Plant Reproduction and Ecology Quiz

Nectar and Nectarines: Evolution

• Nectar is a nexus of plant-animal interactions, providing a habitat for microbial interactions.
• Nectar contains nesocodin, a compound that makes nectar appear red.
• Nectar attracts specific pollinators.
• Nectar-producing organs exhibit diverse structures and mechanisms across angiosperms.

Nectar Evolution

• Nectar and nectary diversity can be examined through an evolutionary developmental framework.
• Nectary development involves factors that coordinate structure and function.
• Gain or loss of nectaries influences nectary core components and characteristics.
• Mechanisms behind nectar differences between species include:
  • Some plants do not produce nectar because they are pollinated by wind or water.
  • Primary pollinator rewards (e.g., oils, scents, pollen) may have shifted.
  • The mating system may have shifted. (This appears to be related to self-pollination)

Shifts in Mating Systems

• Outcrossing occurs between different individuals.
• Selfing occurs via self-pollination.
• Approximately 20% of flowering plants are self-pollinating.
• Self-pollination relates to reductions in floral traits like flower size, pollen, scent, nectar, floral pigmentation, etc.
• These traits often evolve together, due to phenotypic intergration
• Traits from different modules can also evolve independently

Dr. Liao's Research

• Investigation focuses on understanding whether reduced nectar production evolves independently from other floral traits in selfing syndrome.
• Methods include: Studying Ipomea cordatotriloba (CORD) versus Ipoema lacunosa (LAC) to identify modules using recombinant inbred lines(RILS).
• RILS are created via
• crossed CORD and LAC parents to create F1 hybrids
• selfing F1 created F2 generation
• the F2 is a shuffle population of different genotypes/phenotypes
• Dr. Liao selfed each F2 line, which resulted in more homozygous F3
• F3 is used to identify genomic regions related to phenotypes of interest via statistical methods

Measuring Phenotypic Traits

• Methods employed to measure phenotypic traits include: nectar volume, sugar content, nectary size, seed traits (length, width, mass).
• Statistical comparisons are done between traits to find significant differences.
• Genetic data is used to understand variance using variance-covariance components.
• ddRADseg is used to find genotype and phenotype data.
• The results indicate three distinct clusters, with seeds, nectar, and flowers forming their own clusers
• The analysis finds that correlations within clusters are higher than between clusters

Genetic Basis of Nectary Development

• Nectaries are important for flowering plant development.
• Transcription factors (Crab's Claw in core eudicots & Stylish in non-core eudicots) affect nectary development.
• Monocots often have septal nectaries, embedded within the gynoecium, which are visually detected through plant sectioning.

Single-cell RNA Sequencing

• ScRNA-seq is used to identify clusters of cells that are associated with nectaries in bananas.
• Methods
• Nectary cells are located at the top half of the gynoecium in bananas "Ice Cream" (Musa)
• comparison between the top/bottom halves of gynoecium
• ScRNA-seq clusters are used to identify
• metabolic genes associated with nectary functions (sucrose synthase, sucrose-phosphate synthase, B-fructofuranosidase)
• transcription factors which include copies of AG, AGL11/STK, YABBY2
• Drawbacks of this technique
• Spatial information of cell placement is not available in ScRNA-seq.
• Spatial information, as well as cell types, have to be inferred.
• To get complete information on cells, combining it with spatial transcriptomics will allow for better understanding of the issue.

Radial Branching in Brown Algae

• Brown algae, stramenopiles, are marine organisms that vary in size.
• They are independently evolved from all other multicellular eukaryotes.
• Similar branching patterns exist between brown algae species and A. Thaliana.
• Branching patterns significantly influence the 3D structure of an organism.
• Radial branching occurs in Fucales and Sargassaceae.
• Growth occurs at terminal or apical meristems in stems, this trait mirrors those in higher plants.
• Sympodial and monopodial are different types of branching in brown algae.

Mapping Branching in Sargassaceae

• Research suggests that 5000 brown algae species exist.
• Transcriptomics (without needing a full genome) is used to examine the genomes of these species.
• New data was combined with existing data to understand CA Stephanocystis and Sargassums.

Studying Branching Developments

• Dichotomous (sympodial) branching is hypothesized to stem from a singular apical cell.
• The apical cell periodically splits to create two dichotomous branches.
• In terms of radial branching, apical cell division patterns influence the overall branching patterns and eventually organismal form.

Plasticity

• Plasticity is the ability of a genotype to express different phenotypes depending on environmental conditions.
• Examples include
• Bicyclus Ananya butterfly eyespots vary based on the wet/dry seasons.
• Mouse lines might have differences in size or whisker length given the same genome
• This can be related to nutrient levels, genetic mutation, etc,

Why Plasticity Impacts Evolution

• Plasticity can allow populations to survive in new or changing environments.
• This "buying time" allows beneficial mutations to occur (plasticity can lead to evolution).
• Plastic responses enable early expressions of adaptive phenotypes.
• Plasticity is sometimes critical for phenotypic changes, which may eventually lead to genetic changes and mutations, enabling adaptation.
• It can help ensure the survival of a species enabling its existence through challenging conditions within the niche.

Case Study of Tomato Hornworms

• Temperature affects the pigmentation of tomato hornworm.
• Lower temperatures result in black pigmentation.
• Higher temperatures result in green pigmentation.
• Heat shocking plastic hornworms can lead to either the retention of a monophenic black color, or a polyphenic green color.
• Through breeding, they were able to increase and decrease plasticity over generations of the black and green polyhenic variations.
• The results indicate that the green polyphenic line is more plastic and the black monophenic line has no plasticity.

Case Study: Side-Blotched Lizards

• These lizards can change color to match their environment.
• This plasticity enables them to adapt to different environments.
• This results in genetic mutations that allow for adaptive responses, given that they were ancestrally plastic.

How Plasticity-Led Evolution Works

• Environmental changes trigger phenotypic changes in organisms through phenotypic plasticity.
• Selection favors variation leading to heritable changes (genetic accommodation/selection).
• Resulting in adaptive refinement of favored phenotypes (e.g., larger size in blue tadpoles).
• Resulting in novel polyphenisms.
• Selection may cause the loss of plasticity, via genetic assimilation. A novel phenotype results regardless of environmental triggers.

Case Study: Spadefoot Toads

• Spadefoot toads normally develop as omnivorous tadpoles, but they can develop into carnivorous tadpoles (if they eat larger prey).
• Carniverous forms can eat larger animal prey leading to faster metamorphosis, which can result in larger adult sizes, and better reproduction
• Carniverous forms are advantageous in drought conditions when ponds dry up quickly
• This shows plasticity for a single species in environmental conditions.

Case Study: Fetal Alcohol Syndrome

• Ethanol is a devastating human teratogen.
• Human exposure to ethanol (during gestation) can affect the frequency of offspring defects in the short-term or long-term.
• Fetal alcohol syndrome results from exposure to ethanol during pregnancy.
• Severity and types of alcohol-induced variants depend on the alcohol dosage and the developmental stage at the time of prenatal exposure (Wilson's 2nd and 6th principle)
• Most critical period of development is the first trimester, which is when most major defects arise.
• The effect of ethanol on the developing organism is complex and includes its effects on neuron migration.
• Animal models have shown that ethanol exposure can cause cell death in cranial neural crest cells, which are important for facial development.

Developmental Origins of Disease

• Non-adaptive responses to injury or toxins can result in phenotypic malformations.
• Adaptive responses to environmental variation can be advantageous for survival.
• Immediate responses for offspring survival (acute plasticity) may have future costs but these can be an advantage in the short run.

Predictive Adaptive Response

• Response to environmental cues acting early in the life cycle
• Induced by early environmental factors, and used by environmental plasticity, to modify the phenotype where the advantage of the induced phenotype is primarily in a later phase of the life cycle
• Results in permanent change of the physiology/anatomy, in response to environmental conditions.
• This is in response to a range of developmental environments, and not just extreme ones.
• Some examples are the response to metabolic syndrome (Type II diabetes), obesity, high blood pressure.