Genetic Diversity And Occurrence Of Supernormal Clutches Of Saunders's Gull Saundersilarus Saundersi

The Saunders' s Gull(Saundersilarus saundersi)is a globally vulnerable species.Approximately 95% of the world population breeds within three areas.The population size of Shandong Province had increased by 33 times in the past five years.We also found more and more supernormal cluthes along with the growth of the population.To find out whether the genetic diversity patterns had changed and to explore the causes of supernormal clutches,the following three studies were conducted in the breeding populations within China.And some conservation implications were proposed based on research findings.1.Breeding population dynamics and habitat changeBased on the annual field survey data in the past three years,we updated the population size data estimated in The IUCN Red List.The breeding population in China was estimated to 166 800 indivduals in 2016,95% of which bred within four atificial wetlands.The population of Shandong Province increased to 7 112 individuals in 2016,among which 1436 gulls bred at an artificial island of Dawenliu management station,with the area less than 200m2.The population size of Liaoning Province was declining in the past three years.The current population size was 8 642 individuals,only bred in the shrimp pond at Nanxiaohe,with the area less than 260 000m2.The population size of Jiangsu Province was also on the decline in the recent three years,the current population bred in the reclamation zone of Tiaozini in Dongtai,Yancheng City and the tidal area of Xiaoyangkou in Rudong,Nantong City.2.Genetic diversity and phylogeographic structure of S.saundersiBoth mitochondrial sequences and nuclear microsatellites were employed to explore the genetic diversity and phylogeographic structure of the breeding S.saundersi in China.Unexpectedly high genetic diversity was observed in both mitochondrial and nuclear markers for every population.There was no evidence of phylogeographic structure among the three breeding populations.Considering the declining population size of Liaoning and Jiangsu,it may therefore be expected that the increased increased Shandong population and the high gene flow among populations in China may derive from the natal dispersal or breeding dispersal of Liaoning and Jiangsu populations.Our research revealed the gull possess three important characteristics: high dispersal capacity,high gene flow potential and high ability to adapt to the newly restored wetlands.For any threatened colonially breeding waterbirds,the population can be rehabilitated with application of these measures if the species also has these features.3.Ocurrence of supernormal clutchesBlood and egg-membrane samples were collected from supernormal and normal clutches of S.saundersi at Dawenliu.We determined whether there was the phenomenon of “extra-pair copulation,EPC” or “conspecific brood parasitism,CBP” among these cluthes,with microsatellite DNA markers.According to the analysis by Cervus v3.0,we found that there were both EPC and CBP among Dawenliu population.The occurrence proportion of CBP and EPC in supernormal cluthes was 100% and 42%;while there was no occurrence of CBP and 42% of the nests exsit EPC in normal cluthes.The results of SPSS19.0 showed that there was a high correlation between the cluth size and the offspring number of CBP.The bigger the clutch size was,the higher offspring proportion of CBP occurred.Considering these results,we speculated that the occurrence of supernormal clutches might be a CBP mixed breeding strategy when the gulls under extreme environmental pressure.Additionally,there are male extra-pair offsprings found in two in five nests of EPC(the clutch size was four).But we need more samples to analysis whether clutches with normal nesting density also exsit these phenomenon.4.Conservation implicationsAccording to the research,we suggest to conduct the conservation of S.saundersi and its habitat from species conservation,gennetic management and habitat adjustment.We monitored a stray dog by infrared camera in the summer of 2016 within Liaoning breeding habitat,we also found more and more chicks died from disease in Liaoning and Shandong,so we should control predators and disease for species conservation.For gennetic management,we proposed that the breeding populations of S.saundersi could be defined as the same MU.This means that any population can be rehabilitated or re-introduced to establish a separate viable subpopulation without concern of the genetic differentiation and the low genetic diversity.We should also pay attention to disease and human disturbance control.For habitat adjustment,we suggest to conduct the work from habitat reconstruction and maintenance of exsting habitat: through habitat restoration and habitat enhancement to rehabilitate this gull population or to introduce the gull to a new place;vegetation succession and coverage vegetation should be controled for the current habitat.