Wilkinson_&_Reillo_1994

Wilkinson_&_Reillo_1994 - Female choice response to...

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Female choice response to artificial selection on an exaggerated male trait in a stalk-eyed fly GERALD S. WILKINSON AND PAUL R. REILLOt Department of Zoology, University of Maryland, College Park, Maryland 20742, U.S.A. SUMMARY Quantitative genetic models for the evolution of exaggerated male traits through female mate choice predict that selection on male ornaments should cause a correlated response in female preferences. Furthermore, female selectivity should be inversely related to costs of mate choice. Here we use a stalk- eyed fly, Cyrtodiopsis dalmanni (Diptera: Diopsidae), which exhibits pronounced sexual dimorphism in eye span, to evaluate these predictions. Field observations reveal that each evening females aggregate while males disperse among roosting sites where mating occurs. A positive regression between male relative eye span and the number of females in an aggregation suggests that sexual selection acts on male eye span. Mate choice experiments in the lab, using flies after 13 generations of bidirectional selection on male relative eye span, reveal that females from long eye-span lines and an unselected population preferred long eye-span males. Short eye-span line females, however, preferred short eye-span males, demonstrating a genetic correlation between female preference and a sexually selected male trait. Eye span of the largest male in a field aggregation correlated positively with female age, as estimated by amount of eye pigment, and was independent of egg number, thereby providing no evidence that mate choice impairs female survival or fecundity. 1. INTRODUCTION The evolution of exaggerated male traits by female mate choice is highly controversial (Kirkpatrick & Ryan 1991; Maynard Smith 1991). One view main- tains that male ornaments coevolve with female preferences. Selecting an ornamented mate causes genes that influence expression of male trait and female preference to reside in the same offspring, creating linkage disequilibrium (Lande 1981; Kirkpatrick 1982). The magnitude of the resulting genetic cor- relation can influence evolutionary outcome. If the genetic correlation is high relative to the heritability of the male ornament, then a runaway process can occur (Lande 1981). Otherwise, the trait and preference increase until viability selection against further trait elaboration balances sexual selection. A genetic cor- relation between ornament and preference has also been assumed in some, but not all (Grafen 1990), good- genes models of the handicap principle (Zahavi 1977). Handicap refers to a costly male ornament that indicates viability. Evolution of female preferences for handicaps requires genetic variation for viability and depends on the magnitude of the genetic correlations between female preference, male ornament and vi- ability (Iwasa et al.
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This note was uploaded on 07/01/2011 for the course L 567 taught by Professor Curtis during the Fall '10 term at Indiana State University .

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Wilkinson_&_Reillo_1994 - Female choice response to...

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