| Amphioxus,an extant species of Cepholochordata,is closely related to Vertebrata and plays an important role in the evolution of animals.In this paper,the growth and development of three species of amphioxus,Branchiostoma floridae(Bf),B.belcheri(Bb)and B.japonicum(Bj)cultured in the laboratory,were observed and compared.Hybridization between different species were carried out,and the growth and development of hybrid F1 generation and parent F1 were observed and compared.The main morphological characteristics were compared between hybrids and parents.The hybrids were also identified by gel electrophoresis detection technology.Those study can provide basic biological data for amphioxus breeding.The main findings are as follows:1.Comparison on growth and development of three species of amphioxusThrough the cultivation and observation of three species of amphioxus hatched in the same date,it was found that the growth rate of the larvae was: B.floridae > B.japonicum > B.belcheri.B.floridae larvae began to metamorphose at an average age of26 days,with a body length of 3.77 mm and 11 gill slits,and finished metamorphosis at an average age of 31 days,with a body length of 3.83 mm and 15 gill slits.B.japonicum began to metamorphose at an average age of 59 days when the body length was about5.27 mm and 17 gill slits,and finished metamorphosis at an average age of 77 days when body length were about 5.39 mm and 19 gill slits.B.belcheri began to metamorphose at an average age of 66 days when its body length was about 4.76 mm and 15 gill slits,and finished metamorphosis at an average age of 82 days when body length was 4.97 mm and17 gill slits.The growth rate of adults is: B.floridae > B.belcheri > B.japonicum.B.floridae is better than B.belcheri or B.japonicum in growth and development,spawning frequency and survival rate.In the laboratory model research of amphioxus,it is more advantageous to choose B.floridae as the research object.2.Hybridization test of B.floridae and B.belcheriThrough hybridization test,the hybrid offspring between Branchiostoma floridae and B.belcheri were obtained and compared with parents on the growth and development and morphological characteristics.The results showed that the growth and development speed of the parental Bf F1 was the fastest,followed by the orthogonal(Bf♀ × Bb♂)hybrid F1,and then the anticross(Bb♀ × Bf♂)hybrid F1.The growth and development of the parental Bb F1 was the slowest.Thus,at last,the growth and development speed of the hybrids was between in those of the parents,which means the hybrid showed a mid-parent heterosis.The cluster analysis of morphological characters showed that the characteristics of the orthogonal hybrids were similar to those of the parental B.floridae,and the anticross hybrids were similar to the parental B.belcheri.It showed a maternal effect.The designed specific primers were used to distinguish between B.floridae and B.belcheri,and it was found that both the orthogonal hybrid F1 and the anticross hybrid F1 have two bands of Bf and Bb at the same time,indicating that B.floridae and B.belcheri can be interspecies hybridization.2.Hybridization test of B.floridae and B.japonicumHybridization between B.floridae and B.japonicum were carried,and only the hybrid Bf♀ × Bj♂ F1 was obtained.The growth and development of hybrid F1 and parent F1 were compared.The results showed that the growth and development of the parent Bf F1 was the fastest,followed by the hybrid F1 and then parent Bj F1.It indicated that the growth and development speed of hybrid F1 also showed the advantage of middle parent.Using cluster analysis of morphological characteristics,we know that hybrid Bf♀ × Bj♂F1 first clustered with parent B.japonicum,and then clustered with parent B.floridae.It shows that the hybrid offspring have paternal tendency.Molecular identification also confirmed that B.floridae and B.japonicum can be hybridized between two species.3.Preparation and observation of B.floridae chromosome specimensA large number of chromosome mitotic phases can be prepared by using B.floridae embryonic cells in the late blastocyst stage.The metaphases are complete and well dispersed and the chromosomes are mostly rod-shaped and punctate.The metaphase can also be prepared from the callus cells of B.floridae adult after tail cutting,which better solves the problem of materials for B.floridae chromosome preparation.The karyotype of B.floridae was analyzed preliminarily,and the karyotype formula was2n=38=2sm+2st+34t,NF=40. |
