The Last Changes Taxonomy, Phylogeny and Evolution of Plant-Parasitic Nematodes Hamid Abbasi Moghaddam* and Mohammad Salari** *M.Sc
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Biological Forum – An International Journal 7(2): 981-992(2015) ISSN No. (Print): 0975-1130 ISSN No. (Online): 2249-3239 The last changes Taxonomy, Phylogeny and Evolution of Plant-parasitic Nematodes Hamid Abbasi Moghaddam* and Mohammad Salari** *M.Sc. Student, Department of Plant Protection, Faculty of Agriculture, University of Zabol, IRAN **Associate Professor, Department of Plant Protection, College of Agriculture, University of Zabol, IRAN (Corresponding author: Hamid Abbasi Moghaddam) (Received 28 August, 2015, Accepted 29 November, 2015) (Published by Research Trend, Website: www.researchtrend.net) ABSTRACT: Nematodes can be identified using several methods, including light microscopy, fatty acid analysis, and PCR analysis. The phylum Nematoda can be seen as a success story. Nematodes are speciose and are present in huge numbers in virtually all marine, freshwater and terrestrial environments. A phylogenetic framework is needed to underpin meaningful comparisons across taxa and to generate hypotheses on the evolutionary origins of important properties and processes. We will outline the backbone of nematode phylogeny and focus on the phylogeny and evolution of plant-parasitic Tylenchomorpha. We will conclude with some recent insights into the relationships within and between two highly successful representatives of the Tylenchomorpha; the genera Pratylenchus and Meloidogyne. In this study, we present last changes taxonomy, phylogeny and evolution of plant-parasitic nematodes. Keywords: Phylogeny, taxonomy, plant-parasitic nematode, evolution comparative anatomy of existing nematodes, trophic INTRODUCTION habits, and by the comparison of nematode DNA Members of the phylum Nematoda (round worms) have sequences (Thomas et al. 1997, Powers et al. 1993). been in existence for an estimated one billion years, Based upon molecular phylogenic analyses, it appears making them one of the most ancient and diverse types that nematodes have evolved their ability to parasitize of animals on earth (Wang et al. 1999). They are animals and plants several times during their evolution thought to have evolved from simple animals some 400 (Blaxter et al. 1998). One point is clear; nematodes million years before the "Cambrian explosion" of have evolved to fill almost every conceivable niche on invertebrates able to be fossilized (Poinar, 1983). The earth that contains some amount of water. Nematodes two nematode classes, the Chromadorea and Enoplea, are extremely abundant and diverse animals; only have diverged so long ago, over 550 million years, that insects exceed their diversity. Most nematodes are free- it is difficult to accurately know the age of the two living and feed on bacteria, fungi, protozoans and other lineages of the phylum (Fig. 1). Nematodes are nematode (40% of the described species); many are multicellular animals in the group Ecdysozoa, or parasites of animals (invertebrates and vertebrates (44% animals that can shed their cuticle. Also included in this of the described species) and plants (15% of the group with nematodes are insects, arachnids and described species). crustaceans. In contrast to some of their relative Order Triplonchida invertebrates, nematodes are soft-bodied. Thus, very CHANGING PERSPECTIVES IN NEMATODE few nematodes have been fossilized (22 species from PHYLOGENY AND CLASSIFICATION 11 genera) and exactly what ancestral nematodes looked like remains unknown. While we do not know In the face of overwhelming diversity, a phylogenetic the morphology of the first nematodes, it is probable framework is needed to underpin meaningful that they were microbial feeders in the primordial comparisons across taxa and to generate hypotheses on oceans. The oldest known fossil nematodes are only the evolutionary origins of interesting properties and 120-135 million years old; by then nematodes had processes. Our understanding of nematode relationships diversified to feed on microbes, animals and plants has a varied and at times turbulent history, reflecting (Poinar et al. 1994, Manum et al. 1994). The oldest not only wider developments in phylogenetics, but also fossil nematodes are found in amber and are commonly the expertise and perspectives of those few systematists associated with insects. This is probably due to the fact who produce comprehensive classifications. Until that tree sap, which fossilizes to make amber, captures recently, the data for most nematode phylogenies and preserves insects and their associated nematodes consisted of relatively few morphological characters much more easily than an animal- or a nematode- derived primarily from light microscopy and often by infested portion of a plant. Much of what we know individual effort of the lone taxonomist. about the evolution of nematodes is inferred from the Moghaddam and Salari 982 Fig. 1. Order Rhabditida. Moghaddam and Salari 983 Molecular phylogenetics, bioinformatics and digital suspicions held by several proponents of earlier communication technologies have substantially altered morphological systems, i.e., that many important the dynamics of nematode systematics, creating anatomical features have arisen repeatedly during conditions where collaborative strategies are much evolution, and that one of the two traditional classes more productive than individual effort. This approach (Secernentea) is deeply phylogenetically embedded was exemplified by the analyses of Blaxter et al. (1998) within the other (Adenophorea). In an effort to translate based on small subunit (SSU) rDNA sequences of 53 the implications of SSU rDNA sequences into nematode species. Just seven years later, SSU rDNA classification, De Ley & Blaxter (2002, 2004) proposed sequences are available in public databases for more a system based primarily on the molecular backbone of than 600 nematode species. The basic topology SSU phylogenies (Fig. 2), but also incorporating other obtained by Blaxter et al. (1998) appears to remain characters. The result combines elements from many quite robust, although a number of important groups previous systems, and introduces some new features remain to be included. Also, it is increasingly clear that with respect to ranking (use of infraorders; Fig. 3). For some important aspects of nematode phylogeny cannot the sake of convenience, we will follow the be resolved by SSU data alone. Two of the major nomenclature of this system here, in order to outline the features of SSU analyses have independently confirmed major features of SSU-based nematode phylogenies. Fig. 2. Schematic overview of the evolution of the phylum Nematoda derived from SSU rDNA sequence data (based on Holterman et al. 2006). Major lineages of plant-parasites are indicated by dotted boxes (Tylenchomorpha, Dorylaimida and Triplonchida). It is noted that the infra order Tylenchomorpha is possible a polyphyletic group; it includes the members of Clade 12 and the Aphelenchoididae, a family within Clade 10. Moghaddam and Salari 984 BACKBONE OF NEMATODE PHYLOGENY the first to exploit the potential of small subunit ribosomal DNA (SSU rDNA) sequence data to resolve Analysis of large EST data sets recently reconfirmed phylogenetic relationships among nematodes. the placement of the phylum Nematoda within the Holterman et al. (2006) presented a subdivision of the superphylum Ecdysozoa (Dunn et al. 2008), a major phylum Nematoda into 12 clades based on a series of animal clade proposed by Aguinaldo et al. (1997) that mostly well-supported bifurcations in the backbone of unites all moulting animals. Blaxter et al. (1998) (53 the tree (339 taxa) (Fig. 2). taxa) and Aleshin et al. (1998) (19 taxa) were among Fig. 3. Summarized SSU phylogeny of Nematoda with example taxa, ecological range and higher classification (adapted from De Ley & Blaxter, 2002). P = phtypoarasitic, Z = zooparasitic. The under-representation of marine nematodes in these phylogenetic tree of nematodes-it is hard to find a phylogenetic overviews was, to some extent, lifted by morphological, ecological or biological characteristic SSU rDNA-based papers from Meldal et al. (2007) that has not arisen at least twice during nematode and Holterman et al. (2008a). Recently, a phylogenetic evolution. Convergent evolution appears to be an tree based on 1,215 small subunit ribosomal DNA important additional explanation for the seemingly sequences covering a wide range of nematode taxa persistent volatility of nematode systematics. One of was presented by van Megen et al. (2009). The overall the peculiarities of the phylum Nematoda is the topology of this phylogenetic tree resembles that of multitude of times that (animal- or plant-) parasitic Holterman et al. (2006). However, the support values lifestyles have arisen. Understanding the phylogenetic for the backbone tend to be lower. The deep history of the acquisition of particular phenotypes subdivision of the phylum Nematoda should be associated with successful parasitism permits fuller regarded as a 'work in progress', and a multi loci appreciation of the evolutionary constraints approach will be required for a more definitive experienced by organisms adapting to new hosts. framework. The extensiveness of convergent evolution Plant-parasitism has evolved independently in each of is one of the most striking phenomena observed in the three major clades in the phylum Nematoda (Fig. 2). Moghaddam and Salari 985 Fig. 4. Summarized SSU phylogeny of Rhabditida with example taxa, ecological range and higher classification (adapted from De Ley & Blaxter, 2002). Note the use of infraorder