A hike in the Sierra foothills

October 31, 2022 • 12:30 pm

Yesterday my friend Phil and I took a long hike (though it was only 3.4 miles long, it was a tortuous path with ups and downs) in the Sierra Nevada foothills: we took the Western States Trail near Auburn, which connects with other trails going all the way east to Lake Tahoe.

There are several viewpoints looking down to the North Fork of the American River, below. About fifty years ago they proposed to build the Auburn Dam here, which would have filled this beautiful valley with water. But the project ran out of money, and work on the dam was suspended.  I am glad. Think of all the animals and plants that would be killed by this flooding! But some day they may finish the dam.

We found a vine of wild grapes (Vitis vinifera, the ancestor of Concord grapes) and decided to mash them up to see if black flies (D. persimilis or D. pseudoobscura, species I worked on) could be caught. Their ecology, including what adults and larvae feed on, is virtually unknown, and I spent a long time during my postdoc trying to find out, No success. Here we have a native, wild-grown berry that might attract flies, so we put a grape moosh in a vial and left it during our hike.

Phil placing the grape mash in a cool area at the base of a tree. Sadly, when we returned there were no flies, or other insects, on the mash. It’s curious that two of the most genetically well-studied species of Drosophila (by Dobzhansky, my academic grandfather) have an ecology that’s a mystery. This is also true of D. melanogaster, the genetically best-studied species of fruit fly, but where it lives in Africa—if it’s still extant in the wild—is unknown.

A humongous cone of gray pine (Pinus sabiniana), a California endemic. Each bract hides a tasty seed (“pine nuts”), which the squirrels work hard to obtain:

An extracted pine nut, itself covered with a hard shell.

Christmas berry or toyon (Heteromeles arbutifolia), a perennial shrub native to the west coast of North America.

Below is one of the two great finds we made on our hike, though it’s not rare: it’s a cynipid wasp gall on the stem of an interior live oak (Quercus wislizenii). Galls are structures that are “made” by larval insects whose mothers laid eggs on either stems or leaves of plants.

In this case the mother was the live oak apple gall wasp (Callirhytis quercuspomiformis). This species of tree, like others, can be parasitized in this way by several species of wasps, but each species makes only one type of gall. In this case a yellow, golf-ball-sized gall also has prickles to protect it against predators.

Below: clearly, two wasp eggs were laid, and the larvae somehow form this gall (as all galls are formed) by hijacking the plant’s developmental system to form a large, hard tumor that protects the larvae until they pupate and hatch. The adults then chew themselves out of the gall.

This is an amazing evolutionary phenomenon, for a gall can be regarded as an “extended phenotype” of the wasp (or whatever insect makes it), which has evolved to make the plant build a house for the larvae. Even the spines on the gall, which protect it against predators, are somehow coded in the wasp’s DNA: wasp genes that somehow make the plant’s own genes produce spikes. I’m not an expert on galls, but I think we have no idea how the insect manipulates the genome of the plant to make such a structure.

Galls are one of the marvels of natural selection, and something that Phil and I discussed in detail on our hike. It’s a great mystery, too, and would be a fascinating–though formidable–problem for scientists and Ph.D. students to work on. How do the parasite’s genes hijack the plant’s genes to mold such amazing structures?

Here is a different gall (the thickened part of the stem) made by a different wasp, but on the same species of oak–the interior live oak. The shape of the gall is diagnostic of the insect species that produced it. Galls can appear on both stems and on leaves.

This was our second great find. I saw a woodpecker flying by, and it settled in a nearby tree. It turned out that this was an acorn woodpecker (Melanerpes formicivorus), and it had several mates on a dead oak branch. You may know of this woodpecker, as it’s famous for its “granaries”: trees or branches in which it drills holes to store acorns over the winter.  They are also cooperative breeders. Here are three on a dead oak branch; you can see the holes for storing acorns:

Wikipedia‘s description of this storage system:

Acorns are stored in small holes drilled especially for this purpose in “granaries” or “storage trees”–usually snags, dead branches, utility poles, or wooden buildings. Storage holes–always in dead tissue such as bark or dead limbs–are used year after year, and granaries can consist of thousands of holes, each of which may be filled by an acorn in the autumn. Access to acorn crops influences the composition of acorn woodpecker communities. In one study in New Mexico, there were about 90% of non-breeding adults per social unit in 1976, a year of a poor acorn crop. The following year, 1977, there was a significant increase in acorn production and a correlating decrease in non-breeding adults per unit.

Although acorns are an important back-up food resource, acorn woodpeckers primarily feed on insects, sap, and fruit. They can be seen sallying from tree limbs to catch insects, eating fruit and seeds, and drilling holes to drink sap.

The woodpeckers then collect acorns and find a hole that is just the right size for the acorn. As acorns dry out, they are moved to smaller holes and granary maintenance requires a significant amount of the bird’s time. The acorns are visible, and a group defends its granary against potential cache robbers like Steller’s jays and western scrub-jays.

It’s interesting that they find acorns to fit the holes, and move the acorns as they shrink.  Look at all the holes in this tree!

Here you see some of the holes filled with acorns:

After the hike, when it had become hot, there was nothing else to do but find a brewski in the lovely small town of Auburn. I didn’t want an overhopped IPA at the local brewpub, but went for a refreshing cherry-flavored gose beer, a variant of Belgian fruit beers.

A fitting end to our hike:

33 thoughts on “A hike in the Sierra foothills

  1. That looks like a lot of fun! The first thought on how insects induce galls to form is that there is something in their poop. That could be wrong, but that is where I’d start looking.

  2. The information about the galls was fascinating: parasitic genes highjacking host genes. It sounds like something off a sci-fi movie, but here it is as real as can be.

  3. The information about the galls was fascinating: parasitic genes highjacking host genes. It sounds like something out of a sci-fi movie. Yet here it is, as real as can be.

    1. So that is interesting. A kind of protein injected from saliva in the case of an aphid that induces galls. I was wondering if there are diverse ways to do the job. For example, maybe in some species the mother delivers a small sample of viruses when she lays an egg, and the viruses proliferate and induce gall formation.

  4. Thanks for the virtual trail trek. The woodpeckers are gorgeous.

    So was the brewski a form of lambic? Sour? I’ve been finding some nice domestic lambics lately…or sometimes they’re called “sour ale”.

    1. It wasn’t sour, and didn’t taste a lot like the cherry lambics I’ve had in Belgium. It was simply a refreshing tipple. They had a lot of homebrewed beers on offer, but I wanted only one.

  5. I understand why pine nuts are so expensive! We picked/harvested some in Utah a few years ago and it took forEVER to get a handful (plus they stick to you).

    1. I picked/harvested pine nuts in Nevada ONCE! You’d have to be a starving squirrel to go through all that trouble!
      Yes, it is understandable they are pricey. Though I’m sure they have industrial “pine-nut gins” that make quick work of it. Costco has the best prices I’ve found.

      1. I’ll bet squirrels have much better teeth and claws than we do for the job🤓 I have bought pine nuts at Costco, and keep them in the freezer.

        1. Yeah, I’m sure squirrels have no quarrels with the pinecone’s fire-proof protection of hidden-nut delights. Squirrels? Damn, I love those critters.

          Pine nuts. They do last forever in the freezer…I should know, I think I have a bag that’s at least 10 years old and the nuts are still perfect when defrosted and toasted. “They” say the nuts last a year in the freezer (same thing with stock, and fume is even stricter at 3 months…it’s all bullocks) not so, I say. I do keep the majority in vacuum sealed bags and a smaller amount (easy access) in 16 oz. jars. Good way to manage nuts imo. I’m a nerd on food storage issues…insert glasses emoji here

          1. Fume??
            I’ve got much older stuff in my deep freeze🤓 maybe 6 kinds of nuts, homemade stocks, peaches, rhubarb, raspberries…pesto…

              1. Oh, yeah, bien sûr! Should have made some tonight from all the bones left in my supposedly filleted sea bass🤓

  6. Delightful!

    I have another short gall-themed RWP in the works … things get in the way … I learned about them here – was in my backyard, seen them my whole life, and never knew – fascinating objects! Thanks to the RWP readers for the education!

  7. Gall wasps seem to have odd life cycles (partly parthenogenic). And chestnuts, also in the Fagacae with oaks and beeches, have their own gall wasp, Dryocosmus kuriphilus, that produce small reddish galls on stems. They, in turn, have their own parasitic wasp, and the general experience is that once you get gall wasps on your chestnut trees, wait till next year and the parasitic ones will clean things up.

  8. Re the ecology of Drosophila pseudoobscura. I recall Herman Spieth marching triumphantly into Tim Prout’s office one day in 1983 or 1984, holding a rotting acorn adorned with fly pupae. Spieth told us that these were the pupae of D. pseudoobscura, and that the mystery of the species’ ecology was solved—acorns were the larval resource for D. pseudoobscura. Today I searched for publications on this result, and I found two papers giving evidence for Spieth’s claim:
    Spieth, H. 1987. Drosophila fauna of a native California forest (Diptera: Drosophilidae). Pan-Pacific Enromologist 63(3):247-255.
    Spieth, H. 1988. Native larval substrate of pseudoobscura. Drosophila Information Service 67(1).
    Mystery solved?

    1. I haven’t read those papers (they were published after I gave up on the problem), but acorns can’t be the sole host of the flies, even if they are a natural host. That’s because plenty of black flies occur in areas where there are no acorns, like Death Valley or the piñon pine/juniper forests of California.

      UPDATE: I’ve now read one of them, which shows only that if you put black flies together with mushy parasite-infested acorns, you can get them to lay eggs and produce adults. It does NOT show that acorns are used in this way in nature, or are a natural breeding site at all. I suspect the other paper is like this, as well, as I knew Herman at Davis when he was making his “discoveries”.

      1. You’re right, Jerry, Herman’s approach couldn’t rule out other possible resources for the flies even in the open oak woodlands he was studying. I wonder if in the intervening decades anyone has solved the problem for pseudoobscura in Death Valley oases. Maybe those black berries of the native Washingtonia palms?
        In a related subject, if anyone has a photo of an acorn with D. pseudoobscura pupae, I’d be grateful for it. An intro bio lecture of mine has been calling out for such a photo for decades.

      2. Interesting; I was not aware of this issue.
        At least in my part of the California desert there are plenty of scrub-oaks in the pinyon-juniper zone. I am not familiar with Death Valley, but there are doubtless scrub-oaks on the higher mountainsides. It’s hard to think of a more consistently available fruit of any kind in the desert. The flies may of course have alternate hosts as well.

  9. Thanks for taking us along on your trek! The side project with grapes made me smile – you know you’re in good company with those sorts of adventures!!

  10. There’s a rather sickly gray pine overhanging my rear boundary fence, so each year I get a few massive pine grenades. ‘My side, my cones’, I get enough so that visitors ask if it’s a good idea for me to wear a hard hat when I’m working in my garden.

    Right next to the pine is a happier Brewer [weeping] spruce — both likely gifts from Rudy C, my former downslope neighbor, who built the first house in the neighborhood in the mid 1950s, Rudy worked at a forestry nursery, and it seems, showed up with random conifers as home-warming gifts. Rudy’s most spectacular legacy trees are the dozen or more BigTrees [Sequoiadendron giganteum scattered around my ‘hood. They reach awesome size in a few decades, and I’ve met newbies think these exotic conifers are ‘old growth’ — centuries or millenia.

  11. Hello Jerry
    I believe the parents of the Concord grape is the American fox grape Vitis labrusca. Vitis vinifera is the European grape.
    Stuart MacLeod

    1. That is correct. There is, in addition to Vitus labrusca, Vitus riparia and several other native North American species.

      If you have ever tasted V. labrusca and V. vinifera, as grapes, you will find that they taste very different. And the characteristic flavor note in the non-vinifera grapes, usually described as “foxy” is very clear. And it is clear in the wine made from non-vinifera grapes.

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