Digest: Female squid influence insemination success after mating to show a preference for smaller males

Abstract

In systems where females mate with multiple males, females caninfluence insemination success to favor the males they find mostattractive. When a female influences insemination success, it isknown as cryptic female choice (CFC) because her influence oftenoccurs after mating (post copulation) inside the reproductive tractand out of sight. For example, female fowl show CFC by eject-ing sperm from subdominant males after forced mating (Pizzariand Birkhead 2000), while female yellow dung flies can alter thepaternity outcomes of their multiple partners (Ward 2000). His-torically, it has been difficult to disentangle both the mechanismsand outcomes of CFC from those of male–male competition, suchas sperm competition, as both influence sperm storage and pater-nity (Birkhead and Pizzari 2002). Furthermore, CFC is hard toobserve, so studies of CFC have had to rely on indirect measuressuch as second male paternity, where CFC is inferred if offspringpaternity does not reflect a male’s mating success (Ward 2000).