The guts of the Golden Bear harpaline

Dichierus strenuus. Image by Joyce Gross

Dichierus strenuus. Image by Joyce Gross

Don’t get me wrong. DNA sequence data is fantastic for phylogenetic studies and all kinds of biological investigations. But I must say that looking at ACGT doesn’t give me much of a thrill. I’m a morphologist at heart, what trips my switch is seeing something new, or at least new to me.

Recently I have been looking more carefully at the morphology of the western North American endemic harpaline genus Dicheirus, or the Golden Bear harpalines. It’s a small genus of five species-level taxa distributed from northern Baja to southern British Columbia, east to Montana, with some questionable records from Utah and Arizona. All the species are covered with hairs and in several species they have really long golden setae and so that’s why I call them the Golden Bear harpalines.

During routine male and female genitalia dissections I noticed something very peculiar about the hind gut. Not so many people spend time pondering the alimentary canal structures in carabids, though there is a fairly extensive but scattered  descriptive literature. The only review of the guts I know are papers by K. Yahiro in the 1990s.  What struck me was the position of the rectal pads in Dicheirus; which are arranged distinctly in two rows of three, while all the published descriptions I looked at and what I have found in previous dissections is that all six pads are in a single row at the anterior end of the rectum.

Dicheirus brunneus female dissection

Dicheirus brunneus female dissection

We know that these beetles feed on seeds. I have seen them out at night feeding on grass seed many times and participants in last year’s Essig trip got to watch them as well. This simple, yet distinctive difference in the gut structure seems suggestive of a modification that may be related to their diet and/or the seasonally dry oak-woodland and grassland habitat they are often abundant in. The function of the pads in carabids and other insects for osmotic regulation is well-known. Maybe these beetles will be just fine in drought years like this one. We might find this arrangement in other harpalines (none so far), other seed-feeding carabids or carabids living in arid environments. At this point too little is known and one can speculate widely, but I will wait and spend more time looking at guts.  It’s such a cheap thrill.

Oh, yes we do have the classic Golden Bear harpaline, Dicheirus dilatatus here on the UC, Berkeley campus. Maybe a new mascot for our t-shirts?

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About Kip Will

I'm an insect systematist with expertise in carabid beetles, who is always happiest in the bush.
This entry was posted in Carabids, Coleoptera, Entomology. Bookmark the permalink.

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