The genetic structure of a columnar cactus with a disjunct distribution: Stenocereus gummosus in the Sonoran desert

Abstract

Stenocereus gummosus is a columnar cactus endemic to the Sonoran desert that exhibits a disjunct distribution: it is widely distributed in Baja California and restricted to a small coastal area in mainland Sonora. In this paper, we examine the genetic structure and the mating system of this species in order to explore the origin of the disjunction and describe aspects of the pollination biology. Flowers are nocturnal, pollinated mainly by sphingids and self-incompatible. Polymorphism for allozymes (11 loci) was relatively high (P ¼ 75%) but moderate levels of heterozygosity were detected (H o ¼ 0.103 and H e ¼ 0.261). Sonoran populations exhibited higher levels of genetic variation than peninsular populations. H e declined with latitude when just peninsular and two island populations are included. Substantial levels of inbreeding within populations (f ¼ 0.60), moderate differentiation among populations (y ¼ 0.10), and no evidence of isolation by distance were detected. The neighbor-joining phenogram showed Sonoran and island populations nested within peninsular populations. Mainland populations showed greater genetic similarity to island populations, supporting a dispersal hypothesis for the origin of the disjunction. Future studies using DNA markers are suggested in order to better understand the forces that have shaped the genetic structure of this species.

Population Genetic Structure of Two Columnar Cacti with a Patchy Distribution in Eastern Brazil

“…Estimates of genetic variation at the population level in the five studied species were within the range or slightly greater than those reported for other cactus species with relatively large and extensively distributed populations (n=8, P=50.0-89.5, A p =2.20-3.82, H o =0.103-0.169, H e =0.116-0.290; Table 2 in Clark-Tapia and Molina-Freaner, 2003). Our results were also comparable to the high levels of genetic variability found in three bat-pollinated columnar cacti from Venezuela (Nassar, Hamrick & Fleming, 2003).…”

“…Fewer than 15 species have been studied in genetic diversity surveys, with most of the available data being for columnar species (Nassar, Hamrick & Fleming, 2001;Hamrick et al, 2002;Clark-Tapia & Molina-Freaner, 2003;ClarkTapia et al, 2005). These surveys have generally shown that the Cactaceae have high levels of genetic diversity and polymorphism that are comparable to the highest levels reported for longlived woody species (Hamrick, Godt & SiiermanBroyles, 1992).…”

Esterase Polymorphism and the Analysis of Genetic Diversity and Structure in Cactus Populations Descended from Cereus peruvianus Plants Regenerated In Vitro

“…On the other hand, the negative values of F is observed in the F 1 populations contrast with moderate to high levels of endogamy in other Cactaceae species (Nassar et al 2003;Clark-Tapia and Molina-Freaner 2003;Moraes et al 2005;Lambert et al 2006). The low values of F is indicating excess of heterozygous individuals could be the result of human selection (domestication) in the F 1 parent (C 1 -C 14 cultivated plants).…”

“…Pronounced deficiency of heterozygotes found in self-incompatible species of cactus has been inconclusive and hardly explained by Nassar et al (2002Nassar et al ( , 2003 and Clark-Tapia and Molina-Freaner (2003). We believe that the deficit of heterozygous plants in some of these studies was determined by the use of starch gel in electrophoresis.…”

The genetic structure of the gynodioecious Kallstroemia grandiflora (Zygophyllaceae): the role of male sterility and colonization history

“…Few studies, have explored whether North American desert plants show evidence of declining genetic diversity with increasing latitude. Two columnar cacti from Baja California show such a trend, apparently as a consequence of repeated cycles of range expansion and contraction from Southern refuges (Nason et al, 2002;Clark-Tapia and Molina-Freaner, 2003). Very few studies, however, have explored this issue on mainland Mexico (Silva-Montellano and Eguiarte, 2003).…”