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© 2015 The Authors. Manakins (Pipridae) are well know for elaborate male sexual displays and ornate plumage coloration, both of which are thought to have evolved as a consequence of lekking breeding, the prevalent mating system in the family. Less attention has been paid to a handful of 'drab' manakin species, in which sexual dimorphism appears to be reduced or absent. Using character reconstruction, we show that these 'exceptions to the rule' represent phylogenetically independent cases of losses in sexual dimorphism, and as such could provide a focal group to investigate the link between changes in morphology and in life history (e.g. mating system). We take a first step in this direction by focusing on two subspecies of the putatively monomorphic green manakin Xenopipo holochlora to formally confirm that the species is sexually monomorphic in size and plumage color and test the prediction that sexual monomorphism is associated with the loss of lekking behavior in this species. Our results show that size dimorphism is present but limited in the green manakin, with substantial overlap in male and female morphometric measures, and that sexes are largely monochromatic (including from an avian perspective), despite marked coloration differences between subspecies. Behavioral observations indicate that males do not form leks and do not engage in elaborate sexual displays, that there is no stable pair bond formation, and that females provide parental care alone. These findings are consistent with the idea that changes in mating behavior may have driven changes in morphology in Pipridae, and we encourage similar studies on other drab manakins to better understand this relationship.

Abstract Background Many species exhibit geographic variation in sexual signals, and divergence in these traits may lead to speciation. Sexual signals may diverge due to differences in ecology if the environment constrains signal production or transmission. Alternatively, sexual signals may diverge stochastically through sexual selection or genetic drift, with little environmental influence. To distinguish between these alternatives we quantified variation in two putative sexual signals – tail length and plumage color – and a suite of non-sexual morphometric traits across the geographic range of the red-backed fairy-wren (Malurus melanocephalus). We then tested for associations between these traits and a number of environmental variables using generalized dissimilarity models. Results Variation in morphometric traits was explained well by environmental variation, irrespective of geographic distance between sites. Among putative signals, variation in plumage color was best explained by geographic distance, whereas tail length was best explained by environmental variation. Divergence in male plumage color was not coincident with the boundary between genetic lineages, but was greatest across a contact zone located 300 km east of the genetic boundary. Conclusions Morphometric traits describing size and shape have likely been subject to ecological selection and thus appear to track local environmental variation regardless of subspecies identity. Ecological selection appears to have also influenced the evolution of tail length as a signal, but has played a limited role in shaping geographic variation in plumage color, consistent with stochastic divergence in concert with Fisherian selection on this trait. The lack of coincidence between the genetic boundary and the contact zone between plumage types suggests that the sexual plumage signal of one subspecies has introgressed into the genetic background of the other. Thus, this study provides insight into the various ways in which signal evolution may occur within a species, and the geographic patterns of signal variation that can arise, especially following secondary contact.

During the breeding season, male Red-backed Fairywrens (Malurus melanocephalus) can exhibit ornamented (red-black) or unornamented (brown, resembling females and juveniles) plumage. These distinct plumage types represent alternative reproductive tactics and are associated with behavioural differences during the breeding season. However, we lack an understanding of whether and how these plumage types may be associated with behavioural differences during non-reproductive parts of the year. To fill this knowledge gap, we carried out behavioural observations during the nonbreeding season across three years. We hypothesised that ornamented plumage remains associated with mate attraction behaviours outside of the breeding season. We examined the investment of ornamented, moulting, and unornamented males in social behaviours and found that the three plumage types were largely similar in their behaviour except ornamented males courted and, to a lesser extent, allopreened at higher rates than unornamented males. Since concurrent work in the same study population demonstrates increased extra-pair fitness for males who moult into ornamented plumage early, we speculate that ornamentation and courtship behaviour may serve a mate attraction function outside of the breeding season. We argue that future studies should consider individual-level behavioural monitoring throughout the annual cycle to better quantify the complex selection pressures that lead to the coevolution of plumage moult and alternative reproductive tactics in this system. [ABSTRACT FROM AUTHOR]

Seasonally breeding animals often exhibit different social structures during non-breeding and breeding periods that coincide with seasonal environmental variation and resource abundance. However, we know little about the environmental factors associated with when seasonal shifts in social structure occur. This lack of knowledge contrasts with our well-defined knowledge of the environmental cues that trigger a shift to breeding physiology in seasonally breeding species. Here, we identified some of the main environmental factors associated with seasonal shifts in social structure and initiation of breeding in the red-backed fairywren (Malurus melanocephalus), an Australian songbird. Social network analyses revealed that social groups, which are highly territorial during the breeding season, interact in social "communities" on larger home ranges during the non-breeding season. Encounter rates among non-breeding groups were related to photoperiod and rainfall, with shifting photoperiod and increased rainfall associated with a shift toward territorial breeding social structure characterized by reductions in home range size and fewer encounters among non-breeding social groups. Similarly, onset of breeding was highly seasonal and was also associated with non-breeding season rainfall, with greater rainfall leading to earlier breeding. These findings reveal that for some species, the environmental factors associated with the timing of shifts in social structure across seasonal boundaries can be similar to those that determine timing of breeding. This study increases our understanding of the environmental factors associated with seasonal variation in social structure and how the timing of these shifts may respond to changing climates. [ABSTRACT FROM AUTHOR]

Seed and pollen dispersal contribute to gene flow and shape the genetic patterns of plants over fine spatial scales. We inferred fine-scale spatial genetic structure (FSGS) and estimated realized dispersal distances in Phytelephas aequatorialis, a Neotropical dioecious large-seeded palm. We aimed to explore how seed and pollen dispersal shape this genetic pattern in a focal population. For this purpose, we genotyped 138 seedlings and 99 adults with 20 newly developed microsatellite markers. We tested if rodent-mediated seed dispersal has a stronger influence than insect-mediated pollen dispersal in shaping FSGS. We also tested if pollen dispersal was influenced by the density of male palms around mother palms in order to further explore this ecological process in large-seeded plants. Rodent-mediated dispersal of these large seeds occurred mostly over short distances (mean 34.76 ± 34.06 m) while pollen dispersal distances were two times higher (mean 67.91 ± 38.29 m). The spatial extent of FSGS up to 35 m and the fact that seed dispersal did not increase the distance at which male alleles disperse suggest that spatially limited seed dispersal is the main factor shaping FSGS and contributes only marginally to gene flow within the population. Pollen dispersal distances depended on the density of male palms, decreasing when individuals show a clumped distribution and increasing when they are scattered. Our results show that limited seed dispersal mediated by rodents shapes FSGS in P. aequatorialis, while more extensive pollen dispersal accounts for a larger contribution to gene flow and may maintain high genetic diversity [ABSTRACT FROM AUTHOR]