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 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 suggests that Aldrovanda and Dionaea form a clade that is sister to Drosera (sundews). This implies that the common ancestor of Aldrovanda and Dionaea came from an ancient sundew-like plant (Subgerera Regiae + Arcturia)..
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. 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.
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. WHICH EVOLVED FIRST?
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. This tilting trait was acquired in the ancestor of Aldrovanda and was carried over to the Venus flytrap, even if it is no use for the Venus flytrap. It is often manifested in the younger Venus flytraps --- "Recapitulation."
(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. It is known that the Venus flytraps grow underwater for a few months without any harm. The Venus flytraps catch prey in the water, no sweat. Hurricanes and violent storms go through North Carolina every year, flooding the region where Dionaea grows. I assume it's been like this for the past 50 million years.
4) Aldrovanda seems to share more common reproductive features with Drosera than does Dionaea.
There are two types of self-pollination: (not to be confused with self-compatibility in plants (the ability to form seed using self-pollen).
autogamy, pollen is transferred to the stigma of
the same flower.
Some plants have mechanisms to ensure autogamy:
If a plant is self-incompatible, geitogamy can reduce seed production.
Although geitonogamy is functionally cross-pollination involving a pollinating agent, genetically it is similar to autogamy since the pollen grains come from the same plant.
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.
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
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