Life history and reproduction: its all about timing and provisioning
Essential elements from today’s lecture:
In this lecture, we discuss variations in both life history and plant reproduction. It is critical to recognize that environmental gradients and environmental heterogeneity can select for genetically distinct and/or environmentally-induced differences in plant life expectancy and in reproduction patterns.
We first discuss how plants can be classified as annual, biennial, and perennial, reflecting both differences in the age to first reproduction and year-to-year survival probabilities. As environmental harshness and year-to-year variability in moisture increase, so do the fraction of the flora that is annual.
Several clear patterns emerge with respect to adaptation and reproduction, including
1. Fecundity schedules reflect the predictability of the end of the growing season.
2. Reproductive efforts reflect a balance between seed size and number.
Perhaps the greatest diversity on this topic is in how seeds (the next generation) are provisioned.
1. Seed differences appear in several ways, reflecting the potential for increased probability of establishment: energy provisioning, dispersal, germination delay.
2. Plants often produce heteromorphic seeds, as a form of bet hedging, especially in environments with high year-to-year variability.
3. Variations in seed provisioning reflect allocation to storage as lipids versus carbohydrates.
4. Delayed germination (a form of heteromorphic seeds) is associated with differences in seed coat thickness.
Lastly, we integrate these concepts using a hemi-parasitic mistletoe as an example.
1. There are both hemi-parasitic and holo-parasitic mistletoes. Hemi-parasites are autotrophic and attach to host-plant’s xylem; holo-parasites attach to both the host’s xylem and phloem.
2. Mistletoe life expectancy is determined by unpredictable environmental factors: very cold winters and/or drought. This results in a tendency for mistletoe reproduction at an early age.
3. Mistletoe reproductive effort and seed fitness increases with age of the parent, reflecting increases in the provisioning of seeds
Essential elements from today’s lecture:
In this lecture, we discuss variations in both life history and plant reproduction. It is critical to recognize that environmental gradients and environmental heterogeneity can select for genetically distinct and/or environmentally-induced differences in plant life expectancy and in reproduction patterns.
We first discuss how plants can be classified as annual, biennial, and perennial, reflecting both differences in the age to first reproduction and year-to-year survival probabilities. As environmental harshness and year-to-year variability in moisture increase, so do the fraction of the flora that is annual.
Several clear patterns emerge with respect to adaptation and reproduction, including
1. Fecundity schedules reflect the predictability of the end of the growing season.
2. Reproductive efforts reflect a balance between seed size and number.
Perhaps the greatest diversity on this topic is in how seeds (the next generation) are provisioned.
1. Seed differences appear in several ways, reflecting the potential for increased probability of establishment: energy provisioning, dispersal, germination delay.
2. Plants often produce heteromorphic seeds, as a form of bet hedging, especially in environments with high year-to-year variability.
3. Variations in seed provisioning reflect allocation to storage as lipids versus carbohydrates.
4. Delayed germination (a form of heteromorphic seeds) is associated with differences in seed coat thickness.
Lastly, we integrate these concepts using a hemi-parasitic mistletoe as an example.
1. There are both hemi-parasitic and holo-parasitic mistletoes. Hemi-parasites are autotrophic and attach to host-plant’s xylem; holo-parasites attach to both the host’s xylem and phloem.
2. Mistletoe life expectancy is determined by unpredictable environmental factors: very cold winters and/or drought. This results in a tendency for mistletoe reproduction at an early age.
3. Mistletoe reproductive effort and seed fitness increases with age of the parent, reflecting increases in the provisioning of seeds