Behavioral syndrome
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In behavioral ecology, a behavioral syndrome is a correlated suite of behavioral traits, often (but not always) measured across multiple contexts. The suite of traits that are correlated at the population or
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
level is considered the behavioral syndrome, while the
phenotype In genetics, the phenotype () is the set of observable characteristics or traits of an organism. The term covers the organism's morphology or physical form and structure, its developmental processes, its biochemical and physiological pr ...
of the behavioral syndrome an individual shows is their behavioral type. For example, a population may show a behavioral syndrome that includes a positive correlation between
foraging Foraging is searching for wild food resources. It affects an animal's fitness because it plays an important role in an animal's ability to survive and reproduce. Foraging theory is a branch of behavioral ecology that studies the foraging behavi ...
behavior and
mating In biology, mating is the pairing of either opposite- sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reprod ...
behavior. An individual may be more or less aggressive than another individual within this behavioral syndrome, and this aggressive or passive phenotype is that individual's behavioral type. For example, the lizards '' Eulamprus heatwolei'' show a behavioral syndrome with two behavioral types. There is a correlated relationship between how
territorial A territory is an area of land, sea, or space, particularly belonging or connected to a country, person, or animal. In international politics, a territory is usually either the total area from which a state may extract power resources or a ...
an individual is, how likely they are to explore their environment, and what strategy they use to avoid
predation Predation is a biological interaction where one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not kill th ...
. This behavioral syndrome has also been shown to influence the
mating system A mating system is a way in which a group is structured in relation to sexual behaviour. The precise meaning depends upon the context. With respect to animals, the term describes which males and females mate under which circumstances. Recognised ...
of this species; territorial males are more likely to sire offspring with territorial females, and larger territorial males compete less with other males for mates. However, less territorial, or "floater", males and females produce consistently larger offspring than territorial parents or hybrids.


History

''Behavioral syndrome'' is a term that originated in the
psychology Psychology is the scientific study of mind and behavior. Psychology includes the study of conscious and unconscious phenomena, including feelings and thoughts. It is an academic discipline of immense scope, crossing the boundaries between ...
literature. It was originally used to describe human behavioral disorders, including nervous and stereotypical behaviors. These often included pacing, involuntary muscle twitches, and repetitive self-mutilation. The term became less popular in the late 1970s and 80s. Through the 90s, it was infrequently used analogously for "
personality Personality is the characteristic sets of behaviors, cognitions, and emotional patterns that are formed from biological and environmental factors, and which change over time. While there is no generally agreed-upon definition of personality, m ...
" in some behavioral ecology literature, but it was still primarily used in psychology literature to describe inter-individual differences in behavior to model systems like
rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...
s and
primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter including ...
s. While a behavioral syndrome is a concept still used in multiple disciplines, the term was adopted by behavioral ecologists and re-defined in 2004. It has become a popular field of study, both empirically and theoretically.


Evolutionary implications

Often, behavior is considered infinitely
plastic Plastics are a wide range of synthetic or semi-synthetic materials that use polymers as a main ingredient. Their plasticity makes it possible for plastics to be moulded, extruded or pressed into solid objects of various shapes. This adaptab ...
and can easily be adapted to changing environmental conditions. However, the nature of behavioral syndromes implies that there can be constraints on the behavior of an individual. This can (though it is not required to) lead to the non-optimal behavior that has long been puzzling to behavioral ecologists (e.g., attacking a predator when fleeing is a better option). Given that behavioral syndromes come with perceived costs, it would be expected for
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
to have selected against them. As such, there are four primary reasons for the persistence of behavioral syndromes: (1) pleiotropy, linkage disequilibrium, or other mechanistic restrictions; (2) the benefit of consistency to mitigate against errors; (3) the benefits of specialization; and (4) the benefits of predictability in social interactions. It is important to emphasize that while these may mitigate the costs associated with limited behavioral plasticity, behavioral syndromes themselves do not necessarily imply they create sub-optimal behavior. See ''Misconceptions''.


Mechanisms

The field of behavioral syndromes often focuses on describing behavioral types. However, the phenotypic correlations that form behavioral types do not necessarily signify that they have a genetic basis. While behavioral syndromes are theoretically not required to be the byproduct of genetics, understanding if a specific syndrome is genetically based may be important, as this determines heritability. Without a genetic basis, behavioral syndromes must be the result of environmental conditions. Recent studies have shown that some behavioral syndromes have a genetic basis. Additionally, some of these genetic correlations that shape behavioral syndromes can evolve. For example, researchers were able to separate the genetically determined traits of body size, nest size, and foraging behavior in laboratory mice.Bult & Lynch 2005 The simplest way for a behavioral syndrome to form is through a
genetic polymorphism A gene is said to be polymorphic if more than one allele occupies that gene's locus within a population. In addition to having more than one allele at a specific locus, each allele must also occur in the population at a rate of at least 1% to gen ...
, meaning two or more
allele An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...
s at the same
locus Locus (plural loci) is Latin for "place". It may refer to: Entertainment * Locus (comics), a Marvel Comics mutant villainess, a member of the Mutant Liberation Front * ''Locus'' (magazine), science fiction and fantasy magazine ** ''Locus Award' ...
. In one of the best documented examples of this, a single gene (''for'') controls the foraging distance and a suit of related traits in ''
Drosophila melanogaster ''Drosophila melanogaster'' is a species of fly (the taxonomic order Diptera) in the family Drosophilidae. The species is often referred to as the fruit fly or lesser fruit fly, or less commonly the " vinegar fly" or "pomace fly". Starting with ...
''. "Rover" individuals forage father distances as larvae, have an increased activity rates in adulthood and an increased likelihood of encapsulating parasitic wasp eggs. "Sitter" individuals show a relatively decreased response in all of these same categories. Pleiotropic interactions (where one gene may influence multiple traits) is another likely mechanism. Recently, the proteins transcribed across the whole
genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding g ...
(the
transcriptome The transcriptome is the set of all RNA transcripts, including coding and non-coding, in an individual or a population of cells. The term can also sometimes be used to refer to all RNAs, or just mRNA, depending on the particular experiment. The t ...
) of stickleback fish were compared in two different tests: exposed or not exposed to predators. They found that fish exposed to predators showed up- and down-regulation of different genes, compared to those not exposed. Those exposed to predation also developed a behavioral syndrome, while those not exposed to predation did not, suggesting that this change in gene expression may be related to the development of behavioral syndromes. Non-genetic behavioral syndromes have received almost no focus in recent years, although studies of associated traits that appear to be environmentally determined are not uncommon under other names.


Misconceptions

Though behavioral syndromes were simply intended to be defined as a correlated suite of behavioral traits, some misconceptions are frequent in the literature. Misconceptions include the ideas that behavioral syndromes: *must be the same from birth to death, *must be genetically based, *must always include more than one behavior or more than one context, *must not be based on physical traits like size or dominance rank, such as being an "alpha" individual, *must show multiple or discrete behavioral types (rather than a continuum), and *cause individuals to show sub-optimal behavior. While all of these things may be associated with behavioral syndromes and may be interesting avenues to study when they are noted, the definition of behavioral syndromes was not meant to imply any of these things to be necessary. The stability, persistence or a minimum requirement of traits are not in part of the definition. At its core, a behavioral syndrome is simply a statistical measure of correlated behavioral traits.


References

{{Reflist Behavioral ecology Ethology