Female Sexual Preferences Toward Conspecific and Hybrid Male Mating Calls in Two Species of Polygynous Deer, Cervus elaphu s and C. nippon

Abstract

The behavioral processes at the basis of hybridization and introgression are understudied in terrestrial mammals. We use a unique model to test the role of sexual signals as a reproductive barrier to introgression by investigating behavioral responses to male sexual calls in estrous females of two naturally allopatric but reproductively compatible deer species, red deer and sika deer. Previous studies demonstrated asymmetries in acoustic species discrimination between these species: most but not all female red deer prefer conspecific over sika deer male calls while female sika deer exhibit no preference differences. Here, we extend this examination of acoustic species discrimination to the role of male sexual calls in introgression between parent species and hybrids. Using two-speaker playback experiments, we compared the preference responses of estrous female red and sika deer to male sexual calls from conspecifics versus red × sika hybrids. These playbacks simulate early secondary contact between previously allopatric species after hybridization has occurred. Based on previous conspecific versus heterospecific playbacks, we predicted that most female red deer would prefer conspecific calls while female sika deer would show no difference in their preference behaviors toward conspecific and hybrid calls. However, results show that previous asymmetries did not persist as neither species exhibited more preferences for conspecific over hybrid calls. Thus, vocal behavior is not likely to deter introgression between these species during the early stages of sympatry. On a wider scale, weak discrimination against hybrid sexual signals could substantially contribute to this important evolutionary process in mammals and other taxa.

Keywords: Deer; Hybridization; Introgression; Mating; Sexual communication; Sexual preference; Species discrimination; Vocalization.

Fig. 1

Spectrogram of adult male mating vocalizations: a red deer roar, b sika deer moan, and c red × sika F1 hybrid deer wail

Fig. 2

First component factor scores of acoustic parameters, averaged within exemplars. Error bars represent 95 % confidence intervals

Fig. 3

Preference behaviors exhibited by hinds in response to conspecific versus heterospecific or conspecific versus hybrid male mating calls. Box plots represent the preference behaviors of female red deer and sika deer: Instances (a) and total time (c) spent in proximity zones by red deer and instances (b) and total time (d) spent in proximity zones by sika deer. Data from conspecific versus heterospecific playback experiments are sourced from Wyman et al. (red deer hinds) and Wyman et al. (sika deer hinds) for comparison with the conspecific versus hybrid experiments. Upper and lower whisker limits are set to 1.5*IQR (interquartile range) above and below the third and first quartile, respectively. Circles represent mean preference behavior values and stars represent outliers present outside of the whisker limits