Choosing a mate in a high predation environment: Female preference in the fiddler crab Uca terpsichores

Abstract

The interplay between a receiver's sensory system and a sender's courtship signals is fundamental to the operation of sexual selection. Male courtship signals that match a female receiver's preexisting perceptual biases can be favored yet the message they communicate is not always clear. Do they simply beacon the male's location or also indicate his quality? We explored this question in a species of fiddler crab Uca terpsichores that courts under elevated predation risk and that mates and breeds underground in the safety of males' burrows. Sexually receptive females leave their own burrows and are thereby exposed to avian predators as they sequentially approach several courting males before they choose one. Males court by waving their single greatly enlarge claw and sometimes by building a sand hood next to their burrow entrance. Hoods are attractive because they elicit a risk‐reducing orientation behavior in females, and it has been suggested that claw waving may also serve primarily to orient the female to the male. If the wave communicates male quality, then females should discriminate mates on the basis of variation in elements of the wave, as has been shown for other fiddler crabs. Alternatively, variation in elements of the claw waving display may have little effect on the display's utility as a beacon of the location of the male and his burrow. We filmed courting males and females under natural conditions as females responded to claw waving and chose mates. Analysis of the fine‐scale courtship elements between the males that females rejected and those they chose revealed no differences. When predation risk during courtship is high, males' courtship displays may serve primarily to guide females to safe mating and breeding sites and not as indicators of male quality apart from their roles as beacons.

Ecology and signal structure drive the evolution of synchronous displays*

“…Fiddler crab wave displays are visual stimuli that induce the receiver's alertness and beacon signaler location (Perez et al. ). In a group of signaling males, the leading stimulus is most strongly perceived (Reaney et al.…”

“…The burrow is therefore an important mating resource that males advertise through wave displays (Crane ; Perez et al. ). Females with this mating system generally show preference for particular elements of the male wave displays (Oliveira and Custodio ; Murai and Backwell ; Perez and Backwell ).…”

Evaluating the potential impact of bird predation on the SW Atlantic fiddler crab Leptuca uruguayensis

“…Similarly, the species Gelasimus vomeris exhibits different degrees of carapace colors in relation to perceived predation risk [85]. In addition, males of several fiddler crab species build mud structures that serve as landmarks that enable females to reduce predation risk while seeking mates [77,78,86,87]. If we consider that the many antipredator strategies may cause a reduction in the efficiency and/or time available for feeding and reproduction [59,79,[88][89][90][91], then maintaining such strategies may be costly under a scenario of apparently low predation pressure.…”

Robotic crabs reveal that female fiddler crabs are sensitive to changes in male display rate

“…Although females detected that the de-escalating robot was slowing, hence avoided it, the lack of discrimination between the other two males suggests that they made a quick, error-prone final decision. This might be because predators are a greater risk in the presence of multiple signalling males [ 13 ]. Nonetheless, the clear aversion to the de-escalating robot at this point demonstrates that females are capable of resolving the differences between a ‘medium’ and ‘slow’ wave rate.…”