Two reported cytotypes of the emergent orchid model species Erycina pusilla are two different species

Abstract

Each species is characterized by a specific set of chromosomes, which is described as the chromosome portrait or karyotype. In general, such a karyotype is the same for all individuals in the population. An exception to that rule has recently been found in the orchid Erycina pusilla, which has been reported to have two cytotypes with chromosome numbers of 2n = 10 and 2n = 12. Here, we examined the karyotypes of the two cytotypes and found differences in arm ratios and heterochromatin patterns as well as in the presence of satellite chromosomes and in the number and location of rDNA and telomeric repeat sites. These differences are extensive and would have required multiple chromosome rearrangements to generate the differences between the two karyotypes. We also found that F1 hybrids between the parents with the two different chromosome numbers resulted in sterile offspring, in accordance with our previous findings. The combination of hybrid sterility and extensively rearranged chromosomes supports the hypothesis that these two reported cytotypes are, in fact, two different species.

Ploidy Level, Karyotype, and Genome Size of Bletilla Species (Orchidaceae) From China

“…Dysploids with 2n = 2x = 36 and 2n = 2x = 34 in B. striata were found in this study. Dysploidy is an increase or decrease in the chromosome number as a result of structural rearrangements (Shan et al, 2003;Yang et al, 2014;Yeh et al, 2017). Our information on the nuclear DNA contents of B. striata showed that the 2C values in populations with dysploidy (2n = 2x = 34; 2n = 2x = 36) were not significantly different from those in other B. striata populations with 2n = 2x = 32 (Table 1).…”

Chromosome Number and Genome Size Evolution in Brasolia and Sobralia (Sobralieae, Orchidaceae)

“…The family Orchidaceae Juss. is known for its large variation in both chromosome numbers, which varies more than 20-fold (from 2 n = 10 to 2 n = 240; [ 11 , 12 ]), and genome size, which varies more than 168-fold, the second-largest variability in Angiosperms [ 13 ]. It makes Orchidaceae an interesting clade for studies in karyotype evolution, and by inferring the historical karyotype and genome size modifications, it also gives clues about taxonomic delimitations [ 14 , 15 ].…”