Sexual selection (see the Oxford Bibliographies article “Sexual Selection”) is a powerful evolutionary force, selecting fortraits that increase the reproductive success of individuals. Before copulation, sexual selection can occur throughintrasexual selection, typically observed as competition among individuals of the same sex for access to mating partnersof the other sex (see Oxford Bibliographies article on Evolutionary Biology “Male-Male Competition”), and intersexualselection, observed as (typically female) mate choice (see Oxford Bibliographies article on Evolutionary Biology “MateChoice”). When females are sexually promiscuous and mate with multiple males (which is more the rule than theexception in the animal kingdom), these two processes have the potential to continue also after copulation: intrasexualselection as sperm competition (Oxford Bibliographies article on Evolutionary Biology “Sperm Competition”), andintersexual selection as cryptic female choice. The term cryptic is applied because this form of female choice can be hardto observe (e.g., when it occurs inside the female reproductive tract) and hard to quantify with classical measures ofreproductive success (e.g., mating success). In addition, this form of female choice is hard to disentangle from otherepisodes of sexual selection (see below). The framework used to understand female choice occurring after (or sometimesduring) copulation is currently somewhat divergent, since some authors adopt a very broad definition of cryptic femalechoice, while others apply a more conservative definition (see discussion of this under Definition and History). Crypticfemale choice is a relatively young research topic (it first started properly after the publication of Eberhard’s seminal bookFemale Control: Sexual Selection by Cryptic Female Choice [Eberhard 1996, cited under General Overviews] in 1996). Itwas realized early on in the history of the field that a broad range of mechanisms across a variety of species exist throughwhich females can potentially bias the outcome of a copulation (e.g., ejaculate ejection, differential sperm storage, spermchoice—see section Mechanisms and Processes Used as Cryptic Female Choice). As a consequence, measures ofprecopulatory processes or sperm competition can be misleading in species with cryptic female choice, due to femalepostcopulatory influences on fertilization. Yet, although there is no doubt that females have great potential to bias paternityat the postcopulatory stage, cryptic female choice is the least studied of the processes through which sexual selection canoccur (e.g., compared to sperm competition, or male-male competition). This is probably because demonstration of crypticfemale choice is notoriously difficult. It can be challenging to separate pre- from postcopulatory processes, the interactionof male adaptations to sperm competition and female influences on fertilization, and variation in differential embryomortality from female-induced biases in paternity (see Potential Pitfalls in the Study of Cryptic Female Choice). Thestudies that have convincingly been able to separate these processes and demonstrate cryptic female choice are currentlyprimarily from insect, bird, and externally fertilizing species (see Mechanisms and Processes Used as Cryptic FemaleChoice). I here present when we may expect to observe cryptic female choice, how females may benefit from crypticfemale choice, some techniques that can
Oxford Bibliographies, 2016.