1. SNAP TRAP EVOLUTION
There are two snap-trap carnivores today: the Venus flytrap (Dionaea muscipula) and the waterwheel plant ( Aldrovanda vesiculosa). Overwhelming evidence from molecular phylogenetic reconstructions using different regions of DNA sequence (mat K, Chloroplast rbcL) indicates that Dionaea and Aldrovanda are sister to each other, strongly suggesting that these extant snap traps evolved from a common ancestor.
The molecular evidence further reveals that Aldrovanda and Dionaea form a clade that is sister to Drosera (sundews). This suggests that the common ancestor of Aldrovanda and Dionaea came from an ancient sundew-like plant.
Snap Trap Evolved Only Once
That is not to say that these two snap-trap mechanisms we see today in the Venus flytrap and the waterwheel plants are identical. Of course, there are some differences. After all, both lineages had 30-40 million years of completely independent evolutionary paths for crying out loud. Not to forget also that one is terrestrial, the other is aquatic, both traps well fine-tuned in their respective, entirely different environments. We can surely find differences between these snap traps.
What I am saying is
that we do well seeking similarities --- rather than dissimilarities --- when we
strive to unlock the mystery and wonder of these "most wonderful plants in the
2. HOW DID IT HAPPEN?
SNAP TRAP EVOLUTION - A sudden, swift mutation must have occurred in one single individual in a population of ancient sundew-like plants. That individual produced many seeds (offspring) carrying this primitive, but workable, snap-trap trait to the next generation, and to the next, and to the next... The evolution of the snap trap has commenced.
An intriguing question remains as to which lineage evolved first --- Aldrovanda or Dionaea --- from an ancient sundew-like plant? To put it another way, was the common snap-trap ancestor an Aldrovanda-like aquatic plant or Dionaea-like terrestrial plant?
My take --- Aldrovanda...
When we talk about which came first,
we are not suggesting that today's Venus flytrap gave birth to today's
waterwheel plant, or vice versa. We are discussing the possible ways in
which the ancestor of these extant plants diverged tens of millions
of years ago...
1) Lloyd (p.182) - In Venus flytrap, the trap tilts to the right - mainly in younger plants, just like the clear bend seen in the mature Aldrovanda traps (see Lloyd/Darwin) --- Regarding this trap posture, Lloyd commented on the distinct advantage for Aldrovanda but no benefit for Dionaea. However, Lloyd did not extend this observation he made to an evolutionary context.
(p.181) comments on a young Venus flytrap (2 mm trap) ----> "The number of
parenchyma cells ranges between two to four courses with large
interspaces, in this feature again resembling the mature leaves of Aldrovanda much more than do the thicker mature leaves of
3) Venus flytrap is very tolerant of flooding condition - possibly implying an Aldrovanda-like, aquatic ancestor.
4) Aldrovanda seems to share more common reproductive features with Drosera than does Dionaea.
Sepals / Petals
anthers / filament
Pistil - Style
evidence points to a common origin of the two snap traps (Aldrovanda &
Dionaea), suggesting that the snap-trap mechanism evolved only once -- therefore, the basic
mechanism for these snap traps must be similar... actually identical...
further indicates that the common
ancestor of these snap traps diverged from an ancient
sundew-like plant --- perhaps the ancestor of the basal taxa, such as Drosera regia.
mechanism for leaf motion common throughout Drosera-Aldrovanda-Dionaea
evolution is most likely to be a sudden (or relatively quick) drop of turgor pressure on one side of the structure in question, creating an
imbalance of pressure on the structure to cause it to bend.... In this
process, the other side (epidermis) might be forced to stretch a little .... The
recovery of the bending (or snapping for that matter) is achieved as a result of the side (epidermis) that lost turgor pressure restoring
its lost pressure and then some
to counter the stretch of the other side. This is accomplished by slow,
Physical motions in plants are caused by different pressures between the opposite sides of the structure in question: one side expands, the other side shrinks, or both --- due to either turgor change or cell growth.
1) In Drosera tentacle bending, the pressure differential between the opposite sides of the tentacle (stalk) occurs near the base first, and then gradually moves upward in the direction toward the tentacle tip.
2) In Aldrovanda snapping also, the sudden pressure differential between the inner and outer epidermis in the motor region occurs near the midrib of the trap, and then gradually moves upward (within the motor region) during the tightening phase of the trap closure...
3) In Dionaea snapping, the sudden pressure differential on the upper and lower epidermis of the lobes seems to occur in the upper half of the lobes --- that effectively causes the snap-through buckling of the trap lobes --- and then the pressure slowly moves downward toward the midrib during the narrowing phase of the closure...
1. Drosera (sundews) ---- Illustrations
Adhesive - Stalked gland secretes mucilage, exhibits nastic/tropistic
movement to secure prey.
Snap trap (aquatic).
Aldrovanda vesiculosa snap trap closure
Well, based on my repeated
trials of measuring the screen image of this video, I concluded that, indeed,
the A-B distance got shorter (in the left view of the video) after trap
snapping, and therefore, the Aldrovanda closure is driven by warping of
the motor zone of the lobes. This is in concert with the traditionally-held
view by many past investigators, including ...
3. Dionaea (Venus flytrap) ---- Illustrations
Copyright (c) 2017 Makoto Honda. All Rights Reserved.