[Taxacom] an interesting paper on Long Distance Dispersal

Michael Heads m.j.heads at gmail.com
Sat Jul 7 23:03:06 CDT 2018


Hi Les,

You wrote: ‘certain marine taxa, such as cumaceans, which are small benthic
crustaceans with almost no swimming ability and no larvae, have not made it
to Hawaii. Most likely that is because they could only get there by
travelling along the bottom, meaning they would have to crawl through the
abyss.... not going to happen, temperature and pressure’.

However, samples from the Kuril–Kamchatka Trench and the adjacent abyssal
plain at depths 4830–5780 m included 72 species of cumaceans from 23 genera
and 6 families (Lavrenteva & Mühlenhardt-Siegel in *Deep Sea Research II*,
111: 301, 2015). This makes the absence from Hawaii even more interesting.



I’m curious to know if there are other young, isolated volcanic islands
that do not have cumaceans (a quick search didn’t turn up any reference to
them in French Polynesia, Cook Islands etc.). They *are* present on the South
Sandwich islands - young islands, surrounded by abyss, and ‘how some
sedentary taxa (e.g infaunal tanaids and cumaceans) get there is a mystery
still’ (Kaiser et al., Antarctic Sci. 20: 281. 2008). I think they probably
‘got there’ by migrating with the migrating volcanic island arc.

Absences from Hawaii are often as dramatic as the better-known endemics.
For example, the plant *Begonia* thrives more or less throughout the wet
tropics globally, but is absent from Hawaii (although there are naturalized
species). Its intercontinental distribution is attributed to dispersal
across the oceans (Moonlight et al., 2018 J. Biogeog), so the absence from
Hawaii would be attributed to *lack* of transoceanic dispersal, i.e.
‘chance’. (Nevertheless, the sister group of *Begonia* is a Hawaiian
endemic, *Hillebrandia*).



Hawaii is often assumed to have been colonized by all its terrestrial
groups since 30 Ma, as no subaerial land is thought to have existed between
34 and 30 Ma. However, this depends on a method for calculating the former
heights of volcanoes that underestimated their current heights by up to
1000 m, and so it probably underestimated the former heights also (see my
Tropics book, p. 319).

On Thu, Jul 5, 2018 at 5:41 AM, Les Watling <watling at hawaii.edu> wrote:

> Apropos the recent discussion re dispersal vs vicariance. As a recent paper
> in PeerJ makes clear, the size of the dispersing organism matters. As does
> mobility, and a host of other factors.
>
> In the case of tardigrades it was long assumed that wind was the major
> dispersion agent, but the authors demonstrate, as much as one likely can,
> that bird feathers are an effective agent for something as small as a
> tardigrade.
>
> https://peerj.com/articles/5035/
>
> Not a too-likely method for primates other than in sci-fi stories(!).
> Primates probably could wander long distances, but why would they?
> Especially if their needs are being met where they are. In which case
> rafting on continental chunks might be what carries them around.
>
> But I think bird feathers also work for seeds of some species, and
> something as unusual as terrestrial amphipods. In Hawaii, some animals,
> such as terrestrial amphipods have no likelihood of dispersing over the sea
> on rafts or other floating objects because of their osmotic intolerance to
> sea water. On the other hand, we also know that certain marine taxa, such
> as cumaceans, which are small benthic crustaceans with almost no swimming
> ability and no larvae, have not made it to Hawaii. Most likely that is
> because they could only get there by travelling along the bottom, meaning
> they would have to crawl through the abyss.... not going to happen,
> temperature and pressure. But 3 species of cumaceans have now made it, most
> likely in ship ballast water.
>
> As with cumaceans, shallow water octocorals, a regular feature of most
> tropical coral reefs, are essentially absent from Hawaii. There are a few
> (maybe 4?) species of very small soft corals that can be found in shallow
> pools or in water a few meters deep. But the normal reef habitat has no
> octocorals. However, at depths greater than about 350 m, octocorals become
> abundant and diverse, exceeding more than 100 species, and inhabiting
> depths to over 3000 m. So the deep sea species have made it, easily, but
> the shallow species have not. Low dispersal capability in the latter, and
> long distance larvae in the former?
>
> In the end, I think the debate needs to be more carefully circumscribed
> with respect to the organisms. And, from where I sit, I see both
> panbiogeography and LDD each explaining some patterns.
>
> Best,
> Les
>
>
>
>
>
>
> Les Watling
> Professor, Dept. of Biology
> 216 Edmondson Hall
> University of Hawaii at Manoa
> Honolulu, HI 96822
> Ph. 808-956-8621
> Cell: 808-772-9563
> e-mail: watling at hawaii.edu
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-- 
Dunedin, New Zealand.

My books:

*Biogeography and evolution in New Zealand. *Taylor and Francis/CRC, Boca
Raton FL. 2017.
https://www.routledge.com/Biogeography-and-Evolution-in-New-Zealand/Heads/p/book/9781498751872


*Biogeography of Australasia:  A molecular analysis*. Cambridge University
Press, Cambridge. 2014. www.cambridge.org/9781107041028


*Molecular panbiogeography of the tropics. *University of California Press,
Berkeley. 2012. www.ucpress.edu/book.php?isbn=9780520271968


*Panbiogeography: Tracking the history of life*. Oxford University Press,
New York. 1999. (With R. Craw and J. Grehan).
http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC
<http://books.google.co.nz/books?id=Bm0_QQ3Z6GUC&dq=panbiogeography&source=gbs_navlinks_s>


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