Selection for conspicuous visual signals in a fiddler crab

Sexual selection has an undeniable influence in the evolution of the spectacular diversity of courtship signals in the animal kingdom. A long history of study has pointed to mechanisms through which sexual selection can act: it can favor signals that are reliable indicators of species identity or effectively transfer mate quality information. In some species, these mechanisms have the potential to shape signal evolution. This is the case in fiddler crabs. Males court females by waving their sexually dimorphic claw. Females recognize conspecific males by the species-specific display, while intraspecific variants of the display appear to be indicators of male quality. We investigated which of these mechanisms prevail by using robotics to test female responses to waves of different heights in the fiddler crab, Austruca mjoebergi. We reveal that, although the studied species shares a sympatric habitat, females did not significantly more often approach the species’ average signal. We found evidence that more conspicuous, higher signals were more likely to attract females, although the effect was not particularly strong. We discuss our results in the light of other possible scenarios from which sexual selection can act in the evolution of signals.This study was funded by Australian Research Council Discovery Grant (DP160100316) to P.R.Y.B

Driving deaths and injuries post-9/11

Objectives: In the days immediately following the terror attacks of 9/11, thousands of Americans chose to drive rather than to fly. We analyzed highway accident data to determine whether or not the number of fatalities and injuries following 9/11 differed from those in the same time period in 2000 and 2002. Methods: Motor crash data from the National Highway Traffic Safety Administration’s Fatality Analysis Reporting System were analyzed to determine the numbers and rates of fatalities and injuries nationally and in selected states for the 20 days after September 11, in each of 2000, 2001, and 2002. Results: While the fatality rate did not change appreciably, the number of less severe injuries was statistically higher in 2001 than in 2000, both nationally and in New York State. Conclusions: The fear of terror attacks may have compelled Americans to drive instead of fly. They were thus exposed to the heightened risk of injury and death posed by driving. The need for public health to manage risk perception and communication is thus heightened in an era of global fear and terrorism

Handedness in fiddler crab fights

Asymmetric weapons are common in bilateral animals and, in some species, they can occur on either the left- or the right-hand side of the body (lateralization). Fiddler crabs (Uca spp, Decapoda: Ocypodidae) have an enlarged claw that is used in male–male combat over territories and in courtship displays. Males can be either right- or left-handed, and most species have a 1:1 ratio. Past studies have found little effect of handedness on fighting success, fight duration or other measures of combat. Here we show that, while handedness per se, does not affect fighting, handedness matching has a significant effect. In Uca mjoebergi, fights between different-handed males were more likely to escalate to grappling, suggesting that it is harder for the combatants to determine the winner. We suggest that the positioning of the claws during fighting creates distinct forces that result in different outcomes for same- versus different-handed fights. This can represent a strong selective pressure in populations with an uneven handedness distribution where the handedness minority will often engage in different-handed fights. We discuss these results in light of the selective forces that may act on handedness distribution in fiddler crabs

Territorial battles between fiddler crab species

Many species worldwide are impacted by habitat loss. This may result in increased competition both within species and between species. Many studies have demonstrated that when two previously non-overlapping species are forced to compete over a resource, one species is likely to become dominant over the other. This study explores the impact a larger species of fiddler crab (Tabuca elegans-previously known as Uca elegans) has when invading an area previously used solely by a smaller species (Austruca mjoebergi-previously known as Uca mjoebergi). Here we show that, while there are some detrimental effects of living next to a heterospecific, they are relatively minor. New heterospecific neighbours fight more regularly with resident crabs, but each fight is no longer or more escalated than those between the resident and a new conspecific male. The residents are not specifically targeted by intruding heterospecifics, thus, given the large advantage of having a heterospecific neighbour in terms of lowered competition for females, the overall impact of species mixing is probably not as negative as might have been predicted.Funding was provided by the Australian National University and the Australian Research Council (ARC DP120101427)

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

An interim evaluation of a two year cognitive intervention programme in technology education for Key Stage 4 students

This paper is an interim report and evaluation of a two-year intervention programme in technology for students aged 15+ designed and implemented by three teachers. It describes the cognitive models that underpin the intervention.Data has been collected and analysed after one year of the programme. Use has been made of a Piagetian Reasoning Task as a pre/post test and mock GCSE examination results. Actual GCSE examination results will be used to evaluate the full effects of the intervention after the full two-year programme.The results described in this paper suggest that a story is emerging that such an intervention can improve the information processing capability of the student and that specific or near transfer effects have occurred in technology. There is little or no evidence as yet as to whether general or far transfer effects have occurred

Keeping up appearances: male fiddler crabs wave faster in a crowd

Courtship displays are often energetically and temporally costly as well as highly conspicuous to predators. Selection should therefore favour signalling tactics that minimize courtship costs while maintaining or increasing signal attractiveness. In fiddler crabs, males court females by waving their one greatly enlarged claw in a highly conspicuous and costly display. Here, we investigate whether courting males adjust their wave rate, and therefore the cost of courtship, to the current level of competition.We show that display rate increases as competition increases and that when competition is removed, males reduce their display rate by 30 per cent. These results suggest that male fiddler crabs actively reduce the cost of courtship by adjusting their wave rate in response to the immediate level of competition