Burrow structure and use in the sand fiddler crab, Uca pugilator (Bosc)

Uca pugilator, the sand fiddler crab, constructs two kinds of burrows in protected, sandy upper-intertidal and supratidal substrates on the west coast of Florida. Temporary burrows are built and used as a refuge by non-breeding crabs during high tide periods and at night when crabs cease feeding in the intertidal zone. Breeding burrows are constructed and defended by courting males and are the site of mating, oviposition and the incubation of eggs by females. Up to three ovigerous females may be accommodated in a single breeding burrow, each female sequestered in a separate terminal chamber. The construction and defence of burrows specialized for breeding may be an adaptive response by males to the preferences females exhibit when selecting a breeding site.     

Pillar Function in the Fiddler Crab Uca beebei (II): Competitive Courtship Signaling

Male Uca beebei court and attract females into burrows they defend on muddy sand flats in the intertidal zone on the Pacific coast of the tropical Americas. Mating, oviposition and incubation (breeding) occur underground in males' burrows. Some courting males build mud pillars (2 cm high) at the entrance of their burrow. The purpose of this field study was to assess the role of pillars in competitive courtship signaling among males. I studied the effect of pillars on female behavior by recording the responses of wandering females to courtship from males resident at burrows with and without pillars. I also caught females, released them individually in a circular arena with an equal number of empty burrows with and without pillars around its circumference, and chased the females with a simulated avian predator. Females moved to burrows of both types more often when they were courted (82%) than when they were chased (67%). Receptive females were attracted to the burrows of the males that courted them significantly more often (97%) when these burrows had pillars than when they lacked pillars (66%). However, once females entered males' burrows they were equally likely to remain, mate and breed in both types of burrows. Females also more often moved to burrows with pillars (66%) than to burrows without pillars when they ran from the simulated predator. Both male courtship displays and pillars probably provide cues females use to locate males' burrows. The visual similarity between pillars and a display courting males give immediately before they enter their burrows suggests that pillars are icons of the display. The effect of pillars on female behavior, the timing of pillar building relative to when females choose mates, and contrasts in the behavior of males that do and those that do not build pillars suggest that pillar building has evolved due to competition among males to attract females into their burrows.     

Underground mating in the fiddler crab Uca tetragonon: the association between female life history traits and male mating tactics

Brood size and other life-history traits of females affect male investment in mating. Female Uca tetragonon, producing relatively small broods, were attracted to the burrows of males for underground mating (UM) while carrying eggs. Most UM females released larvae and ovulated new broods during the pairing, averaging 3.9 days. While a female was incubating one brood, another brood was developing within the ovaries because the females were feeding adequately during incubation. These findings suggest that in U. tetragonon, a small-brood species, females increase the total number of broods produced by breeding continually. In contrast, in large-brood species, feeding by ovigerous females is relatively brief and not enough to prepare the next brood during incubation, inducing temporal separation between incubation and brood production. Unlike females in other ocypodids where females with large broods remain in the breeding burrows of males, most female U. tetragonon left the male after UM. Wandering in female U. tetragonon after the pairs separate may occur because their small broods are adequately protected by an abdominal flap. Relative brood size probably determines the vulnerability of the incubated broods to the females' surface behavior. Hence, male reproductive success in large-brood species may decrease greatly if males expel their mates after ovulation, although this is not necessarily so in small-brood species. Whether the male drives away the female or not may depend on which behavior within either small- or large-brood species yields the greater male reproductive success. In U. tetragonon some females extruded eggs in their own burrows after surface mating as well as in males' burrows after UM. It was unclear whether females chose a male with a larger burrow as an UM mate unlike several large-brood species. Burrows of both UM males and ovigerous females in U. tetragonon were relatively smaller than those in some large-brood species, indicating that incubation of small broods does not require large burrows. Rather than benefits of UM by female choice, wandering resulting from intersexual conflict, and sperm competition may explain why some females mate in males' burrows in this small-brood species.     

Sexual selection and the physiological consequences of habitat choice by a fiddler crab

In mid-Atlantic salt marshes, reproductively active male sand fiddler crabs, Uca pugilator, use a single greatly enlarged major claw as both a weapon to defend specialized breeding burrows from other males and an ornament to attract females for mating. During the summer breeding season, females strongly prefer to mate with males controlling burrows in open areas high on the shore. Food availability decreases while temperature and desiccation stress increase with increasing shore height, suggesting that the timing and location of fiddler crab mating activity may result in a potential trade-off between reproductive success and physiological condition for male crabs. We compared thermal preferences in laboratory choice experiments to body temperatures of models and living crabs in the field and found that from the perspective of a fiddler crab, the thermal environment of the mating area is quite harsh relative to other marsh microhabitats. High temperatures significantly constrained fiddler crab activity on the marsh surface, a disadvantage heightened by strongly reduced food availability in the breeding area. Nevertheless, when the chance of successfully acquiring a mate was high, males accepted a higher body temperature (and concomitantly higher metabolic and water loss rates) than when the chances of mating were low. Likewise, experimentally lowering costs by adding food and reducing thermal stress in situ increased fiddler crab waving display levels significantly. Our data suggest that fiddler crabs can mitigate potential life history trade-offs by tuning their behavior in response to the magnitude of both energetic and non-energetic costs and benefits.     

Mate acquisition tactics in polyandrous spotted sandpipers (Actitis macularia): the role of age and experience

We consider resource-defense polyandry and mate-access polyandryas female mating tactics in spotted sandpipers (Actitis macularia).These tactics can be distinguished by the resource females defend,female interclutch movement, expected reproductive success aftermoving, and male and female dispersion. We examine these characteristicsrelative to patterns observed in a 17-year study of spottedsandpipers, a species traditionally considered resource-defensepolyandrous. On average, 26% of spotted sandpiper females eachyear were monogamous. Older females were more likely to be polyandrous,and polyandrous females of each age employed different matingtactics. Yearlings were typically sequentially resourcedefensepolyandrous. Two-year-olds were primarily simultaneously polyandrous,exhibiting equivalent proportions of resource-defense and mate-accesspolyandry. Older females were primarily simultaneously resource-defensepolyandrous. Females tended to stay on territories where theyand/or their mates had greater breeding experience (i.e., manyclutches laid for females, many clutches diat hatched for males);females that moved went to territories where their mates hada history of breeding success. Location changes between clutchesby polyandrous females were better described by breeding experienceon a territory than by age.     

Sequential mating patterns suggest extra-pair mating is not part of a mixed reproductive strategy by female red-winged blackbirds

Studies aimed at determining why female birds often produce offspring sired by males other than their social mates generally compare traits of social and genetic mates. Here I examine paternity patterns in nests of the same female red-winged blackbirds (Agelaius phoeniceus) in successive breeding seasons. Returning females preferentially selected their former social mates as their new social mates when those males were present. However, paternity patterns were much less consistent. A female''s behaviour (faithful versus unfaithful) in one year did not predict her behaviour the following year. Females unfaithful in successive years did not prefer the same extra-pair males. Females unfaithful in one year that switched social mates the next year did not preferentially choose their former extra-pair mates as their new social mates. By switching genetic mates, females did not generally improve the quality of their mates. These results, together with previous analyses, suggest that female blackbirds in this population have little control over extra-pair mating. Although females may benefit from extra-pair mating because extra-pair males are generally longer lived, paternity patterns in this population are not consistent with extra-pair mating being part of a finely tuned female reproductive strategy.     

Fitness benefits of polyandry for experienced females

Females often mate with several different males, which may promote sperm competition and increase offspring viability. However, the potential benefits of polyandry remain controversial, particularly in birds where recent reviews have suggested that females gain few genetic benefits from extra‐pair mating. In tree swallows (Tachycineta bicolor), we found that females with prior breeding experience had more sires per brood when paired to genetically similar social mates, and, among experienced females, broods with more sires had higher hatching success. Individual females breeding in two consecutive years also produced broods with more sires when they were more genetically similar to their mate. Thus, experienced females were able to avoid the costs of mating with a genetically similar social mate and realize fitness benefits from mating with a relatively large number of males. This is one of the first studies to show that female breeding experience influences polyandry and female fitness in a natural population of vertebrates. Our results suggest that the benefits of polyandry may only be clear when considering both the number of mates females acquire and their ability to modify the outcome of sexual conflict.     

Familiarity and flexible mating strategies of a solitary rodent, Dipodomys ingens

Because mating is a product of individual reproductive strategies that may vary with changing conditions, we predicted variable mating behaviour in an arid-adapted, territorial rodent, the giant kangaroo rat, Dipodomys ingens. We also predicted that familiarity would facilitate nonaggressive courtship and mating in this solitary rodent. Through direct observations in the field, we found that mating varied from exclusive to multiple partners. Where densities were low, and on nights when multiple females were in oestrus, each animal mated with one member of the opposite sex. In conditions where the operational sex ratio was skewed towards multiple males, males footdrummed and competed for females. Males were able to mate with one or two females in adjacent territories, and they successfully competed for these same females throughout the breeding season. Females that mated exclusively with one male had more pups emerge from the burrow compared with females that experienced male competition. Females allowed nearest neighbour males to enter their burrows, and they engaged in more nonaggressive contact with close neighbours than with other males. Paired encounters in the field showed less aggression towards neighbours than strangers. In laboratory tests, females were less aggressive towards and allowed more contact with familiar than unfamiliar males. These results show that D. ingens can alter mating strategies as conditions change. Familiarity is an important factor in nonaggressive interactions between males and females and may be important to mate preferences in females during reproduction. The less aggressive behaviour to neighbours than to strangers (‘dear enemy’ phenomenon) is consistent with other solitary animals that defend multipurpose territories. Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved.     

The Starling Mating System as an Outcome of the Sexual Conflict

Many bird species demonstrate a variable mating system, with some males being monogamously mated and other males able to attract more than one mate. This variation in avian mating systems is often explained in terms of potential costs of sharing breeding partners and compensation for such costs. However, whenever there is a difference in the optimal mating system for males and females, a sexual conflict over the number of partners is expected. This paper contains a verbal model of how a conflict between male and female European starlings (Sturnus vulgaris),resulting from the fitness consequences of different mating systems for males and females differing over time, determines the mating system. We demonstrate that males and females have contrasting fitness interests regarding mating system, such that males gain from attracting additional mates whereas already mated females pay a cost in terms of reduced reproductive success if males are successful in attracting more mates. We demonstrate how this can be traced to the rules by which males allocate non-sharable care between different broods. Furthermore, we demonstrate that there exist male and female conflict behaviours with the potential to affect the mating system. For example, aggression from already mated females towards prospecting females can limit male mating success and males can circumvent this by spacing the nest-sites they defend. The realised mating system will emerge as a consequence of both the fitness value of the different mating systems for males and females, and the costs for males and females of intersexual competition. We discuss how this model can be developed and critically evaluated in the future.     

Extra‐group mating increases inbreeding risk in a cooperatively breeding bird

In many cooperatively breeding species, females mate extra‐group, the adaptive value of which remains poorly understood. One hypothesis posits that females employ extra‐group mating to access mates whose genotypes are more dissimilar to their own than their social mates, so as to increase offspring heterozygosity. We test this hypothesis using life history and genetic data from 36 cooperatively breeding white‐browed sparrow weaver (Plocepasser mahali) groups. Contrary to prediction, a dominant female's relatedness to her social mate did not drive extra‐group mating decisions and, moreover, extra‐group mating females were significantly more related to their extra‐group sires than their social mates. Instead, dominant females were substantially more likely to mate extra‐group when paired to a dominant male of low heterozygosity, and their extra‐group mates (typically dominants themselves) were significantly more heterozygous than the males they cuckolded. The combined effects of mating with extra‐group males of closer relatedness, but higher heterozygosity resulted in extra‐group‐sired offspring that were no more heterozygous than their within‐group‐sired half‐siblings. Our findings are consistent with a role for male–male competition in driving extra‐group mating and suggest that the local kin structure typical of cooperative breeders could counter potential benefits to females of mating extra‐group by exposing them to a risk of inbreeding.     

The Influence of Physical and Acoustic Experience on Sequential Mate Preference in the Cricket Gryllus bimaculatus. Is Song Important?

Female Gryllus bimaculatus alter their mate choice based on size depending on previous experience with males. Male crickets sing to attract mates and several studies have identified call parameters important in female choice. We tested the hypotheses that exposure to acoustic stimuli before and/or after mating, from males of different sizes, in isolation and together with physical exposure influences female choice (willingness to mate and spermatophore retention time [SRT]). Females exposed to ad lib. song of multiple males post-mating had a shorter SRT than females in acoustic isolation. Exposure to ad lib. song of multiple males prior to mating had no effect on SRT. Females did not alter SRT depending on exposure to acoustic stimuli from males of different sizes either post or ante mating. Females exposed to acoustic and physical stimuli (though gauze) from large males had a shorter SRT than those exposed to small males but only when the exposure was post-mating. We were unable to identify any correlation between call parameters and body size in G. bimaculatus. Females use male song to locate potential mates but physical exposure to males is needed to allow females to judge male size and this exposure only influences SRT if it takes place post-mating.     

Spatial distributions of male and female strawberry poison frogs and their relation to female reproductive resources

In many species with a resource-based mating system, males defend resources to increase their attractiveness to females. In the strawberry poison frog, Dendrobates pumilio, suitable tadpole-rearing sites appear to be a limited resource for females. Territorial males have been suggested to defend tadpole-rearing sites to increase their access to females. In this study we investigate the spatial association between tadpole-rearing sites and the sexes as well as the spatial association of males and females. If strawberry poison frogs have resource defense polygyny, we expect males and females to be associated with tadpole-rearing sites and that females will deposit their offspring in tadpole-rearing sites inside the territories of their mates. To test this hypothesis, home range and core area sizes were calculated for both sexes and the association patterns were compared in two areas that differed in their abundance of tadpole-rearing sites. Home ranges and core areas of females were much larger than male home ranges. Females showed a clumped distribution in the vicinity of tadpole-rearing sites. Males were not clumped and were less associated with tadpole-rearing sites. Females generally did not use tadpole-rearing sites in the territory of their mates and we therefore conclude that males did not defend tadpole-rearing sites for females. Our data are consistent with the general assumption that female distribution is influenced by resource distribution and that male distribution depends on female distribution. Nevertheless, the distribution of D. pumilio females was also influenced by male spacing patterns. Males probably initially establish their core areas where female density is high and then females move among territories to sample males. Males compete vigorously for places with high female density, the defense of which is likely important for enhancing their mating success. In general, the spacing patterns did not differ between populations but the sex ratio was strongly female biased in the habitat with more tadpole-rearing sites, reflecting the direct reliance of females on these resources.     

The effect of claw size and wave rate on female choice in a fiddler crab

How do females select a mate when they have mating preferences for multiple male traits? In experimental studies, female fiddler crabs (Uca mjoebergi) show a strong preference for males with larger claws and higher wave rates. In the field, there is no correlation between male claw size and observed wave rate. Here we document natural mating behaviour and show that females approach males who wave at a higher rate than nearby competitors. On average, an approached male had a significantly larger claw than his two nearest neighbours but did not differ in size from his two closest waving competitors. In general, smaller males were less likely to wave at approaching females. Females therefore approached mates based directly on wave rate but, because smaller males were less likely to wave, this indirectly resulted in female choice for larger than average males. Our study raises two issues. First, how do we relate the field results to previous experimental studies showing a female preference for larger claws? Second, in U. mjoebergi, males defend smaller neighbours against intruders. Our study suggests that one benefit of such defence coalitions is to decrease the number of immediate competitors present during female mate choice by retaining smaller neighbours.     

Female extrapair mate choice in a cooperative breeder: trading sex for help and increasing offspring heterozygosity

Sexual conflict between males and females over mating is common. Females that copulate with extrapair mates outside the pair-bond may gain (i) direct benefits such as resources or increased paternal care, (ii) indirect genetic benefits for their offspring, or (iii) insurance against infertility in their own social mate. Few studies have been able to demonstrate the different contexts in which females receive varying types of benefits from extrapair mates. Here, I examined sexual conflict, female extrapair mate choice, and patterns of extrapair paternity in the cooperatively breeding superb starling Lamprotornis superbus using microsatellite markers. Although extrapair paternity was lower than many other avian cooperative breeders (14% of offspring and 25% of nests), females exhibited two distinct mating patterns: half of the extrapair fertilizations were with males from inside the group, whereas half were with males from outside the group. Females with few potential helpers copulated with extrapair mates from within their group and thereby gained direct benefits in the form of additional helpers at the nest, whereas females paired to mates that were relatively less heterozygous than themselves copulated with extrapair mates from outside the group and thereby gained indirect genetic benefits in the form of increased offspring heterozygosity. Females did not appear to gain fertility insurance from copulating with extrapair mates. This is the first study to show that individuals from the same population mate with extrapair males and gain both direct and indirect benefits, but that they do so in different contexts.     

Mating tactics and courtship behavior inCleogonus rubetra (Fabricius) (Coleoptera: Curculionidae)

Females of the tropical weevilCleogonus rubetra oviposit into fruits of the leguminous treeAndira inermis, and larvae develop in the pulp and seed of these fruits. We hypothesized three alternative tactics by which males might secure matings. By using focal observations of males and by evaluating predictions specific to each hypothesis, we demonstrate that males search within aggregations of conspecifics for receptive females, and upon finding a suitable partner, males mount and perform courtship behavior consisting of stroking the eyes and sides of the female's abdomen. Males also stridulate and emit a sequence of short buzzing sounds. While mounted, males actively prevent rival males from mating with their partner. Males defend their mates for a mean duration of 3.7 h (including copulation). As predicted, paired males were larger than solitary individuals, although the difference was marginally nonsignificant. The overabundance of fruits relative to males, the prolonged period during which females are active, and the probability of last male sperm precedence are factors that may have contributed to the evolution of this female-defense tactic by males. Paired females were significantly larger than solitary females. We observed no competition among females for mates, and the correlation between elytron length of paired males and females was not significant.     

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.     

The use of extrapair copulations for mate appraisal by razorbills, Alca torda

Razorbills (Alca Undo) engaged in extrapair copulations (EPCs)during two phases of their breeding cycle when fertilizationof eggs was not possible, suggesting that EPCs provide nongeneticbenefits. Females actively pursued extrapair mountings afterthey completed egg laying, the first monogamous species reportedto do so. Mountings were performed in mating arenas outsideof the breeding colony, where attendance by postlaying femalesindicated that they sought encounters with extrapair males whiletheir mates were incubating. Postlaying females always successfullyresisted insemination yet positioned themselves to receive mountings.These findings support the hypothesis that resistance to inseminationis a ploy used by females to appraise males. At the end of thebreeding cycle, when males escorted the fledgling to sea, femalesremained at the colony where they consorted and sometimes copulatedwith other males. Nonfertilizable extrapair copulations mayserve two social functions for razorbills: female appraisalof males for future fertilizable EPCs and the appraisal andacquisition of new mates by both sexes.     

Females prefer mating males in the carmine triplefin,Axoclinus carminalis,a paternal brood-guarder

Synopsis This study investigates the role of male mating status in female choice patterns in the carmine triplefin, Axoclinus carminalis, a tripterygiid fish that exhibits paternal care. The distribution of daily reproductive activity is clumped, with many males receiving no mates and some receiving three or more. Females in this species do not prefer larger males, and characteristics of the oviposition site appear to have minimal effects on male mating success. When a female is removed from a male early in the daily spawning period, that male attracts fewer additional females for the remainder of the spawning period than does a control male. These changes in mating success are temporary, and do not affect mating success on subsequent days. A preference for mating males or males that are guarding eggs could provide asymmetric benefits for males to defend oviposition sites. This preference for males with eggs could be acting alone or with other factors such as high variance in oviposition site quality to favor the evolution of paternal care in fishes.     

Morphological correlates of male mating success in Triprion petasatus and Hyla marmorata (Anura: Hylidae)

Summary Multivariate analyses of 18 morphological variables recorded for amplectant males and females and non-amplectant males of Hyla marmorata and Triprion petasatus reveal that in both of these explosive breeding species, mating is significantly non-random. Females of H. marmorata from the relatively aseasonal environment of the Upper Amazon Basin average larger than males, and amplectant males average larger than non-amplectant males. Females of Triprion petasatus from the seasonal environment of the Yucatan Peninsula average larger than males, the sizes of males are significantly correlated with the sizes of the females with which they are paired in amplexus, and amplectant males have shorter internarial distances than non-amplectant males. For both species, non-random mating is interpretable in terms of sexual selection, but the relative importance of male-male competition and female choice cannot be assessed.     

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.