in the diet.
  • Turnover rates
  • Plasma 1 day (short) Whole blood 1 wk (longer)
  • Carbon and nitrogen fractionation factors increase linearly with elemental concentration in the diet.
  • Relationship between the isotopic signature of the diet and the sum of a given tissue’s (at least plasma) isotopic signature + fractionation factor was also positive & linear.
  • USE CONCENTRATION-DEPENDENT MIXING MODELS WHEN ATTEMPTING TO ESTIMATE THE RELATIVE CONTRIBUTION OF DIFFERENT FOOD SOURCES TO AN ANIMAL’S DIET!!!
slide24
Kangaroo metabolism does not cause the relationship between bone collagen δ15N and water availability(Murphy & Bowman, 2006)

Goals

  • Evaluate importance of water availability and dietary δ15N in determining δ15N values in herbivore bone collagen
  • Indirectly determine if ↑ δ15N linked to animal metabolism
  • Assessed if δ15N in grass and Kangaroo bone collagen are constant with respect to a Water Availability Index
  • Examine other factors influencing

δ15N in herbivore bone collagen

does water availability 15 n in animal tissue
Does ↓ Water availability↑δ15N in Animal Tissue?

Plants enriched in arid environs

  • ‘openness’ N cycle theory (Austin & Vitousek 1998)
    • ↑ water in system = ↓ in ratio of N loss to intrasystem N turnover
  • Cryptobiotic crusts

Why ↑ animal δ15N when in water limited systems?

  • Metabolic enrichment ‘theories’
    • ↑ Urea osmolarity, urine excreted is more nitrogen (δ15N) concentrated (Ambrose & Deniro 1986, Sealy 1987)
      • excrete more δ15N deplete urea when arid (Sponheimer 2003)
      • not experimentally shown for rats (Ambrose 2000)
    • not tested rigorously…

BUT… can ↑ δ15N be explained by herbivore diet alone?

methods
Methods
  • 173 grass collections (3-4 primary spp/collection)
  • 779 road killed roos
    • macropus sp, grazers…
  • Water Availability Index estimated from mean annual actual and potential evapotranspiration
  • Akaike’s Information Criterion (AIC)

Big study!

slide27

+

slide28

=

data

+

slide29

Results

  • Found relationship of δ15N and WAI similar between grass and kangaroo bone collagen
    • 4.74‰ to 4.79 ‰ enrichment
    • ~0.05‰ variation over entire range of data
slide30

When plotted against annual rainfall Murphy & Bowman’s δ15N relationship fits with

  • Previous Kangaroo work
  • Eutherian herbivores
    • North America & Africa
    • matches
    • Sealey et al 1987 follows similar pattern
slide31

δ13C of bone collagen as proxy

  • negative and weak relationship
    • Found lower δ15N in C4 plants (1.1‰)
    • C4 diet (high δ13C, low protein) = lower consumer δ15N

What about C3 vs C4 grasses?

C4

C3

C3

  • Model gave little support for other variables:
  • slope
  • chenopod

C4

slide32

Summary

  • Strong negative relationship of herbivore δ15N bone collagen and water availability.
  • Near identical negative pattern of δ15N in grass and kangaroo bone collagen with water availability (near constant offset in slopes)
  • Suggest dietary δ15N is main cause of negative relationship between δ15N of kangaroo bone collagen, with water availability and metabolic factors having little discernible effect.
importance
Importance…
  • Ties water availability directly to plant δ15N to animal δ15N values, with little ‘animal’ affect
  • Huge support for historic trophic ecology and past climate change data that rely on direct relationship between herbivores and plants which not confounded by animal metabolism
trophic systems
Trophic Systems

Marine systems 3-4‰/trophic level

Herbivores ~3.2‰

Carnivores 5‰

(Hobson & Welch 1992)

trophic systems1
Trophic Systems
  • Marine food chains tend to have longer food webs
  • Diet affects, as ascend trophic chain, ↑ %N in diet

expect more catabolism = discrimination @ high trophic level

  • Trophic enrichment commonly produces 3:1 slope for δ15N and δ13C ratios
slide41

Diet-Hair d15N Equilibration

Hair

Dietary 15N values changed from 2.5‰ to 7.8‰.

Dietary equilibration took ~8-10 weeks

discrimination
Discrimination
  • Tissue effects

Feathers more enriched than plasma or wb

diet tissue relationship
Diet Tissue Relationship
  • C & N signatures linearly related with tissue signatures + discrimination factors
slide46

Turnover Rates

  • Correlated linearly with metabolic rate of tissue
  • Different species have different turnover rates for same tissues

Likely related to size, mass specific metabolic rates, life history factors

half-life for wb C in bear > crow > quail > warbler

slide47

Turnover Rates

  • Plasma (1-5 days)
  • Whole Blood (5-35 days)
  • Feces (
  • Feathers, Hair, Nails, Hoof (time when grown, maybe a lag here)
  • Bone
  • Teeth
implications
Implications

WUE

NPP

N demand

CO2

‘openness’ of N cycle

δ15N in plants

δ15N in herbivores

slide50
Pearson
  • Funk/questions
    • variability in initial mass and mass change following dietary switch among treatment groups (shows they like carbs
    • Diets did not have ↑ δ15N values w/

↑ % insects

    • Fractionation vs. discrimination
co2 effects on 15 n
CO2 effects on δ15N

(Coltrain et. Al. 2004)