Winter Reproduction of Peromyscus in Rider Park, Lycoming Co., PA K.W Hopkins, A.K. Smolarek, and D.R. Broussard Department of Biology, Lycoming College, Williamsport, PA Introduction Mammals in temperate latitudes use many environmental cues as signals to reproduce or not to reproduce. These signals can include food resource level, temperature, and daylength (photoperiod). Studies have shown that photoperiod is a common reproductive cue among seasonally reproducing rodents. In species of rodents with large geographic distributions, those in areas with longer average photoperiods in the winter reproduce more frequently compared to those in areas with shorter photoperiods in the winter. For example, male and female Peromyscus maniculatus (deer mice) in Texas reproduce on average 12 months out of the year whereas populations in Michigan reproduce only a few months out of the year specifically in late spring and summer Patterns of winter reproduction in Pennsylvania populations of deer mice are poorly understood. In fact, some southern PA populations have been shown to reproduce throughout winter for unknown reasons while other populations in the state only reproduce in the spring and summer. This study focused on the winter reproduction of local Peromyscus maniculatus and Peryomyscus lecoupus (white-footed mouse) populations and how their patterns compare to those reported for other populations in different latitudes. The study will be carried out at Rider Park which is an 870 acre park with wooded and meadow habitats located in Lycoming County north of Williamsport. Methods In Rider Park, four transects were set up in straight lines. Each transect consisted of 30 traps placed 10 yards apart. Two of the transects were in bushy field areas and the other two transects were set up in a wooded areas. Sherman live traps were used to capture both species of mice and were baited with a mixture of peanut butter and oats. Traps were set in the evenings. The following morning, the traps were checked. Each mice captured was fitted with numbered metal ear tags. With each captured mouse, the body weight, sex, and sexual condition were monitored. For males, sexual condition was assessed by the position of the testes. If testes were scrotal (visible) then the mouse was regarded as reproductively active. If the testes were not descended (not seen), then the mouse was considered as reproductively inactive. Females were regarded as reproductively active if they were pregnant or lactating. For Peryomyscus that were recaptured, the measurements were monitored over a period of 3 months to gain insight into cues for the onset of reproduction. Figure 1. Results for Photoperiod from January 19 through April 9 Figure 2 shows results for Temperature from January 19 through March 21 Figure 3. Number of reproductive Mice in Rider Park RESULTS A total of 720 trap nights (1 trap set for one night) in 6 sessions yielded 42 individual Peromyscus captured (Table 1). Photoperiod showed a steady increase from the start of the study. Day length increased approximately 3 hours from mid January to late April (Figure 1). The temperature was collected for each day. As seen in Figure 2, the temperature varied extremely. Also there heavy snow fall and a persisting layer of ice on the ground. Random snow fall contributed to drastic changes in temperature from day to day. There was a low of -21 o C and a high of 16 o C. The temperature and snow also affected the amount of days that allowed for trapping of mice to prevent them dying overnight. Table 1 includes the two type of Peromyscus caught, P. leucopus and P. maniculatus. A total of 32 P. maniculatus were caught, 17 male and 15 female with 3 recaptures in each. Male P. maniculatus had an averaging weight of grams and female P. maniculatus weight averaged grams. Only 2 male P. leucopus were caught and were recaptured. The male P. leucopus had a weight averaging grams. Figure 3 incorporates the amount of daylight with the amount of the reproductive mice. When daylight was less than 12 hours, only 1 mouse was considered reproductive. When there was more than 12 hours of light, 14 out of the 18 mice were considered reproductive. Discussion The Peromyscus species are very similar to one another especially with their physical characteristics. Peromyscus maniculatus and Peromyscus leucopus also have a widely overlapping geographic range. The only physical difference is that the P. maniculatus has a sharply bi-colored tail while P. leucopus has a fuzzy bio- colored tail. This made it hard to distinguish the species in the field. There were four transects where traps were set up. The forest area was supposed to target P. leucopus and the brushy fields were supposed to target P. maniculatus. However, no mice were found in the two forest transects. More P. maniculatus were captured then P. leucopus. This was probably caused by the fact that the natural habitat of the brushy field favors the P. maniculatus. The natural habitat for P. leucopus favors the forest and there was a longer lasting ice layer of snow that formed on the forest floor. Trapping of Peromyscus began in January when the photoperiod was 9 hours and 48 minutes of daylight. The study ended in April with 12 hours and 57 minutes of daylight. When there was less than 12 hours of daylight, only one male mouse caught had his testes descended. This mouse was actually caught when there was 11 hours and 42 minutes of daylight. When there was over 12 hours of daylight, the amount of mice that were reproductive increased dramatically. The percentage of mice that were reproductive was 69.3%. This percentage does not include recaptured mice. Temperature was very random with snow fall and there was no correlation with reproductively leading us to believe that the photoperiod is very influential as their main cue to start reproduction. As the photoperiod increased, there was more Peromyscus that were reproductive. Future studies can include continuous trapping throughout the year. Also geographical and controlled lab studies that control photoperiod should be conducted to gain further insight into Peromyscus. # of Male Avg. Male weight # of Female Avg. Female weight P. maniculatus g g P. lecoupus420.13gN/A Table 1: The average mass in grams of Peromyscus