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Applications of C in animals: Diet and resource partitioning, resource allocation All using differences in 13C C3 and C4 plants Renewable and nonrenewable resources: Amino acid turnover and allocation to reproduction in Lepidoptera O’Brien et al. (2002 ) Hawkmoth (Amphion floridensis) O’Brien et al. (2000): How do nectar nutrients relate to fecundity? Percentage of adult dietary carbon Egg d13C increased rapidly from a value similar to larval d13C and reached an asymptotic value, lower than diet d13C carbon contributed to eggs should come from two different pools: larval and adult Grape leaves Nectar C3 or C4 Natural variation in d13C in food sources was used for tracing sources of egg amino acid carbon Experiment Larvae Vitis (normal C3 host) d13C = -30.11 Depleted in d13C Adult Sucrose solution: (1)C3 beet sugar (d13C= -24.76) (2)C4 cane sugar (d13C = -11.25 ) Calculating the Proportion of Adult and Larval Carbon in TOTAL Egg Amino Acids Fractionation effects associated with amino acid synthesis or import from adult and larval diets should be the same for C3 fed and C4 fed females p = proportion of aa’s carbon derived from adult diet 1 – p = proportion of aa’s carbon derived from larvae diet Compound-specific d13C analysis of amino acids 13 amino acids were resolved: -6 were nonessential (i.e. carbon skeletons can be synthesized from sugars in nectar, and therefore adult source) -6 were essential (i.e. cannot be synthesized by animals) + 1 “sort of” essential because animals cannot synthesize its ring structure from scratch. Ala Gly Ser Thr Val Leu Pro Asp Glu Iie Phe Lys (Tyr) Young females eggs = Old female’s eggs in amino acid composition (no sign of senescence) Adult diet had a significant effect on non-essential d13C indicating substantial incorporation of carbon from adult diet Day’s significant effect extent to which adult dietary carbon is incorporated varied Adult dietary carbon was not incorporated into any of the essential amino acids Variation of the proportion of aa’s carbon derived from adult diet over time Non-essential amino acids Allocation of essential and non-essential aa’s into the egg differs Essential aa’s (~50% egg aa’s) derive exclusively from larval sources (contribute 35% of total egg carbon) Non-essential aa’s increasingly derive from adult diet, accesing endogenous sources of amine nitrogen (explains asymptotic behavior) Bottom line: Essential amino acids come from larval carbon sources Ecosystem Collapse in Pleistocene Australia and a Human Role in Megafaunal Extinction Miller et al. (2005) Genyornis newtoni Emu - Dromaius novaehollandie Humans colonized Australia between 55 and 45 ka Most of Aussie’s large animals became extinct between 50 and 45 ka Ecosystem change Large browsers were disproportionally affected Changed fire regime beginning in 45ka recorded in terrestrial & marine sediments Is the arrival of humans related to these extinctions? Approach: Isotopic traces of diet from eggshells & marsupial teeth were used to monitor ecosystem before and after human colonization Eggshells of two contemporaries species of “big-flightless birds” were analyzed: Emu, Dromaius novaehollandie (extant species) Genyornis newtoni (extinct ~45ka) Eggshell analysis Dated eggshells: shells 14C ; sandgrain age, amino acid racemization in egg Paleodiet: Bird eggshells are a calcite biomineral containing 3% organic matter sequestered within calcite crystals. (Stable for > 106 years) Ccarb = Calcite Carbon - from blood Corg = Carbon from Organic residues - from protein sources Used a general bird diet (feeding trials of Ostriches) -> egg shell organic offset (fractionation) 3 ‰ Fractionation diet to egg – d13Corg ~ 3 ‰ AVERAGE offset between d13Ccarb & d13Corg : ~ 10.4 ‰ (Emu) ~ 11.1 ‰ (Genyornis) these averages were used to approximate the fractionation between the two types of carbon sources and thus d13Ccarb can be adjusted to the same scale as d13Corg and using the 3 ‰ fractionation value they can be plotted as diet…. Emu Winter nester 50-45ka mean dietary d13C decreased by 3.4 ‰ Prior to 50ka - variable diet (C4 & C3 plants) More restrictive diet Only 40% of the isotope variance observed in Emu Wet years C4 (grasslands) Dry years C3 (shrubs and trees) 45ka - present restricted to C3 plants Always includes some C4 diet sources Is this change a regional phenomena? Samples were collected from 3 widely separated regions of the Aussie continent Can we find the same change in other animal groups?? Wombat tooth enamel samples were analyzed (also a strict herbivore) -An abrupt ecological shift occurred about 50 to 45 ka in Australia -Climatic forcing is unlikely (previous major climatic shift did not result in such massive extinctions), and climate change between 60 to 40 ka was not large Emu Genyornis change was seen at the base of the food web -a change in fire regime caused ecosystem reorganization: C4 dominated grasslands C3 fire-adapted grasslands and chenopod/desert scrub Or Ancient Diets, Ecology, and Extinction of 5-MillionYear-Old Horses from Florida MacFadden et al. (1999) High-crowned teeth (Hypsodonty): Grazing on abrasive plants Short-crowned teeth: Browsing diet Not quite… Horses in Bone Valley - - Excellent fossil record -6 species -two diverse clades of advanced hypsodonts with similar dental morphologies (and similar yet varying body sizes!) -Existed during a time of major global change -Preceded a terrestrial massive extinction event at ~ 4.8 Ma. The similar dental morphology implies same food source and potential competition Corresponds to a horse from an older level that shows short-crowned (i.e. browsing) tooth 3 independent methods for determining diet: -Tooth crown height -Carbon isotopic ratios from fossil tooth enamel (C3 vs C4 plants) d13C C3 plants ~ -27 ‰ (-36 - -22‰) d13C C4 plants ~ -13 ‰ (-16 - -9‰) -Tooth Wear: browsing tends to produce pits, while grazing leads to parallel scratches Microwear on enamel from a horse tooth. Magnification x 50 Hypsodonty Index Species/taxon HI* N. eurystyle 2.4 P. simpsoni >3.5 N. minor C. emsliei A. stockii D. mexicanus Modern grazers¶ Modern browsers# 141 51 2.4 2.1 3.1 2.3 >1 <1 Estimated body mass (kg) Clade history after ~4.8 Ma Extinct Extinct 63 105 101 268 - *HI = molar crown height / anteroposterios occlusal length Short crowned teeth = Browsers High crowned teeth = Grazers N. peninsulatus C. emsliei in Florida Extinct Equus spp. - Equines (medium and large) medium 3-toes hipparionines tiny & small Figure 2. Microwear is analyzed by plotting the mean number of scratches versus pits per unit area (0.5 mm2). Abbreviations of modern browsers (shaded circles) and grazers (open circles) are given in the footnotes to Table 1. Extant grazers have, on average, more scratches and less pits than browsers. C3 = C4 tiny medium Almost exclusively C4grass feeder small medium ??? – Mixed feeder, but with both browse (low MI) and C4 plants (rarely found) Medium & large Figure 3. Mean d13C versus MI for the Bone Valley horses (large symbols with vertical lines, data from Table 1; individual d13C sample data are indicated by small symbols).