Mate guarding in the swallowHirundo rustica

Summary The importance of mate guarding by males in the monogamous swallowHirundo rustica was studied by temporarily detaining the males. Mate guarding reduced the frequency of extra-pair copulations and of sexual chases involving female mates. Males participated in sexual chases more frequently if they had a non-fertile female. Neighbouring males of ‘widowed’ females increased their own mate guarding presumably in response to the experimentally increased rate of sexual chases. Neighbouring males with a fertile female increased their mate guarding more than did males with a non-fertile female. Addition of eggs to swallow nests in the post-fledging period of the first brood induced mate guarding by male nest owners. These males also copulated more frequently with their mates than did control males. Neighbouring male swallows responded to the increased mate guarding by showing sexual interest in the guarded females. removal of eggs from swallow nests during the laying period, leaving only one egg in the nest, resulted in reduced nest attendance by females. Male mates responded by increasing their mate guarding intensity as compared to controls, and neighbouring males showed an increased sexual interest in these females.     

Parental investment, potential reproductive rates, and mating system in the strawberry dart-poison frog, Dendrobates pumilio

We studied the effect of relative parental investment on potential reproductive rates (PRRs) to explain sex differences in selectivity and competition in the dart-poison frog Dendrobates pumilio. We recorded the reproductive behavior of this species in a Costa Rican lowland rainforest for almost 6 months. Females spent more time on parental care than males, and `time out' estimates suggest that PRRs of males are much higher than than those of females, rendering females the limiting sex in the mating process. Males defended territories that provide suitable calling sites, space for courtship and oviposition, and prevent interference by competitors. Male mating success was highly variable, from 0 to 12 matings, and was significantly correlated with calling activity and average perch height, but was independent of body size and weight. Estimates of opportunity for sexual selection and variation in male mating success are given. The mating system is polygamous: males and females mated several times with different mates. Females were more selective than males and may sample males between matings. The discrepancy in PRRs between the sexes due to differences in parental investment and the prolonged breeding season is sufficient to explain the observed mating pattern i.e., selective females, high variance in male mating success, and the considerable opportunity for sexual selection. Received: 9 June 1998 / Received in revised form: 27 March 1999 / Accepted: 3 April 1999     

Sexual selection for male parental care in the sand goby, Pomatoschistus minutus

Male parental care is typically thought to come at a cost to mate attraction and future mating success. However, it has also been hypothesized that paternal care may be under sexual, as well as natural, selection, such that good fathers actually attract more mates. Here we show experimentally that in the sand goby, Pomatoschistus minutus, females prefer to mate with males that provide higher levels of parental care. We manipulated male behavior using (1) different nest sizes and (2) an application of low-O₂ water in the nests, and found that females consistently preferred males with elevated levels of care in dichotomous mate choice tests. This complements our earlier study in which we showed that males increase the amount and quality of care they provide in the presence of females. Our results demonstrate that male care may have evolved as a result of sexual selection rather than natural selection alone, and furthermore, that male care may not necessarily be in conflict with mate attraction.     

Operational sex ratios and behavioural sex differences in a pipefish population

In the pipefish Syngnathus typhle, only males brood embryos in specially developed brood pouches, supplying oxygen and nutrients. Laboratory studies have shown that this elaborate paternal care has led to sex-role reversal in this species: males limit female reproductive rate, females are the primary competitors for mates and males exercise greater selectivity in accepting mates. In the first field study of this pipefish, we describe mating behaviour in the wild and test the hypothesis that temporal variations in the operational sex ratio (OSR) determine sex differences in mating behaviour. Our study comprised two reproductive seasons of two sequential mating periods each, the latter separated by a lengthy interval of male brooding. During mating periods, females displayed to all males without wandering and males moved about searching for females, without reacting to all females. The OSR was least female-biased (or even male-biased) at the onset of the breeding season, when most pipefish were simultaneously available to mate, but became strikingly female-biased as males' pouches were filled. The OSR remained substantially female-biased during the second mating period, because few males became available to remate at any one time. As hypothesised, female-biased OSRs resulted in more female-female meetings. As well, females were above the eelgrass more often than brooding males, thus exposing themselves to conspecifics and/ or predators. In the second year, males arrived earlier than females on the breeding site and male pregnancies were shorter, because of higher water temperatures, so rematings occurred earlier. Males met more often during that year than the previous one, but male competitive interactions were still not observed. The field results support laboratory studies and demonstrate that behaviours associated with female-female competition are more prominent when the OSR is more female-biased. Correspondence to: A. Vincent     

Female spawning patterns and male mating success in the sand goby Pomatoschistus minutus

In June 1989 in a study conducted near Träminne Zoological Station, Finland (60° N 23° E) I investigated whether or not male mating success could be explained by female choice for male size in sand gobies (Pomatoschistus minutus). Male mating success was constrained by nest size and increased markedly with increasing nest size. I also found a negative correlation between the length of spawning females and the fullness of the nest. As large females lay more eggs, they also need to find a nest with more space available for the eggs. The size of males without eggs was the same across nest size, whereas the size of males with eggs significantly increased with increasing nest size. This is interpreted as female discrimination against males as mates in nests that are often contested. There was no correlation between a male's size and his mating success when males with no eggs in their nests were excluded. A male removal experiment, however, showed that, in a specific nest, when male size increases so does mating success, whereas, if male size decreases, mating success also decreases. It is concluded that in the sand goby females prefer to mate with larger males, especially when the male possesses a high-quality nest that he most probably will have to defend against other males.     

Sexual dimorphism and male mating success in the tentacled blenny, <Emphasis Type="Italic">Parablennius tentacularis</Emphasis> (Teleostei: Blenniidae)

Although external sexually dimorphic traits are commonly found in males of combtooth blenny species, little is known about the benefit they can convey to male mating success. Indeed, while female preferences for large males have been demonstrated in some species, the possible role played by dimorphic ornaments has been neglected. We now report on the tentacled blenny, Parablennius tentacularis, a species where males are characterized by bulb glands on the anal fin and both sexes exhibit a dark spot on the dorsal fin and orbital tentacles. Males are territorial, make nests in empty bivalve shells, and provide solitary parental care for the eggs. Using morphometric analysis and field collected data on male and female external features, nest characteristics and number of eggs in the nests, we have assessed the development of dimorphic traits in both sexes and male mating success. The results reveal that orbital tentacles of males are more developed and more variable in size than those of females. Larger males exhibit longer orbital tentacles and larger anal glands but do not necessarily occupy larger nests. Male mating success is significantly correlated with the inner nest surface area and with orbital tentacle size but not with body size. These results provide support for a primary role of male ornaments in enhancing blenny male mating success and are discussed in the context of mate choice for direct and indirect benefits.     

Correlates of male reproductive success in the browncheek blenny,Acanthemblemaria crockeri (Blennioidea: Chaenopsidae)

Summary Acanthemblemaria crockeri exhibits a resource defense polygyny mating system with male parental care. Females preferred to mate with the larger of two males in laboratory experiments, and male size was positively correlated with the number of eggs defended by males at two sites in the Gulf of California, Baja California, Mexico. Females appeared to avoid mating with males defending heavily-fouled shelters. The role of other factors including the intensity of male courtship coloration and displays in determining male reproductive success was studied in Bahia San Carlos, Sonora, Mexico by providing glass vials as shelters. This provided a non-destructive technique for counting of eggs defended by males and allowed repeated assessment of the reproductive success of individual males. Males varied greatly in their duration of residency of shelters and in their color score and intensity of courtship displays. The number of eggs received by males was positively correlated with their duration of residency in shelters, and females appeared to avoid mating with new residents. Mated males deserted shelters less frequently and were more likely to receive future matings than were unmated males. The mean color score of males was unrelated to their reproductive success, while the intensity of male courtship displays was negatively correlated with the number of eggs received. This may have resulted because female mate choice is based on multiple criteria, including some that more accurately reflect the quality of parental care afforded by males.     

Sex ratio and the sexual conflict about brood care in a biparental mouthbrooder

The pay-off of deserting and leaving a mate to care for the offspring alone is generally assumed to depend mainly on the availability of alternative mating partners and on the potential spawning rate of males and females. Eretmodus cyanostictus is a monogamous mouthbrooding cichlid in which the clutch is successively incubated first by the female and then by the male. It has been suggested that parents are constrained to monogamy due to low remating probabilities for both sexes. We tested this hypothesis by varying the sex ratio experimentally. Mate desertion by either sex was not significantly higher when additional potential mates were present (males: 8.3%, females: 0%) than when there were no other same-sex conspecifics present (males: 0%, females: 0%). Males lost their mate to a male intruder during their incubation in 26.7% of cases. Pair members were more active and showed more aggression when same-sex conspecifics were present. Behavioural differences between treatments were strongest during the incubation period of a given sex. If no desertion takes place, sexual conflict may be expressed also on a second level, the amount of parental care each parent provides. Indeed, males took the offspring later when additional females were present, although male incubation time did not differ between treatments. A hitherto undescribed display behaviour of females was clear evidence of a conflict about the timing of shift of young. In conclusion, offering alternative mating opportunities did not strongly favour mate desertion in E. cyanostictus. It rather revealed a conflict between mates about when to shift the young.Communicated by M. Abrahams     

Lekking behavior in the neotropical frog Ololygon rubra

Summary This is the first study to document in detail the satisfaction of Bradbury's four criteria for categorizing any anuran as a classical lekking species. The paternal care of male neotropical frogs, Ololygon rubra, consisted of minimal contributions of their genes. Males competed acoustically at traditional, defended, clustered sites (Fig. 1, Table 3) to attract gravid females, who paired with the males at these locations but took the amplectant males to oviposition sites away from the pairing sites. Individual males apparently did not control resources necessary for attracting females, because there were no correlations between male numbers and measured habitat variables, or between male numbers and oviposition sites. On chorusing nights, males always arrived at their display arenas before any females were observed. Females moved freely among clusters and males, before making their choices of mates. However, males employed other mate acquisition strategies that tended to undermine the initial female choices. The predictions that lekking species should have a relatively extended breeding season, a highly biased operational sex ratio (OSR), and an absence of male control of resources essential for female acquisition were also evaluated and corroborated. These frogs have two long breeding seasons encompassing a total of about 6 months (Fig. 2). There were strongly male biased nightly OSRs (Table 1), that contributed to high variance in male reproductive success (RS), but reduced indices of sexual selection, and a relatively low coefficient of variation (CV) of male RS (Table 5) compared to other amphibians. Thus, all of this evidence supports the conclusion that O. rubra in coastal Guyana uses a lek mating system.     

The mating system of two hybridizing species of water striders (Gerridae)

Summary We studied oviposition, feeding and mating behavior of the water striders Limnoporus dissortis and L. notabilis in sympatric and allopatric populations occurring on semi-permanent ponds in Alberta and British Columbia, Canada. Here we describe the mating system of the species and consider the evolution and maintenance of reproductive strategies employed by both sexes. Females of both species oviposited along edges of floating vegetation, either with a guarding, postcopulatory male in attendance, or alone and independent of copulation. Some females ovipositing alone were discovered by males, and when pressed for copulation, either (1) abandoned oviposition or (2) copulated and then resumed oviposition. Females that oviposited with a guarding male laid more eggs than those that completed oviposition alone. Most breeding females accepted prey offered experimentally, while a large proportion of males rejected prey but responded to model gerrids with aggressive displays and mating behavior. Males displayed three mating tactics: (1) territorial-signaling (TS), (2) patrol-signaling (PS), and (3) silent patrolling (SP). All territorial males produced surface waves from oviposition sites before attempting to mate. Some patrolling males signaled, while approaching potential mates as an aid in sex discrimination, but others did not signal and mounted both males and females. When presented with dead gerrid models, males of L. notabilis discriminated between sexes while those of L. dissortis mounted both male and female conspecifics. Collectively, males employing TS tactics fertilized more eggs than patrolling males and TS males of L. notabilis fertilized relatively more eggs than those of L. dissortis. Individual males switched frequently between territorial and patrolling behavior both under natural conditions and in field exclosures. TS males gave more signals per encounter than PS males suggesting that signaling varies with male dominance. Choice of tactic did not depend upon hunger level and was not associated with significant differences in body length in single-species populations. However, in a mixed population, the smaller males of L. dissortis were rarely territorial and signaled infrequently.     

Responses of male white ibises to their mate's extra-pair copulations

Summary I intensively observed the mating behavior of 134 pairs of white ibises for over 15 000 pair hours to examine the responses of males to extrapair copulations (EPC) involving their mates. Females often cooperated completely in apparently fertile EPCs. Male mate-guarding was vigorous and effective. Males did not respond to apparent sperm competition with forced-pair copulation, physical punishment, or abandonment of their mates. I found no negative correlation between degree of female promiscuity and the amount of parental care her mate gave to the entire brood. Males also did not reduce paternal care given to the young most likely to be the result of an EPC. I hypothesize that males are constrained in the behaviors they can use to avoid misplaced paternity in this species. While male mate-guarding reduces the opportunities for female involvement in EPC, the behaviors used by males to protect paternity apparently have not prevented the evolution of female receptiveness during EPC attempts.     

Female encounter rate and the calling behavior and mating propensity of male Requena verticalis (Orthoptera: Tettigoniidae)

Mating effort, the energy exerted in finding and persuading a member of the opposite sex to mate, may be influenced by how frequently potential mates are encountered. Specifically, males that frequently encounter females may reduce calling effort and be less eager to mate than males that infrequently encounter females. An experiment was set up to test this hypothesis, using the tettigoniid Requena verticalis. We examined the song structure, calling activity and mating propensity of individual males exposed to one of five different encounter rates with virgin females. Song structure and calling effort were significantly altered by an encounter with a female. After an encounter, males significantly increased chirp rate and decreased variability in interchirp interval. Encounters also stimulated a male to call and to continue to call for up to two hours. The elapsed time since mating affected mating propensity but not calling activity. Mating propensity asymptotically increased to reach a maximum by day 17 since last mating. However, neither the frequency of encounters, nor the number of previous encounters experienced by a male, influenced calling activity or the propensity of a male to mate. The significance of changes in song structure and calling activity following an encounter, and of increasing male mating propensity over time, are discussed. Correspondence to: G.R. Allen     

Underwater oviposition in a damselfly (Odonata: Coenagrionidae) favors male vigilance,and multiple mating by females

Summary Female Enallagma hageni oviposit underwater where they are inaccessible to males. I demonstrate that males guard submerged females rather than perch sites, and are behaviorally distinct from lone males at the water. In contrast to lone males, which always attempt to copulate with females presented to them, guarding males exhibit a conditional latency to remating which corresponds closely to the time required by females to oviposit a complete clutch of eggs. By ovipositing underwater, females decrease the risk that their eggs become exposed. Risks associated with submerged oviposition favor both mate guarding, and multiple, within-clutch matings by females. Both guarding mates and lone males rescue females that float on the water surface as the result of improper resurfacing. Such behavior reduces the mortality risk to females from 0.06 to 0.02 per oviposition bout. By remating between bouts, females benefit from the additional vigilance of lone males, who rescue floating females 1.4 times as often as original mates. A second consequence of multiple mating is an increase in the selective advantage of vigilance by mates. Because receptive females become scarce by early afternoon, whereas male density remains high, a male has little (3%) chance of encountering a second receptive female that day. However, he incurs a 42% risk of losing fertilizations if he abandons a mate. For male E. hageni mate guarding functions in the context of both natural and sexual selection. It insures that a mate lives to lay a complete egg clutch in addition to protecting a male's sperm investment.     

Costs of exclusive male parental care in the sea spider <Emphasis Type="Italic">Achelia simplissima</Emphasis> (Arthropoda: Pycnogonida)

Sea spiders are one of the few marine invertebrates whose males care exclusively for offspring. The costs of parental care, however, have never been addressed for any species of pycnogonid. Costs may be significant for brooding sea spiders of Achelia simplissima, since males carry up to 12 egg masses simultaneously and actively aerate those eggs by moving their ovigerous legs back and forth. This study explored four potential costs to males as a result of parental care: predation, dislodgment, movement and feeding patterns, and frequency of epibionts. Brooding males were found to experience significantly higher frequencies of predator attacks and epibionts, as well as a lower rate of movement compared with nonbrooding males. Interestingly, brooding males were harder to dislodge than nonbrooding males and experienced no change in feeding frequency as a result of parental care. This is the first study to provide evidence that parental care may be costly for male pycnogonids in terms of individual survival and future reproductive success.     

Reproductive defence priorities of male willow ptarmigan (Lagopus lagopus): enhancing mate survival or extending paternity options?

Summary Cock willow ptarmigan (Lagopus lagopus) closely guard their mates from predators and conspecific males, and vigorously defend their nests and young. In view of potential costs and benefits of behavioural guarding descisions, I designed a test to examine if, when and how males altered defence priorities. Cock willow ptarmigan were very attentive to their mates throughout the breeding season, unaccompanied hens comprising less than 3% of the sightings of mated females. From the second week of incubation until shortly after hatch, males attempted to guard both mates and offspring. Males guarded mates preferentially over nests until the third week of incubation; they then changed their priority to defence of offspring (nest and/or chicks). The overall defence response initially was strong, but decreased after the first week of incubation. Strength of response increased again in late incubation, and declined as chicks began to fly. Consistency of defence decisions was highest during prenesting and egg laying and lowest during late incubation. Since males defended their mates for a longer period than required for protection of paternity, hypotheses predicting enhanced mate survival and extended paternity options through renesting were examined. Removal of males did not result in reduced survival or increased weight loss of widows during incubation. In light of heavy nest depredation and displacement pressures by conspecifics, mate guarding throughout incubation enhanced male fitness by ensuring paternity in renesting attempts.     

Allopaternal care in the fathead minnow,Pimephales promelas: females prefer males with eggs

Summary Some species of fishes with exclusive male parental care exhibit the phenomenon of allopaternal care; that is, some males acquire and care for other males' eggs. We conducted a series of experiments to investigate the dynamics and evolution of allopaternal care in one such species, the fathead minnow (Pimephales promelas). In choosing a nest site, a newly reproductive male tended to take over the nest site of a parental male by evicting the resident male, rather than occupy a physically identical empty nest site. The new male generally cared for the old male's eggs, and in most cases, daily egg survival improved under the new male's care. When males were given a choice among unguarded nest sites, they preferred to occupy nest sites already containing eggs. When eggs were randomly assigned to nesting males, females preferred to spawn with males who had eggs in their nest sites. Thus, it appears that female preference for males with eggs led to the evolution of allopaternal care in the fathead minnow.     

Parental care and mate attraction in the Florida flagfish, <Emphasis Type="Italic">Jordanella floridae</Emphasis>

Theory suggests that there is a trade-off between mate attraction and investment in parental care. Yet, under some circumstances, such as in species with uniparental male care, it is conceivable that males who provide more care also attract more females, and hence avoid this cost. We tested these two alternative hypotheses using the Florida flagfish, Jordanella floridae, which is a highly sexually dimorphic species with male parental care. We predicted that if components of male care behavior primarily serve offspring survival, they should display these behaviors more in the presence of eggs than without eggs. We also predicted that males should show a trade-off between display, and other activities directed to other fish, and care behaviors. Alternatively, if care has a positive effect on mating success, we expected males to show care even in the absence of eggs, and that they should display more care in the presence of females. We found that care behavior mostly depended on the presence of eggs, males increased care when they guarded eggs, and there was a negative relationship between rates of interaction and care behavior. Most care was exhibited in the absence of other fish while the presence of males and females both had a negative effect on care behavior. There was no difference in care behavior with males or females present. Only nest-visitation rates were highest in the presence of females, suggesting that this behavior is used as part of the courtship. These results support the idea that male care in this species is primarily influenced by natural selection. Males did, however, display fanning and other egg-directed behaviors even in the absence of eggs. The level of these behaviors was constant and independent of display behavior. Hence, it seems that care may be used in mate attraction before the male has received his first clutches.     

Parental care sex differences in the brown bullhead,Ictalurus nebulosus (Pisces,Ictaluridae)

Summary Males were the principal care-givers in the brown bullhead, Ictalurus nebulosus. Direct observations on individually tagged adults in nature revealed that males attended broods at closer distances than females and were the most frequent lone care-givers. However, females often participated in parental care and in some cases assumed the typical male role in the absence of the male. In the presence of her mate, females generally performed different care-giving functions than males. Females attended broods at a distance and chased other fishes more frequently than males. Males remained directly over the brood guarding. A series of mated pairs in each of three reproductive conditions were captured and examined. Different pairs were compared between reproductive conditions for body weight, body condition, gonadal-somatic index, and a gut-contents index. The inital costs of reproduction, as measured by weight loss, condition change, and gonadal-somatic index change, were more severe in females than males. During breeding and subsequent care-giving, males did little or no feeding whereas females increased their feeding during the same time period. However, males appeared to sustain only minor weight and condition losses due to care-giving. I suggest that males were the principal care-givers because the net benefits of remaining at the nest were greater than the net benefits of leaving. Males had little opportunity to mate with more than one female each season, and offspring had little chance of survival in the absence of a care-giving adult. Considerable variation in female behavior occurred which suggests that the net benefits of care-giving were nearly balanced with the net benefits of leaving the brood. The relative importance of feeding versus care-giving by females may vary with slight differences between females and the behavior of their mates as care-givers.Present address: Department of Zoology, Ohio State University, 1735 Neil Avenue, Columbus, Ohio 43210, USA     

Multiple mate choice criteria and the importance of age for male mating success in the microhylid frog, Cophixalus ornatus

We examined multiple mate choice criteria in Cophixalus ornatus, a terrestrial breeding, microhylid frog. Mate choice consisted of three stages: mate attraction (male calling), courtship (male behavior between the call site and the nest), and nest site selection by the female. For male C. ornatus, the possession of a call with low dominant frequency relative to calling neighbors increased the probability that they would attract females. Dominant frequency was negatively correlated with age independent of male mass and snout vent length. When escorting the female from the call site to their nest, males traveled along more convoluted paths than when returning to the nest alone. The convolution of the path was, therefore, considered an aspect of courtship. Females released eggs into nests with structural characteristics typical of nests constructed by older males. Thus, females increased their chances of locating an acceptable nest by preferentially approaching males with lower dominant frequencies. This study is the first to demonstrate that age, independent of mass or snout-vent length, can influence call characteristics in anurans, and it is also the first to demonstrate the importance of male age to female mate choice in an amphibian.     

Sexual selection and the function of a melanin-based plumage ornament in polygamous penduline tits <Emphasis Type="Italic">Remiz pendulinus</Emphasis>

Melanin-based ornaments are often involved in signaling aggression and dominance, and their role in sexual selection is increasingly recognized. We investigated the functions of a melanin-based plumage ornament (facial ‘mask’) in male Eurasian penduline tits Remiz pendulinus in the contexts of male–male aggression, mating success, and parental care. The penduline tit is a passerine bird with a unique mating system in which both sexes may mate with several mates in a breeding season, and one (or both) parent deserts the clutch. Our study revealed that mask size of males is more likely an honest signal used by females in their mate choice decisions than a trait involved in male–male competition. First, mask size increased with both age and body condition, indicating that the mask may signal male quality. Second, males with larger masks paired more quickly and had more mates over the breeding season than males with smaller masks. Third, we found no evidence that male mask size signals male–male aggression or dominance during competitive encounters. The increased mating success of large-masked males, however, did not translate into higher reproductive success, as nestling survival decreased with mask size. Therefore, we conclude that there is either no directional selection on male mask size or males with larger masks receive indirect, long-term benefits.