New Guinea is situated at the convergent boundary of the Australian and Pacific plates.
Present-day New Guinea is a geologically young landmass of heterogeneous origin, composed of many terranes 33 , including obducted ophiolites, accreted oceanic island arcs, continental slivers and the Australian continental margin 8 , The spine of New Guinea is a 1,km-long and up to km-wide central highland chain. It includes a major fold-and-thrust belt in the central range that represents the deformed passive margin of the Australian continent, to the north of which are ophiolite belts oceanic or arc lithosphere displaced during island arc—continent collision and accreted island arc terranes.
Early studies interpreted New Guinea in terms of terranes 33 , 35 , which are fault-bounded crustal fragments each with its own geological character, and suggested that at least 32 terranes had been added to the Australian margin in a series of collisions linked to subduction during the Cenozoic. A tentative plate tectonic model based on this terrane concept was outlined by Struckmeyer et al. In their model there is no role for the Philippine Sea plate and they interpreted several small plates between the Pacific and Australian plates. This orogeny was restricted to eastern New Guinea and initiated uplift and emergence of the Papuan Peninsula.
Hall 29 , and Hill and Hall 30 proposed a very different model. They suggested there was subduction during the Paleogene beneath a Philippines—Halmahera—Caroline intra-oceanic arc system after the Australian plate began to move rapidly northwards in the Eocene. This caused a change to sinistral oblique convergence with the Philippine Sea and Pacific—Caroline Plates, which resulted in Paleogene arc fragments being displaced westwards along the New Guinea margin and sliced into many smaller terranes. It is in this region that there were possibly small emergent areas during the Miocene.
Nonetheless, despite significant differences in interpretation of events and plate tectonic reconstruction, the two models 28 , 29 , 30 have some features in common as far as the distribution of land is concerned.
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From the Oligocene until the Late Miocene there was likely to have been only small areas of land at the Pacific margin north of New Guinea. Disconnected islands may have formed where there were volcanic arcs, at local uplifts near to plate boundaries and in the Mobile Belt. There was shelf carbonate deposition along much of northern Australian margin in what are now the New Guinea ranges.
The major differences between the two models for biogeographers are that the first model 28 would suggest the Papuan Peninsula as an area of early lineage diversification and a successive phylogenetic tree branching pattern along the central range in an east—west direction, whereas the alternative 29 , 30 implies much younger colonization and diversification, centred on the Central Range.
The ongoing diversification suggests species have continuously colonized the plentiful, newly formed, biologically empty habitat. However, as highlighted by the calculated carrying capacity of the radiation, the diversification process might experience a slowdown in the next million years, corresponding to a saturation of ecological niches and habitat on the island. This pattern would imply that the rate of diversification will eventually exceed the pace of ecological opportunity formation fostered by the ongoing orogeny of the island. The ancestral character state reconstructions revealed two important ancestral traits: an early occurrence at montane elevation, and an origin in the central orogen.
In a geologically dynamic landscape like New Guinea, it is however difficult to infer ancestral altitudinal preference, because we have data only from present-day distributions. Ancestral New Guinea Exocelina might have colonized lower altitudes, diversified and undergone passive uplift to the high altitudes. They may also have colonized higher altitudes and migrated into lower areas as compensation for uplift into zones with colder temperatures.
We suggest a complex mixture of both scenarios, as we uncovered several altitudinal shifts in our analysis. Ancestral Australian Exocelina are lowland species 37 , which suggests lowlands may be the ancestral New Guinea habitat. During mountain uplift along the northern margin of the Australian plate, an initial colonization out of Australia 37 would have reached emerging islands that might have had some elevation already.
At that stage, the emerging orogen would have been an insular setting supporting lineage diversification, analogous to the initial branching found in rainbow fishes Strong landscape changes during the uplift as well as significant amounts of volcanism during the late Neogene followed by Quaternary climate change 9 likely shifted environmental conditions. These changes would have further promoted the isolation of populations and fuelled lineage diversification 7 , 12 , The extremely structured central highland chain itself, with ongoing formation of rich aquatic resources in particular during the formation of extensive foothill chains, provided the setting for random colonization of new areas followed by isolation and speciation in remote valleys or mountain blocks Interestingly, New Guinean Exocelina are almost exclusively associated to running waters, and there is evidence that species in such habitats are weak dispersers.
This trait has been suggested to enhance allopatric speciation and micro-endemism in diving beetles 39 , and could therefore represent one of the underlying mechanisms fostering this astonishing radiation. More generally, tropical species are thought to be adapted to rather narrow climatic conditions because they do not experience seasons Colonization of new vertical bands might therefore be rare enough to support isolation. Others have proposed that the present-day diversity of the New Guinea fauna is the product of ancient geological processes and landmass collisions.
Instead, we found that this was not the case. Previous hypotheses assigned a central role to these terranes in the diversification of diverse arthropod lineages on drifting island arcs. Closely related species would have reached closer geographic proximity only after terrane collision It also implies that islands arcs did indeed provide terrestrial ecosystems over a long period of time, which is far from being unambiguously proven ref.
Our results provide strong evidence for an alternative and more complex scenario, namely that recent environmental change in the central highlands has been the primary driver of diversification in New Guinea. Instead, the data indicate repeated colonization in the recent past. Present-day alpha-diversity thus appears more related to colonization events than to local diversification in a given terrane. The pattern expected from an older, island-arc scenario was seen only in clade 1, where single species occurred in each of the Cyclops, Bewani and Adelbert Mountains. While the clade was comparatively old, the species in each mountain range appear to have arisen in the last 2 Myr.
This suggests recent allopatric speciation along the north coast as opposed to on ancient islands adrift. There have been only two colonization of Exocelina , both of which appear to be recent Fig. This does not lend support to hypotheses of evolution on terranes adrift. The sister species to all other New Guinea Exocelina occurred in the Adelbert Mountains of the NCR, but its origin was the central orogen according to the ancestral range reconstructions.
Related species occur along the central orogen as well. The hypotheses of early mountain building in eastern New Guinea were also not supported by our biological data. Exocelina diving beetles have colonized the Papuan Peninsula up to the Herzog Mountains out of the central orogen at least six times in comparatively recent time. Distribution at high altitude in clades 2 and 3 was usually allopatric, related species occurring on different mountains. Thus, Exocelina do not exhibit a pattern described by Diamond 6 , who identified ecological montane speciation in the absence of ecotones as a source of New Guinea bird diversity, where sister species occupy sharply delineated altitudinal zones on the same mountain.
Allopatry appears to be the main mechanism in Exocelina, in general along more or less the same altitudinal zone as far as can be seen from our sampling. This differs from speciation patterns observed in the few other studies of running water organisms, where there is evidence that speciation may follow the river course longitudinally in peripatric speciation. Spatial patterns of speciation in running waters have interested ecologists since Illies 41 , who suggested that warm-adapted lineages of aquatic insects arose from cold-adapted ones, with evolution within river systems progressing downstream.
They suggested a headwater ancestor with primarily downstream evolution of the clade. In contrast, Malagasy mayflies Ephemeroptera appear to have diversified from lowland ancestors to colder and faster-flowing upstream sections The syntopic or near-syntopic presence of closely related Exocelina species in the Weyland area Fig. There are no detailed ecological studies of Exocelina species in New Guinea.
We observed that the relatively recent clade 6 includes many lowland species adapted to peripheral habitats along fast-flowing streams. Species in clades 2 and 3 live in habitats with slower flows that are similar to the habitat of the older lineages of Exocelina that occur in Australia. This suggests diversification into new, more extreme habitats, with the result that more emerging habitats are being utilized. Here, too, denser sampling is needed to further study mechanisms at work, that is, possible niche segregation and different abundances among sites.
In summary, our extensive biological data set implicates recent diversification and repeated colonization of sites by distantly related lineages as the primary drivers of the diversity patterns found in New Guinea Exocelina. Despite the clear biological results, a number of questions remain. In terms of geology, the origin of the Weyland and Wandammen regions remain unresolved. The extent and configuration of land available for colonization is still uncertain, but the general setting summarized above provides the framework for investigations of the biological evolution of New Guinea.
scubascenetaunton.com/images/the/2680-deals-on.php Data from biologists and a large selection of organisms could potentially inform geologists about land configurations in the past, supporting a truly integrative science. Using standard protocols Supplementary Table 1 we obtained sequences from 94 in-group species from across New Guinea and representing all known morphological groups Supplementary Table 2 Three species of Exocelina from Australia and New Caledonia were included as close outgroups as well as two representatives of the subfamily Copelatinae ; Copelatus irregularis , Lacconectus peguensis and Thermonectus sp Dytiscinae in order to root the tree.
We used Bayesian inference BI and maximum likelihood ML on the concatenated data set containing one specimen per species and seven different partitioning strategies Table 1 to account for expected differences in sequence evolution in different genes. The best model for each partition was selected under jModelTest 2. An additional scheme was tested based on the partitions selected in PartitionFinder 1. The BI analyses were run in MrBayes 3.
The best strategy of partitioning was selected afterwards based on Bayes factors BF 48 and effective sample size ESS criteria approximated under Tracer 1. BF tests were based on marginal likelihoods calculated using stepping-stone sampling to account for harmonic mean unsuitability to deliver unbiased estimates 50 , BF values superior to 10 were considered good indicators of a significantly better partitioning scheme over another, and ESS values greater than indicative of a good convergence of the runs We set the ucld. Therefore, we used a relaxed clock model allowing rate variation among lineages.
The best topology recovered from the BI phylogenetic reconstructions was fixed by manually editing the. These bands are following altitudinal zonation and to some degree generalized due to regional differences in zonation 61 , Finally, the central mountain range as well as the inferred older terranes closely attached to it in the north, and which drop into lowlands, marking a comparably clear-cut transition towards the NCR.
We used the approach developed by Stadler 64 to estimate putative shifts in speciation and extinction rates in possibly incomplete phylogenies. As an input, the function requires the number of sampled taxa in the phylogeny as well as an estimation of the current species richness in the clade.
The best-fitting model was selected on the basis of likelihood ratio tests. We also used the method of Etienne et al. Hence, we explored the effect of diversity on speciation and extinction rates. Finally, we constructed LTT plots to visualize diversification rate over time using ape 63 for the 94 species included in this study and TreeSim 65 to draw the LTT of 1, simulated topologies accounting for missing taxa under a constant rate model Most of our collecting localities only contain samples from one puddle or several small waterholes along one stream segment less than m long.
These data were used to evaluate the extent to which sister species or close relatives co-occur.
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How to cite this article: Toussaint, E. The towering orogeny of New Guinea as a trigger for arthropod megadiversity. Mayr, E. Birds on islands in the sky: Origin of the montane avifauna of Northern Melanesia.