Monday, December 11, 2006 - 8:35 AM

Gradient sensitivity of female color morphs to temperature in the damselfly Megalagrion calliphya (Odonata: Coenagrionidae)

Idelle Cooper,, Indiana University - Bloomington, Indiana University-Bloomington, Bloomington, IN, David Foote,, U.S. Geological Survey, Kilauea Field Station, Hawaii National Park, HI, and Lori Tango,, University of Hawaii, Pacific Cooperative Studies Unit, University of Hawaii at Manoa, Honolulu, HI.

Color polymorphisms limited to females are common in odonates. Typically, one female morph appears lightly-colored and cryptic while the other looks like the brighter-colored conspecific male. Maintenance of any dimorphism within populations is an evolutionary puzzle because a slight, consistent advantage to one morph will quickly lead to fixation. Female-limited dimorphisms in particularly have been intriguing biologists for over 100 years; the evolutionary cause and maintenance remain unknown despite molecular evidence that selection is maintaining the dichromatism. Previous studies have focused on sexual selection and suggested that the male mimic may serve as a strategy of females to avoid costly sexual interactions. However, recent studies cast doubt on this explanation. I discovered a female-limited dichromatism in the Beautiful Hawaiian Damselfly, Megalagrion calliphya (Coenagrionidae), which appears to be the only species in the endemic radiation to display such variation. My gradient survey reveals that the male-colored morph increases in frequency from 0% to 97% over an elevational increase of 1400 meters. Conditions throughout this gradient are very similar except for temperature, which decreases at higher elevations. Recent lab and field experiments which test the effect of temperature on female morph suggest that body color plays an important role in thermal balance. It has often been suggested that variable selection over geographic ranges or in time may be responsible for the maintenance of extensive genetic variation. Our gradient surveys and thermoregulation experiments elucidate the role of body color in thermoregulation and suggest an adaptive significance of male-colored females.

Species 1: Odonata Coenagrionidae Megalagrion calliphya (damselfly)

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