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Toth A.L. (2010) Development, Evolution and Behavior. In: Breed M.D. and
Moore J., (eds.) Encyclopedia of Animal Behavior, volume 1, pp. 500-506
Oxford: Academic Press.
© 2010 Elsevier Ltd. All rights reserved.
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Development, Evolution and Behavior
A. L. Toth, Pennsylvania State University, University Park, PA, USA
ã 2010 Elsevier Ltd. All rights reserved.
Introduction
The goal of this article is to explore the relationships
between evolution, development, and behavior. There are
two main reasons why such considerations are important to
the field of animal behavior – one is the important mechanistic links between behavior and development, and the
second relates to conceptual insights that can be gained
from the field of evolutionary developmental biology.
With respect to the first topic, it is abundantly clear that
behavior and development are intimately linked. The brain
develops both during embryological and adult stages, and
this development can be a link between the environment
and plasticity in individual behavioral responses. In addition,
some forms of behavior develop and change over the lifetime
of an individual, and thus can be considered developmental
processes themselves. Second, studies of the molecular
genetic basis of morphological development have progressed further than those of behavior. Molecular developmental biology paired with a comparative, evolutionary
perspective has given rise to the field of ‘evo-devo,’ which
can provide several lessons that can be applied to the study of
behavior. These include the importance of conserved genes
and changes in gene regulation in generating novel phenotypes
and the utility of breaking down (behavioral or morphological) phenotypes into constituent parts, or ‘modules.’
In the sections that follow, both mechanistic and conceptual links between behavior and development are
discussed. The first section explores the various ways in
which behavior and development are interrelated and also
how behavioral and morphological phenotypes differ but
must be considered simultaneously. Then, the field of
evolutionary developmental biology and some of the
major tenets of evo-devo that can be applied to the
study of behavior are described. Next, specific examples
from across different animal taxa are reviewed that illustrate how considerations of the principles of evo-devo and
the behavior-development relationship can advance our
understanding of how behavior evolves. Finally, the article concludes by suggesting future directions for a more
comprehensive integration of development and behavior
that could lead to further insights into animal behavior.
Relationships Between Behavior
and Development
In many ways, the study of behavior is the study of
development. Like any other organ, the nervous system
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develops during both embryological and adult stages
(though certainly to varying degrees) and its development is
highly responsive to external and internal environmental
factors. Interestingly, some of the same genes can affect
both nervous system development during embryonic stages
and neural function and behavior in adult animals. One
example is the gene fruitless in the fruit fly Drosophila
melanogaster. This gene is important for the development
of male-specific neuronal projections into abdominal muscles used in mating, but also affects courtship behavior in
mature animals. In fact, fruitless derives its name from a
particular mutation that causes males to court other males.
In addition, there are many known instances of mechanistic links between certain forms of behavior and morphological or physiological development – this can be the
result of pleiotropic effects of specific hormones or genes on
both the nervous system and other organs. For example, in
many vertebrates, testosterone is important in sex determination of the gonads and brain during embryological
development, but can also have effects on male aggressive,
territorial behavior during adulthood. In female insects,
juvenile hormone levels during development influence
ovary size and can also affect various forms of adult behavior, including egg-laying and foraging. A prominent example of the pleiotropic effects of insect hormones on both
reproduction and behavior involves ‘oogenesis-flight syndrome,’ in which ovarian development is associated with
sedentary behavior, and a shut-down of ovarian development is associated with sustained flight. In two species of
migratory locusts, Locusta migratoria and Schistocerca gregaria,
this syndrome is exhibited in the extreme. Two entirely
different locust morphs exist – larger solitary locusts that
have narrow foraging ranges, cryptic coloration, and high
ovarian development; and smaller gregarious locusts that fly
hundreds of miles in search of food, are brightly colored,
and have lower ovarian development. In both species, two
hormones (juvenile hormone and corazonin) stimulate various aspects of the solitary phase including green coloration,
reproductive physiology, and solitary-like behavior.
Although behavior and development are in many ways
intimately linked, research in the fields of ethology and
development have proceeded quite separately. Several
reasons likely account for this separation. First, there is a
general perception by biologists that behavioral phenotypes are farther removed from genes than developmental
phenotypes; behavior is generated by neurons in real time
at a rate that is much more rapid than even the fastest
known changes in gene expression, whereas development
proceeds gradually over hours, weeks, or even years.
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In addition, whereas morphological phenotypes are stable
or slowly changing, behavioral phenotypes are more
unpredictable and fleeting, often making them harder to
measure. For these reasons, in-depth studies of the genetic
basis for behavior began later and have progressed more
slowly than such studies of development.
Although some behaviors consist of stereotyped action
patterns, many behaviors are more complex and require
long-term maturation or a process of development to come
to fruition. Such behavioral development may or may not
require learning and/or restructuring of the nervous system. Notable examples of behavioral development include
song learning and development by songbirds, the transition from hive work to foraging in honeybees, and juvenile
play behavior (e.g., play fighting and play hunting) by a
wide range of vertebrate animals, especially mammals.
By recognizing behavioral phenotypes as developmental
phenotypes themselves, it may be fruitful to apply a similar
approach to the study of behavior as has been historically
used to study development.
Basics of ‘Evo-Devo’
During the early history of evolutionary thought, evolution and development were considered to be inseparable.
Studies of embryology were used to infer evolutionary
relationships among organisms, typified by Ernst Haeckel’s
famous insight that ‘ontogeny recapitulates phylogeny.’
Although such comparisons can be useful, subsequent
studies in embryology showed that this view is an oversimplification. The adoption of a population-level focus
on evolution with the rise of the modern synthesis of
genetics and evolution led to a formal separation of the
fields of evolution and development until fairly recently.
With the application of molecular genetics to developmental biology, the fields of evolution and development
were eventually reintegrated in the ‘evo-devo synthesis,’
and numerous important findings have already emerged
from this relatively new hybrid field.
One of the major discoveries in developmental biology
was the revelation that something so complex as multicellular development is genetically orchestrated via precise
changes in the timing and location of gene expression.
This insight stemmed from the elucidation of a hierarchical cascade of transcription factor genes that lead to the
differentiation of segments during embryological development. This developmental cascade was first studied in
the fruit fly D. melanogaster and the set of genes controlling
early embryological development were elucidated in
remarkable detail. This groundbreaking work by Lewis,
Nusslein-Volhard, and Wieschaus was awarded with the
Nobel Prize in Physiology and Medicine in 1995. By
using a comparative approach and studying the molecular
genetics of development in other species, the pioneers of
evo-devo made a startling discovery. It turns out that
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many of the same genes regulating early development in
insects, specifically, the homeotic or Hox genes which
determine the identity of segments, also control the
development of segmentation in vertebrates, even in a
similar anterior-to-posterior pattern (Figure 1).
Cross-species studies of the molecular basis for development have fueled the evo-devo synthesis, and in some cases,
the findings have even caused biologists to rethink how new
structures arise during evolution. A case in point involves
the evolution of image-forming eyes in animals. The compound eyes of arthropods and the camera-like eyes of vertebrates differ hugely in their basic structure, and were long
considered to be a classic example of convergent evolution.
However, this interpretation was called into question with
the discovery of the primary role of Pax6 genes, first identified as affecting vertebrate eye development and subsequently found in Drosophila. Further studies revealed
another member of the Pax gene family to have a role in
complex eye development in a jellyfish, suggesting Pax
involvement in eye development may predate the evolution
of the common ancestor of both insects and vertebrates. This
finding suggested that vertebrate and insect eyes could have
arisen from a proto-eye shared by a common ancestor. Yet
another (less likely) possibility is that the Pax genes were coopted to regulate eye development multiple times during
animal evolution, and represent a remarkable example
of convergent evolution on both genetic and phenotypic
levels. Although these issues have not yet been completely
resolved, the realization of these complexities of conservation and convergence would not have been possible without molecular genetic studies. A similar depth of study will
be necessary to untangle these issues for behavior that are
the apparent result of convergent evolution.
Evo-devo studies across a diversity of animals including butterflies, ants, and stickleback fish have provided
additional insights into how evolution occurs. In particular, it has been fruitful to study convergent morphologies
that have evolved repeatedly in several relatively closely
related species. Studies of stickleback fish have shown that
a convergent phenotype (the reduction of bony armor)
can be attained via evolutionary changes in the same
molecular pathways, but by altering different individual
genes within the pathway. On the other hand, studies of
winglessness in worker ants have shown that the genetic
pathways that maintain a particular phenotype over evolutionary time can change. Although wing loss evolved
only once early in ant evolutionary history, the network of
wing development genes is interrupted at different points
in different species of modern ants.
Insights to Be Gained from an Evo-Devo
Approach to Behavior
As described earlier, comparative studies of the genetic
basis for development have uncovered the deep extent of
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Figure 1 Diagram mapping hox genes to specific segments in both a Drosophila and mouse embryo. Adapted from Carroll SB
(1995) Homeotic genes and the evolution of arthropods and chordates. Nature 376: 479–485.
conservation of gene function across organisms and led to
a more careful consideration of the roles of conservation
versus convergence in evolution. The field of evo-devo is
also beginning to provide broadly generalizable principles
about the evolutionary process itself, making it all the
more important for behaviorists to consider an evo-devo
approach. For example, some authors have suggested a
shift in the focus of the levels of selection in evolution
from the gene to the phenotype. In addition, evo-devo
also forces one to consider the importance of nongenetic,
or epigenetic, influences on phenotypes, including the
external environment and social (e.g., maternal) effects.
Some have suggested that epigenetic effects can lead to
the evolution of novel phenotypes even before such
changes are fixed by mutations in the gene sequence.
The field of evo-devo has led to several main insights, each
of which can provide useful lessons for the study of animal
behavior: (1) the importance of changes in gene regulation (in
addition to changes in coding regions of genes) in generating
morphological diversity, (2) the idea of a shared ‘genetic
toolkit’ for development consisting of a core set of deeply
conserved genes that are used repeatedly across taxa to
generate diversity in form, and (3) the idea of modularity,
that is, that morphology can be broken down into several
distinct components that tend to be repeated in series and can
be added, deleted, or shuffled, to create novel morphologies.
The Importance of Gene Regulation
Mutations in the coding regions of genes can disrupt the
basic function of a protein, which can have severe if not
lethal effects on the organism. Alterations in gene regulation involving the timing and location of the expression of
genes, on the other hand, can result in more subtle
changes in phenotype. Thus, regulatory changes have
been proposed to be more likely targets for natural selection, which could result in more gradual evolutionary
changes. There is a growing base of examples from
evo-devo showing the importance of regulatory changes
in generating morphological diversity. For example,
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changing the localization of transcripts of specific Hox
genes can result in a variety of morphological novelties
ranging from the patterns on butterfly wings to the shape
and number of appendages. Studies of postdevelopmental
changes in brain gene expression suggest that this may
also be generalizable to behavior. Soon after the shocking
discovery that humans and chimpanzees have 98% of
their DNA sequences in common, biologists hypothesized that it is differences in gene regulation, rather than
differences in coding sequence, that must explain the
huge differences in behavior and intelligence between us
and them. The application of global gene expression
analysis to this question has indeed uncovered largescale changes in brain gene regulation between chimps
and humans. Another example of the importance of gene
regulation comes from rodents. The localization of vasopressin receptors (V1aR) in a brain region (ventral striatum) in several species of voles makes all the difference
between promiscuous, absentee fathers and monogamous,
paternal males.
There are different levels at which changes in gene
regulation can affect a phenotype – at the transcriptional
or translational levels. In addition, a distinction has been
made between two different types of transcriptional
gene regulation: (1) cis regulatory change – a change
in gene regulatory sequences that affects transcription of
a given gene nearby, and (2) trans regulatory change – a
change in one gene that regulates the expression of other
genes that may be in a different part of the genome.
Mounting evidence from developmental biology suggests
that cis regulatory changes appear to be extremely important in the evolution of morphological changes across
species. More detailed studies of the gene regulatory networks that affect variation in behavior both within and
across species will be needed before an assessment of the
importanc of cis versus trans regulation can be made for
the field of behavior.
Genetic Toolkits for Behavior?
Studies of the genetic basis of development across a wide
variety of taxa suggest that the existence of a ‘genetic
toolkit’ for development, that is, a core set of genes or
pathways that underlie morphological development and
that are used repeatedly during evolution to generate
diversity in body form. Prominent examples from development are homeotic (Hox) genes in segmentation and
Pax genes in eye development across both vertebrate and
invertebrate animals. Does a similar ‘genetic toolkit’ for
behavior exist as well? Or do behavioral phenotypes rely
more on new genes to generate behavioral novelty? Studies across both vertebrate and invertebrate animals suggest that such toolkits may indeed underlie several basic
forms of behavior (aggression, reward, and sociality), as
discussed below.
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Many animals exhibit aggressive behavior, which can
vary widely in the form of expression (from biting to
stinging to highly ritualized aggressive displays) and in
the context in which it is used (i.e., to defend a territory, to
gain access to mates, to establish a position in a dominance
hierarchy). Nonetheless, research on the mechanistic basis
of aggressive behavior in both vertebrate and invertebrate
animals suggests that these behaviors may share common
molecular underpinnings. For example, low levels of the
neuromodulator serotonin affect aggressive behavior in
mice and have also been associated with impulsive aggression in humans. In lobsters, both extremely elevated and
depressed levels of serotonin are associated with increased
aggression. This is one example of the same molecule
being associated with aggression across taxa in which
opposite patterns of regulation can affect similar behaviors across species. Thus, the serotonin pathway may be
evolutionarily labile, that is, easily changed during evolution to regulate behavioral differences, though the exact
pattern of regulation may vary across taxa.
An important aspect of motivation is that the performance of some behaviors produce a self-reinforcing sensation of ‘reward.’ The reward system has long been
known in mammals, typified by drug addictions in
humans and mice that seek electric stimulation of the
‘pleasure center’ of the brain in preference to food. In
vertebrates, the main neurotransmitter that has been associated with reward is dopamine. Dopamine is released in a
certain brain region (nucleus accumbens) in response to
eating and sexual activity. Elegant work on the molecular
basis of pair bonding in voles has demonstrated a connection between expression of the vasopressin V1aR receptor
in the ventral pallidum, but pair bonding can only occur
when dopamine is actively present in the same brain
region, suggesting that pair bonding has evolved to
become a rewarding stimulus. Recent studies with insects
suggest that invertebrates possess a reward system not so
different from that of vertebrates. Research with crickets,
flies, and honeybees suggest that dopamine instead mediates the learning of negative, aversive stimuli whereas a
related neurochemical, octopamine, can affect learning
and perception of rewarding stimuli such as food.
Eusociality, the complex form of social behavior that is
defined by the presence of reproductive queens and workers that forgo their own reproduction to aid the reproduction of others has evolved multiple times in animals
from termites to bees to naked mole rats. With striking
convergent evolution of social form across such a wide
variety of animal taxa, the study of the evolution of
eusociality provides a good system to test for the existence of a ‘genetic toolkit’ underlying the evolution of
complex social behavior. It has long been known that
nutritional asymmetries among individuals within a social
insect colony relate to differences in reproductive capacity and body form, and contribute to the development of
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different castes, including kings and queens, workers, and
worker subcastes that specialize in particular colony tasks.
Recent studies at the molecular level suggest that certain
genes or pathways are associated with sociality across
multiple taxa, many of which relate to nutritional and
metabolic processes. For example, the storage protein
Hexamerin is associated with caste differences in distantly
related insects (termites and paper wasps). In addition,
genome-wide studies of gene expression have repeatedly
uncovered important differences in metabolic enzymes in
numerous lineages (bees, wasps, and ants). Finally, differences in the regulation of deeply conserved genes that
control feeding behavior (including the foraging gene and
the insulin pathway) appear to regulate behavior across
independently evolved lineages of ants, bees, and wasps.
These studies suggest that eusociality, a complex form of
social organization, evolved in part by changes in the
regulation of deeply conserved genes regulating feeding
and nutritional physiology. Further studies of the molecular genetic basis of eusociality in even more distantly
related taxa, for example, mole rats, will provide a crucial
test of this hypothesis, and will allow us to assess how
broadly such a ‘genetic toolkit’ applies.
The Evolution of Behavioral Modules
Modules can be defined as distinct phenotypic units,
developing more or less independently from each other,
that make up part of a larger whole. It is intuitive that
animal body plans are modular. Vertebrates have repeating series of vertebrae, and insect body plans are clearly
organized into segments – just think of a caterpillar.
Comparative anatomical studies and gene-level studies
have shown that such modules can be reorganized to
give rise to new body structures. Additional modules can
be added, subtracted, or fused to form new structures. For
example, in vertebrates, jaws evolved from modular series
of gill arches in early fish, and skulls from fused elements
of several vertebrae. In insects, repeated pairs of segmented appendages have evolved into specialized mouthparts and antennae, and the thorax has evolved from the
fusion of three ancestral body segments.
Although somewhat less obvious than for morphology,
some behaviors are also modular in structure. Many
behaviors can be broken down into constituent parts,
which often occur sequentially over time. This is true
for both short-term sequences of behavior and behavioral
phases that occur over the course of a lifetime. Breaking
down complex behaviors into smaller component behaviors (or behavioral modules) can be a useful entree into
detailed studies of the mechanisms underlying these behaviors. In the following paragraph, two examples of modular behaviors – one describing a set of behavioral modules
expressed on a short time scale, and the other involving
more long-term behavioral phases – are described. In each
case, modules appear to have been reorganized to generate
novel forms of behavior during evolution.
Courtship behavior in Drosophila fruit flies is a complex
affair. The general sequence consists of several stages (or
behavioral modules), as follows: first, the male orients
toward the female; then he taps her with his antennae;
then he begins singing a courtship song by buzzing his
wings; then he licks her genitals; then he mounts, and
finally, if successful, he copulates. This is the general series
of steps, but the sequence varies across species, with various elements that are either prolonged, shortened, or
elaborated. The courtship song itself consists of modules
of different forms of sound that vary widely across species.
Elements of this courtship behavior vary across Drosophila
spp., and there is evidence that in some cases, differences
in courtship sequence, especially song, can act as speciesisolating mechanisms. In the same way in which Drosophila
courtship songs may help to isolate species, bird songs may
do the same, facilitated by reorganizing different combinations of trills and whistles, which in some cases appear to
be behavioral modules of song.
With regard to eusocial insects, a great mystery that
has intrigued biologists since Darwin relates to the evolution of queens and workers. Given the fact that in most
species, any female egg can become a worker or a queen,
how can such extreme differences in morphology and
behavior arise from the same genome? One hypothesis
utilizes the idea of behavioral modules. If we imagine a
solitary maternal insect, its behavior can be broken down
into two distinct behavioral modules: (1) egg-laying and
(2) maternal provisioning of brood with food collected
during foraging. It has been suggested that an ancestral
ovarian cycle consisting of these two basic modules of egglaying and foraging/provisioning could be uncoupled.
Instead of being separated in time as in solitary maternal
wasps, the two behaviors could become separated into
different individuals – queens that focus on egg-laying
and workers that specialize in foraging/provisioning.
Thus, worker behavior, which involves caring for siblings,
may have evolved from maternal foraging/provisioning.
Recent evidence at the molecular level supports the idea
that worker behavior evolved from maternal behavior;
similar patterns of brain gene expression underlie both
maternal and worker behavior in primitively social Polistes
metricus paper wasps.
Further expansions of an ancestral groundplan may
have occurred among workers later in social insect evolution, in two contexts. First, colonies show a division of
labor among nest workers and foragers; nest workers have
higher reproductive capacity than foragers, and recent
results suggest that the brain gene expression patterns of
honeybee nest workers are indeed more queen-like than
those of foragers. Second, we see a fine-tuned division of
labor for foraging in honeybees; bees that forage for pollen
have more well-developed ovaries and higher levels of
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expression of the egg-yolk protein Vitellogenin than bees
that forage for nectar. Thus, these two ancestral modules
of egg-laying and foraging may have been separated multiple times during social insect evolution to produce
specialized individuals, giving rise to a division of labor.
The Co-evolution of Behavior and
Development
Thus far, behavior and morphological development as
separate phenotypic entities have been considered. However, in many cases, behavior and morphology coevolve.
This may be due to similar selection pressures causing
parallel evolution of the two or due to constraints
imposed by pleiotropic effects of genes that affect behavior and morphology concurrently. As discussed earlier,
there have been several studies of hormonal effects on
both behavior and development suggesting the possibility
of common mechanistic elements to the regulation of
physiology, development, and behavior. However, to
date, there have been few studies that have attempted to
examine whether the same genes or pathways underlie
both developmental and behavioral differences within
and across species. This is an area ripe for study, and in
the following section, two particularly promising models
for addressing this question are summarized.
Three-spined stickleback fish (Gasterosteus aculeatus)
have been important model systems for studying the
evolution of development. These fish have evolved from
marine to freshwater forms multiple times in several
widely separated geographical areas. They thus provide
a perfect system to examine the roles of conservation
and convergence in phenotypic (both morphological
and behavioral) evolution. Each time sticklebacks have
invaded freshwater habitats, and this has been accompanied by a reduction in the presence of armored plates
along the lateral side of the body as well as shortened
pelvic spines, which are protection against predators. In
many freshwater populations, sticklebacks have further
diversified into distinct benthic (bottom dwelling) and
limnetic (surface dwelling) forms, which show differences
in jaw morphology that are related to differences in their
feeding habits. These benthic and limnetic forms show
consistently different patterns of foraging behavior, courtship, and aggressive behavior. It remains to be seen
whether some of the same genes that regulate morphological differences are also used to regulate behavioral
differences, or whether different toolkits are employed
for each. If different tookits exist, it is an intriguing
question as to whether such toolkits coevolve via common
regulatory elements that control numerous different pathways, or whether there are no such common regulatory
elements to link pathways.
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Horned scarab beetles are found worldwide, with
striking variation in the presence/absence of horns and
in their size and morphology. In some dung beetles, males
take alternative forms: territorial, large-horned males, and
nonterritorial small-horned males. The horns are used in
combat between males for dung resources, and such contests help assure them possession of dung territories and
access to females. Recent studies have begun to elucidate
the molecular basis of horn development in dung beetles
and suggests an important role for the insulin pathway in
affecting energy allocation to horns (vs. other morphological features) resulting in allometric changes in horn size.
There is also a correlation across species between horn
size and behavior: beetle species that tunnel into dung
have large horns, whereas those that roll dung on the
surface do not. Given the role of various insulin pathway
genes in regulating feeding and social behavior in insects,
it will be intriguing to test whether the insulin pathway
also affects tunneling and aggressive behavior in beetles.
Future Directions
Evo-devo has been extremely successful in elucidating
several important principles about how morphological
evolution can occur (as described in ‘Basics of EvoDevo’). Notably, the major insights from evo-devo have
resulted from pairing molecular genetics data with comparative methods by studying a wide variety of species.
The mechanistic basis of behavior, while traditionally
believed to be harder to dissect than that of development,
has nonetheless already hinted at similar findings to evodevo – namely, that changes in the regulation of deeply
conserved genes are likely to result in behavioral evolution and that a core set of genes, or ‘genetic toolkit,’ may
be used repeatedly during the evolution of novel behaviors. The studies of the mechanisms responsible for the
evolution of behavior have focused mainly on a handful of
species (e.g., rodents, honeybees, and fruit flies). Reflecting on the history of evo-devo, it is clear that behavioral
studies could also benefit greatly from a much expanded
comparative analysis of behavior. This need may be fulfilled by a general broadening of the taxa considered for
comparison to include distantly related species with similar patterns of behavior. Well-resolved phylogenies are
needed in order to carefully choose species that are informative in a phylogenetic context (e.g., species in basal
lineages or species within a branch of a phylogenetic
tree that appear to have evolved similar behaviors
independently).
One of the main obstacles to such studies has been the
lack of gene sequence information and genetic resources
for nonmodel genetic species. New technologies are
quickly getting around this roadblock. For example, it is
now possible to manipulate gene expression patterns in a
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number of model organisms through the use of pharmacological treatments or RNA interference (RNAi). In addition, next generation sequencing methods, which generate
huge amounts of data at a fraction of the cost of traditional
sequencing, are improving rapidly. Such methods are now
being effectively used to generate large databases of
expressed genes for a wide variety of ecologically and
evolutionarily important species.
Such technological improvements can help pave the
way for new and creative ways to study the molecular
genetic basis of behavior in a wide variety of species.
These advances, when coupled with an evo-devo perspective on behavior, promise to yield major insights into
behavioral evolution in the near future.
See also: Caste in Social Insects: Genetic Influences
Over Caste Determination; Drosophila Behavior Genetics;
Evolution: Fundamentals; Genes and Genomic Searches;
Honeybees; Integration of Proximate and Ultimate
Causes; Play; Social Insects: Behavioral Genetics; Sociogenomics; Threespine Stickleback; Zebra Finches.
Further Reading
Abouheif E and Wray GA (2002) Evolution of the gene network
underlying wing polyphenism in ants. Science 297: 249–252.
Barron AB and Robinson GE (2008) The utility of behavioral models and
modules in molecular analyses of social behavior. Genes, Brain, and
Behavior 7: 257–265.
Carroll SB (1995) Homeotic genes and the evolution of arthropods and
chordates. Nature 376: 479–485.
Carroll SB (2008) Evo-devo and an expanding evolutionary synthesis:
A genetic theory of morphological evolution. Cell 134: 25–36.
Carroll SB, Grenier J, and Weatherbee S (2004) From DNA to Diversity:
Molecular Genetics and the Evolution of Animal
Design, pp. 272. Malden, MA: Wiley-Blackwell.
Cresko WA, Amores A, Wilson C, et al. (2004) Parallel genetic basis for
repeated evolution of armor loss in Alaskan threespine stickleback
populations. Proceedings of the National Academy of Sciences of
the United States of America 101: 6050–6055.
Emlen DJ, Lavine LC, and Ewen-Campen B (2007) On the origin and
evolutionary diversification of beetle horns. Proceedings of the
National Academy of Sciences of the United States of America
104(supplement 1): 8661–8668.
Hudson ME (2008) Sequencing breakthroughs for genomic ecology and
evolutionary biology. Molecular Ecology Resources 8: 3–17.
Kozmik Z (2005) Pax genes in eye development and evolution. Current
Opinion in Genetics & Development 15: 430–438.
Love AC and Raff RA (2003) Knowing your ancestors: Themes in the
history of evo-devo. Evolution & Development 5: 327–330.
Nusslein-Volhard C and Wieschaus E (1980) Mutations
affecting segment number and polarity in Drosophila. Nature
287: 795–801.
Raff RA (2000) Evo-devo: The evolution of a new discipline. Nature
Reviews Genetics 1: 74–79.
Robinson GE and Ben-Shahar Y (2002) Social behavior and
comparative genomics: New genes or new gene regulation?
Genes, Brain, and Behavior 1: 197–203.
Toth AL and Robinson GE (2007) Evo-devo and the evolution of social
behavior. Trends in Genetics 23: 334–341.
West-Eberhard MJ (2003) Developmental Plasticity and
Evolution, pp. 794. New York, NY: Oxford University Press.
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