Submitted to: Entomologia Experimentalis et Applicata
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/28/2012
Publication Date: 4/15/2013
Citation: Harwood, J.F., Vargas, R.I., Carey, J.R. 2013. Leg impairement magnifies reproductive costs in male Mediterranean fruit flies, Ceratitis capitata. Entomologia Experimentalis et Applicata. 147(1):73-81. DOI:10.1111/EEA.2013-12042. Interpretive Summary: Insects frequently accumulate injuries with age in nature. A frequent outcome of impairment is an increased risk of mortality and a reduction in life expectancy. General life history theory predicts that an increase in the risk of mortality should lead to an increase in reproductive effort, as explained by the terminal investment hypothesis. Despite the widespread occurrence of acquired injury in nature, there is a paucity of experimental data for the effects of impairment on life history trade-offs between reproduction and survival. One method for testing for the effects of impairment in insects has been the surgical removal or manipulation of external anatomical structures. The primary objective of this study was to determine the effects of impairment on the risk of mortality and the cost of reproduction in male Mediterranean fruit flies. A secondary objective was to quantify the effect of early life reproductive experience on late life mortality when combined with amputation. This study conducted at Agricultural Research Service (ARS), USDA, PBARC, Hilo, HI, indicated that the risk of mortality was greater for males that were paired with females early in life than for males that remained unpaired. Amputation induced impairment increased the risk of mortality and shortened the life expectancy of males, regardless of the age when the leg segments were removed. Impaired males experience the same reduction in life expectancy due to female access as the intact males, despite the additional risk of mortality from the impairment caused by external damage does not appear to elicit an increase in reproductive effort in male medflies, as expected through the terminal investment hypothesis, but instead increases the cost of mating.
Technical Abstract: Injuries frequently accumulate with age in nature. Despite the commonality of injury and the resulting impairment, there are limited experimental data for the effects of impairment on life history trade-offs between reproduction and survival in insects. We tested the effects of artificial injury and the resulting impairment on the reproductive costs and behavior of male medflies, Ceratitis capitata (Wiedmann) (Diptera: Tephritidae). Treatment flies were impaired by amputating tarsomere segments 2-5 from the right foreleg at either eclosion or age 22 days. The effect of impairment and age on the cost of reproduction was tested by varying the timing of female availability among the treatments. Courtship behavior and copulation rates were observed hourly from age 2 through 5 days to determine the effects of impairment on reproductive behavior. Female access combined with the impairment reduced the life expectancy of males more than the impairment alone, while the health effect of amputation was influenced by age. Conversely, the risk of death due to impairment was not influenced by the males' mating status prior to amputation. The males' copulation success was reduced due to impairment, while courtship behavior was not affected. Impairment does not reduce the males' impulse to mate but decreases the females' receptivity to copulation, while also increasing the cost of each successful mating. Overall, minor impairment lowers the reproductive success of males while also reducing longevity.