[Taxacom] Ghost moth as a subduction zone weed

John Grehan calabar.john at gmail.com
Sat Aug 29 09:40:55 CDT 2020


Hi Ken,

Occurrence in New Guinea is a perfectly reasonable possibility, although
geographic proximity is not always a predictor of occurrence in this region
as there are many well known taxa that occur on surrounding islands but
skip New Guinea itself. Admittedly in the case of Phassodes this is an
insect that is not well known or extensively collected, even from Fiji
where it has been mostly recorded (and even then only from one of the two
main islands - perhaps because one has the international airport and most
collectors stay with that island). The moth is probably very abundant in
all localities, but appears to be rare or infrequent at light. On that
basis and given the new Solomons record it is reasonable to suppose that
its distribution range could be more extensive. However, New Guinea itself
has been quite well collected for Lepidoptera for more than a century and
while other ghost moths have turned up (but only three genera so far, and
all also present in Australia) I would put money (if I had any to spare) on
the absence being real.

The current range of Phassodes does conform to a pattern of other non-New
Guinea distributions that extend north of New Guinea between the
Philippines and Fiji-Tonga, including a group of frogs. My present
anticipation is that Phassodes is really part of that pattern. The
outstanding question is to what extent that range includes or not the more
northwestern islands of Bougainville, New Britain, and New Ireland. If one
were to consider geographic proximity it would be these islands are much
closer than New Guinea. They currently have no records of any ghost moths
as was noted by collectors very early in the literature. If Phassodes were
to one day turn up in New Britain region of New Guinea, I would see e the
northern margin, particularly the Finistere Range as more of a possibility,
but there is a major biotic difference between New Guinea and New Britain
in other groups, including (if I recall the number correctly) a 70%
difference in the bird fauna, even though the geographic gap is very small.

What is needed (as far as Phassodes might be concerned) is future
collecting that includes a focus on ghost moths (that might fly at dusk for
example) in the rest of the Solomons as well as further north. I guess that
it is not likely in my lifetime. The Solomons specimen turned up entirely
by fortuitous accident when my co-author visited an insect fair in Europe
some years ago and saw the specimen for sale by a commercial collector.
Right place and right time or this occurrence may still have remained
obscure. Ghost moth taxonomy is sometimes like running in the dark.

John Grehan

On Fri, Aug 28, 2020 at 9:19 PM Kenneth Kinman via Taxacom <
taxacom at mailman.nhm.ku.edu> wrote:

> Hi John,
>         Interesting.  But now that there has finally been one specimen
> discovered in the Solomon Islands, wouldn't it seem somewhat likely that
> there are also species of Phassodes in Papua New Guinea that have not yet
> been discovered.   The Solomon Islands are closer to New Guinea than they
> are to Fiji and Samoa.
>                                 --------------Ken
>
> ________________________________
> From: Taxacom <taxacom-bounces at mailman.nhm.ku.edu> on behalf of John
> Grehan via Taxacom <taxacom at mailman.nhm.ku.edu>
> Sent: Friday, August 28, 2020 1:50 PM
> To: taxacom <taxacom at mailman.nhm.ku.edu>
> Subject: [Taxacom] Ghost moth as a subduction zone weed
>
> For those interested, following article provides a biogeographic model for
> the origin of a ghost moth genus (Phassodes) endemic to some Pacific
> oceanic islands. Accessible at
> http://hbs.bishopmuseum.org/pubs-online/bmop.html
>
>   Taxonomic revision and biogeography of Phassodes Bethune-Baker, 1905
> (Lepidoptera: Hepialidae), ghost moth descendants of a subduction zone weed
> in the south-west Pacific. Grehan, J.R. & Mielke, C.G.C. Bishop Museum
> Occasional Papers 136: 1–37 (2020)
>
>  Abstract. Phassodes Bethune-Baker, 1905 is distributed in Fiji (P.
> vitiensis (Rothschild, 1895)), the Solomon Islands (P. walteri sp. n.),
> Samoa (P. samoa sp. n.), and American Samoa (P. tutuila sp. n.). It is the
> only genus of Hepialidae endemic to oceanic islands. Monophyly of the genus
> is supported by four unique features, and a sister group relationship with
> the Australian genus Abantiades Herrich-Schäffer, 1855 is supported by four
> shared derived features. There are also some features shared between
> Phassodes and other genera: a) the southern Andean genus Andeabatis Nielsen
> & Robinson, 1983 (shape and structure of the male genitalia), b) the
> Peruvian Viridigigas Grehan & Rawlins, 2016 and c) the Chilean Puermytrans
> Viette, 1951 (presence of a basal forewing scent gland). The distribution
> of Phassodes coincides with the Vitiaz Trench, an extinct subduction zone
> that marks a former boundary between the Indo-Australian and Pacific
> plates. It is proposed that the common ancestor of Phassodes and Abantiades
> diverged through vicariance when the subduction zone along the east coast
> of Australia (East Gondwana), along with its island arc, began retreating
> into the Pacific between 90 and 75 Ma. Survival of the genus on volcanic
> islands is attributed to metapopulation dynamics, with continuous
> transference of populations from older, subsiding islands to newly emergent
> ones. This model suggests that Phassodes species originated much earlier
> than the individual islands they now occupy.
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