Evolution of extreme sexual dimorphisms : structural and behavioral convergence among broad-headed male Drosophilidae (Diptera). American Museum novitates ; no. 2939
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Date
1989
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New York, N.Y. : American Museum of Natural History
DOI
DOI
Abstract
"Males with broad heads (hypercephaly) have arisen 21-24 times in various taxa of flies; 11 instances are in the Drosophilidae. Details of the morphological modification of the male head vary among the hypercephalic taxa, with drosophilids possessing all the types of modifications seen in other hypercephalic flies. Cephalic modifications include distension of the eyes and/or various cranial sclerites or plates (i.e., facial, parafacial, fronto-orbital, occipital plates, and the frontal vitta and ocellar triangle). Reproductive behavior of hypercephalic drosophilids and their close relatives is described for some species and reviewed for others. Measurements are given on eye and head shapes and comparisons are made of approximate optical resolutions. Associated with hypercephaly is aggressive male behavior (head butting and jousting) and vision enhanced for either binocularity (in the pedunculate eye forms) or frontal resolution (those species with conical eyes). Relative growth was compared among the drosophilids using regressions of log10 measurements of head width on thorax length. Hypercephaly is a consequence, despite the manner of modification, of accelerated growth of certain head sclerites, which is manifested in Zygothrica as well by abnormal growth of setae. Predisplacement of growth onset and hypermorphosis rarely contribute to the sexual dimorphism. Only Zygothrica latipanops males were found to occur in two discrete classes (alpha and beta, or extremely and moderately hypercephalic males). A phylogenetic analysis of the apomorphies associated with hypercephaly provided the following hypothesis: in order from the most to least inclusive feature is territoriality, a frontal approach prior to male fighting, head butting, and then, at the apical node, are hypercephaly with its associated optical features and jousting. No recourse is made to explanations of natural or sexual selection regarding origins of correlated traits"--P. [1].
Description
25 p. : ill. ; 26 cm.
Includes bibliographical references (p. 23-25).
Includes bibliographical references (p. 23-25).
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