Linking genetic diversity, mating patterns and progeny performance in fragmented populations of a Mediterranean shrub

Abstract

Summary1. The long-term persistence of fragmented plant populations is predicted to be threatened by a loss of genetic variability and increasing inbreeding, which might lower offspring fitness through inbreeding depression. Assessing plant progeny performance together with measurements of genetic diversity and mating patterns is therefore essential in the understanding of the role of the historical (i.e. genetic diversity in adults) and contemporary (i.e. current mating patterns) genetic effects of fragmentation on inbreeding depression, thus, on recruitment potential. 2. We evaluated genetic diversity, mating patterns and progeny performance at different life stages in seven populations of a Mediterranean shrub (myrtle Myrtus communis) that differed in size and degree of isolation (Large, Small-connected and Small-isolated populations). The study was conducted in the Guadalquivir Valley (SW Spain), a chronically and severely fragmented landscape characterized by c. 1% of woodland cover. 3. Parameters of genetic diversity (A r , H o and H e ) of adult plants were in general higher in the Large populations than in the two types of Small populations, which were similar. Outcrossing rates were higher in Small-connected populations (mean: t m = 0AE62), intermediate in Large (t m = 0AE35) and lower in Small-isolated populations (t m = 0AE13), and were positively correlated with the genetic diversity of progenies. 4. Several measurements of progeny performance were higher in Small-connected populations, intermediate in Large and lower in Small-isolated populations, in particular those related with the quantity of viable seedlings produced (germination and survival). Outcrossing rates rather than the genetic diversity of adult plants were positively correlated with these measurements of progeny performance. 5. We thus conclude that contemporary mating patterns (outcrossing rates) have a more critical influence on progeny performance than either population fragmentation or the historical levels of genetic diversity. 6. Synthesis and applications. It may be possible to enhance either the fitness or certain levels of genetic diversity in progenies by promoting outcrossed matings in fragmented populations of selfcompatible plant species. In our study species, this would be feasible either by controlling honeybee Apis mellifera hives or maintaining and ⁄ or enhancing landscape connectivity around small patches.

The genetic diversity of Sardinian myrtle (Myrtus communis L.) populations

“…A major influence on this result was the high variability contributed by the candidate cultivars, which were selected from wild populations growing in several distinct environments across Sardinia (Table 1). An additional positive factor relates to the significant degree of self-pollination of the species (Mulas and Fadda, 2004;González-Varo et al 2010), since it has been established that this mating system tends to conserve within population genetic diversity more effectively than does cross-pollination (Barrett, 2013;Cowling, 2013). Both the present ISSR genotyping and the AFLP-based system used by Agrimonti et al (2007) uphold the idea that within population gene flow is much more prevalent than that occurring between populations.…”

Mating patterns and pollinator mobility are critical traits in forest fragmentation genetics

“…There are numerous cases in the literature that demonstrate a link between the offspring fitness of animal-pollinated woody plants and increasing selfing caused by habitat fragmentation (Cascante et al, 2002;Fuchs et al, 2003;Quesada et al, 2004;Hirayama et al, 2007;González-Varo et al, 2010;Breed et al, 2012a). The mechanism whereby fitness is influenced because of increased selfing has been clearly articulated in the literature on inbreeding and inbreeding depression (for example, Keller and Waller (2002)).…”

“…There are numerous studies that demonstrate how reduced pollen diversity received into plant canopies can associate with reduced offspring fitness in fragmented systems (Hoebee and Young, 2001;Cascante et al, 2002;Fuchs et al, 2003;González-Varo et al, 2010;Breed et al, 2012a); however, more work is required to investigate the mechanism of this fitness impact. Increased correlated paternity has been hypothesised to associate with less pollen competition to fertilise receptive ovules (Breed et al, 2012a).…”

Transplant experiments reveal edge effects and inconsistent maternal effects on seedling performance in the pioneer tree <i>Ficus tonduzii</i> (Moraceae)

“…While distance from the nearest forest edge was significant in predicting ex situ growth, it was again not linearly related to ex situ growth (basal diameter: R 2 ＝0.69, P＝0.26, height: P＝0.83), potentially due to small sample size of maternal trees. Seed quality is often reduced for trees in small fragments or for isolated trees in fragmented landscapes (e.g., Cascante et al 2002;reviewed in Sugiyama and Peterson 2013a) due to inbreeding depression (Aguilar et al 2008;Gonzalez-Varo et al 2010). Such effects of forest fragmentation may impact both maternal and paternal (pollen) trees and seeds from these trees may result in small seedlings with reduced performance.…”