Publication Date

2011

Document Type

Honors Thesis

Department

Biological Sciences

Keywords

Amoebida-Geographical distribution, Amoebida-Phylogeny, Arcellinida-Geographical distribution, Arcellinida-Phylogeny, Biogeography, Phylogeny, Biodiversity, Testate amoebae, Cryptic species, Group I intron

Abstract

Microbes, including viruses, bacteria, archaea, fungi, protists, and microalgae, comprise most of the Earth's biomass. They are critically important in maintaining the ecosystem processes, as well as for understanding evolutionary history. However, the morphological criteria used to describe microbes typically fail to provide much information on their evolutionary relationships. Morphospecies in testate amoebae, for instance, are defined by variations in their tests (shells): composition (proteinaceous or agglutinated), shape of the aperature (circular, oval or almost linear), and overall shape (Charman, 1999). However, variations among individuals in these characters are problematic in terms of identifying mophospecies. Thus, assessing phylogeny and biodiversity based on morphology alone may often reflect the diversity in phenotype but not genetic diversity (Charman, 1999), which often results in underestimating biodiversity and misclassification of microbes. Molecular analyses based on gene sequencing are needed to understand better the complexities of the microbial world. Here, we used specific primers to target small subunit ribosomal DNA (SSU-rDNA) of testate lobose amoebae in order to assess the biodiversity, biogeography, and evolutionary relationships among four Hyalospheniidae morphospecies. Our molecular analysis suggests that members within a morphospecies are not monophyletic but are interdigitated with other morphospecies. We further see no clear geographical patterns in the distribution of morphospecies due to the high levels of hidden genetic diversity. Evidence of morphological plasticity and microbial reproductive life cycle may explain the confusion in the interpretation of biodiversity based on morphology diversity. The results highlighted in this study suggest methods that will aid future hypothesis testing in the study of phylogeny and microbial diversity.

Language

English

Comments

53 p. : col. ill. Honors project-Smith College, Northampton, Mass., 2011. Includes bibliographical references (p. 31-35)

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