[Taxacom] Hygrobia (was Eurasia-Australian distribution)

Stephen Thorpe stephen_thorpe at yahoo.co.nz
Sun Jul 25 16:50:25 CDT 2010

massive speculation going on here in this thread!
distributions of organisms tend to have a big random element (random extinction, 
random dispersal events), so trying to "retro-rationalize" them in any great 
detail is probably futile...
how about this little known example: the weevil genus Rhopalomerus occurs in 
N.Z. and Chile (and maybe Australia and New Caledonia). Most species are from 
N.Z., including R. tenuirostris - the only Chilean species, which occurs in 
native forests from sea level to the high mountains throughout Chile and New 
Zealand, and appears to be native to both countries!
then there are gymnusine staphylinids, restricted to the Holarctic, except for 
one species from the subantarctic Auckland Islands!
similarly agyrtids, Holarctic except for a New Zealand genus ...
apparently there is a fungal taxon known only from N.Z. and Cuba, but in this 
case that is also the distribution of experts on the taxon!


From: Jason Mate <jfmate at hotmail.com>
To: Taxacom <taxacom at mailman.nhm.ku.edu>
Sent: Mon, 26 July, 2010 9:31:37 AM
Subject: Re: [Taxacom] Hygrobia (was Eurasia-Australian distribution)

I have no idea what is behind their distribution: that is why it is so 
interesting (if you care for water beetles that is). 

The chinese Hygrobia appears indeed to have disappeared from its former 
haunt. However I would loath to claim it is extinct. I know of 2 
coleopteran species that were apparently extinct but have surfaced 
recently. Most of the old collecting localities in China are been built 
over but these were coastal localities so the extinction pattern is very
much stacked against coastal habitats.

Of the australian 
Hygrobia I know australiasiae is common; nigra has a wide range; watsi 
is endangered. The latter lives in bogs in W Australia, not very good 
real state in that heck of the woods!

In any case, Aspidytidae and Amphizoidae are either extremely
poorly known and sampled, or extremely relictual.  Aspidytidae in
particular, having been only been recognized since 2002, may be found in
far more localities in Africa and Asia in the future, so their seemingly
"curious" distribution may not appear so curious in the future.        
    I'm not sure whether or not all of this will affect my hypothesis
that Dytiscidae has outcompeted Hygrobiidae (or other families in the
superfamily), thus forcing them into relictual (and relatively
specialized) distributions and life-styles.  Aspydites too has a bizarre 
distribution (two species one in China and the other in South Africa). However 
they are fairly specialised (hygropetric flows), an infrequently sampled habitat 
so other species may have been overlooked. The ZA species was collected from an 
upwelling by the road during the dry season (pers. comm.) and it wasn´t rare. 
But when another collector went during the winter  (lots of water everywhere) he 
couldn´t find a single one. The chinese species is from a waterfall and I 
believe it is only known from the type locality. Another good example is 
Meruidae from  Venezuela (El Tobogán) and all the Myxophagans that are turning 
up in South America, all from hygropetric habitats.

Amphizoidae (and Psephenidae) though are not very mysterious. Their distribution 
(NA, Japan, China) is a pattern that is endlessly repeated with many other taxa.

The even bigger question is
perhaps whether the common ancestor of these four families lived in
rivers or ponds.  

Hygrobia´s alternate stroke pattern is "primitive" i.e. not very good at 
swimming. I think it is more likely that it was the first attempt a hydradephaga
so ponds and puddles are most likely

In any case, that common ancestor most likely lived in
Eurasia, which would suggest that Hygrobia evolved there and then
invaded Australia, not vice versa.  Either way, one can't help but
wonder if Hygrobiids may still exist in places like New Guinea, waiting
to be discovered.  
H. watsi´s location in bogs in W Australia makes me think that Hygrobia is 
Gondwanan. But it is just a guess. PNG would be a good candidate to look for 
other Hygrobias, considering the shared history. Still M- Balke has been 
collecting there several times and hasn´t come accross any: the mystery deepens!



> From: kennethkinman at webtv.net
> Date: Sun, 25 Jul 2010 13:18:20 -0500
> To: taxacom at mailman.nhm.ku.edu
> Subject: [Taxacom] Hygrobia (was Eurasia-Australian distribution)
> Hi Jason,
>        So, do you think the distribution might more likely be the result
> of an association of Hygrobia with a particular kind of plant?  I read
> that Hygrobia uniquely (among adephagans) contains a couple of acidic
> compounds, so perhaps it depends on a plant to supply those compounds
> (or their chemical precursors).  Leopoldo noted the Damasonium
> distribution, but I'm not sure its distribution is quite close enough to
> be suggestive of a strong association (although both apparently like
> acidic ponds).
>          ------Ken
> P.S. Are the species of Hygrobia in Australia common where they occur?
> The Chinese species apparently is not, and might even now be extinct.
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