Recent experiments indicate that male preferential harassment of high-quality females reduces the variance in female fitness, thereby weakening natural selection through females and hampering adaptation and purging. We propose that this phenomenon, which results from a combination of male choice and male-induced harm, should be mediated by the physical environment in which intersexual interactions occur. Using Drosophila melanogaster, we examined intersexual interactions in small and simple (standard fly vials) versus slightly more realistic (small cages with spatial structure) environments. We show that in these more realistic environments, sexual interactions are less frequent, are no longer biased towards high-quality females, and that overall male harm is reduced. Next, we examine the selective advantage of high- over low-quality females while manipulating the opportunity for male choice. Male choice weakens the viability advantage of high-quality females in the simple environment, consistent with previous work, but strengthens selection on females in the more realistic environment. Laboratory studies in simple environments have strongly shaped our understanding of sexual conflict but may provide biased insight. Our results suggest that the physical environment plays a key role in the evolutionary consequences of sexual interactions and ultimately the alignment of natural and sexual selection.
Preliminary assay: Effect of the physical environment on sexual activity
This file contains data from the Preliminary Assay – Effect of the physical environment on sexual activity. Each row is the data from a single replicate arena. The columns indicate the mating arena in which individuals were held (cage vs. vial), the experimental Block (1 vs. 2), and the average sexual activity directed toward individual females across all observation periods for that replicate. Sexual activity included singing to the female, chasing her, as well as attempted and actual copulations.
Preliminary_assay.csv
Assay 1: Effect of the physical environment on male sexual behavior
This file contains data from Assay #1 – Effect of the physical environment on male sexual behavior. Each row is the data from a 1 minute observation of a single female. The columns indicate the mating arena in which the female was held (cage vs. vial), the replicate number (10 replicates of each arena were performed), the colour with which the female was dusted (red vs. green), and the Day (1-3) and Time (morning, noon, afternoon) of the observation. FlyOnFood indicates whether the female fed on live yeast at any point during the observation (1 = yes, 0 = no), Number_interactions is the total number of sexual activities directed toward the female by males where sexual activity included courtship (i.e. singing, chasing) and attempted copulation (actual copulations were rare and observations in which this occurred were excluded, as indicated by the blank cells). Interaction_duration is the total duration of all sexual encounters involving the female during the 1 minute observation (including actual copulations).
assay1.csv
Assay 2: Effect of the physical environment on male-induced harm
This file contains data from Assay #2 – Effect of the physical environment on male-induced harm. Each row is the survival and fecundity data from females from a single replicate arena. The columns indicate whether the replicate experienced high or low male exposure, the mating environment in which individuals were held (cage vs. vial), the number of females that survived (survived) out of a total of 35, the proportion that survived, and the average fecundity of 10 of the surviving females (avg_fecundity).
assay2.csv
Assay 3: Effect of the physical environment on how male choice alters selection on females
This file contains data from Assay #3 - Effect of the physical environment on how male choice alters selection on females. Each row is the data from the females of one colour (red vs. blue) from one replicate. Thus, each replicate is represented in two rows (once for blue females and once for red). The columns indicate the replicate label ID, the mating arena type (cage vs. vial), the treatment type (choice vs. no choice), the size of the focal females (large vs. small), the colour with which the focal females were dusted (red vs. blue), the number of surviving females (out of 17), the survival percentage, and fecundities for each of seven females, the average fecundity of these seven, and replicate type. Replicate type notes whether the arena contained females that were large only, small only, or mixed (small and large) and whether the arena was a cage or vial. Mixed vials can be RB or BR, indicating whether large females were dusted red or blue (respectively) with small females being dusted the alternate.
Assay3.csv