Tuesday, September 30, 2008

Marshall et al. AJTMH 2005

Abstract. Malaria kills more than one million people a year, and understanding the historical association between its most notorious causative agent, Plasmodium falciparum, and its mosquito vectors is important in fighting the disease. We present a phylogenetic analysis of a number of species within the mosquito subgenus Cellia based on a selection of mitochondrial and nuclear genes. Although some of these relationships have been estimated in other studies, generally few species were included and/or statistical support at many nodes was low. Here we include two additional species of anthropophilic P. falciparum malaria vectors and reanalyze these relationships using a Bayesian method that allows us to simultaneously incorporate different models of evolution. We report data that indicate a paraphyletic relationship between five anthropophilic African mosquito vectors. Such a relationship suggests that these species can serve as independent natural experiments for anopheline immunologic responses to regular, prolonged contact with P. falciparum.

Marshall, JC, JR Powell, and A Caccone. 2005. Phylogenetic relationships of the anthropophilic Plasmodium falciparum malaria vectors in Africa. American Journal of Tropical Medicine and Hygiene 73: 749-752.

Sunday, September 28, 2008

Sites & Marshall AREES 2004

Abstract: Species are routinely used as fundamental units of analysis in biogeography, ecology, macroevolution, and conservation biology. A large literature focuses on defining species conceptually, but until recently little attention has been given to the issue of empirically delimiting species. Researchers confronted with the task of delimiting species in nature are often unsure which method(s) is (are) most appropriate for their system and data type collected. Here, we review twelve of these methods organized into two general categories of tree- and nontree-based approaches. We also summarize the relevant biological properties of species amenable to empirical evaluation, the classes of data required, and some of the strengths and limitations of each method. We conclude that all methods will sometimes fail to delimit species boundaries properly or will give conflicting results, and that virtually all methods require researchers to make qualitative judgments. These facts, coupled with the fuzzy nature of species boundaries, require an eclectic approach to delimiting species and caution against the reliance on any single data set or method when delimiting species.

No one definition has as yet satisfied all naturalists; yet every naturalist knows vaguely what he means when he speaks of a species.

Darwin (1859)

Sites, JW & JC Marshall. 2004. Operational criteria for delimiting species. Annual Review of Ecology, Evolution, and Systematics. 35: 199-227.

Marshall & Ramirez TREE 2004

This is a book review we wrote for the journal Trends in Ecology and Evolution.  In it we compare a socio-political phenomenon that Yale law professor Amy Chua describes with what is happening with scientific research in developing countries and how open-source scientific journals can help ease these tensions.

Marshall, JC and A Ramirez-Bautista. 2004. Politics, science, and global tensions. Trends in Ecology and Evolution 19: 117-118.

Agapow et al. QRB 2004

Abstract: Species are defined using a variety of different operational techniques. While discussion of the various methodologies has previously been restricted mostly to taxonomists, the demarcation of species is also crucial for conservation biology. Unfortunately, different methods of diagnosing species can arrive at different entities. Most prominently, it is widely thought that use of a phylogenetic species concept may lead to recognition of a far greater number of much less inclusive units. As a result, studies of the same group of organisms can produce not only different species identities but also different species range and number of individuals. To assess the impact of different definitions on conservation issues, we collected instances from the literature where a group of organisms was categorized both under phylogenetic and nonphylogenetic concepts. Our results show a marked difference, with surveys based on a phylogenetic species concept showing more species (48%) and an associated decrease in population size and range. We discuss the serious consequences of this trend for conservation, including an apparent change in the number of endangered species, potential political fallout, and the difficulty of deciding what should be conserved.

Agapow, P, ORP Binida-Emonds, KA Crandall, JL Gittleman, GM Mace, JC Marshall, A Purvis. 2003. The impact of species concept on biodiversity studies. The Quarterly Review of Biology 79: 161-179.

Sites & Marshall TREE 2003

Abstract: The literature about species concepts might be larger than that about any other subject in evolutionary biology, but the issue of empirically testing species boundaries has been given little attention relative to seemingly endless debates over what species are. The practical issue of delimiting species boundaries is nevertheless of central importance to many areas of evolutionary biology. The number of recently described methods for delimiting species suggests renewed interest in the topic, and some methods are explicitly quantitative. Here, we review nine of these methods by summarizing the relevant biological properties of species amenable to empirical evaluation, the classes of data required and some of the strengths and limitations of each.

Sites, JW & JC Marshall. 2003. Delimiting species: a Renaissance issue in systematic biology. Trends in Ecology and Evolution 18: 462-470.