It’s all in your head: the role of quantity estimation in sperm competition

Abstract

The study of animal cognition has provided valuable data throughout the years, yet its reliance on laboratory work leaves some open questions. The main question is whether animals employ cognition in daily decision-making. The following discussion uses sperm competition (SC) as a test case for demonstrating the effect of cognition on routine choices, in this case, sexual selection. Cognition is manifested here by males' ability to represent the number of rivals competing with them. I claim that response to SC is driven by quantity estimation and the ability to assess competition magnitude cognitively. Hence, cognition can determine males' response to SC, and consequentially it can be selected within this context. This supports the argument that cognition constitutes an integral part of an individual's toolbox in solving real-life problems, and shows that physical and behavioural phenomena can expose cognition to selection and facilitate its evolution.

Flexible memory controls sperm competition responses in male Drosophila melanogaster

“…There is also evidence lobes can form a long term memory trace distinct from those formed in the / lobes [27,35]. This dynamic control of behaviour may therefore underlie the ability of males to use the length of time they are exposed to a rival to estimate the risk of SC in a capricious social environment [7,12]. It is worth noting that the sperm competition response comprises both alteration of mating duration and ejaculate, which may become uncoupled after constant rival exposure [36].…”

Female meadow voles, Microtus pennsylvanicus, respond differently to the scent marks of multiple male conspecifics

“…Quantity estimation can be accomplished using non-numerical continuous cues such as amount estimation, which can co-vary with numerosity (Argillo et al 2011; Carazo et al 2012; Shifferman 2011). However, previous work has shown that meadow voles do not select the donor that provided scent marks that covered more surface area than those of another donor.…”

Quantity Estimation Based on Numerical Cues in the Mealworm Beetle (Tenebrio molitor)

“…Part of the problem lies in the difficulty of establishing whether quantity estimation in non-human animals is based on a computation of numerosity itself (i.e., quantity estimation sensu stricto ), or on non-numerical continuous cues that co-vary with numerosity (i.e., amount estimation; Agrillo et al, 2011; Shifferman, 2012). Quantity estimation is often investigated by exploring the capacity of animals to discriminate between two sets of objects differing in numerosity (e.g., Carazo et al, 2009).…”

“…As a matter of fact, the field of numerical cognition has experienced a gradual shift from extensive training in captivity or in artificial settings to considering spontaneous expression of numerical competence, and toward understanding how numerical competence functions for particular animals in their natural environments (e.g., Hager and Helfman, 1991; McComb et al, 1994; Uller et al, 2003; Flombaum et al, 2005; Hanus and Call, 2007). Sperm competition provides an ideal context in which to study numerical cognition in many invertebrates (Shifferman, 2012). Sperm competition makes reference to the evolutionary battle of males for the fertilization of a given set of ova (Parker, 1970).…”

“…Both SCR and SCI will co-vary with the number of males present around the time of mating, and males of many species have been show to respond to increasing numbers of rival males by increasing their allocation to sperm competition strategies (e.g., sperm investment and/or mate guarding; Simmons, 2001). Unfortunately, amount and quantity estimation are confounded in most available sperm competition studies, so we know very little about whether quantity estimation in this context relies on numerical or non-numerical cues (reviewed in Shifferman, 2012). …”