Intraspecific chromosome variation in Zamia (Zamiaceae, Cycadales)

The Wollemi Pine (Wollemia nobilis, Araucariaceae) was discovered in 1994 in a remote area of the Wollemi National Park (New South Wales, Australia). With only around 40 adult trees known to be growing in the wild, it is one of the worlds rarest plant species. The results of the first cytological study are reported, including a chromosome count (2n = 2x = 26), karyotype illustration and nuclear DNA C-value (4C = 55.74 pg), obtained using Feulgen microdensitometry. The results are compared with data available on species in the other two genera of the Araucariaceae, Araucaria and Agathis, and with other gymnosperms.

“…Only a few families show variable base chromosome numbers, including Taxaceae, Podocarpaceae and Zamiaceae (e.g. Murray, 1998;Hair & Beuzenberg, 1958;Moretti et al, 1991).…”

Section: Results and Discussion W Y O T Y P E Analysismentioning

confidence: 99%

Chromosome number, karyotype and DNA C-value of the Wollemi Pine (Wollemia nobilis, Araucariaceae)

Hanson¹

2001

“…Chromosomal fission decreases genetic hitchhiking by severing transcentromeric linkages, allowing for direct selection on newly unlinked genes (Todd, 1970; Levin, 2000). High chromosome numbers in Zamia have been correlated with morphological variability and stressful or widely variable habitats (Moretti & Sabato, 1984; Moretti et al ., 1991; Caputo et al ., 1996; Vovides & Olivares, 1996; Napolitano et al ., 2004). Moretti & Sabato (1984) speculated that stressful habitats might cause chromosomal fission, allowing species to invade and survive in a wider habitat range than their relatives with lower chromosome numbers.…”

Section: Discussionmentioning

confidence: 99%

Chromosomal fission accounts for small-scale radiations in Zamia (Zamiaceae; Cycadales)

Olson¹,

Gorelick²

2011

Zamia is unique among Cycadales in its diversity of morphology, ecology and chromosome numbers. The chromosome numbers in Zamia range from 16 to 28, excluding 20, manifest as both interspecific and intraspecific series. It has long been recognized that Robertsonian transformations (chromosomal fission or fusion) probably dominate karyotype evolution in Zamiaceae, although it has been debated whether chromosome numbers are increasing or decreasing. We re-analyse published karyotypes of Zamia spp., relating both chromosome forms and sizes to recent phylogenetic data. We show that karyotype evolution is most probably moving towards increased asymmetry, with higher numbers of smaller chromosomes, thus supporting chromosomal fission. We also address additional hypotheses for increasing chromosome numbers, namely pericentric inversions and unequal translocations. Finally, we discuss the role of these chromosomal changes in evolutionary radiations.

“…The variability in the chromosome numbers reported for Xamia (Norstog, 1980(Norstog, , 1981Vovides, 1983;Moretti & Sabato, 1984;Moretti, 1990;Moretti et al, 1991), with 2n = 16-28, is unsurpassed by any other cycad genus studied so far. <@mi.…”

Section: Introductionmentioning

confidence: 91%

Karyotype polymorphism in the cycad Zamia loddigesii (Zamiaceae) of the Yucatan Peninsula, Mexico

Vovides

Olivares

1996

The cycad %amia loddigesii Miq. forms a morphologically variable complex on the Yucatan peninsula, Mexico. Several diploid chromosome numbers have been found in the species: In= 17, 24, 25, 26 and 27. Differing karyotypes and chromosome numbers were found in individuals of the same population and die karyotypes differ widely in numbers of metacentric and telocentric chromosomes present. Centrometric fission as well as pericentric inversions and unequal translocations are suggested to be the probable mechanisms for this karyotype variation. There appears to be a correlation between high chromosome number and increasing dryness of the habitats. Coupled with the strongly asymmetrical karyotypes, this suggests that karyotype evolution in Z‐ loddigesii is recent.