Population size, viability and genetic diversity in the orchid Gymnadenia conopsea

In this thesis, I combined controlled crosses with genetic and demographic data to examine how a main conservation value indicator, population size, was associated with estimates of population viability. I focused on the still common, but decreasing, perennial orchid Gymnadenia conopsea at two spatial scales—locally on the island Öland, in SE Sweden, and regionally across Scandinavia. I aimed to determine whether: (1) population size or density could predict the strength of heterosis and inbreeding depression, (2) local density variation within populations affected self-pollen transfer and relatedness of individuals, (3) genetic diversity increased with population size or density, and genetic differentiation and diversity predicted the strength of heterosis, (4) population growth rate increased with population size and genetic diversity, and (5) large-scale genetic structure indicated several independent colonization events in Scandinavia, with clear genetic groups and genetic diversity hotspots. I found heterosis to decrease and inbreeding depression to increase with local density in Öland populations. The proportion of deposited self-pollen decreased with local density, but established individuals located in sparse patches were not more related than those in dense ones, possibly due to high inbreeding depression at early life stages. Genetic diversity increased with population size, but neither population genetic differentiation or within population genetic diversity was related to the strength of heterosis or inbreeding depression. I found the majority of Öland populations to be declining, and population growth rate to increase with population size. This relationship was driven by higher survival in large populations, and most likely reflects that population size was positively associated with local habitat quality and stability. Population growth rate was not related to the amount of genetic diversity within the population, suggesting declines are not driven by genetic erosion. At the Scandinavian scale, I identified three genetic groups, consistent with two independent post-glacial colonizations followed by admixture. High genetic diversity was found in southern and central populations, while low diversity was seen in marginal populations along the Atlantic coast. In conclusion, population size was associated with both genetic diversity and population viability at the Öland scale. Genetic diversity was not related to the strength of heterosis or population viability, suggesting that demographic metrics can be more informative than genetic metrics, regarding conservation priority

Population size, viability and genetic diversity in the orchid Gymnadenia conopsea

In this thesis, I combined controlled crosses with genetic and demographic data to examine how a main conservation value indicator, population size, was associated with estimates of population viability. I focused on the still common, but decreasing, perennial orchid Gymnadenia conopsea at two spatial scales—locally on the island Öland, in SE Sweden, and regionally across Scandinavia. I aimed to determine whether: (1) population size or density could predict the strength of heterosis and inbreeding depression, (2) local density variation within populations affected self-pollen transfer and relatedness of individuals, (3) genetic diversity increased with population size or density, and genetic differentiation and diversity predicted the strength of heterosis, (4) population growth rate increased with population size and genetic diversity, and (5) large-scale genetic structure indicated several independent colonization events in Scandinavia, with clear genetic groups and genetic diversity hotspots. I found heterosis to decrease and inbreeding depression to increase with local density in Öland populations. The proportion of deposited self-pollen decreased with local density, but established individuals located in sparse patches were not more related than those in dense ones, possibly due to high inbreeding depression at early life stages. Genetic diversity increased with population size, but neither population genetic differentiation or within population genetic diversity was related to the strength of heterosis or inbreeding depression. I found the majority of Öland populations to be declining, and population growth rate to increase with population size. This relationship was driven by higher survival in large populations, and most likely reflects that population size was positively associated with local habitat quality and stability. Population growth rate was not related to the amount of genetic diversity within the population, suggesting declines are not driven by genetic erosion. At the Scandinavian scale, I identified three genetic groups, consistent with two independent post-glacial colonizations followed by admixture. High genetic diversity was found in southern and central populations, while low diversity was seen in marginal populations along the Atlantic coast. In conclusion, population size was associated with both genetic diversity and population viability at the Öland scale. Genetic diversity was not related to the strength of heterosis or population viability, suggesting that demographic metrics can be more informative than genetic metrics, regarding conservation priority

Data from: Fine-scale genetic structure in the orchid Gymnadenia conopsea is not associated with local density of flowering plants

<p><span><strong>Premise</strong>:</span><span> Density-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.</span></p> <p><span><strong>Methods</strong>: </span><span>To evaluate whether relatedness decreases with local density, we analysed 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.</span></p> <p><span><strong>Results</strong>: </span><span>There 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%.</span> <span>EEMS suggested that rocks and bushes may act as barriers to gene flow within a population.</span></p> <p><span><strong>Conclusions</strong>: </span><span>The 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 <em>G. conopsea</em>.</span></p><p>Funding provided by: Swedish Research Council for Environment Agricultural Sciences and Spatial Planning<br>Crossref Funder Registry ID: https://ror.org/03pjs1y45<br>Award Number: 2018-01397</p&gt

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

Premise: Density-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. Methods: To 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. Results: There 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. Conclusions: The 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

Data from: The price of looking sexy: visual ecology of a three level predator-prey system

Colour signals and colour vision play a pivotal role in intraspecific communication and predator-prey interactions. However, the costs of expressing conspicuous sexual signals at multiple trophic levels have been largely overlooked. Sexual signals can also experience character displacement in sympatric populations of closely-related species, leading to potential changes in conspicuousness. We here investigate a bird-damselfly-fruit fly predator-prey system, where two closely related damselfly species have conspicuous, sexually selected wing coloration. The damselflies can occur in sympatry and allopatry and reproductive character displacement in the coloration size has been previously reported. We quantify the damselfly wing reflectance from replicated sympatric and allopatric populations, and use receptor noise models to investigate the visual discriminability of the wing coloration for the bird, damselfly and fly vision systems, against natural backgrounds. We perform electroretinograms to study damselfly eye sensitivity. We also estimate damselfly predation risk in natural populations. We find that the chromatic component of wing coloration makes males highly discriminable to the predator, but not to the prey. However, female wing coloration is predominantly cryptic for the predator and prey, and interestingly, also for male damselflies. A female being cryptic to conspecifics likely reduces male harassment. The estimates of predation risk partially support the discriminability results. We also show that there is no difference in colour vision sensitivity between the two damselfly species and sexes, and no difference in wing coloration or its discriminability between sympatric and allopatric populations. Our results suggest that sexually selected traits can be antagonistically selected by predators and prey, and that this antagonistic selection can be sex-dependent: males are paying a large cost in terms of conspicuousness, while females remain mostly cryptic. Our study thus emphasizes the need for investigating visual communication at multi-trophic levels since the degree of colour discriminability can differ between predators, prey and the focal species

Effects of experimental rewilding on butterflies, bumblebees and grasshoppers

Grassland ecosystems are species-rich habitats that are rapidly declining globally posing serious concerns for biodiversity conservation. This situation is particularly relevant in agricultural areas in Europe. As traditional management practices and livestock grazing regimes ceased, rewilding could be a potential avenue to tackle current biodiversity declines. To test this hypothesis, we set up a 3-year experiment where 12 horses were introduced in three 10-hectare enclosure replicates (four horses per enclosure). Horses were kept without supplementary feeding to mimic ecosystem functions of wild horses. We applied Generalized Linear Mixed Effects Models and a backward stepwise model selection procedure to elucidate factors that modulate insect richness induced by grazing. Our results show that plant species richness, the proportion of flowers and plant height play a significant role for butterfly and bumblebee richness, while the opposite effect was detected for grasshoppers. However, the effect on grasshoppers was counterbalanced by increased grasshopper species richness in habitats adjacent to horse latrines

Data from: Antagonistic natural and sexual selection on wing shape in a scrambling damselfly

Wings are a key trait underlying the evolutionary success of birds, bats, and insects. For over a century, researchers have studied the form and function of wings to understand the determinants of flight performance. However, to understand the evolution of flight, we must comprehend not only how morphology affects performance, but also how morphology and performance affect fitness. Natural and sexual selection can either reinforce or oppose each other, but their role in flight evolution remains poorly understood. Here, we show that wing shape is under antagonistic selection with regard to sexual and natural selection in a scrambling damselfly. In a field setting, natural selection (survival) favored individuals with long and slender forewings and short and broad hindwings. In contrast, sexual selection (mating success) favored individuals with short and broad forewings and narrow-based hindwings. Both types of selection favored individuals of intermediate size. These results suggest that individuals face a trade-off between flight energetics and maneuverability and demonstrate how natural and sexual selection can operate in similar directions for some wing traits, that is, wing size, but antagonistically for others, that is, wing shape. Furthermore, they highlight the need to study flight evolution within the context of species’ mating systems and mating behaviors

Antagonistic natural and sexual selection on wing shape in a scrambling damselfly

Wings are a key trait underlying the evolutionary success of birds, bats, and insects. For over a century, researchers have studied the form and function of wings to understand the determinants of flight performance. However, to understand the evolution of flight, we must comprehend not only how morphology affects performance, but also how morphology and performance affect fitness. Natural and sexual selection can either reinforce or oppose each other, but their role in flight evolution remains poorly understood. Here, we show that wing shape is under antagonistic selection with regard to sexual and natural selection in a scrambling damselfly. In a field setting, natural selection (survival) favored individuals with long and slender forewings and short and broad hindwings. In contrast, sexual selection (mating success) favored individuals with short and broad forewings and narrow-based hindwings. Both types of selection favored individuals of intermediate size. These results suggest that individuals face a trade-off between flight energetics and maneuverability and demonstrate how natural and sexual selection can operate in similar directions for some wing traits, that is, wing size, but antagonistically for others, that is, wing shape. Furthermore, they highlight the need to study flight evolution within the context of species’ mating systems and mating behaviors

Reflectance spectra of damselfly wings.

This compressed file contains the reflectance spectra data for each individual damselfly. The folders are organized by sex (male/female), then by population, and then by species (virgo/splendens). The sympatric populations are: Focks, Husby, Länna, Skytt, Stora and Valsk. The allopatric populations for C. virgo are Ekdal, Flenm, Läbyv, Nackb, Riala and Svana. The allopatric populations for C. splendens are Bergs, Gurre, Hällby, Orsun, Vatve and Vikst. Each individual file is named as follows: Population_sex (m for male/f for female) species (v for virgo/s for splendens)_individual number_repeated measurement. For example Hallb_fs_05_02 means that this individual was captured at Hallb population, it is the splendens female number 5, and this is the second repeated measurement