The effects of claw regeneration on territory ownership and mating success in the fiddler crab Uca mjoebergi

Underlying male quality is often reflected in the condition of sexually selected traits. In fiddler crabs, male success in both intra- and interspecific interactions is highly dependent on the size of the major claw. However, males are often forced to autotomize their major claw. Claw regeneration significantly altered the structure of a males' major claw in Uca mjoebergi. We found, however, that claw regeneration did not affect signal quality. Both males and females were unable to visually distinguish a regenerated claw from an original claw. Although regenerated males were inferior fighters, males were able to compensate for this fighting disadvantage by avoiding fights with other males. Regenerated males were, however, less likely to acquire and defend high-quality territories and consequently suffered a decrease in mating success

Robust estimation of bacterial cell count from optical density

Optical density (OD) is widely used to estimate the density of cells in liquid culture, but cannot be compared between instruments without a standardized calibration protocol and is challenging to relate to actual cell count. We address this with an interlaboratory study comparing three simple, low-cost, and highly accessible OD calibration protocols across 244 laboratories, applied to eight strains of constitutive GFP-expressing E. coli. Based on our results, we recommend calibrating OD to estimated cell count using serial dilution of silica microspheres, which produces highly precise calibration (95.5% of residuals <1.2-fold), is easily assessed for quality control, also assesses instrument effective linear range, and can be combined with fluorescence calibration to obtain units of Molecules of Equivalent Fluorescein (MEFL) per cell, allowing direct comparison and data fusion with flow cytometry measurements: in our study, fluorescence per cell measurements showed only a 1.07-fold mean difference between plate reader and flow cytometry data

Temporal constraints and female preference for burrow width in the fiddler crab, Uca mjoebergi

We studied sampling behaviour and mate choice in the fiddler crab Uca mjoebergi. Once a female selects a mate, she copulates in his burrow and remains there until releasing her aquatic larvae. U. mjoebergi occurs in habitats that are inundated only by the highest amplitude spring tides. Females can only release their larvae during these tides, and release before or after will result in complete failure of reproductive effort. Matings occur over a 5-day period near the end of neap tides. Our results suggest that within the mating period, females adjust their larval developmental rates by selecting specific burrows in which to incubate their clutches. We found that at the start of the mating period, females chose larger males as mates. Since male size was positively correlated to burrow width, females were selecting wide burrows and effectively incubating at lower temperatures. This would slow down the developmental rates of larvae. In contrast, females that mated late in the mating period selectively chose small males. By incubating in narrower, warmer burrows, these females may increase the developmental rates of larvae. We propose that females are selecting burrows to influence incubation rate and ensure timely release of their larvae. Female U. mjoebergi appear to adjust their preference for the direct benefits of mate choice to increase their reproductive success

Risk-taking behavior predicts aggression and mating success in a fiddler crab

Evidence is growing that an individual's propensity to take risks in the presence of a predator is correlated to behaviors that can affect individual fitness. We examined whether risk-taking behavior predicts aggression, surface activity levels, and mating success in male fiddler crabs, Uca mjoebergi. Risk-taking behavior was highly consistent among individuals, remained stable over time, and was unrelated to male size. We found that males that took greater risks in the presence of a potential predator also behaved more aggressively when searching for a new territory. In addition, bold males exhibited higher surface activity levels and spent more time courting females compared with their shy counterparts. Although risk-taking behavior was independent of other sexually selected traits, it accurately predicted male mating success in U. mjoebergi. We suggest nonsexually selected traits, such as risk taking, may represent important behavioral predictors of success in other species

Dishonest signalling of fighting ability and multiple performance traits in the fiddler crab Uca mjoebergi

1. Signals used during male combat are expected to be honest indicators of fighting ability. However, recent studies show that dishonesty in male signalling is more prevalent than previously believed. 2. Here we show that regenerated (leptochelous) claw

Temporal constraints and female preference for burrow width in the fiddler crab, Uca mjoebergi

Abstract We studied sampling behaviour and mate choice in the fiddler crab Uca mjoebergi. Once a female selects a mate, she copulates in his burrow and remains there until releasing her aquatic larvae. U. mjoebergi occurs in habitats that are inundated only by the highest amplitude spring tides. Females can only release their larvae during these tides, and release before or after will result in complete failure of reproductive effort. Matings occur over a 5-day period near the end of neap tides. Our results suggest that within the mating period, females adjust their larval developmental rates by selecting specific burrows in which to incubate their clutches. We found that at the start of the mating period, females chose larger males as mates. Since male size was positively correlated to burrow width, females were selecting wide burrows and effectively incubating at lower temperatures. This would slow down the developmental rates of larvae. In contrast, females that mated late in the mating period selectively chose small males. By incubating in narrower, warmer burrows, these females may increase the developmental rates of larvae. We propose that females are selecting burrows to influence incubation rate and ensure timely release of their larvae. Female U. mjoebergi appear to adjust their preference for the direct benefits of mate choice to increase their reproductive success

Paternity analysis of two male mating tactics in the fiddler crab, Uca mjoebergi

The fiddler crab Uca mjoebergi mates both underground in male-defended burrows and on the surface near female-defended burrows. The reproductive tract of Uca species facilitates last-male precedence, suggesting that males that do not guard-mated females are likely to gain very little paternity if the female re-mates with another male. Here, we test the reproductive success of burrow and surface matings using paternity analysis. We found that 100 % of the females that mated in burrows extruded a clutch of eggs. Furthermore, we show conclusively, for the first time in a fiddler crab species, that last-male sperm precedence results in the majority of the female's eggs being fertilised by the burrow-mated male. In contrast, surface matings resulted in significantly fewer females extruding eggs (5. 6 %). Paternity analysis also revealed that more than half of the clutches from burrow-mated females showed low levels of extra-pair paternity from previous matings. Although multiple matings appear common in U. mjoebergi, burrow-mated males that guard females are guaranteed a successful mating with extremely high rates of assured paternity. Surface matings therefore appear to be an opportunistic tactic that may increase male reproductive success in a highly competitive environment

Experiments with robots explain synchronized courtship in fiddler crabs

Male fiddler crabs (Uca mjoebergi) produce highly synchronized courtship waves. Is this a cooperative behaviour because females preferentially approach groups that wave synchronously? Or is it a competitive behaviour because of female choice for males that wave first, with the resultant selection on males generating synchrony as an epiphenomenon [1]? To find an answer we used robotic male crabs to measure female mating preferences. We show that females do not prefer males waving in synchrony, but they strongly prefer males that wave first ('leaders'). Synchrony therefore appears to be a by-product of competitive interactions between males

Experimental evidence for a seasonal shift in the strength of a female mating preference

The costs and benefits of mate choice can vary both spatially and temporally. Phenotypic plasticity in mate choice, which could be due to changes in choice criteria (e.g., acceptance thresholds) or shifts in underlying mating preferences (i.e., relative values assigned to different males), can therefore increase reproductive success. We examined shifts in female mating preference for male claw size between 2 seasons (winter and summer) in the fiddler crab Uca mjoebergi. We used custom-built robotic crabs in 2-stimulus mate choice experiments conducted in the field. Females showed a consistent preference for larger claw size, but this was significantly weaker during winter. This seasonal difference was observed for 2 successive years. We propose that the change in female preference for claw size is due to a seasonal difference in the value of a larger burrow, which strongly influences burrow temperature. Burrow temperature largely determines larval development rate and larvae release in fiddler crabs is constrained to a narrow time window where survival is optimal. Females appear to alter their preference for burrow width, which is signaled by claw size, between winter and summer, potentially allowing them to optimize developmental time of larvae and/or to reduce mate search costs. Copyright 2010, Oxford University Press.