So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

The influence of diet on the distribution of nitrogen isotopes in animals was investigated by analyzing animals grown in the laboratory on diets of constant nitrogen isotopic composition. 
The isotopic composition of the nitrogen in an animal reflects the nitrogen isotopic composition of its diet. The δ^(15)N values of the whole bodies of animals are usually more positive than those of their diets. Different individuals of a species raised on the same diet can have significantly different δ^(15)N values. The variability of the relationship between the δ^(15)N values of animals and their diets is greater for different species raised on the same diet than for the same species raised on different diets. Different tissues of mice are also enriched in ^(15)N relative to the diet, with the difference between the δ^(15)N values of a tissue and the diet depending on both the kind of tissue and the diet involved. The δ^(15)N values of collagen and chitin, biochemical components that are often preserved in fossil animal remains, are also related to the δ^(15)N value of the diet. 
The dependence of the δ^(15)N values of whole animals and their tissues and biochemical components on the δ^(15)N value of diet indicates that the isotopic composition of animal nitrogen can be used to obtain information about an animal's diet if its potential food sources had different δ^(15)N values. The nitrogen isotopic method of dietary analysis probably can be used to estimate the relative use of legumes vs non-legumes or of aquatic vs terrestrial organisms as food sources for extant and fossil animals. However, the method probably will not be applicable in those modern ecosystems in which the use of chemical fertilizers has influenced the distribution of nitrogen isotopes in food sources. 
The isotopic method of dietary analysis was used to reconstruct changes in the diet of the human population that occupied the Tehuacan Valley of Mexico over a 7000 yr span. Variations in the δ^(15)C and δ^(15)N values of bone collagen suggest that C_4 and/or CAM plants (presumably mostly corn) and legumes (presumably mostly beans) were introduced into the diet much earlier than suggested by conventional archaeological analysis.

Influence of Diet On the Distribtion of Nitrogen Isotopes in Animals

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A DNA test to sex most birds.

Background 
Stable isotope analysis is increasingly being utilised across broad areas of ecology and biology. Key to much of this work is the use of mixing models to estimate the proportion of sources contributing to a mixture such as in diet estimation.


Methodology 
By accurately reflecting natural variation and uncertainty to generate robust probability estimates of source proportions, the application of Bayesian methods to stable isotope mixing models promises to enable researchers to address an array of new questions, and approach current questions with greater insight and honesty.


Conclusions 
We outline a framework that builds on recently published Bayesian isotopic mixing models and present a new open source R package, SIAR. The formulation in R will allow for continued and rapid development of this core model into an all-encompassing single analysis suite for stable isotope research.

/pdf/source-partitioning-using-stable-isotopes-coping-with-too-4qd1pzfyh0.pdf

Source partitioning using stable isotopes: coping with too much variation.

To understand the ecology of migratory animals it is important to link geographic regions used by individuals including breeding, wintering, and intermediate stopover sites. Previous conventional approaches used to track animal movements have relied on extrinsic markers and typically the subsequent recovery of individuals. This approach has generally been inappropriate for most small, or non-game animals. The use of intrinsic markers such as fatty acid profiles, molecular DNA analyses, and the measurement of naturally occurring stable isotopes in animal tissues offer alternative approaches. This paper reviews the use of stable isotope analyses (primarily δ13C, δ15N, δ34S, δD, δ87Sr) to trace nutritional origin and migration in animals. This approach relies on the fact that foodweb isotopic signatures are reflected in the tissues of organisms and that such signatures can vary spatially based on a variety of biogeochemical processes. Organisms moving between isotopically distinct foodwebs can carry with them information on the location of previous feeding. Such an approach has been used to track animal use of inshore versus offshore, marine versus freshwater, terrestrial C3 versus marine, terrestrial mesic versus xeric, and C3 versus C4 or Crassulacean acid metabolism foodwebs. More recently, the use of stable hydrogen isotope analyses (δD) to link organisms to broad geographic origin in North America is based on large-scale isotopic contours of growing-season average δD values in precipitation. This technique, especially when combined with the assay of other stable isotopes, will be extremely useful in helping to track migration and movement of a wide range of animals from insects to birds and mammals. Future research to refine our understanding of natural and anthropogenic-induced isotopic gradients in nature, and to explore the use of stable isotopes of other elements, is recommended.

Tracing origins and migration of wildlife using stable isotopes: a review

Studies of birds that use stable isotopes as dietary tracers require estimates of how quickly stable isotopes in tissues are replaced by isotopes derived from the diet. However, isotopic turnover rates in animals in general, and birds in particular, are poorly understood. We established the turnover rates of '3C in tissues of grown Japanese Quail (Coturnixjaponica) by switching the diet of an experimental group from a wheat-based (C3) diet to a corn-based (C4) diet and sampled tissues periodically for 212 days. An exponential model described patterns of isotopic turnover in all tissues. Turnover rates for quail tissues were ranked liver > blood > muscle > bone collagen with the half life of carbon ranging from 2.6 days in liver to 173.3 days in bone collagen. A similar diet-switch experiment was conducted on captive American Crows (Corvus brachyrhynchos) and feather samples were assayed isotopically. Stable isotope values of crow feathers reflected diet during periods of growth. We suggest that stable isotope analysis could be used to determine relative contributions of endogenous and exogenous nutrient sources for feather growth and egg production in captive and wild birds.

Assessing Avian Diets Using Stable Isotopes I: Turnover of 13C in Tissues

For migratory birds, early arrival and physical condition on the breeding grounds are important determinants of reproductive success and fitness. Differences in arrival times often exceed a month, and later arriving individuals are often in poorer condition. Habitat-specific isotopic signatures indicate that the quality of winter habitats occupied by American redstarts (Setophaga ruticilla) determines their physical condition and spring departure dates, which in turn result in variable arrival schedules and condition on temperate breeding grounds. These findings link events in tropical winter grounds with those in temperate breeding areas for a migratory songbird and provide evidence that winter habitats may be limiting.

https://science.sciencemag.org/content/sci/282/5395/1884.full.pdf

Linking Winter and Summer Events in a Migratory Bird by Using Stable-Carbon Isotopes

Stable isotopes are being increasingly used in wildlife forensics as means of determining the origin and movement of animals. The heavy isotope content of precipitated water and snow (dDp, d 18 Op) varies widely and systematically across the globe, providing a label that is incorporated through diet into animal tissue. As a result, these isotopes are potentially ideal tracers of geo- graphic origin. The hydrogen and oxygen isotope tracer method has excellent potential where (1) spatial variation of precipitation isotopes exist, and (2) strong, mechanistic relationships link precipitation and isotope ratios in biological tissue. Here, we present a method for inter- polation of precipitation isotope values and use it to create global basemaps of growing-season (GS) and mean annual (MA) dDp and d 18 Op. The use of these maps for forensic application is demonstrated using previously published isotope data for bird feathers (dDf) in North America and Europe. The precipitation maps show that the greatest potential for applying hydrogen and oxygen isotope forensics exists in mid- to high-latitude conti- nental regions, where strong spatial isotope gradients exist. We demonstrate that dDf/dDp relationships have significant predictive power both in North America and Europe, and show how zones of confidence for the assignment of origin can be described using these predic- tive relationships. Our analysis focuses on wildlife forensics, but the maps and approaches presented here will be equally applicable to criminal forensic studies involving biological materials. These maps are available in GIS format at http://www.waterisotopes.org.

/pdf/global-application-of-stable-hydrogen-and-oxygen-isotopes-to-2e4aoz7gud.pdf

Global application of stable hydrogen and oxygen isotopes to wildlife forensics.

Studies using stable-isotope analysis to infer diet require a knowledge of how stable-isotope ratios in consumer tissues are related to dietary values. We determined 61'3C and 6'5N diet-tissue fractionation factors for blood, liver, muscle, bone collagen and feathers of domestic chickens (Gallus gallus), Japanese Quail (Coturnix japonica) and Ring-billed Gulls (Larus delawarensis) and for blood and feather samples of adult Peregrine Falcons (Falco peregrinus) raised on known isotopic diets. In most cases tissues were enriched in 613C and 615N compared to diet. However, fractionation values differed among species, diets, and tissue types and this variation must be considered in isotope dietary studies. We found little evidence that isotopic fractionation factors are influenced by age in adult birds and provide fractionation factors appropriate for granivores feeding in a C-3 biome and for higher trophic-level piscivores and carnivores. American Crows (Corvus brachyrhynchos) raised on a perch diet grew faster and showed lower nitrogen diet-tissue fractionation values than crows raised on a plant-based diet. We suggest that nutritional stress caused substantial increases in diet-tissue fractionation values due either to: (1) mobilization and redeposition of proteins elsewhere in the body; or (2) amino acid composition changes in tissues.

Keith A. Hobson

Papers

Tracing origins and migration of wildlife using stable isotopes: a review

Assessing Avian Diets Using Stable Isotopes I: Turnover of 13C in Tissues

Linking Winter and Summer Events in a Migratory Bird by Using Stable-Carbon Isotopes

Global application of stable hydrogen and oxygen isotopes to wildlife forensics.

Assessing Avian Diets Using Stable Isotopes II: Factors Influencing Diet-Tissue Fractionation