Mate Choice Pattern Of The Crested Ibis

Crested ibis?Nipponia nippon?is the first class national protected animals and is listed as“endangered”by the International Union of Conservation of Nature?IUCN?Red List.The birds once distributed widely across Russia,China,Korean peninsula and Japan until they declined to near extinction in 20 centry due to overharvesting,habitat loss and food pollution caused by pesticides abuse.In 1981,the last population consisted of 7 birds was found in Shaanxi,China,which founds all the crested ibises over the world today.Although great population growth has been achieved for the past 40 years,high embryonic mortality rate and low fledging rate in captive population was limiting the further recovery of this species.Between 2014 and 2017,we studied the wild crested ibises in Xiazhu Lake,Deqing County,Zhejiang Province,and revealed the mate choice pattern by examining the relations between nuptial plumage,body morphology and MHC variation and between the offspring quality and parental types.Main results are shown as below:?1?Randomization tests showed mutual but different major histocompatibility complex?MHC?-based mate choice pattern between the sexes.Female crested ibises preferred MHC heterozygous males[P_c-values at single locus,haplptye and multilocus level were smaller than 0.05]while male crested ibises avoided to mate with females that carried MHC class?allele DAB*d??₈²=26.99,P_c<0.01?and MHC haplotype HT03??₈²=18.74,P_c<0.05?.?2?Analyses of nuptial plumage colorant reflectance spectra showed that female-preferred?MHC heterozygous?males secreted less-bright colorant than female-nonpreferred?MHC homozygous?males?all P-values<0.01?.A positive correlation was found between male MHC multilocus heterozygosity and male nuptial plumage total reflectance?r=-0.55,P-value<0.01?and ultraviolet reflectance?r=-0.69,P-value<0.01?.Further mediation analysis showed that male plumage ultraviolet reflectance could mediate the MHC-based female mate choice?95%confidence intervals did not include zero?,i.e.females could“see”MHC heterozygosity via male ultraviolet reflectance and chose mate on this basis.Analyses of nuptial plumage colorant reflectance spectra showed that DAB*d-free females secreted more reflecting colorant than DAB*d-carrying females but the difference did not reach significant level?all P-values>0.1?.?3?Analyses of body measurements showed that MHC heterozygous males were larger and heavier than MHC homozygous males,but the differences did not reach significant level?all P-values>0.1?.DAB*d-free females were larger?P-values<0.05?and heavier?P-value<0.01?than MHC-nonpreferred DAB*d-carrying females.Further mediation analysis showed that female body mass could mediate the MHC-based male mate choice?95%confidence intervals did not include zero?,i.e.males could“see”DAB*d absence via female body mass and chose mates on this basis.?4?Paternal MHC heterozygosity was positively correlated with the number of fertilized egg?Wald?²:5.89-9.99,all P-values<0.05?and maternal DAB*d absence was positively correlated with the mean egg initial weight?Wald?²:10.12-10.39,all P-values<0.01?;both paternal MHC heterozygosity?Wald?²:7.35-12.05,all P-values<0.01?and maternal DAB*d absence?Wald?²:3.39-3.98?were correlated with the number of fledglings.?5?P-P?mother that carried preferred MHC types and father that carried preferred MHC types?parent pairs yield the highest offspring fledging rate?about78%?among all types of parent pairs.Significantly higher offspring survival were observed in P-P parent pairs than in NP-NP?mother that carried nonpreferred MHC types and father that carried nonpreferred MHC types?parent types?20%-38%?using Fisher's exact test?all P-values<0.05?.?6?Comparisons of reproductive outcomes between captive artificially matched pairs and free-mating pairs showed that the latter produced larger number of fertilized egg,more fledglings and higher fledging rate?all P-values<0.05?,while the same set indexes of reproductive outcomes between training pairs and wild pairs did not show any significant differences?all P-values>0.1?.These results indicated that the free-mating mate choice mechanisms are beneficial to enhancing crested ibis reproductive outcomes.Our results have important guiding significance for the relevant departments to develop a detailed genetic management plan for artificial and wild populations of the crested ibis.