Epaulet Color and Sexual Selection in the Red-Winged Blackbird: A Field Experiment

Abstract

Resumen. La mancha alar en los machos de Agelaius phoeniceus funciona tanto en el contexto intra-sexual como inter-sexual, pero existe poca evidencia de que ésta covaríe con el éxito reproductivo en esta especie, que ha sido bastante estudiada. Utilizamos un análisis de pasos usando caracteres territoriales de los machos, éxito de apareamiento y éxito reproductivo de los machos no manipulados para estimar la selección direccional actual. El tamaño de los territorios tuvo un efecto positivo sobre el número de compañeros de una pareja. El número de compañeros adquiridos fuera de la pareja tuvo un efecto positivo sobre el número de polluelos extra-pareja, y el número de polluelos volantones intra-y extra-pareja tuvo un efecto positivo sobre el número total de volantones. También intensificamos el rojo de la mancha alar de machos territoriales silvestres para determinar si los machos manipulados y control diferían en su comportamiento territorial, éxito de apareamiento o éxito reproductivo. En comparación con los machos control, los machos manipulados incurrieron en tasas más altas de traspaso de límites y de disputas territoriales, perdieron sus territorios más frecuentemente y no fueron capaces de producir crías extra-pareja. Sin embargo, a pesar de estas diferencias, el éxito reproductivo alcanzado por los machos control y manipulados no difirió significativamente, probablemente debido a que los machos con las manchas rojas intensificadas asignaron más tiempo a comportamientos de vigilancia anti-depredatorios y fueron más agresivos ante un depredador simulado que los machos control. Una falta aparente de selección sexual actual sobre el color de la mancha alar puede ser una forma de contrarrestar la selección sexual en la que la agresividad hacia machos con manchas más rojas se opone a la preferencia por parte de las hembras de manchas más rojas, o puede ser el resultados de que los machos compensan la pérdida de cópulas extra-pareja al aumentar su cuidado parental.Abstract. The epaulets of male Red-winged Blackbirds (Agelaius phoeniceus) function in both intersexual and intrasexual contexts, but there is little evidence that they covary with reproductive success in this well-studied species. We used path analysis of male/territory traits, mating success, and reproductive success of unmanipulated males to estimate current directional selection. Territory size had a positive effect on number of within-pair mates. Number of extra-pair mates had a positive effect on number of extra-pair fledglings, and number of within-pair and extra-pair fledglings had positive effects on total number of fledglings. We also reddened epaulets of free-living territorial males to determine whether manipulated and control males differ in territorial behavior, mating success, or reproductive success. Compared with control males, males with reddened epaulets incurred elevated rates of trespassing and territorial challenges, lost their territories more often, and were unable to produce extra-pair offspring. Despite these differences, howev...

The effect of habitat and body size on the evolution of vocal displays in Thraupidae (tanagers), the largest family of songbirds

“…As a result, if eavesdroppers in closed habitats rely more on acoustic signalling than vision compared to open habitats, we might expect birds in forests to evolve higher frequency songs within narrower bandwidths to avoid detection by unintended receivers such as predators or brood parasites (Hale, ; Lima, ). While the AAH assumes that bird song is selected for maximum distance propagation, the cost of eavesdropping by predators and parasites might counteract the benefit of auditory signals reaching additional potential mates or rival conspecifics (Mougeot & Bretagnolle, ; Yasukawa et al ., ).…”

Effects of age and experience on the responses of territorial and floater male Red-winged Blackbirds to models of receptive females

“…I used presentations of taxidermic models of female Red‐winged Blackbirds in copulation‐solicitation postures to observe the behavior of males in five categories: (1) ASY floaters, (2) second‐year (SY) floaters, (3) experienced territorial males, (4) inexperienced territorial males, and (5) immediate territorial neighbors through the breeding season. I used this information to determine if (1) copulation behavior and success differed among floaters, territorial males, and territorial neighbors, (2) copulation behavior changed during the breeding season, and (3) copulation success rates of floaters, territorial males, and neighbors were consistent with fertilization success rates previously estimated by molecular paternity assignments for this study population (Yasukawa et al ).…”

“…Of 77 successful copulations, 57 (74.0%) were by territory owners, 7 (9.1%) by neighbors, and 13 (16.9%) by floaters. DNA fingerprinting results from 1992 to 1994 (Yasukawa et al ) used to calculate expected frequencies (owners = 0.67, neighbors = 0.22, and floaters = 0.11) revealed that territory owners and floaters were overrepresented and neighbors underrepresented (χ 2 2 = 8.8, P = 0.012; Fig. B) in the number of successful copulations, assuming that all unassigned nestlings were sired by floaters.…”

“…Yasukawa et al () used DNA minisatellite fingerprinting methods to assign paternity to 100 nestlings from 35 nests during the breeding seasons of 1992–1994 at Newark Road Prairie. Sixty‐seven nestlings were assigned to territory owners and 22 to other territorial males (neighbors).…”

Genetic diversity does not explain variation in extra‐pair paternity in multiple populations of a songbird

“…DNA from samples collected before 2000 were extracted using the methods reported in their respective studies ( Table 1; Yasukawa et al, 2009). DNA from samples collected after 2000 was extracted with a Qiagen DNeasy Blood and Tissue Kit (Hilden, Germany) and evaluated for concentration and purity using a Nanodrop spectrophotometer.…”