纳特竖蟾(无尾目:滑背蟾科) 的细胞遗传、与相关属物种的核型相似性并兼论其分类地位

摘要

本文报道纳特竖蟾(Eupemphix nattereri Steindachner,1863)巴西3个产地标本的核型,均为2n=22,由1对端部和10对中或亚中部着丝点染色体组成.仅一对NORs位于No.11染色体对长臂端部,而其位置有别于常见的具有标志性意义的近着丝点位置.该NORs的位置为rDNA为探针的荧光原位杂交(FISH)所确认.各染色体对中,着丝点C-带明显,插入或端带偶见.某些标本的No.8同源染色体对间C-带的大小随异染色质化的程度不同而变化.居于较小的实验标本量,这种在3个产地的雌或雄性标本之一中观察到的C-带异型现象可能为种下细胞地理学变异,亦或为细胞学意义的性染体分化.3产地之一的标本核型的No.11着丝点C-带异染色质化的程度较高.CMA3染色检测到部分GC-rich区域,DAPI染色未显示任何AT-rich区.成功获得BrdU复制带,并将其与滑背蟾类动物(leiuperid)中近缘属及物种进行对比分析.比较结果表明,纳特竖蟾的核型与斑符泡蟾种组(Physalaemus signifer group)难以相互区别,而与肿肋蟾属(Pleurodema Tschudi,1838)极为相似.核型数据支持形态学上将纳特竖蟾、二光肿肋蟾[Pleurodema diplolister (Peters,1870)]和短头肿肋蟾[P.brachyops(Cope,1869)]划为同一分支的观点[动物学报 53(2):285-293,2007].%Eupemphix nattereri Steindachner,1863 from three localities in Brazil showed 2n=22 karyotype,with metacentric or submetacentric chromosomes and one telocentric pair 11.The specimens have a single pair of Ag-NOR,at the distal region of the long arms of chromosomes 11,although Ag-positive labeling was frequently observed in the proximal region of these chromosomes.The true Ag-NOR was confirmed by FISH with an rDNA probe,which never hybridized in any other chromosome site.C banding pattern is predominantly centromeric,with some interstitial or telomeric bands.Chromosomes 8 presented either gain or loss of interstitial heterochromatin,leading to size variation between the homologs in some specimens.Since the heteromorphism occurred in specimens from the three localities and in both male and female collected in one of them,at present,the possibility of geographical karyotypic variation and of cytologically differentiated sex chromosomes was ruled out,due to the small sample size.An increased amount in the centromeric heterochromatin of the chromosome 11 was seen,but only in specimens from one of the localities.CMA3 staining revealed some GC-rich repetitive regions,whereas with DAPI no particular bright AT-rich site was detected.BrdU replication banding was obtained for the first time,but karyotypic comparisons with leiuperids of related genera were based on standard stained chromosomes.The karyotype of Eupemphix nattereri is indistinguishable of those presented by the representatives of Physalaemus signifer group analyzed so far.Moreover,the species is karyologically very close to the species of Pleurodema Tschudi,1838,so that our cytogenetic data agree with the proposal based on morphological characters of including Eupemphix nattereri,Pleurodema diplolister (Peters,1870) and P.brachyops (Cope,1869) in the same clade[Acta Zoologica Sinica 53(2):285-293,2007].