[Taxacom] an interesting paper on Long Distance Dispersal

Michael Heads m.j.heads at gmail.com
Thu Jul 12 17:06:37 CDT 2018


Hi Les,

Thanks very much for the long mail.

Have proper overall distribution maps of Cumacea (not just GBIF etc.) ever
been published? Without maps, it’s hard to do much in the way of
biogeographic analysis.

Without knowing the distribution of cumaceans on other Pacific islands it’s
difficult to say whether their absence from Hawaii is for ecological
reasons – e.g. they couldn’t get there, or phylogenetic – they are not
there, *as such*, but are represented by their sister group, and this
allopatry reflects their original vicariance. (Cf. begonia, absent as such
from Hawaii, but represented there by its sister group).

For example, if cumaceans are widespread throughout the Pacific islands,
but absent only on Hawaii and SE Polynesia, this would suggest phylogenetic
reasons. This is because Hawaii-SE Polynesia is a standard centre of
endemism and absence. Endemics include marine and terrestrial plants,
invertebrates and vertebrates  that display a very wide range of ecology
and means of dispersal (see my Tropics book pp. 340-344).

For example, in the sea-urchin *Diadema paucispinum*, Lessios et al. (2001)
recorded Hawaii – SE Polynesia clades. They interpreted these as the result
of ‘chance arrival of larvae’ and inferred ‘high rates of gene flow’
between the localities. Nevertheless, they noted that the Hawaii – SE
Polynesia connection runs *across* both the North and the South Equatorial
Currents and so the affinity is ‘remarkable’ as it indicates a ‘tremendous
capacity for dispersal’. Instead the affinity could be due to vicariance.

   In the surgeonfish *Acanthurus triostegus*, Marquesas Islands
populations are geographically closest to those in the Tuamotu and Society
Archipelagosn (all SE Polynesia), although genetically they are closest to
Hawaiian populations (Planes and Fauvelot, 2002).  The authors concluded:
‘These observations favor the hypothesis of biogeographic vicariance as an
evolutionary process leading to the differentiation of the *A.
triostegus *populations
in the Hawaiian and Marquesas Archipelagos’ (p. 391). They also cited
congruent biogeographic patterns in other Hawaiian and Marquesan coral reef
fishes.

On Mon, Jul 9, 2018 at 3:42 AM, Les Watling <watling at hawaii.edu> wrote:

> Hi Michael,
> Thanks for the comment. I realize that I was probably much too cryptic in
> my note about cumaceans. The issue is not that some species cannot survive
> the abyss, we've known about abyssal cumaceans since the time of the
> Challenger. The problem is the shallow species. They cannot descend into
> the abyss, walk across it, and then re-emerge in shallow water. Well, for
> the most part. Where this generalization breaks down is exactly where you
> point to, at high latitudes. That is because around the southern end of the
> world, and to a certain extent in the northern end of the North Atlantic,
> the water is cold top to bottom. However, we did an analysis of cumaceans
> collected at all depths around the Faroes a number of years ago and we
> found there seemed to be a deep barrier at about 1 deg C, irrespective of
> depth.
>
> Most people think of depth = pressure as a barrier, but that is only once
> depths of about 3000 m are reached. Shallower than that, most animals have
> physiological difficulties because of temperature. In the Antarctic ocean
> increases in temperature of about 2 deg C can exert major physiological
> problems and so most species get moribund when brought to the surface of
> the ship where temperatures could be 3 or 4 deg warmer than the seawater.
> But places such as the South Sandwich Islands have temperatures from the
> surface to several thousand meters depth that are essentially the same.
> That is, no shallow thermocline to limit distribution. I would have to
> check, but I would suspect the cumaceans at SSI are merely deep cold water
> tolerant species that can live at a wide range of depths due to a lack
> temperature gradient. Same as NZ as I note below.
>
> So, for cumaceans, and I suspect also for other groups of direct
> developers that have no swimming or rafting capabilities, there is no way
> for shallow water dwellers to get to the shallow waters of some places,
> such as Hawaii, even though the hot spot producing the chain has a very
> long history, if you include the Emperors as well. As you note, it would be
> interesting to see what other isolated volcanic islands show for this and
> related groups.
>
> A counter example of small crustaceans that have managed to get to Hawaii
> and have done very well, that is, are well-established and to a certain
> extent have Hawaiian endemics are the amphipods and tanaids. They do not
> swim well and have direct development so cannot disperse via larvae. But
> both groups are quite capable of living on drifting seaweed, palm trees,
> whatever floats. I don't know the total numbers but there are at least 100
> amphipod species documented from Hawaii and the tanaids are just now being
> looked at, but I think 15 or so species are known. For the amphipods, it is
> clear that most of the families present are associated with seaweed in one
> way or another. Some sediment-dwelling species are present, however. These
> two groups of crustaceans have the same issues confronting cumaceans, but
> they can live on drifting things whereas cumaceans most likely cannot.
>
> On the other hand, shallow water cumaceans most likely do and can get
> carried around by drifting micro-continents, etc. Some years ago I wrote a
> short paper about the cumaceans of New Zealand. It got subsumed into a
> larger multi-author Species 2000 volume put together by Dennis Gordon so
> its hard to find. But here is the essence of the story. There are only 8
> families of cumaceans known. But two are very under-represented in New
> Zealand. All families show very high endemicity at the genus level,
> indicative of their long isolation with subsequent speciation. In the case
> of the deep-water (bathyal) species, most were new to science and most are
> members of widespread deep genera.
>
> So, with that I would just note that in looking at the distribution of any
> group we need to be cognizant of their natural history and not posit
> mechanisms for their getting around that clearly are inapplicable. I don't
> doubt vicariance is important, and likely the major mechanism spreading
> life forms around the planet, but it is not the only mechanism as these
> isolated islands show.
>
> Hope this helps,
> 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
>
>
>
>
>
>
> On Sun, Jul 8, 2018 at 12:03 AM Michael Heads <m.j.heads at gmail.com> wrote:
>
>> 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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>>> Nurturing Nuance while Assaulting Ambiguity for 31 Some Years, 1987-2018.
>>>
>>
>>
>>
>> --
>> 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>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>
>>


-- 
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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