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

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

Male brood provisioning rates provide evidence for inter‐age competition for mates in female Cooper's Hawks Accipiter cooperii

Life history theory predicts that individuals should maximize lifetime reproductive success (LRS) by breeding as soon as they reach sexual maturity, yet many species delay breeding, either because there are insufficient available mates or breeding sites, or because delayed breeding yields higher LRS. Accipitriform species, such as Cooper's Hawk Accipiter cooperii, exhibit both delayed breeding and delayed plumage maturation. However, in certain circumstances, first‐year females in non‐definitive plumage do breed and apparently compete with older females for high‐quality breeding territories. We predicted that these young females are at a competitive disadvantage compared with older females and that older females would have both higher reproductive success and be able to acquire higher quality nesting territories. We conducted brood counts and measured prey delivery rates by male Cooper's Hawks in an expanding urban population located in Albuquerque, New Mexico (USA), to assess our prediction. We found that older females had higher reproductive success, fledging 1.6 more offspring than younger females, and that they occupied territories where males provisioned at higher rates of 0.37 more prey items per 2‐h period. Our results showed that older females fared better than first‐year females but it is unclear if this is the result of passive or active competition. Older females initiated nesting 14.3 days sooner than first‐year females and thus may have filled vacant, high‐quality territories before first‐year females began seeking mates. Additionally, first‐year females were never observed persistently to confront older females for breeding territories, but they did actively compete against each other. First‐year females may defer to older females who, in a direct competitive interaction, would be most likely to prevail. Thus, delayed plumage maturation in Cooper's Hawks may serve to focus competition for nesting territories within age classes.     

Explicit experimental evidence for the effectiveness of proximity as mate-guarding behaviour in reducing extra-pair fertilization in the Seychelles warbler

Extra-pair copulations (EPCs; copulations outside the pair bond) are widespread in birds and may result in extra-pair fertilizations (EPFs). To increase reproductive success, males should not only seek to gain EPFs, but also prevent their own females from gaining EPFs. Although males could reduce the number of EPCs by their mates, this does not necessarily mean that they reduce the number of EPFs; indeed several studies have found no association between EPCs and EPFs. Male Seychelles warblers (Acrocephalus sechellensis) follow their partner closely during the period when the pair female is most receptive (fertile period). We show that males that guarded their mates more closely were less likely to have extra-pair young in their nest. This study on the Seychelles warbler is the first to provide explicit experimental evidence that mate guarding is effective in reducing EPFs. First, in territories where free-living males were induced to stop mate guarding during the pair female's fertile period, extra-pair parentage was higher than in the control group. Second, in the experimental group, the probability of having an extra-pair nestling in the nest was positively associated with the number of days during the fertile period for which mate guarding was artificially stopped. Thus, male mate guarding was effective in reducing the risk of cuckoldry.     

Effects of extra-pair and within-pair reproductive success on the opportunity for selection in birds

The number of mates, their fecundity, and the number of extra-pairfertilizations can all affect male reproductive success in biparentalspecies. Extra-pair mating in birds has been of particular interest,because it could generate strong levels of sexual selectioneven when a species is socially monogamous. We examined howextra-pair fertilizations affect the opportunity for selectionin the sexually dimorphic common yellowthroat (Geothlypis trichas)and the sexually monomorphic house wren (Troglodytes aedon).We were able to identify sires for at least 95% of all nestlings,and, thus, we were able to make a nearly complete accountingof male reproductive success. Although extra-pair fertilizationswere common in yellowthroats (26% of young) it contributed little(21%) to the total variance in male reproductive success. Mostof the variance in reproductive success (58%) was attributableto the male's within-pair success, which was influenced primarilyby the number of young produced by each mate and the proportionof within-pair young sired. Despite a moderate level of extra-pairfertilizations (10% of young) in house wrens, almost all ofthe variance in male reproductive success (97%) was attributableto within-pair success, particularly the number of social mates.Although extra-pair fertilizations generally increase the variancein male reproductive success, within-pair reproductive successmay be the major source of variation in male reproductive success.Thus, sexual dimorphism in monogamous birds may be influencedmore by the number of mates and their fecundity than by extra-pairmatings.     

Reproductive consequences of bilateral asymmetry for individual male red-winged blackbirds

We used morphological and breeding data from a 2-year fieldstudy of red-winged blackbirds (Agelaius phoeniceus) to testthe hypothesis that males characterized by low levels of bilateralasymmetry (i.e., high developmental competence) realize a reproductiveadvantage. Specifically, we evaluated each of several distinctcomponents of male reproductive success relative to asymmetrymeasures made on five bilaterally paired characters. Resultsof a male removal experiment generally failed to support theprediction that symmetry would be associated with success incompetition for access to breeding territories: establishedterritory owners and nonterritorial replacement males were effectivelyindistinguishable in this regard. Similarly, there was no indicationthat symmetrical males were more likely to establish territoriesin high-quality marsh habitat than in marginal upland fieldhabitat. Finally, monitoring of breeding activity in high-qualityhabitat revealed that male symmetry was generally unrelatedto recruitment of social mates (i.e., harem size), the productivityof those mates (average female reproductive success), withinpairpaternity (assessed using DNA-based analysis of parentage),or extrapair mating success. Collectively these results indicatethat symmetry is not an important determinant of reproductivesuccess among individual male red-winged blackbirds. This observation,in combination with the results of several other recent investigations,suggests that the fitness consequences of subtle departuresfrom perfect symmetry may be less significant and/or less ubiquitousthan initially suggested.     

Red coloration of male northern cardinals correlates with mate quality and territory quality

I investigated how mate quality and territory quality influencean extravagant ornament in a socially monogamous species thatdefends multipurpose territories. Northern cardinals (Cardinaliscardinalis) are a highly dichromatic, socially monogamous species,and males are a brilliant red. I conducted a 3-year field studyof northern cardinals and found that redder males produced moreoffspring in a breeding season. Two selective factors mediatedthis fitness gain. Redder males were paired with earlier breedingfemales, an established measure of mate quality in birds. Second,redder males obtained territories of higher quality, as measuredby vegetation density. Interactions among these factors werealso important in explaining variance in male reproductive success.Multivariate analysis indicated that earlier breeding increasedreproductive success independent of territory quality. In turn,territory quality contributed to male reproductive success throughits effect on nest survival and possibly through its role in attractingan earlier breeding female.     

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."     

Sexes of a monomorphic species differ in preference for mates with a novel trait

We investigated the different roles of the sexes in the originationof novel traits in the sexually monomorphic Javanese mannikinLonchura leucogastroides. We introduced a red feather as anevolutionarily novel trait in both sexes and tested their preferencesfor prospective mates with this trait. Males rejected femalesbearing the red feather and preferred to court unadorned females.In contrast, females partly preferred adorned males. Specifically,previously unattractive males gained in attractiveness and could increasetheir reproductive success when bearing the ornament, whereas previouslyattractive males lost in attractiveness, but this did not affect theirreproductive success. We introduced two other novel traits inmales and investigated the females' response to these in matechoice tests. Each of the three new traits interacted with thenatural attractiveness of males. The more attractive a malewas before ornamentation, the more it lost in attractiveness afterornamentation and vice versa. Thus, the position of the traitdid not affect the interaction. Because males rejected adornedfemales and females partly preferred adorned males, novel traitsmight evolve by intersexual selection in males rather than infemales. This can lead to a sexual dimorphism with conspicuoustraits in males. Our study reveals a new insight into the mechanismof the evolution from monomorphism to dimorphism with ornamentaltraits in males.     

Sequential mate encounters: female but not male body size influences female remating behavior

Whether and how individuals choose sequentially among matesis an important but largely neglected aspect in sexual selectionstudies. Here, we explore female remating behavior in the cellarspider Pholcus phalangioides. We focus on body size as one ofthe most important traits involved in mate choice. Large andsmall females (n = 216) were double mated with large or smallmales in all eight possible combinations. All females copulatedwhen virgin, but only 82% accepted a second male. The chanceof a female remating was not significantly predicted by thebody size of the second or first male or by the size differencebetween the two. In contrast, a previous study demonstrateda male size effect in that larger males monopolized femalesuntil egg laying when two males of different sizes were present.We suggest that sequential encounters are more common undernatural conditions than male monopolization of females becauseestimates of concurrent multiple paternity together with observationsin a natural population do not favor mate guarding as the predominantmating strategy in this species. It follows from our study thatthe intensity of sexual selection on male size may be greatlyoverestimated when using a competitive laboratory setting fora species in which females generally encounter mates in a sequentialfashion. Female remating probability was significantly predictedby female size, with large females remating with higher probabilitythan small females. Thus, when mating with large females, malesmay gain higher fertilization success through increased femalefecundity but also face a higher sperm competition risk.     

Kin recognition and incest avoidance in a group-living insect

Mate choice theories predict that animals evolved strategiesto mate with optimally genetically dissimilar partners, providingfitness benefits. In group-living species, when adults do notdisperse, assessment of relatedness between conspecifics canbe a key factor for choosing mates. Here, we report for thefirst time, kin recognition abilities and their implicationin mate choice in the gregarious cockroach, Blattella germanica(L.). Binary choice tests showed that females mated preferentiallywith nonsibling rather than with sibling males, thus avoidingincest. In addition, inbreeding induced an important decreaseof their reproductive success. Contrary to what could be expectedwhen females had the choice between a nonsibling strain memberand a nonstrain member, they did not avoid mating with distantlyrelated nonstrain members, and extreme outbreeding induced anincrease of their reproductive success. Furthermore, our matechoice experiments disentangled the influences of familiarityfrom those of relatedness and evidenced that kin discriminationwas based on genetic cues independently of familiarity. Phenotypematching was a plausible mechanism for kin recognition. Contraryto many insect species, body size was not a salient criterionfor mate choice and had no consequences on reproductive success.     

Mate fidelity in a polygamous shorebird,the snowy plover (Charadrius nivosus)

Social monogamy has evolved multiple times and is particularly common in birds. However, it is not well understood why some species live in long‐lasting monogamous partnerships while others change mates between breeding attempts. Here, we investigate mate fidelity in a sequential polygamous shorebird, the snowy plover (Charadrius nivosus), a species in which both males and females may have several breeding attempts within a breeding season with the same or different mates. Using 6 years of data from a well‐monitored population in Bahía de Ceuta, Mexico, we investigated predictors and fitness implications of mate fidelity both within and between years. We show that in order to maximize reproductive success within a season, individuals divorce after successful nesting and re‐mate with the same partner after nest failure. Therefore, divorced plovers, counterintuitively, achieve higher reproductive success than individuals that retain their mate. We also show that different mating decisions between sexes predict different breeding dispersal patterns. Taken together, our findings imply that divorce is an adaptive strategy to improve reproductive success in a stochastic environment. Understanding mate fidelity is important for the evolution of monogamy and polygamy, and these mating behaviors have implications for reproductive success and population productivity.     

Breeding site fidelity in willow ptarmigan: the influence of previous reproductive success and familiarity with partner and territory

Summary Breeding site fidelity is high in willow ptarmigan: only 9% of males and 31% of females switched territories between years. Unpaired males were more likely to switch territories than paired males. For paired males, survival of their previous partner and reproductive success in year x did not influence probability of switching in year x+1. A female was more likely to switch territories if her previous partner disappeared. If her partner returned, she had a higher probability of switching if she did not produce chicks the previous year. Most hens moved to the territories of older males, although hens paired with unfamiliar older males did not have higher reproductive success than those paired with yearlings. Individuals that paired with their previous partner laid earlier and produced heavier chicks than those paired with unfamiliar partners. Excluding birds paired with familiar partners, survival and reproductive success in year x+1 was similar for males and females that did or did not switch territories. Males had a higher probability of producing chicks after switching than before, but females were more likely to lose their clutch after switching. For both sexes, birds that switched territories were as successful as the birds that replaced them on their former territories. We conclude that high site fidelity in willow ptarmigan is maintained because of the benefits of pairing with a familiar partner.     

Feeding territoriality and the reproductive consequences in brown skuas<Emphasis Type="Italic"> Catharacta antarctica lonnbergi</Emphasis>

In the maritime Antarctic, brown skuas (Catharacta antarctica lonnbergi) show two foraging strategies: some pairs occupy feeding territories in penguin colonies, while others can only feed in unoccupied areas of a penguin colony without defending a feeding territory. One-third of the studied breeding skua population in the South Shetlands occupied territories of varying size (48 to >3,000 penguin nests) and monopolised 93% of all penguin nests in sub-colonies. Skuas without feeding territories foraged in only 7% of penguin sub-colonies and in part of the main colony. Females owning feeding territories were larger in body size than females without feeding territories; no differences in size were found in males. Territory holders permanently controlled their resources but defence power diminished towards the end of the reproductive season. Territory ownership guaranteed sufficient food supply and led to a 5.5 days earlier egg-laying and chick-hatching. Short distances between nest and foraging site allowed territorial pairs a higher nest-attendance rate such that their chicks survived better (71%) than chicks from skua pairs without feeding territories (45%). Due to lower hatching success in territorial pairs, no difference in breeding success of pairs with and without feeding territories was found in 3 years. We conclude that skuas owning feeding territories in penguin colonies benefit from the predictable and stable food resource by an earlier termination of the annual breeding cycle and higher offspring survivorship.Research licence: Umweltbundesamt Bonn 13.4-94003-1/5-7.     

Extrapair paternity and the opportunity for sexual selection in long-distant migratory passerines

Extrapair fertilizations (EPFs) are frequently documented insongbirds; however, the extent to which this reproductive tacticcontributes to variance in male reproductive success and hencethe strength of sexual selection on males remains little studied.Using 2 approaches, intraspecific and comparative, we test thehypothesis that the contribution of EPFs to variance in malefitness increases with migration distance in north temperatesongbirds. Using data on the genetic mating system of the scarletrosefinch Carpodacus erythrinus, a long-distance migrant, weshow that the number of extrapair mates and within-pair paternityare the most important components of variance in male reproductivesuccess. There was no evidence of a trade-off between extrapairand within-pair success of individual males as males successfulin procuring EPFs were less likely to be cuckolded. Comparativedata reveal that the opportunity for sexual selection due toEPFs is positively associated with both migration distance andbreeding synchrony in north temperate passerines, and we discussseveral mechanisms that could extend these relationships. Ingeneral, these data suggest that EPFs have a potential to playan important role in the evolution of sexually selected traitsin long-distance migratory songbirds such as rosefinches.     

Territory and male quality do not influence settlement of yearling female willow ptarmigan

A common assumption in territory and mate selection models isthat individuals evaluate the qualities of territories and/orpartners and then choose the best ones. We determined whetherthis assumption was correct for yearling female willow ptarmigan(Lagopus lagopus). Yearling females did not choose partnersbased on the characteristics of the territories or of the malesthat we measured. In addition, the first females to settle didnot appear to obtain better territories or better partners thanthose settling later; date of settling was not related to subsequentsurvival, reproductive success, or quality of chicks produced.To evaluate whether choices of territories and partners wereconsistent among females, we manipulated settlement such thattwo sets of yearling females had the same suite of territoriesand males available. We found no consistent patterns of territoryand mate choice. We concluded that, in this population, yearlingfemales did not choose where to settle based on the relativequalities of territories or partners. Females may have beenunable to assess differences among territories when settlingbecause all territories were covered with snow.     

Reproductive skew among males in a female-dominated mammalian society

The purpose of this study was to document patterns of reproductiveskew among male spotted hyenas (Crocuta crocuta), a speciesin which many normal mammalian sex roles are reversed. We usedpaternity determined from 12 microsatellite markers togetherwith demographic and behavioral data collected over 10 yearsfrom a free-living population to document relationships among reproductive success (RS), social rank, and dispersal statusof male hyenas. Our data suggest that dispersal status andlength of residence are the strongest determinants of RS. Natalmales comprise over 20% of the adult male population, yet theysire only 3% of cubs, whereas immigrants sire 97%. This reproductiveadvantage to immigrants accrues despite the fact that immigrants are socially subordinate to all adult natal males, and it providesa compelling ultimate explanation for primary dispersal inthis species. High-ranking immigrants do not monopolize reproduction,and tenure accounts for more of the variance in male reproductivesuccess than does social rank. Immigrant male hyenas rarelyfight among themselves, so combat between rivals may be a relativelyineffectual mode of sexual selection in this species. Instead,female choice of mates appears to play an important role in determining patterns of paternity in Crocuta. Our data supporta "limited control" model of reproductive skew in this species,in which female choice may play a more important role in limitingcontrol by dominant males than do power struggles among males.     

Trade-offs between postcopulatory riding and mate location in the blue milkweed beetle

In the blue milkweed beetle, Chrysochus cobaltinus (Coleoptera:Chrysomelidae), males remain stationary on females' backs forprolonged periods after a single, brief copulation. Lone malesoften attack pairs, and takeovers, in which rival males replacethe resident on the female's back, are common. I used removalexperiments to measure the effect of postcopulatory riding onlatency to remating. Females whose males were removed were morelikely to remate in the next 2 h than females that were allowedto remain paired. When females were removed, males were alsomore likely to remate in the 2-h period following removal thanwere males allowed to continue riding. This indicates that malesdelay remating by their mates at the expense of mating opportunitieswith additional females. The predicted reproductive successof guarding and nonguarding males was calculated using a modelbased upon experimentally derived latencies to remating andsimulated levels of last male paternity. Guarders outperformednonguarders when the proportion of offspring sired by the lastmale (P₂) was 0.4 or greater. Data on survival and lifetimemating success were used to evaluate survival trade-offs ofpostcopulatory riding. Although males sacrificed feeding timeto ride on females' backs, there was a positive relationshipbetween the proportion of time males spent riding and theirlongevity in the patch. These results indicate that postcopulatoryriding has no survival costs and indicate that postcopulatoryriding can be an effective paternity assurance mechanism evenwhen takeovers are common.     

The large-male advantage in brown antechinuses: female choice, male dominance, and delayed male death

Male-biased dimorphism in body size is usually attributed tosexual selection acting on males, through either male competitionor female choice. Brown antechinuses (Antechinus stuartii) aresexually dimorphic in size, and heavier males are known to siremore offspring in the wild. We investigated four possible mechanismsthat might explain this large-male reproductive advantage. Wetested if there is a female preference for large males, a femalepreference for dominant males, if larger males compete moreeffectively for mates, and if there is a survival advantagefor large males during the mating season. We established nestinggroups of males in captivity and conducted mate choice trialsin which males from nesting groups either could or could notinteract. We assessed male dominance rank and recorded survivaltimes after mating. Females did not prefer larger males directly.The results suggest that the other three mechanisms of sexualselection tested account for the large-male advantage: largemales competed more successfully for mates, so were sociallydominant; females rejected subordinates (males they saw losingtwice in contests to previous mates); and dominant males survivedfor longer after their first mating. Females judged male rankbased on direct observation of male competitive interactionsat the time of mating and apparently could not distinguish rankfrom male scent. Effects of size and dominance on male reproductivesuccess are not confounded by age because male antechinusesare semelparous.     

Microsatellite identification of extrapair sires in a socially monogamous warbler

Few studies of avian mating systems have identified the siresof extrapair young, and hence it has been difficult to determinethe scale at which reproductive interactions occur. For instance,females may be free to copulate with any male in the population(a "global" scale of interactions), or females may be restrictedto copulating only with males on neighboring territories (a"local" scale). The scale of such interactions has importantconsequences for an understanding of the evolutionary causesand consequences of extrapair fertilizations. We used five hypervariable microsatellite loci and multilocus DNA fingerprintingto examine parentage of more than 400 nestling black-throatedblue warblers (Dendroica caerulescens). Extrapair fertilizationswere common, and the microsatellite markers allowed us to identifythe sires for 89% of the young analyzed. Most identified extrapairsires were males on neighboring or nearby territories, andmost nestlings for whom we could not identify a sire came fromterritories at the edge of the study plot. Thus, reproductive interactions appear to be more local than global in this population.Extrapair fertilizations contributed significantly to totalvariation in male reproductive success. However, the standardizedvariance in male reproductive success (0.68-0.74) was not substantiallygreater than that for females (0.53-0.60), and the contributionof extrapair fertilizations (9-14%) was much lower than thecontribution of within-pair fertilizations (75-77%). This suggeststhat the local scale of reproductive interactions may limitvariation in male reproductive success and hence the opportunityfor selection.     

Male and Female Soldier Beetles Relax Choice for Mate Quality Across Daily Courtship Periods

Mutual mate choice occurs when members of each sex will reject some potential mates in efforts to encounter better prospects later. The decision to reject may represent the interaction between mate preferences, mate availability, and temporal constraints. Theory predicts that mutual mate choice will favor relaxed choosiness as mate availability and time for courtship decline. We explored mutual mate choice in the soldier beetle, Chauliognathus pennsylvanicus (Cantharidae), where courtship consisted of males attempting to secure evasive females. We employed field observations, laboratory experiments, and stochastic simulations to investigate the decline in choosiness over the daily courtship period, during which individuals can mate at most once. We found that reproductive success of males and females increases with mate size and mating frequency. Females biased copulations toward larger mates by attempting to evade suitors, while males biased copulations by releasing the smaller females they capture. However, late in the day males and females may increase reproductive success by accepting rather than rejecting lower quality mates to maintain high mating rates. Stochastic simulations indicated that reproductive success, the product of mating frequency and mean mate size, was maximized in males and females by incrementally reducing mate standards across daily courtship periods. In the field, large males who rejected small females early in the daily courtship period rarely did so later. Large females used less effective evasive maneuvers later in the courtship period, resulting in copulations with progressively smaller males. These results support models of mutual mate choice that predict that individuals of high quality will maximize reproductive success by relaxing choosiness as the courtship period wanes.