Effect of age on female choice in the field cricket, Gryllus interger

Female choice is an important element of sexual selection that \nmay vary among females of the same species. Few researchers have \ninvestigated the causes of variation in selectivity with respect to \npotential mates and overall level of motivation toward a stimulus \nsource representative of a mate. This study demonstrates that \nfemale age may be one cause of variation in female choice. Females \nof different ages may have different mate preferences. As females \nage, they have less time left to reproduce, and their residual \nreproductive value decreases. This should correspond to a higher \nreproductive effort which may be represented as increased \nmotivation and/or decreased selectivity. \nThe effect of age on mate choice in Gryllus integer was \ninvestigated by using a non-compensating treadmill, called the Kugel, \nto measure female phonotaxis. Artificially generated male calling \nsongs of varying pulse rates were broadcast in either a singlestimulus \nor a three-stimulus experimental design. The pulse rates \nused in the calling song stimuli were 70, 64, 76, 55 and 85 pulses per \nsecond. These corresponded to the documented mean pulse rate for \nthe species at the experimental temperature, one standard deviation \nbelow and above the mean, and 2.5 standard deviations below and \nabove the mean, respectively. Test females were either 11-14 days \nor 25-28 days post-ecdysis. Trials usually were conducted two to \nseven hours into the scotophase. \nIn the single-stimulus experiment, females were presented \nwith stimuli with only one pulse rate. Older females achieved higher \nvector scores than younger females, indicating that older females are more motivated to mate. Both groups showed little phonotactic \nresponse towards 55 or 85 pIs, both of which lie outside the natural \nrange of G. integer calling song at the experimental temperature. \nNeither group discriminated among the three pulse rates that fell \nwithin the natural range of calling song. \nIn the three-stimulus experiment, females were presented \nwith stimuli with one of three pulse rates, 64, 70 or 76 pIs, In \nalternation. Both age groups had reduced responsiveness in this \nexperiment, perhaps due to an increase in perceived male density. \nAdditionally, younger females responded significantly more to 64 \nand 70 pIs than to the higher pulse rate, indicating that they are \nselective with respect to mate choice. Older females did not \ndiscriminate among the three pulse rates. Therefore, it was \nconcluded that selectivity decreases with age. \nA further study was conducted to determine that these effects \nwere due to age and not due to the differing periods without a \nmating between the two age groups. Again, stimuli were presented \nin a three-stimulus experimental design. Age was held constant at \n28 days and time since last mating varied from 11 to 25 days. \nFemales varyIng in time since last mating did not differ in their \nresponses to the calling song pulse rates. This indicated that the \nincreased motivation and decreased selectivity exhibited In the \ninitial experiments were due to age and not to time without a mating. \nNeither time of trial nor female weight had an effect upon female \nphonotaxis. Data are discussed in terms of mate choice, residual \nreproductive value, and costs of choice.