Reproductive Tactics Of Conspecific Brood Parasitism In Mandarin Duck Aix Galericulata

Conspecific brood parasitism(CBP)is a widespread female alternative reproductive tactic.Brood parasites bypass some of the costs of egg-tending and brood-care by laying eggs in the nest of conspecific females who provide parental care to the parasitic eggs and offspring.Over the past several decades interspecific brood parasitism(IBP)has been well studied.However,CBP is far less well appreciated by researchers and the factors that favour parasitism remain unclear for most species including Mandarin duck Aix galericulata.Observational methods in field were used in previous studies on CBP of Mandarin duck,however,those field methods were always of poor accuracy in some other species.In this study,molecular technique was used to explore the factors that facilitate CBP in Mandarin duck?Information about Native Mandarin duck nesting in artificial nestboxes remain insufficient.In this study,the breeding parameters of Mandarin duck were investigated.Occupation rate of nestboxes was,laying rate of a nest was 1.1 eggs/day,incubated clutch size was 13.4,proportion of nest abandonment was 47.5%,hatching success was 85.5%.In addition,40%of the females returned for breeding,which is a moderate return rate in other waterfowl.Frequency of CBP in Mandarin duck(CBP broods:77.5%;CBP offspring:40.9%)is much higher than that of both native and introduced population where CBP was determined using non-genetic methods.Compared to other waterfowl species whose CBP rates have been estimated using genetic techniques,the proportion of CBP young was among the highest of those studies.In addition to genetic method,three non-genetic methods were used to determine parasitism.Compared with the results of genetic method,to some extent,the field methods based on laying rate,clutch size and egg morphology all underestimated the CBP frequency(30.4%?27.5%and 12.5%of nests were misclassified as nonparasitic nests respectively).The method using egg morphology was relatively less laboriousandmore reliable,and the result of which should be valuable for CBP frequency investigation.Results of this study shows that 1)CBP in Mandarin duck was not a nonadaptive behavior derived from nest competition:number of available nestboxes was not a restricted factor;in the experiment of egg addition,the nests where parasitic eggs were laid was not incubated by any female(which indicated that there was no nest competitor in CBP).2)CBP was a temporally and spatially flexible alternative reproductive tactic:parasitism and nesting can occur in the same breeding season;laying behavior(to parasitize or not)of a female can be different in different year;CBP occurred throughout the breeding season.3)number of host-parasite pairs was not affected by distance between nests;4)each a parasite laid multiple eggs parasitically(4.89±2.98,1-13,n=35);those eggs were distributed among multiple nests(2.66±1.3,1-6;n=35);laying multiple parasitic eggs per nest(1.65±1.08,1-5,n=89);5);data of this study is consistent with fecundity enhancement hypothesis.Study on cost of host shows that 1)larger clutches were incubated longer,but only 0.14 day was prolonged by each additional egg;enlarged clutch size was unrelated to hatching success and hatching success was similar among parasitic and nonparasitc nests;2)Host did not adjust her clutch size by laying less eggs in her own nest or reject eggs frequently in response to CBP;3)There were 47.5%of abandoned nests which cannot be excluded as the result of CBP.Theoretical estimation predicted that,in a nest,when value of host eggs/parasite eggs is very small(<1/6),cost of nest abandonment is able to be less than keep on incubating.As nest abandonment in this study often occurred in egg laying stage when clutch size was relatively small,cost of host maybe not severe.4)host can have inclusive fitness benefit through kin-biased CBP,as relatedness of host and parasite was higher than expected.In conclusion,CBP may be a beneficial tactic for Mandarin duck,through which female can increase her fitness benefit(both direct benefit and inclusive benefit),coupled with potentially low cost(or even gain benefit),CBP was frequently adopted by native Mandarin duck as an alternative reproductive tactic.However,further study on explicit fitness costs and benefits to both the host and the parasite still need to be determined and so as to fully reveal the basis of adaption of this intriguing behavior.