Diptera: Chironomidae) ⇑ M.N
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Molecular Phylogenetics and Evolution 59 (2011) 458–468 Contents lists available at ScienceDirect Molecular Phylogenetics and Evolution journal homepage: www.elsevier.com/locate/ympev Systematics and biogeography of the Gondwanan Orthocladiinae (Diptera: Chironomidae) ⇑ M.N. Krosch a, , A.M. Baker a, P.B. Mather a, P.S. Cranston b a Biogeosciences, Queensland University of Technology, 2 George St., Brisbane 4001, Australia b Department of Entomology, University of California, 1 Shields Av., Davis 95616-8584, USA article info abstract Article history: Restrictions to effective dispersal and gene flow caused by the fragmentation of ancient supercontinents Received 26 October 2010 are considered to have driven diversification and speciation on disjunct landmasses globally. Investigat- Revised 31 January 2011 ing the role that these processes have played in the development of diversity within and among taxa is Accepted 3 March 2011 crucial to understanding the origins and evolution of regional biotas. Within the chironomid (non-biting Available online 12 March 2011 midge) subfamily Orthocladiinae (Diptera: Chironomidae), a group of genera that are distributed across the austral continents (Australia, New Zealand, South America) have been proposed to represent a relict Keywords: Gondwanan clade. We used a molecular approach to resolve relationships among taxa with the aim to Continental drift determine the relative roles that vicariance and dispersal may have played in the evolution of this group. Dispersal Vicariance Continental biotas did not form monophyletic groups, in accordance with expectations given existing Lars Brundin morphological evidence. Patterns of phylogenetic relationships among taxa did not accord with expected Austral patterns based on the geological sequence of break-up of the Gondwanan supercontinent. Likewise, West Wind Drift divergence time estimates, particularly for New Zealand taxa, largely post-dated continental fragmenta- tion and implied instead that several transoceanic dispersal events may have occurred post-vicariance. Passive dispersal of gravid female chironomid adults is the most likely mechanism for transoceanic movement, potentially facilitated by West Wind Drift or anti-cyclone fronts. Estimated timings of diver- gence among Australian and South American Botryocladius, on the other hand, were congruent with the proposed ages of separation of the two continents from Antarctica. Taken together, these data suggest that a complex relationship between both vicariance and dispersal may explain the evolution of this group. The sampling regime we implemented here was the most intensive yet performed for austral members of the Orthocladiinae and unsurprisingly revealed several novel taxa that will require formal description. Ó 2011 Elsevier Inc. All rights reserved. 1. Introduction proposed sequence of continental break-up, whereas others imply that alternative mechanisms may have influenced modern distri- Since the time of the early biogeographers, atypical distribution bution patterns (see Sanmartin and Ronquist, 2004). patterns have been recorded among members of the southern The supercontinent Gondwana, which rifted from its northern hemisphere fauna and flora, whereby close morphological similar- sister Laurasia during the break-up of Pangaea 215 mya, com- ities were recognised among taxa on different southern continents prised all current austral continents and minor landmasses: South (Hooker, 1844, 1855, 1860; Darwin, 1859; Wallace, 1876). The America, Africa, Australia, Antarctica, Zealandia (formerly Tasman- development of continental drift theory and a general consensus tis – New Zealand–New Caledonia), proto-New Guinea, India and of the order of Gondwanan continental fragmentation (Scotese Madagascar (Dietz and Holden, 1970; Scotese et al., 1988; et al., 1988; McLoughlin, 2001) provides a framework against McLoughlin, 2001). Gondwana – proposed by some to have been which patterns of relationships among disjunct austral taxa can of Precambrian origin (Scotese et al., 1999) – apparently persisted be tested. Studies of disjunct austral taxa have revealed a variety as a single entity for approximately another 50 million years after of phylogenetic patterns, many of which appear to follow the rifting from Pangaea (Cracraft, 1974; Sanmartin and Ronquist, 2004) before fragmentation was initiated around 165 mya (Scotese et al., 1988). The continental block that consisted of South America, ⇑ Corresponding author. Fax: +61 7 3138 1535. Australia, Zealandia (New Zealand–New Caledonia) and Antarctica E-mail addresses: [email protected] (M.N. Krosch), [email protected] remained relatively connected until around 80 mya when the (A.M. Baker), [email protected] (P.B. Mather), [email protected] smaller Zealandia block split from western Antarctica and drifted (P.S. Cranston). 1055-7903/$ - see front matter Ó 2011 Elsevier Inc. All rights reserved. doi:10.1016/j.ympev.2011.03.003 M.N. Krosch et al. / Molecular Phylogenetics and Evolution 59 (2011) 458–468 459 northeast, a process that opened up the Tasman Sea (Sanmartin have revealed the presence of similar disjunct clades of potential and Ronquist, 2004). This block is thought to have been submerged Gondwanan origin. Several described genera are now considered periodically throughout the Tertiary period, before finally splitting to belong to one of these groups, including Australian Echinocladius around 40 mya (but see Ladiges and Cantrill, 2007). Australia be- (Cranston, 2000b), New Zealand Naonella (Boothroyd, 1994), Paul- gan to separate from the eastern side of Antarctica during the late freemania (Cranston and Krosch, 2011) and Tonnoirocladius (Cran- Cretaceous (90 mya), with full separation and the opening of the ston, 2007), South American Ferringtonia (Sæther and Andersen, Southern Ocean occurring around 35 mya (Veevers et al., 1991). 2010) and Barbadocladius (Cranston and Krosch, in press), Limnoph- The final stage of Gondwanan fragmentation involved the rifting yes (known from South America and now New Zealand – Sæther, of South America from Antarctica approximately 30 mya (Barker 1990a,b), Anzacladius (from Australia and New Zealand – Cranston, and Burrell, 1977; Lawver and Gahagan, 2003), thereby opening 2009), Botryocladius (from Australia and South America – Cranston the Drake Passage and initiating the Circumpolar Antarctic Current and Edward, 1999) and Pirara (known from Australia, New Zealand and associated West Wind Drift effects (Cook and Crisp, 2005b). and South America – Boothroyd and Cranston, 1995). These dis- Based on this reconstruction of continental evolution, the expected junct austral taxa generally inhabit similar environments – i.e., phylogenetic pattern for austral taxa according to a simple vicari- cool, pristine, often upland to montane streams – to the taxa inves- ance history is thus that African taxa form a sister group to New tigated by Brundin (1966) and thus may represent a relict Gondwa- Zealand, southern South American and Australian taxa, with New nan clade within the Orthocladiinae. Beyond these preliminary Zealand taxa then sister to southern South American and Austra- suggestions, attempts to describe phylogenetic relationships lian taxa. among these proposed Gondwanan genera have been limited to Phylogenetic relationships that show close concordance with postulations of similarity contained within species descriptions the proposed geological sequence for the break-up of Gondwana and morphology-based phylogenetic reconstructions based on can provide clear evidence for vicariance as the major mechanism only a subset of taxa (Cranston and Edward, 1999; Cranston, that has driven disjunct distributions. A broad range of invertebrate 2000b, 2007; Sæther and Andersen, 2010). taxa with varying dispersal capabilities exhibit phylogenies consis- Accurate resolution of the phylogenetic relationships among tent with this pattern (e.g., Thayer, 1985; Shaw, 1990; Henderson, proposed Gondwanan orthoclads is thus important as a compari- 1991; Hunt and Cokendolpher, 1991; Parsons, 1996; Gauld and son not only to morphology-based ideas of the evolutionary affin- Wahl, 2000; Sequeira and Farrell, 2001), including several groups ities of the Gondwanan orthoclad genera, but to the work of within the Diptera (e.g., Munroe, 1974; Yeates and Irwin, 1996; Brundin and the wider literature concerning the historical effects Cranston and Edward, 1999). Incongruence between taxon phylog- of the fragmentation of Gondwana on austral taxa. Thus, we aim enies and the geological sequence of continental fragmentation, on here to resolve phylogenetic relationships among proposed the other hand, historically has led to speculation that long-dis- Gondwanan orthoclad taxa using molecular data and to infer their tance transoceanic dispersal post-vicariance may explain current biogeographical history with regard to the break-up of the super- distributions and taxonomic relationships. In particular, many continent. Given patterns revealed by Brundin for other austral plant taxa on the southern continents exhibit relationships and/or chironomid groups, we expected that evolutionary relationships divergence times that do not correspond with continental break- among the proposed Gondwanan orthoclads would follow the geo- up; for example, taxa in New Zealand and Australia that share a logical sequence of continental fragmentation, reflecting diversifi- most recent common ancestor to the exclusion of other austral cation largely driven by vicariance.