At 09:36 11/06/01 -0700, Peter wrote:
>There are also problems within exquisita and gracilis too that need to be
>resolved. At this stage I don't think the exquisita's from the Kimberley's/WA
>are exquisita, I think they are more closely related to gracilis (although
>they look more like exquisita it seems). Anyway, the morphological
>differences between these species are trivial (first dorsal fin placement
>relative to the anal fin, it is forward in exquisita, behind in gracilis).
>Also, biogeographically it doesn't make sense and also ecologically since
>exquisita is usually somewhat upland/escarpment in its occurrence while
>gracilis is lowland. The "exquisitas" in WA are all lowland.
>
>While we are at it.....preliminary allozyme data on trifasciatas from Darwin
>and Cape York suggests they may be sufficiently different to be called
>separate species, don't have any from the East Coast to compare them to.
>Haven't sequenced fish from both areas yet though.
That makes sense to me - you might be interested in the following:
>Global sea levels are currently higher than at anytime during the last
>120,000 years, separating Australia and New Guinea by sea. However, Torres
>Strait has been acting almost consistently as a land-bridge since the last
>interglacial about 118,000 years ago up until 5-6,000 years ago, when
>marine transgression closed the bridge (Chapell 1983; Chapell 1994).
>
>About 12,000 years ago, sea levels were low enough that the Arafura Sill,
>53 m below current sea level, was exposed, and 20,000 years ago, sea
>levels were 120 m below present levels (Chapell 1994). The Arafura Sill is
>a broad feature nearly 100 km wide, with a total relief of less that 2 m
>(Torgersen et al. 1983) that extends from the north-eastern extent of
>Arnhem Land to New Guinea east of Pulau Dolak and west of the mouth of the
>Fly. Between 12,000 and 55,000 years ago, the Gulf of Carpentaria was
>large inland lake (Chapell 1994) (Figure 12). The mighty Fly River flowed
>into the lake before being diverted to the east (est. 27,000 years ago,
>Blake and Ollier, 1971; 35-40,000 years ago, Torgersen et al., 1988;
>McCulloch et al., 1989). Pollen studies have shown that the vegetation
>surrounding the lake was very much as it is today in the open savannah
>country. The lake would have been fresh or brackish for much of its
>existence. If it connected to the sea, and no channel is evident from
>bathometry, then it would have done so to the west.
>
>Evidence from deep core drilling reveals a pattern of establishment and
>marine inundation of Lake Carpentaria that appears to have been repeated.
>It was a freshwater lake in the Jurassic then inundated by a marine
>transgression (in limestone deposits), and there was a further freshwater
>episode in the Miocene, followed by another marine transgression
>(McConneckie, 1996, personal communication).
>
>The current distribution of a number of northern turtle species can be
>explained by the opportunities the lake and the exposed Arafura Sill
>provided. Chelodina rugosa of Australia and Chelodina siebenrocki of New
>Guinea are indistinguishable electrophoretically (Georges et al. 2001) and
>poorly differentiated morphologically (Rhodin and Mittermeier 1976), and
>we regard them as a single taxon once forming a contiguous series of
>populations that circled Lake Carpentaria. Lack of variation shown by
>Emydura subglobosa subglobosa from southern Papua New Guinea and Emydura
>subglobosa worrelli from the Australian rivers discharging into the Gulf
>of Carpentaria (Georges and Adams 1996) can be similarly interpreted. So
>too can the distribution of Chelodina novaeguineae, and preliminary
>morphological analyses indicate that Elseya lavarackorum from the Gulf
>country and Elseya branderhorsti from southern New Guinea are very closely
>related. It seems that a number of contiguous turtle distributions have
>been disrupted in the last few tens of thousands of years by the
>inundation of Lake Carpentaria.
>The Arafura sill that defined the western boundary of Lake Carpentaria
>would also have provided a land-bridge to New Guinea presumably with
>drainages flowing west to the Timor Sea. This would have allowed potential
>interchange of forms between West Papua, Arnhem Land and the Kimberley via
>coastal rivers and associated habitat quite different from that provided
>by Lake Carpentaria. It would also have isolated the turtle fauna from
>these western and west-central rivers from those flowing into the eastern
>seaboard of Australia and south eastern New Guinea. This may explain the
>high level of endemism for the region from the Kimberley and western
>Arnhem Land -- Emydura victoriae, Carettochelys insculpta, Elseya dentata,
>Elseya sp. [Sth Alligator], Chelodina sp. [Cadell] and Chelodina
>burrungandjii. Carettochelys presumably entered Australia from New Guinea
>via the opportunities that arose from the Arafura Sill land bridge.
This is an extract from Evolution and Zoogeography of the Australian
Freshwater Turtles by Arthur Georges and Scott Thomson, Applied Ecology
Research Group and CRC for Freshwater Ecology, University of Canberra, ACT
2601, Australia.
It would make sense to me that the distribution of freshwater turtles would
be something similar along the lines of rainbowfish distribution???
Of interest is the 'undescribed' turtle found in the South Alligator River.
It may be that certain rivers in the north have their own species of
Trifasciata and Splendida and they might not be only different colour
varieties?
All the more reason to maintain and breed your rainbowfishes by river and
not by species.
Adrian.
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At 09:36 11/06/01 -0700, Peter wrote:
There are also problems within exquisita and gracilis too that need to be
resolved. At this stage I don't think the exquisita's from the Kimberley's/WA
are exquisita, I think they are more closely related to gracilis (although
they look more like exquisita it seems). Anyway, the morphological
differences between these species are trivial (first dorsal fin placement
relative to the anal fin, it is forward in exquisita, behind in gracilis).
Also, biogeographically it doesn't make sense and also ecologically since
exquisita is usually somewhat upland/escarpment in its occurrence while
gracilis is lowland. The "exquisitas" in WA are all lowland.
While we are at it.....preliminary allozyme data on trifasciatas from Darwin
and Cape York suggests they may be sufficiently different to be called
separate species, don't have any from the East Coast to compare them to.
Haven't sequenced fish from both areas yet though.