Keith A. Tarvin

PROMISCUITY DRIVES SEXUAL SELECTION IN A SOCIALLY MONOGAMOUS BIRD

Abstract Many socially monogamous species paradoxically show signs of strong sexual selection, suggesting cryptic sources of sexual competition among males. Darwin argued that sexual selection could operate in monogamous systems if breeding sex ratios are biased or if some males attract highly fecund females. Alternatively, sexual selection might result from promiscuous copulations outside the pair bond, although several recent studies have cast doubt on this possibility, in particular by showing that variance in apparent male reproductive success (number of social young) differs little from variance in actual male reproductive success (number of young sired). Our results from a long-term study of the socially monogamous splendid fairy-wren (Malurus splendens) demonstrate that such comparisons are misleading and do not adequately assess the effects of extra-pair paternity (EPP). By partitioning the opportunity for selection and calculating Bateman gradients, we show that EPP has a strong effect on male annual and lifetime fitness, whereas other proposed mechanisms of sexual selection do not. Thus, EPP drives sexual selection in this, and possibly other, socially monogamous species.

Genetic similarity of social mates predicts the level of extrapair paternity in splendid fairy-wrens

Why females mate with multiple males, particularly in socially monogamous species, is one of the central unanswered questions in sexual selection and behavioural ecology. Recent theory suggests that socially monogamous females may improve the genetic quality of their offspring by mating with extrapair males with whom they are more genetically dissimilar (relative to their social mates), because decreased genetic similarity between mates may lead to decreased inbreeding depression of offspring and other benefits. We found that levels of extrapair paternity in splendid fairy-wren, Malurus splendens, broods were predicted by genetic similarity between social mates. Females whose entire broods were sired by extrapair males were more genetically similar to their social mates than they were to their extrapair mates, but females were no less similar to their extrapair mates than they were to the average male from the population. Within-pair young (WPY) from mixed-paternity broods showed higher levels of inbreeding and lower heterozygosity than did their extrapair nestmates or WPY from broods without extrapair paternity. Several processes could account for these patterns, including female choice of genetically dissimilar mates, differential sperm investment by males or differential survival of embryos as a function of genetic dissimilarity between mates, or postcopulatory processes such as sperm competition, cryptic female choice, or interactions between sperm and ova. Regardless of the mechanism, our results suggest that female splendid fairy-wrens may indirectly benefit from extrapair mating because it leads to lower levels of inbreeding and increased heterozygosity in their offspring.

Evolutionary relationships among blue- and black-plumaged populations of the white-winged fairy-wren (Malurus leucopterus)

The white-winged fairy-wren (Malurus leucopterus) exhibits striking plumage colour variation between the Australian mainland and two islands (Dirk Hartog Island and Barrow Island) off the coast of Western Australia. Adult males on the mainland are bright blue with white wings and adult males on the two islands are black with white wings. To examine evolutionary relationships within this species, we sequenced 980 base pairs of two mitochondrial genes from 34 individuals from both islands and five mainland sites. Birds on Barrow Island were the most genetically distinct. Specimens from Dirk Hartog shared a unique character with, and were most similar to, birds from the Western Australian mainland. The black-andwhite-plumaged subspecies from the two islands were not each other’s closest relatives. Mapping of plumage evolution produced two equally parsimonious hypotheses: (1) black plumage arose from blue plumage convergently on the two islands, or (2) black plumage arose from blue plumage once and was followed by a re-evolution of blue plumage in mainland Western Australia birds. Levels of genetic differentiation in this species were low but genetic differentiation was discovered between morphologically identical eastern and western populations of the mainland subspecies, which is evidence for a current barrier to gene flow on mainland Australia. ZO0 Ev t h i le A. C. Dr et .

Carotenoid-Based Ornaments of Female and Male American Goldfinches (Spinus tristis) Show Sex-Specific Correlations with Immune Function and Metabolic Rate

Conspicuous ornamentation has been linked to immunological and physiological condition in males of many species. In species where both sexes are ornamented, it is unclear whether the signal content of ornaments differs between males and females. We examined the immunological and physiological correlates of carotenoid-based bill and plumage ornamentation in American goldfinches Spinus tristis, a species in which bright orange bills are sexually monomorphic but yellow plumage is sexually dimorphic during the breeding season. Because bill color is dynamic over short periods while plumage color is static over longer time frames, we tested whether these signals have the potential to provide temporal information about immunity and condition. In both sexes, bill color (but not plumage color) was negatively related to leukocyte differential, a measure of recent stress, while plumage color (but not bill color) was positively related to resting metabolic rate. In females, bill color also positively correlated with immunoglobulin Y, a component of acquired immunity, while plumage color positively predicted natural antibody levels, a component of innate immunity. In males, neither bill color nor plumage color predicted immune function, suggesting that the mechanisms underlying these signals vary with sex. Our results demonstrate that dynamic signals such as bill coloration do not merely reflect the same information provided by static signals but that these two classes of signal provide information about different temporal aspects of phenotypic quality. Furthermore, our results indicate that a signal expressed in both sexes has the potential to provide different information depending on the sex of the bearer.

Patterns of Dominance and Aggressive Behavior in Blue Jays at a Feeder

We studied interactions among Blue Jays (Cyanocitta cristata) visiting a feeder in south-central Florida over a 4-year period to examine the influence of sex, time of year, and body size on dominance and aggression, describe changes in dominance among individuals over time, and test for the presence of linear dominance hierarchies. Males dominated females throughout the annual cycle, and in all 24 of the male-female significant dyads. We cannot reject the hypothesis that male dominance over females results from the larger body size of males. We infer that males also were more aggressive than females because they were involved in more interactions than expected by chance. Females became more, and males became less, aggressive immediately prior to the breeding season, but fluctuations in aggression did not lead to shifts in intersexual dominance. Dominance relationships among a few high-ranking males were intransitive and changed over time. Dominance hierarchies, characterized by reversals, circular triads, and unknown relationships, were not linear. Whereas linear hierarchies have been shown to exist in New World jays that live in small, stable social groups, we suspect the variable constituency and instability of flocks precludes the emergence of strictly linear hierarchies in the genus Cyanocitta.

Microhabitat factors influencing predation and success of suburban Blue Jay Cyanocitta cristata nests

nest tree, and nest concealment, were not related to nest predation, although distance from a nest to the nearest building was inversely related to duration of nest survival. The latter relationship suggests human activity may decrease nest predation in suburban areas. Density of vegetation surrounding nests did not influence nest fate, thus providing no support for the habitat complexity hypothesis. Instead, failed nests occurred in patches containing fewer trees of the same species, size class and vine cover as the nest tree. Because this pattern was not an effect of size or species of either the nest tree or neighboring trees, nor an effect of vines in the nest tree or neighboring

HABITAT AND NESTING SUCCESS OF BLUE JAYS (CYANOCITTA CRISTATA): IMPORTANCE OF SCALE

Abstract Nesting success of birds often is influenced by habitat features surrounding nests. However, few studies have investigated habitat influences at multiple levels and spatial scales. We examined the relationship between Blue Jay (Cyanocitta cristata) nesting success and habitat at three levels (macrohabitat, microhabitat, and nest site) and at three different scales within the microhabitat level (3.1, 0.3, and 0.07 ha circular plots surrounding nests) in central Florida. We defined successful nests as those fledging at least one offspring. An eight-fold difference in probability of nesting success existed among seven distinct macrohabitats, with Mayfield success estimates ranging from 8 to 63%. However, no difference in number of fledglings per nest existed among macrohabitats when unsuccessful nests were excluded from the analysis. Macrohabitats in which nests were more often successful had more extensive slash pine (Pinus elliottii) forest. Logistic regression analyses indicated that slash pine canopy cover was significantly related to nesting success at all three microhabitat scales, although the tree species in which a nest was placed was unimportant to nesting success. Other microhabitat and nest-site features were unrelated to nesting success. Strong circumstantial evidence indicates predation was the major cause of nest failure, but relative abundance of one potential predator, the gray squirrel (Sciurus carolinensis), was not related to nesting success in macrohabitats or slash pine canopy cover within microhabitats. In this study, logistic regression models using habitat features measured at higher levels and larger scales had better predictive power, indicating that habitat may have influenced predation at scales larger than that of a typical nest patch.

Dynamic Status Signal Reflects Outcome of Social Interactions, but Not Energetic Stress

Social defeat induces stress-responses in a wide array of vertebrates and can generate winner-loser effects. Dynamic condition-dependent signaling systems that reflect preparation for subsequent agonistic interactions, and thereby mediate winner-loser effects, should be more sensitive to competitive history than to non-social sources of stress. Bill color of female American goldfinches (Spinus tristus) is a dynamic condition-dependent ornament that functions as a signal of competitive status and mediates intrasexual agonistic social interactions. We tested the “social experience signaling hypothesis” in female goldfinches by (1) manipulating a non-social energetic stressor by experimentally elevating flight costs via wing-clipping in free-ranging birds, and (2) manipulating social experience by staging competitive interactions among captive birds. Bill color change did not differ between wing clipped and non-clipped females, even though stress-response, as measured by the heterophil to lymphocyte (H:L) ratio, increased significantly in clipped females relative to unclipped females. In contrast, winners and losers in the social experience experiment differed significantly in the degree and direction of bill color change following social contests, with bill color increasing in winners and decreasing in losers. These results suggest that dynamic bill color of female American goldfinches signals recent social history, but is less sensitive to some stressors stemming from non-social sources, and thereby suggest that signals can evolve sensitivity to specific types of processes relevant to the context in which they are used.

Arboviral Infection in Two Species of Wild Jays (Aves: Corvidae): Evidence for Population Impacts

Abstract We examined the prevalence of antibodies to three mosquito-borne arboviruses in blue jays, Cyanocitta cristata, and Florida scrub-jays, Aphelocoma coerulescens, to identify the effects on host survival, the influence of sex and age on infection, and the temporal patterns of antibody prevalence. Blood samples from 306 blue jays and 219 Florida scrub-jays were collected at Archbold Biological Station (Lake Placid, FL) from April 1994 through December 1995. Sera were analyzed for hemagglutination-inhibition antibody to eastern equine encephalitis (EEE) and St. Louis encephalitis (SLE) viruses, and neutralizing antibodies to EEE, Highlands J (HJ), and SLE viruses. Overall, 31.4% of blue jay samples and 22.1% of scrub-jay samples had antibodies to EEE. Antibodies to HJ were detected in slightly >15% of samples in each jay species, and SLE was detected in <3% of the samples in each jay species. A single EEE virus isolation was made from the blood of an 11-d-old scrub-jay nestling. Survival of adult blue jays seropositive to EEE was significantly lower than that of seronegative birds based on resight rates, but infection did not seem to affect survival of adult or juvenile Florida scrub-jays.

Same trait, different receiver response: unlike females, male American goldfinches do not signal status with bill colour

In species in which both sexes have similar ornamentation, the ornaments often function as sexual or social signals in both sexes. However, males and females may use ornaments in different signalling contexts. We previously demonstrated that carotenoid-based bill colour of female American goldfinches, Spinus tristis, functions as a signal of status during intrasexual, but not intersexual, competition. Here we test whether male bill colour functions as a competitive status signal during both intra- and intersexual contests. We tested whether focal males and females avoided feeding adjacent to taxidermic male models as a function of the models’ experimentally altered bill colour. We additionally tested whether male bill colour functions as a mate choice signal by presenting females with a choice of two live males with experimentally altered bill colour. In the status signal experiment, neither focal males nor females avoided male models with more colourful bills, as was predicted by the status-signalling hypothesis. These results indicate that male bill coloration does not function as a signal of competitive status and that the signal function of male bill colour does not parallel that of female bill colour. In our mate choice experiment, females showed no preference for male bill colour, suggesting that male bill colour may have some yet untested signalling function or that male bill colour may no longer be under selection. Our findings suggest that selection can lead to different signalling strategies in males and females, even in species that express mutual ornamentation.