Continental Speciation in the Tropics: Contrasting Biogeographic Patterns of Divergence in the Uroplatus Leaf-Tailed Gecko Radiation of Madagascar C
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Journal of Zoology Journal of Zoology. Print ISSN 0952-8369 Continental speciation in the tropics: contrasting biogeographic patterns of divergence in the Uroplatus leaf-tailed gecko radiation of Madagascar C. J. Raxworthy1, R. G. Pearson1, B. M. Zimkus1,Ã, S. Reddy1,w, A. J. Deo1,2,z, R. A. Nussbaum3 & C. M. Ingram1 1 American Museum of Natural History, New York, NY, USA 2 Department of Biology, New York University, New York, NY, USA 3 Division of Amphibians and Reptiles, Museum of Zoology, University of Michigan, Ann Arbor, MI, USA Keywords Abstract speciation; biogeography; systematics; Reptilia; Gekkonidae; Madagascar. A fundamental expectation of vicariance biogeography is for contemporary cladogenesis to produce spatial congruence between speciating sympatric clades. Correspondence The Uroplatus leaf-tailed geckos represent one of most spectacular reptile radia- Christopher J. Raxworthy, American tions endemic to the continental island of Madagascar, and thus serve as an Museum of Natural History, Central Park excellent group for examining patterns of continental speciation within this large West at 79th Street, New York, NY 10024- and comparatively isolated tropical system. Here we present the first phylogeny 5192, USA. Email: [email protected] that includes complete taxonomic sampling for the group, and is based on morphology and molecular (mitochondrial and nuclear DNA) data. This study ÃCurrent address: Department of includes all described species, and we also include data for eight new species. We Herpetology, Museum of Comparative find novel outgroup relationships for Uroplatus and find strongest support for Zoology, Harvard University, 26 Oxford Paroedura as its sister taxon. Uroplatus is estimated to have initially diverged Street, Cambridge, MA 02138, during the mid-Tertiary in Madagascar, and includes two major speciose radia- w USA. Current address: Department of tions exhibiting extensive spatial overlap and estimated contemporary periods of Zoology, The Field Museum, 1400 S Lake speciation. All sister species are either allopatric or parapatric. However, we found Shore Drive, Chicago, IL 60605, no evidence for biogeographic congruence between these sympatric clades, and z USA. Current address: University of dispersal events are prevalent in the dispersal–vicariance biogeographic analyses, Pittsburgh School of Medicine, Pittsburgh, which we estimate to date to the Miocene. One sister-species pair exhibits isolated PA 15213, USA. distributions that we interpret as biogeographic relicts, and two sister-species pairs have parapatric distributions separated by elevation. Integrating ecological niche Editor: Andrew C. Kitchener models with our phylogenetic results finds both conserved and divergent niches between sister species. We also found substantial intra-specific genetic variation, Received 14 December 2007; revised 7 April and for the three most widespread species, poor intra-specific predictive perfor- 2008; accepted 14 April 2008 mance for ecological niche models across the latitudinal span of Madagascar. These latter results indicate the potential for intra-specific niche specialization doi:10.1111/j.1469-7998.2008.00460.x along environmental gradients, and more generally, this study suggests a complex speciation history for this group in Madagascar, which appears to include multiple speciation processes. Although substantial recent advances have been made been considered problematic for detecting speciation pat- regarding phylogenetic inference, our understanding of the terns (e.g. Cracraft, 1994; Barraclough & Nee, 2001; Losos processes of speciation remains incomplete (Turelli, Barton & Glor, 2003). In addition, extinction of lineages represents & Coyne, 2001; Gavrilets, 2003; Butlin, 2004; Coyne & Orr, another general problem for inferring speciation history, 2004; Doebeli et al., 2005). This is especially the case where the loss of species reduces the degree of biogeographic concerning the dominant mode of speciation of continental congruence recoverable between clades (Wiley, 1988; Cra- biotas. In contrast to islands and archipelagos (where craft, 1994; Barraclough & Nee, 2001; Crisci, Katinas & species are frequently isolated and segregated by obvious Posadas, 2003). Both spatial shifts and lineage losses de- oceanic barriers to dispersal), continental regions induce a grade the biogeographic signatures associated with alterna- far greater degree of uncertainty about the extent of geo- tive modes of speciation, which are also used in phylogenetic graphic isolation between populations. Post-speciation dis- comparative methods to infer modes of speciation (e.g. tribution shifts, driven by climate change, biotic interactions Lynch, 1989; Chesser & Zink, 1994; Barraclough, Vogler & (e.g. competition), adaptation or other factors, have long Harvey, 1998; Dimmick et al., 1999; Barraclough & Vogler, Journal of Zoology 275 (2008) 423–440 c 2008 The Authors. Journal compilation c 2008 The Zoological Society of London 423 Contrasting patterns of tropical continental speciation in geckos C. J. Raxworthy et al. 2000; Johnson & Cicero, 2002; Bouchard, Brooks & Yeates, locality data. Uroplatus geckos are both arboreal and 2005; Lukhtanov et al., 2005; Fitzpatrick & Turelli, 2006; nocturnal, with species distributed in all regions of Mada- Jiggins et al., 2006). gascar with the exception of the most arid southern spiny Ideally, therefore, continental speciation studies should forest, and the very highest montane regions above 2400 m be preferably based on groups and regions that minimize (C. J. Raxworthy, pers. obs.). problems of distribution shifts and lineage extinctions, and Prior phylogenetic analyses that have included this genus maximize speciation events for analysis. These selection are based on: (1) morphological data: two generic level criteria have received little discussion to date, although analyses (Bauer, 1990; Kluge & Nussbaum, 1995), and one Coyne & Orr (2004, 172, 175) proposed that tropical groups species level phylogeny that included six species (Bauer & offer the best conditions for comparative phylogenetic Russell, 1989); (2) a fragment of 16S mtDNA molecular speciation (see also Moritz et al., 2000), a conclusion data that included seven species (Glaw et al., 2006); and (3) supported by the results of Lessa, Cook & Patton (2003) two nuclear genes (RAG-1 and PDC), and two mitochon- who found little evidence for range expansion in the late drial genes (ND2 and cyt b) that included 10 species (Green- Quaternary in tropical compared with temperate regions. baum et al., 2007). However, all these studies have been The Indian Ocean continental island of Madagascar, in incomplete in their taxonomic sampling for the genus (due many respects, represents an ideal region to study specia- to combinations of known and unknown sampling gaps at tion. The island is 1000 km in length, with a surface area of the time of publication, and earlier taxonomies that included 586 000 km2; it is positioned almost entirely in the tropics, erroneous synonyms), and morphological and molecular and has experienced relatively modest shifts in climate data have not yet been included in a combined analysis. compared with many temperate regions (Burney, 2003; Here, we present the first taxonomically comprehensive Wells, 2003); has been tectonically almost static, moving phylogeny for Uroplatus, combining molecular and mor- o81 latitude over the last 45 million years (Royer et al., phological data, and we simultaneously use vicariance and 1992; Smith, Smith & Funnell, 1994); and has been isolated dispersal methods, as well as species ecological niche models (as an island) from all other land masses for 87–91 million to explore the group’s speciation history. We use: (1) multi- years (Storey et al., 1995; Torsvik et al., 2000). Conse- ple vicariance and dispersal methods to explore biogeo- quently, many of the radiations of species in Madagascar graphic patterns within the phylogeny; (2) sister-species are endemic to the continental island, which, because of its ecological niche models projected into geographic space to size serves as a mini-continent. The biota also excludes many explore the geography of speciation; and (3) intraspecific groups found on neighboring landmasses, thus resulting in a ecological niche models to infer potential intraspecific niche combination of spectacular taxonomic imbalance, ende- variation. Based on these results, we examine the support for mism and species richness (Krause, Hartman & Wells, alternative speciation scenarios for Madagascar, and com- 1997; Yoder & Nowak, 2006). pare these findings to other isolated continental gecko Although recent phylogenetic analyses have included groups. endemic taxa from Madagascar, a focus of most studies has centered on the origins of radiations in Madagascar via Materials and methods either Gondwanan vicariance or oceanic dispersal (reviewed in Yoder & Nowak, 2006). No phylogenetic studies we are Taxonomic sampling and characters aware of have specifically targeted the geographic speciation history of endemic clades within Madagascar. Conse- We selected nine Gekkonidae genera to serve as outgroups quently, processes driving species radiation within this for our phylogenetic analyses of Uroplatus (Table 1, see island continent remain poorly explored, although patterns Supplementary Material). Ingroup sampling of Uroplatus of regional endemism and phylogeographic structure have included all 12 described species, and the eight species been described for some groups