Diversification of Legume-Feeding Psyllids (Hemiptera, Psylloidea) and Their Host Plants (Leguminosae, Genisteae)

Percy, Diana M (2001) Diversification of Legume-Feeding Psyllids (Hemiptera, Psylloidea) and Their Host Plants (Leguminosae, Genisteae). PhD thesis, University of Glasgow.

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Psyllids ('jumping plant lice') are small phytophagous insects that are related to aphids, scales and whiteflies (Hemiptera, sternorrhyncha). Psyllids are highly host specific, occurring on one or a few closely related hosts, and they predominantly feed on dicotyledonous angiosperms. In the subfamily Arytaininae (Psylloidea, Psyllinae) there are five psyllid genera that feed exclusively on shrubby legumes in the Genisteae (Leguminosae, Papilionoideae), and the species diversity for both plant and insect groups is highest in the Mediterranean. I made a detailed field survey of psyllids on Genisteae hosts in the western Mediterranean, including southern Iberia, NW Africa and two of the Macaronesian archipelagos (Canary Islands and Madeira). These collections (over 300) of both psyllids and legumes provided the basis for the taxonomic, phylogenetic and co-diversification analyses presented in this study. I have reassessed the classification of the legume-feeding psyllids native to Macaronesia, and I have revised the taxonomy of one genus (Arytainilla). I present evidence that the largest Macaronesian group has a unique island origin distinct from the predominantly continental genera. This Macaronesian group, which also has three continental members, is described as a new genus in order to clarify the monophyly and placement of this group within the Arytaininae. Seventeen new psyllid species in four arytainine genera, discovered in continental and Macaronesian regions, are proposed. I constructed phylogenies for both the arytainine psyllids and their legume host plants, in order to compare colonization, biogeographic patterns and island radiations. I present a phylogenetic study of the Palaearctic arytainine psyllids that incorporates both morphological data (adult and nymphal characters) and molecular data (mitochondrial genes: cytochrome oxidase I and II, including the intervening tRNA leucine; and the small ribosomal subunit tRNA). To investigate the evolution of the island legumes and to establish the relationships between continental and island host plants, a molecular phylogeny of part of the Genisteae was generated from sequences of the nuclear region: ITS1-5.8S-ITS2. The legume phylogeny shows a Mediterranean origin for the Canarian Genisteae (Adenocarpus, Genista and Teline), and a diphyletic origin for Teline - with two distinct island groups nested within Genista. The psyllid phylogeny shows that the two largest genera are paraphyletic, but there is some evidence that the Genisteae-feeders, as a whole, are monophyletic. The phylogenetic analyses for both psyllids and legumes highlight the problems of establishing host-parasite interactions using traditional morphological classifications alone. Colonization and biogeographic patterns among the island psyllid species implies a close correlation between the radiation of psyllids and the diversity of their host plants. Psyllid and legume phylogenies are compared in order to establish the extent of phylogenetic congruence between the insects and their host plants. To test assumptions of cospeciation, an absolute time scale is applied to both plant and insect phylogenies. A comparison of psyllid and legume phylogenies suggests that, whilst rare cospeciation events may play a significant role in promoting diversification, historical reconstructions of psyllid-legume interactions are complicated by systemic host switching. Psyllids appear to be opportunistic specialists with host switching occurring when the plant lineage fluctuates in geographical abundance, population structure or through dispersal. However, preadaptation is evident in many cases where selection of a new host may be constrained by plant chemistry and architecture. Successful establishment by a psyllid colonist is more likely when available hosts are phylogenetically and ecologically related to the original host. A history of parallel cladogenesis between psyllid and legume lineages is rejected in favour of a fluctuating lineage model of co-diversification which presents a more realistic interpretation of the present day pattern of host associations.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Additional Information: Adviser: Rob Page
Keywords: Evolution & development, Entomology
Date of Award: 2001
Depositing User: Enlighten Team
Unique ID: glathesis:2001-76018
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 19 Nov 2019 17:06
Last Modified: 19 Nov 2019 17:06
URI: https://theses.gla.ac.uk/id/eprint/76018

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