Why are dodders ectoparasitic?

Old pic of my C. subinclusa

Anyone with a passing familiarity with heterotrophic parasitic plants knows that they are mostly invisible. Monotropa, Rafflesia, Orobanche, Pholisma: all undetectable lumps and/or strings buried in their hosts or in the ground, shortlived flowers notwithstanding.






So why the hell doesn't Cuscuta do that?






The dodder literature is silent on the matter, but we can make a few deductions. First off: Cuscuta is in the bindweed family. This seems a bit too on the nose, if you ask me, like it's from some sort of video game with a questionable understanding of biology that went "oh they don't look similar but they're related because they're both twine vines!" What's next, dodders with wings?
I mean, monotropes don't superficially look like free-living members of Ericaceae either but it doesn't feel that weird to me that they're related.

But obviously this is real life so Cuscuta really is in the Convolvulaceae apparently [shrug]. According to a low-effort glance at the taxonomy literature the genus's position in the family is unclear, but I do think that the twining ability shared by dodders and morning glories is a synapomorphy of the clade (I have no proof but I do feel that this isn't one of the cases where climbing behavior convergently evolves multiple times within a family).

If we assume this to be true then the evolution of Cuscuta's particular growth habit is not particularly surprising. One is tempted to conclude that evolutionary constraints have so far prevented dodders from becoming full endoparasites, and that this is a highly imperfect solution because evolution is imperfect, and/or that perhaps given more time to evolve the distant descendants of dodders may circumvent said constraints and become fully internal parasites.




Is that really the story, though? I mean, don't get me wrong, evolution is imperfect but I find that it is not as imperfect as people tend to think sometimes. A lot of traits that get handwaved away as "oh just arbitrary stuff caused by phylogenetic history, not everything the blind watchmaker does has to have a function" actually turn out to be pretty important adaptive features.

I suspect external climbing is an important part of the dodder life history strategy. The dodders I've worked with (and seemingly other dodders, from what I've seen online) appear to be tender-shoot specialists, and apparently die of malnutrition on sufficiently mature stems even when they manage to penetrate them. Which is a bit weird, since mature stems carry nutrients to the more nutritious juvenile tissues at their tips and if you've encircled the former it seems like you could intercept the nutrients going to the latter right? But leafhoppers and aphids able to feed on mature stems also tend to preferentially move to and feed directly on tender shoots when they can afford it, so I suppose whatever logic governs nutrient extraction efficiency applies to both the herbivorous insects and herbivorous plant in question. Also, dodders seem to feed only or mainly on plant parts they are wrapped around and not the rest of the plant; I have repeatedly seen strawberry petioles and nightshade stems that have been wrapped rapidly wither and die while all adjacent uninfested ones on the plant remain healthy. Though I have seen both C. subinclusa and C. californica form green islands on dying host tissue in certain circumstances (though not others), so some limited level of nutrient redirection seems likely.

Suppose you are a dodder and wish to maximize your intake from tender shoots while minimizing the volume of tissue you grow, given realistic environmental constraints. To get from one tender shoot to another on an adjacent branch, an obligate stem endoparasite would have to grow all the way down the branch and all the way up the other branch. Why do that when you can just bridge the gap by growing across? It's much less of a distance, and air is presumably a less resistant medium to grow through than rigid plant tissue. Plus being ectoparasitic allows dodders to span multiple hosts at once; this seems not that common in wild adult subinclusa and californica, but is apparently a major means of spread for temperate dodders, and juvenile subinclusa (in order to get at the part of the tree that's nonwoody enough to actually penetrate mechanically, since regardless of how nutritious it is or isn't the main trunk is just too thick to drill through) often start out feeding on small herbaceous plants and gradually climb taller and taller plants until they reach the edible portions of the tree.

You may have seen me occasionally complaining about my dodders mindlessly climbing upwards the same way ladybugs and a lot of other foliage-inhabiting insects do; while it's definitely pretty annoying in captivity (since when the old host is exhausted and you put a new host that's shorter next to it the dodder often struggles to find it), the adaptive benefits of this in nature are pretty clear.

Today's non-adventure

Checked the "loose sands Notibius zone" part of Santa Fe Dam Recreation Area (too lazy to take a pic so here is a pic of the entrance in winter, it looks about the same but browner since Rhus/Malosma/Lepidospartum/Ericameria/cacti make up most of the remaining green vegetation, also the interior is aesthetically similar to the entrance not as disturbed looking) to see if it had any cool summer endemics the more stable sand elsewhere lacks.

Kind of disappointed the Cryptocephalus there were still spurcus, also found a whole bunch of 5mm-ish microweevils on scalebroom flowers I didn't keep because they looked like they might be gall inquilines (weevil larvae as a general rule are endophages on seeds and other high-calorie plant parts and these were too fat to fit into any of the seeds nearby. Even if they were stem borers or root eaters though I'm not willing to take any chances because I only have one scalebroom myself and it's still in its whiteleaved "larval" stage, assuming that's even the oviposition host, and I don't happen to have either mature individuals or any individuals of any of the other plants in that microhabitat).

No big deal though, I was expecting pretty much exactly all this to happen (and I did take home both the spurcus I caught anyways, for genetic diversity, so I'm not exactly complaining). I wonder if the unmarked and/or sunshine yellow morph lives in my area? Well, probably not the latter, that's probably a high-desert special, but unmarked beige ones seem likelier. The stripes undoubtedly help them camouflage on marcescent leaves/seedheads of pinebush so I've been looking on scalebrooms for stripeless ones, albeit to no avail (scalebrooms seem to provide poorer habitat somehow [probably due to their vestigial adult leaves translating to poorer microclimate protection and poorer edible leaflitter], this year I only saw one on that plant and it was striped and it got away).

The previous spurcus are both gone [one released after it laid enough eggs, the other escaped and died and I still feel extremely bad about its death] so my current cryptocephaline population remains at two, not counting the 32 eggs.

PSA: postmetamorphic larval memory retention

 A lot of you have probably seen those recent viral news stories about the Japanese boy who wrote a study about swallowtails remembering stuff from their time as caterpillars. Just noting here that: 1. this is not the first experiment of its kind 2. Manduca sexta adults only seem to remember fifth instar memories.

I assume hemimetabolous insects tend to remember more of their juvenile lives.

Cryptocephalus hunting again

 

Have continued to be bored to the point of serious mental illness. Went to the Santa Fe Dam soft chaparral a few times again to see if I could bag anything because collecting bugs is my unhealthy coping mechanism apparently.

Now, the thing about the soft chaparral here is that whenever the summer dry season hits and the bushes "die" (aestivate) the already low insect density drops even further (the hard chaparral and sclerophyll oak forest stay active a bit longer into the season because they are by nature less arid habitats). It's our version of winter; it's when life drains out of the world; it's the end-scene of HG Wells' Time Machine with the quiet beach and the endless night and the red-overripe sun waiting to burst. It's kind of sad that extremophiles (for all their tenacity) are still so helpless against natural extremes. Why can there be only a few snow crane flies, a single Antarctic midge? Why must serpentine flora be forced into stunted growth? Why does Mono Lake lack a second brineshrimp?

Nevertheless, life still goes on, albeit not very vigorously. The cacti here do not turn brown, of course, because they are cacti (Narnia and Chelindea continue to suck on their fruits all summer but the few cactus genera here don't seem to host much more than that at any time of year, unlike in, say, parts of Arizona, so I will not be mentioning them further), and Malosma plus the lemonadeberries stay almost as alive, but they seem to support even fewer local insect taxa than the cacti this time of year so will not be mentioned further either. This leaves us left, for the most part, with the summer-specialist dandelion guild: Lepidospartum squamatum (scalebroom), Ericameria pinifolia (pine goldenbush), Lessingia glandulifera (vinegar tarweed), Heterotheca grandiflora (telegraphweed). I'm tired and not in the mood to talk fluidly any more right now so suffice it to say:

- the above pic is one of the lushest microhabitats left right now (not pictured: miles of brown desolation)
- summer-specialist insect guild largely gone from soft chaparral, the occasional Eleodes acuticauda notwithstanding; many of the other spp. emerge and die earlier in the summer when the growing season is ending but not ended for the summer-dormant shrubs; no Elicinae seen
- Cryptocephalus spurcus is still in season as it eats goldenbushes and scalebrooms, which are both blooming and lush
- yesterday I caught a mating female of Cryptocephalus spurcus
- it seems to be slightly (but only slightly) less behaviorally problematic than C. sanguinicollis but "slightly" can make a big difference; after some initial struggling I've successfully gotten it out of "too scared to eat and rest" mode and so far it has not resumed panicking/flying as sanguinicollis has always done in my care (hoping I don't jinx it)
- to my unsurprise I am still exactly as bored and mentally ill as before

Update 7/31: caught a second one. First one has made exactly one egg capsule so far, it has the cool helical ridges typical of this genus (which is formed, if you weren't aware, by the female turning the egg spirally as it defecates, which I assume is the simplest way to coat a round object without missing any spots).

What is it like to be a leafhopper?: a speculative essay

Imagine that you live on a tower of pipes so tall it extends beyond view.

Imagine that it is filled with juice, and that you are thirsty; you bite into its soft side, and it takes a while before you can get at the juice, but you do manage.

And it tastes good. It tastes so good. You never want to stop. You drink for hours and time speeds up and the outside world fades away. You don't even notice you are asleep by the time the sun has set, and the next day you hardly realize you are awake.

You are rudely returned to full consciousness by a dry sensation in your mouth. Evidently your tower only has so much juice to give. How? You were only there for a few moments (you had not moved from the spot in two weeks) it was hardly enough (it was more enough than you could ever remember) you do not feel well-rested at all (you were designed to never know peace).

Fortunately, there is another pipetower to the north, and the journey there is not too arduous. When you arrive you will find it to be as juicy as the first one used to be, but it will not feel satisfying either because when you are satisfied you will not feel.

yeah it molted

My suspicions were correct, it was Penestragania ivanpah

putting this thing on the strawberry clover with the Tiaja

Penestragania?

 Creeping around suspiciously at Plymouth Elementary's so-called native garden when I saw this thing on a palo verde, figured it's polyphagous enough that I could rear it to adult for ID to kill two birds with one clover (two clovers with one stone? Okay the metaphor is breaking down pretend I said nothing). Gonna release it after that probably.

2 Tiaja left

But thank God for Trifolium fragiferum.

Tiaja squeeze campaign

 With the last Xerophloea dead (a juvenile brown widow murdered it, even though I checked for brown widows a few days before that and found none) all I have left are the four Tiaja, which I've still not managed to get any eggs out of. Apparently white clovers freak out when taken indoors and gradually die from dehydration even when well watered, some quirk of the angiosperm root physiology I think.

They stay frightened for longer after handling than the Xerophloea did, sometimes freezing and then not feeding for a whole 12 hours after being moved, and since like many hoppers they don't actually know how to walk directionally towards their food it's been a headache (after the freezing wears off they tend to walk off the plant even if they were sitting on it).

Bought some more plants as potential food while I was exhibiting milkweed bugs at CalBG for their milkweed festival thingy. The hoppers didn't seem to like their new hosts much, I'm going to try feeding them an attached dodder now (previous dodder being fed was detached branches, which are more convenient to supply but cannot live long enough for eggs to hatch).

Released all adult beetles several days back

The rotten wood is doing that thing again where it gets all moldy and gross and it was stressing them out to the point they weren't sleeping, and I didn't have the energy to deal with it. Based on my observations I'm pretty sure the Megapenthes would've been pretty stressed during its waking hours even in a clean enclosure though, as even after I moved it to a clean container full of garden soil (which itself it kept spreading its elytra like it wanted to fly (but never flew; perhaps room temps too cold to flap wings)?

Anyways, guess I'll have to concentrate on sucking hoppers and plants for now. I still have 1 vial of rotten wood that never went bad and still smells nice though and I'm hoping that I can make more of whatever saproxylic microbes are responsible for the smell and mold suppression so I can inoculate other rotten-wood-making containers with them.

Well actually some of the E. lecontei larva vials are also clean-smelling, I lied.

I ignored Easter to catch beetles and emit depression

https://www.bugguide.net/node/view/2526641
https://www.bugguide.net/node/view/2526642

Caught these two, will attempt to breed. Of note is that Megapenthes contains at least one species of conservation concern in Europe.

Update: Stenochidus is being difficult, it's panicking and behaving abnormally because it's in an enclosed space, will probably release once I have the time. I figured this would happen given that it seems to happen to a lot of small flying plant-dwelling beetles but wanted to test. Put it on a potted plant in the meantime to soothe it (by making it think it's not on the ground).