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C C Chen - One of the best experts on this subject based on the ideXlab platform.
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the dual roles of armigeres subalbatus prophenoloxidase v in parasite Melanization and egg chorion Melanization in the mosquito ar subalbatus
Insect Biochemistry and Molecular Biology, 2015Co-Authors: I Y Tsao, Bruce M. Christensen, J W Chen, C C ChenAbstract:Abstract Phenoloxidases (POs) play key roles in various physiological functions in insects, e.g., cuticular sclerotization, wound healing, egg tanning, cuticle formation and melanotic encapsulaction of pathogens. Previously, we identified five POs, designated As-pro-PO I–V, from the mosquito Armigeres subalbatus and demonstrated that the functions of As-pro-PO I, II and III, were associated with filarial parasite Melanization, blood feeding and cuticle formation, respectively. In the present study, we delineate the dual functions of As-pro-PO V. We found that the level of As-pro-PO V mRNA in mosquitoes was significantly increased after microfilaria challenge or blood feeding, and decreased to normal level after oviposition. Knockdown of As-pro-PO V by dsRNA resulted in significant decreases in the degree of microfilaria Melanization, egg chronic Melanization rates and egg hatching rates in Ar . subalbatus . Further transfection and electrophoretic mobility-shift assays verified the As-pro-PO V gene might regulated by both AP-1, a putative immune-related regulatory element and CdxA, a developmental regulatory element. The binding of AP-1 and CdxA motif with mosquito nuclear extracts was significantly enhanced after microfilaria challenge and blood-feeding in Ar . subalbatus , respectively. These results indicate that As-pro-PO V is a critical enzyme that is required for both an effective Melanization immune response and egg chorion Melanization in this mosquito.
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role of dopachrome conversion enzyme in the Melanization of filarial worms in mosquitoes
Insect Molecular Biology, 2005Co-Authors: C Y Huang, Bruce M. Christensen, C C ChenAbstract:Melanization is an effective defence reaction of mosquito hosts against invading parasites. In mosquitoes, the biosynthesis of melanin is initiated by the hydroxylation of tyrosine to DOPA by phenoloxidase (PO). DOPA is a branch point of the Melanization reaction; it may be oxidized to dopaquinone by PO or be decarboxylated to dopamine by dopa decarboxylase. Further oxidation of dopaquinone by PO produces dopachrome. Dopachrome is then converted to 5, 6-dihydroxyindole by dopachrome conversion enzyme (DCE) to produce melanin. The conversion of dopachrome is a rate-limiting step of the Melanization reaction, and the presence of PO and DCE significantly accelerates Melanization reactions. In this study, a cDNA encoding DCE was cloned from the mosquito Armigeres subalbatus. Real-time PCR analysis revealed increased transcripts from haemocytes in microfilariae (mf)-inoculated mosquitoes. Gene silencing using double-stranded RNA was used to elucidate the role of DCE in the Melanization reaction of parasites in Ar. subalbatus. The levels of both DCE transcripts and protein in gene knockdown mosquitoes were dramatically reduced. Compared with controls, the degree of Melanization of mf in DCE-knockdown mosquitoes was significantly decreased. These results suggest that DCE is a critical enzyme that is required for effective Melanization immune responses.
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effect of prophenoloxidase expression knockout on the Melanization of microfilariae in the mosquito armigeres subalbatus
Insect Molecular Biology, 2001Co-Authors: Shinhong Shiao, Bruce M. Christensen, Stephen Higgs, Zach N Adelman, S H Liu, C C ChenAbstract:Melanization is an effective defence reaction used by mosquito hosts to kill malarial and filarial worm parasites. Although phenoloxidase (PO) has long been considered to be the key enzyme in the biosynthesis of melanotic material in insects, there is no direct evidence verifying its role in parasite Melanization. To elucidate the role of PO in the Melanization of microfilariae (mf) by mosquitoes, a double subgenomic Sindbis (dsSIN) recombinant virus was used to transduce Armigeres subalbatus mosquitoes with a 600 base antisense RNA targeted to the highly conserved copper-binding region of an Ar. subalbatus PO gene. Compared with controls, haemolymph PO activity in mosquitoes transduced with antisense RNA was significantly reduced. When these mosquitoes were challenged with Dirofilaria immitis mf, the Melanization of mf was almost completely inhibited. These data verify that PO is an essential component of the biochemical pathway required for the Melanization of parasites, and that the dsSIN expression system represents a useful tool in the functional analysis of endogenous gene expression in mosquitoes.
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molecular cloning of a second prophenoloxidase cdna from the mosquito armigeres subalbatus prophenoloxidase expression in blood fed and microfilariae inoculated mosquitoes
Insect Molecular Biology, 2001Co-Authors: L H Huang, Bruce M. Christensen, C C ChenAbstract:Melanization constitutes an important component in various aspects of insect life, including cuticular sclerotization, egg-shell tanning, Melanization of parasites and wound healing. Recently, a cDNA encoding prophenoloxidase (pro-PO), a key enzyme in the biosynthesis of melanotic material in insects, was cloned from microfilariae (mf)-inoculated mosquitoes, Armigeres subalbatus. However, results of Northern blot analyses indicated that two pro-POs might be present in Ar. subalbatus and these pro-POs might be responsible for two distinct physiological functions, egg-shell tanning and Melanization of parasites. Subsequently, the second pro-PO cDNA (As-pro-PO II) was cloned from blood-fed Ar. subalbatus by rapid amplification of cDNA ends polymerase chain reaction. The 2210 bp As-pro-PO II cDNA contains a 41 bp 5'-non-coding region, a 2064 bp open reading frame and a 105 bp 3'-non-coding region. A hydrophobic signal peptide for endoplasmic reticulum targeting is not found in the N-terminal region. The deduced amino acid sequence of As-pro-PO II shares a high degree of identity (81.5%) with that of the As-pro-PO I obtained from mf-inoculated Ar. subalbatus. Both Northern blot and reverse transcription polymerase chain reaction analysis demonstrated that these two mosquito pro-POs are persistently expressed in mosquito haemocytes and not in fat body, midgut, or ovaries. The expression of As-pro-PO I and As-pro-PO II in mosquitoes is associated with Melanization of mf and blood feeding, respectively.
Bruce M. Christensen - One of the best experts on this subject based on the ideXlab platform.
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the dual roles of armigeres subalbatus prophenoloxidase v in parasite Melanization and egg chorion Melanization in the mosquito ar subalbatus
Insect Biochemistry and Molecular Biology, 2015Co-Authors: I Y Tsao, Bruce M. Christensen, J W Chen, C C ChenAbstract:Abstract Phenoloxidases (POs) play key roles in various physiological functions in insects, e.g., cuticular sclerotization, wound healing, egg tanning, cuticle formation and melanotic encapsulaction of pathogens. Previously, we identified five POs, designated As-pro-PO I–V, from the mosquito Armigeres subalbatus and demonstrated that the functions of As-pro-PO I, II and III, were associated with filarial parasite Melanization, blood feeding and cuticle formation, respectively. In the present study, we delineate the dual functions of As-pro-PO V. We found that the level of As-pro-PO V mRNA in mosquitoes was significantly increased after microfilaria challenge or blood feeding, and decreased to normal level after oviposition. Knockdown of As-pro-PO V by dsRNA resulted in significant decreases in the degree of microfilaria Melanization, egg chronic Melanization rates and egg hatching rates in Ar . subalbatus . Further transfection and electrophoretic mobility-shift assays verified the As-pro-PO V gene might regulated by both AP-1, a putative immune-related regulatory element and CdxA, a developmental regulatory element. The binding of AP-1 and CdxA motif with mosquito nuclear extracts was significantly enhanced after microfilaria challenge and blood-feeding in Ar . subalbatus , respectively. These results indicate that As-pro-PO V is a critical enzyme that is required for both an effective Melanization immune response and egg chorion Melanization in this mosquito.
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role of dopachrome conversion enzyme in the Melanization of filarial worms in mosquitoes
Insect Molecular Biology, 2005Co-Authors: C Y Huang, Bruce M. Christensen, C C ChenAbstract:Melanization is an effective defence reaction of mosquito hosts against invading parasites. In mosquitoes, the biosynthesis of melanin is initiated by the hydroxylation of tyrosine to DOPA by phenoloxidase (PO). DOPA is a branch point of the Melanization reaction; it may be oxidized to dopaquinone by PO or be decarboxylated to dopamine by dopa decarboxylase. Further oxidation of dopaquinone by PO produces dopachrome. Dopachrome is then converted to 5, 6-dihydroxyindole by dopachrome conversion enzyme (DCE) to produce melanin. The conversion of dopachrome is a rate-limiting step of the Melanization reaction, and the presence of PO and DCE significantly accelerates Melanization reactions. In this study, a cDNA encoding DCE was cloned from the mosquito Armigeres subalbatus. Real-time PCR analysis revealed increased transcripts from haemocytes in microfilariae (mf)-inoculated mosquitoes. Gene silencing using double-stranded RNA was used to elucidate the role of DCE in the Melanization reaction of parasites in Ar. subalbatus. The levels of both DCE transcripts and protein in gene knockdown mosquitoes were dramatically reduced. Compared with controls, the degree of Melanization of mf in DCE-knockdown mosquitoes was significantly decreased. These results suggest that DCE is a critical enzyme that is required for effective Melanization immune responses.
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Identification and molecular characterization of a prophenoloxidase involved in Aedes aegypti chorion Melanization.
Insect Molecular Biology, 2005Co-Authors: Seong Ryul Kim, Ruiliang Yao, Q. Han, Bruce M. ChristensenAbstract:Chorion Melanization is a vital biochemical event for the survival of mosquito eggs in the environment. This study describes the identification and molecular characterization of a prophenoloxidase (proPO) involved in chorion Melanization in Aedes aegypti by various biochemical and molecular techniques. Results revealed that transcription of the chorion proPO occurs only in adults, blood feeding greatly stimulated its transcription and haemocytes are responsible for its transcription. Our study provides a solid basis for suggesting an essential role of the isolated proPO in chorion Melanization during chorion hardening and also raises fundamental questions regarding its transportation and distribution in the chorion. This study should serve as a useful reference towards functional elucidation of other proPOs in mosquitoes.
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rapid phagocytosis and Melanization of bacteria and plasmodium sporozoites by hemocytes of the mosquito aedes aegypti
Journal of Parasitology, 2003Co-Authors: Julian F Hillyer, Shelley L Schmidt, Bruce M. ChristensenAbstract:Mosquitoes are vectors of many deadly and debilitating pathogens. In the current study, we used light and electron microscopies to study the immune response of Aedes aegypti hemocytes to bacterial inoculations, Plasmodium gallinaceum natural infections, and latex bead injections. After challenge, mosquitoes mounted strong phagocytic and Melanization responses. Granulocytes phagocytosed bacteria singly or pooled them inside large membrane-delimited vesicles. Phagocytosis of bacteria, Plasmodium sporozoites, and latex beads was extensive; we estimated that individual granulocytes have the capacity to phagocytose hundreds of bacteria and thousands of latex particles. Oenocytoids were also seen to internalize bacteria and latex particles, although infrequently and with low capacity. Besides phagocytosis, mosquitoes cleared bacteria and sporozoites by Melanization. Interestingly, the immune response toward 2 species of bacteria was different; most Escherichia coli were phagocytosed, but most Micrococcus luteus were melanized. Similar to E. coli, most Plasmodium sporozoites were phagocytosed. The immune response was rapid; phagocytosis and Melanization of bacteria began as early as 5 min after inoculation. The magnitude and speed of the cellular response suggest that hemocytes, acting in concert with the humoral immune response, are the main force driving the battle against foreign invaders.
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effect of prophenoloxidase expression knockout on the Melanization of microfilariae in the mosquito armigeres subalbatus
Insect Molecular Biology, 2001Co-Authors: Shinhong Shiao, Bruce M. Christensen, Stephen Higgs, Zach N Adelman, S H Liu, C C ChenAbstract:Melanization is an effective defence reaction used by mosquito hosts to kill malarial and filarial worm parasites. Although phenoloxidase (PO) has long been considered to be the key enzyme in the biosynthesis of melanotic material in insects, there is no direct evidence verifying its role in parasite Melanization. To elucidate the role of PO in the Melanization of microfilariae (mf) by mosquitoes, a double subgenomic Sindbis (dsSIN) recombinant virus was used to transduce Armigeres subalbatus mosquitoes with a 600 base antisense RNA targeted to the highly conserved copper-binding region of an Ar. subalbatus PO gene. Compared with controls, haemolymph PO activity in mosquitoes transduced with antisense RNA was significantly reduced. When these mosquitoes were challenged with Dirofilaria immitis mf, the Melanization of mf was almost completely inhibited. These data verify that PO is an essential component of the biochemical pathway required for the Melanization of parasites, and that the dsSIN expression system represents a useful tool in the functional analysis of endogenous gene expression in mosquitoes.
Susan M Paskewitz - One of the best experts on this subject based on the ideXlab platform.
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silencing the genes for dopa decarboxylase or dopachrome conversion enzyme reduces Melanization of foreign targets in anopheles gambiae
Comparative Biochemistry and Physiology B, 2008Co-Authors: Susan M Paskewitz, Olga AndreevAbstract:The production of melanin is a complex biochemical process in which several enzymes may play a role. Although phenoloxidase and serine proteases are clearly key components, the activity of other enzymes, including dopa decarboxylase and dopachrome conversion enzyme may also be required. We tested the effect of knockdown of gene expression for these two enzymes on Melanization of abiotic targets in the mosquito, Anopheles gambiae. Knockdown of dopa decarboxylase and dopachrome conversion enzyme resulted in a significant reduction of Melanization of Sephadex beads at 24 h after injection. Knockdown of a third enzyme, phenylalanine hydroxylase, which is involved in endogenous production of tyrosine, had no effect on bead Melanization. Quantitative analysis of gene expression demonstrated significant upregulation of phenylalanine hydroxylase, but not the other two genes, following injection.
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a role for lysozyme in Melanization of sephadex beads in anopheles gambiae
Journal of Insect Physiology, 2006Co-Authors: Bin Li, Susan M PaskewitzAbstract:Abstract Melanization of foreign targets in the mosquito, Anopheles gambiae , was studied using a model Sephadex bead system. A mosquito factor that was deposited on beads and prevented bead Melanization (MPF) was purified. The N-terminal sequence of the factor identified it as lysozyme c-1 (Lys c-1). Gene silencing of Lys c-1 mediated by RNA interference resulted in a significant reduction in the MPF activity compared with controls. The purified Lys c-1 protein reduced dopachrome formation by mosquito hemolymph phenoloxidase in solution assays in vitro. In vivo, Lys c-1 might inhibit Melanization of beads by blocking attachment of critical factors to the bead surface or by inhibiting PO directly. This work indicates that insect lysozymes can play unexpected roles in mediating Melanization of foreign targets.
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gene silencing of serine proteases affects Melanization of sephadex beads in anopheles gambiae
Insect Biochemistry and Molecular Biology, 2006Co-Authors: Susan M Paskewitz, Olga AndreevAbstract:Serine proteases play an important role in activation of prophenoloxidase (proPO), a critical enzyme in the production of melanin. We tested the effect of knockdown of gene expression for five clip domain serine proteases on Melanization of abiotic targets in Anopheles gambiae. Knockdown of CLIPB4 resulted in a striking lack of Melanization of Sephadex beads while knockdown of CLIPB8 caused a strong shift towards incompletely melanized beads. Knockdown of CLIPB1, B9 and B10 had lesser effects. CLIPB4 and CLIPB8 are strong candidates for activating enzymes in the proPO enzymatic cascade.
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a factor preventing Melanization of sephadex cm c 25 beads in plasmodium susceptible and refractory anopheles gambiae
Experimental Parasitology, 1998Co-Authors: Susan M Paskewitz, Michael A RiehleAbstract:Abstract Paskewitz, S. M., and Riehle, M. 1998. A factor preventing Melanization of Sephadex CM C-25 beads inPlasmodium-susceptible and refractoryAnopheles gambiae. Experimental Parasitology90, 34–41. One major quantitative trait locus controls Melanization of both malaria ookinetes and Sephadex CM beads in a refractory strain of the mosquito,Anopheles gambiae.Hemolymph transferred from a nonmelanizing,Plasmodium-susceptible strain (4arr) to a melanizing,Plasmodium-refractory strain (L35) caused a reduction in the Melanization of CM beads. In addition, when beads were first incubatedin vivoin susceptible mosquitoes and then recovered, washed, and transferred to refractory mosquitoes, a strong reduction in Melanization was observed. No changes in Melanization were observed when beads or hemolymph were transferred in the opposite direction or within a strain. Incubation of beadsin vitroin refractory or susceptible hemolymph resulted in a reduction of Melanization when these beads were subsequently transferred to refractory mosquitoes. This reduction was significantly stronger when susceptible hemolymph was used as the incubating medium. Protection from Melanization was observed after 3-, 6-, and 24-h incubations of beads in susceptible mosquitoes with longer incubations resulting in greater protection. Treatment of protected beads with 1 M NaOH resulted in the loss of the protection but treatment with 1% sodium dodecyl sulfate (SDS), 1% SDS/DTT/boiling, or 1 M NaOAc (pH 8.9) did not. These results show that a Melanization-preventing factor covalently binds to the surface of CM beads in susceptible mosquitoes and can subsequently prevent Melanization in refractory mosquitoes.
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a shared genetic mechanism for melanotic encapsulation of cm sephadex beads and a malaria parasite plasmodium cynomolgib in the mosquito anopheles gambiae
Experimental Parasitology, 1996Co-Authors: M J Gorman, A J Cornel, Frank H Collins, Susan M PaskewitzAbstract:APlasmodium-refractory strain ofAnopheles gambiaethat melanizes ookinetes and intrathoracically inoculated CM–Sephadex beads was mated to aPlasmodium-susceptible strain that does not melanize the parasite or the beads. The F1progeny were then backcrossed to the susceptible strain. Backcross progeny were given a blood meal containing infectivePlasmodium cynomolgiB, and the parasites were allowed to develop for 6–7 days, at which time the infected mosquitoes were injected with CM–Sephadex beads. The next day the mosquitoes were dissected and the beads were scored for degree of Melanization while the parasites were scored for degree of encapsulation. A Spearman rank order correlation test of the degree of correlation between the bead Melanization phenotype and the parasite encapsulation phenotype gave a correlation coefficient of 0.74 (P< 0.01). This strong correlation between the two Melanization responses suggests that the mechanisms for differential bead and parasite Melanization of these two mosquito strains share at least one major gene.
Mike A Osta - One of the best experts on this subject based on the ideXlab platform.
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The serine protease homolog CLIPA14 modulates the intensity of the immune response in the mosquito Anopheles gambiae.
Journal of Biological Chemistry, 2017Co-Authors: Johnny Nakhleh, George K Christophides, Mike A OstaAbstract:Abstract CLIP domain serine protease homologues (cSPHs) are positive and negative regulators of Anopheles gambiae immune responses mediated by the complement-like protein TEP1 against Plasmodium malaria parasites and other microbial infections. We have previously reported that the SPH CLIPA2 is a negative regulator of the TEP1-mediated response by showing that CLIPA2 knockdown (kd) enhances mosquito resistance to infections with fungi, bacteria and Plasmodium parasites. Here, we identify another SPH, CLIPA14, as a novel regulator of mosquito immunity. We found that CLIPA14 is a hemolymph protein that is rapidly cleaved following a systemic infection. CLIPA14 kd mosquitoes elicited a potent Melanization response against Plasmodium berghei ookinetes and exhibited significantly increased resistance to Plasmodium infections as well as to systemic and oral bacterial infections. The activity of the enzyme phenoloxidase, which initiates melanin biosynthesis, dramatically increased in the hemolymph of CLIPA14 kd mosquitoes in response to systemic bacterial infections. Ookinete Melanization and hemolymph phenoloxidase activity were further increased after co-silencing CLIPA14 and CLIPA2, suggesting that these two SPHs act in concert to control the Melanization response. Interestingly, CLIPA14 RNAi phenotypes and its infection-induced cleavage were abolished in a TEP1 loss-of-function background. Our results suggest that a complex network of SPHs functions downstream of TEP1 to regulate the Melanization reaction.
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the Melanization response in insect immunity
Advances in Insect Physiology, 2017Co-Authors: Johnny Nakhleh, Layla El Moussawi, Mike A OstaAbstract:Abstract Melanization plays important roles in diverse physiological processes in insects including wound healing, tanning of the cuticle and immunity. Upon infection, pattern recognition receptors activate downstream serine protease cascades that culminate in the activation of prophenoloxidase (PPO), the rate-limiting enzyme in the process of melanogenesis. During the last two decades, diverse genetic and biochemical approaches have been adopted to characterize this process, and a wealth of information has been generated concerning the molecular events that control PPO activation. Importantly, the Melanization reaction was shown to be toxic to parasites, bacteria, fungi and recently viruses. Several studies pointed also to the existence of significant crosstalk between Melanization and other immune responses possibly to coordinate immune attack against invaders. Here, we provide a critical review of the role of Melanization in insect immunity, highlighting the important discoveries but also the gaps that remain to be explored in future studies.
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the Melanization reaction is not required for survival of anopheles gambiae mosquitoes after bacterial infections
Journal of Biological Chemistry, 2007Co-Authors: Anna K D Schnitger, Fotis C Kafatos, Mike A OstaAbstract:The Melanization reaction of insects requires activation of pro-phenoloxidase by a proteolytic cascade leading to melanin production. Studies in adult mosquitoes have shown that bacteria are efficiently melanized in the hemocoel, but the contribution of Melanization to survival after bacterial infections has not been established. Here we show that the Anopheles gambiae noncatalytic serine protease CLIPA8, an essential factor for Plasmodium ookinete Melanization, is also required for Melanization of bacteria in adult mosquitoes. CLIPA8 silencing by RNA interference inhibits pro-phenoloxidase activation and Melanization of bacteria in the hemolymph following microbial challenge. However, CLIPA8 is not required for wound Melanization nor for melanotic pseudotumor formation in serpin2 knockdown mosquitoes, suggesting a specific role for pathogen Melanization. Surprisingly, CLIPA8 knockdown mosquitoes are as resistant to bacterial challenge as controls, indicating that Melanization is not essential for defense against bacteria and questions its precise role in mosquito immunity.
Andras Liker - One of the best experts on this subject based on the ideXlab platform.
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ORIGINAL PAPER Testosterone and melanin-based black plumage coloration: a comparative study
2016Co-Authors: Veronika Bokony, Laszlo Zsolt Garamszegi, Katharina Hirschenhauser, Andras LikerAbstract:Abstract Despite the functional significance of melanin-based plumage coloration in social and sexual signaling, the mechanisms controlling its information content are poorly understood. The T-regulation hypothesis proposes that melanin ornaments signal competitive abilities via the effects of testosterone (T) mediating both Melanization and sexual/aggressive behaviors. Using the phylogenetic comparative approach, we tested whether frontal black Melanization is associated with elevated T around the time of breeding plumage development across all bird species with available T-data. We found a context-dependent relationship between Melanization and T, varying with the type of ornamentation (patchy or full-black) and with the presumed taxonomic distribution of the hormonal control of plumage dichromatism. Within two taxa in which male plumage development is assumed androgen-dependent (Charadriiformes, Corvida), evolutionary increases in male Melanization, and melanin dichromatism correlated with increases in T in most analyses but not within the basal lineage (ratites, Galloanseriformes) with androgen-indepen-dent male plumage. Among Passeroidea with presumably genetically or luteinizing-hormone-based male plumage, Melanization and its dichromatism correlated with T only in species with <100 % frontal Melanization. These results were robust as we controlled for several confounding variables such as mating and parental behaviors. This study is the first to test and support the T-regulation hypothesis interspecifically, suggesting that among-species differences in Melanization may have evolved in response to differ-ences in circulating T in certain avian taxa. Our results imply that the extent of black ornamentation may serve as an honest indicator of male competitiveness in those species that evolved an appropriate hormonal basis (T dependence) for color production
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testosterone and melanin based black plumage coloration a comparative study
Behavioral Ecology and Sociobiology, 2008Co-Authors: Veronika Bokony, Laszlo Zsolt Garamszegi, Katharina Hirschenhauser, Andras LikerAbstract:Despite the functional significance of melanin- based plumage coloration in social and sexual signaling, the mechanisms controlling its information content are poorly understood. The T-regulation hypothesis proposes that melanin ornaments signal competitive abilities via the effects of testosterone (T) mediating both Melanization and sexual/aggressive behaviors. Using the phylogenetic comparative approach, we tested whether frontal black Melanization is associated with elevated T around the time of breeding plumage development across all bird species with available T-data. We found a context-dependent relationship between Melanization and T, varying with the type of ornamentation (patchy or full-black) and with the presumed taxonomic distribution of the hormonal control of plumage dichromatism. Within two taxa in which male plumage development is assumed androgen-dependent (Charadriiformes, Corvida), evolutionary increases in male Melanization, and melanin dichromatism correlated with increases in T in most analyses but not within the basal lineage (ratites, Galloanseriformes) with androgen-indepen- dent male plumage. Among Passeroidea with presumably genetically or luteinizing-hormone-based male plumage, Melanization and its dichromatism correlated with T only in species with <100% frontal Melanization. These results were robust as we controlled for several confounding variables such as mating and parental behaviors. This study is the first to test and support the T-regulation hypothesis interspecifically, suggesting that among-species differences in Melanization may have evolved in response to differ- ences in circulating T in certain avian taxa. Our results imply that the extent of black ornamentation may serve as an honest indicator of male competitiveness in those species that evolved an appropriate hormonal basis (T dependence) for color production.
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melanin based plumage coloration and flight displays in plovers and allies
Wader Study Group Bulletin, 2003Co-Authors: Veronika Bokony, Andras Liker, Tamas Szekely, Janos KisAbstract:Plovers and their allies exhibit an impressive diversity of melanin-based plumage patterns ranging from non-melanized to completely melanized species. We use phylogenetic comparative methods to test whether Melanization has evolved in relation to sexual selection for attracting mates, to selection for signalling territory defence, or to natural selection for camouflage. First, according to sexual-selection theory, melanized plumage has evolved to amplify the courtship displays of males. As predicted by this hypothesis, we found that males with aerial displays had more melanized plumage than males of ground-displaying species. In addition, sexual dimorphism in Melanization was greater in species with display flights than in species with ground displays. Second, Melanization may have evolved through social interactions to signal competitive ability in territory defence. We did not find evidence for this hypothesis, since breeding density was unrelated to the Melanization of either sex. Finally, melanized plumage may camouflage the incubating parent. The latter hypothesis was not supported, since Melanization was unrelated either to the darkness of nest substrate or the extent of vegetation cover. Taken together, our results are most consistent with the sexual-selection hypothesis, and suggest that melanized plumage has evolved to enhance the aerial displays of male plovers.