Animal Behavior/Behavioral Genetics

Behavioral Genetics
A devil, a born devil, on whose nature nurture can never stick; on whom my pains humanely taken, all, all lost, quite lost—The Tempest, William Shakespeare 1610

Behavioral genetics is the field of biology that studies the heritability of behavioral traits in animal (including human) behavior. The field has formed from an overlap of genetics, ethology and psychology.

Basic Concepts
Genetic characteristics are those that are to a large extent determined by genes. Although genes may play a role in many behaviors, they never determine them. There are no genes that directly code for a behavior - genes only code for proteins. However, it is clear that a change in a single protein can cause a host of downstream effects and may even bring about a distinct phenotype.The external environment exerts a strong influence on how all genes are expressed in behavior via a development of nervous and hormonal mechanisms. The Phenotype (i.e., the observable characteristics of an organism) emerges from an interaction of its Genotype (i.e., the organism's genetic composition) with environmental factors. A Gene is the smallest functional unit of heredity and is composed of DNA. It specifies the codes for amino acid chains that make up individual proteins (e.g., serum albumin). A Locus is a section on a chromosome that relates in a meaningful way to a function. Monomorphic loci are loci with a single common segment of code, and which is present in 95-99% of individuals. In contrast, polymorphic loci exist in form of two or more alleles (i.e., versions of the same position of the chromosome) with a combined frequency>0.05. Diploid organisms carry two copies of each gene, one derived from each parent. Homozygous is the condition in which both of these copies for that gene are identical (i.e., the same allele). If the chromosomes contain two different alleles of the gene, it is called heterozygous. In some cases the phenotype of heterozygous individuals follows one allele (i.e., the dominant one) and not the other (i.e., the recessive allele). Recessive phenotypes will only be expressed in cases where the individual is homozygous for that allele. If one gene pattern is well established and common in a particular organism, it is referred to as the wild type allele. In contrast, a mutant allele usually represents a relatively new, and less common modification. Pleiotropy refers to the situation where there is no clear 1:1 correspondence between one particular gene and a particular behavioral trait. For instance, fruitflies with a mutant period gene display a range of behavioral effects, ranging from differences in daily activity rhythms, time of day at which adults hatch from pupae, and the particular patterning of the male's courtship song. Heritability is a statistical estimate of variation in a trait that is attributable to genetic differences among individuals within a group. For instance, the number of arms humans have is heritable and can be expressed as a proportion. Variables such as an individual's fingerprint and height are strongly heritable, while other variables such as musical abilities are much less so.

Classical Genetics
Classical (or Mendelian) genetics examines the distribution of hereditary characteristics of behaviors from one generation to the next. With selective breeding, the presence/absence of specific behaviors can be tracked through the outcomes of sexual reproduction. From such work came the realization that genes existed, that individuals are diploid with one half of the genes contributed by each parents, and that some genes dominate the phenotype over others. The genetics of many diseases follows simple Mendelian rules while examples of behavior in this category are generally few. Rather than in a small number of discrete states, most morphological/behavioral traits (body size, intelligence, boldness) occur across a continuous phenotypic range.


 * Seymour Benzer discovered a series of behavioral mutants in fruit flies, including single gene disruptions of circadian rhythms (period), and various genetic causes in neurodegeneration and aging.
 * Hygienic bees: Hygienic behavior in honey bees involves the ability to detect and remove diseased, larval and pupal brood from the nest before the pathogen becomes infectious. Forming a mechanism of resistance to bee diseases and parasitic mites, it consists of two distinct task-components: uncapping a cells and removing its content. Rothenbuhler (1964) suggested that these two traits were controlled in a simple Mendelian manner by two recessive loci. More recent molecular evidence from quantitative trait loci (QTL) linkage mapping has identified multiple specific stretches of DNA with genes that underly variation in this trait. This work suggests that the genetic basis of hygienic behavior is considerably more complex, and that seven QTLs are associated with hygienic behavior, each controlling only 9-15% of the observed phenotypic variance.

Quantitative Genetics
Quantitative genetics is a mathematical approach to understanding the underlying pattern of inheritance of phenotypic traits. Such traits are often subject to significant environmental influences and usually involve a great number of underlying genes. Although each gene may well follow a simple Mendelian pattern, overall results are not easily characterized in these terms. Quantitative approaches are essential to studying the degree to which relatedness among Individuals is matched by resemblances in behavioral characteristics. It thus aims to estimate the proportion of total phenotypic variance that is explained by relatedness. Aside from cases where multiple genes affect single traits, changes in one individual gene may impact quite a number of different traits. Such instances can be identified and characterized through measures of phenotypic covariance across multiple traits.

Population Genetics
Population genetics concerns itself with mechanisms that change the relative occurrence of genes within a population. It examines how gene frequencies change or become stabilized within populations through behavioral forces such as sexual selection, mating systems, dominance, or territoriality.

Developmental Genetics
Developmental genetics explores how genetics interfaces with ontogenetic processes in behavior. Genetics plays an integral role in the control of cell growth and differentiation, formation of tissues, organs and hormone systems, as well as in the emergence and critical timing of learning opportunities, cognitive abilities, and emotional systems.

Microarray technology is able to characterize levels of activity for many genes simultaneously. This technique measures how many copies of different mRNAs are made when genes are turned on.

Epigenetics
Epigenetics refers to changes in behavior as a result of alterations in gene expression, rather than changes in the nucleotide sequence itself. Modifications over an individual’s lifespan, such as DNA methylation, acetylation, and changes in histones, alter the way in which specific genes are expressed. DNA methylation is a large contributor to epigenetic changes and gene expression. When methylation occurs in the promoter region of the genome sequence, the gene transcription is repressed, turning off that particular gene. Causing different responses to their surrounding environment, these changes may be heritable. Morphological differences in identical twins result when two distinct copies of the same genome diverge as different paths and experiences modify the expression of the basic genetic blueprint, and resulting in differences in morphological traits, personalities, and behavioral responses. While ‘’’Behavioral Genetics’’’ considers observable inter-individual differences in behavior due to genotype, ‘’’Behavioral Epigenetics’’’ bridges genetic mechanisms to the significance of environmental impacts.

Migration paths of European Warblers
Migration has been defined in a number of ways; it can best be described as when animals continue to travel further from their ‘home range’ till such a time that they begin to become responsive to resources. This type of move in birds appears to be strategic, particularly in coping with changes in temperature accompanied by seasonal variation as well as the abundance of food. For several decades studies conducted on the European Sylvia warblers (Garden warblers -Sylvia borin and Blackcaps-Sylvia atricapailla particularly) have shed light on the various aspects of migration such as the underlying mechanisms. These birds have proved to be excellent models for studying migration as they contain migrant populations that fly to different regions as well as non-migrant populations that remain sedentary. The Blackcaps breed throughout Europe, parts of western Asia and North Africa; those populations from Central and North Europe migrate to Southern Europe and parts of North Africa. Similarly, the Garden warblers migrate from Europe to Northern Africa. In studies on Blackcaps from southern Germany, researchers were able to show that hybrids of migratory and non-migratory populations developed migratory activity; the degree of activity was found to be intermediate to that of the parents. Furthermore, the genetic mechanism appears to be under the control of multi-locus system; if it were governed by a single locus system all F1 generation would be expected to show the same migratory activity. Several questions arise such as how does a juvenile know where to fly and when does a migrant know to end its journey? Vector navigation can be defined as an inherent quality that enables juveniles to determine the direction and duration of flight. Using a series of cross breeding experiments it was determined that the direction of orientation was also under genetic control as the offspring of migratory and non-migratory species showed directional preferences that matched those of the migratory parents. Additional evidence from cross breeding experiments between Austrian Blackcaps (which fly in a southeasterly direction) and German Blackcaps (which fly southwesterly) determined that the offspring flew in an intermediary direction. As for the inexperienced migrant knows when to end its journey this appears to be regulated genetically. According to the vector-navigation hypothesis where the patterns of migration activity as well as the direction for migration appear to be inherited. Additional cross breeding experiments between German Blackcaps and Blackcaps from the Canaries showed that the pattern of activity was found to be intermediate to that of the parents. Through several studies on European warblers, it was shown that the ability to migrate is hereditary as well as the direction in which the birds migrate. The degree of activity (intense migration versus sedentariness) was also inherited.

Parental Behavior and fosB Mutant Mice
Like most mammals, wild-type female mice are generally very effective in their maternal care. However, females that are deficient of this protein exhibit a marked indifference towards their pups.

Behavioral Traits in Breeds of Hunting Dogs
A number of dog breeds have emerged with specializations of behaviors suitable for hunting small game. Such breeds of gun dogs, including pointers, setters, spaniels, and retrievers, readily display behaviors for identifying, flushing, and retrieving small game. In pointing behavior, dogs search for and identity potential prey, but refrain from actually stalking and potentially flushing it. Instead they remain frozen into immobility, facing it from nearby. Retrieving behavior is shown by individuals who seize and return to the pack carrying dead or wounded prey, even when they had not attacked it themselves. The antecedents for such behaviors appear to be widely present during group-hunting of most canine predators. They are largely characteristics of young individuals who have recently joined a pack for the hunt, are not fully participating in it yet, and who are largely restricted to junior, supporting roles. Common breeds of gun dogs combine this fairly intermediate degree of juvenile behavior with fairly adult canine morphologies.

Maternal Behavior of Rats and Epigenetics
An important model system for the study of behavioral epigenetics is found in maternal behavior of rats where the mother’s nurturing and licking of her pups decreases displays of fear and hormonal stress responses later in their lives. The mother’s attention causes specific changes in methylation patterns, histone acetylation, and behavior as adults. The impact alters the expression of genes integral to stress responses, such as glucocorticoid receptor. Preventing the removal of the histone’s acetyl group from the chromatin structure, the epigenetic impact of maternal nurturing can be abolished.