Fluoxetine does not prevent interspecific mating between two hamster species

Abstract

In a recent study we showed that female Syrian hamsters (Mesocricetus auratus) from a laboratory stock readily mated with male Turkish hamsters (M. brandti). We hypothesized that captivity and/ or unconscious selection of the most receptive females by researchers or animal caretakers results in heightened female sexual receptivity and reduces the tendency to reject heterospecific males. To test this hypothesis, we decided to decrease female receptivity by injection of fluoxetine, which increases the levels of serotonin in a number of brain loci, including areas involved in mediating sexual behavior, and determine whether such a decrease in receptivity would result in better discrimination of heterospecific males and rejection of such males as mates. We treated estrous female Syrian hamsters with 20 mg / kg fluoxetine or vehicle and paired them with both a conspecific and a heterospecific male (Turkish hamster) in two sequential tests. All females showed similar behavior -they exhibited lordosis toward both conspecific and heterospecific males. We did not observe any sign of aggression. Latency to display lordosis and the duration of lordosis were not affected by fluoxetine. Fluoxetine thus did not have an effect on the behavior of females toward conspecific or heterospecific males. Independent of treatment (fluoxetine or vehicle injection), females did display lordosis significantly faster and for a longer duration in the presence of a conspecific male, even though these differences were small.

Adult female hamsters require long and sustained exposures to heterospecific males to avoid interspecific mating

“…2a) than in the 10-min delay group (40.3 ± 23.98 s). The duration of lordosis in naïve females measured in previous studies (delBarco-Trillo et al 2009b; delBarco-Trillo and Johnston 2010) was similar than for females in the 8-day delay group ( t 10.9 = 1.15, P = 0.28; Fig. 2a).…”

“…2b). The duration of aggression in both groups was significantly higher than for naïve females in previous studies (delBarco-Trillo et al 2009b; delBarco-Trillo and Johnston 2010; Mann–Whitney tests: P < 0.05; Fig. 2b).…”

“…1a). The duration of lordosis in naïve females (i.e., females that were never exposed to heterospecific males before testing) measured in previous studies (delBarco-Trillo et al 2009b; delBarco-Trillo and Johnston 2010) was similar to the duration of lordosis in females in the 1-hour group ( t 9.8 = 1.47, P = 0.17) and the 4-hour group ( t 11.8 = 1.66, P = 0.12; Fig. 1a); but higher compared to females in the 4-day and 8-day groups ( P < 0.05; Fig.…”

“…These findings indicate that females can discriminate between conspecific and heterospecific males. However, Syrian hamster females do not show an innate mating avoidance of heterospecific males (delBarco-Trillo et al 2009b; delBarco-Trillo and Johnston 2010). Such interspecific mating would be costly to Syrian hamster females because the failure to produce hybrids seems to occur after fertilization due to differences in the number of chromosomes between both species.…”

“…Syrian hamster females that have never encountered heterospecific males are receptive to and do not show any sign of aggression towards such males (delBarco-Trillo et al 2009b; delBarco-Trillo and Johnston 2010). However, when Syrian hamster females were exposed for 8 days to a conspecific male and a heterospecific male across wire-mesh partitions and then paired sequentially with those same two males, the females were aggressive and not receptive when paired with the heterospecific male whereas females were always receptive when paired with the conspecific male (delBarco-Trillo et al 2010).…”