Phylogeny and Taxonomy of the Subfamily Vespinae
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Phylogeny and taxonomy of the subfamily Vespinae (Hymenoptera: Vespidae), based on five molecular markers Suzanna Persson Degree project for Master of Science (120 credits) Biodiversity and Systematics 60 hec Department of Biological and Environmental Sciences University of Gothenburg June 2015 Examiner: Bengt Oxelman Department of Biological and Environmental Sciences University of Gothenburg Supervisor: Urban Olsson Department of Biological and Environmental Sciences University of Gothenburg Table of Content 1 Introduction……………………………………………………………………2 1.1 General background………………………………………………………..2 1.1.1 Phylogenetic inference………………………………………………….3 1.1.2 Vespinae………………………………………………………………...4 1.2 Introduction to the thesis…………………………………………………...9 2 Material and methods………………………………………………………...10 2.1 Taxon sampling…………………………………………………………...10 2.2 DNA extraction, amplification and sequencing…………………………..10 2.3 Sequence alignment, data partitioning, and model selection……………..11 2.4 Phylogenetic inference……………………………………………………15 3 Results………………………………………………………………………..15 4 Discussion……………………………………………………………………27 5 Conclusions…………………………………………………………………..30 6 Acknowledgements…………………………………………………………..31 7 References……………………………………………………………………32 8 Appendix……………………………………………………………………..37 Abstract Sixty-four species have been recognized in Vespinae and divided into four or five genera. Based on Bayesian inference and multi-species coalescent we found that the branching pattern among the genera are unresolved and needs further study, except the clade Vespula + Paravespula where the support was high. We recovered five well supported clades corresponding to named taxa. In the case Vespula rufa and Vespula intermedia respectively Dolichovespula norwegica and Dolichovespula albida our data does not support that they have diverged. We found taxonomically unrecognized divergence within Provespa barthelemyi, Provespa anomala, Paravespula flaviceps and Vespa bicolor. This is also the case in Dolichovespula pacifica where there is also indication of introgression. Paravespula vulgaris also shows indication of introgression. Key words: Wasps, Provespa, Vespa, Vespula, Paravespula, Dolichovespula, Evolution, Bayesian inference, Multi-species coalescent. 1. Introduction 1.1 General background “On the ordinary view of each species having been independently created, we gain no scientific explanation.” – Charles Darwin. When Carl von Linné in 1735 published his book Systema Naturae, he started the work of classifying (categorized based on morphology) all the animal and plant species in the world. By the year 1749 he realised that he was way in over his head with that project and that it was too much for one person to handle alone (Winston, 1999), and he was right. Now, more than two 2 hundred years later, and with about 1.4 million species described, millions of species remain undescribed (Winston, 1999). In 1809, Jean Baptiste de Lamarck published his book Philosophie Zoologique and promoted Aristoteles concept Scala Naturae or the “ladder of life.” He argued that some organisms were higher up on this ladder, and the higher up, the more complex and also more superior the organisms were. This view of thinking implied that organisms had independent origin and that they had evolved at different times. It implies that evolution has a goal to produce high evolved species. He believed that the higher organisms had evolved earlier and therefore had had a longer time to evolve (Baum & Smith, 2013). Charles Darwin, however, in his book On the Origin of Species, argued that all species derived from a common ancestor. Instead of the ladder thinking, Darwin preferred tree thinking to describe the evolution of species. Darwin argued that a common ancestor is an indication and prerequisite that the evolution took place (Darwin, 1859). 1.1.1 Phylogenetic inference In 1953, an event took place that would change the study of molecular evolution - the discovery of the double helix, the structure of DNA (Watson & Crick, 1953). This was the key piece that revealed how the DNA molecule could be the carrier of information from generation to generation and that the information determined how organisms functioned and developed (Page & Holmes, 1998). A DNA sequence consists of four bases, adenine (A), cytosine (C), guanine (G) and thymine (T), where A and G are purines and C and T are pyrimidines. At every nucleotide position, one of these four bases occur. The DNA molecule is a double helix and the two strains are complements. Because the bases have different structures, A always binds to T, and C always binds to G. In the evolutionary process, these bases are continuously substituted by mutations (Baum & Smith, 2013). In time, the bases will either become fixed (fixed mutations) or lost, depending on which base will be inherited by the next generation (Nielsen & Slatkin, 2013). You may calculate the substitutions by mutations in terms of number of substitutions at every nucleotide position in order to get an indication of how long ago two taxa shared a common ancestor. This is called the evolutionary distance or mutation rate (Baum & Smith, 2013). To calculate this we use different kinds of substitution models. The simplest of the models is the Jukes-Cantor model (JC model) which assumes that the bases are equally likely to occur and that the rate of the substitutions is equal (Jukes and Cantor, 1969). But in reality, the bases do not usually occur at the same frequency, and some substitutions occur at a higher rate than others. Purines and pyrimidines have different chemical structure so transitions (substitutions from one purine to another purine or one pyrimidine to another pyrimidine) usually occur at a different rate than transversions (substitutions from one purine to one pyrimidine, or one pyrimidine to one purine). Transitions usually occur at a higher rate (Baum & Smith, 2013). There are several different methods for phylogenetic inference. One of them is maximum parsimony. The parsimony criterion states that the tree that shows the least amount of character changes is the one we choose. Another method is maximum likelihood. The maximum likelihood criterion tries to find the tree that is the most probable that the evolution has made for the observed data. Further, there is Bayesian inference. The Bayesian inference produces trees with the help of prior knowledge and models, and based on the posterior probability (the likelihood of the data and priors), finds the tree that is most probably true (Baum & Smith, 2013). 3 1.1.2 Vespinae Insects have existed for more than 400 million years, which makes them one of the earliest terrestrial groups. Wasps belong to the order Hymenoptera (Fig 1) and the earliest Hymenopteran that have been recognized, due to their distinctive wing venation, are from the Triassic period about 230 million years ago (MYA). The suborder Apocrita evolved about 195 MYA and the infraorder Aculeata about 155 MYA (Grimaldi & Engel, 2005). Fig 1. Phylogeny of the insect orders. Redrawn from Wheeler et al. (2001). One of the characteristic morphological traits of the suborder Apocrita (wasps, bees and ants) (Fig 2) is the “wasp waist,” which is the constriction between the metasoma and mesosoma (Fig 3). This allows for more manoeuvrability in order to control a long ovipositor (Grimaldi & Engel, 2005). Yellowjackets, hornets and Provespa, however, belong to the infraorder Aculeata where the ovipositor has developed into a sting, which injects a venom, for offensive and protective usage. Thousands of other insects mimic wasps that are in their near existence, called mimicry, which reflects the value and success of the sting (Grimaldi & Engel, 2005). The family Vespidae (Fig 4) is the second most well studied among the vespoid aculeates, after the ants (Formicidae). The Vespidae family consist of approximately 4,500 species (Grimaldi & Engel, 2005). Vespidae are recognized by the kidney-shaped eyes, with a distinct inward bend (ocular sinus), folded wings lengthwise while at rest and the forewings with an elongated first sub marginal cell (Douwes et al., 2012). Vespidae is divided into three subfamilies: Eumeninae (potter wasps), Polistinae (paper wasps) and Vespinae (social wasps). The subfamily Vespinae is defined by the following characteristics: abruptly narrow waist called petiole, the mid tibia with two spical spurs, the straight clypeus at the apical margin, and the triangular and serrated mandibles (Fig 5, 6) (Douwes et al., 2012). Archer (1989) recognized five genera in the subfamily Vespinae and 64 species (the number of species is in brackets): Provespa (3), Vespula (10), Vespa (23), Dolichovespula (18) and Paravespula (10). Vespula and Paravespula are sometimes merged as Vespula with species groups, the Vespula vulgaris species group (Vespula sensu Archer, 1989; Archer, 2008) and the Vespula rufa species group (Paravespula sensu Archer, 1989; Archer, 2008). Vespinae belong to the social insects and there are different forms of social behaviour: e.g., subsocial, communal, semisocial and eusocial behaviour (Grimaldi & Engel, 2005). Subsocial behaviour is the simplest form of social behaviour, simply meaning that the brood is cared for 4 during a limited time (Grimaldi & Engel, 2005). Communal behaviour is when females share a nest structure, but each female cares for its brood separately (Grimaldi & Engel, 2005; Gadau et al., 2009). Semisocial behaviour is when the same generation together take care of the brood, but there are no overlapping generations