The trade-off between molt and parental care: a sexual conflict in the blue tit?

Breeding activities and molt are generally thought to be mutuallyexclusive in birds since both are energetically costly and arenormally separated in time. However, sometimes molt overlapswith breeding to some degree. A trade-off between adult somaticmaintenance functions (feather renewal) and parental care isthen to be expected. The consequences of this are largely unknown,and there are few studies that have shown any fitness costsof molt-breeding overlap. We investigated the consequences ofmolt-breeding overlap by removing first clutches of blue titParus casruleus pairs, thereby inducing late repeat clutches.Among the delayed pairs, a high proportion of males and somefemales started their molt already during incubation or nestlingfeeding. Molting males fed their nestlings to a lesser extentthan non-molting ones, and nestling mortality increased as adirect result of the early timing of male molt. Furthermore,the ability to raise an experimentally enlarged brood was negativelycoupled to the molt stage of the male. Our data thus provideevidence that molt-breeding overlap leads to fitness costs,and we discuss the results within the context of sexual conflictand the implications for optimization of avian reproductivedecisions     

Territory switching behavior in a sedentary tropical passerine, the dusky antbird (Cercomacra tyrannina)

Demographic data from an 8-year study of a marked populationshowed that switching territories and mates is common in bothgenders of dusky antbirds (Cercomacra tyrannina), a sedentaryneotropical passerine with year-round territories and pairbonds.We conducted 22 experimental removals and followed six naturaldisappearances to examine territory switching. Antbirds quicklyabandoned territories and mates to move to openings createdby experimental removals. Pairing with the resident on a newterritory was rapid. Unmated birds attracted new mates by singinga gender-specific song that differed from songs given by matedbirds. There were no gender differences in replacement timeor rate. Some vacancies, experimental and natural, were notfilled, suggesting that floaters were rare. Territory and mateswitching were not related to immediate enhancement of reproductivesuccess because the probability of reproducing successfullywas equally poor on all territories. Territory switching maybe an overlooked but common tropical form of territorialitythat increases individual survivorship during periods of lowfood abundance (dry season). We suggest that switching is favoredwhen low annual reproductive success enhances selection fora long lifespan as the primary means to increase reproductivesuccess.     

Female mate assessment and choice behavior affect the frequency of alternative male mating tactics

Explanations for the existence of alternative male mating tacticsfocus primarily on male–male competition. Mating systems,however, are composed of interactions both within and betweenthe sexes, and the role of female behavior in shaping male matingtactics should not be overlooked. By using a dynamic state variablegame model, I examine how female mate assessment and choicebehavior affect the frequency of alternative male mating tactics.When females can accurately assess the quality of males, onlymales with high quality are likely to be chosen as mates, andthus, lower-quality males gain little fitness from courtingfemales. This leads lower-quality males to switch to an alternativemating tactic that attempts to circumvent female mate choice.In contrast, if the abilities of females to accurately assessmales are constrained by assessment costs, imperfect information,or time constraints, or if the pool of available males is smaller,then lower-quality males are increasingly chosen as mates andthey less often use alternative mating tactics. Thus, femalebehavior shapes the frequency of alternative male mating tactics.A consequence of this game between the sexes is that male behavior(i.e., increased alternative mating tactics) decreases the benefitsfemales might otherwise gain from lower assessment costs, clearersignals of male quality, more time to choose a male, and moremales from which to choose a mate.     

Mating behaviour in Moina brachiata (Jurine, 1820) (Crustacea,Anomopoda)

Information on mating behaviour in Anomopoda isavailable for very few species only, though matelocation and recognition certainly play an importantrole in maintaining reproductive isolation betweenspecies. Ephippial females and males of Moinabrachiata were observed in a drop of water under amicroscope for 10–20 minutes. Different combinationsof specimens were used, but copulation was onlyobserved when two males and two ephippial females wereplaced together. Males were very active, and oftentried to grasp a female, whereas females usually madeattempts to escape during the entire period of mating.Three phases were recognized: capture, positioning andcopulation. The male captured the female from thedorsal side, then moved to the ventral side and tooka position with its length axis being perpendicular tothat of the female, forming a sort of cross.Thereafter the pair started rotating around the lengthaxis of the female, while the male pushed thepostabdomen into the females brood pouch. Copulationlasted from 16 to 25 seconds. When different kinds offemales were used, males showed preference forephippial females with an empty ephippium and enlargedovaries. Our results indicate that not only visual andtactile cues may be important in identifying speciesidentity and receptivity of the female, but alsochemical signals.     

Behavioral Interaction Between Males of Cephalonomia tarsalis (Ashmead) (Hymenoptera: Bethylidae) Competing for Females

Male Cephalonomia tarsalis (Ashmead) compete with one another for mates. The behavioral interactions between males for mates occur both on and off females. Males winning the first copulation do not exhibit apparent postcopulatory mate-guarding behaviors, and females accept subsequent copulations with losing males soon after separation. The duration of copulation when a second male is present is shorter than when only one male is present. However, females receive sufficient sperm for their life-time female progeny production in copulations disrupted artificially at 10 s (1/5 of the regular copulation duration) under normal noncompetition situations. This suggests that shorter copulations because of male–male competition could still result in adequate sperm transfer. Larger males were not more successful in competition than small males, but male competitive ability decreased with age.     

The influence of predation risk on threat display in great tits

In wintering birds, conflicts over food are often resolved bythreat displays. For displays to be effective, there oughtto be a cost associated with displaying. We investigated whetherincreased vulnerability to predators due to reduced vigilancecould be such a cost. Conflicts ought then to be resolved usingfewer or less intense displays in conditions of high risk. We also looked for differences between dominants and subordinatesin their reaction to risk. Because there is considerable evidencethat subordinate wintering birds forage in riskier places thandominants, one might expect dominants to be less successfulin conflicts under high predation risk. In our experiment,nine flocks of four or five wintering male great tits were keptin outdoor aviaries. In the predation risk treatment, a stuffedpygmy owl was briefly shown before birds were allowed accessto a feeder. In the control treatment the owl did not appear.The predator presentation caused a reduction in the amountof aggression shown by subordinates, whereas for dominants there was no statistically significant change. Dominants were at leastas successful in subduing subordinates under high risk as underlow risk. A possible interpretation is that our experimentreflected a natural foraging situation for great tits, whereephemeral resources can appear unpredictably. In such situations,dominants may need to be bold to gain priority of access even under increased risk of predation, whereas a subordinate wouldgain little by risking a conflict with small chances of winning.     

Effects of novelty and gregariousness in survival of aposematic prey

We examined the reactions of captive wild great tits to novelunpalatable prey with (1) a traditional aposematic signal (blackand yellow) (2) a novel signal (light pink), and (3) a controlsignal (brown). Prey were offered either singly or in groupsto see whether novel signals with fewer possibilities for synergisticbenefits are more dependent on grouping than are the traditionalsignals. Indeed, responses of birds toward unpalatable preydepended significantly on spatial distribution of prey (groupingversus solitary) and the type of the signal. Birds avoided morethe traditional black and yellow signals than novel pink signalsin both experimental set ups, but both of these prey items survivedbetter in aggregation than solitarily. The success of traditionalsignals may demonstrate the importance of synergistic selectionacross species in the evolution of warning coloration (i.e.,Müllerian mimicry). Unpalatable prey individuals benefitstrongly from using similar color patterns. Our results suggestthat aggregation may be important for the evolution of novelsignals in particular, even if a synergistic selection componentis also present     

Mating games: the evolution of human mating transactions

We propose a new, evolutionary, game-theoretic model of conditionalhuman mating strategies that integrates currently disconnectedbodies of data into a single mathematically-explicit theoryof human mating transactions. The model focuses on the problemof how much resource a male must provide to a female to secureand retain her as a mate. By using bidding-game models, we showhow the male's minimally required resource incentive variesas a function of his own mate value, the value of the female,and the distribution of the mate values of their available alternativemates. The resulting theory parsimoniously accounts for strategicpluralism within the sexes, mate choice differences betweenthe sexes, and assortative mating, while generating a rich setof testable new predictions about human mating behavior.     

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.     

Genetic variation among marine Brachionus strains and function of mate recognition pheromone (MRP)

Recent studies on morphology and genetics of marinerotifer populations have demonstrated the existence ofconsiderable variation. Differences in theglycoprotein structure of a mate recognition pheromone(MRP) probably have a primary role in maintainingspecies boundaries among Brachionus species.This study examined factors involved in mating toclarify their relation with genetic variability. Threeexperiments were performed using 3 Brachionusplicatilis strains (Russia, Germany and Tokyo) and 4B. rotundiformis strains (Hamana, Fiji, Thai andSpain).Selfing and cross mating of 7 rotifer strains wasconducted in the first experiment. Russian malesmated with B. plicatilis females in thefollowing increasing order, based on mating attempts:German, Tokyo and Russia. There was little matingattempts with females of B. rotundiformisstrains. In a second set of experiments, the binding of anantibody (anti-MRP) derived from the MRP of Russianstrain was tested. A fluorescent label was attached toanti-MRP and the antibody reacted with the MRP onfemales of seven strains. The fluorescence intensity,indicating the degree of antibody binding, wasmeasured with epifluorescence microscopy and imageanalysis. The binding intensity of the anti-MRP to theMRP was in the following increasing order: Hamana,Fiji, Spain, German, Tokyo, Thai and Russia.It was expected that when the anti-MRP binds tothe MRP of a female, the males recognition of thefemale would be inhibited. In the third experiment,male mating with females exposed to the anti-MRP wascompared with unexposed females. Russia Tokyo, Thaiand Spain females exposed to anti-MRP, elicited fewermale mating attempts than unexposed females. Matingfrequency and anti-MRP binding significantlycorrelated with genetic distance obtained from isozymeanalysis.     

Primary sex ratio adjustment to experimentally reduced male UV attractiveness in blue tits

The study of primary sex ratio adjustment in birds is notoriousfor inconsistency of results among studies. To develop our understandingof avian sex ratio variation, experiments that test a prioripredictions and the replication of previous studies are essential.We tested if female blue tits Parus caeruleus adjust the sexratio of their offspring to the sexual attractiveness of theirmates, as was suggested by a previous benchmark study on thesame species. In 2 years, we reduced the ultraviolet (UV) reflectanceof the crown feathers of males in the period before egg layingto decrease their attractiveness. In contrast to the simpleprediction from sex allocation theory, we found that the overallproportion of male offspring did not differ between broods ofUV-reduced and control-treated males. However, in 1 year, theUV treatment influenced offspring sex ratio depending on thenatural crown UV reflectance of males before the treatment.The last result confirms the pattern found in the previous bluetit study, which suggests that these complex patterns of primarysex ratio variation are repeatable in this bird species, warrantingfurther research into the adaptive value of blue tit sex ratioadjustment to male UV coloration.     

Genetic variability in mitochondrial DNA in a regional population of the great tit (Parus major)

Genetic variation of mitochondrial DNA (mtDNA) in 18 great tits (Parus major) from three neighboring localities in Sweden was investigated with eight tetranucleotide restriction endonucleases. The 18 individuals could be separated into 13 different maternal lineages. The high number of female lineages present in this regional population contrasts with a low level of sequence divergence between the different mtDNA clones, with a mean of 0.19% sequence divergence between all individuals. There was no obvious spatial structuring of mtDNA clones among the three localities. The presence of a high number of different clones with a low degree of sequence divergence could be explained by the effects of a large long-term effective population size, with the mtDNA clones having diverged about 25,000–200,000 years ago.This study was supported by the Swedish Natural Science Research Council, the Erik Philip-Sörensen Foundation, and the Nilsson-Ehle Foundation.     

The effect of female mating history on sperm precedence in the two-spot ladybird, Adalia bipunctata (Coleoptera, Coccinellidae)

Effects of two different mating regimes on sperm precedencein the two-spot ladybird, Adalia bipunctata, were studied usingthe polymorphic gene for melanism as a marker for paternity.Virgin nonmelanic females (homozygous recessive) were matedto nonmelanic male(s) and then, after laying fertilized eggs,were mated to a melanic male of known genotype. The resultsafter the two successive single matings showed a highly variabledegree of paternity of the second male. Initial multiple matingwith nonmelanic males did not alter the pattern of paternityafter the subsequent single mating with a melanic male, butit had two other effects: (1) the female showed an increasein rejection behavior, and (2) a longer copulation was requiredfor high success of the melanic male. Additional observationsin which families were reared from beetles collected in copulain the field demonstrated that sperm competition also occursunder natural conditions. The outcome of the competition wasvariable with frequent sperm mixing.     

Memory for food caches: not just for retrieval

Many animals use hoarding as a long-term strategy to ensurea food supply at times of shortage. Hoarders employ strategiesthat enhance their ability to relocate caches such as rememberingwhere caches are located. Long-term scatterhoarders, whose cacheshave potentially high pilferage rates, should also hoard ina way to reduce potential cache pilferers' ability to find caches.Previous studies have demonstrated that this could be achievedby hyperdispersing caches to reduce the foraging efficiencyof pilferers. This study investigates whether coal tits (Parusater) indeed place their caches away from existing ones. Inour experiment, birds hoarded food in 3 conditions: when cachesfrom a previous storage session were still present, when cachesfrom a previous storage session were not present anymore becausethe bird had retrieved them, and when caches from a previousstorage session had been removed by the experimenter. We showthat coal tits hoard away from existing caches and that theydo not use cues from extant caches to do this. This evidenceis consistent with the use of memory for the locations of previouscaches when deciding where to place new caches. This findinghas important implications for our understanding of the selectivepressures that have shaped spatial memory in food-hoarding birds.     

Female mate preferences and subsequent resistance to copulation in the mallard

In the majority of socially monogamous bird species, femalessolicit or accept copulations from males other than their partner.Females may gain direct benefits from extrapair males, suchas greater access to resources, or indirect genetic benefitsthat will influence the future success of their offspring. However,one group of birds appears to be the exception to this generalrule; in the wildfowl (Anseriformes), all extrapair copulationsappear to be resisted by females. It has been suggested thatresistance behavior may be a strategy to allow females a greaterchoice of mates, either at the precopulatory level (to promotechoice of copulation partner) and/or the postcopulatory level(to promote multiple mating to increase their choice of sperm).This paper examines the function of female resistance behaviorin one of the dabbling ducks, the mallard (Anas platyrhynchos).Observations on a marked population of wild mallard and experimentswith captive birds found that although females showed a strongpreference for particular males that are the first to molt intotheir breeding plumage, male attractiveness did not influencefemale responses to pair or extrapair copulation attempts. Femaleresistance decreased the likelihood that copulation attemptswould end in successful insemination. The findings did not supportthe hypothesis that females resist copulations to promote femalechoice and the reasons why waterfowl may benefit from avoidingall extrapair copulations are discussed.     

Mating preference of female zebrafish, Danio rerio, in relation to male dominance

Mating success tends to be skewed toward dominant males, thoughfemale mate preferences may not always correlate with male dominance.In this study, we investigated the mating preferences of femalezebrafish, Danio rerio, in the absence of male–male competition.We paired females sequentially with males of known dominancerank, using a nested, repeated measures design, with egg productionas a measure of female mate preference. We predicted that femaleswould spawn more frequently and produce larger clutches whenpaired with males of higher dominance rank. We found significantdifferences among females in the size of clutches produced andamong males in the size of clutches received, but these differenceswere independent of male dominance rank. Male body size wasnot related to either dominance rank or clutch size received.These results indicate that females vary clutch size in relationto the males with which they are paired but that they do notfavor dominant males. Thus, male competition may normally overridefemale mate preference in zebrafish.