| Mate selection is a vital component of sexual selection and an important part of avian reproductive behavior.For social monogamous bird,a high-quality partners will increase the fitness of both sexes.Much of the research has focused on females’ mate choice,while ignoring males’ mate choice.At the same time,extra-pair copulation is common among social monogamous avian,and the choice of extra-pair mates is also one of the research hotspots in the field of mate selection.Considerable research has relied on a single signal to indicate mate selection,which is biased due to the fact that individuals usually exhibit multiple signals simultaneously in real-life situations.What is the relationship between various signals? Which signal affect the choice of social and extra-pair mates in birds? Can multiple signals work together to predict individual reproductive effectiveness? These questions have not yet been consistently answered.Therefore,I intended to use the Varied tit(Sittiparus varius)as the research subject to explore those interrogatives.The Varied tits(Passeriformes)as a typical songbird without sexual dimorphism have bright and diverse plumage colors,an ideal bird species to study the effects of multiple signals on mate selection and reproductive success.In this study,I explored the relationship between multiple signals including acoustic parameters,plumage color and morphology parameters,and tested 3 hypotheses(the multiple message hypothesis,the redundant signal hypothesis,and the unreliable signal hypothesis).I used the first egg laying date as a sign of social mate choice to explore the influences of various signals on the Varied tit’s social mate choice.Additionally,paternity loss was used as an indicator to explore the bird’s extra-pair mate choice.Finally,I explored whether and how the presence of multiple signals could predict the bird’s reproductive success.The results were as follows:(1)Principal component analyses were performed on the acoustic parameters,plumage parameters,and morphology parameters separately for female and male breeders.For female Varied tits(n = 37),two principal components were extracted from morphology parameters,including body length as PC1 and tail length as PC2,and two principal components were also extracted from plumage color parameters,including saturation as PC1 and hue/brightness as PC2.For male Varied tits(n = 38),two principal components were extracted from morphology parameters,including body length as PC1 and a combination of wing length and tail length as PC2,and two principal components were also extracted from plumage color parameters and acoustic parameters.Specifically,the two principal components extracted from the plumage color parameters were the same as those extracted from the female Varied tits,and the two principal components extracted from the acoustic parameters were bandwidth as PC1 and main peak frequency as PC2.(2)Correlation analyses were separately conducted on multiple signals of female and male breeders.The results showed that for female breeders,there was a significant positive correlation between the morphology PC2 and the plumage PC2(r = 0.326,P= 0.040),indicating that the longer the tail length of the female,the brighter and more prominent the hue of its plumage.For male breeders,there was a significant negative correlation between the song PC1 and the plumage PC1(r =-0.417,P = 0.007),indicating that the narrower the song bandwidth,the more saturated the plumage color.There was no correlation among other signals.(3)Correlation analyses were conducted on multiple signals between the social mates.The results showed that the plumage color brightness(r = 0.354,P = 0.037)and saturation(r = 0.363,P = 0.032)of social mate pairs were positively correlated.Individuals preferentially choose social mates whose plumage color phenotype was similar to their own.Afterwards,the breeding nests were divided into two groups,those with extra-pair paternity(EPP)offspring and those without,for separate analyses.The results showed that for the group with EPP offspring(n = 30),there was a significant and highly significant positive correlation between plumage brightness(r = 0.393,P =0.032)and saturation(r = 0.571,P = 0.001)among social partners,while there was no significant correlation between other signals.However,no significant correlations were found among plumage color,morphological parameters,and other signals among social partners in the group without EPP offspring(n = 7).Further analysis was carried out on the signals of female,male parents,and extra-pair partners.The results showed that for both female and male parents,there was no significant correlation between their plumage color and morphology parameters and the extra-pair males.However,there was a significant negative correlation between the difference in plumage brightness of the social partners and the presence of extra-pair offspring in the nest(t =-2.217,P =0.027).This means that the higher the plumage brightness of the male parent relative to the female parent,the less likely for extra-pair offspring to occur in the breeding nest.(4)There was no significant correlation between various signals of male and female parents and the time of mating pair formation.(5)There was no significant correlation between the various signals of the female Varied tit and the presence of extra-pair offspring in the nest;but the plumage color PC1 negatively correlated with the number of extra-pair mates(t =-2.792,P = 0.008),and the proportion of extra-pair offspring(t =-2.285,P = 0.029).The higher the saturation of female plumage color,the fewer extra-pair mates during this breeding season,and lower the proportion of extra-pair offspring.(6)There was no significant correlation between various signals of the male Varied tits and the loss of paternity,but the interaction of acoustic PC2 and plumage color PC1 was positively correlated with the number of extra-pair mate in the nest(t = 2.101,P =0.045),and the interaction term between acoustic PC1 and morphology PC1 was positively correlated with the proportion of extra-pair offspring in the nest(t =3.420,P= 0.002).The higher the peak frequency of male singing,the higher saturation of plumage color,the fewer of extra-pair mates in the breeding nest.The narrower the song bandwidth,the longer the body length,and the lower the proportion of extra-pair offspring in the nest.(7)The acoustic PC2 of the male Varied tits(t = 2.708,P = 0.011)was positively correlated with the total number of offspring(offspring within-pair + offspring withoutpair).The more nests the male sired,the more paternity loss in their own breeding nests(r = 0.345,P = 0.034).(8)Various signals of the male and female Varied tits were not significantly correlated with the clutch size and the reproductive success rate.However,the morphology PC1 of the female was positively correlated with the condition index of the offspring(t =-1.264,P = 0.011)indicating that the longer the body length,the better the body condition of the offspring.The interaction of song PC1 and morphology PC1 was significantly positively correlated with the condition index of offspring(t = 2.972,P = 0.006)indicating that the longer the body length,the narrower the song bandwidth,and the better the body condition of the offspring.To sum up,plumage and morphology parameters of female Varied tits,and the acoustic and plumage parameters of male conform to the backup signal hypothesis,while the morphology signals of male birds do not.The selection of social partners based on plumage color conforms to assortative mating,but the selection of extrapair partners is not related to the above signals and requires further in-depth research.The greater the difference in plumage color between social mates,the lower the probability of paternity loss.The brighter the plumage color of the female,the fewer extra-pair mates,and the lower the proportion of extra-pair offspring in the nest.The better the multiple signals of the male parent,the fewer extra-pair mates,the lower the proportion of extra-pair offspring in the nest,and the more offspring produced.The multiple signals of the male and female cannot predict the clutch size or reproductive success rate of the breeding nest,while it can predict the body condition of the offspring.The longer the body length of the male and female parents,and the louder the male singing,the better the body condition of the offspring. |
