Cichlids

Members of the New and Old World clades of cich-lid fish are reproductively isolated by at least the prezygotic mechanism of female mate choice (see section 4.3.2). Indeed, Smith et al. (2003) argued that male coloration (which affects female mate choice) '. is the central component maintaining separation of cichlid gene pools.' In spite of the reproductive isolation afforded by mate choice, introgressive hybridization has now been Figure 5.10 Body mass of F, hybrids, R. blairi (BB), and R....

Biological species concept

It is somewhat of a false dichotomy to represent the biological species concept as the only framework that is defined by the occurrence, or lack thereof, of genetic exchange. Most, if not all, concepts consider genetic exchange to be of primary concern for defining species (e.g. see Sites and Marshall 2004 for a discussion of several methodologies for delimiting species that assume reproductive isolation). As illustrated above, one has only to read Phylogenetic Systematics (Hennig 1966), the...

Evolution by homoploid hybrid lineage formation in animalssexually reproducing taxa

The North American Rhagoletis pomonella species complex is a paradigm for studies of sympatric diversification due to host shifts. The development of this tephritid fruitfly group as a model evolutionary system began in earnest with the work of Bush (1966). His landmark studies revealed patterns of morphological and genetic variation indicative of organismic divergence through the accumulation of genetic variation, thus allowing individuals to exploit a new habitat in this case a new 'host'...

Propionibacterium acnes

Acne is the most common skin disease and affects approx. 80 of adolescents in the United States (Bruggemann et al. 2004). Surprisingly, the role played by the human skin-commensal bacterium, Propionibacterium acnes, in the development of acne is still debated. Some of the processes that may contribute to this skin disease and in which P. acnes may be involved include damage to host tissues due to bacterial lipases (Miskin et al. 1997) or inflammation caused by heat-shock proteins (Farrar et al....

Pre Darwin Darwin the Modern Synthesis and genetic exchange development of a paradigm

The role of genetic exchange in evolution has been of intense interest and debate for at least a century. However, the accumulation of data sets, the consideration of new models, and the resurrection of old models has led to a paradigm shift, reflected by an appreciation of the importance of gene transfer. In spite of this, arguments emphasizing an unimportant role for genetic exchange are still reflected in recent evolutionary literature (e.g. Coyne and Orr 2004). The goal of this text is to...

Phylogenetic species concept

The origin of the phylogenetic species concept can be traced back at least to Hennig (1966), although Darwin (1859) also presented evolutionary diversification as a bifurcating tree in the only illustration found in On the Origin of Species. However, Hennig's treatment is the basis for the modern phy-logenetic approach for studying evolutionary diversification. In the context of this discussion, Hennig's methodology can be placed within the history-based format of the phylogenetic species...

Dutch elm disease

Similar to the alder tree pathogen, the spread of Dutch elm disease has been marked by introgres-sive hybridization and hybrid lineage formation. Specifically, Brasier and Kirk 2001 defined two subspecies of the organism recognized as the cause of the present-day Dutch elm disease pandemic, the ascomycete fungus Ophiostoma novo-ulmi. The two subspecies, O. novo-ulmi novo-ulmi and O. novo-ulmi americana were originally designated as Eurasian and North American variants, respectively. Brasier and...

Influenza

Genetic reassortment, natural selection, and the origin of influenza strains Like the Darwin's finches, plague bacteria, and Louisiana irises, influenza viral types evolve through a combination of genetic exchange and natural selection Ghedin et al. 2005 . In particular, 'The introduction and subsequent spread in the human population of influenza A viruses with a novel hemagglutinin HA or a novel HA and neuraminidase NA subtype results from a sudden and major change in virus antigenicity ....

Hawaiian silversword complex

It has been argued that species of the Hawaiian genera Argyroxiphium, Dubautia, and Wilkesia constitute '. . . one of the most remarkable examples of adaptive radiation known to science' Carr and Kyhos 1981 . Carr and Kyhos 1981 substantiate their claim by pointing to the 28 species belonging to these three genera that i have bauplans ranging from large basal rosettes that form a single inflorescence before dying, to woody shrubs that annually produce many flowers, to trees, to vines and ii...

Introgressive hybridization hybrid speciation and the evolution of human food sources

. . . we demonstrate that the numerous MHC DRB alleles that are present in modern domestic mammals implies that substantial backcrossing with wild ancestors, either accidental or intentional, has been important in shaping the genetic diversity of our domesticates One of the taxa referred to by Vila et al. 2005 was the domestic dog, Canis familiaris. Though not considered such by most recent immigrants to North America, C. familiaris has not only been a beast of burden and a companion, but also...

Concordance across data sets hybrid zone analyses

Hybrid Zone Map

Robust tests for the presence of ongoing genetic exchange are made possible through examinations of genetic or phenotypic variation and habitat X genotype associations within hybrid zones, especially if made across generations. In particular, such data collected from populations within and outside of putative hybrid zones allow tests for reoccurring admixtures of alleles characteristics normally found in one or other of the parental forms. The utility of such studies, for testing hypotheses...

Evolution by homoploid hybrid lineage formation in plants

The taxonomy of the genus Machaeranthera has had a checkered past, with much controversy surrounding the placement of the genus in relation to other genera, and the alignment of species within the genus itself e.g. Cronquist and Keck 1957 Turner and Horne 1964 Morgan and Simpson 1992 . One example of the controversy associated with the evolutionary phylogenetic associations of Machaeranthera is reflected by the following quote from a paper by Cronquist and Keck 1957 , entitled 'A reconstitution...

Eucalyptus

Individuals of the Camden white gum, Eucalyptus benthamii, can be up to 40 m in height and live for over 150 years NSW National Parks and Wildlife Service 2000 . Though locally abundant, this species is restricted to the alluvial margins of the Nepean River and tributaries of this river southwest of Sydney, Australia Figure 8.1 Butcher et al. 2005 . Its distribution i within agriculturally favorable regions fertile alluvial zones and ii at low elevations in river bottoms has resulted in losses...

Darwins finches

Hybridization and the origin of species variability The most curious fact is the perfect gradation in the size of the beaks in the different species of Geospiza, from one as large as that of a hawfinch to that of a chaffinch, and even to that of a warbler Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends...

Prokaryotic species concept

Reticulate Evolution Pictures

The pervasive effects of lateral gene transfer in the evolutionary history of prokaryotic taxa are now well established Boucher et al. 2003 . This appreciation of the fundamental importance of genetic exchange in the diversification of bacterial species has been factored into some systematic treatments. For example, Rossello-Mora and Amann 2001 reflected the generality of problems inherent in all species concepts as well as the development, in their view, of a scientifically more robust...

Cohesion species concept

The cohesion species concept defines species as ' the most inclusive group of organisms having the potential for genetic and or demographic exchangeability' Templeton 1989 . Templeton 1989 argued that one of the main weaknesses of the biological species concept was its lack of applicability to either asexual organisms or to taxa belonging to syngameons. In Templeton's 1989 terminology the difficulty resulted from either 'too little' or 'too much sex'. Templeton 1989 proposed the cohesion...