Allozyme and DNA sequence comparisons of nine species of Encephalartos (Zamiaceae)

Abstract

Phylogenetic relationships between Encephalartos altensteinii Lehmann, E. arenarius R.A. Dyer, E. horridus (Jacquin) Lehmann, E. latifrons Lehmann, E. lehmannii Lehmann, E. longifolius (Jacquin) Lehmann, E. princeps R.A. Dyer and E. trispinosus (Hooker) R.A. Dyer were studied, using E. ferox Bertoloni f. as outgroup. Three continuous and one discontinuous buffer systems were used and gene products of 14 enzyme coding loci were examined by horizontal starch gel-electrophoresis. Genetic variation was studied in a cultivated population of E. lehmannii and the average heterozygosity value for this population is 13.5%, which falls within the range reported for other cycad species. Fixed allele differences between the species studied was not found at any of the loci studied, which suggest that these species are closely related. DNA sequence analysis of rbcL and ITS 1 & 2 genes (1428 and 895 basepairs, respectively) confirmed the close genetic relationships between these taxa. According to ITS and rbcL sequences E. altensteinii and E. princeps are sibling taxa which form a sister group to E. arenarius, E. horridus, E. latifrons, E. lehmannii, E. longifolius, and E. trispinosus. The genetic distances between both groups were 0.12-0.47% for ITS and 0.08-0.16% for rbcL DNA. The results indicate recent (probably pleistocenic) speciation for this group of cycads, and the relationships are discussed with reference to affinities based on morphology and distribution. # 2001 Elsevier Science Ltd. All rights reserved.

Evidence of constant diversification punctuated by a mass extinction in the African cycads

“…In contrast, taxonomic groups such as gymnosperms are a priori of secondary interest because they are characterized by morphological stasis and low interspecific genetic variation (Van der Bank et al 2001; Vorster 2004). However, the limited genetic variation may be indicative of recent but rapid radiations, thus raising an interesting question of what might have triggered their recent and rapid diversification.…”

Variación genética en especies de cícadas estrechamente relacionadas en Ceratozamia (Zamiaceae: Cycadales) mediante el uso de RAPDs

“…Additionally, Sharma et al (1998), based on genetic distances, found that species in the Macrozamia pauli-guilielmi complex were similar. Van Der Bank et al (2001) had also reported recent divergence in nine species of Encephalartos based on genetic distances; and Sharma et al (1999) reported similar results for the Macrozamia heteromera complex. Pérez-Farrera et al (2004) proposed that this species complex might probably have arisen due to a speciation process that assumes a constant evolution rate and allopatric speciation (Grant, 1985), a hypothesis based on Wright (1943) theory of "isolation by distance".…”

“…Isoenzymes may have different allelic forms (allozymes), mostly selective neutrals and co-dominants, which could be used to quantify allelic frequencies and different measures of genetic variation. Some analyses have been done on a wide range of cycad species, for instance; Zamia pumila (Walters & Deckers-Walters, 1991), Macrozamia pauli-guilielmi complex (Sharma, Jones, Forster, & Young, 1998), the M. heteromera complex (Sharma, Jones, Forster, & Young, 1999), the M. plurinervia complex (Sharma, Jones, & Forster, 2004), nine Encephalartos species (Van Der Bank et al, 2001), Cycas seemannii (Keppel, Lee, & Hodgskiss, 2002) and five species of Dioon have been analyzed (González-Astorga, Vovides, Ferrer, & Iglesias, 2003;González-Astorga, Vovides, Cruz-Angón, Octavio-Aguilar, & Iglesias 2005; Cabrera-Toledo, González-Astorga et al, 2008;Cabrera-Toledo et al, 2010). Genetic variation and species relationships have been studied to a lesser extent with RAPD markers, which are dominants and highly polymorphic, examples are Encephalartos (Chaiprasongsuk et al, 2004), with AFLP, RFLP and RAPDs in Cycas (Mekanawakul & Juntawong, 2004;Sangin, Thongpan, Lindstrom, Sangduan, & Mingmuang, 2004).…”

Climate Predictions Accelerate Decline for Threatened Macrozamia Cycads from Queensland, Australia

“…Some authors consider that the surviving species of cycads are in an evolutionary dead-end and awaiting final extinction [6,9]; however, all species (and individual populations) have an origin, expansions and contractions of range, decline and an eventual extinction [10]. Many cycad species may be of recent origin, with species radiations since the Pleistocene (1.75 million–10,000 years ago) [11], although it has been postulated that the average length of time that a cycad species has existed for is about 54 million years [10]. …”

“…These five species occur allopatrically in generally consistent habitat types, but appear to share common reproductive traits of thermogenic male and female cones and a common pollinating beetle (the weevil Tranes ) [31,32,33] and are probably biologically compatible if individuals from populations could interact genetically. They may be the result of a relatively recent speciation event [29], probably post-Pleistocene, as has been proposed for other cycads [11,27,34]. An alternative hypothesis is that they comprise five metapopulations of a single, highly variable ‘superspecies’ (referred to here as Macrozamia super spp.…”