Inbreeding and outbreeding depression in Stylidium hispidum: implications for mixing seed sources for ecological restoration

Abstract

The benefits of composite rather than local seed provenances for ecological restoration have recently been argued, largely on the basis of maximizing evolutionary potential. However, these arguments have downplayed the potentially negative consequences of outbreeding depression once mixed provenances interbreed. In this study, we compared intraspecific F1 hybrid performance and molecular marker differentiation among four populations of Stylidium hispidum, a species endemic to Southwestern Australia. Multivariate ordination of 134 AFLP markers analyzed genetic structure and detected two clusters of paired sites that diverged significantly for marker variation along a latitudinal boundary. To test for outbreeding depression and to determine the consequences of molecular population divergence for hybrid fitness, we conducted controlled pollinations and studied germination and survival for three cross categories (within-population crosses, short- and long-distance F1 hybrids) for paired sites distributed within and between the two genetically differentiated regions. We found evidence of outbreeding depression in long-distance hybrids (111–124 km), and inbreeding depression among progeny of within-population crosses, relative to short-distance (3–10 km) hybrids, suggesting an intermediate optimal outcrossing distance in this species. These results are discussed in light of the evolutionary consequences of mixing seed sources for biodiversity restoration.

Genetic rescue versus outbreeding depression in Vallisneria americana: Implications for mixing seed sources for restoration

“…For example, despite differences in magnitude between quantitative traits and measures of genetic differentiation, Merilä and Crnokrak (2001) found the measures were positively correlated, suggesting that divergence in neutral markers may be indicative of the degree of genetic differentiation in quantitative traits. Likewise, Hufford et al (2012) were able to use molecular marker data to predict the scale of outbreeding depression while other studies have found measures of genetic diversity, like level of inbreeding and number of alleles, were consistent predictors of heterosis when mixing individuals from different populations (Pickup et al, 2013). Studies like these have led to the creation of plant restoration guidelines for the translocation of individuals that rely primarily on levels of genetic diversity and differentiation (e.g.…”

“…Managing the risks of using local or disparate sources of restoration stock, therefore, needs to account for the genetic context of natural source populations. In general, it appears that mixing slightly differentiated, inbred populations can lead to increased fitness whereas mixing extremely differentiated, locally adapted populations can result in outbreeding depression (Forrest et al, 2011;Hereford, 2009;Hufford et al, 2012;Pickup et al, 2013;Waser, 1993). For example, recent studies by Forrest et al (2011) and Hufford et al (2012) found that plants crossed at intermediate-distances outperform within-population crosses in terms of germination success and survival while long-distance hybrids show signs of outbreeding depression.…”

“…In general, it appears that mixing slightly differentiated, inbred populations can lead to increased fitness whereas mixing extremely differentiated, locally adapted populations can result in outbreeding depression (Forrest et al, 2011;Hereford, 2009;Hufford et al, 2012;Pickup et al, 2013;Waser, 1993). For example, recent studies by Forrest et al (2011) and Hufford et al (2012) found that plants crossed at intermediate-distances outperform within-population crosses in terms of germination success and survival while long-distance hybrids show signs of outbreeding depression. These studies furthermore concluded that spatial autocorrelation and genetic differentiation can be used to determine the optimal distances in which seeds can be mixed for restoration purposes (Forrest et al, 2011;Hufford et al, 2012).…”

“…For example, recent studies by Forrest et al (2011) and Hufford et al (2012) found that plants crossed at intermediate-distances outperform within-population crosses in terms of germination success and survival while long-distance hybrids show signs of outbreeding depression. These studies furthermore concluded that spatial autocorrelation and genetic differentiation can be used to determine the optimal distances in which seeds can be mixed for restoration purposes (Forrest et al, 2011;Hufford et al, 2012). In another study, Pickup et al (2013) found no evidence of outbreeding depression in crosses between pairs of populations across multiple generations, but they did detect evidence of heterosis.…”

Effects of crossing distance on performance of the native wildflower Lobelia siphilitica: Implications for ecological restoration1

“…Alternatively, if mating between individuals from distant populations disrupts co-adapted gene complexes or introduces maladaptive alleles to locally adapted populations, then their offspring can have lower fitness relative to the offspring of crosses between geographically proximate populations (i.e., outbreeding depression; Waser andWilliams 2001, Edmands 2007). Although the genetic mechanisms that can lead to heterosis and outbreeding depression are wellunderstood (Lynch and Walsh 1998), it has been difficult to predict the fitness effects of crosses between populations (Edmands and Timmerman 2003), and crossing studies have found evidence for both heterosis (e.g., Pickup et al 2013) and outbreeding depression (e.g., Hufford et al 2012).…”