Predicting heterosis and inbreeding depression from population size and density to inform management efforts

Söderquist, Linus; Broberg, Anna; Rosenberg, Viktor; Sletvold, Nina

doi:10.1111/1365-2664.13643

Cited by 5 publications

(11 citation statements)

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“…Moreover, our crosses showed that interspecific crosses resulted in either the same (in G. conopsea) or a higher (in G. densiflora) proportion of viable seeds than intraspecific crosses, which may be due to the masking of recessive deleterious alleles expressed during seed development (i.e., hybrid vigor). These crosses further showed that selfing causes a sharp decrease in seed viability in both species, in line with previous results (Sletvold et al 2012;Söderquist et al 2020), suggesting that selfpollination represents a stronger selective pressure than IPT in this system.…”

Section: No Cost Of Pollinator Sharingsupporting

confidence: 91%

“…2012; Söderquist et al. 2020), suggesting that self‐pollination represents a stronger selective pressure than IPT in this system.…”

Section: Discussionmentioning

confidence: 78%

“…Plants were bagged before and after the crosses to exclude pollinators. After fruit collection, seeds were observed under a dissecting microscope as described in Söderquist et al (2020) to estimate seed viability as the proportion of seeds bearing an embryo.…”

Section: Controlled Crossesmentioning

confidence: 99%

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Extensive pollinator sharing does not promote character displacement in two orchid congeners

et al. 2022

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Pollinator sharing between close relatives can be costly and can promote pollination niche partitioning and floral divergence.This should be reflected by a higher species divergence in sympatry than in allopatry. We tested this hypothesis in two orchid congeners with overlapping distributions and flowering times. We characterized floral traits and pollination niches and quantified pollen limitation in 15 pure and mixed populations, and we measured phenotypic selection on floral traits and performed controlled crosses in one mixed site. Most floral traits differed between species, yet pollinator sharing was extensive. Only the timing of scent emission diverged more in mixed sites than in pure sites, and this was not mirrored by the timing of pollinator visitation. We did not detect divergent selection on floral traits. Seed production was pollen limited in most populations but not more severely in mixed sites than in pure sites. Interspecific crosses produced the same or a higher proportion of viable seeds than intraspecific crosses. The two orchid species attract the same pollinator species despite showing divergent floral traits. However, this does not promote character displacement, implying a low cost of pollinator sharing. Our results highlight the importance of characterizing both traits and ecological niches in character displacement studies.

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Section: No Cost Of Pollinator Sharingsupporting

confidence: 91%

“…2012; Söderquist et al. 2020), suggesting that self‐pollination represents a stronger selective pressure than IPT in this system.…”

Section: Discussionmentioning

confidence: 78%

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Extensive pollinator sharing does not promote character displacement in two orchid congeners

et al. 2022

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“…Both populations contain several thousand flowering individuals, with considerable variation in local density (1 to >20 plants/m 2 ). A previous pollen-staining experiment in the Störlinge population documented a 72% increase in the probability of self-pollen deposition in sparse patches (1-3 plants/m 2 ) compared to dense ones (>8 plants/m 2 ; Söderquist et al, 2020). Controlled crosses in the two populations have documented substantial inbreeding depression, with self fertilization resulting in 29% (Alböke) and 56% (Störlinge) fewer seeds than produced by outcrossing (Söderquist et al, 2020).…”

Section: Study Species and Sitesmentioning

confidence: 96%

“…If also seed dispersal mainly is short‐range, local genetic substructuring should depend on density. However, previous controlled crossings have also documented substantial inbreeding depression at the seed stage in Scandinavian populations (Sletvold et al, 2012; Söderquist et al, 2020), potentially weakening the fine‐scale genetic structure. Here, we used SNPs to test the prediction of density‐dependent genetic structure in two large populations with extensive small‐scale density variation, one of which is the population with the documented density‐dependent pollen dispersal mentioned above.…”

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Fine‐scale genetic structure in the orchid Gymnadenia conopsea is not associated with local density of flowering plants

Sletvold,

Joffard,

Söderquist

2024

American J of Botany

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PremiseDensity‐dependent pollinator visitation can lead to density‐dependent mating patterns and within‐population genetic structure. In Gymnadenia conopsea, individuals in low‐density patches receive more self pollen than individuals in high‐density patches, suggesting higher relatedness at low density. Ongoing fragmentation is also expected to cause more local matings, potentially leading to biparental inbreeding depression.MethodsTo evaluate whether relatedness decreases with local density, we analyzed 1315 SNP loci in 113 individuals within two large populations. We quantified within‐population genetic structure in one of the populations, recorded potential habitat barriers, and visualized gene flow using estimated effective migration surfaces (EEMS). We further estimated the magnitude of biparental inbreeding depression that would result from matings restricted to within 5 m.ResultsThere was no significant relationship between local density and relatedness in any population. We detected significant fine‐scale genetic structure consistent with isolation by distance, with positive kinship coefficients at distances below 10 m. Kinship coefficients were low, and predicted biparental inbreeding depression resulting from matings within the closest 5 m was a modest 1–3%. The EEMS suggested that rocks and bushes may act as barriers to gene flow within a population.ConclusionsThe results suggest that increased self‐pollen deposition in sparse patches does not necessarily cause higher selfing rates or that inbreeding depression results in low establishment success of inbred individuals. The modest relatedness suggests that biparental inbreeding depression is unlikely to be an immediate problem following fragmentation of large populations. The results further indicate that habitat structure may contribute to governing fine‐scale genetic structure in G. conopsea.

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Genetic differentiation and diversity do not explain variation in heterosis or inbreeding depression: empirical evidence from a long-lived iteroparous plant

Söderquist,

Karrenberg,

Sletvold

2024

Conserv Genet

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Assisted gene flow can restore genetic diversity when genetic drift has driven deleterious alleles to high frequencies in small, isolated populations. Previous crosses among 20 populations of Gymnadenia conopsea documented the strongest heterosis and the weakest inbreeding depression in sparse and small populations, consistent with fixation of mildly deleterious alleles by genetic drift. We genotyped the populations used for crosses, and used 1200–1728 SNPs to test the following predictions: (1) heterosis increases with genetic differentiation (FST) to donor populations and decreases with genetic diversity in the recipient population, (2) inbreeding depression increases with genetic diversity, and (3) genetic diversity increases, and mean FST to other populations decreases, with population size and density. Pairwise FST ranged from very low to moderate (0.005–0.20) and genetic diversity varied moderately among populations (proportion of polymorphic loci = 0.52–0.75). However, neither FST between populations, nor genetic diversity in the recipient population, were related to the strength of heterosis. There was also no association between genetic diversity and the strength of inbreeding depression. Genetic diversity increased and mean FST decreased with population size, consistent with reduced diversity and increased differentiation of small populations by genetic drift. The results indicate that the loci conferring heterosis are not mirrored by overall population differentiation, and limited additional information on potential source populations for genetic rescue is gained by the genetic data. Instead, the use of controlled crosses can directly reveal positive effects of introducing new genetic material, and is a simple method with high potential in conservation.

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Predicting heterosis and inbreeding depression from population size and density to inform management efforts

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 5 publications

References 66 publications

Extensive pollinator sharing does not promote character displacement in two orchid congeners

Extensive pollinator sharing does not promote character displacement in two orchid congeners

Fine‐scale genetic structure in the orchid Gymnadenia conopsea is not associated with local density of flowering plants

Genetic differentiation and diversity do not explain variation in heterosis or inbreeding depression: empirical evidence from a long-lived iteroparous plant

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