Fauna of New Zealand 72: Micropterigidae (Insecta: Lepidoptera) - Biogeography
Gibbs, G W 2014. Fauna of New Zealand. 72, 127 pages.
(
ISSN 0111-5383 (print),
ISSN 1179-7193 (online)
;
no.
72.
ISBN 978-0-478-34759-3 (print),
ISBN 978-0-478-34760-9 (online)
).
Published 30 Jun 2014
ZooBank: http://zoobank.org/References/D6BC8C34-6D93-4EC7-BCB3-5670B2CFE744
DOI: 10.7931/J2/FNZ.72
Biogeography
Biogeographic links between Australia, New Caledonia, and New Zealand have become a topic for debate, particularly in regard to the role of vicariance or dispersal to account for the trans-oceanic relationships we find today. The topic is further complicated by the question of how much land existed and where it was situated on the crustal block of Zealandia as it separated from eastern Gondwana and was steadily inundated by the sea throughout the Cenozoic, leading ultimately to the modern isolated islands of New Caledonia and New Zealand. These small archaic moths and their moist breeding habitats clearly survived throughout the Cretaceous and Cenozoic periods. The Micropterigidae are thus almost ‘ideal’ candidates for historical biogeographic interpretation. First, their deep fossil record (amber fossils dated from 136, 97, and 37 Ma. see Introduction) and the molecular phylogenetic analysis (Gibbs & Lees 2014) support the notion of an antiquity which extends back to the break-up of the Laurasian and Gondwanan tectonic plates. Second, they survive today on every habitable temperate continent, in both northern and southern hemispheres, and offer suitably speciose groups for analysis. Third, their antiquity, together with the present world distribution pattern of each of the five major micropterigid lineages on separate continents or continental fragments, implies that trans-oceanic dispersal has not contributed to, nor disrupted, their current distribution pattern. Within the New Zealand region, these moths are known from the three main islands and a number of the larger offshore islands that were connected to the mainland during glacial periods of lowered sea levels (e.g., Poor Knights, Little Barrier, Great Barrier, Kapiti) but not from the Kermadecs, Three Kings, Chatham Islands, or any of the Subantarctic Islands.
In an earlier, more intuitive, review of the family in relation to tectonic events in this region, Gibbs (1983) used a morphological/panbiogeographic model in an attempt to explain diversity across the region. The conclusion was that in the SW Pacific region—eastern Australia, New Caledonia, and New Zealand—two distinct ‘species-groups’ overlap, occupying a complex biogeographic region surrounding the Tasman and Coral Seas. Since that time, the world molecular phylogeny, discussed above (Kobayashi et al. 2000, Gibbs 2004), and the COI bar-code analysis (Gibbs & Lees 2014), have resolved three well-supported micropterigid clades in the SW Pacific: an Australian clade that dominates in Australia with outliers in New Caledonia and North Island; a Sabatinca clade that dominates in New Caledonia and New Zealand but has a surprise outlier in SW Australia; and a southern sabatincoid clade with but a single representative in northern Queensland.
In terms of SW Pacific biogeography, the most significant conclusion from the Gibbs & Lees 2014 phylogenetic analysis is that it provides the first evidence that the New Caledonian Sabatinca fauna is likely to have been derived from New Zealand. Of the three known Sabatinca subclades, two are confined to the islands of New Zealand today and one, the incongruella-clade, contains two sister clades, one in New Zealand, the other with at least 50 species in New Caledonia. Rather than assigning their biogeographic history to the modern islands, it would be more honest to say these moths have evolved on the continental block of Zealandia (sensu Mortimer 2008), whatever topography that might imply, but survive today only on the isolated emergent islands of New Caledonia and New Zealand.
Tentative dates, assigned by the application of a relaxed molecular clock calibrated from three micropterigid fossils (Baltimartyria proavitella Rebel—Eocene-Oligocene; Parasabatinca aftimacri Whalley—Aptian-Neocomian; and AMNH Bu 701 from Burmese amber illustrated by Grimaldi & Engel 2002.) and four trichopteran fossils, indicate that the divergence of the Sabatinca lineage might have been initiated at about the time when tectonic events were beginning to separate Zealandia from Australia/Antarctica (i.e., ca 84 million years ago (Ma), whereas the New Caledonian radiation of incongruella-group species began about 52 Ma (Gibbs & Lees 2014). This dating hypothesis, and the survival of the Sabatinca clade on the crustal block of Zealandia, prior to the uplift of the modern islands of New Caledonia (emergent ca 37 Ma (Schellart et al. 2006)) and New Zealand (which commenced uplift toward its present profile ca 23 Ma (Campbell & Hutching 2007)), imply the continuous existence of moist forested land (islands?) in the region. Recent geological studies of the Tasman Sea basin are beginning to offer plausible scenarios for such former land; e.g., Schellart et al. (2009), who have revealed a large slab of subducted continental crust between New Caledonia and New Zealand which is thought to have finally sunk below sea-level at about this time.
The sole member of the ‘Australian-group’ clade in New Zealand, Zealandopterix, diverged from the Australian fauna about 83 Ma, according to the phylogenetic hypothesis of Gibbs and Lees (2014). These phylogenetic studies are thus generally compatible with the 1983 hypothesis, namely that Trans-Tasman relationships in the SW Pacific Micropterigidae (Sabatinca and Zealandopterix) represent vicariant processes that were probably established around the time of the opening of the Tasman Sea and confirming that the faunas of New Caledonia and New Zealand are more closely associated with each other than either is to the Australian fauna (Gibbs & Lees 2014).
Within the New Zealand fauna of 18Sabatinca species the molecular analysis has retrieved a total of seven pairs of sister species, three of which [incongruella/demissa; aurella/doroxena; calliarcha/pluvalis] are likely to have been in existence prior to the uplift of modern New Zealand and are thus difficult to explain through reference to modern geomorphology or geological phenomena. The remaining four pairs, all South Island examples and all allopatric pairs today, can be examined further to look for possible geologically-driven patterns.
The Alpine Fault is by far the most significant South Island tectonic feature, visible from space. This massive strike/slip fault, which has resulted in a total of over 470 km of lateral displacement, can be traced back to its inception 45 Ma but did not become vigorous until about 26 Ma and has been especially active over the past 5 Ma, moving at a rate of 20–30 mm per year horizontally and uplifting the Southern Alps (Campbell & Hutching 2007). Its lateral displacement, as a possible cause of South Island biogeographic disjunctions, has been debated by Heads (1998), Wallis & Trewick (2001), Heads & Craw (2004), Haase et al. (2007) and its potential role in the divergence of a pair of sibling micropterigid species (chrysargyra and aemula) has been noted by Gibbs (2006). Extensive recent West Coast collections of these two species have attempted to define the geographic gap between them more precisely and determine whether sympatric populations exist. To date none have been found. Instead, aemula, with a north-western distribution from the Nelson region south to Mt Hercules, appears to be separated by a mere 35 km from chrysargyra which is found from Franz Josef valley southwards. Both share the same flight season and are indistinguishable in the field, suggesting that further sampling might be needed to resolve the nature of the gap between these two species. The barcode analysis implies that this example is the only instance of speciation in the micropterigid fauna that falls within the Miocene-Holocene era (Gibbs & Lees 2014). Whether geographic fault movement was the driver for divergence, or whether more recent factors such as glacial extirpation (Wallis & Trewick 2001), have served to keep them apart remains a matter for speculation in this case.
The other three examples of sister species evidently relate to earlier events (dated around 25 Ma), but each shows divergence between a species, now centred in the northwest of the South Island, and a sister towards the south of the island. In all cases the molecular diagnoses as sister pairs is correlated with morphological similarities. With the case of heighwayi (north) and weheka (south) in the calliarcha-group, the divergence is along the west coast; whereas the other two include a north-western member (chalcophanes or aurantissima) which has diverged from a south-eastern member (caustica or quadrijuga respectively). The northern members are sympatric over a wide area of north-western South Island while Sabatinca caustica and quadrijuga are sympatric throughout most of their ranges in the south-eastern South Island, the former extending onto Stewart Island. The South Island has undergone extensive geomorphological changes since the estimated timing of species divergence—so much so that it is not realistic to offer associated geological explanations. Moreover, the species pairs are widely separated which, in itself, indicates the speciation events themselves were likely to have taken place on a very different landscape from today. At 25 Ma it was close to the point of maximum marine inundation, implying that perhaps isolation on different islands may have initiated the process and been a driving force for all three examples of diversification. A similar explanation may apply to the example of wide geographical disjunction in Sabatinca calliarcha discussed on p. 27, which is distributed over both North and South Islands but with a gap between the Coromandel Peninsula and NW Nelson.
Attention was drawn to the trio of species doroxena, aurella, and ianthina in previous discussions of New Zealand micropterigid biogeography (Gibbs 1983, 1989). In contrast to the above species pairs with wide allopatry, these three are broadly sympatric over the North Island with two (aurella, ianthina) also extending about half way along the western South Island. Both morphological and molecular interpretations imply a closely related trio, but phylogenetic analysis suggests they represent steps along a ladder leading to the remainder of the aurella-subgroup species. The relaxed molecular clock dating used in this study (Gibbs & Lees 2014) indicates that species divergence between doroxena and aurella occurred late Eocene to early Miocene, i.e., between about 37–18 Ma i.e., at a time of increasing marine inundation when Zealandia is considered to have been an extensive low-lying archipelago, without significant regional variation and possibly lacking montane regions. The advent of a new active plate boundary initiated the uplift of modern New Zealand (Campbell & Hutching 2007). A possible scenario might suggest that divergence from an early chrysargyra-group ancestor was initiated on a northern sector of the Zealandian archipelago and over the course of island submergence and possible recombination, outlying populations were isolated, became distinct, and when amalgamated maintained their identity and original distributions until more active uplift of New Zealand in the early Miocene led to the dispersal of two taxa with very similar ecological requirements (aurella, ianthina), southward along the western South Island.
It should be noted that none of the examples of sister species divergence given above, apart from the case of aemula/chrysargyra, conforms to the prevailing mountain-building or glaciation hypotheses offered by many recent phylogeographic studies of New Zealand biota e.g., review by Wallis & Trewick (2009).
Intensive micropterigid collecting along the mid-West Coast South Island region (associated with the discovery of S. weheka and the mapping of the aemula-chrysargyra interface), has revealed an approximately coincident southern biogeographic limit for four widespread species of these moths, three of which (ianthina, aurella and chalcophanes) extend well into the North Island. The boundary falls within the well-known ‘beech gap’, a zone often attributed to the impact of glacial extirpation during the last ice advance (e.g., Wardle 1988; Wallis & Trewick 2009). Whether this coincident boundary of micropterigids reflects a deeper historical pattern, the impact of Pleistocene ice, or a limit imposed by the present climate is not clear.