Influence of age on reproductive performance in the Seychelles warbler

I studied age-related breeding performance of the cooperativelybreeding Seychelles warbler (Acrocephalus sechellensis) on CousinIsland, Seychelles, during 14 years. The annual number of youngthat fledged is significantly related to territory quality andnumber of helpers in the breeding group. Accounting for thesefactors and for the partner's breeding experience, annual productionof fledglings by breeding birds increases from 2 to 5 yearsand decreases beyond 5 years of age. Age-related changes inreproductive success within breeding individuals, paired withthe same experienced partner and occupying the same breedingterritory with similar amount of food from 2 to 8 years of age,show that Seychelles warblers have higher hatching success andproduce more hatchlings and fledglings as they become older.This is probably not a response to decreasing residual reproductivevalue caused by decreasing life expectancy as they become older.Primiparous warblers produce the same number of fledglings asmultiparous warblers of the same age, have a similar life expectancyas multiparous warblers, and occupy territories with similaramounts of resources available for reproduction. As all warblershave similar access to food before reproduction and similarforaging efficiency, the low reproductive success in youngerwarblers cannot be ascribed to differences in environment butto the bird's ability to breed successfully (e.g., a resultof previous helping and/or breeding experience). Effects ofsenescence on reproduction begin to occur from age 6 for bothsexes. From that age, eggs have lower hatching success, butfledging success remains the same. Birds that start breedingat a young age on a given quality territory produce more fledglingsin their lifetime than birds that delay breeding. Many old birdsnever fledge young of their own. They have not been able tobreed because of a shortage of breeding territory vacancies.[BehavEcol 7: 417–425 (1996)]     

The effectiveness of mate guarding by male black-throated blue warblers

In many socially monogamous birds, males maintain close proximityto their mates during the fertile period. This is often consideredan effort on the male's part to prevent other males from copulatingwith his mate, but other functions have been suggested andthe effectiveness of males in preventing extrapair fertilizationshas come into question. Moreover, it is unclear whether mateguarding conflicts with other male activities, particularlythe pursuit of extrapair fertilizations. We examined mate guardingby male black-throated blue warblers (Dendroica caerulescens).Behavioral observations showed that males that guarded theirmates more closely were less likely to have extrapair youngin their nests. Moreover, the experimental detention of a malefor 1 h during the fertility risk period increased the probabilitythat a brood would contain extrapair young. Thus, male mate guarding was effective in reducing the risk of extrapair fertilization.Males with many opportunities for extrapair copulations appearedto guard their mates less and consequently had more extrapairyoung in their broods than males with few such opportunities.This suggests that mate guarding may conflict with the pursuitof extrapair fertilizations.     

Sex-specific associative learning cues and inclusive fitness benefits in the Seychelles warbler

In cooperative breeding vertebrates, indirect fitness benefits would be maximized by subordinates that accurately assess their relatedness to group offspring and preferentially help more closely related kin. In the Seychelles warbler (Acrocephalus sechellensis), we found a positive relationship between subordinate-nestling kinship (determined using microsatellite marker genotypes) and provisioning rates, but only for female subordinates. Female subordinates that helped were significantly more related to the nestlings than were nonhelpers, and the decision to help appears to be based on associative learning cues. High levels of female infidelity means that subordinates cannot trust their legitimacy through the male line, consequently they appear to use the continued presence of the primary female, but not the primary male, as a reliable cue to determine when to feed nestlings. By using effective discrimination, female subordinates are able to maximize the indirect benefits gained within a cooperative breeding system otherwise driven primarily by direct breeding benefits.     

No evidence for extra-pair paternity in the western gull

The genetic mating system of western gulls Larus occidentalis breeding on Southeast Farallon Island, California, was determined using multilocus DNA fingerprints of 33 chicks from 22 broods. No extra-pair paternity (EPP) was found, despite extra-pair copulations (EPCs) occurring. This suggests that paternity guards are effective, and that females gain few genetic benefits from EPCs. The EPP in western gulls concurs with that of other seabirds, reinforcing the idea that seabirds generally have a monogamous genetic mating system.     

How female reed buntings benefit from extra-pair mating behaviour: testing hypotheses through patterns of paternity in sequential broods

Extra-pair paternity is an important aspect of reproductive strategies in many species of birds. Given that in most species females control whether fertilization occurs, they are expected to benefit in some way from the extra-pair matings. In this study we use patterns of extra-pair paternity (EPP) in broods of individual reed buntings (Emberiza schoeniclus), both within and between seasons, to test four hypothesized female benefits: (1) assessing potential future partners and seeking (2) genetic diversity (3) good genes, or (4) compatible genes. Reed buntings are socially monogamous, multibrooded passerines with extremely high levels of extra-pair paternity. We studied a population of reed buntings in the Netherlands in 2002 and 2003; 51% of offspring in 74% of nests were extra-pair. We showed that patterns of EPP did not support the first and second hypotheses, since females did not form a pair with previous extra-pair partners, EPP was not evenly distributed among broods and more broods than expected were sired by a single male. Furthermore, there was no relation between a male's within- and extra-pair fertilization success, no consistency in EPP between breeding attempts, no effect of parental relatedness on EPP and several cases of reciprocal paternity. These patterns do not support the good genes hypothesis and are most consistent with the genetic compatibility hypothesis. However, our previous finding that older males are more successful in gaining EPP, suggests some effect of good genes. These hypotheses need not be mutually exclusive, as females may select compatible males above a certain quality threshold (e.g. old males).     

Influence of helping and breeding experience on reproductive performance in the Seychelles warbler: a translocation experiment

Reproductive success of the cooperative breeding Seychelleswarbler (Acrocephalus sechellensis) increases with age. Thisage effect is not due to differential survival or increasedreproductive effort, but to accumulated helping and breedingexperience. In their first year of breeding, reproductive performanceof inexperienced warblers with neither helping nor breedingexperience was significandy lower than that of warblers of thesame age with either previous helping or breeding experience.Reproductive performance was the same for primiparae with helpingexperience and for birds with breeding experience. Female primiparaewith helping experience or breeding experience built betternests and spent more time incubating than inexperienced females,which led to increased hatching success. Male primiparae withhelping experience or males with breeding experience guardedthe clutch better than inexperienced males, which led to reducedegg predation. Even-aged warblers with different previous experienceswere transferred to unoccupied islands, where birds startedbreeding immediately in high-quality territories. The experimentshowed that birds with helping experience produced their firstfledgling as fast as experienced breeders, and significandyfaster than inexperienced birds. Breeding performance did notimprove further with experience after the first successful breedingattempt. Only birds with previous breeding experience who pairedwith inexperienced birds, were likely to change mate. The otherpair combinations remained stable. Thus, primiparous birds withhelping experience have greater lifetime reproductive successthan inexperienced primiparae of the same age. This experimentshows that helping behavior has not only been selected for inthe context of promoting an individual's indirect fitness, butalso in the context of gaining helping experience which translatesinto improved reproductive success when a helper becomes a breeder.[Behav Ecol 7: 326-333 (1996)]     

Explicit experimental evidence for the role of mate guarding in minimizing loss of paternity in the Seychelles warbler

Extra-pair copulations (EPCs) (copulations outside the pair bond) resulting in extra-pair fertilizations (EPFs) are widespread in birds. To increase reproductive success, males should not only seek EPCs, but also prevent their females from having EPFs. Male Seychelles warblers (Acrocephalus sechellensis) follow their partner closely during the period when these females are most receptive (fertile period). The Seychelles warbler is the first species to offer explicit experimental evidence that mate guarding functions as paternity guarding: in territories where free-living males were induced to stop mate guarding during the pair female''s fertile period, the rates of intrusions by other males and successful EPCs (male mounting female) were significantly higher than those observed in the control group and in the absence of mate guarding the frequency of successful EPCs increased significantly with local male density. Male warblers do not assure their paternity through frequent copulations to devalue any sperm from other males: males do not copulate with their partners immediately following a successful EPC obtained by their partners, the frequency of successful within-pair copulations does not increase with the frequency of successful EPCs and females initiate all successful copulations and are capable of resisting copulation attempts.     

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.     

Decoy presentations as a means to manipulate the risk of extrapair copulation: an experimental study in a semicolonial raptor, the Montagu's harrier (Circus pygargus)

Mate guarding and frequent copulations are two alternative paternity assurance strategies found in birds. In species with intensecourtship feeding, like raptors, the "frequent copulation"strategy is expected because male food provisioning conflictswith mate guarding. We evaluated experimentally the paternityassurance behavior of a semicolonial raptor, the Montagu'sharrier Circus pygargus, using decoy presentations to simulateterritorial intrusions. Breeding pairs were exposed to maleand female decoys at different periods during the female's reproductive cycle. Agonistic responses to decoys were intra-sexual,and the timing and intensity of male attacks toward male decoyssupported responses related to the risk of extrapair copulation(EPC): Male aggression peaked during the presumed fertile periodand almost disappeared after clutch completion. During thefertile period, copulation rate was significantly higher, andcopulations lasted longer, during male decoy presentations than during controls. Males also spent more time close to the femaleduring male decoy presentations compared to controls, bothduring the early prelaying and fertile periods, but not duringincubation. In the fertile period, males also increased presencetime close to the female in the hour following the removal of the male decoy. Conversely, female decoy presentations hadno significant effect on copulatory behavior or male presencetime. These results showed that the risk of EPC can be experimentallymanipulated by the means of decoy presentations, simulatingmale territorial intrusions, and that male Montagu's harriersincrease their short-term copulation frequency and female surveillancewhen they perceive themselves at an increased EPC risk.     

Inclusive fitness of 'kissing cousins': new evidence of a role for kin selection in the evolution of extra-pair mating in birds

Social monogamy is nearly ubiquitous across avian taxa,but evidence from a proliferation of studies utilizing molecular paternity analysis suggests that sexual monogamy is the rare exception rather than the rule (Griffith et al. 2002). Efforts to explain the prevalence of extra-pair paternity (EPP) have largely focused on the potential fitness benefits for offspring genetic quality, as females are less likely to benefit directly from seeking extra-pair mates. In particular, there has been considerable interest in the degree to which EPP may represent an adaptive female strategy to avoid inbreeding (or outbreeding)depression when paired with a highly related (or unrelated)social mate (Kempenaers 2007). Others have argued that, because relatives share many genes identical by descent,females might increase their own inclusive fitness by providing additional breeding opportunities to genetically related males (Waser et al. 1986; Kokko & Ots 2006). Thus, in the absence of significant inbreeding depression, pursuing EPP with relatives should be favoured by kin selection, although there exist few unambiguous empirical examples of such preferences in the literature. In this issue of Molecular Ecology, Wang &Lu (2011) present an analysis of mating patterns with respect to genetic relatedness of social and extra-pair partners in the ground tit (Parus humilis), a facultative cooperative breeder in which socially monogamous pairs occasionally form cooperative groups with unpaired helper males (Fig. 1). Consistent with the predictions of the kin-selection hypothesis, females in both bi-parental and cooperative groups preferentially engaged in extra-pair matings with relatives, irrespective of relatedness to their social mates, and while suffering no apparent costs of inbreeding depression in their progeny. These finding shave several exciting implications for our understanding of avian mating system diversity and the evolution of cooperative breeding.     

Effect of Extra-Pair Paternity on Effective Population Size in a Reintroduced Population of the Endangered Hihi, and Potential for Behavioural Management

We collected genetic and behavioural data on hihi (Notiomysts cincta, an endangered New Zealand bird) after reintroduction to Mokoia Island to assess the effect of extrapair copulation on effective population size (N_e), and investigate the potential for increasing N_e through behavioural management. DNA fingerprinting revealed that 46% of chicks (n = 188) resulted from extra-pair paternity, and 82% of broods (n = 56) had at least one extra-pair chick. Of the extra-pair young, 34%(n = 89) were from unpaired males, and the remainder were from paired males. Variance in reproductive success (VRS) among individuals changed between years, and the relative variance among males and females depended on the sex ratio. VRS increased when measured over longer time scales, the variance in recruits being three times higher than the variance in the number of hatchlings. Extra-pair copulation increased VRS by 150% in 1 year and decreased it by 30% in another year, but this only caused a 4% decrease and 8% increase, respectively, to N_e/N. Although there is potential to manage VRS in this species through behavioural management, a more important factor is adult lifespan, which is the main correlate of lifetime reproductive success as well as the determinant of generation time. The high annual mortality rate in Mokoia hihi (females = 64%, males = 52%) has prevented the population from growing, so the key factors limiting N and N_e/N are the same.     

Ultrastructural evidence for the presence of actin filaments in mouse eggs at fertilization

Summary Mouse eggs at fertilization were permeated with glycerol solutions and then reacted with heavy meromyosin to show actin filaments by electron microscopy. The meiotic area of the egg surface is devoid of microvilli and is supported by a thick layer (0.6–0.8 m in width) of submembranous filaments. A much thinner layer (less than 0.3 m) is present in the remaining non-meiotic microvillous area and underlying its membrane is a very thick layer of cross-filaments and filament bundles.     

Population genetics suggests effectiveness of habitat connectivity measures for the European tree frog in Switzerland

1.  Governmental authorities in many countries financially support the implementation of habitat connectivity measures to enhance the exchange of individuals among fragmented populations. The evaluation of the effectiveness of such measures is crucial for future management directions and can be accomplished by using genetic methods.
2.  We retraced the population history of the European tree frog in two Swiss river valleys (Reuss and Thur), performed comprehensive population sampling to infer the genetic structure at 11 microsatellite markers, and used first-generation migrant assignment tests to evaluate the contemporary exchange of individuals.
3.  Compared with the Thur valley, the Reuss valley has lost almost double the number of breeding sites and exhibited a more pronounced genetic grouping. However, similar numbers of contemporary migrants were detected in both valleys. In the Reuss valley, 81% of the migration events occurred within the identified genetic groups, whereas in the Thur valley migration patterns were diffuse.
4.  Our results show that the connectivity measures implemented in the Reuss valley facilitated effective tree frog migration among breeding sites within distances up to 4 km. Nevertheless, the Reuss valley exhibited high genetic differentiation, which reflected the impact of barriers to tree frog movement such as the River Reuss. By contrast in the Thur valley, a larger number of breeding sites have been preserved and high admixture indicated exchange of individuals at distances up to 16 km.
5.   Synthesis and applications . We show that genetic methods can substantiate the effectiveness of connectivity measures taken in conservation management at the landscape scale. We urge responsible authorities from both river valleys to continue implementing connectivity measures and to create a dense network of breeding sites, as spatial gaps of 8 km are rarely traversed by tree frogs.     

The role of the androconia in the mating behaviour of the European skipper, Thymelicus lineola, and evidence for a male sex pheromone

Abstract. Laboratory experiments were carried out to determine the role and characteristics of male scent scales (androconia), located in patches (stigmata) on the forewings of Thymelicus lineola (Ochsenheimer) (Lepidoptera: Hesperiidae). In behavioural tests, there were 30—40% fewer matings of virgin females by males with the stigmata removed or where females had their antennal sensilla covered with nail polish, when compared to sham-treated controls. These reductions occurred despite a large increase in male courtship activity. No physical contact was observed between male wings and female antennae during mating. A scanning electron microscope study of male wings and female antennae showed that: (1) lysis zones form over time on the androconia and pieces (osmo-phores) distal to these zones break off; (2) while few of these zones are present at emergence they are numerous in-day-old males; (3) during a single episode of courtship and mating approximately two-thirds of the available osmophores break off, yet the commonly observed courtship between males does not appear to result in osmophore release; and (4) osmophores were never observed on the female antennae. Electroantennogram recordings (EAGs) indicated that: (1) female antennae responded strongly to odours from male forewings but not from other parts of either males or females; (2) female antennae responded more strongly to young field-collected males than to newly-emerged or old, field-collected males; (3) female antennal response to male forewings was reduced if the androconia were scraped off, and was eliminated if the stigmata were removed; (4) male antennae gave weak EAG responses to both male and female forewings. We conclude that males release pheromone via the breakage of osmophores during courtship. We propose that the frequently observed refusals by females of courting males are at least partially dependent on the quantity or quality of male pheromone released, which are in turn correlated with the male's age and mating status.     

Corn as a source of mycotoxins in Indonesian poultry feeds and the effectiveness of visual examination methods for detecting contamination

Every truck load of corn (n=52) entering and every batch of poultry feed (n=290) leaving a Bogor feedmill over one year was analysed for aflatoxins, zearalenone, ochratoxin A and sterigmatocystin. Fifty loads of corn and 274 of the batches of chicken feed contained aflatoxins. Zearalenone was detected in 11 corn samples but was not found in the formulated feed. Ochratoxin A was detected in one corn sample, but not in feed. Corn can account for all of the aflatoxin in the feed since levels were always lower in the finished product. There was no quantitative association between the proportion of bright green-yellow fluorescent, purple or mouldy kernels and the mycotoxin contents of the composite samples. Nevertheless, the absence of abnormal kernels indicates higher quality corn since the highest levels of mycotoxins occurred in the abnormal kernels.     

Short allele dominance as a source of heterozygote deficiency at microsatellite loci: experimental evidence at the dinucleotide locus Gv1CT in Gracilaria gracilis (Rhodophyta)

In this study, we compared the genotypes obtained at a microsatellite locus using two methods of amplification and detection of variation in a set of individuals belonging to the red alga haplo-diploid species, Gracilaria gracilis . The methods varied in their capacity to detect longer alleles in heterozygotes, resulting in an apparent heterozygote deficiency. We attributed this bias in favour of short alleles to competition leading to the preferential amplification of shorter alleles (short allele dominance). To test this hypothesis, we created artificial heterozygotes (mixtures of two haploid DNA samples) and showed that long alleles already less intense than short alleles, 'suffer' more from being in association.     

Utilization of glutathione as an exogenous sulfur source is independent of gamma-glutamyl transpeptidase in the yeast Saccharomyces cerevisiae: evidence for an alternative gluathione degradation pathway

gamma-Glutamyl transpeptidase (gamma-GT) is the only enzyme known to be responsible for glutathione degradation in living cells. In the present study we provide evidence that the utilization of glutathione can occur in the absence of gamma-GT. When disruptions in the CIS2 gene encoding gamma-GT were created in met15Delta strains, which require organic sulfur sources for growth, the cells were able to grow well with glutathione as the sole sulfur source suggesting that a gamma-GT-independent pathway for glutathione degradation exists in yeast cells. The CIS2 gene was strongly repressed by ammonium and derepressed in glutamate medium, and was found to be regulated by the nitrogen regulatory circuit. The utilization of glutathione as a sulfur source was, however, independent of the nitrogen source in the medium, further underlining that the two degradatory pathways were distinct.