Slipper orchid evolution: does anyone care?

[VAAlbert]

So would you tend to chalk that one up to converging/diverging pollination syndromes? IE: the species that have been hypothesized to to mimic other rewarding plants (Paph. micranthum looking like a Rhododendron, etc.) have infolded labellums to trap entering bees while the others (Most non-Parvi Paphs) are structured in order to facilitate flies slipping into the labellum?

I would say that the inflated pouch character is a 'primitive' one, inherited from the slipper common ancestor, which probably relied on some sort of bee pollination. That would make the occurrence of fly pollinated flowers the subject of convergent evolution -- in Paphs (the lineage including all species with pouch frontal margins that turn outwards, e.g., the barbatas), Phrags (lorifolias et al.), and at least 2 groups of cyps (margaritaceum group; guttatum, e.g.). It is actually quite remarkable to find a group of plants that 'evolves' a fine-tuned trapping/pollination system for bees, which are comparatively 'smart', only to evolve further to trap stupid things like flies. In other words, slippers became opportunists. Another group of plants that had this same transition, i.e., bee-->fly pollination made its way onto the pages of one of the top journals in biology: Nature! And I think this other example only showed ONE shift from bees to flies!

BW,

Vic

 

[VAAlbert]

OK, not bees to flies, but still bees (resin collectors) to more generalized pollination syndromes.

Nature 394, 632 (13 August 1998); doi:10.1038/29210

Switch from specialized to generalized pollination

W. SCOTT ARMBRUSTER1 AND BRUCE G. BALDWIN2

1 Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775, USA and Department of Botany, Norwegian University of Science and Technology, N-7034 Trondheim, Norway
e-mail: [email protected]
2 Jepson Herbarium and Department of Integrative Biology, University of California, Berkeley, California 94720, USA

The once prevalent view that the evolution of extreme ecological specialization is accompanied by a loss of potential for adapting to new conditions, and thus is irreversible, has been challenged by several recent examples,,. However, we know of no modern phylogenetic studies showing reversal in pollination relationships from extreme specialization to generalization, although such reversals are theoretically expected,. Here we present molecular phylogenetic evidence for an evolutionary shift in Dalechampia (Euphorbiaceae) vines from a highly specialized relationship (pollination by one or a few animal species,) with resin-collecting bees to generalized pollination by a variety of pollen-feeding insects. This shift was associated with dispersal from Africa to Madagascar, where the specific resin-collecting pollinators are absent. These results show that plants dispersing beyond the range of their specific pollinators may succeed by evolving more generalized pollination systems.

 

[Heather]

I'm late, but I'm definitely interested too!

So far so good...very glad you joined us Vic!

 

[gonewild]

Perhaps not very well at all, unless the potential hybridization event took place long enough ago for genetic variation to have 'sorted' itself out. And this sorting out can indeed be analyzed at the population genetic level.

V

How many generations would "long enough ago" be to sort out a natural hybrid as a distinct specie? Can this happen rapidly or does this require a great span of time?

 

[silence882]

Perhaps not very well at all, unless the potential hybridization event took place long enough ago for genetic variation to have 'sorted' itself out. And this sorting out can indeed be analyzed at the population genetic level.

V

hmmmm

So what would the presence of a natural hybrid in a pool of species do to the cladogram that's generated using molecular phylogenetics? Would the presence of a hybrid mess up the results for the rest of the species?

--Stephen

 

[Rick]

I would say that the inflated pouch character is a 'primitive' one, inherited from the slipper common ancestor, which probably relied on some sort of bee pollination. That would make the occurrence of fly pollinated flowers the subject of convergent evolution -- in Paphs (the lineage including all species with pouch frontal margins that turn outwards, e.g., the barbatas), Phrags (lorifolias et al.), and at least 2 groups of cyps (margaritaceum group; guttatum, e.g.). It is actually quite remarkable to find a group of plants that 'evolves' a fine-tuned trapping/pollination system for bees, which are comparatively 'smart', only to evolve further to trap stupid things like flies. In other words, slippers became opportunists. Another group of plants that had this same transition, i.e., bee-->fly pollination made its way onto the pages of one of the top journals in biology: Nature! And I think this other example only showed ONE shift from bees to flies!

BW,

Vic

Ah. We've had this discussion before.:clap: I've found some new info to add to this discussion. The shift to flies could be be construed to actually be an advance into a very specific niche. The type of flies utilized by slippers are hover flies (and there are lots of species to get plant specific associations too), and the mimic is very specific to lure female flies to lay eggs against a potential (fake) food source for its larvae (esentially a predatory flie). Also the visual acuity and discerning capabilties of flies is superior to bees (this is the newer info I read), so bees are more on autopilot than syrphid flies in finding their particular resources. Subsequently it could be construed that its easier to trick a bee than a flie.

Another way to look at this is that bees and plants go a long ways back in development of a cooperative arangement (food for pollen transport). So its not that far of a stretch to see a plant species break into the system ((maybe for energetic reasons (no food production required)) to get some free pollen transport from a pretty dependable engrained mass transit system.

The hover fly system is quite a break from this as there is no preexisting plant -flie mutual arangemnt that I can think of. In the case of fly pollenation its a 2 step process in that plants have a negative association with aphids (fly bait), and flies have an association with aphids (prey). So the plant came up with a way to get the two associations together (with a criter that's not on autopilot with good visual acuity). Now that's advanced.

 

[VAAlbert]

The shift to flies could be be construed to actually be an advance into a very specific niche. The type of flies utilized by slippers are hover flies (and there are lots of species to get plant specific associations too), and the mimic is very specific to lure female flies to lay eggs against a potential (fake) food source for its larvae (esentially a predatory flie).

This does seem to be the case in Paph rothschildianum, though I'm not aware of similar results from other slippers. I have to go back to the Paph villosum example, but I don't think the conclusion was brood-site deception.

Also the visual acuity and discerning capabilties of flies is superior to bees (this is the newer info I read), so bees are more on autopilot than syrphid flies in finding their particular resources. Subsequently it could be construed that its easier to trick a bee than a flie.

Certainly, some bees are bumblers, but I think we'll have to look through some of the literature on Cyp to see whether bumble bees are the predominant pollinators! Other bees are far more specific pollinators. It could well be that Paph micranthum, e.g., is pollinated by bumble bees; it has such a huge pouch.

Another way to look at this is that bees and plants go a long ways back in development of a cooperative arangement (food for pollen transport). So its not that far of a stretch to see a plant species break into the system ((maybe for energetic reasons (no food production required)) to get some free pollen transport from a pretty dependable engrained mass transit system.
The hover fly system is quite a break from this as there is no preexisting plant -flie mutual arangemnt that I can think of. In the case of fly pollenation its a 2 step process in that plants have a negative association with aphids (fly bait), and flies have an association with aphids (prey). So the plant came up with a way to get the two associations together (with a criter that's not on autopilot with good visual acuity). Now that's advanced.

A great idea! Brood-site deception could certainly be viewed as an advanced trait. However, I question whether brood-site deception occurs with all of the outwardly-turned pouch Paphs, e.g. The staminodia of Paph villosum, e.g., and rothschildianum, e.g., would then seem to me to be different sorts of attractants, perhaps to different sorts of flies.

One problem with brood-site deception being a major force in Paph evolution (e.g.) is that the Barbata slippers, which are by far the most numerous fly-pollinated species, don't have have the roths-type staminode features (aphid nest -like) and they rarely occur in sympatry (in the same place), leading one to suspect that the different floral forms (incl. staminodia) MAY have evolved in allopatry (geographical isolation, e.g., in small populations). Of course, I don't KNOW the latter, but it makes some deductive sense to me.

There are broadly distributed, outwardly-turned pouch Paphs, but we can't yet say whether these distributions result from range expansion, or whether they are relictual. In other words, I wonder whther staminodia of Barbatas eally are finely adapted to different pollinators at all.

But, I digress -- you are perfectly logical at the HIGHER (sectional) level (in taxonomy, which happens to reflect phylogeny), e.g., in the ancestor of Barbatas, if their pollination system could be considered advanced as you intriguingly suggest! There is also a nice paper out recently on deception of Cyp guttatum flowers; I'll look that one over again.

Regardless, I think we can probably agree that the slipper orchids have become opportunists re: fly pollination!

best wishes,

Vic

 

[kentuckiense]

Certainly, some bees are bumblers, but I think we'll have to look through some of the literature on Cyp to see whether bumble bees are the predominant pollinators! Other bees are far more specific pollinators. It could well be that Paph micranthum, e.g., is pollinated by bumble bees; it has such a huge pouch.

Cypripedium acaule is bumblebee pollinated. I'd wager that C. kentuckiense is as well. The orifice is simply gigantic!

 

[kentuckiense]

Looks like Cypripedium macranthos var. rebunense may be bumblebee pollinated as well. Check out:

"Bumblebee pollination of Cypripedium macranthos var. rebunense (Orchidaceae); a possible case of floral mimicry of Pedicularis schistostegia (Orobanchaceae)" by Sugiura et al.

 

[VAAlbert]

I wonder whther staminodia of Barbatas eally are finely adapted to different pollinators at all.

Hi again,

Thanks for your input Kentuckiense! BTW, re: the above, 2 things:

- I don't mean to say that Barbata Paphs don't occur in the same geographic regions, but it seems to me that they usually occur isolated from one another in terms of 'microgeography', e.g., even elevation on the same mountain, or on differnt rock substrates on the same little peninsula.

- A 'radiation of forms', such as we do see with the barbatas, and yes, to a degree, with their staminodes, need not be an 'adaptive radiation'. Evolutionary change, and fixation of new morphological forms, can certainly take place in the absence of natural selection on those forms.

The latter is is in fact exactly what I'm working on with the Hawaiian endemic mints! Such radiations can occur by random chance, when certain alleles (versions; mutants) of different genes become dominant in small populations simply because the small population size favors the fixation of any mutant that comes up, be it a 'good' one or a 'bad' one. Random changes like these can of course become the subject of natural selection LATER, and this has certainly happened in some other systems.

So, while the barbatas are probably pollinated by flies, they need not be pollinated by different species of flies, or even be adapted to different species of flies; the Barbata species could simply be isolated from one another by space or even flowering time, and their distinct (sometimes!!!!) morphologies amongst each other could be 'frozen accidents' of seed dispersal and fixation of new genotypes.

For example, Paph curtisii(/superbiens) can co-occur with Paph tonsum, and the natural hybrid is known. Reproductive isolation can be leaky, and bugs can go after whatever they find.

Clearly more to talk about here - I'm having fun!

All best,

Vic

 

[VAAlbert]

It seems that Cyp guttatum serendipitously traps bees that are otherwise after other nearby flowers:

Pollination of a slippery lady slipper orchid in south-west China: Cypripedium guttatum (Orchidaceae)
HANS BÄNZIGER1,2 , HAIQIN SUN1 and YI-BO LUO1*

Cypripedium guttatum was studied in north-west Yunnan at 3490 m a.s.l. The flowers are rewardless 'kettle traps'. The structure of the lip, where pollinators are temporarily kept prisoner, and the method of their capture, are unusual in being Paphiopedilum- rather than Cypripedium-like. The deceptive orchid does not mimic any of the diverse flowers concurrently blooming in the habitat, all being visited by the polylectic pollinators of C. guttatum, viz. Lasioglossum virideglaucum, L. clypeinitens and L. sauterum, besides two additional probable pollinators and four non-pollinating visitors (all Halictidae; three new species). The bees got caught when they tried to climb onto the staminode and their forelegs slid down its slippery downward ridges, causing them to tumble to the pouch bottom. To leave, they had to climb a tunnel leading past the stigma to the anthers where a pollen smear was acquired while extruding themselves from the narrow exit. The similarities with myiophylous Paphiopedilum are discussed in view of the possibility that they may foreshadow evolutionary transitions between melittophily and myiophily found in slipper orchids. © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society, 2005, 148, 251–264.

Cyp guttatum does have an inwardly folded lip, but the infold is basically fused to the other side of the lip surface, such that the pouch very much resembles that of an (e.g.) Barbata Paph. Cyp guttatum does not come out in a 'primitive' position in the published phylogenetic trees on slippers.

Best,

V

 

[VAAlbert]

Re: Paph villosum:

The mesmerizing wart: the pollination strategy of epiphytic lady slipper orchidPaphiopedilum villosum(Lindl.) Stein (Orchidaceae)

HANS BÄNZIGER

Department of Entomology, Faculty of Agriculture, Chiang Mai University, Chiang Mai, 50200, Thailand

November, 1994, December, 1995 Available online 26 April 2002.


Abstract

Paphiopedilum villosumwas studied in hill evergreen forests (at up to 35 m above ground level) in North Thailand between 1990 and 1994. Flowering lasted 4·5 months: flower longevity 2–3 months. During 224 hours of flower-watching, less than 100 specimens of Syrphidae (Diptera) were seen in the vicinity of the flowers; 15 cases of pollen acquisition were mainly by femaleEpisyrphus alternans, Syrphus fulvifacies, Betasyrphus serariusamong 6 spp. of pollinators. Populations peaked during the main flower opening period, one month before the maximum number of open flowers was reached in early February. The flowers are ‘kettle-traps’ without known reward, luring mainly by food deception. Long distance attraction is probably by a urine-like odour (attraction to mammalian excretions had hitherto been little reported) and colour contrast. Close range lure is by the glittering staminode (probably mimicking droplets of honeydew/moisture) centred by a slippery wart (faking a perch) at which pollinators fly, immediately losing their grip and tumbling into the pouch, preventing wing action and falling being disrupted by a trough-shaped frame. Escape is up the tunnel, past the stigma, to the exit where, pressed by several mechanisms against the anther, the hoverfly scoops off very sticky pollen which has a viability of at least 8 weeks. Capsule formation averaged 8%.

Botanical Journal of the Linnean Society
Volume 121, Issue 1 , May 1996, Pages 59-90

This would seem to support the 'dumb fly' conjecture for many Paph species that have outfolded lips but don't have glandular, rothschildianum-like staminodes.

V

 

[VAAlbert]

BUT, here is more from the Paph villosum paper! -->

The slippery methods with which C. guttatum captures its pollinators contrasts with those in its congeners C. yunnanense and C. flavum. In these the bees crawl down the wide infolded flaps of the pouch, which are not slippery, and then enter the interior much like they enter a tubular flower such as Salvia brachyloma (unpubl. observ., this study). The staminode plays no direct role in capture, though it may initially function as a false nectar guide in attracting the bees from a distance.

The pollination strategies of C. guttatum are reminiscent of those seen in Paphiopedilum spp., although in the latter case the pollinators are hoverflies. The staminode has a direct and pivotal role in triggering the pollinator's capture; its slippery surface and adjunct flight interfering devices dispatch pollinators into the pouch. The staminode operates in three different ways.

In the first type, found in P. rothschildianum and P. callosum, the pollinators manage to grip the staminode for a few seconds while laying an egg before losing their hold. In the second, observed in P. villosum and P. charlesworthii, food-seeking pollinators try to grip a very slippery wart protruding from the staminode, losing their hold instantly. In the third, found in P. parishii and P. bellatulum, they grip the staminode's flattish surface, also without intent of laying, and slide off shortly afterwards. In the first type the pollination syndrome is based on 'perfidious' brood-site deception (leading to the death of the pollinator's progeny); in the second and third types it is based on 'opportunistic' food deception, possibly with a faint brood-site deception also at work (but without deleterious effects)....

Seems there is quite some diversity in lsipper pollination, much of it not published in detail.

Best again,

Vic

 

[VAAlbert]

So what would the presence of a natural hybrid in a pool of species do to the cladogram that's generated using molecular phylogenetics? Would the presence of a hybrid mess up the results for the rest of the species?

Well, it can certainly screw things up. For example, when we've looked at the Hawaiian mints, which are a VERY young group of plants, we see what could be termed 'intergeneric hybrids', but still, we are not sure if these genera are natural in the first place. Regardless, the hybrid nature of these plants is real, since we get 2 different genotypes for plants with the same morphology; the cladogram places them on different parts of the tree.

There has been some theoretical work on the influence of hybridization on cladograms, and I am certainly not the first to have seen and published on this in other plants!

Regarding how many generations it would take for a 'hybrid' population to stabilize into separate 'species', that would depend entirely on the impact level of either random processes (e.g., in small populations, as I described in an earlier post) or natural selection. And we can't get a better idea of this without detailed experiments in the field and the lab.

Bottom line, however, is that hybrid speciation is known to occur in plants. It usually is accompanied by polyploidization, but NOT ALWAYS.

Regards,

Vic

 

[NYEric]

This is awesome! You know, the inturned labellum folds, etc.

STOP! You're making me all sticky! :drool:

 

[Rick]

BUT, here is more from the Paph villosum paper! -->



Seems there is quite some diversity in lsipper pollination, much of it not published in detail.

Best again,

Vic

You also need to look at the natural history of the pollinators. The genera mentioned are all Syphidae and all use aphids as a larvae food source. Typically the males are atracted to flowers for nectar and pollen (just like bees). However it was noted that the villosum pollinators were females (ie looking for brood sites). In the case of villosum and species with similar staminodal structures (as opposed to roth and related fuzzy staminodes). The staminode looks like it has a big aphid (or aphid producing honeydew) in the center of it, and would subsequently count as another form of brood dececption as alluded to in posibility in the paper.

 

[Rick]

Another factor in pollinator specificity would be homerange size of pollinator.

For example, many of the native bees in the US are territorial and have relatively small well defined home ranges. (subsequently passing pollen around a small number of plants).

The imported honey bees are far less discriminant, have very large ranges without well defined borders.

This has reshaped some plant demographics in the US since the introduction of hiving honey bees.

 

[VAAlbert]

Thanks, Rick!

There's clearly a lot to learn about slipper natural history.

best,

Vic.

 

[Rick]

What's the weather like in Oslo today?

We had a high of 35 until the front went through, and tonights low is supposed to be 16:sob:


I'll be burning propane tonight!!

 

[Braem]

Hi Victor,

Evolution is important and off course evolution of orchids is of special importance to us orchid freaks. However, it would be of special interest that you explain the methods used and explain what the results of those methods tell us, and what they don't tell us.

regards
Guido

Hi all,

I saw a post somewhere in another thread that stated something to the effect that the various and sundry details of evolution and 'precise' taxonomy of the slippers wasn't so important to him/her, since he/she felt him/herself more of a horticulturalist. Pls. correct me if I'm wrong!

Well, I'll bet that some of you out there are interested in slipper orchid evolution, like I am. I'd love to discuss issues from hobbyist to advanced levels. My previous work with slippers has been in molecular phylogenetics and taxonomy; my present research includes evolutionary developmental genetics (the study of the genes behind morphological features) and comparative genomics (evolutionary studies of large numbers of genes among species and what they tell us). Plus some molecular phylogenetics, currently in the mint family.

Best wishes,

Vic.