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Introduction:
The evolutionary patterns of symbiotic organisms are inferred using cophylogenetic methods. Congruent phylogenies indicate cospeciation or host-switches to closely-related hosts, whereas incongruent topologies indicate independent speciation. Recent studies suggest that coordinated speciation is a rare event, and may not occur even in the highly specialized associations. The cospeciation hypothesis was mainly tested for free-living mutualistic associations, such as plant-pollinator interactions, and host-parasitic systems but was rarely tested on obligate, mutualistic associations involving intimate physiological interactions. Symbionts with lower partner selectivity may not experience coordinated speciation due to frequent switching of partners. On the other hand, symbionts with high partner selectivity may influence each other’s evolution owing to the highly interdependent lifestyles. Symbiont association patterns are also influenced by habitat and it has been proposed that symbiotic interactions are stronger in warm regions as compared to cooler regions (also referred as latitudinal gradient of biotic specialization). This hypothesis however, has recently been challenged and it has been suggested that a gradient of biotic specialization may not exist at all. Reliable species concepts are a prerequisite for understanding the association and evolutionary patterns of symbiotic organisms. The species concepts of many groups traditionally relied on the morphological species concept, which may not be adequate for distinguishing species due to the: i) homoplasious nature of morphological characters, an due to the inability to distinguish cryptic species. Thus phylogenetic species concept along with coalescent-based species delimitation approaches, which utilize molecular data for inferring species boundaries have been used widely for resolving taxonomic relationships. Lichens are obligatory symbiotic associations consisting of a fungal partner (mycobiont) and one or more photosynthetic partners, algae, and/or cyanobacteria (photobionts). I used the lichen forming fungal genus Protoparmelia as my study system, which consists of ~25-30 previously described species inhabiting different habitats, from the arctic to the tropics. This makes Protoparmelia an ideal system to explore the association and evolutionary patterns across different macrohabitats.
Objectives:
The objectives of this thesis were to 1. Elucidate the phylogenetic position of Protoparmelia within Lecanorales, and infer the monophyly of Protoparmelia; 2. Understand species diversity within Protoparmelia s.str. using coalescent-based species delimitation approaches; and 3. To identify the Trebouxia species associated with Protoparmelia using phylogenetic and species delimitation approaches and to infer the association and cophylogenetic patterns Protoparmelia and Trebouxia in different macrohabitats.
Results and discussion:
Chapter 1: Taxonomic position of Protoparmelia
In the first part of this study I explored the taxonomic position of Protoparmelia within the order Lecanorales. Overall this study included 54 taxa from four families, sequenced at five loci (178 sequences). I found Protoparmelia to be polyphyletic and sister to Parmeliaceae.
Chapter 2: Multilocus phylogeny and species delimitation of Protoparmelia spp.
In this part of the study, I identified and delimited the Protoparmelia species forming a monophyletic clade sister to Parmeliaceae i.e., Protoparmelia sensu stricto group, based on the multilocus phylogeny and coalescent-based species delimitation approaches. I included 18 previously described and three unidentified Protoparmelia species, which represents ~70% of the total described species, and 73 other taxa, sequenced at six loci. I found that the sensu stricto group comprised of 25 supported clades instead of 12 previously described Protoparmelia species. I tested the speciation probabilities of these 25 clades using species delimitation softwares BP&P and spedeSTEM. I found nine previously unrecognized lineages in Protoparmelia and I propose the presence of at least 23 species for Protoparmelia s.str., in contrast to the 12 described species included in the study.
Chapter 3: Association and cophylogenetic patterns of Protoparmelia and its symbiotic partner Trebouxia
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The small conoidean Hemilienardia ocellata is one of the easily recognizable Indo-Pacific “turrids”, primarily because of its remarkable eyespot colour pattern. Morphological and molecular phylogenetic analyses revealed four species that share this “characteristic” colour pattern but demonstrate consistent differences in size and shell proportions. Three new species – Hemilienardia acinonyx sp. nov. from the Philippines, H. lynx sp. nov. from Papua New Guinea and H. pardus sp. nov. from the Society and Loyalty Islands – are described based on the results of phylogenetic analyses. Although the H. ocellata species complex clade falls in a monophyletic Hemilienardia, H. ocellata and H. acinonyx sp. nov. possess a radula with semi-enrolled or notably flattened triangular marginal teeth, a condition that diverges substantially from the standard radular morphology of Hemilienardia and other raphitomids.
In this review (third part), several species within the Nassarius pauperus complex from the eastern Indian Ocean and western Pacific are treated, including a revised concept of Nassa paupera Gould, 1850, type species of the genus Reticunassa Iredale, 1936. In the most recent taxonomic revision, several species had been synonymized with Nassarius pauperus (Gould, 1850), despite distinctive differences among these species in shell morphology. We sequenced a fragment of the mitochondrial COI and the nuclear 28S genes of all available Nassarius pauperus complex species. Automatic barcode gap discovery and reciprocal monophyly were applied to propose species delimitation hypotheses and to support a new concept of the genus. Using morphological and molecular characters, Reticunassa is elevated to full genus rank. Six new species are described: Reticunassa visayaensis sp. nov., R. poppeorum sp. nov., R. annabolteae sp. nov., R. goliath sp. nov., R. intrudens sp. nov. and R. thailandensis sp. nov., while R. tringa (Souverbie, 1864) is recognized as a valid species.