D Ong Pimpla ky sinh bac 2 tren Limneria
2.NGUON GOC CUA KY SINH TRUNG 1 Nguon goc ngoai ky sinh trung
2.1. Nguon goc ngoai ky sinh trung
Hien tucmg ky sinh bat nguon tir dong vat song tu do. Ddi vdi hau het ngoai ky sinh deu the hien phuong thurc dinh dudng tir to tien song tu do chuyen sang dinh dudng bang mo va mau cua vat chu.
Phan ldn ngoai ky sinh bat nguon tir dong vat an thit (vi du nhu dia, rep, mu6i, a'u triing ruoi....). Cac dong vat ke tren rat it sai khac so vdi cac dong vat an thit song tu do gan gui trong cay chung loai phat sinh.
De trd thanh vat ky sinh, dong vat an thit khong chi co mat tren vat chu de’ lay thuc an ma la ca qua trinh tiep xuc lau dai, qua nhieu the he.
Hang loat cac trudng hop ngoai ky sinh bat nguon tir dong vat co ddi song co dinh. Vi du nhu don bao Infusoria (Trichodina). To tien ciia no co ddi song co dinh bang cach bam chac vao day ao, ho hoac bam vao cac co the song d nude va song tu do. Sau do, mot sd loai trong don bao nay (nhu Coronula sp.) luon sau vao da vat chii (ca) va chuyen sang ddi song ngoai ky sinh.
2.2. Nguon goc noi ky sinh triing
Noi ky sinh triing bat nguon tir ddi song ngoai ky sinh. Vi du, don bao Infusoria (Trichodina) la ngoai ky sinh triing d mang va da ca, nhung mot sd loai trong chung, vf du nhu T. urinaria ky sinh d ca hong chuyen sang ddi song noi ky sinh trong tui bai tiet, ong d in bai tiet hay ong dan trung.
Mot vf du dien hinh nua la san la don chii (Polystoma integerrimum) song d mang nong noc, khi nong noc bien thai thanh ech chung chuyen vao song d tui nieu ech va trd thanh noi ky sinh triing.
2.3. Nguon goc kv sinh triing dudng mau
Dang noi ky sinh triing dac biet la ky sinh triing dudng mau. Hien nay co hai quan diem:
- Mot sd nha nghien cuu cho rang, ky sinh triing dudng mau d dong vat co xuong song trudc day la ky sinh triing dudng ruot ciia dong vat khong xuong song. Dong vat
khong xuong song (vf du: cac loai con trung) hut mau ddng vat co xuong song. Tu do, ky sinh trung dudng ruot cua cac con trung nay thfch nghi d£n vdi moi trudng dinh dudng la mau cua dong vat co xuong song. Den luc nao do, cac ky sinh trung nay tir rudt ciia cdn trimg chuyen sang co the dong vat co xuong song qua hoat dong chfch hut cua cdn trung, va co su thfch nghi Mn thur hai vdi moi trudng dinh dudng mdi la mau cua dong vat co xuong song.
- Quan diem ngupc lai cho rang, ky sinh triing dudng mau cua dong vat co xuong song trudc day la ky sinh triing dudng ruot cua chfnh dong vat co xuong song do. Dan dan, chung xam nhap vao trong mau va tim tha'y d moi trudng mdi dieu kien thuan Id hon cho su t6n tai va phat trien. Qua nhieu the he, chung mat dan kha nang song d moi trudng dinh dudng d iu tien (dinh dudng trong dudng rudt vat chu) va thfch nghi l£n thu hai vdi moi trudng dinh dudng la mau vat chu.
Ro rang, ca hai quan diem tren ddu dung, vi cac nhom ky sinh triing dudng mau thuoc dong vat don bao co nguon goc khac nhau.
Cac dai dien ky sinh trimg dudng mau trong nganh Sporozoa deu co nguon gdc tir ky sinh trung dudng rudt cua dong vat co xuong sdng.
Ddi vdi dai dien ky sinh trimg dudng mau cua giong Trypanosoma, ngudi ta cho rang vat chu dau tien ciia chung la dong vat khong xuong sdng, ma chu y£u la nhung cdn triing khong co phuong thurc dinh dudng chuyen hoa bang mau. T6 tien
Trypanosoma song trong rudt cua ddng vat khong xuong sdng, do su tiep xuc cua ddng vat khdng xuong song vdi dong vat co xuong song ma ky sinh triing nay vao mau dong vat co xuong song. Qua trinh tien hoa lam cho chung thfch nghi dan. Mdi trudng dinh dudng man tot hon d ruot, nhung chung van khdng danh mat kha nang song d ruot cdn trimg.
Chuang 2