| Parental care plays a vital role in the evolution of mating relationships in birds with complex mating systems(monogamy,polygyny,polyandry,and promiscuity).Both sexes of brood parasitic birds do not participate in parental care,which provides a unique opportunity to explore the particular mating system of birds.The results of studies on the territorial behavior of brood parasitic birds are contradictory.Judging the spatial distribution of egg-laying areas based on the paternity analysis of offspring is of great value for understanding the territory behavior of male and female individuals.It is also helpful to understand the influence of spatial utilization patterns on mating systems.The common cuckoo(Cuculus canorus)is a typical brood parasitic bird widely distributed in Eurasia.Early observations on the European common cuckoo suggested that its mating relationship was obvious monogamy.However,in recent years,it has been identified by the genetic method that the mating system of common cuckoo in Europe and Korea is polygamous,and there are overlapping areas in the egg-laying space of different individuals.In this study,we further identified the genetic mating system of the common cuckoo,parasitic in the nest of the oriental reed warbler(Acrocephalus Orientalis)in Liaohekou National Nature Reserve.We analyzed the influence of the spatial pattern of egg-laying on the mating system.Three hundred common cuckoo genetic samples(144 adults and 156 progeny)were collected over six years(2015-2019 and 2021).Genotyping of microsatellite DNA amplification products and sequencing of mitochondrial control region amplification products were used to construct the genetic relationship.The genetic mating system is analyzed,combined with the spatial position of offspring(eggs),to judge the spatial distribution of offspring(minimum convex polygon method).The results are as follows:(1)Spatial analysis of offspring(eggs)showed that the distance between the parasitic nest(CC-CC)was significantly shorter than that between the parasitical nest and the non-parasitical nest(CC-ORW)(female: P < 0.01,df=68,t=5.321;male: P <0.01,df=54,t=4.556).The result indicated that the common cuckoo preferred to select the nest of oriental reed warblers closer to the previous parasitic nest.Secondly,the distance between the parasitic nests of the half-sibling relationship(CC-siblings)is significantly shorter than the distance between the parasitic nests of the non-related(CC-non-related)(female: P = 0.003,df=176,t=-2.774;male: P = 0.038,df=138,t=-2.095).This further indicated that the spatial distribution of the offspring of the same common cuckoo is relatively concentrated.In addition,when analyzing the overlapping degree of the spatial distribution of the offspring from different individuals,we found that the average overlapping proportion was 42.4%(female:43.02%;male: 41.78%).The results showed that the individual common cuckoo could hardly have an exclusive egg-laying area but has a considerable overlapping area among the population.(2)Through paternity tests and the analysis of sibling and half-sibling relationships,we found that only 1.56% of families were monogamy,while 98.44% of families were polygamy(56.25% for polyandry,42.19% for polygyny;n = 64).The fitting linear model of the number of spouses to the number of offspring indicated that the genetic spouse number of male and female common cuckoos tended to have multiple mates.In summary,we found that common cuckoo breeds in this region all had a considerable spatial overlap of egg-laying(or progeny)regions.This shared spatial utilization may be an essential factor leading to genetic polygamy.In addition,the tendency of genetic polygamy was also related to the different parental reproductive strategies provided by brood parasitic birds.However,more behavioral observations and studies are needed to confirm whether the genetic polygamy tendency of common cuckoo reflects the real social mating relationship. |
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