The Waiting Game: A Case Study
The Waiting Game: A Case Study on the Behavioral Ecology of Long-Tailed Manakins
Manakin Case Study Parts 2 and 3
The Waiting Game: A Case Study on the Behavioral Ecology of Long-Tailed Manakins by Susan Bandoni Muench, Department of Biology, SUNY Genesea, Geneseo, NY
Part II – Kinship
Charles Darwin (1859) was the first biologist to raise the question of why individuals might forego their own reproduction and assist others. He raised the question in reference to non-reproductive workers among the social insects. Darwin concluded that the workers might derive a benefit from contributing to the reproductive success of their relatives (this developed into what is called kin selection or the kin hypothesis). Later, Hamilton (1964a, 1964b) coined the term inclusive fitness to describe the sum of direct and indirect reproductive contributions. Indirect reproductive contributions are those of close relatives who share genes with an individual and therefore are able to pass these genes on. Through the concept of inclusive fitness, it is possible to explain some otherwise puzzling behaviors as increasing an individual’s indirect fitness. According to Hamilton, altruistic behaviors should occur when the cost to the actor’s direct fitness is off-set by gains in indirect fitness. David McDonald and Wayne Potts (1994) decided to test the hypothesis that pairs of cooperating males in the long-tailed manakin are closely related. They collected tissue samples from 33 pairs of birds, and examined variation in micro satellite loci. This means that the researchers were looking at the diversity of genes and messages for the genes at specific places, or loci, on chromosomes (or DNA molecules). The researchers identified four polymorphic loci, each with two to four alleles. Alleles are messages for a trait. Using the micro satellite data, they calculated relatedness coefficients (see Textbox below). Relatedness is considering kin – how closely related are individuals to each other. The higher the R value (closer to 1), the more closely related individuals are to one another. Values of this relatedness coefficient can vary from -1 to 1, with full siblings expected to have values of 0.5. Negative values result when two individuals share fewer alleles than the expected based on the frequencies of those alleles in the population. For more description of this see the textbox on relatedness coefficients below. The data are shown in Table 1.
Table 1. Relatedness coefficients.
Pairs of cooperating males in the lek with R > 0 16
Pairs of cooperating males in the lek with R < 0 17
Mean relatedness coefficient (with confidence limits) -0.014 (-0.35, 0.7)
Questions
1. What do these data suggest?
2. The kin selection hypothesis can be reformulated in at least one other way given the data above. What is another way that kinship could show an effect, and how would you test for this?
For More Information ? Textbox: Relatedness Coefficients
In studies of the long-tailed manakin, two measures of relatedness are used. Although these measures are somewhat similar, they are calculated in different ways and used for different purposes. The first, Wright’s coefficient of relatedness, is a measure of how many genes relatives should share on average, given relationships that are known. Wright’s coefficient of relatedness, r, is calculated as .5n, where n is the number of links in the genealogy, summed for the number of shared ancestors. Thus, full siblings are separated by two steps in the genealogy and share two ancestors, resulting in an r value of 0.5. Halfsiblings are separated by the same number of steps in the genealogy, but share only one ancestor, and so are related by only 0.25. First cousins are separated by four steps, but share two ancestors, for a relatedness coefficient of 0.125. The second, the relatedness coefficient of Queller and Goodnight (1989), is used to estimate relatedness when the exact relationships among individuals are unknown. Individuals may share an allele either by descent or because that allele is common in the population. This relatedness coefficient, R, is calculated by comparing an allele frequency for one individual (1, .5 or 0 in a diploid species) to that of a reference individual, as well as in comparison to the population, summed over many alleles. Thus, R = ? (py-p)/? (px-p). Values of this relatedness coefficient can vary from -1 to 1, with full siblings expected to have values of 0.5. Negative values result when two individuals share fewer alleles than the expected based on the frequencies of those alleles in the population.
Part III – Cooperation An alternative way of exploring the role of kin selection is to investigate whether cooperating relatives might be more successful than cooperating unrelated males. In this case, unrelated males might still form pairs if relatives were unavailable.
McDonald and Pott’s data are shown in the table below.
Table 2. Coefficients of relatedness for pairs of cooperating males.
Comparison R- 0 R – 0
Pairs mating during the field season 7 4
Pairs displaying more than 10 times 6 3
Questions
1. What do these data indicate? Make sure to explain your thoughts fully.
2. What other possible explanations can you propose to explain the association between the alpha and beta males? You should be able to think of several here.
3. Formulate an hypothesis to test one of your proposed explanations. Remember an hypothesis is general (and a prediction is specifIC
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