[Taxacom] an interesting paper on Long Distance Dispersal

Les Watling watling at hawaii.edu
Sun Jul 8 18:46:50 CDT 2018


Hi John,

A volcano erupts in the middle of the Pacific Ocean over a hotspot. If it
erupts a sufficient amount of lava, it becomes an island, otherwise joins
the multitudes of seamounts present today in the Pacific. Usually,
according to current theory, the hotspot stays relatively motionless, but
the plate above it moves carrying the volcano with it. After a few tens of
millions of years, crustal cooling and the weight of the mountain gradually
pushes the crust down. Erosion causes loss of the mountain mass to the
surrounding abyssal seafloor. In a few cases, such as the Hawaiian Ridge
there is sufficient lava production to make a ridge between the volcanoes
that is shallower than the abyssal seafloor, but still deep, that is, at
bathyal depths. Same is true for the Cretaceous igneous plateaus mapped in
Fig 6.1 in Heads' book. By the present day they have all drifted well to
the west with the motion of the Pacific plate. There are Cretaceous
seamounts south of Hawaii. But we do not know if they were ever at the
height of islands. Maybe they were and maybe the Line Islands were also.

So, how do organisms get to an isolated newly emergent volcano? What
geological process am I missing? Or are you suggesting there are sunken
land masses that were once emergent that could have provided local
dispersion?

Plate tectonics only works to carry the island/seamount away from the
hotspot. It does not carry the island/seamount into the vicinity of a large
continental mass... at least not often, and when it does usually that is
because a trench is near the large landmass and the volcanoes get carried
into the trench and buried. The Emperor/Hawaiian chain has been in
existence for more about 85 million years. But none of the seamounts or
islands in that chain are near any other land mass. Same is true for a very
large number of islands in the South Pacific. New Zealand is the exception,
not the rule, with respect to tectonic processes. We know when NZ broke
away from Australia and Antarctica. But out in the central S Pacific there
are thousands of seamounts and numerous islands that originated in the
middle of the plate. Plate movement projections back cast to the date of
the formation of the seamounts do not show them near South America.

So colonization can only have occurred by some local dispersal mechanism,
which I see in some references has now been appropriated by
panbiogeography. So I guess the latter can explain everything....  Well, I
have never had any problem with the generalized track idea of Croizat. In
fact, it matches nicely the independently derived ideas of the
palaeontologist James Valentine who recognized that provinces, ecosystems,
and assemblages of species must have been all evolving and changing
together as some at least loosely circumscribed units as the earth and
climate was changing. Granted, not many biogeographers have adopted
Valentine's ideas either.

 I will briefly note one other factor that needs to be considered, at least
for the deeper fauna of the world ocean. And that is that the ocean
underwent a drastic cooling since the Eocene-Oligocene boundary. This was
the result of the opening of the Drake Passage between South America and
Antarctica and followed the previous opening between Tasmania and
Antarctica. The result was the development of a circum-Antarctic current,
continued cooling of that water mass that then sank and began to fill the
Atlantic, Indian, and Pacific basins, eventually setting up the water
masses we see today. So it seems likely that all deep water fauna, at least
deeper than mid bathyal, either went extinct as the cooling occurred or
evolved in place, if such evolution was possible. The end result of course
is that the deep water fauna does not go back to the Cretaceous but is much
more recent (perhaps Miocene?) than that. That age issue needs to be
accounted for when considering distributions of deep marine fauna, and
perhaps shallow forms too as at least the high latitude communities will
also have been subjected to cooling.

I have a deadline approaching so I will need to drop this for a while, but
will be happy to pick up the discussion in a week or so.

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 12:01 PM John Grehan <calabar.john at gmail.com> wrote:

> Les,
>
> I would be interested to know what you regard as evidence that Hawaiian
> mphipods and tanaids  "managed to get to Hawaii" independent of any
> geological process.
>
> Also interested in examples you mentioned that are not 'explained' by
> panbiogeography.
>
> John Grehan
>
> On Sun, Jul 8, 2018 at 11:42 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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>> >>
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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
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
>> >
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>> Nurturing Nuance while Assaulting Ambiguity for 31 Some Years, 1987-2018.
>>
>
>


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