2003

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Many life history characteristics show phenotypic plasticity, with characters assuming different values in different environmental circumstances. For example, in most temperate bird species, the character laying date has low (early) values in warm ‘early’ springs, and high (late) values in cool ‘late’ springs. Historically, ecologists and endocrinologists have taken very different approaches to understanding this phenotypic plasticity. Endocrinologists have been primarily interested in understanding the neuro-endocrine control mechanisms that underlie phenotypic plasticity, while evolutionary ecologists have sought to understand the selection pressures that account for phenotypic plasticity in life history traits. For example, an endocrinologist might explore how changes in temperature interact with day length to stimulate the HPG axis, while the evolutionary ecologist would focus on how laying date affects reproductive success at different temperatures, and hence how the optimal laying date would vary with temperature (the optimal ‘reaction norm’). Evolutionary ecologists know, of course, that phenotypic plasticity must be underlain by physiological control mechanisms, but they have usually ignored the details and simply assumed that hormonal mechanisms do not influence the outcome of selection. Whether or not this is true has become more than an intellectual question. Environments are changing rapidly and whether or not animals can keep up will depend in part of the details of control mechanisms – are they flexible enough to change with the environment or could they pose constraints on what is possible? This workshop will strive to answer questions like these by focusing on the nature of adaptation and constraint.

There are several ways in which hormones might influence the outcome of evolution:

1a) Hormones may be costly. Costs might include energetic costs or interference with other physiological mechanisms, such as the immune system. If these costs translate into fitness costs, they will act as selection pressures on the reaction norm, and influence the outcome of evolution.

1b) Hormones may cause trade-offs. If single hormones have multiple effects, they may create trade-offs between different fitness-related life-history traits. Here we are concerned with those cases where hormones create trade-offs (= for some reason single hormones have multiple effects, and this creates trade-offs that would not otherwise exist). There may be other cases where hormones modulate trade-offs that exist for some other reason (for example a trade-off may exist between two charcaters because of resource allocation constraints. Then, a hormone which increased one of the characters would also decrease the other). In the first case the hormone would influence the reaction norm that would finally evolve, and in the second case not.)

2) Tightly integrated hormonal control systems may create evolutionary inertia. Hormonal control systems are often characterized by tight integration involving signaling cascades and feedback. Such systems may be difficult to modify evolutionarily without a loss of functionality.

3) Hormonal control systems may embody ‘rules of thumb’ that do not function well under novel environmental circumstances. The reaction norms that organisms currently express are the result of selection acting on their ancestors, so they are only expected to be adaptive within the range of environmental conditions in which they evolved. Extrapolating these reaction norms in novel environmental conditions may result in the expression of non-adaptive phenotypes. It becomes critical to know whether mechanisms can adjust with time.

These possibilities raise interesting and urgent questions – including how organisms will react to climate change – that cannot be answered without understanding how selection pressures and hormonal control systems interact. If evolutionary ecologists have the questions, it is the endocrinologists who have the knowledge that will underpin the answers. This workshop is about bringing endocrinologists and evolutionary ecologists together to make a start in answering the question:

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SESSION II: TIGHTLY INTEGRATED HORMONAL CONTROL

AND EVOLUTIONARY INERTIA

POSTERS:

Frédéric Angelier: Corticosterone and foraging effort in a pelagic seabird

N.M. Goodship, Kate L. Buchanan & R.J. Cowie: Begging signals: The role for testosterone

Thierry Charlier: Plasticity in the expression of the steroid receptor coactivator-1 (SRC-1) in Japanese quail

A. M. Dufty, Jr.: Should nestlings secrete corticosterone in response to adult alarm calls?

Leonida Fusani: Sexy or masculine? Hormone-mediated trade-offs in birdsong

Tom P. Hahn, M. E. Pereyra, and S. M. Sharbaugh: Effects of photoperiod on brain GNRH plasticity and peripheral reproductive physiology in three species of cardueline finches

Oliver P. Love, Katherine E. Wynne-Edwards & Tony D. Williams: Maternal corticosterone sex-specifically mediates the trade-off between quantity and quality of offspring in European starlings

Oliver Love: Nest decomposition modulates the trade-off between current reproduction and maternal condition in the European starling

Sharon E. Lynn, Brian G. Walker, John C. Wingfield: Hormones and paternal behavior in longspurs and buntings: Does the need for paternal care constrain behavioral responses to testosterone?

Anne Peters: To court or to care: testosterone and the trade-off between mating and parental effort

Katrina G. Salvante, Francois Vezina & Tony D. Williams: Egg production in energetically challenging conditions: The physiological mechanisms underlying the trade-off between maintaining maternal condition and current reproduction

SESSION III: HORMONAL ‘RULES OF THUMB’

IN NOVEL ENVIRONMENTS

Discussion workshops

Summary of discussion workshops

Workshop summaries by Peter Sharp, Trevor Price & Tony Williams

General discussion

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Three endocrine cascades that are thought to be tightly integrated will be discussed and evaluated with respect to their potential to slow down or prevent passage to a sufficiently adaptive peak following a change in the adaptive landscape: (1) the hypothalamic-pituitary-gonadal axis (HPG), especially as related to onset of reproductive maturity, a key component of fitness, and seasonal onset of breeding; (2) the pathway involved in activation of mating effort behavior such as copulation and singing that begins with gonadal steroidogenesis and continues with brain steroid metabolism, gene transcription regulation by steroids, and interactions of steroids with peptides and neurotransmitters; (3) the sex determination/sexual differentiation cascade. It will be argued that (3) is more likely to be a source of inertia than (1) or (2).

The ability of individuals to adjust energy expenditure while foraging will determine the amount of resources that can be expended on fitness-related activities. Because a trade-off between foraging costs and investment in reproduction is predicted, understanding hormonal mechanisms governing foraging decision is essential. Corticosterone is believed to trigger foraging activities. However, elevated corticosterone levels can also induce nest desertion. How then individuals modulate corticosterone secretion to optimise foraging and reproductive success? By concurrently measuring corticosterone levels and precise components of foraging effort in incubating albatrosses, we showed that variations in corticosterone levels below level inducing nest desertion govern foraging decisions to maximise foraging efficiency (foraging success/energy expended).

Short paper: Glucocorticoid reactivity predicts timing of territorial abandonment during storms

C.W. Breuner & T.P. Hahn

Physiological mechanisms underlying the trade-offs between current and future reproduction are not well understood. While it is clear that chronic stressors inhibit reproduction, allowing an animal to redirect energy resources away from young towards self-maintenance, it is not clear what role the acute stress response plays. In the sub-alpine breeder the mountain white-crowned sparrow, early spring storms often decimate food availability within a few hours, and force animals to abandon current territorial defense to seek refuge at lower elevation. We have strong evidence supporting a role for the acute stress response in mediating the timing of this behavioral decision.

As a reliable, costly signal, begging behaviour is theoretically expected to be more intense for individuals of greater need. The endocrine system, and in particular testosterone, has been proposed as a mechanism to control begging behaviour. We test the hypothesis that begging intensity co-varies with testosterone and hunger, using nestling pied flycatchers (Ficedula hypoleuca). Over a 2hr food deprivation period, begging and testosterone levels were quantified. Begging intensity increased with time since the last feed, while testosterone and begging were positively correlated. The results from this study confirm the potential of the endocrine system to control nestling begging signals.

Short paper: Reproductive estradiol concentration is a hyper-variable mammalian species trait.
Wendell O. Challenger* & Katherine E. Wynne-Edwards
*Current address: Statistics, Simon Fraser University, Burnaby, Canada

Reproductive estradiol concentration is a hyper-variable mammalian trait that is not explained by phylogenetic relationships and that spans as many orders of magnitude as body mass. There is evidence that diet explains estradiol concentrations at the level of order and clear evidence that selection has occurred within genera. Results suggest that, over evolutionary time, estradiol concentration is a labile trait. Both domestication and endocrine disruption might also affect the validity of different animal models for endocrine evolution.

Long talk: Modulation of steroid-dependent male sexual behavior and neural gene expression: a potential role for steroid-receptor coactivator

This study focuses on the importance of the nuclear receptor coactivator SRC-1 in the activation by testosterone of male sexual behavior in quail. By disrupting SRC-1 expression in the POM, we were able to significantly reduce the expression of male copulatory behavior in response to exogenous testosterone. The steroid-dependent POM volume by Nissl staining and aromatase and vasotocin expression within thePOM were also significantly altered upon SRC-1 expression down-regulation. Taken together, these findings indicate that SRC-1 functions as a critical regulatory molecule in the brain to modulate steroid-dependent gene transcription and behavior.

Poster: Plasticity in the expression of the steroid receptor coactivator-1 (SRC-1) in Japanese quail

Analysis of nuclear receptors action on the eukaryotic genome highlights the importance of steroid receptor coactivators on gene transcription. In quail, male sexual behavior is activated by a localized action of testosterone (T) or its metabolite, estradiol in the preoptic area but females never show male-typical copulatory behavior even after exposure to high doses of T despite a similar distribution and concentration of steroid receptors. We investigated here the potential role of SRC-1 in this sexually differentiated response to steroids. Contrary to published results (Neuroendo 2002, 76:292), we found here through the analysis of mRNA by real time quantitative polymerase chain reaction (qPCR) and protein by western blot (WB) that sexually mature females had higher concentrations of SRC-1 in the preoptic area-hypothalamus (HPOA) compared to males. This discrepancy may be caused by the short ovulation cycle associated with rapid endocrine changes that could affect SRC-1 expression in females like T does in males. Additional studies should be carried out to solve this discrepancy. We also quantified SRC-1 mRNA and protein in (HPOA) of castrated males treated or not with T. Here again, SRC-1 mRNA was increased by T in one experiment but not in the replicate. The potential reason for these conflicting results would be the differential manipulation of the birds during the two experiments. This hypothesis is strengthened by recent work obtained in rats indicating that stress can regulate SRC-1 expression in hypothalamus and hippocampus. We are currently looking at the expression profile of SRC-1 protein in the HPOA and other tissues in male quail after stress. Together, these data support the idea that SRC-1 is not constitutively expressed but regulated by steroids, stress and possibly other unidentified factors. Differential controls could also take place in specific brain nuclei, which could only be identified by immunohistochemistry and in situ hybridization.

Poster: Parental effort and the modulation of hormone responses to stress: a role for prolactin?

What is the proximate basis for the trade-off between current reproduction and survival (i.e.: future reproductions)? Corticosterone is known to rapidly rise in response to stress; leading to a cessation of reproductive activities. This can be considered as adaptive because it may promote survival during stressful periods. Alternatively, reducing the corticosterone response to stress might be considered a hormonal tactic to maximize current reproduction; even this may entail survival costs. However, despite its key role in avian parental behaviour, a role for prolactin in mediating reproductive decisions during stressful situations has never been addressed. We present evidences that parental effort can modulate the prolactin response to stress and suggest that prolactin shows potential for mediating some life-history trade-offs, as does the extensively studied corticosterone.

The different life history stages that make up the annual cycle in birds have evolved to occur at the most appropriate time, generally without overlapping with other stages, and yet using the whole time available to them. The accurate timing of each stage, and the relationship between successive stages, is crucial to survival. The major proximate factor in timing is the annual cycle of photoperiod. In starlings, and probably other species, photoperiod controls the start and duration of the breeding season through a dual effect on the gonadotrophin-releasing hormone (GnRH) neurones. Firstly, long photoperiods in late spring or summer switch off GnRH synthesis and this process is reversed by short photoperiods during autumn. Between these two events, the reproductive system is totally inactive. Birds are said to be photorefractory – essentially pre-pubertal – during this period. This photorefractory period is a rule; it is inviolate in that no non-photoperiodic factor appears to have any effect. Gonadal maturation results from the second photoperiodic effect – GnRH secretion rate is proportional to photoperiod. Maturation begins after resumption of synthesis. During this stage, non-photoperiodic cues (e.g. temperature, food, stress, social interactions) may have a modulating input. This culminates in egg-laying. Gonadal regression precedes the ending of GnRH synthesis, and again, non-photoperiodic cues (behaviour, temperature) may have an input, and may be coordinated by prolactin. The timing and rate of postnuptial moult are ultimately controlled photoperiodically, again possibly via prolactin. Prolonged breeding delays the start of moult (prolactin-effect), which results in an accelerated moult and poorer plumage quality. Thus, breeding constrains moult, and moult constrains breeding.

Poster: Should nestlings secrete corticosterone in response to adult alarm calls?

Many nestlings respond to alarm calls with anti-predator behaviors, but their physiological responses are unknown. In semi-precocial American kestrel nestlings, alarm-call induced corticosterone secretion could mobilize energy reserves, preparing the nestlings to defend themselves. However, elevated corticosterone secretion has detrimental effects on development, so there may be a cost involved. Nestling kestrels, 15-20 days old and capable of producing an adrenocortical response, did not respond hormonally to broadcast of alarm calls. While this suggests a possible constraint, birds closer to fledging age might respond hormonally to alarm calls, perhaps preparing them to fledge prematurely in a last-ditch effort to escape.

The androgen testosterone controls the development of song in male songbirds. Testosterone, however, can be transformed into oestrogen in the brain. In the canary, testosterone is required for the development of masculine song, whereas its oestrogenic metabolites are responsible for the development of a sexually selected feature of song, the syllable repetition rate. Thus, hormone metabolism modulates trade-offs between different aspects of secondary sexual traits: too little oestrogen leads to “unattractive” songs, whereas too much oestrogen results in unstable songs.

Short paper: Courtship as an assemblage of displays with their own control mechanisms

Elaborate courtship often involves displays derived from different behavioural contexts. The male ring dove has three main courtship displays: bowing, chasing, and nest-soliciting. The first two displays are also used in aggressive interactions with other males, whereas the nest-soliciting is performed by both males and females during nest-building and incubation. We have shown that bowing and chasing are androgen-dependent, whereas nest-soliciting is modulated by oestrogen. Thus, it appears that the three courtship displays have been co-opted from other displays and assembled to form the courtship but each maintaining its separate hormonal control mechanisms.

Poster: Effects of photoperiod on brain GNRH plasticity and peripheral reproductive physiology in three species of cardueline finches

Seasonal neural plasticity is common in the brains of adult songbirds, particularly in the song control system and the septo-infundibular GnRH system. Comparisons among closely related species can help to clarify the significance of this plasticity. We tested effects of prolonged exposure (4.5 months) to either long (20L:4D) or short days (5L:19D) on septo-infundibular GnRH and peripheral endocrine physiology in males of three cardueline finch species: pine siskins (Carduelis pinus), common redpolls (Carduelis flammea), and white-winged crossbills (Loxia leucoptera). Redpolls are seasonal breeders, siskins are flexible seasonal breeders, and crossbills are temporal opportunists. All three species showed increases in circulating luteinizing hormone (LH, measured by RIA) and gonad size (by laparotomy) in response to long days, but only siskins and redpolls appeared to become photorefractory (spontaneous gonadal collapse and completion of feather molt on long days). Likewise, down-regulation of the GnRH system (assessed by immunocytochemistry) occurred after 4.5 months only in long day siskins and redpolls, not crossbills. irGnRH cell number, size (area, perimeter), and staining intensity relative to background were all dramatically and significantly reduced in long day (putatively refractory) redpolls and siskins, but only cell size (area) declined significantly in long day crossbills. These findings are consistent with the idea that down-regulation of septo-infundibular GnRH may be specific to a state of absolute photorefractoriness (which evidently did not develop in crossbills), and suggest that differences in neural plasticity in the GnRH system may underlie interspecies differences in reproductive biology, such as temporal flexibility of reproductive timing.

In September 2004, we suddenly lost an outstanding ornithologist, Ebo Gwinner. Ebo was an amazing scientist whose large body of work spanned various fields, in particular biological rhythms, behavioral endocrinology, bird migration, and learning. To honor Ebo’s many important contributions to science, I will review some of his major findings. He was most intrigued by proximate questions on mechanisms that control behavior, but always from an ecological and evolutionary viewpoint. His integrative approach lead him to conduct unique comparative lab and field work on birds from across the globe. Ebo was one of the founding fathers of the ESF/NSF network.

Long talk: Seasonal flexibility in the utilization and actions of steroid hormones - A mechanism to avoid costs?

Testosterone (T) regulates territorial aggression in male vertebrates during the breeding season, but long-term elevation of circulating T concentrations might incur costs such as suppressed immunity. I propose that physiological mechanisms exist that allow individuals to minimize the costs of T. Year-round territorial spotted antbirds only elevate T levels during periods of high-intensity aggressive encounters but otherwise keep levels low. They have elevated DHEA levels (a precursor of T, probably produced in the adrenals) during the non-breeding season, from which they could produce T in specific areas in the brain. Brain steroid receptors and enzymes change seasonally suggesting differential production and action of certain steroids during breeding versus non-breeding seasons. Finally, the costs of T in birds may vary seasonally as T administration to house sparrows depresses immunity during the breeding season only. Modes of hormone action appear to be evolutionarily flexible and might serve to minimize potential costs.

Short paper: Can physiological and behavioral mechanisms associated with different life history strategies track changes in environmental selection pressures?

Behavioral, ecological, hormonal, and biogeochemical studies are revealing how events during the non-breeding period can constrain reproduction by affecting arrival time and body condition. An example of the "connectivity" of annual cycle events, is the American Redstart (Setophaga ruticilla), a species that shows ecologically linked variation in overwintering strategies (behavioral and physiological) that is related to subsequent breeding success. However, recent change in environmental conditions on both the wintering and breeding grounds poses the question: Can behavioral and physiological mechanisms that once supported different life history strategies *keep up* with possible rates of change in environmental selection pressures?

Keynote: An evolutionary perspective on tightly integrated control and evolutionary inertia

Keynote: An evolutionary perspective on hormonal ‘rules of thumb’ in novel environments

To what extent, and in what ways, might hormonal control systems influence the course of evolution? In these introductory talks, I briefly review the possibilities, drawing analogies with other forms of mechanistic constraint, and suggest what kinds of evidence may be needed to clarify the evolutionary role of hormones. In particular, I highlight the need to distinguish between maladaptive constraints arising directly from the hormonal control of trait expression, and adaptive mediation by hormones of tradeoffs that arise for other reasons. I argue that the latter role is more plausible, but that even if hormonal mechanisms do not create novel constraints, they will nevertheless influence the course of evolution by modulating the pattern of resource acquisition and allocation tradeoffs. The strength of this influence, however, depends largely on the flexibility of the regulatory mechanisms involved. I briefly consider how this issue might be addressed within an adaptive framework, and argue that the contrast between proximate and ultimate approaches is more apparent than real – what is required is a shift of focus from adaptive behavioural outcomes to adaptive regulatory mechanisms.

Long talk: Testosterone and co-evolution of the sexes: natural, sexual, and correlated responses to selection.

Because natural and sexual selection can act differently on males and females, the sexes may diverge in phenotype, hastened or constrained by correlated responses to selection. Hormones mediate sex-limited and sex-biased expression and thus act as proximate mediators of these sex differences. Given their pleiotropic effects within and across sexes, hormones can also constrain the evolution of sexual dimorphism, We focus on testosterone and its phenotypic effects in female birds. In two parts we will summarize available information on female sensitivity to testosterone from the literature and report results from the field on female response to experimentally elevated testosterone.

The field endocrinology approach substantially enhances traditional methods used to assess food availability in seabirds. Temporal changes in food availability can be quantified by measuring concentrations of the stress hormone corticosterone in the blood of undisturbed individuals (“baseline levels”, indicate current food availability), and the rise in blood levels of corticosterone in response to a standardized stressor: capture, handling and restraint (“maximum acute stress-induced levels”, indicate recent nutritional history). A long-term study of seabirds breeding in Alaska has revealed direct relationships among corticosterone levels, food abundance, reproductive performance and persistence of individuals in populations.

Short paper: Are long photoperiods that override non-photoperiodic factors responsible for maladaptive breeding dates in Mediterranean blue tits (Parus caeruleus)?

In non-domesticated, avian species, the relative importance of the photoperiodic and non-photoperiodic factors influencing later stages of the breeding cycle, such as egg laying dates, remains unclear. Based on findings of laboratory experiments in blue tits, an explanation is provided for why the relative importance of the non-photoperiodic factors decreases with the progress of the season, i.e. with longer photoperiods. The hypothesis can explain observed maladaptive breeding dates in free-living populations. The underlying endocrine mechanisms of changes in the perception of non-photoperiodic factors with changes in photoperiod and the progress of the season remain to be explored.

Poster: Maternal corticosterone sex-specifically mediates the trade-off between quantity and quality of offspring in European starlings

Corticosteroids have recently been proposed to have secondary effects on sex allocation and offspring phenotype in birds since they are intimately tied to physiological/physical condition through their prominent role in homeostatic energy balance. Notably, birds exhibit elevated baseline corticosterone (CORT) as body condition or habitat quality decreases. We have been examining the evolutionary consequences of elevated baseline CORT for reproductive females and offspring in wild European starlings, a sexually-size dimorphic passerine. Experimentally elevating maternal CORT during laying has resulted in 1) elevated yolk CORT, 2) female-biased sex ratios at hatching and 3) male offspring hatching at significantly lower masses and growing more slowly than control males; female offspring were unaffected. Elevated maternal CORT thereby resulted in a biased investment in the less costly sex (females) both directly via a sex ratio bias and indirectly via modulation of male offspring phenotype. This suggests that maternal CORT may be a physiological mechanism sex-specifically modulating the trade-off between offspring quantity and quality in relation to maternal condition or habitat quality.

Poster: Nest decomposition modulates the trade-off between current reproduction and maternal condition in the European starling

In birds, parents can reduce the energetic costs of raising nestlings by improving the thermal properties of the nest, potentially increasing fitness either directly via increased offspring survival and/or indirectly via an improvement in parental condition. We observed in a wild, nest-box breeding colony of European starlings, Sturnus vulgaris, that nests decompose by the end of the breeding period. Hypothesizing that if heat was produced as a by-product during decomposition, we measured both nest and ambient box temperature and combined this with measurements of reproductive success (e.g., nestling growth/survival and adult condition) to examine whether nest decomposition shifted nest temperatures away from external ambient temperatures, potentially increasing reproductive success. During periods of low ambient temperature we found that compared with non-decomposing nests,decomposing nests (1) were significantly warmer relative to ambient box temperature, (2) exhibited lower nestling mortality, and (3) reduced mass losses in females attending nestlings. Starlings appear to benefit from heat produced via nest decomposition during chick provisioning, similar to the use of heat from decomposition in some birds and reptiles during incubation. Nest decomposition may allow some cavity-nesting bird species to cope with low ambient temperatures during reproduction and may modulate some of the predicted costs of reproduction and therefore the trade-off between current reproduction and maternal condition.

Poster: Hormones and paternal behavior in longspurs and buntings: Does the need for paternal care constrain behavioral responses to testosterone?

In most birds that show paternal care, extending elevated testosterone (T) secretion into the nestling phase reduces provisioning, suggesting a trade-off between testosterone and parental care. However, in several species, this trade-off appears not to exist.

Two ecological constraints have been hypothesized to drive this insensitivity to T: (1) a short breeding season that limits breeding opportunities, and (2) a need for paternal care to ensure reproductive success. We tested these hypotheses within a phylogenetic framework using members of the Calcarius/Plectrophenax clade. Our data suggest that T insensitivity in this clade is related to the importance of paternal care.

Short paper: Correlational selection and the evolution of suites of hormonally mediated traits

Correlational selection, which occurs when a trait's effect on fitness depends on co-expression with another trait, may lead to the evolution of integrated suites of traits. Because hormones mediate the expression of such suites, they may act both to constrain and to facilitate the evolutionary integration of functionally related traits via correlational selection. I present an example of how correlational sexual selection may have led to the integration of an attractive plumage trait and body size in dark-eyed juncos, and suggest that a similar mechanism may lead to the evolution of testosterone mediation of attractive traits and behavior in males.

Short paper: Are endocrinological “rules of thumb” sufficient to explain the movement of a Dendroica warbler hybrid zone?

I offer an example demonstrating how hormonal “rules of thumb” can be useful in predicting shifts in species’ ranges through time. Over the past 5,000 years, Townsend’s warblers (Dendroica townsendi) have been replacing hermit warblers (D. occidentalis) through a series of moving hybrid zones in western North America. Male Townsend’s outcompete male hermits in areas of sympatry, and mate with female hermits to produce viable hybrid offspring. I investigate costs and benefits of elevated androgen levels and aggression in Townsend’s and hybrid males, and ask if these “rules of thumb” are adjusted according to historical selection pressures.

Poster: To court or to care: testosterone and the trade-off between mating and parental effort

Male reproduction is a trade-off between offspring care and pursuit of additional mating opportunities, presumed to be regulated by testosterone. I studied this trade-off in superb fairy-wrens, Malurus cyaneus, a species where courtship and care occur concurrently. They live in pairs and cooperative groups with 1-4 male helpers. All males show extensive paternal care despite 76% extra-group paternity. Throughout the period of offspring care males engage in frequent extra-pair courtship. Although testosterone treatment of males in pairs resulted in dramatic reduction of paternal effort, it failed to elevate extra-group courtship to levels seen when males have helpers to assist with care.

Short paper: Does testosterone mediate a trade-off between investment in competitive behaviour and parental care in male songbirds?

The trade-off hypothesis of testosterone (T) secretion predicts that T regulates the allocation of reproductive effort between competitive behaviour for mates and territories, associated with high T levels, and investment in paternal care, associated with low T levels. We tested this hypothesis in the great tit Parus major and the European starling Sturnus vulgaris by implanting males with exogenous T at the start of the breeding season. Our results show that both species vary strongly in the degree of behavioural responsiveness to T alterations. These different responses might be partly explained by differences between both species in mating system, further breeding opportunities and the importance of paternal care for successful breeding.

Poster: Egg production in energetically challenging conditions: The physiological mechanisms underlying the trade-off between maintaining maternal condition and current reproduction

Avian reproduction is generally timed to synchronize chick-rearing with periods of increased food abundance. Consequently, the energetically-demanding period of egg production may coincide with periods of lower food availability, fluctuating temperature, and more unstable weather, thus potentially limiting the amount of resources laying females have for egg formation versus self-maintenance. I investigated the physiological basis of this trade-off between reproductive effort and self-maintenance by manipulating the energetic demands of laying females (via ambient temperature manipulation) and assessing concurrent changes in maternal lipid and yolk precursor metabolism, energetics (RMR), and reproductive output in captive-breeding Zebra Finches (Taeniopygia guttata).

Short paper: Global climate change, local effects: Florida scrub-jays breed 11 days earlier now than they did in 1980

Florida Scrub-Jays have advanced clutch initiation over the past 25 years. Because the two latest breeding years (1992 and 1998) were strong el Niño years and because el Niño strongly affects Florida’s weather patterns, we investigated the relationship of the Southern Oscillation Index (SOI) and timing of breeding. SOI and breeding were in marked antiphase, with exceptionally low SOI in1992 and 1998. Although there is no evidence of air temperature warming, nearby sea surface temperatures (SST), that affect local rainfall patterns, have increased. Early breeding is associated with intermediate rainfall levels, while too little or too much rain delays reproduction.

Short paper: Ontogeny of reproductive response to photostimulation in European starlings: implications for evolutionary inertia in the brain-pituitary-gonad axis

In many bird species, first-year females lay later in the season and consequently lay fewer eggs than second-year and older females. Whether reduced reproductive output in young females is an adaptive response to inexperience in an ultimate sense or a maladaptive consequence of inexperience in a proximate sense might be determined by understanding the mechanisms for this ontogenic change. In European starlings (Sturnus vulgaris) differences in photostimulation experience between first- and second-year females influence output of the brain-pituitary-gonad axis. Therefore, selective forces would need to overcome the inherent inertia of this axis to exert evolutionary change.

Short paper: Experimental increase of corticosterone levels affect begging behaviour and immune response in nestling house sparrows

Begging behaviour is thought to convey information on the nutritional needs of chicks and parents are thought to respond accordingly. However, given the potential conflict of interests between parents and offspring, one might expect nestlings to beg more than their actual condition would require. This raises the question of the reliability of the signal. Previous studies have shown that experimental increase of corticosterone (CORT) enhances begging behaviour in the black-legged kittiwake. In this study we wished to test the idea that, although increased corticosterone levels might provide benefits in terms of higher rate of parental provisioning, it also provokes costs in terms of reduced efficiency of the immune system. In agreement with the predictions we found that nestlings facing daily injections of CORT begged more than their control nest-mates. However, they also had a poorer immune response and a lower body mass than control chicks. Interestingly, contrary to the prediction, parents did not feed CORT nestlings more than the control. Overall, these results show that hormones can be costly and generate physiological trade-offs between traits.

Friday evening lecture: Some basic principles of endocrinology: possible constraints on evolution?

Hormones can be placed in two major chemical categories: peptides and proteins (with genes that encode them) and non-peptides such as steroids, modified free fatty acids and modified amino acids. The latter are regulated by biosynthetic enzymes (with genes that encode the enzymes not the hormones). This presentation will briefly outline basic principles of hormone synthesis, processing, packaging and release. Once in the blood how are hormones transported to target sites and how do they get to target cells? At the target cell hormones interact with receptors to have their effects – types of receptors and how they influence cells will be reviewed. Finally mechanisms by which hormone signals can be altered and/or terminated will be addressed. It is possible that some of these processes may be points where constraints on evolution occur. Outlining these basic principles is an attempt to allow ecologists and evolutionary biologists to familiarize themselves with endocrine processes and perhaps identify where such constraints might arise.

Keynote: Hormone-behavior Interactions during the life cycle and in different environments: how and why?

There is now extensive evidence that male-male interactions over territories and receptive mates can modulate secretion of testosterone. Furthermore, the pattern of response, or whether an individual responds at all, has been related to mating system. How essentially identical aggression is modulated in non-breeding life history stages is not fully resolved, but does appear to be dependent upon aromatization of testosterone and an estradiol receptor-mediated mechanism. How these patterns vary in relation to diverse habitats is even less well known. There is accumulating evidence that prolonged high levels of circulating testosterone may incur costs that may potentially reduce fitness. These include interference with paternal care, exposure to predators, risk of injury, loss of fat stores and possibly impaired immune system function and oncogenic effects. Six hypotheses have been proposed to explain how these costs of high testosterone levels in blood may be avoided and may also be relevant for other hormones that have a highly specialized suite of actions in one life history stage (such as breeding), but also have a limited action in other life history stages when the full spectrum of effects would be inappropriate. However, recent studies of several taxa of closely related emberizines reveal that hormone-behavior interrelationships are much less uniform than we thought. At the extremes of breeding ranges (high latitude), breeding seasons are brief and circulating testosterone levels are not socially modulated. In northern Zonotrichia and Calcarius, males actually become insensitive to the behavioral effects of testosterone possibly as a mechanism to maintain paternal care. At mid-latitudes, most males show social modulation of testosterone secretion especially in response to experimental challenges. In contrast, an equatorial population of Zonotrichia capensis, shows a fixed pattern of testosterone secretion that is not socially modulated. Such variation in pattern and degree of social modulation appears to be independent of mating system and offers an ideal opportunity to compare populations to determine the ecological basis of this variation, evolution of patterns and the mechanisms underlying them.

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Frédéric Angelier, Centre d’Etudes Biologiques de Chizé, France angelier@cebc.cnrs.fr

Wendell Challenger, Simon Fraser University, British Columbia, Canada wchallen@sfu.ca

Olivier Chastel, Centre d’Etudes Biologiques de Chizé, France chastel@cebc.cnrs.fr

Alistair Dawson, Monks Wood Centre of Ecology And Hydrology, UK asda@ceh.ac.uk

Philip Gienapp, Netherlands Institute of Ecology, Heteren, The Netherlands p.gienapp@nioo.knaw.nl

Diego Gil, Museo Nacional de Ciencias Naturales, Madrid, Spain dgil@mncn.csic.es

Marcel Lambrechts, Centre d’Ecologie Fonctionnelle et Evolutive (CNRS), Montpellier, France

Kate Lessells, Netherlands Institute of Ecology, Heteren, The Netherlands k.lessells@nioo.knaw.nl

Oliver Love, Simon Fraser University, British Columbia, Canada olovea@sfu.ca

Anne Peters, Max Planck Institute for Ornithology, Seewiesen, Germany peters@orn.mpg.de

Katrina Salvante, Simon Fraser University, British Columbia, Canada kgsalvan@sfu.ca

Stephan J. Schoech, University of Memphis, Memphis TN USA sschoech@memphis.edu

Hubert Schwabl, Washington State University, Pullman WA USA huschwabl@wsu.edu

Gabriele Sorci, Pierre et Marie Curie University, Paris, France gsorci@snv.jussieu.fr

Marcel Visser, Netherlands Institute of Ecology, Heteren, The Netherlands m.visser@nioo.knaw.nl

Tony D Williams, Simon Fraser University, British Columbia, Canada tdwillia@sfu.ca

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