Resting and active evolution.
Possible preadaptations in the early evolution of Angiosperms.
WHEN REFERRING THIS MATERIAL, PLEASE CITE:
Ploompuu, T. Resting and active evolution. Puhkuse teooria. Schola biotheoretica XXIX. Tartu. Sulemees 2003 P. 70-75. (in Estonian)
Two types of evolution: macroevolution (periods of progress and periods of small activity) and microevolution (quite equable specialisation). We can see the microevolution as a “permanent passive respiration” of evolution and macroevolution as a “active work” of evolution.
Small activity is not resting yet. Resting is an active preparation to active period. In resting time must proceed shaded changes that include presumptions for following activity.
Is macroevolution a work after resting always? Big changes in evolution can evolve:
But sometimes can see big changes in evolution without important changes in environment. This situation can induce:
One possible complex of preadaptations can see in early evolution of Angiosperms.
Possible preadaptations in the early evolution of Angiosperms.
The first Angiosperms were insect pollinated plants. Predators of angiosperms had bisexual cones. Only these presumptions enable to reconstruct a evolution process of flower.
There is yet popular the theory of forming of angiosperms in dry mountain areas (Axelrod, 1952 ref. Molnar 2001, Speer 2003) – there have not found fossils of (very) early angiosperms and it is grounded by characteristics of sedimentation – in these areas does not deposit organic sediments. I think, these dry conditions did not need insect pollination.
There does not help also possible first possible pollutants – insects, possible consumes of pollen evolve yet in Carbon (too early for theoretical first Angiosperms), possible nectar consumers evolve in Triassic, but modern pollinators evolve with first angiosperms in Cretaceous (in same time of adaptive radiation of “ready” Angiosperms) (Labandeira 2003).
1. Why, where was needed especially insect pollination? The first possible pollinators (pollen-consumers = “flower-parasites”) did not start evolution of insect pollination. It started in specific conditions.
There is not remarkable possibility for evolving fist insect pollinated plants in dry areas –wind can pollinate perfectly there. The most possible region of first angiosperms is SO Asia (summarised by Molnar 2001). Various fragments of the region migrated until Carbon to Cretaceous through tropic oceans or were at tropic oceans. By these data can presume, that there was many places with very humid climate, there were many fog forests in mountains. These conditions are very difficult for wind pollination and maybe insects, being parasite on male part of cone, were alone possible pollinators; especially of small plants of ground vegetation (subherbal-herbal). First known angiosperms were obviously small herbal water plants (Sun et al., 2002) (or shade swamp plants?)
2. In moist conditions was alternative opportunity to insect pollination – apomixis. Of course, specialisation to apomictic seed ontogenesis is bad in long time – complex evolution is not enough fast without recombination. Besides apomixis was also useful to save opportunity for development of embryo after fertilisation (insect pollinators were rare in this part of community in time). In this case the apomixis is better than self-pollination – the self-pollination closes possibility of future cross-pollination. It is possible, that regulation of relations between apomixis and cross-pollination is evolutional cause of evolving of double fertilisation of angiosperms. It is possible, that the primary function of central cell was restoration of diploid cell for development of apomictic seed. If succeed to pollinate pre-flower, was essential to close the apomictic seed development, was essential to close the way of ontogenesis of apomictic “surrogate-embryo”. One possible simple way to close the way of apomixis is fertilisation of central cell. Fertilised central cell has “abnormal” ploidity (3n), which obviously has high efficiency for change the cell development. Old theory of forming of triploid endosperm in evolution step-by-step for better co-operation of embryo and mother-plant by intermediate genotype (Friedman, Williams 2003) is not convincing – Gymnosperms have normal co-operation of embryo and mother genotype. Also, at grafting can effectively co-operate tissues of different genera.
3. Pollination by insects made possible high isolation of similar (able to cross) populations of different habitats. Accelerated development of species and specialisation. But in excellent conditions small shade plant can mature very fast – it accelerated also evolution of them. Faster evolution of early angiosperms gives soon them possibility to over-compete Gymnosperms in their traditional habitats. Angiosperms were “awoke” and started their adaptive radiation in Cretaceous.
Adaptation of pre-angiosperms to “unimportant” (by part in substance turnover), “secondary” econiche of community was also preadaptation for successful adaptation to evolution. “Adaptation to evolution” – this means acquiring of possibility of faster evolution in absolute time in comparison with other taxa of the same life form.
There are two possible causes for adaptive radiation:
The same type of resting time preadaptations can see also in formation of eucaryotic cell (Ploompuu 1999).
The resting time can presume also for evolving of dominate mammals – the cosmic catastrophe was only a inducement in right time, which awoke adaptive radiation, which were matured in evolutional resting of vertebrates.
Alternation of insect fauna in early Cretaceous was a result of changed habitat – result of changing of flora, not a result of preadaptation.
Cause of punctuated equilibrium is obviously fast occupying of new big habitat or moreover, the “resting of evolution”. Especially the last favour the great missing of intermediate forms.
We can describe doing perfectly – it exists, it is describable by visible and measurable step-by-step in its being and changing. Resting seems as not-doing, but during resting evolve powers and phenomenon, which are not possible in continuous activity. It is difficult to describe processes in resting – how can describe objects, missing in first view? Sleeping human is doing nothing! Maybe, the catastrophes are good alibi for lack of understanding of importance of resting – preadaptations – in evolution?
Axelrod, A.J. 1952. A theory of angiosperm evolution. Evolution. 6: 29-60 ref. Molnar (2001), Speer (2003).
Friedman, W.E., Williams, J.H. 2003. Modularity of the angiosperm female gametophyte and its bearing on the early evolution of endosperm in flowering plants. Evolution, 57(2), pp. 216-230.
Ploompuu, T. 1999 /Why the eukaryotic cell memory was needed/ Miks oli vaja eukarüootset rakumälu. Biosüsteemide mälu teooria. Schola biotheoretica XXV. Tartu. Sulemees Lk. 51-56.
Sun, G., Ji, Q., Dilcher, D.L., Zheng, S., Nixon, K.C., Wang, X.. 2002. Archaefructaceae, a New Basal Angiosperm Family. Science, 296 (5569), pp. 899-904.
Clive, D. 2003 Homebox Genes and Macroevolution. http://www.mlamutations.com/myrants/macroevolution/macroevolution.html
Labandeira C.C. 2003 Fossil Insect Palynivory and Pollination: Role of Plant Damage Coprolites and Gut Contents. http://www.geo.arizona.edu/palynology/dung/labandeira.html
Molnar S. 2001. Angiosperm Origins and Evolution. http://www.geocities.com/we_evolve/Plants/angiosperm.html
Speer, B.R. 2003 Anthophyta: fossil record http://www.ucmp.berkeley.edu/anthophyta/anthophytafr.html