[Syrphidae] Re: Male genitalia rotation

[Jeroen van Steenis]

Dear All

There is some interesting reading in Reemer et al 2009. De Nederlandse
Zweefvliegen'' in which the species Criorhina asilica is known to have both
copulating positions, head-to-head and tail-to-tail. In Volucella bombylans
there is another position, belly-to-belly adjacent to the head-to-head. So
the rotation of the genitalia does not imply there is a fixed position in
these species, and possibly this accounts for more Syrphidae.

Hope this helps.

Best wishes,

Jeroen

Op wo 10 feb. 2021 om 17:04 schreef Francis Gilbert <
Francis.Gilbert at nottingham.ac.uk>:

> 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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