[Syrphidae] Re: Male genitalia rotation

[Francis Gilbert]

I do not think the degree of rotation in syrphid genitalia is fully understood yet. I don't think it is the full 360 degrees of the Schizophora, but it is hard to be certain because of great confusion in the identification of the tergites and sternites of the postabdomen in syrphids, plus a lack of evidence.

Whether less than 360 degrees provides a bit of flexibility in mating position, I don't know. Some end-to-end matings have the male upside down, whilst others they are both upright.

If Ximo's paper is correct and end-to-end requires a different kind of rotation, then those syrphids mating like that should either have unrotated or even more rotated genitalia. However, Sphaerophoria is one of the ones that actually has been studied (Zaka-ur-Rab 1979) but unfortunately his account is also one of the hardest to understand, and probably is full of mistakes.

The crucial evidence of rotation from internal anatomy (particularly tracheae, nerves and the ejaculatory duct) are only available from Gäbler (who suggested only a 90 degree turn in Eristalis) and Griffiths (in "Syrphus", from serial sections, but not reported in detail). There is plenty of evidence from Schizophora of all three elements crossing over in segments 7-8.

Francis

From: syrphidae-bounces at lists.nottingham.ac.uk [mailto:syrphidae-bounces at lists.nottingham.ac.uk] On Behalf Of ximo mengual sanchis
Sent: 10 February 2021 15:30
To: Hoverfly discussion list <syrphidae at lists.nottingham.ac.uk>
Subject: [Syrphidae] Male genitalia rotation

Dear all,

this publication came out a couple of years ago, and since then, I wonder if Sphaerophoria or Ornidia (whose species copulate in an end-to-end position) are examples of "reverse evolution".

https://phys.org/news/2019-02-evolutionary-rotation-genitalia-tied-success.html

Any ideas? Maybe the authors were not aware of the diversity of positions in higher Brachycera...

Ximo
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