PHYLOGENETIC ANALYSIS OF THE EVOLUTION OF ALTERNATIVE SOCIAL BEHAVIOR IN THE MANAKINS (AVES: PIPRIDAE)

Phylogenetic analyses of lekking, lek spatial organization, and cooperative and coordinated lek display in the manakins (Aves: Pipridae) demonstrate that variation in social behavior in the group has a strong, phylogenetic component. Two of the three classes of social behavior examined also show significant phylogenetic constraints. Current adaptive plasticity models are insufficient to explain the phylogenetic variation in these behaviors in the manakins. These findings support the conclusion that vertebrate reproductive social behavior has an evolutionary history, and that it is not determined solely by adaptive individual plasticity to current conditions. The evolution of social behavior, particularly through sexual selection, can have historical consequences that can limit subsequent behavioral adaptation.     

Local genetic structure in a white-bearded manakin population

Local genetic structure was studied in lekking white-bearded manakins in a study area on northern Trinidad, West Indies. The study population consisted of nine leks, at which a total of 238 birds were caught. By genotyping the individuals at eight polymorphic microsatellite loci we inferred some males on leks to be related (r = 0.25) as we found an average number of 14.8 half-sib relationships and two full-sib relationships per lek. We found that the sampled birds belonged to one genetic population that was slightly inbred (FIS and FIT = 0.02). Kinship coefficients decreased with increasing geographical distance, indicating that related birds displayed at the same or nearby leks. However, leks did not consist of only one family group because the average genetic distance (aij) between males within leks was higher than when comparing males on leks within close proximity. These patterns suggest limited male dispersal, that some type of kin recognition process between individuals may exist in this species and that males on leks may be more likely to establish themselves as territory-holding birds if a relative is already present.     

Plumage brightness predicts male mating success in the lekking golden-collared manakin, Manacus vitellinus

The evolution of colorful plumage has been dramatic in lekkingspecies. Several studies show that the size of colorful traitsinfluence female choice in leks; however, relatively littleis known about the specific function of color, in particularits spectral properties, in lekking taxa. To determine the importanceof color in a lekking species, we monitored the mating successof male golden-collared manakins, Manacus vitellinus, and relatedthis to spectral measures of their colorful plumage, as wellas other morphological and behavioral traits shown to be importantin other lekking species. We found that lek centrality, malebody size, and plumage brightness were associated with malemating success. Only plumage brightness, however, entered amultiple regression model, indicating that plumage is the overallbest predictor of mating success. These results provide evidencethat the spectral properties of colorful plumage predict malemating success in a lekking species and provide important insightinto why many lekking birds are dichromatic and elaborate incoloration.     

UNIDIRECTIONAL INTROGREESION OF A SEXUALLY SELECTED TRAIT ACROSS AN AVIAN HYBRID ZONE: A ROLE FOR FEMALE CHOICE?

Hybridization can be an evolutionary creative force by forming new polyploid species, creating novel genetic variation or acting as conduits of potentially advantageous traits between hybridizing forms. Evidence for the latter is often difficult to find because alleles under positive selection can spread rapidly across a hybrid zone and sweep to fixation. In Western Panama, an avian hybrid zone between two species of manakins in the genus Manacus exists where the unidirectional introgression of bright, yellow plumage into a white population provides evidence for the importance of hybrid zones as conduits of advantageous traits. Several lines of indirect evidence suggest that sexual selection favoring yellow plumage drives this asymmetrical spread, but more direct evidence is lacking. Along the edge of the hybrid zone, both yellow- and white-collared manakins are found in the same mating arenas or leks and compete for the same females ("mixed leks"), providing us with a unique opportunity to understand the dynamics of yellow plumage introgression. We studied these mixed leks to determine whether yellow males have a mating advantage over white males and, if so, whether the mating advantage is driven by male-male interactions, female choice, or both. We found that yellow males mated more than white males, suggesting that sexual selection favoring yellow males can, indeed, explain the spread of yellow plumage. However, we found that this advantage occurred only in mixed leks where the frequency of yellow males is greater than white males. This suggests that the advantage of yellow males may depend on the presence of other yellow males, which may slow the rate of introgression in leks where yellow frequency is low such as in areas where yellow males are beginning to colonize the white population. This, along with the geographic barrier posed by major rivers in the hybrid zone, may initially limit or slow the spread of yellow plumage. Finally, we found that yellow and white males were similar in aggression and body size, and held comparable positions within leks. Because these traits or factors are often important in or dictated by aggressive male-male interactions, these comparisons indicate that male-male interaction is not the primary mechanism for the spread of yellow plumage. However, white and yellow males received similar numbers of courtship visits from females but differed in the number of matings, suggesting that females actively rejected white in favor of yellow males. Our results indicate that sexual selection by female choice has driven the unidirectional introgression of yellow plumage into the white population, providing a mechanism for how hybrid zones act as conduits of novel and advantageous traits.     

Isolation and characterization of microsatellite loci in the blue manakin,Chiroxiphia caudata (Aves,Pipridae)

We designed primers for amplifying 11 polymorphic microsatellite loci in the blue manakin, Chiroxiphia caudata, a neotropical passerine bird which inhabits a critically endangered tropical ecosystem, the Brazilian Atlantic forest. Based on genotypes from 24 individuals from a single population, we detected between four and 22 alleles per locus with observed heterozygosities ranging from 0.54 to 0.92. These highly variable loci will be useful for determining levels of population differentiation and assessing the impact of habitat fragmentation on levels of genetic variation in isolated populations of these birds.     

Energetics of the acrobatic courtship in male golden-collared manakins (Manacus vitellinus)

In lek mating systems, females choose mates through indicators of quality, which males may exhibit by their performance of courtship displays. In temperate regions, displaying seasons are brief (one to two months), whereas in the tropics courtship seasons may be prolonged. Moreover, in temperate-breeding animals lekking behaviour can be energetically demanding, but little is known about the energy costs of lekking in tropical animals. Daily, over the course of a nearly seven-month-long breeding season, male golden-collared manakins (Manacus vitellinus) of Panamanian rainforests perform acrobatic courtship displays that markedly elevate heart rates, suggesting that they require high energy investment. Typically, animals of tropical lowland forests (such as manakins) exhibit a ‘slow pace of life’ metabolic strategy. We investigated whether male manakin courtship is indeed metabolically costly or whether the birds retain a low daily energy expenditure (DEE), as seen in other tropical species. To assess these questions, we calibrated manakin heart rate against metabolic rate, examined daily lek activity and, using telemetry, obtained heart rates of individual wild, lekking male manakins. Although metabolic rates peak during courtship displays, we found that males actually invest minimal time (only approx. 5 min d⁻¹) performing displays. As a consequence, the DEE of approximately 39 kJ d⁻¹ for male manakins is comparable to other lowland tropical species. The short, intense bursts of courtship by these birds make up only approximately 1.2% of their total DEE. Presumably, this cost is negligible, enabling them to perform daily at their arenas for months on end.     

Modification of the visual background increases the conspicuousness of golden-collared manakin displays

Effective visual communication requires signals that are easyto detect, transmit, receive, and discriminate. Animals canincrease the probability that their visual signals would bedetected by evolving signals that contrast with their visualbackground. Animals can further enhance this contrast by behaviorallymodifying the existing visual background. Male golden-collaredmanakins (Manacus vitellinus) clear leaf litter from the groundto form courts, which are used as display arenas. Using reflectancemeasures of the signal (male plumage) and the visual background(cleared court and adjacent litter), the irradiance measuresof ambient light during display, and published measures of photoreceptorsensitivity of a Passerine, we test the hypothesis that court-clearingaugments the contrast between male plumage and the visual background.We find that the chromatic and brightness contrasts of goldenpatches used during courtship are greater against the clearedcourt than against adjacent litter. In addition, we find thatcleared courts provide a less variable background for thesecolor patches, resulting in displays that consistently contrastthe visual background. These results suggest that behavioralmodification of the visual background may act to increase theconspicuousness of colorful male plumage during display, providingan explanation for why golden-collared manakins, and possiblyother species, build or clear display courts.     

Isolation and characterization of microsatellite markers from the white-ruffed manakin Corapipo altera (Aves, Pipridae)

We describe 15 polymorphic microsatellite loci from the white-ruffed manakin Corapipo altera, a common understory bird of Neotropical lowland and montane evergreen forests from eastern Honduras to northwestern Colombia. These markers were developed in order to assess population structure and genetic diversity in a fragmented landscape, and to study gene flow between forest fragments. Primers were tested on a population of 159 individuals from the Coto Brus region of southwestern Costa Rica. We found between four and 23 alleles per locus, and observed heterozygosities ranging from 0.23 to 0.93.     

It takes two to tango: reproductive skew and social correlates of male mating success in a lek-breeding bird

Variance in reproductive success among individuals is a defining characteristic of many social vertebrates. Yet, our understanding of which male attributes contribute to reproductive success is still fragmentary in most cases. Male–male reproductive coalitions, where males jointly display to attract females, are of particular interest to evolutionary biologists because one male appears to forego reproduction to assist the social partner. By examining the relationship between social behaviour and reproductive success, we can elucidate the proximate function of coalitions in the context of mate choice. Here, we use data from a 4-year study of wire-tailed manakins (Pipra filicauda) to provide molecular estimates of reproductive skew and to test the hypothesis that male–male social interactions, in the context of coordinated displays, positively influence a male''s reproductive success. More specifically, we quantify male–male social interactions using network metrics and predict that greater connectivity will result in higher relative reproductive success. Our data show that four out of six leks studied had significant reproductive skew, with success apportioned to very few individuals in each lek. Metrics of male social affiliations derived from our network analysis, especially male connectivity, measured as the number of males with whom the focal male has extended interactions, were strong predictors of the number of offspring sired. Thus, network connectivity is associated with male fitness in wire-tailed manakins. This pattern may be the result of shared cues used by both sexes to assess male quality, or the result of strict female choice for coordinated display behaviour.     

Variable visual habitats may influence the spread of colourful plumage across an avian hybrid zone

Several studies have shown that hybridization can be a creative process by acting as a conduit for the spread of adaptive traits between species, but few provide the mechanism that favours this spread. In the hybrid zone between the golden- (Manacus vitellinus) and white-collared (Manacus candei) manakins, sexual selection drives the introgression of golden/yellow plumage into the white species; however, the mechanism for the yellow male's mating advantage and the reasons why yellow plumage has not swept further into the white species remain mostly speculative. We quantified the colour properties of male plumage, the background and the ambient light at the hybrid zone, and allopatric golden and white populations. As measured by the perceived difference in colour between plumage and background, we found that yellow plumage appears more conspicuous than white plumage in the hybrid zone and allopatric golden-collar habitats, whereas white plumage appears more conspicuous than yellow plumage in the allopatric white-collared habitat. These results suggest a mechanism for the unidirectional spread of yellow plumage across the hybrid zone but slowed movement beyond it.