Variability of Female Responses to Conspecific vs. Heterospecific Male Mating Calls in Polygynous Deer: An Open Door to Hybridization?

Males of all polygynous deer species (Cervinae) give conspicuous calls during the reproductive season. The extreme interspecific diversity that characterizes these vocalizations suggests that they play a strong role in species discrimination. However, interbreeding between several species of Cervinae indicates permeable interspecific reproductive barriers. This study examines the contribution of vocal behavior to female species discrimination and mating preferences in two closely related polygynous deer species known to hybridize in the wild after introductions. Specifically, we investigate the reaction of estrous female red deer (Cervus elaphus) to playbacks of red deer vs. sika deer (Cervus nippon) male mating calls, with the prediction that females will prefer conspecific calls. While on average female red deer preferred male red deer roars, two out of twenty females spent more time in close proximity to the speaker broadcasting male sika deer moans. We suggest that this absence of strict vocal preference for species-specific mating calls may contribute to the permeability of pre-zygotic reproductive barriers observed between these species. Our results also highlight the importance of examining inter-individual variation when studying the role of female preferences in species discrimination and intraspecific mate selection

A methodology for Raman characterisation of MoDTC tribofilms and its application in investigating the influence of surface chemistry on friction performance of MoDTC lubricants

In this study, Raman spectroscopy has been employed to understand the influence of surface chemistry on friction in a tribocontact. Tribotests were conducted using molybdenum dialkyldithiocarbamate (MoDTC) lubricant in a steel/steel sliding contact. First, surface chemistry during the high friction regime, at the beginning of the test, and at the low friction regime, after long test durations, is investigated. Second, the influence of temperature on the surface chemistry of the resulting wear scars was investigated. The results show that at the beginning of tribotests with MoDTC lubricant, iron oxides are formed at the tribocontact which results in high friction. At longer test durations, adsorbed MoDTC on the ferrous surface decomposes to form MoS2 and low friction is observed. Surface chemistry at the tribocontact has been found to vary depending on the test temperature. At high temperatures, MoS2 is formed which provides friction reduction while at low temperatures, molybdenum oxide species and amorphous sulphur-rich molybdenum (MoSx) species are formed which do not provide friction reduction. Furthermore, it has been shown that MoS2 formed within the tribocontact at high temperatures has a slightly disordered crystal structure as a result of tribological processes