Adaptive significance of winter pair bond in male pintail, Anas acuta

To test the female-advantage hypothesis that has been proposed to explain the adaptive significance of winter pair bonds in ducks, we examined the feeding and social behaviors of the northern pintail, Anas acuta. The female-advantage hypothesis assumes that male attendance offers paired females the benefits of increased social status and access to food, as well as less harassment from conspecifics, allowing them to spend more time feeding. Paired females dominated unpaired females, but neither time budgets of feeding nor frequency of feeding was significantly different between unpaired and paired females. The female-advantage hypothesis predicts that paired males spend less time feeding because they must closely guard their partners from harassment by male conspecifics. Paired males defended their mates by chasing and pecking the unpaired males. However, both time budgets of feeding and frequency of feeding were significantly higher in paired males than in unpaired males. Unpaired males frequently approached females while swimming. They performed courtship displays, mostly toward unpaired females. Paired males spent more time feeding by saving time and energy in courtship. We consider that the advantage of winter pairing for males comes from having a mate plus having an increase in feeding frequency. Received: February 20, 2000 / Accepted: May 22, 2000     

Male Defense of the Breeding Cavity and Factors Affecting the Persistence of Breeding Pairs in the Stomatopod,Gonodactylus bredini (Manning) (Crustacea: Hoplocarida)

In Caribbean Panama, nonreproductive male and female stomatopods are solitary and defend their own coral-rubble cavities. When breeding pairs form, however, males assume all responsibility for cavity defense. To compare success in cavity defense and defensive tactics among paired and unpaired males, and to examine the tendency for paired stomatopods to exchange their present mates for larger (higher quality) individuals, we introduced same-sized and 15% larger male, and same-sized and 15% larger reproductive female intruders to paired and unpaired male residents in a balanced design. Paired males were more successful at cavity defense than unpaired males, evidently because paired males strike intruders more than unpaired males, and because intruders fight less intensely against paired males than against unpaired males. Paired males occasionally attempted extrapair copulations, but showed little tendency to abandon their mates in favor of larger females. Paired females, however, mated readily with intruder males that evicted resident males. Populationwide female breeding synchrony and prolonged female receptivity before oviposition reduce variance in male mating success and may force males to guard the breeding cavity to assure their paternity. Uncertainty about the reproductive condition of intruder females may prevent males from exchanging mates.     

Increased vigilance of paired males in sexually dimorphic species: distinguishing between alternative explanations in wintering Eurasian wigeon

In animal pairs, males are often more vigilant than females.This is generally assumed to result from mate guarding (eitheragainst predators or other males). However, when males haveconspicuous secondary sexual characteristics, they could beconstrained to be more vigilant because of a higher predationrisk than females. We attempted to distinguish between the "maleconstraint hypothesis" and two variations of the mate-guardinghypothesis by studying the vigilance behavior of the sexuallydimorphic wigeon during early winter, when some males are inbreeding plumage and some are not and when not all males arepaired. The proportion of time spent vigilant by paired malesin breeding plumage was five times higher than any other categoryof males or females. We found no significant differences betweenthe vigilance levels of unpaired male wigeon in cryptic andin breeding plumage and therefore rejected the male constrainthypothesis. As vigilance levels of paired and unpaired femalesdid not differ either, we rejected the hypothesis that pairedmales invest in vigilance to reduce their mate's need to bevigilant to predation risks. Paired females interacted lessfrequently with other wigeon than unpaired ones, and it is probablyto protect their female from other males that paired male wigeonincrease their vigilance times.     

Pairing Patterns in Japanese Beetles (Popillia japonica Newman): Effects of Sex Ratio and Time of Day

Size-related patterns between unpaired and paired individuals and between males and females of a given pair give clues about both a species' sexual behavior and the environmental factors affecting its sexual behavior. We studied the mating patterns of Japanese beetles (Popillia japonica) in east–central Illinois. The frequency of male–female pairs varied significantly among days and within a day, with pairs being significantly more common in the morning and the evening. The sex ratio on the food plants was significantly male biased, but although the sex ratio fluctuated among days and among time periods, the variation in the frequency of mating pairs was not explained by variation in the sex ratio. We found no assortative pairing with respect to size, but sizes of paired and unpaired individuals did differ. Paired females were larger than unpaired females at all time periods. In contrast, paired males were larger at 0700 and smaller at 1000, and little difference existed at other times of the day. The size of males and females, sex ratio, and pairing frequency also differed among days. Much of this variation in size and pairing frequency was related to a seasonal effect: later in the summer, beetles of both sexes were smaller and pairs were less common. Interestingly, pairs were also less frequent on days with higher average temperatures. This between-day variation in pairing, in combination with the within-day pairing differences, suggests that the temperature may alter the cost, and hence likelihood, of pairing in this species.     

Sex-specific timing of mate searching and territory prospecting in the nightingale: nocturnal life of females

Formal models have shown that diel variation in female mate searching is likely to have profound influence on daily signalling routines of males. In studies on acoustic communication, the temporal patterns of the receivers'' signal evaluation should thus be taken into account when investigating the functions of signalling. In bird species in which diel patterns of signalling differ between males singing to defend a territory or to attract a mate, the diel patterns of mate and territory prospecting are suggested to depend on the sex of the prospector. We simulated newly arriving female nightingales (Luscinia megarhynchos) by translocating radio-tagged females to our study site. The mate-searching females prospected the area mostly at night, visiting several singing males. The timing of female prospecting corresponded to the period of the night when the singing activity of unpaired males was higher than that of paired males. In contrast to females, territory searching males have been shown to prospect territories almost exclusively during the dawn chorus. At dawn, both paired and unpaired males sang at high rates, suggesting that in contrast to nocturnal singing, dawn singing is important to announce territory occupancy to prospecting males. In the nightingale, the sex-specific timing of prospecting corresponded to the differential signalling routines of paired and unpaired males. The temporal patterns in the behaviour of signallers and receivers thus appear to be mutually adapted.     

Conflicting Territory Use in Males and Females of a Monogamous Ungulate,the Kirk's Dikdik

In monogamous mammals it is often unclear why males do not defend larger territories to attract more than one female. I investigated the territoriality of the monogamous Kirk's dikdik, Madoqua kirki, a dwarf antelope, in which food resources increase with territory size and some males defend enough resources for more than one female. Yet, all males are paired monogamously. When males were removed from small territories, their female partners spent more time outside of their territories than females in large ones. When females were removed, their male partners almost never left. Pairs in small territories spent more time together than pairs in large ones. Paired males left mostly together with their females, apparently not on their own initiative. Presumably because females in small territories left more often, their males spent more time outside in the female's company than males in large territories. I argue that males in smaller territories can keep better track of their females and that they can effectively reduce their females' time outside. Male intrusion pressure was unrelated to territory size, but it increased in the presence of unguarded females. If large territories decrease the ability to mate guard, and if unguarded females attract competing males, then defending large territories may be uneconomical, even it they could attract more than one female. On the other hand, territories must be large enough to satisfy the requirements of a single female.     

The influence of conspecific chemical cues on walking behavior of <Emphasis Type="Italic">Ixodes ricinus</Emphasis> males

The influence of female and male cues on the male searching behavior of the sheep tick, Ixodes ricinus (Acari: Ixodidae), was studied under constant laboratory conditions by means of a computerized video tracking system. Males were released into an open glass arena in which one half had been exposed for 1 h to 5 freely walking unfed females or five males. The obtained track data were analyzed to reveal if male walking pattern was random or affected by cues of conspecifics left on the arena surface. The results showed that males spent significantly more time and walked a significantly longer distance in the area with female cues compared to the control area. Moreover, the walking path of males was more tortuous on the cues half than the control half. In contrast, walking behavior of males was not affected by male cues in any observed parameter. These results provide the first evidence that unfed females leave sex-specific semiochemicals on a substrate during their walk and that these cues have an effect on male searching behavior. Since this effect was not observed when female cues were 24-h old, the semiochemicals seem to either evaporate or are subject to degradation. The biological significance of these findings for mate-searching in I. ricinus males is discussed.     

Plasma steroid hormones in relation to behavioral sex role reversal in the spotted sandpiper, Actitis macularia

Plasma samples collected from spotted sandpipers during the reproductive season were analyzed for testosterone, dihydrotestosterone (DHT), estradiol-17 beta and progesterone. Prior to incubation, plasma testosterone and DHT levels were significantly greater in males than in females. Estradiol levels of paired females were significantly greater than those of paired males. Testosterone and DHT levels of unpaired resident and paired males were significantly greater than those of incubating and brooding males. A 25-fold decline in testosterone occurred in males from the 1- or 2-egg stage to the 3-egg stage, when incubation is initiated. In females, testosterone values were low in unpaired, brooding, and transient birds. Paired females had levels 7-fold greater than unpaired birds. In both sexes, there was a strong correlation between testosterone and DHT levels. Prolactin values were negatively correlated with testosterone and DHT in males. These results indicate that the high level of intrasexual competition for mates among female spotted sandpipers is not based upon a total reversal of the normal male/female levels of androgens and estradiol. Territoriality and intense competition for mates in females may be based upon enhanced receptivity of neural centers to moderate hormone levels. Relative changes in testosterone between unpaired and paired females indicates that this hormone may play a role in mate acquisition and territoriality of these sex role-reversed females.     

Lifetime patterns of pairing success in male Ortolan Buntings Emberiza hortulana

Analyses of lifetime fitness in birds are typically based on estimates of breeding success, in particular the number of offspring fledged. Small and isolated bird populations often have a male‐skewed adult sex ratio, so that male lifetime productivity depends to a large degree on pairing success, but few studies have focused on patterns of lifetime pairing success. The Norwegian population of Ortolan Buntings Emberiza hortulana is strongly male‐skewed, such that in any year about half of all males are unpaired. Pairing success of first‐year males (16–44%) was significantly lower than for older males (52–89%). Lifetime pairing success was correlated with lifespan and was strongly skewed, with a majority of males being paired only once or never, and only 11% paired three or more times despite a stable lifetime annual survival rate of 63%. Males that were paired in one year were more likely to be paired the next year than males that were unpaired in the previous year. The shortage of females caused even the older males to have a substantial probability of becoming unpaired, and 49% of long‐lived males (known as adults for at least 4 years) were unpaired after years in which they were paired. Pairing success in the Ortolan Bunting therefore follows similar age‐related and lifetime patterns in breeding success documented in other species. However, even the older males ran a high risk of not being paired, contrasting with earlier distinctions between pre‐breeding and breeding lifespans. I discuss the importance of knowledge of pairing success for the management of endangered and declining populations.     

Spawning tactics of paired males of the dark chub,Zacco temmincki,reflect potential fitness costs of satellites

Synopsis Paired males of the dark chub, Zacco temmincki, buried released eggs by vibrating their anal fin, but this behavior was prevented and eggs were cannibalized when many satellites (males and females) were present. A number of satellite males also caused a loss to paired males in sperm competition on spawning grounds far from shelters. Paired males followed repeating tactics, which were defined as successive spawning acts at the same redd, in most cases, but occasionally did shifting tactics which refer to spawning acts conducted successively at different redds. The proportion of the shifting tactic was not correlated with the dominance status of paired males. The shifting tactic was not advantageous in performing spawnings frequently. The calculation of the total advantage of both tactics indicated that the shifting tactic itself was not more beneficial than the repeating tactic at any density of satellites. Since a number of satellites stayed around the redd when no spawning pair was present, or pursued a pair or a single dominant male moving between spawning grounds, the occasional shifting tactics of paired males functioned to confuse and disperse satellites. The spawning tactics of paired males apparently reflected potential fitness costs of satellites. Paired males mainly spawned at the redds near shelters, despite the fact that more satellites were present to devour eggs, presumably because they could obtain many females and monopolize fertilizations.     

Division of labor in the monogamous goby,Valenciennea longipinnis, in relation to burrowing behavior

Feeding and burrowing behavior of the monogamous gobiid fish,Valenciennea longipinnis, were studied on the coral reef at Sesoko Island, Okinawa, Japan. These fish usually live in pairs, the male and female feeding in close proximity to one another upon benthic animals and constructing several burrows cooperatively for purposes of shelter or spawning. Paired females fed more and burrowed less frequently than their mates. Because burrow maintenance was mostly conducted by the latter, the paired females performed work much less frequently than solitary females. Thus, the paired females may be able to allocate more energy toward egg production. The division of labor related to burrowing behavior in this species may be an effective way to increase reproductive success for both sexes. Moreover, the fameles burrowed even less frequently when paired with larger males, probably because burrowing ability may be correlated with mouth size in males. This is a likely reason for the preference of females to mate with larger males.     

Pairing success and sperm reserve of male Gammarus pulex infected by Cyathocephalus truncatus (Cestoda: Spathebothriidea)

Manipulative parasites with complex life cycles are known to induce behavioural and physiological changes in their intermediate hosts. Cyathocephalus truncatus is a manipulative parasite which infects Gammarus pulex as intermediate host. G. pulex males display pre-copulatory mate guarding as a response to male-male competition for access to receptive females. In this paper, we tested the influence that C. truncatus-infection might have on male G. pulex sperm number and pairing success. We considered 3 classes of G. pulex males in our experiments: (i) uninfected males found paired in the field, (ii) uninfected males found unpaired in the field, or (iii) infected males found unpaired in the field. Both infected males and uninfected unpaired males paired less with a new female than uninfected paired males did. Furthermore, infected males appear to be at a strong disadvantage when directly competing for females with a healthy rival male, and had fewer sperm in their testes. We discuss the potential effect of male and female mating strategies on such male host mating alteration.     

Validation of a Method for Quantifying Male Mating Preferences in the Guppy (Poecilia reticulata)

Male and female mating preferences are commonly inferred from association times spent with potential mates in a dichotomous‐choice test. However, this assessment method is rarely validated, particularly so for male mating preferences. Using the Trinidadian guppy (Poecilia reticulata), an important model species in the study of sexual selection, we tested whether a male’s mating preference for either of two stimulus females in a dichotomous‐choice test predicted his mating behaviours directed at the preferred female when he was allowed to swim freely with both females. First, we presented individual males with two females that differed in body length in a dichotomous‐choice apparatus in which the male could only use visual cues to assess the paired females. We quantified male mating preference as the duration of time a focal male spent associating with each female. Immediately following this test, the focal male was allowed to swim freely with both females, and we quantified the time he spent sexually pursuing each female and the number of courtship sigmoid displays and copulation attempts he directed at each female. On average, males did not significantly prefer either of the two stimulus females in either of the two tests; however, the magnitude of male preference for the larger female tended to increase as the size difference between the paired females increased. More importantly, there was a significant positive relationship between male association time in the dichotomous‐choice test and both the time spent sexually pursuing and the number of courtship sigmoid displays directed at the same female initially preferred in the dichotomous‐choice test. Collectively, these results confirm that association time measured in a dichotomous‐choice test is a reliable predictor of male mating preferences in the Trinidadian guppy.     

Paternity in horseshoe crabs when spawning in multiple-male groups

Unpaired or satellite male horseshoe crabs, Limulus polyphemus, are attracted to and often form a group around a pair (a female with an attached male) that is nesting in the high intertidal zone. These males are engaged in sperm competition. We observed nesting pairs and their associated satellites in the wild, collected and reared their eggs and used genetic markers to examine paternity. We found that the unpaired, satellite males are highly successful at fertilizing eggs; two satellites can leave the attached male with few fertilizations. Two satellites together are each as successful as one spawning with a pair. A satellite's location around the female greatly affects his success, and males compete for access to a position over the dorsal canal between the prosoma and opisthosoma of the female and under the front margin of the paired male where they are most likely to fertilize eggs. Although eggs and sperm retain their viability for some time after spawning, nearly all eggs are fertilized by the satellites that are around the nesting pair at the time of egg laying and by the attached male. A number of factors including beach current, female size and male behaviour affect the outcome of sperm competition in this externally fertilizing species. Copyright 2000 The Association for the Study of Animal Behaviour.     

Cost of reproduction: a comparison of survival rates of breeding and non‐breeding male ortolan buntings

The cost of reproduction is expected to influence survival or future reproduction. Most previous studies have assessed cost of reproduction in relation to natural and experimental variation in number of offspring produced. The ortolan bunting Emberiza hortulana is a passerine bird species with biparental care, and the Norwegian population of the species has an extraordinarily skewed sex ratio with only about half of the males attracting a female, and therefore provides a rare opportunity to compare survival of males that have paired and bred with that of non‐breeders (unpaired males), which have not paid a cost of reproduction. Results showed that survival rates of paired (65.0%) and unpaired (64.2%) males did not differ. However, when comparisons were restricted to paired males that definitely had nestlings, their survival rate (76.8%) was significantly higher than that of unpaired males, and the same was the case when comparisons were further restricted to paired males that had offspring recruiting to the population the next year (76.8% survived). Males breeding successfully are likely to be a biased subset of high quality males. In analyses of a subset of males that had bred successfully when young, there was no difference in survival of paired and unpaired individuals when these males were older. In conclusion, breeding male ortolan buntings did not appear to pay a cost of reproduction in terms of reduced survival to the next year compared to non‐breeding males. These results may be explained by non‐breeding males also incurring extra costs during the breeding season, and that costs of reproduction are not shared equally among sexes in the ortolan bunting and other bird species with biparental care.     

Diel variation in a dynamic sexual display and its association with female mate-searching behaviour

Dynamic sexual signals often show a diel rhythm and may vary substantially with time of day. Diel and short-term fluctuations in such sexual signals pose a puzzle for condition capture models of mate choice, which assume a female preference for male traits that reliably reflect a male's quality. Here we experimentally manipulated the food supply of individual male field crickets Gryllus campestris in their natural habitat in two consecutive seasons to determine (i) the effect of male nutritional condition on the fine-scaled variation of diel investment in acoustic signalling and (ii) the temporal association between the diel variation in male signalling and female mate-searching behaviour. Overall food-supplemented males signalled more often, but the effect was only visible during the daytime. In the evening and the night, signal output was still high but the time spent signalling was unrelated to a male's nutritional condition. Females' mate-searching behaviour also showed a diel rhythm with peak activity during the afternoon, when differences among calling males were highest, and where signal output reliably reflects male quality. These findings suggest that males differing in nutritional condition may optimize their investment in signalling in relation to time of day as to maximize mating success.     

The effects of male harassment on mating duration in the seed bug,Togo hemipterus

Harassment on mating pairs by solitary males is usually considered an attempt by the male to (1) take over the female, (2) guard the female against further insemination (when the solitary male has previously copulated with this female), or (3) influence mating duration. Paired males of a seed bug repel harassment on mating pairs by solitary males by firmly grasping females using their legs and/or genital claspers; in this way, mating duration is prolonged. Male fertilization success increases as mating duration increases. Males of the seed bug, Togo hemipterus (Scott) (Heteroptera: Lygaeidae), use seminal substances to inhibit female remating. These substances induce protracted female refractory periods and are transferred to the females in a time‐dependent manner. Consequently, mating duration has important effects on fitness in this species. We observed harassment on T. hemipterus mating pairs by solitary males, and examined conflicts between paired and solitary males over mating duration. None of the solitary males were able to take over a mating female, and this may be due to the unique male genital structure in this species. All conflicts over mating duration resulted in wins by the paired males over the solitary males. Paired males prolonged mating durations, whereas severe harassment on mating pairs by solitary males shortened durations. We show that even though there is no immediate reward for the solitary male (i.e., it is unable to take over the mating female), this harassment behavior may be adaptive.     

Probability of detection of Flammulated Owls using nocturnal broadcast surveys

ABSTRACT Broadcasts of conspecific vocalizations are used to increase detection rates on surveys of secretive bird species, yet the assessment of detectability necessary to fully interpret such survey data is frequently lacking. We used radiotelemetry to evaluate the probability of detection of 17 radio‐tagged male Flammulated Owls (Otus flammeolus) using conspecific broadcast surveys in Idaho during 2005 and 2006. Probability of detection among the 11 paired, five unpaired, and one unknown pairing status owls was 100% during the pair‐bonding and incubation periods of the breeding season, after which it declined to less than 15% during the postfledging period. Paired males showed a different pattern than unpaired males. Following hatching of eggs, detectability of paired males declined gradually over a 6‐week period, whereas detectability of unpaired males dropped sharply for a 4‐week period before increasing during the postfledging period. We suggest that surveys for Flammulated Owls be conducted during the pair‐bonding and incubation periods when high detectability permits stronger inference concerning the presence or absence of owls based on broadcast survey detections.     

Behavioural and genetic assessment of reproductive success in a spawning aggregation of the Australian giant cuttlefish, Sepia apama

The only known spawning aggregation of cuttlefish occurs in winter in southern Australia. The operational sex ratio in this aggregation is highly skewed towards males (range 11:1 to 4:1). Using SCUBA, we videotaped females as they mated with up to six males/h. Females rejected and accepted mates of any status or size. We obtained individual eggs and tissue samples from females and their mates and determined paternity by microsatellite DNA analysis. Thirty-nine eggs were sampled during 17 observational sequences (trials); 22 eggs were sired by a sampled male. One-third of the females mated with multiple males and 67% of females' eggs had multiple sires (N=9). Given our restricted sampling, these results probably underestimate actual levels of multiple paternity. Males competed to guard and copulate with females, and spent most of the copulation time flushing water into the female's buccal area. Thus, we predicted a high probability of fertilization of the next-laid egg(s) by the last male to mate, but this prediction was not statistically supported by our data. Fertilization success did not differ significantly between paired consorts (36%) and unpaired males (31%), or between large (33%) and small males (29%). Females used sperm from paired, unpaired and sneaker males as well as from previous matings to fertilize eggs. Our results indicate that this mating system has a high level of multiple mating and multiple paternity and that males of any size or status can obtain successful fertilizations.     

Function and genetics of long versus short copulations in the cactophilic fruit fly,drosophila mojavensis (diptera: drosophilidae)

Variation in copulation duration of Drosophila mojavensisstrains was influenced by both sexes. Males maintained predominant control, as copulation duration of pairs from different strains was more similar to that of the strain from which the male was derived, but female origin also contributed significantly to the duration of copulation. Variation among strains was controlled by genes acting additively in both sexes. The size of both males and females also affected copulation duration. Small males copulated longer on average than large males, while males paired with large females copulated longer than those paired with small females. The importance of copulation duration to fitness was tested by correlation analyses with male size, female size, female remating latency, and number of eggs laid prior to female remating. Longer copulations stimulated earlier oviposition, possibly by increasing accessory gland secretions that are passed by males during copulation.