So far in this course we have dealt entirely with the evolution of characters that are controlled by simple Mendelian inheritance at a single locus. There are notes on the course website about gametic disequilibrium and how allele frequencies change at two loci simultaneously, but we didn’t discuss them. In every example we’ve considered we’ve imagined that we could understand something about evolution by examining the evolution of a single gene. That’s the domain of classical population genetics. For the next few weeks we’re going to be exploring a field that’s actually older than classical population genetics, although the approach we’ll be taking to it involves the use of population genetic machinery. If you know a little about the history of evolutionary biology, you may know that after the rediscovery of Mendel’s work in 1900 there was a heated debate between the “biometricians” (e.g., Galton and Pearson) and the “Mendelians” (e.g., de Vries, Correns, Bateson, and Morgan). Biometricians asserted that the really important variation in evolution didn’t follow Mendelian rules. Height, weight, skin color, and similar traits seemed to

Human biochemical genetics

Biotic resistance describes the ability of resident species in a community to reduce the success of exotic invasions. Although resistance is a well-accepted phenomenon, less clear are the processes that contribute most to it, and whether those processes are strong enough to completely repel invaders. Current perceptions of strong, competition-driven biotic resistance stem from classic ecological theory, Elton’s formulation of ecological resistance, and the general acceptance of the enemies-release hypothesis. We conducted a meta-analysis of the plant invasions literature to quantify the contribution of resident competitors, diversity, herbivores and soil fungal communities to biotic resistance. Results indicated large negative effects of all factors except fungal communities on invader establishment and performance. Contrary to predictions derived from the natural enemies hypothesis, resident herbivores reduced invasion success as effectively as resident competitors. Although biotic resistance significantly reduced the establishment of individual invaders, we found little evidence that species interactions completely repelled invasions. We conclude that ecological interactions rarely enable communities to resist invasion, but instead constrain the abundance of invasive species once they have successfully established.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1461-0248.2004.00657.x

A meta‐analysis of biotic resistance to exotic plant invasions

1. Introductory remarks 2. Convolvulacaea 2. Scrophulariaceae, Gesneriaceae, Labiatae, etc. 4. Cruciferae, Papaveraceae, Resedaceae, etc. 5. Geraniaceae, Leguminosae, Onagraceae, etc. 6. Solanaceae, Primulaceae, Polygoneae, etc. 7. Summary of the heights and weights of the crossed and self-fertilised plants 8. Difference between crossed and self-fertilised plants in constitutional vigour and in other respects 9. The effects of cross-fertilisation and self-fertilisation on the production of seeds 10. Means of fertilisation 11. The habits of insects in relation to the fertilisation of flowers 12. General results Index.

The Effects of Cross and Self Fertilisation in the Vegetable Kingdom: CONVOLVULACEÆ

Charles Darwin recognized that flowering plants have an unrivalled diversity of sexual systems. Determining the ecological and genetic factors that govern sexual diversification in plants is today a central problem in evolutionary biology. The integration of phylogenetic, ecological and population-genetic studies have provided new insights into the selective mechanisms that are responsible for major evolutionary transitions between reproductive modes.

/pdf/the-evolution-of-plant-sexual-diversity-3oy16xml4e.pdf

The evolution of plant sexual diversity.

Do invasive plant species have greater phenotypic plasticity than non-invasive species? And, if so, how does this affect their fitness relative to native, non-invasive species? What role might this play in plant invasions? To answer these long-standing questions, we conducted a meta-analysis using data from 75 invasive/non-invasive species pairs. Our analysis shows that invasive species demonstrate significantly higher phenotypic plasticity than non-invasive species. To examine the adaptive benefit of this plasticity, we plotted fitness proxies against measures of plasticity in several growth, morphological and physiological traits to test whether greater plasticity is associated with an improvement in estimated fitness. Invasive species were nearly always more plastic in their response to greater resource availability than non-invasives but this plasticity was only sometimes associated with a fitness benefit. Intriguingly, non-invasive species maintained greater fitness homoeostasis when comparing growth between low and average resource availability. Our finding that invasive species are more plastic in a variety of traits but that non-invasive species respond just as well, if not better, when resources are limiting, has interesting implications for predicting responses to global change.

Do invasive species show higher phenotypic plasticity than native species and, if so, is it adaptive? A meta‐analysis

The Evolution and Function of Stylar Polymorphisms in Flowering Plants

Enantiostyly is a plant sexual polymorphism in which female sex organs are deflected to the left or right -- resulting in 'mirror-image' flowers -- but, although it occurs in at least a dozen unrelated families of flowering plants, its adaptive significance has been unclear. Here we show that a mendelian locus governs the inheritance of style orientation and that this curious form of sexual asymmetry functions to promote cross-pollination in bee-pollinated plants.

/pdf/solving-the-puzzle-of-mirror-image-flowers-2kuwb2shxn.pdf

Solving the puzzle of mirror-image flowers.

C4 plants have been reported to have Rubiscos with higher maximum carboxylation rates (kcatCO2 ) and Michaelis–Menten constants (Km) for CO2 (Kc) than the enzyme from C3 species, but variation in other kinetic parameters between the two photosynthetic pathways has not been extensively examined. The CO2/O2 specificity (SC/O), kcatCO2 , Kc, and the Km for O2 (Ko) and RuBP (Km-RuBP), were measured at 25 � C, in Rubisco purified from 16 species of Flaveria (Asteraceae). Our analysis included two C3 species of Flaveria, four C4 species, and ten C3-C4 or C4-like species, in addition to other C4 (Zea mays and Amaranthus edulis) and C3 (Spinacea oleracea and Chenopodium album) plants. The SC/O of the C4 Flaveria species was about 77 mol mol 21 , which was approximately 5% lower than the corresponding value in the C3 species. For Rubisco from the C4 Flaverias kcatCO2 and Kc were 23% and 45% higher, respectively, than for Rubisco from the C3 plants. Interestingly, it was found that the Ko for Rubisco from the C4 species F. bidentis and F. trinervia were similar to the C3 Flaveria Rubiscos (;650 mM) while the Ko for Rubisco in the C4 species F. kochiana, F. australasica, Z. mays, and A. edulis was reduced more than 2-fold. There were no pathway-related differences in Km-RuBP. In the C3-C4 species kcatCO2 and Kc were generally similar to the C3 Rubiscos, but the Ko values were more variable. The typical negative relationships were observed between SC/O and both kcatCO2 and Kc, and a strongly positive relationship was observed between kcatCO2 and Kc. However, the statistical significance of these relationships was influenced by the phylogenetic relatedness of the species.

/pdf/the-biochemistry-of-rubisco-in-flaveria-1cqln5t0ss.pdf

The biochemistry of Rubisco in Flaveria

Which conditions favour the evolution of hermaphroditism or separate sexes? One classical hypothesis states that an organism’s mode of locomotion (if any) when searching for a mate should influence breeding system evolution. We used published phylogenies to reconstruct evolutionary changes in adult mate-search efficiency and breeding systems among multicellular organisms. Employing maximum-likelihood analyses, we found that changes in adult mate-search efficiency are significantly correlated with changes in breeding system, and this result is robust to uncertainties in the phylogenies. These data provide the first statistical support, across a broad range of taxa, for the hypothesis that breeding systems and mate-search efficiency did not evolve independently. We discuss our results in context with other causal factors, such as inbreeding avoidance and sexual specialization, likely to affect breeding system evolution.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1420-9101.2008.01524.x

Moving to mate: the evolution of separate and combined sexes in multicellular organisms

Enantiostyly, the deflection of the style to the left or right side of the floral axis, is a sexual polymorphism reported from at least 10 angiosperm families in both monocotyledons and dicotyledons. To investigate variation in the enantiostylous condition, we examined sex‐organ reciprocity and the arrangements of left‐ and right‐styled flowers in 15 enantiostylous species from eight genera in six families. Enantiostyly can be expressed at three distinct levels of structural organization. In “monomorphic enantiostyly,” individual plants produce both floral forms, either mixed within an inflorescence or segregated between left‐ and right‐styled inflorescences. In “dimorphic enantiostyly,” plants are exclusively left‐ or right‐styled and this condition is a genetic polymorphism. Enantiostyly is most commonly associated with the reciprocal deflection of a pollinating anther (“reciprocal enantiostyly”), although there is a continuum in stigma‐anther position, ranging from no reciprocal anther to complete reci...

https://www.jstor.org/stable/10.1086/378537

Linley K. Jesson

Papers

The Evolution and Function of Stylar Polymorphisms in Flowering Plants

Solving the puzzle of mirror-image flowers.

The biochemistry of Rubisco in Flaveria

Moving to mate: the evolution of separate and combined sexes in multicellular organisms

The comparative biology of mirror-image flowers.