[Mark Melton]

The three species of Fallceon shown here are all out of the Russian River. They are usually found with Baetis and Camelobaetidius nymphs. They prefer a clean gravelly bottom with a moderate to fast flow. The three species shown here are Fallceon quilleri (5.5-7 mm), F. thermophilos (5-5.5 mm), and an unknown Fallceon sp. (5-5.5 mm). All measurements exclude antennae and cerci.

Fallceon quilleri females

Fallceon quilleri female

Fallceon quilleri male

Fallceon quilleri female

Fallceon quilleri female

Fallceon quilleri male

Fallceon thermophilos male

Fallceon thermophilos male

Fallceon thermophilos female

Fallceon thermophilos females

Falllceon thermophilos female and unknown Fallceon sp. male

Fallceon quilleri female. Fallceon thermophilos female and male.

Unknown male Fallceon sp.

Unknown male Fallceon sp.

Fallceon thermophilos male and unknown Fallceon sp.

Unknown Fallceon sp. male.

Unknown Fallceon sp. male.

Male Fallceon thermophilos and unknown Fallceon sp. male.

Female unknown Fallceon sp.

 

[greenriver]

Mark- thank you for posting your pictures.

 

[Mark Melton]

Mark- thank you for posting your pictures.

You're welcome.

 

[MGTom]

Thanks for your posts. I never thought we had many mayflies, but our bugs seem similar to yours and the more I look the more I find. No wonder the hare's ear nymph is good, it looks like all of them, at least to me.

 

[cabezon]

Hi Mark,
Very cool photographs. As I was going through your post, I was struck by the sexual dimorphism in these mayflies. As these larvae are non-reproductive at this stage, what would be the "value" of dimorphism in color (or morphological features, such as eye size, etc.)? At one level, one would think both sexes would converge on the color patterns and anatomical features that maximize larval growth and survival. Might this reflect the limits of what changes can occur from the larval molt to adult molt for insects that lack a pupal stage? What I mean is that if a male adult benefits from larger eyes to find females (or whatever) and there are limits to how much the eyes can expand from one molt to the next, then the larval male will accept having slightly larger (but suboptimal) eye size in the larval stage because the larger eyes have such a large advantage as an adult?
Is there similar sexual dimorphism in aquatic insects that have a substantial pupal period, such as say caddisflies or midges?
Thank you for posting this whole series.
Steve

 

[Mark Melton]

Thanks for your posts. I never thought we had many mayflies, but our bugs seem similar to yours and the more I look the more I find. No wonder the hare's ear nymph is good, it looks like all of them, at least to me.

There are a hell of a lot of mayflies everywhere. All it takes to find them is a little patience and the willingness to look. As far as the hare's ear nymph, as long as it looks like a generic nymph it should do the job.

Hi Mark,
Very cool photographs. As I was going through your post, I was struck by the sexual dimorphism in these mayflies. As these larvae are non-reproductive at this stage, what would be the "value" of dimorphism in color (or morphological features, such as eye size, etc.)? At one level, one would think both sexes would converge on the color patterns and anatomical features that maximize larval growth and survival. Might this reflect the limits of what changes can occur from the larval molt to adult molt for insects that lack a pupal stage? What I mean is that if a male adult benefits from larger eyes to find females (or whatever) and there are limits to how much the eyes can expand from one molt to the next, then the larval male will accept having slightly larger (but suboptimal) eye size in the larval stage because the larger eyes have such a large advantage as an adult?
Is there similar sexual dimorphism in aquatic insects that have a substantial pupal period, such as say caddisflies or midges?
Thank you for posting this whole series.
Steve

Steve,
I think that the larger eye size in the males corresponds to there being no pupal state and the relatively short lifespan of mayflies, especially the males which are essentially flying sperm depositories. It puts a time constraint on them, essentially since there is no pupal state to develop the eyes, and not enough time to fully develop them in the adult stage.
I'm not aware of any similar sexual dimorphism in caddisflies, and I haven't studied midges enough to know of any. But don't midges have dissimilar antennae, with the male's having more ornate antennae, able to pick up the female's pheromones?

 

[cabezon]

Hi Mark,
Thank you for sharing your insights. Are you (or @Taxon) aware of any scientific papers on this topic of metamorphic constraints? Do you tend to find male and female larvae of mayflies in the same habitat? Might their differences lead to some microhabitat segregation?
Steve

 

[Taxon]

Are you (or @Taxon) aware of any scientific papers on this topic of metamorphic constraints?

I am not.

 

[Mark Melton]

Hi Mark,
Thank you for sharing your insights. Are you (or @Taxon) aware of any scientific papers on this topic of metamorphic constraints? Do you tend to find male and female larvae of mayflies in the same habitat? Might their differences lead to some microhabitat segregation?
Steve

Steve,
I'm not aware of any papers. You might try googling it on Google Scholar. I do find male and females in presumably the same habitat. I use a fine mesh kitchen sieve for a lot of my sampling and more often than not get males and females out of the same one square foot.

 

[cabezon]

Steve,
I'm not aware of any papers. You might try googling it on Google Scholar. I do find male and females in presumably the same habitat. I use a fine mesh kitchen sieve for a lot of my sampling and more often than not get males and females out of the same one square foot.

Hi Mark,
Thank you. I have done a brief search through Google Scholar but I have not found anything that strikes me as addressing my questions (and my interest in the topic extends only so far...).
Steve

 

[Troutnut]

Great pictures Mark!

 

[Richard Olmstead]

Nice photos and I really appreciate the back and forth on the scientific question of whether a simpler developmental sequence would be more likely to show sexual dimorphism!