How We Understand Sexual Selection and Male Phenotype Among the Birds of Paradise
The smears were examined for blood protozoa as well as microfilarial larvae of filariid nematodes. Haemoproteus spp. and Plasmodium spp. were counted as the number of protozoa per 10,000 red blood cells (RBC). Leucocytozoon spp., Trypanosoma spp., and microfilaria were counted as the total number of each type on the slide. About one half of the samples were scored for parasites withoutknowledge of the identity of the host.
Over time, genes associated with these aesthetically pleasing features are passed down and the attributes become more prominent within the species. This process is known as sexual selection. Natural selection is usually about competition for resources, but sexual selection is about competition for mates. On an island with abundant resources and few predators, females are the number one decider in how males evolve. Sexual dimorphism, strong physical distinctions between the sexes, is not found in all birds of paradise. All five birds in the Manucodia genus are monomorphic, with almost no plumage variation between the sexes. These species are also monogamous. One possible explanation for this is related to diet. Species where males and females share coloring tend to feed on less nutritious simple fruits like figs. Males must work with females to forage and successfully raise young, leaving no time for outside courtships. This isn’t an issue for species that eat a diverse and reliable diet of fruits and insects. Females are able to raise hatchlings alone, freeing up the male to court other females with his magnificent and much-needed plumage. Carola Parotia (Parotia carolae), Superb bird of paradise (Lophorina superba), and Blue bird of paradise (Paradisaea rudolphi) all have wildly different displays they perform for their female counterparts. During the Carola Parotia dance, males lift their flank feathers to form a tutu-like skirt and hop and waggle across the forest floor. Superb bird of paradise snap their breast shield and back plumes into a complete physical transformation, creating an ellipse of blue and black feathers around their head. Resembling nothing like a bird, they hop around the females, rhythmically snapping their tail feathers as they go. Blue bird of paradise hang upside down from the branches, pulsating with their blue and violet feathers spread out like a fan. During the show, Blue bird of paradise produce a low, soft buzzing sound.
In particular, the analysis of selection on females has highlighted a growing uncertainty about whether classical sexual selection can explain the evolution of ornamental traits in both sexes. This debate has major implications for our understanding of general patterns in biology, such as sexual dimorphism, sexual dichromatism and the expression of ornamental traits in both males and females of a species (e.g. mutual ornamentation). The evolution of ornamental traits in males is almost universally ascribed to sexual selection, presumably because male–male competition for sexual resources is usually so overt. By contrast, similar traits expressed in females have been explained in three different ways. The original view, favoured by Darwin, is that ornamental traits in females arise from selection acting on males and are simply the result of correlated inheritance—what we might today call ‘shared genetic architecture’. One of the main points of controversy relates to the array of social mechanisms influencing ornamental traits, and whether it is so broad that a more general theory than sexual selection is required to account for patterns of phenotypic evolution. Such questions have resurfaced periodically over the last century, generally inspired by conflicting views about how selection operates on ornamental traits in females (Huxley J. S. 1938).
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