金毛弓背蚁行为谱与社会分工的研究

本研究在室内模拟自然蚁巢的结构和条件下,使用个体标记和直接观察法对一巢金毛弓背蚁Componotus tonkinus的行为类型和社会分工进行了研究。共34只来自同一巢穴的工蚁被标记。在持续一周的观察过程中对每只蚂蚁所执行的每种行为的频率进行了统计和聚类分析。结果表明：金毛弓背蚁可以区分出12种基本行为类型;该蚂蚁的成员大致可以分为5个功能组, 即繁殖（蚁后1个）、觅食（由10个工蚁组成,主要负责觅食）、巢穴内的维护及护育（由16个工蚁组成,主要负责巢穴的维修、清理及护育）、巢穴的防卫（包括3个工蚁,行巢穴防卫）及不活跃型（含5个工蚁）。     

Social environment and reproductive interference affect reproductive success in the frog Rana latastei

Variation in the social environment produces selection on morphologicaland behavioral traits. It is less clear how the social environmentgenerates variation in demography through behavioral mechanisms.Theory suggests that one aspect of social environment, relativeabundance of heterospecifics, influences the intensity of reproductiveinterference and its demographic effects. These effects arecountered by species recognition and female preferences. Westudied the effects of social environment on reproductive successin replicated, mixed breeding populations of two ranid frogs,Rana latastei and Rana dalmatina, the former being of internationalconservation concern. We manipulated the social environmentof female R. latastei experimentally by varying the relativeabundance of potential conspecific and heterospecific sexualpartners. We measured amplexus frequency and recorded the reproductivesuccess of R. latastei females. When conspecific males wererelatively uncommon, (1) the absolute and relative frequenciesof conspecific amplexus decreased, indicating a breakdown ofsexual isolation, (2) oviposition was less frequent, and (3)the percentage of viable embryos in deposited clutches decreased.R. latastei females in an environment of low relative conspecificabundance (1:5, R. Latastei:R. dalmatina) demonstrated 6.8%the reproductive success of females in an environment exclusivelywith conspecifics. We present a model for the dependence ofconspecific amplexus on the social environment. We discuss severalmechanisms that may influence reproduction by R. latastei, andwe support conservation of the species' preferred habitat toreduce opportunities for reproductive interference that occurat shared breeding sites.     

Brood discrimination, nest mate discrimination, and determinants of social behavior in facultatively quasisocial beetles (Nicrophorus spp.)

In this study we investigated ecological determinants of socialityin burying beetles (Nicrophorus spp.), potential conflicts ofinterest among reproductive females, and the effects of nestingfailure and costs of fighting on cooperation. Burying beetlesare known to form monogamous pairs when exploiting small vertebratecarcasses. More complex social behavior in this group is poorlyunderstood. We conducted experiments in which one or two females(N. defodiens, N. orbicollis) were provided small or large carcasseson which to breed. On large but not on small carcasses, twofemales often formed cooperative breeding associations (jointlyprepared a carcass and fed young). In N. defodiens, but notN. orbicollis, two females produced a larger brood than singlefemales on large carcasses. In both species, the reproductiveoutput per female was less for two than for one female. Thepresence of a second female did not decrease the preparationtime of a carcass (discovery of resource to egg hatch). Conflictwas evident between females. Trials employing females of similarsize were more likely to result in injury than trials usingfemales of dissimilar size (N. tomentosus, N. defodiens, N.orbicollis). In N. tomentosus, those associations that persistedthe longest resulted in the fewest injuries. After care of youngwas initiated, conflict among familiar nest mates was not observed.There was no evidence that breeding females could discriminatebetween brood; use of a genetic marker (N. orbicollis) demonstratedthat females fed related and unrelated young alike. Femalesof similar size (high potential cost of fighting for the dominantindividual) were not more likely to form cooperative breedingassociations than females of dissimilar size (low cost of fightingfor dominant). Females of a species subject to a high rate ofnest failure (N. defodiens) were more likely to cooperate thanfemales of a species with a low rate of nest failure (N. orbicollis).It is argued that limited reproductive opportunities, difficultyin controlling rivals' access to a large carcass, and the superabundantlarval food supply represented by a large carcass, but not kinselection, have contributed to the evolution of cooperativebehavior in this group. In addition, we hypothesize that beetlesmight initially tolerate consexual rivals on large carcasseswhen there is a high likelihood of nesting failure, therebyavoiding potentially costly conflicts.     

Some Aspects of the Nesting Behavior and Reproductive Biology of Sea Turtles

Basic reproductive data from 21 green turtle (Chelonia mydas),8 leatherback (Dermochelys coriacea), 7 hawksbill (Eretmochelysimbricata), 7 olive ridley (Lepidochelys olivacea),6 loggerhead(Caretta caretta), 1 Kemp's ridley (Lepidochelys kempi), and1 flatback (Chelonia depressa) populations are provided. Someintraspecific and interspecific relationships between size ofnester and clutch, egg size and hatchling size are analyzed.Measurements of reproductive rates (=numbers of hatchlings perfemale per year) in 11 populations varied from 35 to 200 inan olive ridley and loggerhead colony, respectively. Nestingbehavior of each species is described in terms of type of nestingemergence and time spent on the nesting beach (=chelonery).The relatively large number of yolkless eggs laid by many leatherbacksand by some hawksbills invites further study. Some aspects ofsea turtle nesting behavior and reproduction are compared tothose of other chelonians.     

Male tactics and reproductive success in the harem polygynous bat Saccopteryx bilineata

Alternative tactics in reproductive behavior enable individualsto maximize their fitness in relation to competitors in thesame population. In many taxa, territoriality is a common tacticof males to increase their reproductive success. In the batSaccopteryx bilineata, territorial males defend roosting areasfor females against other males and court females throughout the year. Peripheral males in the same colonies do not defendterritories but compete with territorial males for reproductionwith females. In this study, we monitored the behavior of themales in a natural colony over three reproductive seasons.We compared morphological and age data and measured the reproductiveoutput of males adopting the territorial or peripheral tactic.No differences in body size or weight were detected betweenmale types, but the probability of adopting a tactic seemedto be age dependent. Peripherals were often young males andreplaced territorials in several cases, whereas the oppositecase was not observed. Peripherals were not excluded from reproduction,but territorials were more likely to reproduce. Variation in reproductive success was high within both male tactics, andthe reproductive success of some peripherals was comparableto territorials, but, on average, the reproductive successof territorials was more than twice as high. Therefore, behavioraltactics do not seem to be equally profitable in general butmay represent different phases in the reproductive life of manyS. bilineata males.     

Juvenile social play and yearling behavior and reproductive success in female Belding’s ground squirrels

Benefits of play behavior have been described for individuals during the juvenile period; however, it is less clear whether benefits of juvenile play commonly extend beyond the period of juvenile development. I evaluated possible associations between juvenile social play and yearling maternal territorial behavior and reproductive success in female Belding’s ground squirrels (Urocitellus beldingi). Higher rates of juvenile social play were associated with greater intensity of territorial aggressive and vigilant behavior during gestation but not later phases of the yearling reproductive cycle, suggesting that both juvenile play and later experience may influence maternal territorial behavior in yearling females. Juvenile social play was also a reliable predictor of whether a yearling female successfully weaned a litter, raising the possibility that juvenile play behavior influences yearling reproductive success via effects on maternal territorial behavior in female U. beldingi. Other factors were also related to reproductive success in yearling females. Body mass at the beginning of the yearling reproductive period was not correlated with juvenile social play but was associated with the likelihood of successfully weaning a litter. Yearling females whose mother was still alive were more likely to wean a litter than those whose mother was not alive. Mothers and yearling daughters tended to have maternal territories near each other, and mothers with a surviving yearling daughter expressed aggressive behavior at elevated rates and directed aggression toward intruders on the daughter’s territory. Overall, results of the study suggest that juvenile social play is among the variables that influence maternal territorial behavior and reproductive success in yearling female U. beldingi, and are consistent with the idea that juvenile play has benefits beyond the juvenile period for female U. beldingi.     

杀扑磷抗性获得对奥氏钝绥螨发育历期与繁殖能力的影响

为探索杀扑磷抗性获得对奥氏钝绥螨Amblyseius womersleyi Schicha发育历期与繁殖能力的影响,研究了在25℃与30℃温度下,奥氏钝绥螨的杀扑磷抗性系与敏感系的发育历期与繁殖能力。结果表明：奥氏钝绥螨的杀扑磷抗性系与敏感系的交配产卵行为习性没有差异。在25℃与30℃温度下,奥氏钝绥螨的各发育历期、产卵期、产卵高峰期,每雌日产卵量与总产卵量,卵孵化率及雌雄成螨性比等,在杀扑磷抗性系与敏感性系之间无明显差异。结果说明杀扑磷抗性获得对奥氏钝绥螨的发育历期与繁殖能力没有明显影响。     

Parasites delay worker reproduction in bumblebees: consequences for eusociality

Workers in eusocial insects usually tend the brood of the queenand so achieve representation in the next generation throughaiding relatives to reproduce. However, workers of some eusocialspecies, such as bumblebees, are capable of reproductive activityeven in the presence of the queen (in queen-right colonies),and worker reproduction is associated with aggressive behaviorsand egg cannibalism, both of which reduce colony efficiency.Thus, factors that affect worker ovariandevelopment, a preconditionfor reproduction, can influence social harmony and colony productivity.Parasites are a ubiquitous and important part of the bioticenvironment of all organisms. Here we show that parasites playan important role in the reproductive physiology of worker bumblebeesin queen-right colonies of Bombus terrestris, affecting thepattern and timing of ovarian development and oviposition. Workersfrom colonies parasitized with the intestinal trypanosome Crithidiabombi had less developed ovaries than workers of the same agefrom unparasitized colonies. In addition, parasitized colonieswere smaller than unparasitized colonies for about the firsthalf of colony development. This generated further demographiceffects such that workers were on average younger in parasitizedthan in unparasitized colonies around the time of the onsetof worker oviposition, and worker oviposition occurred significantlylater in parasitized colonies. Workers in parasitized coloniestherefore had lower individual reproductive potential and werecooperative for a larger proportion of the colony cycle thanthose in unparasitized colonies. In this system, where transmissionof the parasite between years probably occurs only in infested,young queens, this effect may represent an adaptation on thepart of the parasite to ensure its successful passage throughthe winter. Parasites, by reducing the cost of worker cooperation,may facilitate queen control over her worker force and playan important role in moderating the social organization of eusocialinsect colonies.     

Male mating strategies and the mating system of great-tailed grackles

Great-tailed grackles (Quiscalus mexicanus) are sexually dimorphic,dichromatic, colonially nesting blackbirds. In this study, males pursued three basic types of conditional mating strategies,each of which employed a different set of mating tactics. Territorialmales defended one or more trees in which several females nested.They achieved reproductive success by siring the offspringof their social mates and through extrapair fertilization.Resident males lived in the colony but did not defend territoriesor have social mates. Transient males passed through the colony, staying no more than a few days, and probably visited more thanone colony. Residents appeared to queue for access to territories,but transients did not. Residents and transients gained allpaternity through extrapair fertilizations and provided noparental care. Territorial males sired the majority of offspring,but residents and transients also sired small numbers of nestlings. Territorial males were larger and had longer tails than nonterritorialmales. The number of social mates was related to body size,and males that sired nestlings were heavier and had longertails than males with no genetic reproductive success. Malesthat gained paternity through extrapair fertilization wereheavier and had longer tails than males that did not. The matingsystem of great-tailed grackles can best be categorized as "non-faithful-female frank polygyny."     

Genetic evidence for kin-based female social structure in common eiders (Somateria mollissima)

Kin-based social groups are commonly studied among cooperativelybreeding species but have been less studied in "nontraditional"group breeding systems. We investigated the presence of kin-basedsociality among females in the common eider (Somateria mollisima),a colonial nesting sea duck that exhibits high levels of natalphilopatry in females. Previous studies of female socialityin common eiders have been restricted to observations duringbrood rearing. However, aggregations of female common eidersare also observed during other periods of the life cycle suchas colony arrival and nesting. Here we apply a novel, empiricalframework using molecular markers and field sampling to geneticallycharacterize female social groups at several stages of the commoneider life cycle. When compared with mean estimates of interindividualrelatedness for the entire colony, significantly higher levelsof relatedness were found between females within groups arrivingto the colony in flight, between females and nearest neighborsat the time of nest site selection, and between groups of femalesdeparting the colony with ducklings. Both full-sibling and half-siblingequivalent relationships were also found within these groups.Therefore, throughout each of several stages including in-flightcolony arrival, nesting, and brood rearing, we provide the firstgenetically confirmed evidence of female kin-based social groupsin common eiders and anseriformes in general.     

The success of alternative reproductive tactics in monogyne populations of the ant Solenopsis invicta: significance for transitions in social organization

Newly produced queens from monogyne (single-queen) coloniesof the ant Solenopsis invicta usually initiate reproductionindependently, that is, without worker assistance. However,some recently mated queens attempt to bypass this risky phaseof new colony foundation by entering established nests to reproduce,although it is unclear how often these queens are successfulin natural populations. We surveyed a mature monogyne populationof S. invicta in both 1995 and 1996 for colonies headed by queensincapable of independent colony founding (diploid-male-producingqueens) in order to estimate the frequency of colonies thatare headed by queens that initiated reproduction within establishednests (adopted queens). Using the frequency of diploid-male-producingqueens among the recently mated queens in this population, weestimated that the overall rate of queen replacement by adoptedqueens is about 0.7% per colony per year. Although theory suggeststhat a change to a novel queen reproductive tactic could beassociated with a fundamental change in social organization(queen number), this does not appear to be the case in monogyneS. invicta. However, the evolution of nest-infiltrating reproductivetactics by queens in a monogyne population and the evolutionof multiple-queen societies may result from similar ecologicalpressures facing newly mated queens. We therefore incorporatethis strategy into an existing theoretical framework that wasdeveloped to explain the evolution of alternative social organizationsin ants, providing testable predictions regarding the distributionand frequency of queen adoption in other single-queen ant societies.     

Dominance and aggression in social groups of male and female rats

Two experiments were performed to examine aggression and dominance in domestic male and female $\text{Rattus norvegicus}$ living in small mixed-sex (3 males and 3 females) groups. Experiment 1 examined the development of aggression in females. A single female (alpha) within each of the six colonies tested showed the preponderance of attacks on male intruders placed into the home-cage when male colony residents were absent. Over 12 weeks of intruder-aggression training female alphas showed only a mild nonsignificant elevation of aggressive behavior. A comparison of aggression of male and female colony alphas tested with opponents of each sex revealed that aggression was mainly directed at like-sex opponents, and that female attack was more defensive in character than male attack regardless of opponent sex. The highest intensity of aggression occurred when male alphas confronted male intruders. Although intruders never showed offense toward male residents, 61% of intruding males showed offense in response to attack by females.Experiment 2 investigated the relationship between aggressive dominance and competitive measures of dominance within each of 10 mixed-sex colonies. Alpha stat s of male and female colony residents did not reliably predict priority of access to food or water in tests of direct resource competition with like-sex colony members. When colony males were simultaneously tested for copulation, the copulatory behavior of alpha males was significantly greater than that of other colony males. Results are discussed in relation to the role of aggression in the reproductive strategy of male and female $\text{Rattus norvegicus}$.     

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.     

Preadaptation for parthenogenetic colony foundation in subterranean termites Reticulitermes spp. (Isoptera: Rhinotermitidae)

Thelytokous (all-female producing) parthenogenesis, in some cases, involves reproductive advantages against obligate sexual reproduction. However, the completion of parthenogenesis takes multiple steps without the help of males, and thus preadaptation that meets those requirements will be an important factor for the evolution of parthenogenesis. The Japanese subterranean termite, Reticulitermes speratus, is known to have the ability of parthenogenetic colony foundation, where females that failed to mate with males found colonies cooperatively with partner females and reproduce by parthenogenesis. In this study, we compared the parthenogenetic ability and the colony initiation behavior among six Reticulitermes species in Japan. All species other than R. speratus were not able to reproduce parthenogenetically. Nevertheless, females of these species without the parthenogenetic ability performed homosexual female–female colony initiation and produced eggs without fertilization. In addition, in one species without parthenogenetic reproduction, R. kanmonensis, female–female pair initiated founding behavior as quickly as a heterosexual pair. These results suggest that female–female colony initiation and virgin egg-laying are predominant characters among the genus Reticulitermes and provide a preadaptive condition for parthenogenetic colony foundation in R. speratus.     

Intercolonial encounters and xenophobia in the common mole rat, Cryptomys hottentotus hottentotus (Bathyergidae): the effects of aridity, sex, and reproductive status

The ecological constraints prevalent in arid environments havepromoted the evolution of social groups with a high reproductiveskew in mole rat species occurring there. Outbred social bathyergidsface conflict between maintaining colony integrity to enhancepersonal foraging success and hence survival, and dispersalto maximum individual lifetime reproductive success (LRS). Thisconflict will be a crucial determinant of the response of colonymembers to the presence of foreign conspecifics. We investigatedhow ecological constraints, sex, and reproductive status influencethe outcome of meetings between foreign common mole rats (Cryptomyshottentotus hottentotus) in a series of dyadic encounters. Individualsfrom two localities, at the extremes of an aridity gradient,were used to assess the effects of aridity. The effects of sexand reproductive status were investigated by trials betweenindividuals of differing sex and status. The arid populationrevealed substantially higher levels of rejection than the mesicpopulation. Sex and status played a significant role in moderatingindividual response. For both populations, encounters betweendifferent-sexed individuals produced lower levels of rejectionthan those between same-sexed individuals. For the mesic site,rejection was greatest for encounters between reproductive animals.Conversely, for the arid site, the levels of rejection werecomparatively high and comparable for all combinations of reproductivestatus. Ecological constraints, sex, and reproductive statusare significant factors in interactions between foreign commonmole rats, ultimately influencing individual survival, colonyintegrity and the differential LRS of all colony members. Ourresults provide insight into the evolution and maintenance offamily groups within the bathyergids.     

Quantitative Differences in Nourishment Affect Caste-Related Physiology and Development in the Paper Wasp Polistes metricus

The distinction between worker and reproductive castes of social insects is receiving increased attention from a developmental rather than adaptive perspective. In the wasp genus Polistes, colonies are founded by one or more females, and the female offspring that emerge in that colony are either non-reproducing workers or future reproductives of the following generation (gynes). A growing number of studies now indicate that workers emerge with activated reproductive physiology, whereas the future reproductive gynes do not. Low nourishment levels for larvae during the worker-rearing phase of the colony cycle and higher nourishment levels for larvae when gynes are reared are now strongly suspected of playing a major role in this difference.Here, we present the results of a laboratory rearing experiment in which Polistes metricus single foundresses were held in environmental conditions with a higher level of control than in any previously published study, and the amount of protein nourishment made available to feed larvae was the only input variable. Three experimental feeding treatments were tested: restricted, unrestricted, and hand-supplemented. Analysis of multiple response variables shows that wasps reared on restricted protein nourishment, which would be the case for wasps reared in field conditions that subsequently become workers, tend toward trait values that characterize active reproductive physiology. Wasps reared on unrestricted and hand-supplemented protein, which replicates higher feeding levels for larvae in field conditions that subsequently become gynes, tend toward trait values that characterize inactive reproductive physiology. Although the experiment was not designed to test for worker behavior per se, our results further implicate activated reproductive physiology as a developmental response to low larval nourishment as a fundamental aspect of worker behavior in Polistes.     

Female eviction, abortion, and infanticide in banded mongooses (Mungos mungo): implications for social control of reproduction and synchronized parturition

Most cooperatively breeding species exhibit high reproductiveskew, where reproduction within the social group is monopolizedby a dominant pair. In many of these species, social controlof reproduction is the mechanism driving reproductive skew:individuals within the social group actively reduce the reproductivesuccess of others. In species where females do not suppressconception in other females, alternative routes to skewing thesocial group's reproductive output include inducing abortionin rivals, evicting them, or killing their young. This studyexamines instances of female eviction, abortion, and infanticidein a cooperatively breeding species with low preparturitionreproductive skew, the banded mongoose (Mungos mungo). Althoughinstances of these behaviors are rare in this species, aspectsof their occurrence have implications for social control ofreproduction. Abortion can be induced by the stress of beingevicted. The readmittance of females that abort suggests thatreducing communal litter size is a possible selective pressurefor eviction. This is supported by the occurrence of evictionevents in groups with relatively high numbers of reproductivefemales and by the eviction of young reproductive females. Thetiming of abortion events suggests that synchronization of parturitionwith other females in the group is a major selective pressure.Infanticide could represent the selective pressure for synchronizedparturition. Alternatively, synchronization may minimize competitiveasymmetry between pups born to different females. This paperalso describes incidences where a female aborts or gives birthto her litter over different days in order to synchronize parturition:behavior previously unrecorded in mammals.     

稻褐飞虱雄虫第二种鸣声及其生殖竞争意义

本文研究了稻褐飞虱Nilaparvata lugens雄虫第二种鸣声(SMVS)及其生殖竞争意义,结果如下：1.SMVS是2头或2头以上同种雄虫共栖一处时才产生的特殊信号,不同密度, 不同虫龄雄虫SMVS的呜叫习性不同,虫龄和温度对SMVS有明显影响。2.具SMVS行为的雄虫在求偶、交配系列行为中的优势逐步明显,最终成功交配的SMVS雄虫达70.2%,而非SMVS雄虫仅“14.9%。3.回放SMVS录音可以显著降低稻褐飞虱交配率(下降41.0%)。 SMVS是一种生殖竞争信号,具种的专一性。     

Reproductive Inhibition of Female Peromyscus leucopus: Female Competition and Behavioral Regulation

Maturational delay of young female mice as the result of exposureto grouped female odors and reproductive inhibition as the resultof exposure to isolated adult females have both been observed(Drickamer, 1974; Skryja, 1978). Each has the potential to reducethe growth rate of populations. Reductions in a female's reproductionfacilitated by social stimulation from other females, whileeffective in reducing population growth, may in the case, ofmaturational delay and reproductive inhibition be an epiphenomenonor exadaptation of selection for improved relative reproductivesuccess in the females possessing these abilities. The ultimateoutcome of these selective processes may be the buffering ofpopulation numbers, but the selective forces may operate tomaximize a female's relative reproductive success. A females'relative reproductive success can be maximized by either increasingher own reproduction or decreasing the reproductive output ofother females. A body of evidence exists to suggest that inPeromyscus mamculatus and Peromyscus leucopus, females are physiologicallyconstrained and unable to increase their own reproduction. Ifthe assumption of physiological restraint is correct, then themost effective way for females to maximize their relative reproductivesuccess is to reduce the reproductive output of their competitors.In this paper, maturational delay and reproductive inhibitionas they affect both the adult female and young females are discussed.Examination of these effects reveals that while they can beeffective in population regulation, their main function andthe selective process that produced them is at the level ofindividual reproduction.     

Male-caused failure of female reproduction and its adaptive value in alpine marmots (Marmota marmota)

We studied reproductive performance of free-living alpine marmots (Marmotamarmota) for 14 years in the National Park of Berchtesgaden, Germany.Female reproduction was influenced by body condition and social factors.Reproduction depleted fat reserves, and only females emergingfrom hibernation with sufficient body mass were able to reproducesuccessfully. Marmots lived in social groups in territoriesdefended by a dominant male and female. Subordinate femalesnever reproduced, regardless of body mass. Territory takeoversby males impaired reproduction of dominant females, but onlyif the takeover occurred after the mating period. Reproductivefailures occurred despite clear signs of pregnancy such enlargednipples or late molt. Decreasing progesterone levels after themating period and the lack of evidence for direct infanticideby new territorial males suggest a block of pregnancy as a likelyexplanation for reproductive failures in groups with male takeoversduring gestation. Rendering female reproduction impossible increasedfuture reproductive success of new territory owners. Nonparous femalessaved the energetic cost of maternal investment and thus emergedwith higher body mass in the following spring. In line withthis, females failing to wean young had higher reproductivesuccess in the subsequent year.