Vicariance and Ecological Dispersal in Papilio Subgenus Achillides (Papilionidae) and Some Other Butterflies of Asia and the Southwest Pacific
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Biogeographia – The Journal of Integrative Biogeography 34 (2019): 101–117 Vicariance and ecological dispersal in Papilio subgenus Achillides (Papilionidae) and some other butterflies of Asia and the Southwest Pacific JOHN R. GREHAN Reasearch Associate, McGuire Center, Florida Museum of Natural History, Gainesville, FL 32611(USA). email: [email protected] Keywords: allopatry, Gondwana, panbiogeography, Papilio, South-east Asia, vicariance. ABSTRACT Biogeographic patterns are reviewed for four widespread Southeast Asia butterfly groups in the superfamily Papilionoidea: Papilio subgenus Achillides Hübner, 1819 (Papilionidae), the birdwing butterflies (Papilionidae tribe Troidini), Genus Polyura Billberg, 1820 (Nymphalidae), and Genus Vanessa Fabricius, 1807 (Nymphalidae). The patterns of allopatry and sympatry are shown to be consistent with the vicariance of widespread ancestors with distributions including parts of Asia and Australasia, followed by secondary range expansion. Aspects of the distributions that are correlated with tectonic structures provide evidence of the age and origin of these butterflies in South-east Asia and Australasia. The transpacific affinities of the Troidini are consistent with a Pacific ancestry linked with former Cretaceous landscapes. The multi-island ranges of many of the butterfly species in Southeast Asia represent examples of metapopulation structure in which groups survive and persist in a region over long periods of time, even where individual islands are ephemeral. INTRODUCTION have geographically localized distributions, Butterflies are generally vagile organisms even when there are no obvious barriers to capable of flight over extended distances, range expansion. Both widespread and sometimes even between continents. It is localized butterfly taxa may show patterns of therefore not surprising that many species are allopatry where sister taxa (species level or widespread over continental regions and, often, higher) occupy different geographic sectors, so multiple oceanic islands. In contrast, though, they effectively ‘replace’ each other in many butterfly species and some higher taxa geographic space. Allopatry is a recurrent Grehan, 2019 Biogeographia 34: 101–117 101 characteristic of many taxa spanning almost all 2015, Kodandaramaiah et al. 2018). But these taxonomic levels in both animals and plants. It programs assume that a paraphyletic basal is evolutionarily significant because isolation is grade in area A indicates a centre of origin in A. required for differentiation to occur between For example, if four taxa in two areas, A and B, different localities (Croizat 1958, Craw et al. have a phylogeny A (A (A+B)), a centre of 1999, Heads 2012, 2014, 2017). origin in A is proposed, followed by dispersal Traditional attempts to provide a to B. However, this common pattern can also be mechanism for allopatry have relied on an explained by differentiation of a widespread evolutionary model of chance dispersal. In this ancestor already present in A and B, followed historical model, migrations from one set of by overlap in A (Heads 2014, 2017). The result localities (center of origin) manage to of such programs is to show support for fortuitously cross a barrier one time (or just a sequential chance dispersal when none actually few times) so that the colonists are isolated and exists. can diverge. This is Darwin’s (1859) model of The introduction of molecular dating at evolution – organisms are constantly migrating first sight seems to be an ideal method for away from centers of origin to colonize new assigning a definitive age to the origin of taxa. regions (Croizat 1964). It is a model of It also made biogeography easy for the evolution in which movement is used to explain specialist, as there was no further need to have divergence, and it has been widely applied to a general knowledge of biogeographic patterns; studies of butterfly allopatry (e.g. Aduse-Poku each taxon could be assigned its own, unique et al. 2009; Condamine et al. 2013a, b, Sahoo et history, rather than having a shared history with al. 2018). The problem with this model is that it other taxa through tectonic processes (Croizat requires single or rare dispersal events that 1958). Every group could be studied in somehow land colonizers in different places so isolation with a simple demarcation between that all the descendants are neatly allopatric. dispersal and vicariance depending on the Most allopatric distribution patterns are group’s age. If a taxon was only 10 million common to many taxa, but in the chance years old, for example, it could not have been dispersal theory, every individual pattern influenced by tectonic events dating as much as requires a separate dispersal event (that happens 100 million years ago. only once in each taxon) – there is no common If fossil-calibrated divergence estimates cause (Heads 2012). represented actual or maximum clade ages, this The adoption of center of origin and approach would indeed provide a general dispersal explanations has been justified by method for evaluating the evolution of widespread acceptance of two problematic allopatry. But no matter how many studies have principles. The first is the assumption that misrepresented fossil-calibrated estimates as dispersal-vicariance programs provide actual or maximal ages, it does not change the empirical evidence of chance dispersal or fact that they cannot represent anything but vicariance. The second is that fossil-calibrated minimum clade age and they cannot be turned molecular divergence dates provide an accurate into anything else (Heads 2005, 2014). Reliance (even if sometimes imprecise) representation of on fossil-calibrated molecular clock ages for the age of taxa. clades has resulted in decreased attention being Dispersal-vicariance analyses are widely given to the details of distribution and tectonics used to support sequential chance dispersal (Heads 2019). In reality, fossil-calibrated (usually unidirectional) as the mechanism of for molecular estimates cannot falsify earlier the evolution of butterfly allopatry (e.g. Aduse- origins of groups, and these may be predicted Poku et al. 2009, Condamine et al. 2013a, b, from other methods of dating, such as 102 Biogeographia 34: 101–117 Grehan, 2019 correlation between clade distribution and allopatric differentiation (vicariance) or tectonic events (Heads 2019). dispersal (as secondary range expansion). An alternative biogeographic approach 4. Comparisons are made among presented here examines the relationship the Papilionoidea butterfly groups Polyura between phylogenetic affinity and geographic (Nymphalidae), tribe Troidini (Papilionidae) distribution to identify the extent and nature of and Vanessa (Nymphalidae). allopatry between sister clades in Papilio 5. Examples of distributional subgenus Achillides of Asia and the Southwest relationships or boundaries that coincide with Pacific. This method is based on the general tectonic features are discussed along with the biogeographic principle that allopatry historical implications of the correlations for constitutes evidence of vicariance, while dating evolution. geographic overlap of taxa is evidence of subsequent range expansion by ecological These steps in methodology reflect the dispersal (Craw et al. 1999, Heads 2012, 2014, assumption that the actual geographic patterns 2017). In this vicariance model, ecological of distribution are historically informative dispersal allows a group to survive and even about the biogeographic significance of expand its range, but does not itself lead to phylogenetic divergence (Craw et al. 1999). divergence; divergence requires isolation The principal geographic distinction is between through geological or ecological disruption of allopatry (which is consistent with a general the ancestral distribution range. Patterns of biogeographic model of in situ allopatric allopatry and distributional overlap in divergence, i.e. vicariance), and geographic Achillides are documented here to assess the overlap of taxa (which is consistent with range relative impact of vicariance and dispersal in a expansion by subsequent ecological dispersal) tectonically complex region. Comparisons are (Croizat 1958, 1964, Craw et al. 1999, Heads also made with other Asian and Southwest 2012, 2014, 2017). Since the individual Pacific butterflies to characterize examples of distributions of taxa are historically butterfly allopatry in these regions and assess informative, this approach does not require the their historical significance with respect to a priori subdivision of geography into geological evolution. predefined areas, such as ‘Wallacea’ (e.g. Lohman et al. 2011). Most of the distributional ranges of MATERIALS AND METHODS Achillides species mapped by Condamine et al. Distributional and phylogenetic information on (2013a) are at a very broad geographic scale Achillides (from Condamine et al. 2013a) is and may be locally imprecise, particularly for mapped below in the following sequence: distributional limits within mainland Asia. 1. The distribution ranges of the However, for the purposes of this article, the four principle Achillides clades (referred to as distributional boundaries provided by clades 1-4) are mapped to illustrate the extent Condamine et al. (2013a) are sufficient to of allopatry and sympatry. identify patterns of allopatry and range overlap. Future mapping of distribution for this group at 2. Three of the Achillides clades a finer geographic level will also allow more that have