Aggressive interactions and intermale spacing in choruses of the leaf-folding frog, Afrixalus delicatus

Intermale spacing was examined in caged Afrixalus delicatuschoruses. Males maintained an individual distance using an advertisement call, an encounter call and physical combat (or the threat of combat). An increase from low to intermediate chorus size (2-4 males) led to a decrease in nearest calling neighbour distances. At high chorus sizes (5-8 males) males maintained a minimum individual distance of 30-35 cm. New calling males were not accommodated in the chorus once eight males were calling. As the chorus size increased, a greater number of aggressive interactions were required to maintain the minimum distance. The spatial separation of calling males reduces the number of competitors when space is limited. The maintenance of a preferred minimum individual distance may increase a male’s reproductive success by reducing acoustic interference with neighbouring males as well as providing a clear pathway for female approach

Alternative mating tactics and male mating success in two species of fiddler crab

The use of alternative male mating tactics can determine the strength of sexual selection on male traits and have implications for sexual dimorphism. We examined size-based mating success in two species of fiddler crabs where males use each of two alternative tactics to obtain matings. In Uca annulipes, larger males were more successful when using the primary mating tactic (burrow mating) but the full size range of males mated when using the secondary tactic (surface mating). In Uca urvillei, both burrow and surface mating males were larger than the average sized male in the population. Standardised directional selection gradients indicated that selection on male size was stronger in U. urvillei than U. annulipes, reflecting the differences between species in male mating success. Our results also showed that sexual size dimorphism was greater in the species with stronger sexual selection on male size than in the species with weaker sexual selection

Total interactions data final

Interaction data for Uca sp

Fiddlers on the roof: elevation muddles mate choice in fiddler crabs

Biological signaling usually occurs in complex environments, yet signals are most often studied in controlled experiments that strip away this complexity. Male fiddler crabs possess one enlarged claw that is waved during courtship displays, and females preferentially respond to larger claws and faster waves. Fiddler crab vision is evolutionarily specialized to their predominantly level mudflat habitats, although some populations inhabit topographically complex environments. Here, we investigated how the elevation of signaling males relative to receiving females affects attractiveness. Experiments with robotic crabs revealed a strong female aversion to males signaling from atop small ( > 2cm) mud mounds. This aversion entirely masked previously documented strong preferences for large claws and faster waving. Our results suggest that variation in signaling environment might substantially weaken selection on males, thereby helping to maintain genetic variation in courtship traits

Frequency and Latency of Autotomy of a Sexually Selected Fiddler Crab Appendage

© 2019 Elsevier B.V. Autotomy is a predator defence mechanism by which individuals voluntarily release an appendage to escape a predator or escape a fouled moult. The decision to autotomize is driven by the costs of autotomy (i.e., the loss of the appendage) vs. the risk of predation. In many cases, autotomized appendages have few alternative functions, yet male fiddler crabs autotomize the sexually selected large claw that is critical for mate attraction. We conducted an experiment with Austruca mjoebergi to understand the role of claw autotomy by males during the mating season. Males more readily autotomized a leg relative to the enlarged claw, reflecting the much greater cost of being without the major claw. Larger crabs had a lower probability of claw autotomy than did small crabs, reflecting the greater fitness cost of claw autotomy experienced by larger crabs. The sexually selected fiddler crab claw is a multifunction structure with benefits that may outweigh the survival probability resulting from autotomy when individuals are threatened by predation

Female preferences for timing in a fiddler crab with synchronous courtship waving displays

Studies of sexual communication typically focus on the design and information content of a signal of interest, but the timing of signal production relative to nearby competitors can be crucial. Male fiddler crabs, Uca mjoebergi, court females with a stereotyped claw-waving display, and males are often observed waving in synchrony with nearby claw-waving males. Using female mate preference experiments with robots that imitate male claw waves, we found evidence that females are more attracted to males whose waves immediately precede a synchronous group of waves (leaders); females also favoured males that waved in opposite phase to a synchronous group (alternators). By contrast, males whose waves lagged behind a group of synchronous wavers (laggards) were no more attractive. We discuss a simple sensory process that could explain how this female preference arises. Our results agree with past findings suggesting that synchrony in fiddler crabs occurs as an epiphenomenon of adaptive male responses to female preferences