Multiple Signaling Functions Of Song In A Polymorphic Species With Alternative Reproductive Strategies

Vocal traits can be sexually selected to reflect male quality, but may also evolve to serve additional signaling functions. We used a long-term dataset to examine the signaling potential of song in dimorphic white-throated sparrows (Zonotrichia albicollis). We investigated whether song conveys multifaceted information about the vocalizing individual, including fitness, species identity, individual identity, and morph. We also evaluated whether song traits correlate differently with fitness in the two morphs, as the more promiscuous strategy of white, relative to tan, morph males might impose stronger sexual selection. Males with high song rates achieved higher lifetime reproductive success, and this pattern was driven by white morph males. In addition, males that sang songs with many notes survived longer, but this pattern was less robust. Thus, song traits reflect differences in fitness and may more strongly affect fitness in the white morph. Song frequency was unrelated to fitness, body size, or morph, but was individual specific and could signal individual identity. Songs of the two morphs displayed similar frequency ratios and bandwidths. However, tan morph males sang songs with longer first notes, fewer notes, and higher variability. Thus, song could be used in morph discrimination. Variation in frequency ratios between notes was low and could function in conspecific recognition, but pitch change dynamics did differ between four different song types observed. Our results support a multiple messages model for white-throated sparrow song, in which different song traits communicate discrete information about the vocalizing individual

Actuarial Senescence In A Dimorphic Bird: Different Rates Of Ageing In Morphs With Discrete Reproductive Strategies

It is often hypothesized that intra-sexual competition accelerates actuarial senescence, or the increase in mortality rates with age. However, an alternative hypothesis is that parental investment is more important to determining senescence rates. We used a unique model system, the white-throated sparrow (Zonotrichia albicollis), to study variation in actuarial senescence. In this species, genetically determined morphs display discrete mating strategies and disassortative pairing, providing an excellent opportunity to test the predictions of the above hypotheses. Compared to tan-striped males, white-striped males are more polygynous and aggressive, and less parental. Tan-striped females receive less parental support, and invest more into parental care than white-striped females, which are also more aggressive. Thus, higher senescence rates in males and white-striped birds would support the intra-sexual competition hypothesis, whereas higher senescence rates in females and tan-striped birds would support the parental investment hypothesis. White-striped males showed the lowest rate of actuarial senescence. Tan-striped females had the highest senescence rate, and tan-striped males and white-striped females showed intermediate, relatively equal rates. Thus, results were inconsistent with sexual selection and competitive strategies increasing senescence rates, and instead indicate that senescence may be accelerated by female-biased parental care, and lessened by sharing of parental duties

Data from: Developmental stress and telomere dynamics in a genetically polymorphic species

A central objective of evolutionary biology is understanding variation in life-history trajectories and aging rate, or senescence. Senescence can be affected by tradeoffs and behavioral strategies in adults, but may also be affected by developmental stress. Developmental stress can accelerate telomere degradation, with long-term longevity and fitness consequences. Little is known regarding whether variation in developmental stress and telomere dynamics contribute to patterns of senescence during adulthood. We investigated this question in the dimorphic white-throated sparrow (Zonotrichia albicollis), a species in which adults of the two morphs exhibit established differences in behavioral strategy and patterns of senescence, and also evaluated the relationship between oxidative stress and telomere length. Tan morph females, which exhibit high levels of unassisted parental care, display faster reproductive senescence than white females, and faster actuarial senescence than all of the other morph-sex classes. We hypothesized that high oxidative stress and telomere attrition in tan female nestlings could contribute to this pattern, since tan females are small and potentially at a competitive disadvantage even as nestlings. Nestlings that were smaller than nest mates had higher oxidative stress, and nestlings with high oxidative stress and fast growth rates displayed shorter telomeres. However, we found no consistent morph-sex differences in oxidative stress or telomere length. Results suggest that oxidative stress and fast growth contribute to developmental telomere attrition, with potential ramifications for adults, but that developmental oxidative stress and telomere dynamics do not account for morph-sex differences in senescence during adulthood

Breeding synchrony and extrapair paternity in a species with alternative reproductive strategies

Breeding synchrony may affect the tradeoff between pursuing multiple mates and avoiding paternity loss, translating into differences in the rate of extrapair paternity (EPP). However, diverse empirical relationships between breeding synchrony and EPP remain challenging to explain. We examined whether the relationship between breeding synchrony and EPP varied with male morph, age, body size, or breeding density in the white-throated sparrow Zonotrichia albicollis. In this species, males of two genetically determined morphs pursue alternative mating strategies. Breeding synchrony positively correlated with EPP within polygamous white morph males, which have high rates of EPP and cuckoldry, but was unrelated to EPP within tan morph males, which prioritize mate guarding and paternal care. As previously reported, males that gained EPP were primarily white males. Males gained EPP more often than expected by chance during their mate’s fertile period and on neighboring territories. Since extrapair copulation appears primarily male-driven in this species, these results indicate that white males focus extra-pair mating effort during periods of high synchrony and during their mates’ fertile periods, even at the expense of paternity loss within their own nests. Breeding density, male age, and male size did not modify the relationship between breeding synchrony and EPP. However, older white males had higher cuckoldry rates, perhaps reflecting declines in performance associated with senescence. Results suggest that, even within species, mating strategy may modify how breeding synchrony affects rates of EPP, with positive relationships manifest only within subsets of individuals that pursue a strategy of polygyny at the expense of paternity loss

Oxidative stress data for nestling white-throated sparrows

This data file contains levels of total antioxidant capacity (OXY), reactive oxygen metabolites (ROM), and oxidative stress (OS) measured in nestling white-throated sparrows (Zonotrichia albicollis). OS was calculated as: mM ROMs/mM TAC x 1000. Also provided are nestling morph (white (W) or tan (T)), nestling sex, day in the nestling stage, basic body measurements, growth rates, and the time and date of blood sampling

Telomere data for nestling white-throated sparrows

This data file contains relative telomere length (RTL) data for nestling white-throated sparrows. Also included in the file are total antioxidant capacity (OXY), reactive oxygen metabolite (ROM), and oxidative stress (OS) levels. OS levels were calculated as: mM ROMs/mM OXY x 1000. In addition, we list nestling morph (white (W) or tan (T)), nestling sex, and nestling age (in days). Note that only 5 and 6 day old nestlings were used in our analysis, whereas some nestlings in this dataset were either younger or older. Basic body measurements and time and date of sampling are also given, along with information regarding each nestling's size rank within the brood. The largest nestling received size rank 1, and so forth until the brood size was reached

Data from: Extrapair mating and the strength of sexual selection: insights from a polymorphic species

Extra-pair mating could drive sexual selection in socially monogamous species, but support for this hypothesis remains equivocal. We used lifetime fitness data and a unique model species, the dimorphic white-throated sparrow (Zonotrichia albicollis), to examine how extra-pair mating affects the potential for sexual selection. The morphs of this species employ distinct reproductive strategies, with white males pursuing extra-pair mating at higher rates than tan counterparts. Social and extra-pair mating is disassortative by morph, with paternity exchange occurring primarily between pairs composed of white males and tan females. We predicted stronger sexual selection as quantified by Bateman gradients and standardized variance in reproductive success in white compared to tan males. Furthermore, because males drive extra-pair mating, we predicted costs of multiple mating and a negative Bateman gradient in tan females. The Bateman gradient for lifetime reproductive success was larger in white than tan males, and extra-pair mating contributed more to the Bateman gradient for white males. However, the Bateman gradient was positive in tan females. White males had higher variance in annual reproductive success than tan males or females, but variance in lifetime reproductive success did not differ between the morphs or sexes. Moreover, extra-pair mating did not increase variance in male reproductive success relative to apparent patterns, and within-pair success accounted for much more variance than extra-pair success. Although extra-pair mating in white males increases Bateman gradients, and potential for sexual selection via mate numbers, these latter results call the overall importance of extra-pair mating in driving selection into question

White-throated sparrow birth and death years

This data package contains the datasets used to examine rates of actuarial senescence in the four morph-sex classes of the white-throated sparrow (Zonotrichia albicollis) in R package BaSTA. Three files total are required: (1) A birth-death year file, containing the birth and death years (unknown entered as 0) for all individuals included in the data set, (2) A survival matrix, with a line entered for each time an individual was re-sighted, (3) A covariate matrix, listing the sex and morph of each individual. This is the birth-death year file

WTSP Covariates

This file contains the datasets used to examine rates of actuarial senescence in the four morph-sex classes of the white-throated sparrow (Zonotrichia albicollis) in R package BaSTA. Three files total are required: (1) A birth-death year file, containing the birth and death years (unknown entered as 0) for all individuals included in the data set, (2) A survival matrix, with a line entered for each time an individual was re-sighted, (3) A covariate matrix, listing the sex and morph of each individual. This is the covariate file