Abstract
Abstract Sexual selection mediated by multimodal signals is common among polygynous species, including seasonally breeding mammals. Indirect benefit models provide plausible explanations for how and why mate selection can occur in the absence of direct benefits. Musth — an asynchronous reproductive state in male elephants — facilitates both inter- and intrasexual selection via indirect benefits, and it is further communicated through a multimodal signal. In this review, we synthesise existing evidence that supports the hypothesis that musth is a multimodal signal subject to sexual selection and that male elephants increase their direct fitness by propagating this signal while females accrue indirect benefits. Musth is characterised by a suite of physiological and behavioural changes, serving to facilitate copulation between the sexes, and via multisensory modalities musth conveys honest information about the condition of a male. Female elephants mate preferentially with musth males, increasing their own fitness in the absence of direct benefits. In addition, musth resolves dynamic dominance hierarchies among male elephants and often eliminates the need for costly physical combat. Future work in this field should investigate potential postcopulatory selection mechanisms in elephants, including sperm competition and cryptic female choice. These topics join other fundamental questions related to sexual selection, signalling, and indirect benefits that are still unanswered in elephants.
Highlights
Since Charles Darwin’s exploration of the theory in ‘The Descent of Man, and Selection in Relation to Sex’ (1871), biologists have shown keen interest in sexual selection (Maynard Smith, 1991; Andersson, 1994; Jones & Ratterman, 2009)
The purpose of this review is to summarise the current evidence that musth is a multimodal signal shaped by sexual selection and to pose further possibilities for research not often explored in large, long-lived mammals; we provide possible explanations for how elephants utilise multiple sensory channels in the musth signal and why depending on musth as a sexual signal could have evolved via inter- and/or intrasexual selection
Female elephants should exert a high degree of intersexual selection to choose an appropriate mate because fecundity in elephants is low (Seth-Smith & Parker, 1967; Thapa, 2009; Moss et al, 2019); there is much investment in offspring with exceedingly long interbirth intervals (Moss, 1983; Lee & Moss, 1986; Chelliah & Sukumar, 2015)
Summary
Since Charles Darwin’s exploration of the theory in ‘The Descent of Man, and Selection in Relation to Sex’ (1871), biologists have shown keen interest in sexual selection (Maynard Smith, 1991; Andersson, 1994; Jones & Ratterman, 2009). A well-known example of a sexually selected trait with multiple signal components is rut, a heightened reproductive period in some seasonally breeding ungulates (Mysterud et al, 2004; Pelletier & Festa-Bianchet, 2006) In these species, food resources and mating potential are seasonal; both sexes focus reproductive efforts simultaneously, making competition for mates intense. Musth is distinct from other sexually selected traits in mammals; it is asynchronous and regularly occurring, is likely influenced by a range of intrinsic, environmental, and social pressures, and acts to signal reproductive intent to conspecifics of both sexes, providing information about mate quality (intersexual selection) and competitive ability (intrasexual selection) (Figure 1).
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