Severe outbreeding and inbreeding depression maintain mating system differentiation inEpipactis(Orchidaceae)

Abstract

In hermaphroditic plants, theory for mating system evolution predicts that populations will evolve to either complete autonomous selfing (AS) or complete outcrossing, depending on the balance between automatic selection favouring self-fertilization and costs resulting from inbreeding depression (ID). Theory also predicts that selection for selfing can occur rapidly and is driven by purging of genetic load and the loss of ID. Therefore, selfing species are predicted to have low levels of ID or even to suffer from outbreeding depression (OD), whereas predominantly outcrossing species are expected to have high levels of ID. To test these predictions, we related the capacity of AS to the magnitude of early-acting inbreeding or OD in both allogamous and autogamous species of the orchid genus Epipactis. For each species, the level of AS was assessed under controlled greenhouse conditions, whereas hand-pollinations were performed to quantify early costs of inbreeding or OD acting at the level of fruit and seed production. In the autogamous species, the capacity of AS was high (> 0.72), whereas in the allogamous species AS was virtually absent (< 0.10). Consistent with our hypothesis, allogamous Epipactis species had significantly higher total ID (average: 0.46) than autogamous species, which showed severe costs of OD (average: -0.45). Overall, our findings indicate that strong early-acting ID represents an important mechanism that contributes to allogamy in Epipactis, whereas OD may maintain selfing in species that have evolved to complete selfing.

Immigrant and extrinsic hybrid seed inviability contribute to reproductive isolation between forest and dune ecotypes of Epipactis helleborine (Orchidaceae)

“…Because several studies have shown that Epipactis species can rapidly evolve towards selfing (Pedersen and Ehlers , Squirrell et al , Brys and Jacquemyn ) and because selfing itself can act as a reproductive barrier preventing interspecific mating (Brys et al ), we investigated whether the capacity to self autonomously differed between the two ecotypes. Two months before flowering, ten individuals were selected in one forest and one dune population and transferred to a pollinator‐free greenhouse.…”

Reproductive Assurance Maintains Red-Flowered Plants of Lysimachia arvensis in Mediterranean Populations Despite Inbreeding Depression

“…This expression, proposed by Sletvold et al (2012) or Delmas et al (2014), derives and is equivalent to that from Ågren and Schemske (1993). The inbreeding depression coefficient ranges between 1 and −1; if W o > W s , δ values are positive and inbreeding depression exists, while in W i > W o , δ values are negative and outbreeding depression occurs (Brys and Jacquemyn, 2016). Inbreeding depression coefficients for each color morph and site were calculated separately at different life stages (partial inbreeding depression coefficients) and then, cumulative inbreeding depression coefficients were also calculated.…”

Dynamics, Persistence, and Genetic Management of the Endangered Florida Panther Population

“…Negative fitness responses resulting from mating between individuals from highly divergent populations of copepods were noted by Hwang et al (). Other examples of outbreeding depression in varied species of plants are provided by Fenster and Gallaway (), Waser et al (), Goto et al (), and Brys and Jacquemyn (). In general, however, outbreeding depression is thought to be less of a concern when implementing conservation measures such as genetic introgression (Miller et al , Whiteley et al ).…”

“…Hedrick et al () provided evidence for the declining effect of genetic introgression on the Isle Royale population of wolves after only 2 or 3 generations. Whereas heterosis is expected to increase individual fitness, it can also result in outbreeding depression (Fenster and Gallaway , Waser et al , Goto et al , Waller , Brys and Jacquemyn ). Depending on the mechanisms, outbreeding depression may not become evident until generations subsequent to the first filial (F1) generation (Pickup et al , Waller ).…”