INTRODUCTION
Phenotypic plasticity is defined as the capacity of a genotype to produce alternative phenotypes depending on the environmental context it is exposed to (Gause, 1947; Levins, 1963; Bradshaw, 1965). In particular, adaptive phenotypic plasticity allows organisms to adjust their phenotype in order to cope with contrasting environmental conditions (Demmig-Adams et al. , 2008). Whether adaptive phenotypic plasticity can evolve or not depends on its associated costs and is contingent on a certain degree of environmental predictability (DeWitt, Sih and Wilson, 1998; Reed et al. , 2010; Botero et al. , 2015). More specifically, plasticity in reproductive behaviour and strategies (reproductive plasticity ) is a central component of individual fitness, particularly so in the face of high spatio-temporal heterogeneity in socio-sexual contexts (Dewsbury, 1982; Gage, 1995; Kokko and Rankin, 2006; Rebar, Barbosa and Greenfield, 2019). For this reason, reproductive plasticity is often considered to be a key determinant of population responses to rapid environmental change (Agrawal, 2001; Charmantier et al. , 2008).
Across the animal kingdom, sexual selection is generally male-biased (Bateman, 1948; Janicke et al. , 2016), and because relatively high variance in reproductive success increases the adaptive value of phenotypic plasticity, males can be expected to display high plasticity in reproductive behaviour (Bretman, Gage and Chapman, 2011). Male plastic responses to intra-sexual competition are rather well documented across distant taxa (delBarco-Trillo and Ferkin, 2004; Aragón, 2009; Bretman, Gage and Chapman, 2011). For instance, males of different species have been shown to strategically adjust mating duration (Bretman, Fricke and Chapman, 2009; Mazzi et al. , 2009), mate guarding behaviour (Carazo et al. 2007), sperm transfer (Gage, 1991; Gage and Baker, 1991), and even seminal fluid protein transfer (Wigbyet al. , 2009) in response to the socio-sexual environment (e.g. sperm competition risk and/or intensity cues; Shifferman, 2012). Ultimately, high intra-sexual competition can even lead to the evolution of adaptive alternative strategies in reproductive behaviour (Hurtado-Gonzales and Uy, 2010).
Recently an empirical study reported that, in Drosophila melanogaster , short-term perception of female cues ahead of access to reproduction (termed sexual perception ) can increase male reproductive performance in a competitive environment (Corbel et al. , 2022). This plastic response to female cues seems to be adaptive, and may explain previously documented survival and reproductive costs linked with sexual perception in males (Gendron et al. , 2014; Harvanek et al. , 2017; García-Roa, Serra and Carazo, 2018). Interestingly, this study found that sexual perception benefits tended to be rapidly induced (noticeable as early as over the first 24 hours following access to females), and spanned across the lifespan of males. Given that male plastic responses to sexual perception can magnify the opportunity for selection (Carazo et al. , 2017; García-Roa, Serra and Carazo, 2018; Corbel et al. , 2022) and may help explain ageing in response to sensory stimuli (Gendron et al. , 2014; Harvanek et al. , 2017), identifying the mechanisms responsible for such male plasticity could provide valuable information.
Here, we aimed to investigated the short-term fitness consequences of sexual perception in detail. To this aim, we studied the effect of sexual perception on several short-term pre- and post-copulatory fitness components in D. melanogaster males. Similarly to other polygamous species with high intra-sexual competition, pre-copulatory fitness of males of this species is modulated by male-male competition and female choice, both of which contribute to determine male mating success in a competitive scenario (Dow and Von Schilcher, 1975; Andersson, 1994; Arbuthnott et al. , 2017). Post-copulatory male fitness, in turn, is largely driven by sperm competitiveness (mostly sperm-offense, see Fricke et al. , 2010; Simmons and Fitzpatrick, 2012). Additionally, male manipulation of female reproductive behaviour via the transfer of accessory gland proteins within the seminal fluid is known to benefit male post-copulatory fertilisation success (Chenet al. , 1988; Aigaki et al. , 1991; Chapman, 2001; Chapmanet al. , 2003; Liu and Kubli, 2003; Fiumera, Dumont and Clark, 2005; Ravi Ram and Wolfner, 2007; Fricke et al. , 2009; Hopkinset al. , 2019). In fact, there is ample evidence that males strategically adjust their seminal fluid protein transfer depending on the socio-sexual environment context they experience (see for instance Wigby et al. , 2009; Hopkins et al. , 2019). Thus, in order to fully capture the effects of sexual perception on short-term fitness, we exposed virgin males to female cues for a period of 24 hours (while preventing mating) and subsequently measured the following male fitness components: a) mating success, b) mating latency and duration, c) sperm competitiveness, and d) ejaculate effects on female receptivity and oviposition rate.