Crickets increase sexual signalling and sperm protection but live shorter in the presence of rivals

Abstract

The sociosexual environment animals experience through their life can shape the evolution of key life history traits, including longevity. Male–male competition, for instance, may influence the resources allocated to traits involved in male reproductive success. Here, I test whether lifelong exposure to a competitor male influences male investment in pre‐ and post‐copulatory sexual traits (calling effort and sperm quality) and how this affected the oxidative status and longevity of male field crickets (Gryllus bimaculatus). As expected, the visual exposure to a mating competitor promoted a higher calling effort in the male crickets but resulted in a decline in the haemolymph antioxidant content. The haemolymph antioxidant content negatively covaried with the antioxidant content of the sperm but interestingly, only when the males were exposed to a competitor. This suggests that when mating competition is high, males may prioritize sperm antioxidant protection against somatic maintenance. Finally, I provide evidence that male–male competition imposes additional costs to reproduction, as males exposed to a mating competitor lost a significant proportion of body antioxidant defences and body mass over time and in long term, had a reduced lifespan. Overall, this study strongly suggests that intrasexual competition may impose additional oxidative costs during reproduction for males, with negative consequences on lifespan. Moreover, the results highlight the role of oxidative stress as a physiological mechanism underlying the trade‐off between reproduction‐longevity and through which sexual selection may contribute to the evolution of senescence patterns.

Social dominance and reproduction result in increased integration of oxidative state in males of an African cichlid fish

“…Accordingly, studies have shown that reproductive effort can increase oxidative damage and decrease antioxidant capacity in a range of animal species (Christe et al, 2012; Sawecki et al, 2019; Sharick et al, 2015; Stier et al, 2012), and that oxidative stress can negatively affect survival or lifespan (Archer et al, 2013; Bize et al, 2008). In many animals species, social dominance is associated with breeding, and similarly, there is cumulative evidence that social dominance results in an oxidative cost, especially when high dominance is linked to intense agonistic interactions (Beaulieu et al, 2014; Border et al, 2019; van de Crommenacker et al, 2011) and/or increased reproductive effort (Cram et al, 2015; Noguera, 2019; Silva et al, 2018). At the same time, there are also several studies suggesting there is no oxidative cost of social dominance and/or reproduction and that breeding may even reduce oxidative stress (Blount et al, 2016; Costantini et al, 2014; Garratt et al, 2013).…”

Acoustic signalling in Orthoptera

“…It is common for males to put more effort into singing (greater singing effort or higher duty cycle) if they can hear rival males (e.g. Anichini et al, 2018;Callander et al, 2013;Mhatre and Balakrishnan, 2006;Morris et al, 2002;Noguera, 2019;. Males of one Mecapoda bush-cricket species simply start singing as soon as a rival does (Krobath et al, 2017).…”

Heightened perception of competition hastens courtship

“…Previous studies have shown that male calling effort is strongly affected by the social environment, whether that be developmental plasticity caused by the perception of future competition at the juvenile stage (Kasumovic et al 2012;Kasumovic et al 2013), flexibility caused by recent or current exposure to rival males (Callander et al 2013;Noguera 2018), or current access to potential mates (Houslay et al 2017). Here we show that males also exhibit an increase in calling effort when exposed directly to another male.…”

“…The same study demonstrated that signalling investment is highly responsive to the availability of a potential mate: males are more likely to signal, and signal for longer, if a female is present relative to when absent. In related species of crickets, the recent or current presence of rival males at adulthood can increase calling effort (Callander et al 2013;Noguera 2018), suggesting plasticity of signalling behaviour based on perceived competition. Manipulations of the juvenile social environment have also indicated that crickets can perceive future competition rates and adjust investment in reproductive tissues (Bailey et al 2010) and agespecific calling effort (Kasumovic et al 2013) accordingly.…”