Trap diversity and evolution in the family Droseraceae

[shartmeyer]

A new review has been published in PBS (Plant Signaling & Behavior) and is now online (open access, link below). Recent investigations revealed how the snap-traps of Aldrovanda vesiculosa (waterwheel plant) and Dionaea muscipula (Venus’ flytrap) work mechanically and how these apparently similar devices differ as to their functional morphology and shutting mechanics. Recently, it was also shown that there exists a higher diversity of different tentacle types and trap configurations in Drosera than previously known which presumably reflect adaptations to different prey spectra. Based on these recent findings, we finally comment on possible ways for intrafamiliar trap evolution.

Trap diversity and evolution in the family Droseraceae

Simon Poppinga, Siegfried R.H. Hartmeyer, Tom Masselter, Irmgard Hartmeyer and Thomas Speck

Remark May 15: Thank you Bob, I corrected the link above. Interestingly the other link still works on G+. 

[adamcross]

Interesting study, thanks for the link.

I have one point of query. The paper states that "Today’s Aldrovanda and Dionaea are thought to be relict members of an ancient snap-trap clade that once was much more diverse, involving several events of diversification and extinction. (referenced to the recent McPherson/Bailey book 'Dionaea')" However, a pre-extant lineage has only been determined for Aldrovanda- determined, I must add, predominantly by limited seed and pollen records supplemented by only a single vegetative fragment from a relatively recent ancestor. The explicit presence of snap-trap carnivory is therefore unconfirmed in any extinct species within Aldrovanda, and the fossil record is distinctly lacking for Dionaea. Only Aldrovanda shows evidence of expansion/extinction events resulting in speciation.

Is not this statement a little erroneous then? There is no evidence to suggest that snap-trap carnivory ever diversified within the genus Dionaea, and very little conclusive evidence to suggest similar early diversification within Aldrovanda. Also, while it is not as widely supported, the theory has also been postulated that snap-trap carnivory in Aldrovanda and Dionaea evolved separately (primarily due to the geological disjunction between the two genera, even around the 65Mya mark, and the uncertainty of phylogenetic trees using chloroplast DNA analysis).

[ICPS-bob]

It seems that the link to the article has changed to:
www.landesbioscience.com/journals/10/article/24685/

[Apoplast]

May 14, 2013 16:58:03 GMT adamcross said:

There is no evidence to suggest that snap-trap carnivory ever diversified within the genus Dionaea, and very little conclusive evidence to suggest similar early diversification within Aldrovanda.

Hi Adam - That's an interesting and thought provoking statement. I haven't read the paper yet, but the idea that a fairly complex trait might evolve without any diversification, without any sampling of alternative trajectories on a fitness landscape. What would that look like? It's a really fascinating idea. I'm going to have to ponder this. This has been a fun couple days on this forum for me! I've gotten to do some good thinking.

Hi Shartmeyer - Thanks for letting us know about this paper! I look forward to reading it.

[coline]

May 14, 2013 18:23:13 GMT Apoplast said:

May 14, 2013 16:58:03 GMT adamcross said:

There is no evidence to suggest that snap-trap carnivory ever diversified within the genus Dionaea, and very little conclusive evidence to suggest similar early diversification within Aldrovanda.

Hi Adam - That's an interesting and thought provoking statement. I haven't read the paper yet, but the idea that a fairly complex trait might evolve without any diversification, without any sampling of alternative trajectories on a fitness landscape. What would that look like? It's a really fascinating idea. I'm going to have to ponder this. This has been a fun couple days on this forum for me! I've gotten to do some good thinking.

Hi Shartmeyer - Thanks for letting us know about this paper! I look forward to reading it.

I also think so about that, it is very interesting on how did Dionaea have a so tiny range of distribution with no close relatives nor fossil history about it that make it a descendant or survivor from evolution. it is quite clear for aldrovandra with its large distribution area, but Dionaea is really a mistery for me.

[ICPS-bob]

The diversity of Dionaea "mutants", some of which are registered cultivars, suggests to me that there have likely been "alternative trajectories on a fitness landscape". Certainly some of these weird forms are tissue culture sports, but they suggest a dead-end genetic signature that might well have been expressed now and then over the eons. Such variations include: color ranging from pale green to dark purple; long cilia (fingers) to none; extreme cupped trap to inverted cup; long thin petioles to short fat petioles; large traps and plants to tiny almost invisible plants; numerous trigger hairs to no trigger hairs; misshapen traps incapable of trapping prey; etc. That a particular form greatly dominates the narrow native habitat niche in North Carolina may simply be that the typical form is best-suited to those conditions. If seeds were widely dispersed and some germinated and became established in diverse habitat, perhaps after being isolated over a very long time we would see different forms that had become dominant.

[Apoplast]

Hi Bob - I agree. The genetic variability that seems to be latent in VFT's does suggest there has at least been a wider range or other variability in the evolutionary history. I'm uncertain whether this is strong evidence that there has been divergence into different species, but it does further support my having trouble imagining how such a distinct trait as the snap trap on a VFT would evolve without any divergence. I know it's just a feeling, which is of course highly unscientific. But your observation lends further support.

How can a distinct species/genus evolve as only one lineage, contiguous population? Do we know if that ever happens?

[adamcross]

Apoplast, you might consider that snap-trap carnivory is itself a divergence, rather than a baseline trait. The common opinion is that snap-trap carnivory evolved from a common Drosera-like ancestor; therefore, snap-traps might simply represent one successful trajectory on the fitness plane of that Drosera-like ancestor's evolution.

[ICPS-bob]

Consider for a moment the mutant commonly called Dionaea "Pom Pom". It doesn't take much imagination to see it as a proto-Drosera (or vice-versa). I certainly do not want to suggest that such anomalies are anything more than food for thought.

rziemer.cpphotofinder.com/rziemer/zphotos/VFTPomPom7568.jpg

[adamcross]

Similarly Bob, I'm not claiming to have the answers (we might never know!)- more questioning the evidence and theory behind the Poppinga et al. statement.

That said, I'm in the final stages of completing a genetic study on Aldrovanda using much higher resolution techniques than published previously; the results of outgroup comparisons with these techniques might shed a little light on the ancestral relationships of the group.