Reproductive success and genetic divergence among varieties of the rare and endangered Astragalus cremnophylax (Fabaceae) from Arizona, USA

Abstract

Populations of Astragalus cremnophylax from Arizona and related A. humillimus from New Mexico were assessed for morphological, reproductive, genetic, and ecological differences. Results suggest that some of the taxa (i.e., A. cremnophylax var. cremnophylax and A. humillimus) are poor reproducers and environmental fluctuation is not likely a factor contributing to low fecundity in these species. Astragalus cremnophylax var. cremnophylax appears to have low fecundity due to inbreeding depression. Allozyme data from 18 loci show little within-population and taxon genetic variability. Most genetic variability is distributed among populations and taxa. The population of A. cremnophylax var. cremnophylax from the Grand Canyon (South Rim) was genetically depauperate, indicative of the bottleneck caused by historic trampling at this viewpoint. Cape Final, a population of A. cremnophylax var. cremnophylax on the Grand Canyon (North Rim) is genetically different from typical materials of this taxon (South Rim) and is more closely related to other taxa within this species complex. However, the other varieties of A. cremnophylax are more closely related to A. humillimus than the population at Cape Final, suggesting potential species status for Cape Final materials based on allozyme divergence.

Population decline in Adenostoma sparsifolium (Rosaceae): an ecogenetic hypothesis for background extinction‡

“…In accordance with genetic load theory, S/O ratios are not distributed randomly among seed plants but differ at high levels of significance between species in terms of life form, longevity, breeding system, and genetic variability (Wiens, 1984; Wiens et al ., 1987, 2002; Nickrent & Wiens, 1989; Lamont & Wiens, 2003; Allphin, Brian & Matheson, 2005).…”

“…Because genetic variation in natural populations is often associated with reproductive fitness (Ledig, 1986; Wiens et al ., 1989; 2002; Levin, 1991; Allphin & Windham, 2002; Allphin, Brian & Matheson, 2005), we assessed genetic variation using starch gel electophoresis within and between two populations of co‐occurring chamise and redshank at the lower Stunt Road and upper Castro Crest study sites. The variation was then compared with the measures of fitness we studied.…”

The mechanism of background extinction

“…We stress that among these species there is little evidence that the high rates of embryonic abortion rates are strongly influenced by limited resource availability or their re‐allocation (Harper & Wallace, 1987; Wiens et al ., 1987, 2002, 2011; Marshall & Ludlam, 1989; Owen, 1995; Allphin, Wiens & Harper, 2002; Allphin, Brian & Matheson, 2005, and additional citations listed in those publications). The species in question appear to be long‐lived relicts; seedlings are typically rare, but precise, long‐term demographic data for seedling survival are available only for Adenostoma sparsifolium Torr.…”

Genetic Variation in Past and Current Landscapes: Conservation Implications Based on Six Endemic Florida Scrub Plants

“…Many of our study species show substantial fluctuations in relation to fire [48,49], and lack of fire history data across our study populations may hamper our ability to understand geographic patterns of genetic variation. Past events such as bottlenecks, founder events, low effective population sizes, and local extinctions may also have affected patterns of genetic variation in idiosyncratic ways [89,90].…”