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Peter Arcese - One of the best experts on this subject based on the ideXlab platform.
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purifying selection in the toll like receptors of song sparrows Melospiza melodia
Journal of Heredity, 2018Co-Authors: Martha J Nelsonflower, Ryan R Germain, Elizabeth A Macdougallshackleton, Sabrina S Taylor, Peter ArceseAbstract:Variation in immune gene sequences is known to influence resistance to infectious diseases and parasites, and hence survival and mate choice, across animal taxa. Toll-like receptors (TLRs) comprise one essential gene family in the vertebrate innate immune system and recognize evolutionarily conserved structures from all major microorganism classes. However, the causes and consequences of TLR variation in passerine birds remain largely unexplored. We examined 7 TLR genes in song sparrows (Melospiza melodia), a species that is studied across North America. We then examined sequences from 4 unduplicated TLRs (TLR1LB, TLR3, TLR4, and TLR15) from birds in 2 parts of the species' range (N = 27, N = 6), tested for evidence of selection, and conducted pilot analyses of the role of TLR heterozygosity in survival. We identified 45 SNPs: 19 caused changes in amino acid sequences and 2 of these were likely deleterious. We found no evidence of codon-level episodic positive selection but detected purifying selection at codons in all TLRs. Contrary to expectations we found no strong correlation between heterozygosity at TLRs and inbreeding coefficient f (estimate ± standard error [SE] = -0.68 ± 0.37, Radj2 = 0.08, F1,25 = 3.38, P = 0.08). In addition, pilot analyses revealed no relationship between TLR heterozygosity and survival (β ± SE: 0.09 ± 2.00, P = 0.96), possibly due to small sample size. Further analyses of genetic diversity in TLRs are likely to advance understanding of the effects of innate immune gene diversity on the fitness and persistence of wild populations.
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the consequences of polyandry for sibship structures distributions of relationships and relatedness and potential for inbreeding in a wild population
The American Naturalist, 2018Co-Authors: Ryan R Germain, Peter Arcese, Jane M ReidAbstract:AbstractThe evolutionary benefits of simultaneous polyandry (female multiple mating within a single reproductive event) remain elusive. One potential benefit could arise if polyandry alters sibship structures and consequent relationships and relatedness among females’ descendants, thereby intrinsically reducing future inbreeding risk (the indirect inbreeding avoidance hypothesis). However such effects have not been quantified in naturally complex mating systems that also encompass iteroparity, overlapping generations, sequential polyandry, and polygyny. We used long-term social and genetic pedigree data from song sparrows (Melospiza melodia) to quantify cross-generational consequences of simultaneous polyandry for offspring sibship structures and distributions of relationships and relatedness among possible mates. Simultaneous polyandry decreased full sibships and increased half-sibships, on average, but such effects varied among females and were smaller than would occur in the absence of sequential polya...
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nest site preference and reproductive performance of song sparrows Melospiza melodia in historically extant and colonist shrub species
Canadian Journal of Zoology, 2017Co-Authors: Merle Dora Crombie, Ryan R Germain, Peter ArceseAbstract:Many studies report mixed results on the influence of invasive plants on native animals, partly due to uncertainties about habitat preference and reproductive performance in native animals before and after plant invasion. We used vegetation surveys 20 years apart and 18 years of breeding data from Song Sparrows (Melospiza melodia (A. Wilson, 1810)) to compare nest-site preference and reproductive performance during the colonization of Mandarte Island, British Columbia, by one shrub species native to the region but historically absent from the island (red elderberry, Sambucus racemosa L.) and another species that is exotic to North America (Himalayan blackberry, Rubus armeniacus Focke = Rubus bifrons Vest). Nest-site preference declined where red elderberry increased but was unrelated to change in the cover of Himalayan blackberry. Song Sparrows nested in trailing blackberry (Rubus ursinus Cham. and Schltdl.) and its exotic congener Himalayan blackberry in preference to two common shrubs native to Mandarte...
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nest defense and parental investment in song sparrows Melospiza melodia
Canadian Journal of Zoology, 2016Co-Authors: Nina Morrell, Kate M Johnson, Corey E Tarwater, Peter ArceseAbstract:Individual variation in nest defense behaviour is common in altricial birds, but despite clear predictions about why such variation exists, there is no consensus on its causes. We tested for an influence of five predictors of individual variation in nest defense behaviour, including time of season, offspring age, parental age and sex, and clutch size in a well-studied Song Sparrow (Melospiza melodia (A. Wilson, 1810)) population. We recorded parental responses to a standardized human approach and used model selection to assess support for each predictor. Parents tended to approach observers less closely and alarm-call less as the breeding season progressed, indicating a modest seasonal decline in parental nest defense, which is consistent with the hypothesis that the reproductive value of offspring influenced parental defense behaviour. Clutch size effect estimates were insignificant, but it was weakly supported as a predictor of nest defense, which is expected if parental investment in defense and curren...
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distinguishing individual quality from habitat preference and quality in a territorial passerine
Ecology, 2014Co-Authors: Ryan R Germain, Peter ArceseAbstract:Theory predicts that animals breeding in heterogeneous landscapes preferentially occupy habitats likely to maximize individual fitness, but identifying those habitats has proved problematic. Many studies develop metrics of habitat quality linked to site-specific reproductive output measured in successive years, but few separate the independent effects of individual “intrinsic quality” from those due solely to the attributes of the habitats themselves. In many populations, processes such as competitive territory defense, longevity, site-fidelity, and variation in breeding density and territory size over time have the potential to limit the degree to which individual and habitat quality will be positively related in nature. However, the effects of these processes on estimates of habitat or site-specific reproductive output have not been thoroughly investigated. We show that, in an insular population of Song Sparrows (Melospiza melodia), females nested preferentially in breeding sites with high mean reproduc...
Lukas F Keller - One of the best experts on this subject based on the ideXlab platform.
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a microsatellite based linkage map for song sparrows Melospiza melodia
Molecular Ecology Resources, 2015Co-Authors: Pirmin Nietlisbach, Lukas F Keller, Glauco Camenisch, Thomas Bucher, Jon Slate, Erik PostmaAbstract:Although linkage maps are important tools in evolutionary biology, their availability for wild populations is limited. The population of song sparrows ( Melospiza melodia) on Mandarte Island, Canada, is among the more intensively studied wild animal populations. Its long-term pedigree data, together with extensive genetic sampling, have allowed the study of a range of questions in evolutionary biology and ecology. However, the availability of genetic markers has been limited. We here describe 191 new microsatellite loci, including 160 high-quality polymorphic autosomal, 7 Z-linked and 1 W-linked markers. We used these markers to construct a linkage map for song sparrows with a total sex-averaged map length of 1731 cM and covering 35 linkage groups, and hence, these markers cover most of the 38–40 chromosomes. Female and male map lengths did not differ significantly. We then bioinformatically mapped these loci to the zebra finch ( Taeniopygia guttata) genome and found that linkage groups were conserved between song sparrows and zebra finches. Compared to the zebra finch, marker order within small linkage groups was well conserved, whereas the larger linkage groups showed some intrachromosomal rearrangements. Finally, we show that as expected, recombination frequency between linked loci explained the majority of variation in gametic phase disequilibrium. Yet, there was substantial overlap in gametic phase disequilibrium between pairs of linked and unlinked loci. Given that the microsatellites described here lie on 35 of the 38–40 chromosomes, these markers will be useful for studies in this species, as well as for comparative genomics studies with other species.
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extra pair paternity and the variance in male fitness in song sparrows Melospiza melodia
Evolution, 2012Co-Authors: Christophe Lebigre, Peter Arcese, Lukas F Keller, Rebecca J Sardell, Jane M ReidAbstract:The variance in fitness across population members can influence major evolutionary processes. In socially monogamous but genetically polygynandrous species, extra-pair paternity (EPP) is widely hypothesized to increase the variance in male fitness compared to that arising given the socially monogamous mating system. This hypothesis has not been definitively tested because comprehensive data describing males' apparent (social) and realized (genetic) fitness have been lacking. We used 16 years of comprehensive social and genetic paternity data for an entire free-living song sparrow (Melospiza melodia) population to quantify and compare variances in male apparent and realized fitness, and to quantify the contribution of the variances in within-pair reproductive success (WPRS) and extra-pair reproductive success (EPRS) and their covariance to the variance in realized fitness. Overall, EPP increased the variance in male fitness by only 0-27% across different fitness and variance measures. This relatively small effect reflected the presence of socially unpaired males with zero apparent and low realized fitness, small covariance between WPRS and EPRS, and large variance in WPRS that was relatively unaffected by EPP. Therefore, although EPP altered individual males' contributions to future generations, its impact on population-level parameters such as the opportunity for selection and effective population size was limited.
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are there indirect fitness benefits of female extra pair reproduction lifetime reproductive success of within pair and extra pair offspring
The American Naturalist, 2012Co-Authors: Rebecca J Sardell, Peter Arcese, Lukas F Keller, Jane M ReidAbstract:AbstractThe forces driving extra-pair reproduction by socially monogamous females, and the resulting genetic polyandry, remain unclear. A testable prediction of the hypothesis that extra-pair reproduction partly reflects indirect selection on females is that extra-pair young (EPY) will be fitter than their within-pair young (WPY) maternal half-siblings. This prediction has not been comprehensively tested in a wild population, requiring data on the lifetime reproductive success (LRS) of maternal half-sib EPY and WPY. We used 17 years of genetic parentage data from song sparrows, Melospiza melodia, to compare the LRS of hatched EPY and WPY maternal half-siblings measured as their lifetime number of hatched offspring, recruited offspring, and hatched grandoffspring. EPY hatchlings were not significantly fitter than WPY hatchlings for any of three measures of LRS. Furthermore, opposite to prediction, EPY hatchlings tended to have lower LRS than their maternal half-sibling WPY hatchlings on average. EPY also t...
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heritability of female extra pair paternity rate in song sparrows Melospiza melodia
Proceedings of The Royal Society B: Biological Sciences, 2011Co-Authors: Jane M Reid, Peter Arcese, Rebecca J Sardell, Lukas F KellerAbstract:The forces driving the evolution of extra-pair reproduction in socially monogamous animals remain widely debated and unresolved. One key hypothesis is that female extra-pair reproduction evolves through indirect genetic benefits, reflecting increased additive genetic value of extra-pair offspring. Such evolution requires that a female's propensity to produce offspring that are sired by an extra-pair male is heritable. However, additive genetic variance and heritability in female extra-pair paternity (EPP) rate have not been quantified, precluding accurate estimation of the force of indirect selection. Sixteen years of comprehensive paternity and pedigree data from socially monogamous but genetically polygynandrous song sparrows (Melospiza melodia) showed significant additive genetic variance and heritability in the proportion of a female's offspring that was sired by an extra-pair male, constituting major components of the genetic architecture required for extra-pair reproduction to evolve through indirect additive genetic benefits. However, estimated heritabilities were moderately small (0.12 and 0.18 on the observed and underlying latent scales, respectively). The force of selection on extra-pair reproduction through indirect additive genetic benefits may consequently be relatively weak. However, the additive genetic variance and non-zero heritability observed in female EPP rate allow for multiple further genetic mechanisms to drive and constrain mating system evolution.
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additive genetic variance heritability and inbreeding depression in male extra pair reproductive success
The American Naturalist, 2011Co-Authors: Jane M Reid, Peter Arcese, Rebecca J Sardell, Lukas F KellerAbstract:AbstractThe hypothesis that female extra-pair reproduction in socially monogamous animals reflects indirect genetic benefits requires that there be additive and/or nonadditive genetic variance in fitness. However, the specific hypotheses that male extra-pair reproductive success (EPRS) shows additive genetic variance (VA), heritability (h2), or inbreeding depression, and hence that females could acquire indirect genetic benefits through increased EPRS of sons, have not been explicitly tested. We used comprehensive genetic pedigree data from song sparrows (Melospiza melodia) to estimate VA, h2, and inbreeding depression in the number of extra-pair offspring a male sired per year and the probability that a male would sire any extra-pair offspring per year. Inbreeding depression was substantial: more inbred males sired fewer extra-pair offspring and were less likely to sire any extra-pair offspring. In contrast, estimates of VA and h2 were close to 0, although 95% credible intervals were relatively wide. The...
Jane M Reid - One of the best experts on this subject based on the ideXlab platform.
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the consequences of polyandry for sibship structures distributions of relationships and relatedness and potential for inbreeding in a wild population
The American Naturalist, 2018Co-Authors: Ryan R Germain, Peter Arcese, Jane M ReidAbstract:AbstractThe evolutionary benefits of simultaneous polyandry (female multiple mating within a single reproductive event) remain elusive. One potential benefit could arise if polyandry alters sibship structures and consequent relationships and relatedness among females’ descendants, thereby intrinsically reducing future inbreeding risk (the indirect inbreeding avoidance hypothesis). However such effects have not been quantified in naturally complex mating systems that also encompass iteroparity, overlapping generations, sequential polyandry, and polygyny. We used long-term social and genetic pedigree data from song sparrows (Melospiza melodia) to quantify cross-generational consequences of simultaneous polyandry for offspring sibship structures and distributions of relationships and relatedness among possible mates. Simultaneous polyandry decreased full sibships and increased half-sibships, on average, but such effects varied among females and were smaller than would occur in the absence of sequential polya...
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offspring fitness varies with parental extra pair status in song sparrows Melospiza melodia
Proceedings of The Royal Society B: Biological Sciences, 2012Co-Authors: Rebecca J Sardell, Peter Arcese, Jane M ReidAbstract:Numerous studies have tested for indirect selection on female extra-pair reproduction (EPR) by quantifying whether extra-pair young (EPY) are fitter than their within-pair young (WPY) maternal half-siblings. In contrast, the hypothesis that offspring of EPY and WPY (rather than the EPY and WPY themselves) differ in fitness has not been tested, even though inter-generational effects of parental extra-pair status on offspring fitness could alter the magnitude and direction of indirect selection on EPR. We tested whether offspring of EPY song sparrows, Melospiza melodia, were more likely to recruit or produce hatched or recruited offspring over their lifetimes than offspring of WPY. Hatchlings with one or two EPY parents were more likely to recruit and produce hatched offspring than hatchlings with two WPY parents. Furthermore, these relationships differed between maternal versus paternal extra-pair status. Hatchlings with EPY fathers were more likely to recruit and produce offspring than hatchlings with WPY fathers. In contrast, hatchlings with EPY mothers were as likely to recruit as hatchlings with WPY mothers and tended to be less likely to produce recruited offspring. Depending on the causal genetic and environmental mechanisms, such conflicting inter-generational relationships between parental extra-pair status and offspring fitness could substantially influence the evolutionary dynamics of EPR.
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extra pair paternity and the variance in male fitness in song sparrows Melospiza melodia
Evolution, 2012Co-Authors: Christophe Lebigre, Peter Arcese, Lukas F Keller, Rebecca J Sardell, Jane M ReidAbstract:The variance in fitness across population members can influence major evolutionary processes. In socially monogamous but genetically polygynandrous species, extra-pair paternity (EPP) is widely hypothesized to increase the variance in male fitness compared to that arising given the socially monogamous mating system. This hypothesis has not been definitively tested because comprehensive data describing males' apparent (social) and realized (genetic) fitness have been lacking. We used 16 years of comprehensive social and genetic paternity data for an entire free-living song sparrow (Melospiza melodia) population to quantify and compare variances in male apparent and realized fitness, and to quantify the contribution of the variances in within-pair reproductive success (WPRS) and extra-pair reproductive success (EPRS) and their covariance to the variance in realized fitness. Overall, EPP increased the variance in male fitness by only 0-27% across different fitness and variance measures. This relatively small effect reflected the presence of socially unpaired males with zero apparent and low realized fitness, small covariance between WPRS and EPRS, and large variance in WPRS that was relatively unaffected by EPP. Therefore, although EPP altered individual males' contributions to future generations, its impact on population-level parameters such as the opportunity for selection and effective population size was limited.
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are there indirect fitness benefits of female extra pair reproduction lifetime reproductive success of within pair and extra pair offspring
The American Naturalist, 2012Co-Authors: Rebecca J Sardell, Peter Arcese, Lukas F Keller, Jane M ReidAbstract:AbstractThe forces driving extra-pair reproduction by socially monogamous females, and the resulting genetic polyandry, remain unclear. A testable prediction of the hypothesis that extra-pair reproduction partly reflects indirect selection on females is that extra-pair young (EPY) will be fitter than their within-pair young (WPY) maternal half-siblings. This prediction has not been comprehensively tested in a wild population, requiring data on the lifetime reproductive success (LRS) of maternal half-sib EPY and WPY. We used 17 years of genetic parentage data from song sparrows, Melospiza melodia, to compare the LRS of hatched EPY and WPY maternal half-siblings measured as their lifetime number of hatched offspring, recruited offspring, and hatched grandoffspring. EPY hatchlings were not significantly fitter than WPY hatchlings for any of three measures of LRS. Furthermore, opposite to prediction, EPY hatchlings tended to have lower LRS than their maternal half-sibling WPY hatchlings on average. EPY also t...
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heritability of female extra pair paternity rate in song sparrows Melospiza melodia
Proceedings of The Royal Society B: Biological Sciences, 2011Co-Authors: Jane M Reid, Peter Arcese, Rebecca J Sardell, Lukas F KellerAbstract:The forces driving the evolution of extra-pair reproduction in socially monogamous animals remain widely debated and unresolved. One key hypothesis is that female extra-pair reproduction evolves through indirect genetic benefits, reflecting increased additive genetic value of extra-pair offspring. Such evolution requires that a female's propensity to produce offspring that are sired by an extra-pair male is heritable. However, additive genetic variance and heritability in female extra-pair paternity (EPP) rate have not been quantified, precluding accurate estimation of the force of indirect selection. Sixteen years of comprehensive paternity and pedigree data from socially monogamous but genetically polygynandrous song sparrows (Melospiza melodia) showed significant additive genetic variance and heritability in the proportion of a female's offspring that was sired by an extra-pair male, constituting major components of the genetic architecture required for extra-pair reproduction to evolve through indirect additive genetic benefits. However, estimated heritabilities were moderately small (0.12 and 0.18 on the observed and underlying latent scales, respectively). The force of selection on extra-pair reproduction through indirect additive genetic benefits may consequently be relatively weak. However, the additive genetic variance and non-zero heritability observed in female EPP rate allow for multiple further genetic mechanisms to drive and constrain mating system evolution.
Stephen Nowicki - One of the best experts on this subject based on the ideXlab platform.
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potential trade off between vocal ornamentation and spatial ability in a songbird
Biology Letters, 2013Co-Authors: Kendra B Sewall, Susan Peters, Jill A Soha, Stephen NowickiAbstract:Bird song is hypothesized to be a reliable indicator of cognition because it depends on brain structure and function. Song features have been found to correlate positively with measures of cognition, but the relationship between song and cognition is complicated because not all cognitive abilities are themselves positively correlated. If cognition is not a unitary trait, developmental constraints on brain growth could generate trade-offs between some aspects of cognition and song. To further clarify the relationship between song and cognition in song sparrows (Melospiza melodia), we examined repertoire size and performance on a spatial task. We found an inverse relationship between repertoire size and speed of spatial learning and suggest that a developmental trade-off between the hippocampus and song control nuclei could be responsible for this relationship. By attending to male song, females may learn about a suite of cognitive abilities; this study suggests that females may glean information about a male's cognitive weaknesses as well as his strengths.
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partial song matching in an eastern population of song sparrows Melospiza melodia
Animal Behaviour, 2005Co-Authors: Rindy C Anderson, William A Searcy, Stephen NowickiAbstract:One hypothesis for the function of vocal repertoires in songbirds is that singing multiple song types facilitates song matching, a behaviour in which one male replies to a rival's song with a song of the same type. In eastern populations of song sparrows, low levels of whole song sharing restrict opportunities for matching of entire song types. A male in this population might still match a neighbour by replying with a partially shared song (i.e. a song that contains one or more phrases in common with the neighbour's song). We tested for partial matching in a Pennsylvania population using playback of three categories of song: self song (allowing a full match), stranger song (a control allowing no match) and hybrid self/stranger song (allowing a partial match). We also tested the hypothesis that matching is a directed signal of aggressive intentions by comparing subjects' approach distances between trials in which they did and did not match. Males in our study matched in response to both self song (21 of 39 trials) and hybrid song (23 of 40 trials) at levels significantly greater than expected based on control trials (5 of 40 trials). Males that performed a partial match to a hybrid song approached the speaker more closely than males that did not match, consistent with the hypothesis that partial matching is a directed signal of aggression. Self song matching did not predict approach as successfully.
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vocal performance influences female response to male bird song an experimental test
Behavioral Ecology, 2004Co-Authors: Barbara Ballentine, Jeremy Hyman, Stephen NowickiAbstract:Female songbirds are thought to assess males based on aspects of song, such as repertoire size or amount of singing, that could potentially provide information about male quality. A relatively unexplored aspect of song that also might serve as an assessment signal is a male’s ability to perform physically challenging songs. Trilled songs, such as those produced by swamp sparrows (Melospiza georgiana), present males with a performance challenge because trills require rapid and precise coordination of vocal tract movements, resulting in a trade-off between trill rate and frequency bandwidth. This trade-off defines a constraint on song production observed as a triangular distribution in acoustic space of trill rate by frequency bandwidth, with an upper boundary that represents a performance limit. Given this background on song production constraints, we are able to identify a priori which songs are performed with a higher degree of proficiency and, thus, which songs should be more attractive to females. We determined the performance limit for a population of swamp sparrows and measured how well individual males performed songs relative to this limit (‘‘vocal performance’’). We then compared female solicitation responses to high-performance versus lowperformance versions of the same song type produced by different males. Females displayed significantly more to highperformance songs than to low-performance songs, supporting the hypothesis that females use vocal performance to assess males. Key words: bird song, female choice, indicator mechanism, Melospiza georgiana, motor constraint, sexual selection, vocal performance. [Behav Ecol 15:163–168 (2004)]
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Calibration of song learning targets during vocal ontogeny in swamp sparrows, Melospiza georgiana
Animal Behaviour, 2004Co-Authors: Jeffrey Podos, Susan Peters, Stephen NowickiAbstract:Song learning in songbirds often includes an extended sensorimotor phase, in which birds gradually refine their vocal output to produce accurate copies of previously memorized song models. Increasing accuracy of song model reproduction during this phase occurs as birds refine the neural substrates that underlie vocal control, and as they develop proficiency with the vocal apparatus. We here test the hypothesis that sensorimotor learning also provides birds with an opportunity to calibrate their vocal learning targets, in the event that a bird's own vocal proficiency differs from that required to successfully reproduce song models to which it is exposed. We tutored hand-reared male swamp sparrows with song models that we manipulated to vary in how challenging they would be to reproduce, and then tracked patterns of song development. The calibration hypothesis was supported by two lines of evidence. First, we found that copies of manipulated models underwent comparatively large-scale modifications in syntax and note composition over development, in directions consistent with expectations about motor proficiency relative to the structure of learned models. Second, we found that birds tended to retain selectively, in their crystallized repertoires, song types that appeared to be comparatively easy to produce. Our results are consistent with an ‘active’ model of song learning, and also suggest a specific mechanism by which learning can act as a creative or a stabilizing force in song evolution.
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geographic variation in the organization of song sparrow repertoires
The Auk, 2000Co-Authors: Susan Peters, William A Searcy, M. I.c.h.a.e.l.d. Beecher, Stephen NowickiAbstract:Abstract We asked whether geographic variation exists in the complexity of song repertoires in Song Sparrows (Melospiza melodia) by quantitatively comparing four measures of repertoire organization across four geographically distant populations: (1) repertoire size (the number of distinct song types), (2) the number of “minimal units of production” per repertoire, (3) mean similarity among variants of the same song type (“within-type” similarity), and (4) mean similarity among song types in a repertoire (“between-type” similarity). We found significant geographic differences among populations in three of these four measures, with mean similarity among song types being the exception. In general, relatively sedentary populations in North Carolina and Washington were more similar to each other than to migratory populations in Pennsylvania and Maine. Contrary to our expectation based on prior interspecific analyses of variation in repertoire complexity, the relatively sedentary populations in our sample had m...
John C. Wingfield - One of the best experts on this subject based on the ideXlab platform.
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the presence of water influences reproductive function in the song sparrow Melospiza melodia morphna
General and Comparative Endocrinology, 2012Co-Authors: John C. Wingfield, Kimberley Sullivan, Jessica Jaxionharm, Simone MeddleAbstract:Abstract Cumulative evidence indicates that song sparrows, Melospiza melodia morphna, of western Washington State prefer territories close to water. Densities of territories were higher within 50 m of open water and analysis of stomach contents revealed aquatic organisms. An unusually dry period (less open water) in May and June 1997 had no effect on latency of territorial males to respond to a simulated territorial intrusion (STI), but the number of songs and closest approach to the decoy were lower than those recorded in June 1988 (no major dry periods). A laboratory experiment was conducted in which males and females were exposed to long days to stimulate reproductive development. One group received a bath with water daily and the other group received a dry bath (both groups had ad libitum access to drinking water through a glass tube). Birds with a dry bath tended to show reduced photoperiodically-induced gonadal growth compared with birds that had access to water in the bath. Plasma levels of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) increased following photostimulation in all groups. However, LH levels were higher in females with access to water. There were no differences in hormone levels in any of the other groups. Taken together these novel data indicate that presence and access to open water could be an important environmental cue for song sparrows in western Washington State. Implications for global climate change and droughts are suggested.
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influences of weather on reproductive function in male song sparrows Melospiza melodia
Journal of Zoology, 2009Co-Authors: John C. WingfieldAbstract:Prolonged and severe periods of inclement weather can retard gonadal development in early spring or disrupt the breeding cycle in summer. Previous investigations on the endocrine responses of free-living avian species to storms have been restricted almost entirely to males. This communication presents the endocrine responses of free-living female Song sparrows, Melospiza melodia, during gonadal recrudescence after a severe winter, and during storms in early spring and summer. As in males, gonadal recrudescence was delayed by the severe winter weather, and this effect was exacerbated by an aseasonal snow storm in early spring. Unlike males, female Song sparrows did appear to be stressed by this snow storm, since body mass and fat deposit decreased, and plasma levels of corticosterone increased. A second storm in early summer did not, however, prove to be stressful to females, although males were apparently stressed by the same storm. At the time the early summer storm occurred, young had been fledged and were being fed mostly by the male. Females begin preparing for a second clutch of eggs and do not feed fledglings to the same extent as males. Thus it is possible that males are stressed by storms at this time, because they are feeding several young as well as themselves during a period of reduced availability of food, whereas females are feeding themselves only. These data suggest that, not only do the endocrine responses to inclement weather vary in relation to stage in the reproductive cycle when storms strike, but also that there are sex differences in those responses.
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Seasonal modulation of sickness behavior in free-living northwestern song sparrows (Melospiza melodia morphna)
Journal of Experimental Biology, 2006Co-Authors: Noah T Owen-ashley, John C. WingfieldAbstract:A variety of vertebrate species modulate immune function on a seasonal basis to cope with seasonal energy deficits and competing life-history demands, such as reproduction. Most studies to date have focused upon seasonal variation of cellular and humoral immunity, while neglecting behavioral responses to infection. These behavioral strategies are collectively termed sickness behaviors and are hypothesized to divert energy away from normal activities to combat and overcome infection. Sickness behavior can be triggered experimentally by injecting bacterial lipopolysaccharide (LPS). In this study, we provide the first evidence for seasonal modulation of sickness behavior in a free-living animal. Male song sparrows of western Washington state (Melospiza melodia morphna) are sedentary and territorial year round, except for a brief time during molt. Treatment with LPS decreased territorial aggressive behavior of males in the winter (nonbreeding), but not in the spring (breeding). Subjects were recaptured approx. 25 h after treatment. Recaptured LPS males in the winter lost more body mass than saline-injected controls while LPS males in the spring did not. These data indicate that birds in breeding condition were relatively insensitive to the effects of LPS. On a proximate level, suppression of sickness behavior during breeding is likely mediated by seasonal differences in energy allocation, as wintering sparrows were significantly heavier and had larger subcutaneous fat reserves and lower baseline corticosterone levels than breeding birds. Ultimately, suppression of sickness behavior may represent an allocation strategy to balance current reproductive opportunities with the life-history costs of self-defense.
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androgens and the immunocompetence handicap hypothesis unraveling direct and indirect pathways of immunosuppression in song sparrows
The American Naturalist, 2004Co-Authors: Noah T Owenashley, Dennis Hasselquist, John C. WingfieldAbstract:Abstract: The immunocompetence handicap hypothesis proposes that testosterone (T)‐dependent sexual signals are honest indicators of male health or genetic quality because only high‐quality males are able to withstand the obligate effects of T‐induced immunosuppression. In birds, the basic assumption that T suppresses immune function is equivocal, and the physiological mechanisms underlying T‐induced immunosuppression remain to be investigated. We explored the proximate pathways of T‐induced immunosuppression in song sparrows (Melospiza melodia) by treating captive nonbreeding males with different androgens and measuring several components of acquired immune function. Males implanted with T suppressed cell‐mediated and humoral immune responses compared to males implanted with 5∝‐dihydrotestosterone (DHT), dehydroepiandrosterone, or control (empty) implants. Furthermore, T treatment increased plasma levels of corticosterone and decreased body mass and fat stores in relation to other treatments. The failure ...
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regulation of territorial behavior in the sedentary song sparrow Melospiza melodia morphna
Hormones and Behavior, 1994Co-Authors: John C. WingfieldAbstract:Male song sparrows (Melospiza melodia morphna) of western Washington State show year-round territoriality. Although territorial aggression during the breeding season was accompanied by high circulating levels of luteinizing hormone (LH) and testosterone (T), similar aggression in the non-breeding season occurred when gonadal hormone levels were basal. Experimental removal of territorial males in autumn resulted in new males taking over the territory within a few days. These males had basal levels of LH and T despite establishing a new territory and the accompanying high level of aggression. There was also no difference in plasma levels of corticosterone in replacement versus established territorial males suggesting that social stress was not a factor. To test the possibility that low levels of gonadal steroids, or potentially some gonadal hormone not measured here, might regulate territorial aggression in the non-breeding season, free-living male song sparrows were castrated in early autumn and their aggressive territorial behavior was quantified by a simulated territorial intrusion (STI). Castrates showed the same aggressive responses to STI as controls indicating that establishment and maintenance of a territory was not dependent upon hormones of gonadal origin. Castrated males retained territories throughout the autumn and winter and even into the following breeding season. Further experiments were conducted to establish a role, if any, for T in territorial behavior in this species. During the breeding season when males had high levels of T, the responses to STI continued after the stimuli (caged conspecific male and tape-recorded songs) were withdrawn. Some males continued to patrol the territory and sang for long periods after STI. In contrast, males exposed to STI in autumn showed a strong aggressive response during the challenge, but then territorial aggression abated rapidly when the stimuli were withdrawn. Implants of T into males in autumn reinstated the high level of aggression after withdrawal of STI in a manner similar to that seen during the breeding season. These data suggest that in M. m. morphna T does not activate territorial aggression per se, but may increase the intensity of an aggressive response to STI, and persistence of the behavior after STI is withdrawn.