The Interspecific Pollination And Conspecific Pollen Precedence In Four Species Of Sagittaria In Wuyishan Area

The genus Sagittaria L.belongs to Alismataceae family.Its vegetative and reproductive phenotype are complex,and its habitats are diverse,in addition,it has a wide geographical distribution and there are sympatric distribution and overlapping of florescence in natural populations,which make them a good study system for ecologists and evolutionary biologists.Studies have shown that S.pygmaea Miq.and S.trifolia L.can produce hybrids and there is a conspecific pollen advantage between them.In order to explore the universality of conspecific pollen advantage in Sagittaria and the possibility of hybridization among related species in the same domain,and the reproductive isolation mechanism to avoid interspecific hybridization,we selected representative species of S.guayanensis subsp.lappulas,S.potamogetonifolia Merr.,S.lichuanensis J.K.Chen,and S.trifolia L.from the phylogenetic tree of the genus as our research subjects.Through investigating the specimen information of the China Virtual Herbarium(CVH)and existing literature,the geographical distribution pattern of these4 species of Sagittaria were analyzed.We used these 4 species of Sagittaria as female parents to conduct conspecific and heterospecific pollination experiments and observed pollen tube growth in different carpels from 4 species of Sagittaria.The main research results are as follows:(1)Based on the analysis of 1172 dehydrated specimens of 4 species of Sagittaria,they have the same regional distribution and concentrate in areas located in the Wuyishan area of Fujian Province.(2)The results of fluorescence microscopy showed that the pollen from S.guayanensis subsp.lappulas,S.potamogetonifolia,S.lichuanensis and S.trifolia could germinate normally on the heterospecific stigmas,but the growth rate of the conspecific pollen tube during intraspecific pollination of S.guayanensis subsp.lappulas,S.potamogetonifolia and S.trifolia was significantly faster than heterospecific pollen tube during interspecific pollination,but the growth rate of the heterospecific pollen tube of S.potamogetonifolia and S.trifolia during interspecific pollination was significantly faster than conspecific pollen tube of S.lichuanensis.After interspecific pollination with S.guayanensis subsp.lappulas as the maternal,the growth rate of the pollen tube from S.potamogetonifolia > S.lichuanensis > S.trifolia;after interspecific pollination with S.potamogetonifolia as the maternal,the growth rate of the pollen tube from S.trifolia >S.lichuanensis >S.guayanensis subsp.lappulas;after interspecific pollination with S.lichuanensis as the maternal,the growth rate of the pollen tube from S.potamogetonifolia >S.trifolia >S.guayanensis subsp.lappulas;after interspecific pollination with S.trifolia as the maternal,the growth rate of the pollen tube from S.potamogetonifolia >S.lichuanensis >S.guayanensis subsp.lappulas.The results showed that the conspecific pollen growth advantage existed in the gynoecium of S.guayanensis subsp.lappulas,S.potamogetonifolia and S.trifolia,while did not exist in the gynoecium of S.lichuanensis.This pollen growth advantage could be used as a mechanism of pre-zygotic isolation to avoid interspecific hybridization.(3)The pollen tubes of S.guayanensis subsp.lappulas tended to turn into ovules first in conspecific carpel and the carpel of S.trifolia but the growth of pollen tubes of S.guayanensis subsp.lappulas was hindered in the carpels of S.potamogetonifolia and S.lichuanensiss so that they could not grow into their ovules;the pollen tubes of S.potamogetonifolia tended to turn into their own ovules in the conspecific carpels,but tended to grow directly along the pores at the base of carpel in the heterospecific carpels;the pollen tubes of S.lichuanensis tended to grow directly along the pores at the base of carpel in both the conspecific and heterospecific carpels;the pollen tubes of S.trifolia tended to enter the ovules first in the conspecific carpels,but tended to grow directly along the pores at the base of the carpel in the heterospecific carpels.(4)The development of fruit and seed embryo from interspecific pollination showed that carpel enlargement appeared after the cross pollination of S.guayanensis subsp.lappulas,S.potamogetonifolia,S.lichuanensis and S.trifolia.All the seeds produced by the cross pollination were not fertile,and the proportion of abortive embryo seeds was different,and the proportion was related to the position of the parent and the female parent in the phylogenetic tree.These results indicate that there are postzygotic isolation mechanism in 4 species of Sagittaria after pollination.The above results indicate that the conspecific pollen advantage may be universal in the carpel of the genus Sagittaria;the 4 species of the genus Sagittaria in the same domain cannot hybridize but interspecific reproductive interference will occur;there are both pre-and post-zygote isolation mechanisms in Sagittaria to avoid interspecific hybrization;the conspecific pollen advantage and the degree of interspecific reproductive interference in Sagittaria may be related to the genetic relationship between parents.