Morphological and geographic variation of the cycad Dioon edule Lindl. (Zamiaceae): ecological and evolutionary implications

Abstract

The relationship in geographical distribution and morphological variation of leaflet width and length (diagnostic trait), between and within populations of Dioon edule Lindl., has been investigated throughout its known range in eastern Mexico (from the states of Nuevo León to Veracruz, north to south, respectively). A total of 1832 leaflets were measured for width and length from 154 plants distributed amongst five populations using four leaflet replicas from each of three leaves per plant. For leaflet width and length the variation among populations indicated significant stat‐istical differences (F4,147 = 125.83; P < 0.0001; R2 = 92.17% and F4,147 = 9.04; P < 0.001; R2 = 26.8%), respectively. With respect to leaflet width, the multiple range test showed three groups with a north to south distributional relationship along the range of the species. The correlation coefficient among paired populations, respect to geographical distance and the absolute value of the mean difference of leaflet width in each population, was positive, and different from zero (r = 0.82; P = 0.013). A great variation of important ecological and evolutionary parameters was shown. © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society, 2003, 141, 465–470.

Demography of the cycad Ceratozamia mirandae (Zamiaceae) under disturbed and undisturbed conditions in a biosphere reserve of Mexico

“…Vovides 1990;Pérez-Farrera et al 2000) and suggests that for most populations optimum microhabitats exist in the first stages of the cycads' establishment (cf. González-Astorga et al 2003). This is very typical of tropical species that grow under shade during the first phases of growth (Martínez-Ramos and Alvarez-Bullya 1995;AlvarezBuylla et al 1996;Franco and Silvertown 2004;Jiménez-Lobato and Valverde 2006), and is a possible explanation for seedlings and juvenile plants that are always associated with shade from the mother plants or the tree canopy.…”

Morphometric and geographical variation in theCeratozamia mexicanaBrongn. (Zamiaceae) complex: evolutionary and taxonomic implications

“…From each foliar sample, we measured 17 quantitative morphological variables (Fig. 2, Table 2) selected from among those previously evaluated for morphological variation in Mexican cycads (Gonz alez-Astorga et al, 2003a;P erez-Farrera et al, 2004P erez-Farrera et al, , 2007aVovides et al, 2004a, b;NicolaldeMorej on et al, 2008), some of them deemed diagnostic in taxonomic treatments within the genus Ceratozamia (Brongniart, 1846;Miquel, 1861;Regel, 1876;Thiselton-Dyer, 1883;Schuster, 1932;Vovides et al, 1983). Each specimen was herborized and deposited in the XAL herbarium.…”

“…Studies in this particular biological area have traditionally attempted to understand the role of natural selection, gene flow, inbreeding, and genetic drift, and aimed to determine how these processes have influenced adaptation and organismal distribution and abundance. In plant species, phenotypic and genetic differentiation between populations that occupy environmental mosaics was demonstrated experimentally for the first time by Turesson (1922) and the existence of ecotypes across environmental gradients has been reported in several studies (Stebbins, 1950;Grant & Wilken, 1988;Stevenson, Sabato & V azquez-Torres, 1986; Gonz alez-Astorga, Vovides & Iglesias, 2003a;Gonz alez-Astorga et al, 2003b;Vovides et al, 2004a).…”

“…Within these methods, the main purpose of an analysis of geographical variation is to describe and synthesize patterns of variation in the characteristics of organisms distributed within a given area. Such analysis contemplates both continuous variables and discrete attributes, which can be categorized in taxonomic terms for the recognition of a population or series of populations, or for the interpretation of patterns such as adaptations to environmental factors (Gonz alez-Astorga et al, 2003a). Moreover, geographical analysis can lead to the probabilistic assignment of specimens without a clearly defined identity in terms of population or location of origin (Sneath & Sokal, 1973).…”

“…Morphological variation in these taxa, related to the geographical distribution of the type species Dioon edule Lindl. and Zamia pumila L., has been studied and defined by Gonz alez-Astorga et al (2003a) and Newell (1985), respectively. However, the type species of the genus Ceratozamia has not yet been studied from this perspective.…”