Monogamy in black vultures: genetic evidence from DNA fingerprinting

Recent research has indicated that avian mating systems maycommonly deviate from monogamy due to extrapair fertilizations(EPFs). Because the majority of avian species have long beenconsidered monogamous, accurate measurement of the frequencyof EPFs in a variety of species is important to enhance understandingof the evolution of avian mating systems. We used DNA fingerprintingto investigate the apparently monogamous mating system of blackvultures (Coragyps airaius) by assaying parentage within severalnuclear families. Monogamy is suggested in black vultures becausemated pairs exhibit long-term pair bonding and year-round association,and share incubation and nestling feeding duties equally. Thirtytwobreeders and 36 nestlings representing 16 complete nuclear familieswere tagged for individual identification and sampled for DNAanalysis using 2 restriction enzymes and 3 probes for hypervariableregions. Putative parents were assigned parentage in all cases.We empirically examined the probability of detecting EPFs bycomparing nestlings' fingerprints to those of a putative parentand another randomly chosen adult. All putative parents couldbe assigned with 95%confidence and all outside adults couldbe similarly excluded. There is therefore no evidence for successfulEPFs in this population, indicating a mating system that doesnot deviate from strict monogamy. The complex social behaviorof black vultures may eliminate the opportunity for EPFs dueto the prohibition of copulations in the presence of relatives.     

Genetic monogamy in blue-headed vireos and a comparison with a sympatric vireo with extrapair paternity

Based on the breeding synchrony hypothesis, we predicted, intwo congeners that nest in simiilar habitat but differ in nestingsynchrony, that blue-headed vireos (Vireo solitarius) wouldhave fewer extrapair fertilizations (EPFs) thaii red-eyed vireos(V. olivaceus EPFs were rare in blue-headed vireos (1/37 nestlings),but common in red-eyed vireos (11/19 nestlings). We studiedthe behavior of blue-headed vireos to determine what factorscould promote genetic monogamy. We found no evidence that malesmate guarded to prevent extrapair copulations from occurring.Males did not follow fertile mates closely when mates left thenest (14–25% of female departures) and, during the egg-layingperiod, males were often alone on the nest (22.3 mm/h). Femaleblue-headed vireos, but not red-eyed vireos, obtain direct benefitsfrom social mates such as nest building and incubation (49.1%of the total), and they assess male quality long before becomingfertile. Female blue-headed vireos spent more time incubatingwhen their mates had low incubation effort. Furthermore, maleincubation effort was positively correlated with nest survivalduring incubation. We discuss the evolution of genetic monogamyand sex role convergence in blue-headed vireos in relation toasynchronous breeding.     

Effects of breeding density, synchrony, and experience on extrapair paternity in tree swallows

Breeding density, synchrony, and experience are expected toinfluence the frequency of extrapair paternity in birds. UsingDNA fingerprinting, we examined the effect of these factorson tree swallows nesting at relatively high (grids of nest-boxes)and low (solitary boxes at least 100 m from the nearest neighbor)densities and in relatively synchronous (Alberta) and asynchronous(Ontario) populations in Canada. The mean percentage of extrapairoffspring per nest did not differ significantly between birdsnesting in grids (43%, n = 22 families) and solitary boxes (57%,n = 12 families). Similarly, there was no significant differencein the mean percentage of extrapair offspring per nest betweenrelatively synchronous (60%, n = 12 Alberta families) and asynchronous(41%, n = 22 Ontario families) populations. We also found noconsistent pattern between extrapair paternity and breedingexperience among seven males and seven females examined overtwo to three breeding seasons. Female tree swallows can influencethe fertilization success of extrapair males by active selectionand rejection of copulation partners. We suggest that this abilitylimits the predicted effect of various ecological factors onthe frequency of extrapair paternity     

Temporal changes in food resources,parental feeding and breeding success of Heron Island silvereyes,Zosterops lateralis chlorocephala

The influences of the temporal change in food supply on the parental feeding effort and breeding success of silvereyes,Zosterops lateralis chlorocephala, was investigated on Heron Island, Australia. Food supply (arthropods and figs) declined as the breeding season progressed. The parental feeding rate and growth of nestlings were lower when food supply was poor. When available, dominant pairs fed their young more figs and fewer arthropods than lower ranking pairs. Dominant pairs raised heavier young than lower ranking pairs when food supply was poor, while there were no significant differences between them when food supply was rich. When food supply was rich, pairs delivering greater amounts of arthropods reared nestlings better, whereas feeding more figs did not improve growth of nestlings. When food supply was poor, pairs spending a longer time at the nest reared nestlings better.     

Extrapair paternity, inclusive fitness, and within-group benefits of helping in western bluebirds

In central coastal California, USA, 3–16% of western bluebird ( Sialia mexicana ) pairs have adult male helpers at the nest. Demographic data on a colour-ringed population over a 13-year period indicate that helpers gain a small indirect fitness benefit through increases in the number of young fledged from nests of close kin. A small proportion of adult helpers (16%) that were able to breed and help simultaneously had higher annual inclusive fitness than males that only bred. These males comprised such a minor proportion of helpers that the mean fitness of helpers was still lower than the mean fitness of independent breeders. We used DNA fingerprinting to determine whether extrapair fertilizations alter within-group benefits enough to tip the balance in favour of helping behaviour. Overall, 19% of 207 offspring were sired by males other than their social father and extrapair fertilizations occurred in 45% of 51 nests. Intraspecific brood parasitism was rare so that mean mother-nestling relatedness approximated the expected value of 0.5. Extrapair paternity reduced putative father-offspring relatedness to 0.38. Mean helper-nestling relatedness was 0.41 for helpers assisting one or both parents and 0.28 for helpers aiding their brothers. Helpers rarely sired offspring in the nests at which they helped. Helping was not conditional on paternity and helpers were not significantly more closely related to offspring in their parents' nests than to offspring in their own nests. Although helpers may derive extracurricular benefits if helping increases their own or their father's opportunities for extrapair fertilizations, within-nest inclusive fitness benefits of helping do not compensate males for failing to breed. Breeding failure and constraints on breeding are the most likely explanations for why most helpers help.     

Genetic monogamy in the Common Crossbill ( Loxia curvirostra )

Extrapair paternity seems to be common in socially monogamous passerines, but the genetic mating system of most species is currently unknown. Here, we report the first study of paternity in the socially monogamous Common Crossbill (Loxia curvirostra). We found no evidence of extrapair paternity among 96 offspring in 34 examined broods. An upper 95% confidence limit of 3.1% suggests that extrapair fertilizations were truly infrequent in our study population. Common Crossbills thus seem to represent an exception to the rule of extrapair mating among socially monogamous passerine bird species. A potentially important selective pressure preventing promiscuity in Common Crossbills is the harsh environmental conditions experienced during breeding at wintertime, which may increase the importance of paternal care and limit the time available for seeking extrapair copulations.     

High fidelity on islands: a comparative study of extrapair paternity in passerine birds

It is commonly assumed that the intensity of sexual selectionis lower in island populations. Extrapair paternity (EPP) iswidespread within passerine birds and is indicative of sexualselection. A conservative analysis of the levels of EPP inisland and equivalent mainland populations of passerines revealsthat insular populations are indeed characterized by low levelsof EPP. This supports the idea that the intensity of sexualselection is lower on islands. This relationship has previouslybeen predicted, based on the assumption of low levels of geneticvariation for fitness in such populations. The evidence fromthis analysis suggests that this is just one of several nonmutuallyexclusive hypotheses that may explain the high fidelity ofisland-living females.     

Extrapair paternity is influenced by breeding synchrony and density in the common yellowthroat

The effects of breeding synchrony and density on levels of extrapair paternity in birds are controversial. We used multilocus DNAfingerprinting and microsatellite analysis to examine the effectsof breeding synchrony and density on levels of extrapair paternityin the common yellowthroat (Geothlypis trichas). As in manyNeotropical migrants, breeding synchrony was greatest at thebeginning of the breeding season. Levels of extrapair paternitywere higher after the peak in synchrony, leading to an overallnegative relationship between extrapair paternity and breeding synchrony. However, there was a significant interaction betweenbreeding synchrony and density, as levels of extrapair paternitywere higher only for males breeding when both synchrony anddensity were low. We discuss several possible explanationsfor this interaction, including lower quality males or territoriesin low density areas and greater demands on mate guarding among males with larger territories. Most studies have not consideredsimultaneously the effects of breeding synchrony and densityon extrapair paternity. Our results suggest that ecologicalcorrelates of paternity may be revealed only after testingfor interactions in multivariate analyses.     

Extrapair paternity in the great tit (Parus major): a test of the "good genes" hypothesis

In 1993 and 1994 we determined the frequency of extrapair paternityin broods of great tits, Parus major using multilocus DNA fingerprinting.We found no instances of intraspecific brood parasitism, but40% of broods (31/78) contained extrapair-fathered young and83% of offspring (58/681) were xtrapair We identified the geneticfathers of 60% of the extrapair nestlings (35/ 58). Males withfull and lost paternity did not differ significantly in traitsthat have been suggested to indicate male quality, nor did thegenetic and social fathers of extrapair offspring. In 1993,cuckolded males sired more offspring that recruited to the subsequentbreeding season than males with full paternity. Moreover, eventhough genetic fathers of extrapair young (EPY) sired more fledglingsthan the males they cuckolded, genetic and social fathers ofEPY did not differ in the number of recruits sired. Also, theEPY of a brood did not survive better than their half sibs.Thus, our results do not supportthe hypothesis that femaleschoose better quality males for extrapair matings ("good genes"hypothesis). Further, the level of extrapair paternity differedmarkedly between the two years. Our data show that females areconstrained in their extrapair activities by the availabilityof extrapair mates. This is at least partly due to yearly differencesin breeding synchrony.     

Male rank, female breeding synchrony, and patterns of paternity in the boat-tailed grackle

Species in which males directly defend groups of breeding femalesoftenhave extreme skew in observed male mating success. Inonly a few species,however, has a corresponding skew in fertilizationsuccess been confirmed.Furthermore, the ecological and socialfactors contributing to variation infertilization success needinvestigation. This study examined competition formates andpaternity in the boat-tailed grackle (Quiscalus major).Observationsat colonies of nesting females revealed that the toprankingoralpha males performed more than 70% of the copulations. DNAfingerprintingindicated that alpha males sired less than 40%of nestlings. Nevertheless,analysis of band-sharing scoresamong nestlings from different nests suggestedthat alpha malessired more than three times as many offspring as any otherindividualmale. Because few nestlings were sired by the nonalpha malesthatassociated with colonies, females must have mated withother males while ontrips away from colonies. Analysis of paternitywithin broods revealed that atleast half of all females hadtheir brood fertilized by more than one male.Alpha males' successat fertilizing eggs did not vary with the number ofsimultaneouslyreceptive females within a colony. Our results suggest thatmaleand female behavior in female-defense polygyny results fromcomplexcoevolution of the sexes.     

Genetic evaluation of the mating system in the blue-and-yellow macaw (Ara ararauna, Aves, Psittacidae) by DNA fingerprinting

More than 90% of birds are socially monogamous, although genetic studies indicate that many are often not sexually monogamous. In the present study, DNA fingerprinting was used to estimate the genetic relationships between nestlings belonging to the same broods to evaluate the mating system in the socially monogamous macaw, Ara ararauna. We found that in 10 of 11 broods investigated, the nestlings showed genetic similarity levels congruent with values expected among full-sibs, suggesting that they shared the same parents. However, in one brood, the low genetic similarity observed between nestlings could be a result of intraspecific brood parasitism, intraspecific nest competition or extra-pair paternity. These results, along with available behavioral and life-history data, imply that the blue-and-yellow macaw is not only socially, but also genetically monogamous. However, the occurrence of eventual cases of extra-pair paternity cannot be excluded.     

Low frequency of extrapair paternity in the polygynous great reed warbler, Acrocephalus arundinaceus

We carried out DNA fingerprinting on 553 young (130 broods)great reed warblers (Acrocephalus arundnaceus) in 1987–1991.In the study population, where 40% of the males become polygynous,there was a low frequency of extrapair fertilizations (EPF).When data from all five years were pooled, 3.1% of the youngwere sired by extrapair males (EPF-males) and 5.4% of the broodscontained extrapair young. We found no cases of extrapair maternity;young with 6–17 mismatched DNA bands (n= 17) had highband sharing with their putative mothers (range = 0.52–0.72)but low band sharing with their putative fathers (range = 0.24–0.40).In broods exposed to EPF, on average 53% of the young were siredby EPF-males. We found the genetic father to each of the illegitimateyoung. In all cases the same EPF-male sired all extrapair youngin a brood. Broods containing EPF-young tended to be initiatedlate during the breeding season. Breeding attempts were ratherevenly distributed over two months, thus this breeding asynchronywould have facilitated EPFs. There was no difference in EPFfrequency between broods where the pair males had left theirfemales unguarded during parts of their fertile periods andbroods where males guarded throughout the fertile periods. Nestswith extrapair young had significantly shorter mean distanceto the closest male neighbor and more male neighbors within100 m than nests without extrapair young. We found no indicationthat females engaged in EPF to get parental care from the EPF-males,or because they were forced to copulate with extrapair males.The low frequency of EPF suggested that females did not seekgenetic diversity to their brood. We cannot rule out the possibilitythat females engaged in EPF to insure fertility. However, datasupporting this hypothesis were weak. Instead, our data supportthe conclusion that females engaged in EPF to increase the geneticquality of their offspring, and that females may have used malesong repertoire size as a cue when choosing EPF partners.     

Complete exclusion of nonsires in an analysis of paternity in a natural plant population using amplified fragment length polymorphism (AFLP)

The utility of the new polymerase chain reaction (PCR)-based multilocus DNA fingerprinting technique amplified fragment length polymorphism (AFLP) for paternity analysis in natural plant populations was assessed. In a natural population of 25 plants of Persoonia mollis (Proteaceae), three AFLP primer pairs generated 147 dominant loci. Of these, 125 (85%) were polymorphic, with a mean recessive allele frequency of 0.735. The theoretical expected percentage of offspring for which all males except the true father can be excluded ( P _ET) was 99.9% for this population. The estimates of P _ET drop marginally to 99.6% and 97.6% for larger populations of 100 and 1000 individuals, respectively. A preliminary investigation confirmed the power of AFLP for paternity analysis by assigning paternity, or excluding all known potential sires, for 242 of 252 (96.0%) naturally pollinated seeds. Ambiguous paternity for the remaining 10 seeds was quickly resolved by utilizing two further AFLP primer pairs, ultimately generating over 200 polymorphic loci and resulting in the exclusion of all nonsires for all 252 (100%) seeds. This study highlights the utility of AFLP for paternity analysis because: (i) it generates sufficiently large numbers of highly reproducible polymorphic loci, that are (ii) quickly and accurately scored using an automated DNA sequencer and dedicated software, and (iii) unlike microsatellites, requires no sequence knowledge so it is more easily applied to new study species.     

The influence of gene flow and drift on genetic and phenotypic divergence in two species of Zosterops in Vanuatu

Colonization of an archipelago sets the stage for adaptive radiation. However, some archipelagos are home to spectacular radiations, while others have much lower levels of diversification. The amount of gene flow among allopatric populations is one factor proposed to contribute to this variation. In island colonizing birds, selection for reduced dispersal ability is predicted to produce changing patterns of regional population genetic structure as gene flow-dominated systems give way to drift-mediated divergence. If this transition is important in facilitating phenotypic divergence, levels of genetic and phenotypic divergence should be associated. We consider population genetic structure and phenotypic divergence among two co-distributed, congeneric (Genus: Zosterops) bird species inhabiting the Vanuatu archipelago. The more recent colonist, Z. lateralis, exhibits genetic patterns consistent with a strong influence of distance-mediated gene flow. However, complex patterns of asymmetrical gene flow indicate variation in dispersal ability or inclination among populations. The endemic species, Z. flavifrons, shows only a partial transition towards a drift-mediated system, despite a long evolutionary history on the archipelago. We find no strong evidence that gene flow constrains phenotypic divergence in either species, suggesting that levels of inter-island gene flow do not explain the absence of a radiation across this archipelago.     

Paternity in the Australian brush-turkey, Alectura lathami, a megapode bird with uniparental male care

Male Australian brush-turkeys, Alectura lathami, provide allparental care by building and tending large incubation mounds.Females visit and lay eggs in the mounds of several males sequentially,but they provide no parental care after laying. Because malesand females meet only briefly at mounds to copulate and lay,males have no obvious means of ensuring paternity. I used DNAfingerprinting techniques to determine paternity for 65 brush-turkeychicks. Eighteen chicks (27.7%) did not match the mound-tendingmale. Some of these paternity exclusions were evidently causedby females switching rapidly from one mound to another, butthe majority (23.1% of eggs) appeared to result from femalescopulating with males other than the one in whose mound theywere currently laying. However, the frequency of these copulations(43%) was much lower than the estimated frequency with whichthey fertilized eggs, perhaps because their timing during theovulatory cycle differed relative to most other copulations.The percentage of eggs excluded in paternity analyses rangedfrom 20.0% to 43.8% for individual males but did not appearto affect male parental care. Several factors favor male parentalcare regardless of paternity. Males can accommodate eggs fromseveral females in one mound, which increases the opportunitiesfor additional matings without increasing the cost of parentalcare. In addition, paternity appears to be unpredictable andhard to assess, and a facultative reduction in care would bedifficult without abandoning a mound entirely.     

Manipulation of male quality in wild tits: effects on paternity loss

Extrapair paternity (EPP) has proved to be widespread and highlyvariable among birds and other taxa, including socially monogamousspecies. A multitude of hypotheses have been put forward toexplain this variation, but its occurrence is not fully understood.Male age, social dominance rank, song and breeding density orsynchrony have been among the suggested correlates of EPP, butresults so far are inconclusive. We interspecifically cross-fosteredblue tits (Parus caeruleus) and great tits (Parus major) inthe wild, thus manipulating males to exhibit reduced socialdominance rank, sing aberrant songs, and consequently be perceivedas low-quality males as compared to controls. This allowed usto test if male quality had an influence on loss of paternity.We found no statistically significant differences between cross-fosteredand control males of either species, neither with respect tolevels of cuckoldry nor proportions of extrapair young (EPY)in the broods. Paternity levels were comparable to other studieson the same species. No effect of density could be detectedon levels of EPP either, while an age effect seemed to be presentat least in the blue tit, EPY being almost absent in broodsof older blue tit males. We conclude that the effects of malequality on paternity loss are minor, if any, in these populations.     

Multiple paternity in a philopatric rodent: the interaction of competition and choice

Paternity confusion is often suggested as the benefit that femalemammals accrue by mating with multiple males, but genetic advantagesare also possible. Microsatellite-based parentage analyses demonstratethat female banner-tailed kangaroo rats (Dipodomys spectabilis)commonly mate with more than one male; we asked how male andfemale behaviors interact to influence the characteristics ofmales that sire offspring. Specifically, we compared attributes(age, weight, mobility, relatedness, proximity) of the fathersof 229 known-maternity offspring with those of the other malesaccessible to the mothers. Adult males living adjacent to eachfemale attempt to monopolize access to her, and the nearestmale sires a plurality of offspring, but most mothers' youngare fathered by more than one male and littermates are usuallyhalf-sibs. Male proximity and mobility, but not size, influencethe probability of paternity, suggesting a role for competitivemate searching. Females significantly reduce the inbreedingcoefficient of their offspring by mating with males other than(or in addition to) the nearest male. Fathers are less closelyrelated to the mother in years of high density when unrelatedmales are more accessible to the female. Our results favor thegenetic "bet-hedging" hypothesis, whereby females actively butunselectively seek matings with additional males when the malemost likely to win in mate competition is costly to her (inthis case, genetically less compatible). We anticipate thatgenetic bet hedging will be common in species whose femalesare defendable, especially if they are also philopatric.     

Alternative tactics and individual reproductive success in natural associations of the burying beetle, Nicrophorus vespilloides

Alternative reproductive tactics can be maintained through differentevolutionary avenues. They can be genetically or stochasticallydetermined, in which case they must yield equal fitness, ortheir use can be conditional, in which case the fitness payoffof alternatives may differ. We attempted to assess the reproductivesuccess of alternative reproductive tactics employed by wildmale and female burying beetles in natural associations on carcassesplaced in the field. A beetle's reproductive tactic was definedby its potential involvement in care of larvae, and parentagewas assessed using oligolocus DNA fingerprinting of offspringand potential parents. Both in males and in females, alternativetactics yielded significantly different reproductive benefits:subordinate females (brood parasites) and males (satellite males)had considerably lower reproductive success than dominant oruncontested individuals. Joint breeding was too infrequent forstatistical inferences, generating intermediate offspring numbers.About 15% of offspring were sired by males not present on thecarcass, suggesting that mating away from reproductive resourcescan produce reproductive benefits to males. Our results, inconcert with the observation that beetles using one tactic canbe manipulated into employing the alternative, support the notionthat Nicrophorus vespilloides uses alternatives conditionally,opportunistically employing lower-benefit tactics when moreprofitable tactics are not available, or as additional "on-the-side"tactics to bolster reproductive success.     

Charomid cloning vectors meet the pedipalpal chelae: single-locus minisatellite DNA probes for paternity assignment in the harlequin beetle-riding pseudoscorpion

We describe the first application of the charomid-cloning method for developing single-locus minisatellite DNA probes in a terrestrial arthropod. From a genomic library of the neotropical pseudoscorpion, Cordylochernes scorpioides , we have isolated two probes with heterozygosities exceeding 95%. These probes yielded single-locus patterns after only low stringency washing and in the absence of genomic competitor DNA. Analysis of three pedigrees indicated germline stability and showed no evidence of linkage between the loci. Patterns of allelic transmission generally conformed closely to Mendelian expectations but large offspring numbers did enable detection of one example of significant bias in allele inheritance. Two test cases are presented to illustrate the clarity and power with which these probes can establish paternity: (i) a female mated to three unrelated males, and (ii) a female mated to two of her brothers. In both cases, a single probe could be used to assign the paternity of all offspring.