Abstracts are at end of
meeting schedule (below)
Friday March
17th
09.00-09.45
Ben Sheldon -
Evolutionary ecology of individual variation.
09.45-10.30 Tony Williams – The tyranny of the Golden Mean 20 (or more) years on: individual variation in physiological systems.
11.00–12.30 Session 1: Concepts, theory and technical issues
Wolfgang Forstmeier - Determinants of behavioural individuality: a framework for the evolution of proximate mechanisms.
Leonida Fusani - Variability of hormone-dependent traits: the linear correlation fallacy.
Karen Spencer - The role of developmental conditions in shaping individual phenotypes.
Mark Clark, Wendy Reed, and Ellen Ketterson - Individual-based modeling approaches: incorporating variation into population demography.
Julian Christians – QTL
approaches and individual variation.
14.00–15.30 Session
2: Individual
variation and reproduction
Marcel Eens -
Honesty of bird
song: endocrine and neural
correlates of singing behavior in songbirds.
Marcel E. Visser - Individual variation in laying date in the great tit: genetic variation in reaction norms.
Patrice
Bourgault and Don Thomas -
Between-population differences in the
fitness consequences of individual-based variation in egg investment in
Corsican blue tits (Parus caeruleus).
Camilla
Hinde, Kate Buchanan, and Rebecca Kilner - What
explains individual variation in canary nestling begging
intensity?
Claudio Carere, Piet J. Drent, Jaap M. Koolhaas, Ton G.G. Groothuis - Food availability and sibling competition affect the development of personality traits in great tits (Parus major).
16.30-18.00
Session 3: Individual variation and the stress
axis
Julio
Blas, Gary Bortolotti and Tracy Marchant -
Individual variation in adrenocortical response to stress in
red-legged partridges.
Wada H., Breuner C.W., Salvante K., Wagner E., Curnillon M. and Williams T.D. - Too stressed to be sexy?: acute stress and its relation to reproductive quality.
Frances Bonier -
Physiological mediation
of condition-dependent sex ratio manipulation:
are corticosteroids the missing link?
Mike
Clinchy et al. -
Environmental quality, physiological stress and female mating
strategies in
song sparrows.
Creagh W. Breuner and Rachel S. Sprague - Reduction in CBG capacity during acute stress: using individual variability to explore competing hypotheses.
Saturday
March 18th
09.00-09.45 Gregory F. Ball - Individual variation and the endocrine regulation of behavior and physiology from a cellular/molecular perspective.
09.45-10.30
Bart Kempenaers
- Individuality in
behaviour, hormones and genes
11.00-12.30
Session 4: Individual variation in
other systems
Blandine
Doligez - Maternal
yolk androgens and natal dispersal
in passerine birds: insights on between-individual and between-family
variation.
Joel McGlothlin - Short-term
testosterone increases in dark-eyed juncos: individual
variation and relationships with morphology and behavior.
Maud Poisbleu -
Hormonal correlates of social
dominance status in Anatids.
Anthony J. Porter and
Sharon E.
Lynn - Individual variation or trapping technique? Trapping
initiates
stress response in nonbreeding house sparrows.
Kees van Oers -
Avian
personalities: genes and
environment.
14.00-15.00
Session 5: Individual variation in a
life-history context
Kathryn E. Arnold - Does early nutrition affect behavioural responses to novel situations?
Oliver P. Love, Katrina
G. Salvante, James
Dale and
Tony D. Williams - Individual
and sex-specific
variability of cell-mediated immunity across life-history stages.
David W. Winkler - The ecology and organismal biology of individual variation in Ithaca Tree Swallows.
15.45–18.00 General
discussion and synthesis (Ellen Ketterson,
Michael Romero)
Abstracts
Evolutionary
ecology of individual variation. Ben Sheldon, Edward
Grey Institute, Department of Zoology,
A
central aim of evolutionary ecology is to understand why individuals
differ. Differences between individuals are the raw material on which
natural
selection acts to produce adaptations, and understanding the importance
of the
various processes that potentially contribute to variation among
and
between populations is key to understanding (1) why these populations
have the
characteristics that they do, (2) why populations may differ from one
another
and (3) how they might change in the future. I will review the
conceptual
approaches used to understand variation in quantitative characters in
wild
populations, and illustrate their use with examples from studies of
variation
in the time of breeding among individual birds obtained from long-term
studies
of birds. I will discuss the extent to which these approaches can be
applied to
other traits, and argue that understanding variation in
endocrinological
mechanisms actually provides the potential for key insights into the
reasons
for variation at some of these levels of analysis.
The
tyranny of the Golden Mean 20 (or more) years on: individual
variation in physiological systems. Tony D Williams, Biological
Sciences,
Twenty years ago Al Bennett published a paper in the influential book “New Directions in Ecological Physiology” (1987) arguing that individual variation was an “underutilised resource”. Twenty years on I will describe how well we (physiologists/endocrinologists) have exploited this underutilised resource (or not!) and the extent to which the “tyranny of the Golden Mean” still holds sway. I will then discuss some methodological, experimental and analytical issues relating to use of individual variability. Using examples from the physiological literature I will discuss what we know about repeatability and heritability of physiological traits – as we measure them - and what we know about how individual variability in physiology relates to performance and fitness. A key question throughout the talk will be the extent to which systematic relationships between physiology, performance and fitness that are evident at the interspecies level can also be detected at the inter-individual or intraspecific level. If they can not then what are the implications for our understanding of how selection on individual variability generates inter-specific differences?
Session 1: Concepts,
theory and technical issues
Determinants
of behavioural individuality: a framework for the
evolution of proximate mechanisms. Wolfgang Forstmeier,
Max Planck Institute for
Quantitative genetic analyses can help us identify the proximate causes underlying lifelong persisting individual differences in behaviour (personality differences). Behavioural polymorphism may result from genetic polymorphism, maternal programming, or from effects of the early rearing environment such as sexual imprinting or niche selection within peer groups. Using the example of lifelong lasting individual differences in sex drive of male zebra finches, which are closely mirrored by plasma testosterone levels, I demonstrate the usefulness of an experimental quantitative genetic approach to identify the key factors in creating individuality. I then ask which proximate mechanism is most likely to evolve under which environmental conditions and under which developmental constraints. I predict that increasing costs of behavioural flexibility, i.e. when specialists out-compete generalists, will favour genetic polymorphism or maternal programming, while decreasing predictability of the social environment will favour sexual imprinting or niche choice during puberty.
Variability
of hormone-dependent traits: the linear correlation fallacy.
Leonida Fusani, Department of
Physiology,
Most studies on hormones and behaviour focus on the same old question: does the behaviour ‘depend’ on the hormone? The answer is influenced by a number of critical factors, such as the modalities of the hormonal treatment and the type of control used. Nevertheless, methods developed and validated by behavioural endocrinologists in controlled laboratory conditions are often modified for field experiments without analysing the implications these modifications may have for the interpretation of the results. This highlights the necessity of developing new methods to study evolutionary aspects of hormone-behaviour interactions. Here I will discuss some of critical points raised by the current developments in behavioural endocrinology using examples from my own work and from other studies. First, I will show how the meaning of the term ‘hormone-dependent’ changes between experimental contexts and why we need to understand the nature of the relationships between the hormone and the behaviour. Secondly, I will review the problems relative to experiments involving hormonal manipulation, and the pro and contra of different approaches. Finally, I will discuss the conclusions that can be drawn by these experiments and the theoretical limitations of the currently used approaches.
The role
of developmental conditions in shaping individual phenotypes. Karen
Spencer,
The potential influence of
environmental conditions experienced during development on adult
phenotypes has
recently developed as an important research focus. Whilst much
empirical work
has been directed at the effects of variation in nutrient supply,
another
important hormonal axis linking early conditions to the adult phenotype
is that
mediated via environmentally induced stress. Here I report data from
experiments where nestling zebra finches (Taeniopygia
guttata) were exposed to exogenous corticosterone via oral
administration
for a 10 or 25 day period. Experimental administration of
corticosterone
significantly depressed growth rates in both male and female birds.
Upon
reaching sexual maturity previous exposure to corticosterone also
resulted in
reduced success in competitions for non-food based resources and
reduced sexual
signal quality. These results provide evidence that early life
conditions are important
in shaping adult phenotypes, significantly influencing several
fitness-related
traits. In addition they provide data on the possible long term origin
of
individual variation seen in many of these important life history
traits.
Individual-based modeling approaches: incorporating variation into population demography. Mark Clark1, Wendy Reed1, and Ellen Ketterson2; 1 North Dakota State University, Fargo, ND, 2 Indiana University, Bloomington, IN (m.e.clark@ndsu.nodak.edu).
Understanding physiological and behavioral mechanisms underlying the diversity of observed life-history strategies is challenging because of difficulties in obtaining measures of fitness and in relating fitness to these mechanisms. One approach is to estimate fitness (population growth rate) by incorporating variation in physiological and behavioral traits among individuals into population models. We used this approach to evaluate effects of experimentally elevated testosterone on male fitness in dark-eyed juncos and to evaluate the effects of juvenile survival on optimal clutch size in American coots. This modeling approach provides a way to use information about individuals to evaluate life-histories.
Quantitative trait
loci (QTL) approaches to understanding individual variation. Julian K. Christians, Biological
Sciences,
Phenotypic variation among individuals is caused by both the environment and a potentially large number of genes. In the past two decades an enormous amount of effort has been directed at detecting quantitative trait loci (QTL) in the hopes of identifying the genes responsible for quantitative variation. QTL are naturally-occurring regions of the genome that contribute to continuous variation, rather than major mutations that cause serious abnormalities. Many QTL mapping studies have focused on traits of medical importance in humans and model organisms and on economically-important traits in agricultural species. However, a small number of studies have also mapped ‘ecologically important’ traits with spectacular success. Assuming certain genetic resources (a linkage map of many molecular markers) and the ability to perform controlled crosses, it is potentially (relatively) easy to detect QTL. However, these loci are actually large regions of chromosome that harbour hundreds of genes. Refining the location of QTL to regions that contain only a few genes, and demonstrating that a particular gene is responsible for the phenotypic effects of a QTL is extremely difficult and expensive, even in model organisms. Linkage maps have been developed for some avian species, and developing maps for new species will likely become more tractable, but identifying genes responsible for quantitative variation in natural avian populations will remain a daunting task for some time.
Session 2: Individual
variation and reproduction
Honesty of bird song: endocrine and
neural correlates of singing behavior in songbirds. Marcel
Eens,
Song is one of the most studied
sexually selected
characters. Individual variation in song characteristics has been shown
to
affect reproductive success through mate choice and male-male
competition. A
fundamental question regarding the evolution of sexually selected
signals is
how their honesty is maintained. I will discuss two kinds of potential
costs
that may limit the expression of song. First, in adult songbirds, the
expression
of male song appears to be under the regulation of gonadal steroids,
primarily
testosterone (T). Involvement of circulating T in the regulation of
inter-male
differences in song performance may possibly contribute to the
maintenance of
the honesty of male song performance because of the presumed costs that
elevated plasma T levels entail (for instance immune costs). While the
overall
relationship between testosterone and singing is well established, very
little
is known about how individual variation in plasma testosterone is
related to
individual variation in song characteristics and results are often
conflicting.
Based on a meta-analysis of all available intraspecific studies, I show
that
performance-related song traits such as song rate correlate
significantly with
T, while this is not the case for other song traits. Second, I will
discuss the
neural cost of singing which has been highly debated recently. A
meta-analytical study provides strong intraspecific evidence for
repertoire
size and song length being related to the volume of song control nuclei
in the
brain. The brain space required for having a complex song thus seems to
be a
key constraint in songbirds. Finally, I will present data that there
also
exists a large variation in song complexity and activity among female
European
starlings that appears to give honest information about their quality.
I
discuss whether similar costs as described above are present in females.
Individual variation in
laying date in the great tit: genetic variation in reaction norms. Marcel E. Visser, Netherlands
Institute of Ecology (NIOO-KNAW),
One of
the hypotheses to explain variation in avian laying dates is
that individuals differ in the way their timing of reproduction is
affected by
environmental variables. Some individuals may vary their laying date
strongly
with spring temperatures while others may be relatively insensitive. In
other
words, there may be within population variation in the reaction norm of
laying
date versus temperature. We have
shown in a Dutch great tit population that such variation in reaction
norm
indeed exists, that this variation is heritable and that, due to
climate
change, there is now selection for a steep reaction norm. We are now
following
up this finding with experiments in temperature and photoperiod
controlled
aviaries. We have brought in offspring from early and late pairs. The
pairs are
now kept under two temperature regimes to measure the onset and speed
of gonadal
growth and the laying date of these birds to determine how these
‘early’ and ‘late’ great tits differ.
Between-population
differences in the fitness consequences of individual-based variation
in egg
investment in Corsican blue tits (Parus
caeruleus). Patrice
Bourgault and
This study focuses on the importance of individual variation in egg quality in free-ranging Corsican blue tits in heterogeneous habitats. We show that the range of variation in egg size and yolk mass is high (ratio of the smallest to the highest mean yolk mass = 0.75), and that a large part of this variation is explained by inter-individual differences (repeatability > 0.6). Given the potentially far-reaching consequences of variation in egg size and yolk mass on nestlings’ growth and development, especially for some Corsican populations breeding under harsh environmental conditions, it is surprising to note such a high degree of variability between females. However, few studies have unequivocally demonstrated that egg size affects offspring performance, although it is likely that the disadvantages of small eggs appear only under adverse breeding conditions. Our study system offers this unique opportunity to compare the fitness consequences (nestlings’ growth pattern, fledging mass and survival) of variation in egg investment between populations facing contrasting habitat features. One habitat (deciduous oak wood) offers an extremely high spring peak in caterpillar abundance, coupled with low infestation of ectoparasitic blow-fly larvae, which contrasts with the very low caterpillar abundance and high infestation rates of ectoparasites in the evergreen habitat at the time of hatching. It is very likely that the potential negative effects of egg and yolk size variation on offspring fitness become apparent in this latter habitat. This study thus aims at determining to what extent selection pressures on egg size may differ according to specific ecological context, and could therefore provide a new insight on the consequences of intra- and inter-individual phenotypic variation in egg quality in heterogeneous habitats.
What explains individual
variation in canary nestling begging intensity? Camilla Hinde, Kate Buchanan, and Rebecca
Kilner (cah33@cam.ac.uk)
Previous
work on canary eggs has shown that yolk testosterone (T)
levels increase with each successive egg in the clutch, and that
pre-natal
exposure to these maternal hormones affects chick begging levels
shortly after
hatching. In addition, observations of older chicks found that later
hatched
nestlings, hatching from later laid eggs, beg more intensely than their
older
siblings. Our aims in this study were 1) to investigate the influence
of nestling
T on chick begging intensity and 2) to determine experimentally the
extent to
which individual variation in nestling begging intensity is determined
pre-natally by mothers and post-natally by offspring. We muddled the
hatch
sequence of eggs in a clutch and measured nestling begging intensity
and
nestling T levels five and eight days after hatching to test the
following
predictions. If maternal hormones influence the development of the
nestling
endocrine system, and so affect begging intensity, we predicted that
nestling T
levels should be positively correlated with begging intensity after
hatching
and both should increase with egg number but not hatch rank. However,
if
nestlings can secondarily adjust T production after hatching in
relation to
their competitive environment, we predicted that nestling T and begging
intensity should increase with hatch rank and may or may not vary with
egg
number as well. We will discuss individual variation in chick begging
and
testosterone levels, and the extent to which this is due to parental or
environmental effects.
Food availability
and sibling
competition affect the development of personality traits in great tits (Parus major). Claudio
Carere1,4, Piet J. Drent2,
Jaap M. Koolhaas3, Ton G.G. Groothuis4; 1 Section of Behavioural Neurosciences,
Dipartimento di Biologia cellulare e Neuroscienze, Istituto Superiore
di
Sanità, Rome; 2 Netherlands
Institute of Ecology, Center for Terrestrial Ecology, Heteren, The
Netherlands;
3 Department of Animal
Physiology, University of Groningen, The Netherlands; 4 Department of Animal Behaviour, University
of Groningen, The Netherlands (C.Carere@ulg.ac.be)
Individual
animals vary in the way they cope with challenges in their environment,
comparable with variation in
human personalities.
This variation has a
substantial genetic basis. Here we show the strength of environmental
factors
(food availability and sibling competition) in shaping avian
personality
traits. We manipulated the early rearing condition in two lines (F4)
bidirectionally selected for different personalities (fast line: high
exploration speed and high aggression; slow line: low exploration speed
and low
aggression) with a food rationing protocol inducing an impairment in
growth
rate and an enhancement in levels of offspring solicitation. Growth
impairment
was more marked in the slow line. In a first experiment each nest
contained
experimental and control siblings of the same line (within-nests
design). Slow
chicks became faster than their parents in the exploration tests
regardless of
the treatment, whereas fast chicks had scores similar to their parents
and
showed no treatment effect. As a consequence, the line difference in
exploration behaviour of the offspring was not apparent in the juvenile
phase.
Six months later the offspring of the slow line was still relatively
fast, but
lines differed in exploration, since the fast line became even more
fast.
Food-rationed birds of the fast line were more aggressive than both
controls and
their fathers, while treatment did not affect the slow line. In a
second
experiment, carried out only in the slow line, each nest contained
either
control or experimental siblings (between-nests design). Now, only the
food-rationed chicks became faster in exploration. We suggest that the
shift in
the controls in the within-nests design was due to enhanced sibling
competition, forced by the experimental chick. Indeed, the control
chicks in
the first experiment begged more persistently and had higher
exploration scores
than the control chicks in the between-nests design. Environmental
factors
during ontogeny modulate the expression of phenotypic traits against
the
background of the reaction norm allowed by the genome even in selected
lines of
animals resulting in profound and reliable differences in behaviour.
Session 3: Individual variation
and the stress axis
Individual variation in
adrenocortical response to stress in red-legged partridges. Julio Blas, Gary Bortolotti and Tracy
Marchant, Department of Biology,
We studied intra and inter-individual variation in the adrenocortical response to stress in red-legged partridges (Alectoris rufa). Twenty breeding birds were subjected to a standardized capture, handling and restraint protocol, and the concentration of circulating corticosterone (cort) was determined in blood samples taken at fixed times during the pre-laying and laying periods. Despite handling time having a very significant effect on plasma cort concentration it only explained 47% of the overall variability. A detailed analysis of stress-induced cort levels revealed that neither body condition index nor sex or calendar date affected cort titers. Acute (i.e. stress-induced) levels were lower during laying compared to pre-laying stages, and negatively correlated with the current number of eggs laid at the moment of sampling. Our results support the hypothesis that red-legged partridges down-regulate their adrenocortical response to stress as a function of their current reproductive investment.
Too
stressed to be sexy?: acute stress and its relation to reproductive
quality. Wada H. 1,
Breuner C.W. 1,
Salvante K. 2, Wagner
E. 2, Curnillon M. 2, and Williams T.D. 2;
1 Integrative
Biology, University of Texas at Austin and 2 Biological
Sciences, Simon Fraser University (haruka@mail.utexas.edu).
Individual variation in stress response has been documented in both young and adult vertebrates in numerous studies. However, there is an ongoing debate about what constitutes a ‘good stress response’. Exploring the ties between the glucocorticoid secretion and fitness of individuals can help us understand the ‘good stress response’ in an evolutionary sense. Two main questions of this study are 1) does corticosterone response to stress correlate with reproductive quality in adulthood, and 2) is this response fixed during development, or plastic throughout life? Stress series were taken from both sexes of zebra finches (Taeniopygia guttata) at two ages; day 16 (~2 days before fledging) and again at 3 months of age (sexually mature adults), allowing us to determine the plasticity of the stress axis with age. Males were then subjected to courtship trials while females went through mating trials. Different aspects of individual’s reproductive quality (such as song, clutch size etc.) were then related to various parameters of the individual’s stress response. The data suggest a large individual variation in various aspects of stress response. However, it appears that there is no strong correlation between nestling and adult levels of corticosterone, indicating that the reactivity of the stress axis is plastic beyond the nestling period. We are currently analyzing data correlating corticosterone levels and reproductive qualities in these same individuals.
Physiological
mediation of
condition-dependent sex ratio manipulation: are corticosteroids the
missing
link?
Females are predicted to manipulate the sex ratio of their offspring when the fitness value of sons and daughters differ. In many systems, daughters, regardless of their condition, are more likely than sons to reproduce, whereas high quality sons can leave many more offspring than daughters but low quality sons may fail to reproduce at all. In systems where this is true, a female that can produce high quality offspring should produce more sons, whereas a female constrained to produce low quality offspring should produce more daughters. Variation in numerous factors, including mate quality, habitat quality, rainfall, dominance status, maternal condition, and maternal hormone levels, is associated with skewed offspring sex ratios. It is unclear, however, what mechanisms underlie sex ratio manipulation and which physiological cues indicate to a mother that she should manipulate her brood's sex ratio. Hormonal signals provide organisms with information about variation in individual and local environmental condition. Measures of baseline levels of corticosteroids correlate with indices of food abundance and quality, habitat quality, weather conditions, dominance status, and individual condition. Here I review experimental and empirical data linking corticosteroids to sex ratio manipulation. Given the coincidence between factors that affect sex ratio and factors that affect baseline corticosteroid levels, it seems plausible that corticosteroids could be the missing mechanistic link between conditions favoring sex ratio manipulation and the manipulation itself. Alternatively, baseline corticosteroid levels may simply be correlated with other indicators of condition and quality that are directly involved in adaptive sex ratio manipulation.
Environmental quality,
physiological stress and female mating strategies in song sparrows. Elizabeth A. MacDougall-Shackleton, Michael
Clinchy, Liana Zanette, Bryan D. Neff, John C. Wingfield and Rudy
Boonstra.
Abstract:
Ecological factors such as food availability and predator
pressure that affect reproduction and survival likely also affect
life-history
traits such as mating strategies. We conducted a 2 x 2, manipulative
food
addition plus natural predator reduction experiment on song sparrows
(Melospiza
melodia) that demonstrated: interactive food and predator effects on
egg production,
nest survival and annual reproductive success; as well as food and
predator
effects on the stress physiology of parents. Here we report the effects
on
extrapair paternity (EPP). EPP was more frequent the more challenging
(less
food, more predators) the environment. Correspondingly, females
producing
extrapair offspring appeared more stressed since they had elevated
total plasma
corticosterone, significantly higher plasma glucose and elevated plasma
free
fatty acid levels, and were significantly more anaemic, than females
producing
only within-pair young. There were no significant physiological
differences
between males with full paternity and cuckolded males, nor were there
significant differences in size or symmetry between extrapair and
within-pair
nestling brood-mates. Conceivably, females may be using extrapair
mating to
diversify their offspring and so hedge their bets in challenging
circumstances.
We suggest our results highlight the importance of understanding both
the
ecological and physiological context in which EPP occurs.
Reduction
in CBG capacity during acute stress: using individual
variability to explore competing hypotheses. Creagh W. Breuner and
Rachel
S. Sprague, Integrative Biology,
Within studies of acute stress physiology, increase in glucocorticoid secretion is thought to be the primary mediator of tissue response to stress. Corticosteroid binding globulin may regulate tissue availability of steroid, but has not been considered a dynamic component of the acute stress response. We examined CBG level over the common 60 minute time-frame of the acute capture and handling protocol, to investigate whether CBG capacity is dynamic or static over short stressors. We measured CBG response to capture and handling stress in 9 species of birds, representing 5 orders and 9 families. CBG capacity significantly declined within 30-60 minutes of capture in 5 of the 9 species examined. This decline may serve to significantly increase the level of corticosterone reaching tissues during acute stress. In light of these data, we took a strong inference approach in developing multiple, competing hypotheses which may explain the pattern of CBG decline seen across species. Many of these hypotheses can be tested by looking at patterns of individual variation within a species. We tested two of the hypotheses, reproductive value and body condition, within the long-lived Laysan Albatross. The reproductive value hypothesis predicts that individuals with greater reproductive value (younger animals) should be more sensitive to stressors, favoring self-maintenance over reproductive output, and therefore show a greater decline in CBG during stress. The body condition hypothesis posits that CBG decline will be greater in low condition birds, mobilizing a greater response when the focal animal has less endogenous reserves to deal with the stressor at hand. The Albatross data provide support for the reproductive value hypothesis, but not the body condition hypothesis.
Individual
variation and the endocrine regulation of behavior and physiology
from a cellular/molecular perspective. Gregory F. Ball, Departments of Psychological and Brain
Sciences, Neuroscience and Biochemistry and Molecular Biology, Johns
Hopkins
University, Baltimore, MD 21218 USA (gball@jhu.edu)
Scientists investigating cellular and molecular mechanisms of physiology and behavior have tended to avoid trying to explain individual differences. The goal has rather been to discover general processes that are widely applicable to many species. However, understanding individual variation in many phenomena of interest to avian eco-physiologists will require a consideration of cellular and molecular mechanisms. For example, changes in plasma concentrations of steroid hormones are important in the activation of social behaviors related to reproduction and aggression. Attempts to explain individual and even population differences in these behaviors as a function of variation in plasma steroid hormone concentrations have generally failed. A consideration of cellular variables related to the effectiveness of steroid hormone action such as concentrations of steroid binding proteins as well as the target sensitivity of different brain areas has been useful in some cases. Steroid hormone target sensitivity can be affected variables such as metabolizing enzyme activity, hormone receptor expression as well as receptor co-factor expression. However, no general theory has emerged that might provide a guide for eco-physiologists when trying to explain individual variability. Studies of variation in the response to environmental stimuli such as photoperiod have similarly failed to reveal a key set of variables to be considered though there are many candidates that will be discussed. Two proposals will be made as useful ways to proceed when trying to establish the cellular and molecular basis of individual variation. One will be to learn from studies of large units of intra-specific variation such as population differences and sex differences to provide ideas about variables that might be important in explaining individual variation. The second will be to consider the use of molecular genetic approaches such as the identification of single nucleotide and repeat polymorphisms as a promising avenue for avian eco-physiologists to pursue given the molecular genetic tools that have recently become available for use in avian species.
Session 4: Individual variation in other systems
Maternal yolk
androgens and
natal dispersal in passerine birds: insights on between-individual and
between-family variation. Blandine Doligez
* and Barbara Tschirren
**, * Department
of Biometry and Evolutionary Biology, CNRS - University Lyon I,
Villeurbanne,
France; ** School of Biological, Earth
&
Environmental Sciences, University of New South Wales, Kensington,
Sydney,
Australia; (doligez@biomserv.univ-lyon1.fr).
Dispersal has
long been recognized as a key life-history trait for
many evolutionary processes in wild populations. However, the proximate
mechanisms of dispersal still remain poorly understood. In vertebrate
species,
similarities in dispersal behaviour commonly observed among family
members have
recently been advocated to indicate a genetic basis of dispersal.
However,
these similarity patterns could also originate from common pre- or
post-natal
parental effects. Recent studies have stressed the potential importance
of
pre-natal maternal effects in shaping offspring phenotype and
behaviour,
including dispersal. In oviparous species, androgenic hormones of
maternal
origin that are deposited into egg yolks have been shown to promote the
offspring’s embryonic development and postnatal growth, but also their
social status after independence, thus implying long-lasting effects.
Females
might thus influence their offspring’s dispersal behaviour by modifying
the concentration of androgens deposited in egg yolks, as recently
suggested in
the great tit. We investigated the role of maternal yolk androgens in
shaping
offspring natal dispersal and its potential for explaining intra-family
similarities in dispersal behaviour. The study was conducted in a
fragmented
population of collared flycatchers and great tits, small hole-nesting
passerine
birds, breeding in 15 different discrete woodland patches on the
Short-term testosterone increases
in dark-eyed juncos: individual variation and relationships with
morphology and
behavior.
Quantifying the extent to which individuals
differ from one
another is essential for understanding both how selection acts on
hormonal
mechanisms and how such mechanisms mediate life history
trade-offs. We
studied breeding males in a wild population of dark-eyed juncos and
measured
both baseline levels of testosterone (T) and the magnitude of
short-term
increases in T above baseline in response to a GnRH challenge.
Over a
period of two years, we found that individual differences in response
to a
challenge were more pronounced (i.e. more repeatable) than were
baseline
measures. In addition, we detected seasonal variation in the
magnitude of
the response, positive co-variation between the response and an
attractive
plumage trait, and negative co-variation between the response and
nestling-feeding behavior. We suggest that individual variation
in
sensitivity to a GnRH challenge may predict individual variation in the
resolution of the trade-off between mating effort and parental effort.
Hormonal correlates of social
dominance status in Anatids.
Maud Poisbleau, (poisblea@mail.orn.mpg.de)
Through
case studies on dark-bellied brent geese Branta bernicla
bernicla and dabbling ducks, this work focuses on social dominance
relationships in gregarious species
such as wintering anatids. I used individual behavioural based-studies,
combining results from experiments in captivity and observations in
field
conditions, to (1) underline inter-individuals differences in hormonal
levels
during winter and spring periods and to (2) explore the potential use
of
hormones as indicators of the individual social status.Through their
potential
roles in aggressiveness, individual responses to environmental changes,
or as
health indicators, plasmatic levels of testosterone
and corticosterone are good
indicators of the individual social status of wintering dabbling ducks.
Conversely, there are no obvious direct relationship between hormone
levels and
individual social dominance in groups of wintering brent geese. The
best
estimator of the social dominance score of a goose being the size of
its
family, which is not preserved from one winter to the other, it is
nevertheless likely that the role of
hormones on the winter social status finds its source in the breeding
quarters.
Individual
variation or trapping technique? Trapping initiates stress
response in nonbreeding house sparrows. Anthony J. Porter and
Sharon E.
Lynn, The College of Wooster (slynn@wooster.edu)
Baited traplines are a relatively easy method of capturing and collecting blood samples from large numbers of birds in a short period of time. However, one potential drawback of this technique is that birds may be left in traps for an unknown period of time prior to sampling. We assessed the impact of being left in traps for up to 30 minutes on hypothalamo-pituitary-adrenal (HPA) axis activity in non-breeding house sparrows (Passer domesticus). Traps were baited with seed, and after entering the traps, birds were either removed immediately (controls), or left undisturbed for 15 or 30 min. Birds appeared to be feeding on seed while in the traps. Upon removal from the trap, birds were subjected to standardized capture and restraint protocol in which blood samples were collected to be analyzed for corticosterone (CORT) within 3 minutes of removal, and again at 15, 30, 45, and 60 minutes. Entry into the traps appeared to initiate CORT secretion in all birds. Sparrows that were left in the traps for 30 minutes had significantly higher baseline CORT than controls, and baseline levels were in fact similar to CORT levels measured after 30 min of restraint in controls. Similarly, baseline CORT levels in sparrows removed from the trap after 15 minutes were similar to levels after 15 minutes of restraint in controls. We suggest that the length of time birds spend in a trap prior to sampling may represent a significant source of variation in studies assessing HPA activity. At least one other study has investigated this phenomenon in several species, and taken together with the results of our study, suggest that the influence of trapping techniques on CORT secretion may be species and stage specific.
Avian
personalities: genes and environment.
Meetings like this show that there is currently a burst of interest in consistent individual differences in behavioural and physiological traits. These differences cannot be explained anymore by a deviation from optimality only, but they reflect a possible adaptive mechanism. In the great tit we have shown that individual differences are partly inherited and we have identified several environmental factors that alter the phenotypic expression of different genotypes. Thereby several behavioural and physiological traits are phenotypically and genetically correlated within the same context forming so called behavioural syndromes or personalities. We have also shown that genotypes may well be differently expressed in different contexts, which seems in contradiction to standing theories from human personality research. A possible explanation for this might be that the function of the phenotypic expression of different personality genotypes is non-parallel. This interaction between genotype and environment has however not been tested directly. My main project for the next coming years will therefore focus on this genotype by environment interaction. I am thereby interested whether reaction norms of different genotypes indeed cross and if this changes genetic correlations between traits.
Session
5: Individual variation in a
life-history context
Does early
nutrition affect
behavioural responses to novel situations? Kathryn E. Arnold Division
of Environmental and Evolutionary Biology,
Many animals, including humans, show consistent individual differences in how they respond to novel situations. Exposure to a novel object can, for example, elicit bold exploratory behaviour in some individuals with a continuum of responses through to shy avoidance. In wild birds, there has been a focus on studying the heritability of such behavioural traits. However, studies of mammalian model species have shown that embryonic and neonatal nutritional conditions can have a huge impact on how, as an adult, an individual responds to novel circumstances. In this study we assessed how manipulating amino acid nutrition during the nestling phase of wild blue tits (Parus caeruleus) affected an individual’s responses to novelty as an adult. Within each nest, half the nestlings were hand-fed once per day with an amino acid supplement and the rest with the control treatment. At 14 days, one experimental chick and one control chick per nest, matched for size and sex, were brought into captivity and raised to independence. A novel object was presented to each individual at 38 and 39 days of age. Bolder birds were defined as having both a shorter latency to approach each item and a shorter minimum distance to the object than more shy birds. Within individuals there was a consistent response to the two novel objects. Overall, there was a correlation between the latency and minimum distance to the novel objects. GLMM analyses revealed that females were significantly faster to approach the novel objects and got closer during that time. Heavier birds were found to get closer to the novel objects than lighter individuals, but overall did not have a shorter latency to approach. Neonatal diet was found to affect the relationship between body mass and latency. Among offspring in the control group, lighter offspring were significantly shyer than heavier offspring. Birds that had received an amino acid supplement as nestlings were overall faster to approach the novel objects than controls and their boldness did not vary with body mass. Our results show that neonatal diet produced consistent individual differences in adult behaviour. Thus, variation in early rearing environment provides a non-genetic mechanism for the maintenance of population-level variation in responses to novel situations.
Individual
and sex-specific variability of
cell-mediated immunity across life-history stages. Oliver P. Love 1,
Katrina G. Salvante 1, James Dale 2 and Tony D.
Williams 1,
1 Biological Sciences, Simon
Fraser University and 2 Max
Planck Institute for Ornithology, Starnberg (Seewiesen), Germany
(olovea@sfu.ca).
Organisms must manage physiological systems optimally across
life-history
stages and under varying environmental conditions to maximize fitness.
There
has been much recent integrative research aimed at testing
ecological and
evolutionary questions involving immunocompetence, with numerous
studies
focusing on measures of cell-mediated immunity (CMI) in birds. Research
to date has focused mainly on the short-term management of CMI
at particular life-history stages. We therefore lack basic information
on 1)
how CMI is managed over the long-term across life-history stages in
relation to
varying resources, 2) whether the sexes manage CMI differentially
across these
stages and 3) whether CMI is repeatable within individuals across these
stages.
Here, we examined inter-sexual differences in CMI using a
within-individual
repeated-measures design across the major life-history stages in a
captive
colony of zebra finches (Taeniopygia guttata). Juveniles
sex-specifically managed CMI between fledging and sexual maturity with
males
demonstrating higher CMI at fledging but similar CMI as females at
adulthood.
Adult females and males had similar responses during non-breeding and
during
egg-laying stages on a high-protein diet. However, when females were
laying
while on a low-protein diet they significantly reduced CMI . In
contrast, males
did not modulate CMI with limited proteinavailability. CMI of juveniles
was not
repeatable between either fledging and pre-basic molt or fledging and
adulthood. Adult males showed relatively high repeatability between
non-breeding and egg-laying stage on both diets. CMI in females was
similarly
repeatable between non-breeding and egg-laying on the high-protein
diet,
however in contrast to males repeatability disappeared when females
were laying
on the protein-poor diet. Optimal immunity theory predicts significant
variation across life-history stages as organisms attempt to manage
within-stage immune response to maximize lifetime fitness. In support
of this,
our results clearly indicate that zebra finches manage CMI
sex-specifically
across life-history stages when faced with variation in environmental
quality.
The
ecology and organismal biology of individual variation in Ithaca
Tree Swallows. David W. Winkler, Dept.
of Ecology and Evolutionary Biology,
Most aspects of
reproduction and
breeding behavior show considerable individual variation in Tree
Swallows Tachycineta bicolor nesting near
Maternal hormones in eggs of the communally
breeding smooth-billed ani (Crotophaga ani): effect of
group size
and egg-laying order.
Grégory Schmaltz1, James S.
Quinn1, & Stephan J. Schoech2 1Dept. Biology,
Avian eggs contain
maternal hormones that affect behaviour, growth, immune function,
morphology,
and survival of chicks. In this study, we measured hormonal
concentrations in
eggs of smooth-billed anis (Crotophaga
ani) to understand the female’s influence on offspring success in
this joint-nesting mating system. In anis, females lay eggs either
singly or in
groups of up to five females. Intense egg-laying competition occurs in
multi-female groups with eggs laid early having the highest
probabilities of
egg loss because of egg tossing and burial. We measured concentrations
of
testosterone, estradiol, and corticosterone in ani egg yolks. Results
suggest
that females deposited more testosterone and corticosterone in
late-laid eggs
Vs early laid eggs. Within multi-females groups, females also deposited
more
testosterone and corticosterone as group size increased. Females
therefore seem
to adjust hormonal concentrations in eggs depending on female group
size and
the probability of a given egg to hatch. We hypothesize that these
hormonal
depositions may lead to the production of more competitive chicks in
multi-female nests which may be beneficial during sibling-sibling
competition
with unrelated nestmates.
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