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Hi.

Some of you may have noticed that I have published a paper with the title "Nematode-induced demasculinisation of Dolichopus males (Diptera: Dolichopodidae)" in Zootaxa (1689: 51-62).

The parasite/parasitoid nematodes can have a major effect of the diagnostic characters of the host fly. Many of these 'nematode forms' have in fact been described as new species! Fortunately (for the dolies at least) the nematode is apparently restricted to basic wetlands in the boreomontane zone. It is currently known with certainty only from Scandinavia, but preliminary records have already been made from the central european mountains and from the nearctic.

Although the paper title refers only to Dolichopus, the parasite has a (potentially much) larger host range. I have seen infected Rhaphium and Gymnopternus males and suspect it may not even be Doli-specific.

So, if you work with Diptera brachycera with semiaquatic larvae (or pupae), you may be interested in this paper. If you don't have institutional access to Zootaxa's archive, ask me for a PDF copy.

The photo below shows a typical parasitised male (in this case Dolichopus "cruralis", which is in fact synonymous with Dolichopus lepidus): The coils of a large, cream-coloured nematode can be seen though the tergal membrane. There's a round exit (or entry?) scar visible on the membrane below the hind knee. The male genitalia are unusually small and the rotation+lateroflexion is incomplete. Not all flies are this strongly modified. A large adult Dolichopus (say Dolichopus discifer) with a single parasite can survive with few external signs of attack.

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boreomotane .--- a typo?

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Yes! That's need to described the new species only series of specimens. It would then be much more difficult to make mistakes..

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If allowed by Zootaxa, you can put it up on this site for download. If not, I'd appreciate that digital copy. ;)

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me too.. I'm very interested, Jere. :)

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Ah, but sometimes it does not help. The damage by parasites repeats of a predictable pattern and I have occasionally found high (>10%) infection rates is some cases. So you can collect series of identical, morphologically 'different' specimens and still go wrong :)

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Thanks Jere for interesting paper. I think there is a lot more pairs of synonyms in European species due to demasculinisation. I have not found answer to a question, why do the nematodes like males only?

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As I say in the paper, that may not be the case. I did a statistical test to see whether the preference for males is real, but the result is inconclusive. So it may be merely a random pattern. One should also consider the selection effects acting here: potentially parasitised males can be spotted by the changes in morphology, but changes in females are probably much more subtle. Males with obvious deformities * are examined for parasites at a higher rate than females.

I have yet to see a parasitised females - that does not mean they do not exist :)

Next year I will try to rear the parasite to the free-living adult stage for identificatio - if I can find some parasitised dolies. Unfortunately the sites where it is reasonably common are about 1000 km from my home. Rearing a specialist species such as this may not be easy. We'll see.

* EDIT: Care if needed here: the parasite does not always cause obvious demasculinisation. The effect depends on the host species size and the number of nematodes involved. A single parasite in a large host can cause only minor changes (like in the Dolichopus popularis - D. aemulus pair).

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Hello,

I just read an article by J. Perez on stylopisation of Hymenoptera Andrenidae (1886) and he states the same thing about false species which are nothing more than well known species but castrated by the parasit.

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I think this is a typical problem of overrelying on a single character like that of the male genitalia. Similar mistakes were done by Mihalyi, who described a number of genera in nematode infested Fanniidae. In fact the Nematode does not seem to affect the development of most other external characters, except the male genera.

I think a good species can be defined as at least two major differences from all known species falling into two different categories located on two developmentally distinct regions of the specimen consistent withing a series of individuals.

By categories of differences I mean that a difference should be noted in coloration and chetotaxy, but differences solely on chetotaxy or coloration etc are always suspect. Variation is less likely to affect more than one category of features consistently.

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Thanks Kahis for the article! :D I will read it in July.

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Many of the doli 'species' discussed above fulfill this requirement for a 'good species', but they are anothing but. There are (reasonably) consistent differences in both colour (legs), chaetotaxy (ornamentation of legs) & male genitalia at the same time. Many dolies are strongly sexually dimorphic and sexual intermediates produce 'new' forms of colour and chaetotaxy.