The seminal symphony: how to compose an ejaculate

Abstract

Ejaculates are fundamental to fitness in sexually-reproducing animals: males gain all their direct fitness via the ejaculate and females require ejaculates to reproduce. Both sperm and non-sperm components of the ejaculate (including parasperm, seminal proteins, water and macromolecules) play vital roles in post-copulatory sexual selection and conflict, processes that can potentially drive rapid evolutionary change and reproductive isolation. Here, we assess the increasing evidence that considering ejaculate composition as a whole – and potential trade-offs among ejaculate components – has important consequences for predictions about male reproductive investment and female responses to ejaculates. We review current theory and empirical work, and detail how social and environmental effects on ejaculate composition have potentially far-reaching fitness consequences for both sexes.

Sexual Conflict and Sperm Competition

“…These have been particularly well studied in Drosophila melanogaster (e.g., Wolfner 2002; Chapman 2008), although they are taxonomically widespread (Perry et al 2013). Seminal peptides found in the ejaculate of male D. melanogaster influence many aspects of female physiology and behavior, including female remating rate, egg production rate, and sperm storage.…”

Ejaculate allocation in Brachyura: What do males of Metacarcinus edwardsii respond to?

“…Recently, several authors have stressed that in some cases, the limited resource can be seminal fluid, especially the energetically expensive seminal proteins and lipids, rather than sperm (reviewed by Perry et al 2013). Therefore, a correct evaluation of the reproductive investment by males needs to take at least the amount of accessory fluids in the ejaculate into account.…”

Mate-guarding in a promiscuous insect: species discrimination influences context-dependent behaviour

“…Sperm production and mating both pose non-trivial costs to males (Simmons 2001) and numerous studies have illustrated the interaction between social environment and male sexual behaviour both in insects Wigby et al 2009;Bailey 2011;Billeter et al 2012;Bailey et al 2013;Han and Brooks 2013) and vertebrates (Firman et al 2013; recently reviewed by Kelly and Jennions 2011). While males may employ a variety of strategies in response to sperm competition (including, but not restricted to: changes in sperm number (Wedell et al 2002), ejaculation size (Gage 1991;Garcia-Gonzalez and Gomendio 2004); seminal protein composition (Wigby et al 2009;Perry et al 2013) and sperm morphology (Gage 1994) behavioural changes have the benefit of being ''cheaper'' and may allow for more rapid responses to fluctuations in local environment (Bretman et al 2011). However, failure to discriminate between con-and hetero-specifics may result in males adopting sub-optimal mating strategies, ultimately reducing their fitness.…”