Heterospory Flashcards
1
Q
what is the difference between homospory and heterospory?
A
- Similar plant structures (both have strobili)
- Heterospory plants differ in that sporangium have either a large number or small spores or a small number of large spores whereas homosporous plants have the same number of small spores in each sporangium
2
Q
what are three features of heterospory?
A
- Size differentiation: megaspores and microspores
- Unisexuality of the gametophytes that develop from each spore type (megaspores only become female megagametrophyte and vice versa)
- Endoscopic development of gametophyte
As gametophyte develops inside the spore, it is dependent on spore reserves (cannot photosynthesise)
Next generation sporophytes entirely depend on unused megaspore reserves
3
Q
what is the size difference between micro and megaspores?
A
- Usually a 1000 to a few 1000 times greater volume than microspore
- Microspores are a similar size to homosporous spores
4
Q
in what groups is heterospory occuring?
A
Heterospory occurs in some lycophytes, some monilophytes and all seed plants
5
Q
when did heterospory arise and how many times?
A
- First arose about 370 million years ago in the lycophyte lineage
- Fossils of cyclostigma and bisporangiostrobus
- evolved independently multiple times (suggests it is an adaptation)
6
Q
how is heterospory the precurser of seeds?
A
- Microspores are like pollen and megaspores are like ovules of a pine
- Heterospory was a necessary precursor to the evolution of seeds
7
Q
how is heterospory adaptive?
A
- Size represents nutrient reserve for sporophyte generation and development of gametophyte
- In a shadier, more productive areas there is more competition
- Spore size increased from Silurian to Carboniferous (at the same time there was more shade and crowding developing because of increasing vasculature)
- Large spores (especially heterospory) seems to be an adaptation to novel regeneration niches created by plants themselves
- Heterospory seems to be an adaptation to shady regeneration niches
8
Q
what is the significance of the evolution of seeds?
A
seeds are what freed plants from dependence on water for reproduction
9
Q
A