Direct selection on mate choice: female redlip blennies pay more for better mates

Sexual selection may be reduced by costs of mate choice suchas predation risk and energetic expense. Despite their theoreticalimportance, such costs have rarely been quantified or relatedto the quality of mate obtained. We performed such a study witha wild population of redlip blennies in Barbados. In this coralreef fish, females traveled 0.2–12 m from their feedingterritories to the territories of nesting males, where theyspawned and left their eggs in the males' care. Previous studieshave shown that larger and older males are better parents andare preferred by females. Here, we found that long-distancetrips by females were made primarily toward larger males, andthe extra distance traveled beyond the nearest male was correlatedwith the improvement in size of male obtained. Comparisons withfeeding budgets while the females remained on their home territoriessuggested that costs from lost time and energy were minor, andno predation attempts on females were observed. However, onlonger trips the females faced more aggressive attacks fromdamselfishes, whose territories they crossed. In contrast, noattacks were observed from damselfish when the blennies remainedon their own territories. These attacks appeared to be responsiblefor a greater incidence of scars on females than on males. Thisdifference between the sexes became more pronounced as spawningprogressed, and then decreased as females healed during thenonspawning interval. Thus, female blennies endure a cost ofinterspecific harassment which is correlated with the qualityof mate obtained. This cost may restrain sexual selection inthis species.     

The definition of eusociality

We describe more precise definitions for the term "eusociality"and other social systems. Our criterion for eusociality is thepresence of castes, which are groups of individuals that becomeirreversibly behaviorally distinct at some point prior to reproductivematurity. Eusocial societies are characterized by two traits:(1) helping by individuals of the less-reproductive caste, and(2) either behavioral totipotency of only the more reproductivecaste (facultative eusociality) or totipotency of neither caste(obligate eusociality). We define "cooperative breeding" asalloparental care without castes. Cooperatively breeding societiesmay comprise two types, semisocial (distribution of lifetimereproductive success bimodal), and quasisocial (distributionof lifetime reproductive success unimodal), but this hypothesisrequires empirical analysis. Our definitions conceptually unifystudies of arthropod and vertebrate sociality.     

Energetic constraints and foraging efficiency

Previous research considers foraging options that differ interms of their gross rate of gain b and rate of energy expenditurec. This research argues that maximizing efficiency b/c willmaximize net energetic gain when there is an upper limit onthe amount of energy that can be assimilated. This analysisdoes not include the expenditure during the time for which theanimal is unable to forage because of this constraint. Whenthis expenditure is included, maximizing efficiency is no longeroptimal. Instead the best feeding option is the one with thehighest value of b/(c – c₁), where c, is the metabolicrate when the animal is not foraging.     

Dynamic discarding decisions: foraging theory for high-grading in a trawl fishery

The decision by fishermen to discard or retain fish of low valueto make room for more valuable fish in the hold of a boat (high-grading)is similar to diet choice problems faced by natural foragers.In our study, we apply the rationale of diet choice theory tohigh-grading behavior in the Oregon trawl fishery by treatingfishermen as foragers who must decide how much of each net'shaul to "ingest" before searching for more prey. We derive astate-dependent, temporal model of discarding behavior withina fishing trip. This optimization considers the availabilityof differently valued fish, trip quotas set by the regulatoryagency, and the risk of premature trip termination due to lossof gear or injury. The results indicate that those parametersaffect discarding behavior through their effect on the probabilityof exceeding the allowable catch, which we consider analogousto gut capacity. High-grading (partial prey consumption) occurredthroughout many simulated trips. The predictions were consistentwith the trends in discarding observed in the Oregon trawl fleet.Behavioral models such as ours can be useful to fishery managersby providing a means to explore the potential responses of fishermento new regulations before they are implemented.     

Strategic paternity assurance in the sex-role reversed Eurasian dotterel (Charadrius morinellus): behavioral and genetic evidence

Sex role reversal in birds is usually associated with paternalcare of both eggs and chicks. This pattern of care typicallyleads to the potential rate of reproduction of males being lowerthan that of females. Hence, operational sex-ratio theory predictsthat each male should be under strong selection to avoid beingcuckolded. A male should, therefore, guard his female partner(s)from extrapair copulation attempts by other males. Furthermore,the sexual conflict theory of copulation behavior predicts thatin species with extensive paternal care the male should controlthe temporal pattern of copulations—copulations shouldoccur both frequently and throughout the prelaying period. Wetested these predictions in the Eurasian dotterel (Charadriusmorinsllus), in which the male usually provides all the parentalcare. In accordance with the first prediction, male dotterelsdid "guard" their pair-female prior to egg-laying. Contraryto the second prediction, however, copulations were not frequentand did not occur throughout the pre-laying phase-despite frequentsolicitation by the female, copulations only occurred immediatelyprior to egg-laying. Nevertheless, male-initiated courtshipwas both coincident with the pattern of copulations and morelikely than female-initiated courtship to result in copulation.Our results do, therefore, appear to agree with the centralprediction of the sexual conflict theory that males should controlthe pattern of copulations. We suggest that male dotterels willcopulate only after several days of being paired because theyface a duel risk of cuckoldry from both extrapair copulationand rapid mate switching. We tested the realized incidence ofcuckoldry using DNA fingerprinting. Only 4.6% (2/44) of chickswere not the genetic offspring of the caring male correspondingto 9.1% (2/22) broods affected. The rate of extrapair paternityin the dotterel is, therefore, relatively low compared to thatin many other avian species. We conclude that male dotterelssuccessfully protect their paternity of the brood for whichthey care through a combined strategy of mate guarding and strategictiming of copulations.     

Failure of simple optimal foraging models to predict residence time when patch quality is uncertain

Blue jays (Cyanocitta cristata) were presented with a foragingsituation in which half of the patches they encountered containedno prey and half contained a single prey item. Experimentallydetermined probability distributions controlled prey arrivaltimes in those patches that contained prey. Patch residencein empty patches was studied during four experiments. In thefirst, prey arrival was exponentially distributed. Residencetimes increased with travel time as predicted by a rate-maximizationmodel, but the bird stayed in empty patches much longer thanpredicted. During the second experiment, prey arrival was uniformlydistributed. The jays again stayed longer than optimal, andpatch residence times increased as travel time increased, althoughthe residence time that maximized rate of intake was independentof travel time under these conditions. In the third experiment,exponential and uniform patches were randomly intermixed. Thejays showed larger travel-time effects in the exponential thanin the uniform patch. However, the travel-time effect in theuniform patch was contrary to rate-maximization predictions,and the birds again overstayed in both patch types. In the fourthexperiment, prefeeding at the start of each foraging bout slightlyincreased overstaying rather than decreasing overstaying, aswould be expected if overstaying were due to underestimatingenvironmental quality. Consistent and dramatic overstaying anda travel-time effect under conditions where travel time hasno effect on optimal residence times suggest that the rate-maximizationapproach does not apply to foraging problems involving patchuncertainty.     

Black-and-white plumage in male pied flycatchers (Ficedula hypoleuca) reduces the risk of predation from sparrowhawks (Accipiter nisus) during the breeding season

Bright colors in birds might signal that they are undesirableas prey (aposematic), an idea that has been difficult to test.When stuffed pied flycatchers Ficedula hypoleuca are exposedto migrating sparrowhawks Accipiter nisus in spring or in autumn,the hawks attack cryptic females more often than bright males.To achieve better statistical control and to assess whethermale plumage also reduces predation risk in the breeding seasonand in the nesting habitat of the pied flycatcher, I placedpairs of male and female flycatcher mounts in similar positionsnear 22 nests of sparrowhawks. The hawks attacked mainly femalemounts, verifying that the preference is real. The sparrowhawkscaught at least 19 live pied flycatchers; 12 young, 5 adultmales, 1 adult female, and 1 female or young. Hawks that caughtan adult male seemed to prefer attacking female mounts. I discussthree interpretations of these results, suggesting that black-and-whitemale flycatchers may benefit from being a novel and aberrantprey, at least early in the breeding season.     

Parental provisioning and predation risk in rhinoceros auklets (Cerorhinca monocerata): effects on nestling growth and fledging

We examined the effects of predation risk on the behavior ofrhinoceros auklets (Cerorhinca monocerata) breeding at PineIsland, British Columbia, in 1990. Provisioning parents in someareas of the colony risked predation by bald eagles (Haliacetusleucocephalus). Chicks in high and low predation risk areasof the colony hatched on approximately the same date, receivedsimilar amounts of food to 46 days of age, grew at the samerate, reached similar peak masses, and fledged at similar masses.However, chicks in high predation areas fledged at a youngerage than did chicks in low predation areas. These data are consistentwith the hypothesis that parents in high risk areas terminatedprovisioning several days before those in lower risk areas.Mass at fledging was inversely related to age at fledging inboth high and low risk areas. The regression line for the highrisk habitats lies below that from the low risk habitats, aspredicted by a model that examines optimal time of fledgingfrom the perspective of the parents. We conclude that risk ofpredation represents a significant cost of reproduction to somerhinoceros auklets and that individual auklets within the colonyvary their behavior according to predation risk.     

Testosterone effects on the immune system and parasite infestations in the barn swallow (Hirundo rustica): an experimental test of the immunocompetence hypothesis

The immunocompetence hypothesis predicts that testosterone (T)enhances the expression of male secondary sexual characterswhile exerting a suppressive effect on the immune system therebyexposing hosts to higher intensities of parasite infestations.In a natural population of barn swallow (Hirundo rustica) males,the intensity of infestation by some ectoparasites was negativelycorrelated with tail length and was positively correlated withimmunoglobulin levels, but no clear relationship was observedbetween immune responses (leukocyte counts, immunoglobulins)and tail length. Males implanted with T had higher intensitiesof parasite infestations at the time of recapture than controlmales, and T-implanted males experienced an increase in countsof eosinophils. In T-implanted males, immunoglobulin levelsinitially decreased and then increased as time from implantationelapsed. Among T-implanted males, those with longer tails hada smaller increase in eosinophil counts, tended to experiencea smaller increase of parasite infestations, and were more likelyto survive until the following breeding season than those withshorter tails. The relationships between parasite burden, immunesystem, and exaggeration of tail length in the natural populationof males are consistent with some aspects of the immunocompetencehandicap hypothesis. The results from the manipulation of Tplasma levels are also partly consistent with the hypothesis,since T-implantation resulted in higher levels of parasite infestations,but contradict the assumption of an obligatory immunosuppressiveeffect of T. Higher activation of the immune system of T-implantedmales indicate that high T plasma levels imposed a two-foldcost because of the effects on parasites and the immune responseto parasites, and this suggests that the effect of T on parasitesmight not be mediated by the immune system of the host. Theresults of the manipulation of T plasma levels support the handicapversion of the immunocompetence hypothesis since high quality,long-tailed males paid less in terms of activation of the immunesystem, change in parasite infestations, and chances of survivalthan low-quality, short-tailed males.     

Egg presence, egg loss, and female mate preferences in the sand goby (Pomatoschistus minutus)

We studied the effect of egg presence on female mate choicein a fish with paternal care. Females who were allowed a freechoice between two males mated within a shorter time than femaleswho were randomly assigned to a particular male. When a secondfemale was allowed to choose among the males, she preferredthe same male as the previous female. This result shows thatfemales are concordant in their mate choice. When the initialfemale was randomly assigned to mate with one of two males (forcedchoice), the second female mated randomly with respect to thefirst one. Thus females do not prefer males with eggs. If theinitial female was given a free choice, but the eggs were removedfrom the chosen male, the test female mated randomly. When boththe males initially had mated but one randomly determined male'seggs were removed, the test female preferred the male who wasstill guarding eggs. These experiments show that females avoidspawning in unsuccessful nests. When the females in the freechoice/egg removal experiment mated with the unsuccessful malethere was a considerably bigger size difference in favor ofthis male than when the females mated with the other male. Weconclude that female sand gobies show clear mate preferences,but that they do not prefer males with eggs over males withouteggs. They do, however, avoid mating with males guarding unsuccessfulnests. We therefore suggest that egg loss could be an importantfactor selecting for egg preference.     

Sexual selection for large male size in a polyandrous butterfly: the effect of body size on male versus female reproductive success in Pieris napi

Sexual selection theory predicts that the larger sex shouldbe that for which fitness increases at the faster rate withsize. In butterflies, as in most invertebrates, females areusually the larger sex, but previous comparative analysis hasshown that relative male size increases with female polyandryamong butterflies. In agreement with this pattern, males arelarger than females in the strongly polyandrous green-veinedwhite butterfly, Pieris napi L., and in this article we assessthe size dependence of reproductive success in both sexes. Inan experiment where virgin males and females were released inthe field, we found no strong association between size and malemating success. However, laboratory experiments showed thatthere was a strong correlation between size and the ejaculatethat the male delivered to the female at mating and that largeejaculates delayed female remating for a longer time comparedto small ejaculates. Moreover, female P. napi utilize male-derivednutrients received at mating to increase their fecundity. Hence,large males sire more offspring both by way of donating morenutrients to female egg production and by way of delaying femaleremating (given that the last male to mate with the female willfather most of the offspring). Laboratory experiments showedthat the association between size and fecundity was low, ornonexistent, among P. napi females allowed to mate only once.However, weak size dependence was found for polyandrous females.We hypothesize that size dependence of female fecundity maybe especially weak among polyandrous butterflies because a fundamentalsource of variation in fecundity relates to their ability tofind nutrient giving males, an ability which may be unrelatedto female size. According to this hypothesis there is a causalassociation between weak size dependence of female fecundityand polyandry, and a strong size dependence of male reproductivesuccess that may underlie the comparative pattern of positivecorrelation between relative male size and polyandry.     

Correlates of male quality in the field cricket, Gryllus campestris L.: age, size, and symmetry determine pairing success in field populations

Sexual selection in field crickets (Gryllidae) is well documented.Several studies have identified male traits, such as age andbody size, that influence pairing success in the field. HereI show how these traits covary with male quality by examiningthe degree of fluctuating asymmetry in male Gryllus campestris.Older males were both larger and more symmetrical. Principalcomponents analysis suggests that these three variables wereessentially measures of the same trait, male quality. A comparisonof paired and calling males showed that males of high qualitywere more successful in obtaining mates; paired males were older,larger, and more symmetrical. The area of the harp covariedwith morphological traits and determined the carrier frequencyof the male's call. Information related to male quality wastherefore available for female discrimination.     

Investigating structure and temporal scale in social organizations using identified individuals

Studies of individually identified animals can produce substantialdata sets containing information on the structure and temporalscale of social organizations. However, methods of analyzingsuch data are not well established. Important features of asocial organization are revealed by plotting the rate of persistenceof the associations between pairs of individuals over a rangeof time lags (lagged association rate). The consistency of long-termrelationships can be characterized using the rate of associationof pairs of individuals between their first and last observedassociations (intermediate association rate). A hierarchicalseries of models featuring exponentially decaying lagged associationrates may be fitted to these data. This technique retrievedthe essential parameters of five simulated social organizationsand, when used on real data, portrayed the essential featuresof the patterns of temporal change in relationships betweenanimals. The method should be especially useful for analyzingfissionfusion societies containing 10–10, 000 individuallyidentifiable animals.     

Conflict between sexes in the water strider, Gerris lacustris: a test of two hypotheses for male guarding behavior

We studied the effect of operational sex ratio on female reluctanceand male persistence to mate as well as on the length of copulationand postcopulatory guarding in Gerris lacustris by adding fivesurplus males or females to the basin with a pair in tandem.In the control treatment, a pair alone was tested. Accordingto the copulatory guarding hypothesis (CGH), males should prolongmating and guard females in the presence of surplus males. Accordingto the convenience polyandry hypothesis (CPH), females shouldshow lower levels of resistance to prolonged mating in the presenceof surplus males because the mating male protects the femaleagainst harassment from other males. As expected on the basisof both the CGH and CPH, mating (copulation + guarding) averagedlonger in the male-biased treatment. The behavior of males andfemales during mating suggested that both hypotheses hold true:females showed less resistance to prolonged mating (as predictedfrom CPH), and male behavior suggested stronger efforts to stayon the female when surplus males were present (as predictedfrom CGH). Comparisons of the treatment with surplus femaleswith the results from the mating pair without surplus individualssuggested that the capabilities of water striders in tandemto assess the sex of nearby nonmating striders are limited.     

Suppressed breeding in the field vole (Microtus agrestis): an adaptation to cyclically fluctuating predation risk

The densities of microtine rodents and their main predators,small mustelids, fluctuate synchronously in 3–5-year cyclesin central and northern Fennoscandia. Predation by small mustelidshas been suggested as one of the driving forces in microtinecyclicity, causing deep synchronous declines of several volespecies. We studied experimentally the effects of small mustelidson mating behavior, foraging, and breeding in nonwintered fieldvoles (Microtus agrestis) originating from a cyclic population.By using mustelid odors, we simulated a crash phase environmentwith high predation risk for breeding pairs of voles. In ourexperiments, 87% of the female field voles suppressed breedingwhen exposed to mustelid odors. Both female and male behaviorchanged, and no mating behaviors were observed under the simulatedpredation risk. Weights of both sexes decreased when exposedto mustelid odor, probably due to decreased foraging; weightsof the control females increased due to pregnancy; and no weightchanges occurred in control males. Decreased breeding and foragingpossibilities under high predation pressure may form the basisfor the ultimate explanation for breeding suppression. Thereare at least two different mechanisms for breeding suppression:either mating does not take place or malnutrition in femalesdoes not' allow breeding to occur. Delayed breeding under highrisk of predation, for whatever reason, could increase the probabilityof individuals, especially that of the females, to survive overthe crash to the next, safer breeding season when their youngwould have better possibilities to survive.     

Patch assessment in foraging flocks of European starlings: evidence for the use of public information

A field experiment was carried out to determine whether group-foragingstarlings (Sturnus vulgaris) use public information to helpthem estimate the quality of an artificial resource patch anddepart accordingly. Three kinds of information are potentiallyavailable in a group: patch-sample information, pre-harvestinformation, and public information. These three types of informationcan be combined into four patch assessment strategies: (1) patch-samplealone; (2) patch-sample and pre-harvest; (3) patch-sample andpublic; and (4) patch-sample, pre-harvest, and public. Dependingon the foraging environment we presented to the starlings, eachassessment strategy made a unique set of predictions concerningthe patch departure decisions of pairs of birds based on differencesin their foraging success. The environment was manipulated intwo ways: by altering the variability in patch quality and bychanging compatibility, the ease with which individual birdscould simultaneously acquire both patch-sample and public information.Our observations on patch persistence and departure order demonstratethat the starlings used a combination of patch-sample and publicinformation, but not pre-harvest information, to estimate thequality of the experimental patch. Moreover, our results suggestthat starlings use public information only when it is easilyavailable and ignore it under incompatible conditions. Thisstudy provides the first evidence of public information usein a patch assessment problem.     

Predicting group size in primates: foraging costs and predation risks

We present a direct test of the long-standing hypothesis thatfood competition limits primate group size. Group size is acritical social variable because it constrains most other aspectsof social organization. We develop a simple population-specificindex of indirect feeding competition based on daily foragingcosts. This index explains nearly two-thirds of between-populationvariation in mean group sizes of mostly fruit-eating (but notof mostly leaf-eating) primates. Group size is also significantlyrelated to body size and terrestriality (or use of open country),which are suspected correlates of predation risk, although feedingcompetition remains an important predictor of group size evenwhen these correlates are controlled. Phylogeny also appearsto be important: the differences between observed mean populationgroup sizes and those predicted using ecological factors aremost positive for the Old World monkeys and most negative forthe lemuroids in our sample. The weak relationship between groupsize and feeding competition found for folivorous species maybe explained either by the energetic constraints of a leafydiet or by limits to group size imposed by infanticide as ahabitual male reproductive strategy.     

The location of landmark leks in the small heath butterfly, Coenonympha pamphilus: evidence against the hot-spot model

Two major theories have been developed to explain the locationand evolution of leks. According to the hot-spot model leksare male initiated and occur because males aggregate at locationsof maximum female home range overlap. The alternative femalepreference model, on the other hand, assumes that leks are femaleinitiated, and that females prefer to mate with males that aggregate.Small heath butterfly leks are situated close to landmarks suchas trees and bushes in open grassland. Censuses of wild populationsand experiments with artificial landmarks showed that theirattractiveness increased with height and width measured at themiddle of tree height. Landmark width at field layer heightwas negatively correlated with attractiveness, which suggeststhat a cornet shape is preferred to a pyramid shape. Togetherthese landmark size variables explained 60% of variation inlek size. Release experiments showed that landmarks were approachedby receptive virgin females, but mated females were indifferentto them. Landmark use was correlated to microclimatic conditions.Males preferred wider landmarks during cooler weather. Theyalso competed for the lee side of landmarks. There was no correlationbetween the location of landmarks and the dispersion of matedfemales or emergence sites of females. Hence, receptive femaledispersion was largely determined by their mate-locating behavior,which in turn appeared to result from male dispersion. Leksmay initially have developed around easily detected visual cuesthat offered a more suitable microclimate for male activity.Females visiting these locations would find a suitable matemore rapidly and save valuable time for oviposition. Althoughnonadaptive evolution cannot be excluded, taken together theresults support the female preference model for lek evolution.     

Environmental effects on prenatal growth rate in pronghorn and bighorn: further evidence for energy constraint on sex-biased maternal expenditure

Byers and Moodie (1990) proposed that high levels of maternalexpenditure in polygynous ungulates limit the ability of mothersto support elevated male fetal and neonatal growth rates. Thishypothesis assumes that females in high-expenditure speciesare at or near the maximum level possible and that females inlower-expenditure species are not. To test this assumption,we examined our long-term data on reproduction of pronghorn(Antilocapra americana) and bighorn (Ovis canadensis) at theNational Bison Range (western Montana, USA) and compared gestationlengths, birth weights, and prenatal growth rates of offspringborn following summers of low versus average or above averageprecipitation. In bighorn, these variables were unaffected bythe previous summer's rainfall, but in pronghorn, gestationlength and prenatal growth rate were significantly lower followingdry summers. Extended samples for both species confirmed earlierreports of sex-biased expenditure favoring males in bighornand the absence of sex-bias in pronghorn. Bighorn prenatal littergrowth rates and birth weights, corrected for maternal mass,are 63.5% and 38%, respectively, of pronghorn values. Thesedata support the Byers and Moodie (1990) contention that femalesof high-expenditure species do not show differential expenditureby offspring sex because they are at a reproductive expendituremaximum, whereas females of lower-expenditure species are ableto support excess expenditure in male offspring because optimalallocation to female offspring is farther from such a maximum.     

Dispersal polymorphism and physiological condition of males and females in the ant, Formica truncorum

This study deals with dispersal behavior of sexuals and intraspecificvariation in queen numbers. The specific questions are: (1)Is there an association between male and female dispersal behaviorand the number of queens in a colony? (2) Is there an associationbetween individual behavior and physiological condition? (3)Do males and females from monogyne (one queen per colony) andpolygyne (several functional queens per colony) colonies differwith respect to size, weight, and physiological condition? Theresults show that both males and females are more prone to dispersein monogyne than in polygyne colonies. Moreover, males and femalesof both monogyne and polygyne colonies show dispersal polymorphism,suggesting that an increased tendency of reproductive femalesto stay in the maternal colony may cause monogyne colonies toswitch to polygyny. The propensity to disperse is associatedwith the physiological condition of individuals. Larger andheavier females containing more fat and glycogen preferentiallydisperse, whereas smaller ones with less fat and glycogen moreeasily dealate and mate without a previous nuptial flight. Maledispersal correlates positively to larger size and higher levelsof glycogen; fat contents do not increase during maturation.The females produced in monogyne colonies are larger, heavier,and contain more fat and glycogen than those produced in polygynecolonies. The males produced in monogyne colonies have relativelylonger wings and are heavier than those produced in polygynecolonies. However, there are no differences in size and fatcontents between males from monogyne and polygyne colonies.