Sexual selection for structure building by courting male fiddler crabs: an experimental study of behavioral mechanisms

Males of the fiddler crab Uca musica sometimes build sand hoodsat the entrances of their burrows, to which they attract femalesfor mating with claw waving and other displays. Females significantlymore often approached males with hoods than males without hoods,but once at a burrow, they were just as likely to stay andmate whether the male had a hood or not. To determine how hoodsaffect male attractiveness, we conducted experiments that controlledfor other differences in courtship behavior between buildersand nonbuilders; we removed hood builders' hoods and we addedhood models to nonbuilders' burrows. We then measured the attractivenessof hood builders and nonbuilders with and without hoods. Neithermanipulation measurably affected male courtship behavior. Thepresence of a hood did not increase male—female encounterrates, suggesting that hoods do not attract distant femalesinto a male's courtship range. However, once a male courteda female, she was significantly more likely to approach ifhe had a real or model hood. We obtained direct evidence thatfemales orient to hoods by replacing them with hood modelspositioned about 3 cm away from the openings to males' burrows.Females approached the models, not the courting males, about27% of the time. We conclude that hood building is sexuallyselected because courted females differentially approach hoods,not because hoods attract distant females and not because femalesprefer to mate with hood builders.     

Pillar Function in the Fiddler Crab Uca beebei (I): Effects on Male Spacing and Aggression

Males of 14 species of fiddler crabs (genus Uca) are known to build structures out of mud or sand at the entrances to burrows they court from and defend. A study of spacing, space use and aggression between courting male Uca musica (Zucker 1974, 1981) suggested that the hoods males build reduce territorial overlap and rates of aggression between neighboring males. Thus, each male may have more time to court females during limited lunar, diurnal and tidal mating periods. I studied the courtship and aggressive behavior of male Uca beebei in the field to determine if the pillars males of this species build affect male behavior as do the hoods of U. musica. U. beebei occurs sympatrically with U. musica on the Pacific coast of Panama and is broadly similar in its ecology and mating behavior. Unlike the hoods of U. musica, pillars did not focus a male's activity space away from its closest neighbor nor did they reduce either overlap with neighbors' activity spaces or rates of aggressive interaction among neighbors. Pillar builders courted more but also fought their neighbors more than did males that did not build pillars. The pillars of U. beebei and the hoods of U. musica affect male behavior differently and probably have different functions.     

The role of auditory stimuli in the courtship of Drosophila melanogaster

Simulated courtship song of male Drosophila melanogaster was played to males or females of this species. Upon receiving the song males increase their locomotor activity and start courting each other, whereas females reduce their locomotor activity. In wingless males the locomotor activity difference between the silent control and the experimental sound situation is much larger than in winged males, due to the inactivity of wingless males in the control situation. Males which had been kept singly up to the time of the experiment exhibit higher locomotor and sexual activity than group housed males. A second component of the male courtship song ‘sine song’ is described, together with experiments which investigate the sensory basis of the effect male courtship song has on males.     

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

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.     

Absence of social facilitation of courtship in the wolf spider, Schizocosa ocreata (Hentz) (Araneae: Lycosidae)

Males of many animal species are reproductively limited by the difficulty and time costs of finding mates. Males of such species should be selected to take advantage of any cues that might reveal the location of prospective mates. Cues to female location are not restricted to those produced by females, but might also include the highly apparent courtship displays of males that have already found a female. By “eavesdropping” on these courting rivals, initiating sexual displays when courting rivals are detected (i.e., social facilitation of displays); males might effectively exploit the mate-searching efforts of their rivals. We tested the possibility that male Schizocosa ocreata wolf spiders exhibit social facilitation of courtship behaviors using a combination of live behavioral trials and video playback with single stimulus presentations. When exposed to visual cues from another male, male S. ocreata can discern the presence of another individual whether that individual is courting or not. However, we found no evidence of social facilitation of courtship or chemoexploratory behaviors in response to seismic or visual cues presented in isolation or combined. While complex, multimodal, male courtship signals are important in mate choice by female S. ocreata, males do not appear to use these cues to socially facilitate their own courtship.     

Choosy males in a haplochromine cichlid: first experimental evidence for male mate choice in a lekking species

Current theories of mate choice predict that the level of choosiness of males and females will depend on their relative investment in parental care. Males often invest less than females and are expected to be less choosy, especially in lekking species where males contribute only sperm. Our study of the haplochromine cichlid fish Astatotilapia flaviijosephi, a maternal mouthbrooder, provides the first experimental evidence for male mate choice in a lekking species. In this species the number of eggs spawned is positively correlated with female weight, thus making larger females potentially better mates. In the laboratory, we conducted a simultaneous choice experiment where males had the opportunity to associate with, and court, each of two females that differed in size. Males preferred to court the larger female and spent more time courting during experimental trials involving larger females. This selective allocation of courtship effort to more attractive (i.e. heavier) females suggests that there may be constraints on males in fertilizing multiple females, thus compelling them to be choosy.Copyright 2003 Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour.      

Evolutionary significance of courtship conditioning in Drosophila melanogaster

Males of the fly Drosophila melanogaster initially court mated, unreceptive females but later develop an avoidance reaction against them and even become temporally unresponsive to virgin females. This conditioned inhibition has been described as an associative process, the conditioned stimulus being a mixture of pheromones on the female's cuticle. To assess the evolutionary significance of courtship conditioning we recorded and analysed the male's behaviour during the conditioning process. The time traces of individual males were marked by an abrupt behavioural change. The time he spent courting suddenly decreased, and the frequency of ‘turn-away’ events at the same time sharply increased. Thus, the gradual decline of courtship observed as a group average does not reflect a slow change in motivation of the individual male but rather the interindividual differences of an active, experience-guided all-or-none decision to stop courting and to avoid the female. Three recently collected D. melanogaster strains were each maintained under two distinct mating conditions. Males were kept together with females for either ca. 2 weeks or 18 h. After 21 generations males of the two regimes differed markedly in their behaviour towards mated females. With long interaction periods between males and females, selection favoured courtship conditioning, while with short periods no such selection was observed. Slowly recovering receptivity of mated females may be needed for the maintenance of courtship conditioning. Courtship conditioning in D. melanogaster appears to be a fitness-relevant behaviour adapted to high-density populations with females mating a second time.     

Court Like You Mean It: Male Siamese Fighting Fish are Less Attentive to Courting Males that Have Been Exposed to an Estrogen Mimic

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic ecosystems where they have adverse effects on exposed organisms. In addition to causing physiological changes, EDCs often target fitness‐related behaviors such as locomotion and courtship. Ethinylestradiol (EE2) is an estrogen mimic that has been found to reduce courtship and aggression in males. However, the consequences of these reductions are not always explicitly addressed. One way in which EE2 may lead to decreased fitness occurs when males respond differently to exposed vs. unexposed conspecifics. To examine this, video playback was used to determine whether male Siamese fighting fish, Betta splendens, respond differently to exposed and unexposed males. Males were presented with four different combinations of videos of males played simultaneously: exposed swimming and unexposed swimming, exposed courting and unexposed courting, unexposed courting and unexposed courting, and exposed courting and exposed courting. Males directed more behaviors to the unexposed than the exposed courting male when presented simultaneously, likely because these unexposed males were perceived as a greater threat to mating success. Additionally, males spent more time tracking and gill flaring, two behaviors that are indicative of fight intent, when presented with two courting unexposed males. This combination could be considered the most threatening because there are two rival vigorously courting males present. These results suggest that EE2 exposure could result in exposed males receiving decreased attention from other males. However, since EE2 exposure also decreases competitive and courtship abilities, this would be far outweighed by the costs.     

Cephalic secretion release in the male dwarf spider Oedothorax retusus (Linyphiidae: Erigoninae): An ultrastructural analysis

Secondary sexual traits in males can extend to glandular structures that play a role during courtship and mating. In dwarf spiders (Linyphiidae, Erigoninae), glandular secondary sexual traits are particularly common. Males are characterized by cephalic modifications which produce secretions that females contact with their mouthparts during courtship and/or copulation. We used the dwarf spider Oedothorax retusus as a model species to investigate if and when the contents of the glands are released during a mating sequence and if so, if the gland reservoirs are refilled after mating. To this aim, we quantitatively compared the glandular tissue on the ultrastructural level between a) inexperienced males, b) males that performed courtship, c) males immediately after copulation, and d) males three days after mating. We assessed whether the treatment groups differed in the filling state of the conducting canals and receiving canals (reservoir regions) of the glandular units. Our study shows that courting males as well as males three days after mating did not differ significantly from control (inexperienced) males in the presence of secretions. However, males exhibited significantly less secretion immediately after mating. This strongly suggests that the main function of the secretions is gustatorial courtship and not the emission of volatile pheromones for mate attraction as was previously assumed.     

Burrow ornamentation in the fiddler crab (Uca leptodactyla): female mate choice and male–male competition

Non-biological ornamentation is found in the nests and burrows of different kinds of animals. We evaluated here whether sand hoods constructed by male fiddler crabs (Uca leptodactyla) are one of the signals used by males to attract females during courtship. We observed females when they were walking among the males, and we quantified the proportion of females that visited male burrows with and without ornamentation and the choice to stay in a male’s burrow. Females visited more burrows with hoods than burrows without hoods, and they chose significantly more builder males. Male investment in ornamentation nevertheless decreased when the proportion of females increased in the area. Male investment was not correlated with the proportion of non-builder males nearby, but was positively correlated with overall density. The density sex ratio, however, was more male-biased in high-density than in low-density areas suggesting that even if building attracts females, the function could be related to male competition for mates.     

Sublethal pesticide exposure disrupts courtship in the striped lynx spider,Oxyopes salticus (Araneae: Oxyopidae)

The striped lynx spider, Oxyopes salticus, is a dominant predator of pests in agricultural crops where pesticides are readily applied. While past research shows pesticides directly affect the mortality of agricultural pest predators, recent research has found that pesticide exposure may cause sublethal effects in these organisms. This study examined how residues of three common pesticides (active ingredients: bifenthrin, carbaryl, malathion) impact courtship behaviour of O. salticus. Males provided with cues left by females readily performed courting behaviours. However, when females left cues on a substrate containing bifenthrin and carbaryl, males were less likely to perform courtship behaviours and did so for less time. While males on the malathion treatment showed a trend for reduced courting, this was not significantly different from the treatment without pesticides. The cue produced by females is unknown in this species. However, our study found males reduced their courting over time, suggesting that the cue is ephemeral and not long lived. This study adds important insight into the growing evidence that pesticides greatly impact the ecology of agricultural pest predators and other non‐target organisms by altering their behaviour.     

Female and male interactions during courtship in Calopteryx maculata and C. dimidiata (Odonata: Calopterygidae): Influence of oviposition behaviour

Calopteryx maculata and C. dimidiata damselfly females respond to male courtship with specific displays which signal differences in their receptivity. These include a rejection (wing spreading) and an invitation (wing-flipping) display, as well as a neutral (sit still) response. There are interspecific differences in the likelihood of each female display and in male responses to these displays. C. maculata males persist in courtship irrespective of female response, while C. dimidiata males generally stop courting when the female's response is rejection or neutrality. I suggest that these differences result from interspecific differences in oviposition behaviour. Female C. maculata oviposit at the water surface, which exposes them to disturbance by males attempting to mate. Females are therefore likely to remate to secure postcopulatory guarding when changing oviposition sites and males are expected to be persistent in courtship. Female C. dimidiata submerge to oviposit, which frees them from male disturbance and means that males have less control over female access to oviposition sites. Males therefore have less influence on mating by females and are expected not to persist in courtship of non-receptive females.     

Social context-dependent modification of courtship behaviour in Drosophila prolongata

Induction of alternative mating tactics by surrounding conditions, such as the presence of conspecific males, is observed in many animal species. Satellite behaviour is a remarkable example in which parasitic males exploit the reproductive investment by other males. Despite the abundance of parasitic mating tactics, however, few examples are known in which males alter courtship behaviour as a counter tactic against parasitic rivals. The fruit fly Drosophila prolongata shows prominent sexual dimorphism in the forelegs. When courting females, males of D. prolongata perform ‘leg vibration’, in which a male vibrates the female''s body with his enlarged forelegs. In this study, we found that leg vibration increased female receptivity, but it also raised a risk of interception of the female by rival males. Consequently, in the presence of rivals, males of D. prolongata shifted their courtship behaviour from leg vibration to ‘rubbing’, which was less vulnerable to interference by rival males. These results demonstrated that the males of D. prolongata adjust their courtship behaviour to circumvent the social context-dependent risk of leg vibration.     

Male adaptations to minimize sexual cannibalism during reproduction in the funnel‐web spider Hololena curta

Males of many spider species risk being attacked and cannibalized while searching for, courting, and mating with conspecific females. However, there are exceptions. We show that the funnel‐web spider, Hololena curta, has 3 adaptations that minimize risk to males during courtship and mating, and enhance reproductive success. First, males detected chemical or tactile signals associated with webs of virgin females, and differentiated them from webs of mated females, enabling males to increase encounter rates with virgin females and avoid aggressive mated females. Second, males produced stereotyped vibrational signals during courting which induced female quiescence and suppressed female aggression. Third, when touched by males, sexually receptive females entered a cataleptic state, allowing males to safely approach and copulate. Because males can mate multiple times and the sex ratio in natural populations of H. curta is female biased, overall reproductive output is likely increased by males of this species avoiding sexual cannibalism.     

Delayed courtship in the fiddler crab Uca musica terpsichores

Courting male fiddler crabs of the species Uca musica terpsichores congregate in the upper central portion of the colony, while receptive females leave their burrows located at the colony's periphery and wander among the communally displaying males prior to choosing a mate. I observed that courting males in a newly-established population were significantly smaller than courting males in large high-density colonies. This observation led to a series of translocation experiments designed to ascertain whether high population density influences the size (=age) at which males begin to court. Smaller courting males from a low-density population failed to court after being placed among larger courting males in a high-density population. The reciprocal translocation revealed that smaller noncourting males from the high-density population would start courting shortly after being placed in a low-density population. Smaller males placed in the high-density population were subsequently observed significantly further away from where they were initially placed than were larger males similarly translocated. The results suggest that smaller males delay courtship activities once they are forced, via encounters with larger males, to the periphery of the colony. I believe that both intrasexual selection (competition from larger males) and intersexual selection (female choice of large males) are responsible for the delay in male courtship activities.     

Courtship herding in the fiddler crab <Emphasis Type="Italic">Uca elegans</Emphasis>

Male and female animals are not always complicit during reproduction, giving rise to coercion. One example of a system that is assumed to involve sexual coercion is the mate herding behaviour of fiddler crabs: males push females towards the home burrow with the goal of forcing copulation at the burrow entrance. We recorded and analysed in detail the courtship behaviour of a North Australian species of fiddler crab Uca elegans. Courtship was composed of four main phases: broadcast waving, outward run, herding and at burrow display. During interactions males produced claw-waving displays which were directed posteriorly towards the female and which varied in timing and structure depending on the courtship phase. We suggest that courtship herding in U. elegans is driven primarily by mate choice for the following reasons, (1) females can evade herding, (2) no other reproductive strategies were observed, (3) males broadcast their presence and accompany courtship with conspicuous claw waves, and (4) the behaviour ends with the female leading the male into the home burrow. As an alternative function for herding in U. elegans we suggest that the behaviour represents a form of courtship guiding, in which males direct complicit females to the correct home burrow.     

Courtship in two species of periodical cicadas, Magicicada septendecim and Magicicada cassini

Courtship behaviour of two species of periodical cicadas, Magicicada septendecim and M. cassini, was studied in the field during the 1970, 1973, and 1974 emergences of these insects. In areas where both species were courting there were differences in both male and female courtship patterns, both in acoustic and behavioural components. Experiments with models showed that male M. septendecim were more likely to court crude models of females than were M. cassini males. When females were ‘courted’ with models that could imitate some of male courtship, they were more receptive when the models' ‘songs’ were those of conspecific males. Acoustic differences between species are probably used by females in mate selection, maintaining species separation even in areas where the two species overlap in both space and time.     

The Effect of Male Competition on the Courtship Song of Drosophila melanogaster

The courtship song of Drosophila has been extensively used as a model system for studies of sexual selection and species recognition. Traditionally, the courtship song has been recorded from males placed individually with a female. However, under natural conditions females are exposed to multiple courting males, and the effect of their joint signal on mate recognition by the female is not yet understood. Here, we recorded the courtship behavior of D. melanogaster males singing either individually to a female lpar;1:1) or in the presence of an additional male lpar;2:1). We compared the structure of the male song in the two experimental designs. Our results show that when two males courted a female their songs could overlap each other. Males produced a significantly different signal in the presence of competition; the duration of each song component was significantly shorter and the rate of singing was markedly lower. The present study demonstrates that male competition can dramatically alter the acoustic signal detected by the female.