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...Here, we focus on sexual selection, which since its inception has largely been viewed as a subset of natural selection driven by competition overmates and subsequent variance in reproductive success (=-=Andersson 1994-=-). Sexual selection can operate via female choice (intersexual) and/or male–male competition (intrasexual) and is well established as the primary mechanism through which conspicuous dimorphism in seco...

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...ir fertilizations (Webster et al. 1995). Given that ecological constraints (i.e., spatial and temporal distribution ofmates) have long been thought to impose limits on the degree of sexual selection (=-=Emlen and Oring 1977-=-), here we ask how that relationship is modulated by anthropogenic habitat change. Specifically, we use a two-year study of ecology and paternity in the gray catbird (Dumatella carolinensis) to quanti...

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...lity of exclusion for the paternity analyses (Pet = 0.99). To minimize assigning offspring that match males by chance, we used the maximum-likelihood approach available in the program CERVUS v. 3.03 (=-=Marshall et al. 1998-=-; Kalinowski et al. 2007). Our preliminary simulations used 10,000 cycles and the true typing error (0.015), measured via known mother–offspring comparisons. We used females observed at the nest as pu...

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...onal 27.3% of the variance (eigenvalue = 1.09). Both axes were used as predictors in analyses. Second, we calculated linear selection differentials (β) for each habitat using regression coefficients (=-=Lande and Arnold 1983-=-). To ensure our selection differentialswere comparable to previouswork,we used standardized trait values (mean = 0, unit variance) and relative reproductive success (number of offspring sired/populat...

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...ed landscapes (Smith and Bernatchez 2008). To date, urban ecology research has primarily focused on changes in community structure and the impacts of anthropogenic activities on ecological processes (=-=McDonnell and Pickett 1990-=-; Grimm et al. 2008). Moreover, while our 976 c© 2012 The Authors. Published by Blackwell Publishing Ltd. This is an open access article under the terms of the Creative Commons Attribution Non Commerc...

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...the paternity analyses (Pet = 0.99). To minimize assigning offspring that match males by chance, we used the maximum-likelihood approach available in the program CERVUS v. 3.03 (Marshall et al. 1998; =-=Kalinowski et al. 2007-=-). Our preliminary simulations used 10,000 cycles and the true typing error (0.015), measured via known mother–offspring comparisons. We used females observed at the nest as putative mothers unless th...

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... stems from evidence that social and genetic mating systems are often incongruent, especially in birds, with some males siring offspring in broods raised by other males (Hasselquist and Sherman 2001; =-=Griffith et al. 2002-=-). The offspring resulting from these extra-pair fertilizations could potentially have considerable effect upon variance in mating success and subsequent sexual selection, since they increase the succ...

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...ensity Since the discovery that a substantial number of socially monogamous species exhibit sexual promiscuity (extra-pair paternity), biologists have put forward adaptive (Westneat and Sherman 1997; =-=Petrie and Kempenaers 1998-=-; Griffith et al. 2002) and nonadaptive hypotheses (Arnqvist and Kirkpatrick 2005; Forstmeier et al. 2011) to explain intra- and interspecific variation in EPP rates. To date, the majority of work at ...

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...ir paternity and breeding density Since the discovery that a substantial number of socially monogamous species exhibit sexual promiscuity (extra-pair paternity), biologists have put forward adaptive (=-=Westneat and Sherman 1997-=-; Petrie and Kempenaers 1998; Griffith et al. 2002) and nonadaptive hypotheses (Arnqvist and Kirkpatrick 2005; Forstmeier et al. 2011) to explain intra- and interspecific variation in EPP rates. To da...

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...ized variance in male fertilization success followingWebster et al. (1995). The standardized variance divided by the square of mean success is a measure of the maximum possible strength of selection (=-=Arnold and Wade 1984-=-a). We first calculated variance in apparent male success (var TA, the number of social young produced) and variance in realized reproductive success (var T , the number of offspring sired based on mo...

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...ve opportunities. These results are also consistentwith comparative evidence that density can play an important role in explaining EPP variation at the intraspecific level (Westneat and Sherman 1997; =-=Moller and Ninni 1998-=-; Griffith et al. 2002). Although we observed a relationship between density and EPP in our catbird populations, the relationship need not be causal if other factors that impact EPP rates and breeding...

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...Garant et al. 2007; Kasumovic et al. 2008; Parker et al. 2011). Quantifying these relationships is particularly pertinent given recent evidence that human activities can alter evolutionary processes (=-=Shochat et al. 2006-=-; Smith andBernatchez 2008).Of particular utility will be environment-specific estimates of selection that can quantitatively assess the spatial scale of adaptation and the mechanistic role of ecologi...

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...y and temporally (Gosden and Svensson 2008; Cornwallis and Uller 2010). Traditionally, male reproductive success was measured as the number of social mates a male acquires during the breeding season (=-=Webster et al. 1995-=-;Whittingham andDunn 2005), yet additional sources of variation can arise from biased operational sex ratios in which not all males obtain partners (Price 1984; Dearborn et al. 2001) and from differen...

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...ased operational sex ratios in which not all males obtain partners (Price 1984; Dearborn et al. 2001) and from differences in female quality such that some females produce more offspring than others (=-=Kirkpatrick et al. 1990-=-). A third source of variation stems from evidence that social and genetic mating systems are often incongruent, especially in birds, with some males siring offspring in broods raised by other males (...

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...Moreover, while there is little doubt that EPP can increase the opportunity for sexual selection, the magnitude of its effect appears to vary significantly among species (Freeman-Gallant et al. 2005; =-=Whittingham and Dunn 2005-=-; Albrecht et al. 2007; Dolan et al. 2007). In particular, estimating the effect of extra-pair success on the opportunity for sexual selection may be sensitive to population sampling (i.e., the propor...

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...nt vs. relative) can bemisleading about the effect of extra-pair paternity on the opportunity for sexual selection (Webster et al. 2007), we calculated a Batemans gradient (sexual selection gradient; =-=Arnold 1994-=-) by regression the number ofmates againstmale reproductive success. The slope of this relationship provides a measure of the intensity of sexual selection arising from mating with additional females ...

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...ding density environments. In contrast, lower density environments likely experienced relaxed sexual selection because of limited mate choice opportunities and mate acquisition (Candolin et al. 2007; =-=Candolin and Heuschele 2008-=-). Other recent empirical work has hypothesized that localized density- and frequencydependent interactions between the sexes may emerge as a primary driver of spatial variation in sexual selection (G...

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...natchez 2008). To date, urban ecology research has primarily focused on changes in community structure and the impacts of anthropogenic activities on ecological processes (McDonnell and Pickett 1990; =-=Grimm et al. 2008-=-). Moreover, while our 976 c© 2012 The Authors. Published by Blackwell Publishing Ltd. This is an open access article under the terms of the Creative Commons Attribution Non Commercial License, which ...

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...). A third source of variation stems from evidence that social and genetic mating systems are often incongruent, especially in birds, with some males siring offspring in broods raised by other males (=-=Hasselquist and Sherman 2001-=-; Griffith et al. 2002). The offspring resulting from these extra-pair fertilizations could potentially have considerable effect upon variance in mating success and subsequent sexual selection, since ...

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... utility will be environment-specific estimates of selection that can quantitatively assess the spatial scale of adaptation and the mechanistic role of ecological variation on evolutionary processes (=-=Svensson and Sinervo 2000-=-, 2004).Despite the fundamental importance of an ecological–evolutionary interplay and evidence that the environmental heterogeneity associated with anthropogenic habitat modification will affect the ...

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...res during the breeding season (Webster et al. 1995;Whittingham andDunn 2005), yet additional sources of variation can arise from biased operational sex ratios in which not all males obtain partners (=-=Price 1984-=-; Dearborn et al. 2001) and from differences in female quality such that some females produce more offspring than others (Kirkpatrick et al. 1990). A third source of variation stems from evidence that...

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...ner et al. 1999). Alternatively, extra-pair behavior may be constrained in urban landscapes because of the costs associated with seeking extra-pair mates (i.e., greater distances between territories; =-=Norris and Stutchbury 2001-=-). Regardless of the exact mechanism, individuals breeding in higher density environments experience higher mate encounter rates and are more likely to engage in extra-pair behaviors. Opportunity for ...

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...ma (Cimprich and Moore 1995). Throughout their range catbirds are found breeding in dense shrubs or vine tangles and are often associated with early seral stage successional habitats (Zimmerman 1963; =-=Peck and James 1987-=-). These habitat preferences make catbirds common residents in both the matrix and suburban parks, yet breeding density varies markedly among our study sites with the matrix having lower density than ...

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...ttle doubt that EPP can increase the opportunity for sexual selection, the magnitude of its effect appears to vary significantly among species (Freeman-Gallant et al. 2005; Whittingham and Dunn 2005; =-=Albrecht et al. 2007-=-; Dolan et al. 2007). In particular, estimating the effect of extra-pair success on the opportunity for sexual selection may be sensitive to population sampling (i.e., the proportion of sires sampled;...

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...ted with urban environments can result in behavioral modifications (Slabbekoorn and Peet 2003), morphological divergence (Yeh 2004; Smith et al. 2008), divergent mate choice and reproductive tactics (=-=Candolin et al. 2007-=-; Perlut et al. 2008), and changes in population genetic structure (Bjorklund et al. 2010). Despite these advances no study, to our knowledge, has quantified how human habitat modifications and the ec...

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...Arnold andWade 1984a), and recent evidence suggests that both the strength of selection and the expression of secondary sexual traits can vary both spatially and temporally (Gosden and Svensson 2008; =-=Cornwallis and Uller 2010-=-). Traditionally, male reproductive success was measured as the number of social mates a male acquires during the breeding season (Webster et al. 1995;Whittingham andDunn 2005), yet additional sources...

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...tial and temporal dynamics of selection (Kokko and Rankin 2006; Gosden and Svensson 2008). Thus far, results are mixed ranging from density having a strong impact on the strength of sexual selection (=-=Conner 1989-=-; Clutton-Brock et al. 1997; Bonenfant et al. 2003; Kasumovic et al. 2008; Lehtonen and Lindstrom 2008) to little or no effect (Head et al. 2008; Klug et al. 2010b). Our results show that male body si...

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... Whittingham and Dunn 2004). Moreover, while there is little doubt that EPP can increase the opportunity for sexual selection, the magnitude of its effect appears to vary significantly among species (=-=Freeman-Gallant et al. 2005-=-; Whittingham and Dunn 2005; Albrecht et al. 2007; Dolan et al. 2007). In particular, estimating the effect of extra-pair success on the opportunity for sexual selection may be sensitive to population...

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...oductive success (Price 1984; Andersson 1994). While traits under sexual selection vary widely among taxa, a number of studies have shown body size to be a target of sexual selection (Andersson 1994; =-=Gontard-Danek and Moller 1999-=-). Here, we report that body size was a predictor of a male’s relative reproductive success (WPY and EPY) for catbirds breeding in both matrix and park sites. While male body size is clearly related t...

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...s is fairly well established for some taxa (e.g., plants), our understanding of how environmental heterogeneity impacts phenotypic selection in most animal populations is limited (Garant et al. 2007; =-=Kasumovic et al. 2008-=-; Parker et al. 2011). Quantifying these relationships is particularly pertinent given recent evidence that human activities can alter evolutionary processes (Shochat et al. 2006; Smith andBernatchez ...

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...ter than one mismatch in which case the mother was assumed unknown. Offspring were assigned using both strict 95% and relaxed 80% confidence as well as a total evidence approach (Prodohl et al. 1998; =-=Webster et al. 2004-=-). Under all three scenarios, paternity was only assigned if the presumptive father matched the offspring at five or more loci. Using the total evidence approach, we assigned offspring only if other n...

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...ov(W , E) (Webster et al. 1995). Finally, given that comparisons of variance (apparent vs. relative) can bemisleading about the effect of extra-pair paternity on the opportunity for sexual selection (=-=Webster et al. 2007-=-), we calculated a Batemans gradient (sexual selection gradient; Arnold 1994) by regression the number ofmates againstmale reproductive success. The slope of this relationship provides a measure of th...

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...he breeding season (Webster et al. 1995;Whittingham andDunn 2005), yet additional sources of variation can arise from biased operational sex ratios in which not all males obtain partners (Price 1984; =-=Dearborn et al. 2001-=-) and from differences in female quality such that some females produce more offspring than others (Kirkpatrick et al. 1990). A third source of variation stems from evidence that social and genetic ma...

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...les of intra- versus intersexual selection on trait elaboration.On one hand, large body size could provide advantages duringmale–male competition contests as has been shown for red-winged blackbirds (=-=Searcy 1979-=-; Eckert and Weatherhead 1987). Alternatively, female preference for male size could evolve via direct phenotypic benefits in which larger males provide material advantages (e.g., territory quality an...

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...y (extra-pair paternity), biologists have put forward adaptive (Westneat and Sherman 1997; Petrie and Kempenaers 1998; Griffith et al. 2002) and nonadaptive hypotheses (Arnqvist and Kirkpatrick 2005; =-=Forstmeier et al. 2011-=-) to explain intra- and interspecific variation in EPP rates. To date, the majority of work at both taxonomic levels has focused on ecological factors that can impact the spatial and temporal availabi...

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...ix [SM] and suburban parks [SP]) that vary in habitat quality and breeding density. In particular, density has been shown to explain intraspecific variation in extrapair paternity (Gibbs et al. 1990; =-=Gowaty and Bridges 1991-=-; Lifjeld et al. 1991; Yezerinac et al. 1999; Stewart et al. 2010) and the strength of selection (Bonenfant et al. 2003; Kokko and Rankin 2006; Gosden and Svensson 2008). Overall this study aims to un...

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... having a strong impact on the strength of sexual selection (Conner 1989; Clutton-Brock et al. 1997; Bonenfant et al. 2003; Kasumovic et al. 2008; Lehtonen and Lindstrom 2008) to little or no effect (=-=Head et al. 2008-=-; Klug et al. 2010b). Our results show that male body size in gray catbirds was under the strongest selection in the highest breeding density environments. In contrast, lower density environments like...

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... 2003), morphological divergence (Yeh 2004; Smith et al. 2008), divergent mate choice and reproductive tactics (Candolin et al. 2007; Perlut et al. 2008), and changes in population genetic structure (=-=Bjorklund et al. 2010-=-). Despite these advances no study, to our knowledge, has quantified how human habitat modifications and the ecological factors associatedwith these changes affect the dynamics of selection on phenoty...

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...n increase the opportunity for sexual selection, the magnitude of its effect appears to vary significantly among species (Freeman-Gallant et al. 2005; Whittingham and Dunn 2005; Albrecht et al. 2007; =-=Dolan et al. 2007-=-). In particular, estimating the effect of extra-pair success on the opportunity for sexual selection may be sensitive to population sampling (i.e., the proportion of sires sampled; Freeman-Gallant et...

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... versus intersexual selection on trait elaboration.On one hand, large body size could provide advantages duringmale–male competition contests as has been shown for red-winged blackbirds (Searcy 1979; =-=Eckert and Weatherhead 1987-=-). Alternatively, female preference for male size could evolve via direct phenotypic benefits in which larger males provide material advantages (e.g., territory quality and/or parental care) or via th...

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...ss (Wade and Arnold 1980; Arnold andWade 1984a), and recent evidence suggests that both the strength of selection and the expression of secondary sexual traits can vary both spatially and temporally (=-=Gosden and Svensson 2008-=-; Cornwallis and Uller 2010). Traditionally, male reproductive success was measured as the number of social mates a male acquires during the breeding season (Webster et al. 1995;Whittingham andDunn 20...

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...08). Thus far, results are mixed ranging from density having a strong impact on the strength of sexual selection (Conner 1989; Clutton-Brock et al. 1997; Bonenfant et al. 2003; Kasumovic et al. 2008; =-=Lehtonen and Lindstrom 2008-=-) to little or no effect (Head et al. 2008; Klug et al. 2010b). Our results show that male body size in gray catbirds was under the strongest selection in the highest breeding density environments. In...

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... unless they had greater than one mismatch in which case the mother was assumed unknown. Offspring were assigned using both strict 95% and relaxed 80% confidence as well as a total evidence approach (=-=Prodohl et al. 1998-=-; Webster et al. 2004). Under all three scenarios, paternity was only assigned if the presumptive father matched the offspring at five or more loci. Using the total evidence approach, we assigned offs...

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...tance of an ecological–evolutionary interplay and evidence that the environmental heterogeneity associated with anthropogenic habitat modification will affect the direction and strength of selection (=-=Smith et al. 2008-=-), few studies have documented how selection varies for species that persist in human-dominated landscapes (Smith and Bernatchez 2008). To date, urban ecology research has primarily focused on changes...

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...eding density. In particular, density has been shown to explain intraspecific variation in extrapair paternity (Gibbs et al. 1990; Gowaty and Bridges 1991; Lifjeld et al. 1991; Yezerinac et al. 1999; =-=Stewart et al. 2010-=-) and the strength of selection (Bonenfant et al. 2003; Kokko and Rankin 2006; Gosden and Svensson 2008). Overall this study aims to understand how anthropogenic habitat modifications create a cascade...

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...volutionary processes is fairly well established for some taxa (e.g., plants), our understanding of how environmental heterogeneity impacts phenotypic selection in most animal populations is limited (=-=Garant et al. 2007-=-; Kasumovic et al. 2008; Parker et al. 2011). Quantifying these relationships is particularly pertinent given recent evidence that human activities can alter evolutionary processes (Shochat et al. 200...

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...ed for the largest portion of variance in male body size. 982 c© 2012 The Authors. Published by Blackwell Publishing Ltd. T. B. Ryder et al. Density-Dependent Sexual Selection in a Migratory Songbird =-=Townsend et al. 2011-=-). Overall, our results show that gray catbird populations breeding in the matrix and parks have moderate levels of extra-pair paternity (25% of broods, 13% of offspring). While we failed to find stat...

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... to explain intraspecific variation in extrapair paternity (Gibbs et al. 1990; Gowaty and Bridges 1991; Lifjeld et al. 1991; Yezerinac et al. 1999; Stewart et al. 2010) and the strength of selection (=-=Bonenfant et al. 2003-=-; Kokko and Rankin 2006; Gosden and Svensson 2008). Overall this study aims to understand how anthropogenic habitat modifications create a cascade of effects on ecological factors, reproductive strate...

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...using a Qiagen BioSprint 96 robotic system and DNeasy blood and tissue kit (Qiagen Inc., Valencia, CA, USA). We screened 16 microsatellite primers developed fromNorthernmockingbird,Mimus polyglottos (=-=Hughes and Deloach 1997-=-) and gray catbird (Cabe et al., unpubl. data) and optimized the six most polymorphic of these loci for genotyping. Polymerase chain reactions (PCRs) were run in 10 μL volumes consisting of 30 ng of g...

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... colored leg bands and an aluminum band from US Fish and Wildlife Service (USFWS).At the timeof capture a small blood sample (20–50 μL) was taken from the brachial vein and preserved in lysis buffer (=-=Longmire et al. 1988-=-) for paternity analyses. Detailed morphological measurements including wing, tail, tarsus (mm), and mass (g) were collected at four of the five sites (Delaware excluded) by a single measurer to minim...

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...ished for some taxa (e.g., plants), our understanding of how environmental heterogeneity impacts phenotypic selection in most animal populations is limited (Garant et al. 2007; Kasumovic et al. 2008; =-=Parker et al. 2011-=-). Quantifying these relationships is particularly pertinent given recent evidence that human activities can alter evolutionary processes (Shochat et al. 2006; Smith andBernatchez 2008).Of particular ...

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...tentially have considerable effect upon variance in mating success and subsequent sexual selection, since they increase the success of one male while simultaneously decreasing the success of another (=-=Westneat et al. 1990-=-). As such, the actual reproductive success of males in socially monogamous species is the combined total offspring sired from both within-pair and extra-pair fertilizations (Webster et al. 1995). Giv...

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...habitat quality and breeding density. In particular, density has been shown to explain intraspecific variation in extrapair paternity (Gibbs et al. 1990; Gowaty and Bridges 1991; Lifjeld et al. 1991; =-=Yezerinac et al. 1999-=-; Stewart et al. 2010) and the strength of selection (Bonenfant et al. 2003; Kokko and Rankin 2006; Gosden and Svensson 2008). Overall this study aims to understand how anthropogenic habitat modificat...

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...nd south to Panama (Cimprich and Moore 1995). Throughout their range catbirds are found breeding in dense shrubs or vine tangles and are often associated with early seral stage successional habitats (=-=Zimmerman 1963-=-; Peck and James 1987). These habitat preferences make catbirds common residents in both the matrix and suburban parks, yet breeding density varies markedly among our study sites with the matrix havin...

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...ized variance in male fertilization success followingWebster et al. (1995). The standardized variance divided by the square of mean success is a measure of the maximum possible strength of selection (=-=Arnold and Wade 1984-=-a). We first calculated variance in apparent male success (var TA, the number of social young produced) and variance in realized reproductive success (var T , the number of offspring sired based on mo...

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... medium-sized migratory passerine (ca. 35 g) bird in the family Mimidae that breed from Canada to the southeastern United States and winters along the Gulf coast to the Caribbean and south to Panama (=-=Cimprich and Moore 1995-=-). Throughout their range catbirds are found breeding in dense shrubs or vine tangles and are often associated with early seral stage successional habitats (Zimmerman 1963; Peck and James 1987). These...

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...r parental care) or via the indirect genetic coupling of preference and trait (e.g., Fisherian and indicator mechanisms; Andersson 1994). Regardless of the mechanism, body size is heritable in birds (=-=Garnett 1981-=-; Wiggins1989) such that selection for thismalephenotypewill yield larger offspring that may have a survival advantage in both environmental contexts. Ultimately, if large male body size affects viabi...

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... low density. While both habitat types occur within human-dominated landscapes, all of our study sites fell well within the range of expected variation in breeding density (e.g., 0.3 to >10 pairs/ha; =-=Harcus 1973-=-). Our results suggest that habitat type does not influence the strength of selection, yet the limited overlap in breeding density between park and matrix environments may have influenced our ability ...

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... average more reddish edging on the undertail coverts (Suthers and Suthers 1990). Although catbirds lack apparent sexual plumage signals they are known to exhibit sexual size dimorphism (Raynor 1979; =-=Lent 1990-=-), with males being approximately 3% larger than females in several morphological measures. We conducted this research from May to August in both 2008 and 2009 at five study sites (two SM sites and th...

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...s [SP]) that vary in habitat quality and breeding density. In particular, density has been shown to explain intraspecific variation in extrapair paternity (Gibbs et al. 1990; Gowaty and Bridges 1991; =-=Lifjeld et al. 1991-=-; Yezerinac et al. 1999; Stewart et al. 2010) and the strength of selection (Bonenfant et al. 2003; Kokko and Rankin 2006; Gosden and Svensson 2008). Overall this study aims to understand how anthropo...

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...males tend to average more reddish edging on the undertail coverts (Suthers and Suthers 1990). Although catbirds lack apparent sexual plumage signals they are known to exhibit sexual size dimorphism (=-=Raynor 1979-=-; Lent 1990), with males being approximately 3% larger than females in several morphological measures. We conducted this research from May to August in both 2008 and 2009 at five study sites (two SM s...

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...alyses. Fitness differentials were visualized by fitting relative fitness against traits of interest using a cubic splinemodel and smoothing parameter selected via generalized cross-validation (GCV) (=-=Schluter 1988-=-). Cubic splinemodels thatminimizedGCVwere fit using a generalized additive model in program R using the mgcv package (R Team 2008; Wickham 2009). The contour surface was estimated using a Loess-smoot...

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...wo separate instances (Johnson andBest 1982). Likemany other monogamous species, catbirds lack distinct plumage dimorphism although males tend to average more reddish edging on the undertail coverts (=-=Suthers and Suthers 1990-=-). Although catbirds lack apparent sexual plumage signals they are known to exhibit sexual size dimorphism (Raynor 1979; Lent 1990), with males being approximately 3% larger than females in several mo...