Case Studies: Why do Male Long-tailed Manakins Cooperate during Courtship?
McDonald, D. B. 1989. Correlates of male mating success in a lekking bird with male-male cooperation. Animal Behaviour, 37: 1007-1022.
McDonald, D. B. 1993. Delayed plumage maturation and orderly queues for status: a mankin mannequin experiment. Ethology, 94: 31-45.
McDonald, D. B. and W. K. Potts. 1993. Cooperative display and relatedness among males in a lek-mating bird. Science, 266: 1030-1032.
Trainer, J. M. and R. J. Parsons. 2001. Uniformity of Long-tailed manakin songs from three localities in Costa Rica. The Wilson Bulletin, 113: 431-434.
The long-tailed manakin is a colorful Central American bird with an unusual pattern of courtship. Like the Greater prairie chicken described in chapter 6, groups of male long-tailed manakins display in leks to attract females. Unlike the Greater prairie chicken, however, the long-tailed manakins also court in groups. McDonald (1989) has described display and courtship behaviors of the long-tailed manakin. Each group consists of at least two individuals, an alpha male and a beta male, and sometimes as many as 11 younger individuals. Male long-tailed manakins attract females to the arena with synchronous toledo calls. Courtship consists of leapfrogging and butterfly flights by the alpha and beta males, and small popcorn jumps made by any other males in the group. Courtship is energetically expensive, and typically, only the alpha male will mate, not just with any given display, but over the entire breeding season!
Cooperative courtship thus requires that some individuals forego their own reproduction to further the reproductive efforts of others. Clearly, cooperative courtship does not involve simple reciprocity, as the same individual continues to mate throughout the breeding season. Two other explanations are possible, kinship, and delayed benefit. McDonald and Potts (1993) observed large numbers of leks in the long-tailed manakin over a period of more than ten years to try to understand the unusual mating habits of this species. The exercises below will allow you to review McDonald and Potts' data to draw your own conclusion about the merits of the kinship and delayed benefits explanations.
Investigating kinship:
McDonald used microsatellite markers for four loci to examine the relatedness of 33 groups of cooperating males. They calculated a multilocus coefficient of relatedness (R) using the method of Queller and Goodnight (1989). Values of the coefficient range from -1 to +1, with 0.5 representing the relatedness of siblings. A value of zero represents the background level of relatedness in the population. A positive value of relatedness for the actor and recipient would therefore indicate greater than expected relatedness, and a negative value would suggest that actor and recipient are more divergent than expected.
For the comparisons of the 33 groups of cooperating males, the average value of R obtained was -0.14, and the standard error (obtained through a jackknifing procedure) was 0.1.
This activity contains 10 questions.
Question 1
Based on the results described above and in Table 1, are alpha and beta males related? Does increasing relatedness result in increasing success?
Question 2
It is possible that individuals are very distantly related. In this case, the average value obtained (-0.14) might represent an overshoot of the zero mark. Calculate the 95% confidence limits using the standard error.
Question 3
Using path analysis for pedigrees as described in Box 11.1 of the text book, calculate the degree of relatedness for actors and recipients with the following relationships:
Question 4
Compare the value of the upper confidence interval obtained in question 2 with the values obtained from the path analysis. How distantly related would the birds have to be?
Question 5
Investigating delayed benefits:
McDonald also investigated whether there are delayed benefits for other males, particularly the beta male. From observing leks over a ten-year period, McDonald obtained the results in Tables 2-5. Using these data, answer the questions below.
How often do beta males copulate in comparison to alpha males, and in comparison to more junior males?
Question 6
How likely is it that a beta male will ascend to the alpha role?
Question 7
Why might younger males delay reproduction? What benefits are there for young males to delay reproduction, albeit for a long time?
Question 8
Is the future success of the beta, once he ascends to the alpha position, correlated with the success of the previous alpha? Use a Spearman rank correlation to test whether the new alpha's success in attracting female visitors and in copulating are correlated with the rates of his predecessor (see Table 6). The Spearman rank correlation test may be found in any basic statistics text that covers non-parametric methods.
Question 9
Recently, Trainer and Parsons (2001) found that long-tailed manakin songs exhibit very little geographic variation. Propose a hypothesis based on the experiments described here to explain the low levels of variability in song observed in this species in comparison with close relatives.
Question 10
Male long-tailed manakins exhibit delayed plumage maturation. Alpha and beta males possess mature plumage, whereas the other individual males in a group often still possess juvenile plumage. McDonald (1993) used stuffed birds with mature and immature plumage to investigate responses of cooperating groups to newcomers. What responses would you expect to see?
Attachment:- manakin_data.rar