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80 results for “Sexual dichromatism”
Data from: The bright incubate at night: sexual dichromatism and adaptive incubation division in an open-nesting shorebird
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Data from: Melanin-based sexual dichromatism in the Western Palearctic avifauna implies darker males and lighter females
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Sex‐specific effects of predation risk on parental care in a sexually dichromatic Neotropical songbird
<p>Predation risk affects a broad range of bird behaviours, especially parental care. The adaptive behavioural changes presented by both parents, however, may differ according to different levels of predation risk suffered by each sex. This is especially prominent in sexually dichromatic species, where one of the sexes is more visually conspicuous and hence vulnerable to increased nest predation risk during nest visits. Here, we experimentally investigated how predation risk affects the parental behaviour of a sexually dichromatic Neotropical passerine, the blue-black grassquit (Volatinia jacarina). We used playbacks of known predators and non-predatorial control sympatric species near nesting pairs in the field. Results show that grassquits modify their behaviour according to predation risk and that this behavioural response is sexdependent. Males decrease their nest visit times, become more discreet when moving towards the nest, and stop performing sexual displays after leaving the nest. In contrast, females tend to decrease latency to visit the nest and increase the duration of brooding bouts. These different sex responses reduce nest visual and acoustic detectability, since conspicuous males are readily spotted on nests and cryptic females camouflage nestlings and suppress begging calls. Although these behavioural changes might reduce predation risk, there might be a cost of reduced food load to nestlings and increased brood starvation risk. These changes in nesting activities illustrate the behavioural adaptability of passerines to ensure offspring survival in tropical high predation risk environments.</p>
Data from: Nest shape explains variation in sexual dichromatism in New World blackbirds
Following Charles Darwin, research on sexual dichromatism has long focused on sexual selection driving ornamentation in males. However, Alfred Russel Wallace proposed another explanation – that dichromatism evolves as a result of selection favoring crypsis in incubating females. Many recent studies suggest that evolutionary changes in sexual dichromatism often result from changes in female, in addition to male, plumage, yet the evolutionary mechanisms driving changes in female plumage remain largely unexplained. To test Wallace's hypothesis, we examined variation in sexual dichromatism and nest shape, a proxy for predation risk, among New World blackbirds (Aves: Icteridae). Phylogenetic models reveal an evolutionary correlation between sexual dichromatism and nest exposure. Specifically, we found that transitions in monochromatic lineages with exposed nests toward either concealed nests or dichromatism were common. Although this evidence supports Wallace's hypothesis that female incubation leads to selection for crypsis or concealment, we also found that transitions to monomorphism were common, even in lineages with exposed nests – a result suggestive of a role for positive selection on female ornamentation. These patterns of plumage evolution support a growing body of work emphasizing the importance of developing and testing hypotheses to explain evolutionary changes in female, as well as male, ornamentation.
Data from: Broad-scale variation in sexual dichromatism in songbirds is not explained by sex differences in exposure to predators during incubation
The evolution of sexual dichromatism provoked one of the greatest disagreements between Charles Darwin and Alfred Russel Wallace. According to Darwin the main driving force is sexual selection, whereby choosy females prefer showy males, leading to the evolution of conspicuous male plumage. On the other hand, Wallace suggested that dichromatism may arise because nest predation favors more cryptic females. To test the role of natural selection in the evolution of dichromatism we combined quantitative data on differences in parental share in nest attentiveness (representing the strength of natural selection on males vs. females) with spectrophotometric measurements of dichromatism in 412 species of songbirds from 69 families. We expected to find stronger dichromatism in open-nesting species with more divergent parental roles and in body parts exposed during incubation. Dichromatism was not related to the differences in parental share during incubation, but it was most pronounced in lekking species, migrants, and small species. Our results thus suggest that Wallace's hypothesis is not able to explain broad-scale variation in the dichromatism of songbirds, but point to a role for sexual selection, mutual mate choice, and migration strategy in shaping the extraordinary variation in dichromatism exhibited by songbirds.
Data from: Changes in sexual signals are greater than changes in ecological traits in a dichromatic group of fishes
Understanding the mechanisms by which phenotypic divergence occurs is central to speciation research. These mechanisms can be revealed by measuring differences in traits that are subject to different selection pressures; greater influence of different types of selection can be inferred from greater divergence in associated traits. Here, we address the potential roles of natural and sexual selection in promoting phenotypic divergence between species of snubnose darters by comparing differences in body shape, an ecologically relevant trait, and male color, a sexual signal. Body shape was measured using geometric morphometrics, and male color was measured using digital photography and visual system-dependent color values. Differences in male color are larger than differences in body shape across 8 allopatric, phylogenetically independent species pairs. While this does not exclude the action of divergent natural selection, our results suggest a relatively more important role for sexual selection in promoting recent divergence in darters. Variation in the relative differences between male color and body shape across species pairs reflects the continuous nature of speciation mechanisms, ranging from ecological speciation to speciation by sexual selection alone.
FIGURES 11–12 in A new sexually dichromatic species of Telenomus Haliday (Platygastroidea: Scelionidae) from India
FIGURES 11–12. Female antenna of Telenomus chandishae sp. n.
Data from: Sex-linked genomic variation and its relationship to avian plumage dichromatism and sexual selection
Background: Sexual dichromatism is the tendency for sexes to differ in color pattern and represents a striking form of within-species morphological variation. Conspicuous intersexual differences in avian plumage are generally thought to result from Darwinian sexual selection, to the extent that dichromatism is often treated as a surrogate for the intensity of sexual selection in phylogenetic comparative studies. Intense sexual selection is predicted to leave a footprint on genetic evolution by reducing the relative genetic diversity on sex chromosome to that on the autosomes. Results: In this study, we test the association between plumage dichromatism and sex-linked genetic diversity using eight species pairs with contrasting levels of dichromatism. We estimated Z-linked and autosomal genetic diversity for these non-model avian species using restriction-site associated (RAD) loci that covered ~3 % of the genome. We find that monochromatic birds consistently have reduced sex-linked genomic variation relative to phylogenetically-paired dichromatic species and this pattern is robust to mutational biases. Conclusions: Our results are consistent with several interpretations. If present-day sexual selection is stronger in dichromatic birds, our results suggest that its impact on sex-linked genomic variation is offset by other processes that lead to proportionately lower Z-linked variation in monochromatic species. We discuss possible factors that may contribute to this discrepancy between phenotypes and genomic variation. Conversely, it is possible that present-day sexual selection -- as measured by the variance in male reproductive success -- is stronger in the set of monochromatic taxa we have examined, potentially reflecting the importance of song, behavior and other non-plumage associated traits as targets of sexual selection. This counterintuitive finding suggests that the relationship between genomic variation and sexual selection is complex and highlights the need for a more comprehensive survey of genomic variation in avian taxa that vary markedly in social and genetic mating systems.
FIGURES 1–2 in Sexual dichromatism in a Mexican checkered beetle (Coleoptera: Cleridae: Neorthopleurinae)
FIGURES 1–2. Dorsal habitus of Nelsonoplium jeanae. (1) Female. (2) Male.
FIGURES 11–12 in A new sexually dichromatic species of Telenomus Haliday (Platygastroidea: Scelionidae) from India
FIGURES 11–12. Female antenna of Telenomus chandishae sp. n.
Data from: The effect of colour-producing mechanisms on plumage sexual dichromatism in passerines and parrots
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Data from: Broad-scale variation in sexual dichromatism in songbirds is not explained by sex differences in exposure to predators during incubation
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Data from: Sex-linked genomic variation and its relationship to avian plumage dichromatism and sexual selection
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Data from: Sexually selected dichromatism in the hihi Notiomystis cincta: multiple colours for multiple receivers
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Sex‐specific effects of predation risk on parental care in a sexually dichromatic Neotropical songbird
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Data from: Nest shape explains variation in sexual dichromatism in New World blackbirds
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Data from: Changes in sexual signals are greater than changes in ecological traits in a dichromatic group of fishes
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Data from: Sexual selection and diversification: reexamining the correlation between dichromatism and speciation rate in birds
Theory predicts that sexual selection can serve as an important driver of speciation, but phylogenetic comparative analyses have failed to demonstrate a consistent effect of sexual selection on species richness at macroevolutionary scales. Sexual dichromatism in birds is an example of a phenotypic trait that is hypothesized to reflect the intensity of sexual selection, yet previous studies have reached ambiguous conclusions regarding its role in promoting species diversification. Here, we revisit this problem by pairing published spectrophotometer estimates of plumage dichromatism in the bird-visible range with a newly developed method for modeling speciation rates on phylogenetic trees that explicitly accounts for diversification rate variation through time and among clades. We find little evidence linking dichromatism to speciation across birds, using several measures of dichromatism and macroevolutionary diversification. These results suggest that sexual dichromatism plays a limited role in determining speciation rates at macroevolutionary scales in birds.
Data from: Sexual selection and diversification: reexamining the correlation between dichromatism and speciation rate in birds
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Data From: A macroevolutionary analysis of cryptic coloration in sexually dichromatic grasshoppers of the genus Sphenarium (Orthoptera: Pyrgomophidae).
<p>RGB Data measured from the photographs (data RGB .ods) and Hue, Saturation, Brightness, and climatic data (data HSB.ods)</p>
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