Til;dr a speculation of how kin selection could have driven evolution of inter-generational dialogue in ferns.
Here I offer a very broad review of knowledge about ferns & ‘fern allies’ we have today. The topic is possible organism-level adaptations for kin selection and population structuring.
Why ferns?
Imagine a flowering plant (as a child would draw, to generalize.)
It has roots, a stem, leaves, flowers and fruit. In its flowers, anthers and pistils negotiate pollination like the adults they are. In its fruit, baby plants dream, covered by integuments. The plant is one complex, breathing thing.
On no level it is perfect or ‘harmonious’. There are resource allocation problems, meaning all seeds do not have equal chances to mature. There is competition between fathers. There are herbivores and malformations and volcanic eruptions, and the plant has pretty little defences against them, but -
- when you look at the seed -
- not entirely powerless. The tender sperm meets the egg inside a complex organ, protected from drying out and capable of recognizing specific pollen. The mother plant provides nutrition and encapsules the embryo in layers optimized for both survival and germination. Once established, it becomes an environment for its own progeny: the sporophyte (the adult specimen producing spores) hosts plenty of gametophytes (i.e. the sperm and eggs developing from the spores). The sporophyte is a mighty diploid (or triploid, or more...), while the gametophyte is haploid (generally), meaning it has but one set of chromosomes—half as much inherent genetic diversity to meet all the various demands posed by the environment.
The layout is not so bad, after all.
...and now imagine a fern.
Their spores fall down wherever chance takes them, and they are already haploid. They give rise to small gametophytes, whose sperm must swim for torturous centimetres to reach the ovule of another, or risk adding to genetic load of itself if (and that is a big if) inbreeding is actually possible.
With seeds, you have a fortress with nurseries hidden behind the most capable biochemical locks that have evolved in plants. Without seeds, you have farflung holdings struggling for survival, which your own fronds might deprive of sunlight. And oh, there’s the problem of promoting own genomes without going extinct because of homozygosity.
Can adult sporophytes of seedless land plants communicate with and support their young? Or do they exist in complete separation, occasionally competing for shared resources?
Parts overview
(It would involve pheromones/hormones, ploidy, reticulate evolution, embrionic selection, climate and maybe some Hard Botany, though I will try to keep it to a minimum.)
In Part One, we will recall the four major groups of seedless vascular plants of today and see the difficulties they have to overcome to reproduce at all, not to mention differentially support their own genes.
In Part Two, we will learn how kin selection should be able to work for them, from Wilson (1981) to Greer et alia (2009) and beyond, and see for ourselves how difficult it is to crack the riddle of inbreeding vs outbreeding in the wild. This might take up some space if done rigorously.
In Part Three, we will return to species level and see hybrids competing with their parents, fertilizing and being fertilized and escaping the race by producing vegetative offspring. Yet why, oh why is it seen in some taxa and not in others?
In Part Four, we will see how environment promotes some features of population organisation. The only reason why it is thinkable as a blog-post is… lack of studies, certainly, otherwise we’d be buried under the sheer variety of ecological niches.
Part Five will round up the series, hopefully with some conclusions about how reproduction constraints anatomy and biochemistry and how gamete- and spore-producing generations coexist and flourish.
I might change the plan later on. Sorry for not discussing mosses; they are just too different from the rest, and I don’t know them well enough.
(I cannot tell how often I will be able to post, and if there are any mistakes, please point them out to me.)
Before the seed. Intro
Til;dr a speculation of how kin selection could have driven evolution of inter-generational dialogue in ferns.
Here I offer a very broad review of knowledge about ferns & ‘fern allies’ we have today. The topic is possible organism-level adaptations for kin selection and population structuring.
Why ferns?
Imagine a flowering plant (as a child would draw, to generalize.)
It has roots, a stem, leaves, flowers and fruit. In its flowers, anthers and pistils negotiate pollination like the adults they are. In its fruit, baby plants dream, covered by integuments. The plant is one complex, breathing thing.
On no level it is perfect or ‘harmonious’. There are resource allocation problems, meaning all seeds do not have equal chances to mature. There is competition between fathers. There are herbivores and malformations and volcanic eruptions, and the plant has pretty little defences against them, but -
- when you look at the seed -
- not entirely powerless. The tender sperm meets the egg inside a complex organ, protected from drying out and capable of recognizing specific pollen. The mother plant provides nutrition and encapsules the embryo in layers optimized for both survival and germination. Once established, it becomes an environment for its own progeny: the sporophyte (the adult specimen producing spores) hosts plenty of gametophytes (i.e. the sperm and eggs developing from the spores). The sporophyte is a mighty diploid (or triploid, or more...), while the gametophyte is haploid (generally), meaning it has but one set of chromosomes—half as much inherent genetic diversity to meet all the various demands posed by the environment.
The layout is not so bad, after all.
...and now imagine a fern.
Their spores fall down wherever chance takes them, and they are already haploid. They give rise to small gametophytes, whose sperm must swim for torturous centimetres to reach the ovule of another, or risk adding to genetic load of itself if (and that is a big if) inbreeding is actually possible.
With seeds, you have a fortress with nurseries hidden behind the most capable biochemical locks that have evolved in plants. Without seeds, you have farflung holdings struggling for survival, which your own fronds might deprive of sunlight. And oh, there’s the problem of promoting own genomes without going extinct because of homozygosity.
Can adult sporophytes of seedless land plants communicate with and support their young? Or do they exist in complete separation, occasionally competing for shared resources?
Parts overview
(It would involve pheromones/hormones, ploidy, reticulate evolution, embrionic selection, climate and maybe some Hard Botany, though I will try to keep it to a minimum.)
In Part One, we will recall the four major groups of seedless vascular plants of today and see the difficulties they have to overcome to reproduce at all, not to mention differentially support their own genes.
In Part Two, we will learn how kin selection should be able to work for them, from Wilson (1981) to Greer et alia (2009) and beyond, and see for ourselves how difficult it is to crack the riddle of inbreeding vs outbreeding in the wild. This might take up some space if done rigorously.
In Part Three, we will return to species level and see hybrids competing with their parents, fertilizing and being fertilized and escaping the race by producing vegetative offspring. Yet why, oh why is it seen in some taxa and not in others?
In Part Four, we will see how environment promotes some features of population organisation. The only reason why it is thinkable as a blog-post is… lack of studies, certainly, otherwise we’d be buried under the sheer variety of ecological niches.
Part Five will round up the series, hopefully with some conclusions about how reproduction constraints anatomy and biochemistry and how gamete- and spore-producing generations coexist and flourish.
I might change the plan later on. Sorry for not discussing mosses; they are just too different from the rest, and I don’t know them well enough.
(I cannot tell how often I will be able to post, and if there are any mistakes, please point them out to me.)