Thursday, October 30, 2008

Marshall et al. EA 2008

Abstract- The evolutionary processes at play between island and mainland populations of the malaria mosquito vector Anopheles gambiae sensu stricto are of great interest as islands may be suitable sites for preliminary application of transgenic-based vector control strategies. Sao Tome´ and Prıncipe, located off the West African coast, have received such attention in recent years. This study investigates the degree of isolation of An. gambiae s.s. populations between these islands and the mainland based on mitochondrial and ribosomal DNA molecular data. We identify possible continental localities from which these island populations derived. For these purposes, we used FST values, haplotype networks, and nested clade analysis to estimate migration rates and patterns. Haplotypes from both markers are geographically widespread across the African continent. Results indicate that the populations from Sao Tome´ and Prıncipe are relatively isolated from continental African populations, suggesting they are promising sites for test releases of transgenic individuals. These island populations are possibly derived from two separate continental migrations. This result is discussed in the context of the history of the African slave trade with respect to Sao Tome and Prıncipe.

Marshall, JC, J Pinto, JD Charlwood, G Gabriele, F Santolamazza, F Simard, A della Torre, MJ Donnelly, and A Caccone. 2008. Exploring the origin and degree of isolation of Anopheles gambiae from the islands of Sao Tome and Principe, potential sites for testing transgenic-based vector control. Evolutionary Applications 1: 631-644.

Thursday, October 9, 2008

Parmakelis et al. 2008

Background: If the insect innate immune system is to be used as a potential blocking step in transmission of malaria, then it will require targeting one or a few genes with highest relevance and ease of manipulation. The problem is to identify and manipulate those of most importance to malaria infection without the risk of decreasing the mosquito's ability to stave off infections by microbes in general. Molecular evolution methodologies and concepts can help identify such genes. Within the setting of a comparative molecular population genetic and phylogenetic framework, involving six species of the Anopheles gambiae complex, we investigated whether a set of four preselected immunity genes (gambicin, NOS, Rel2 and FBN9) might have evolved under selection pressure imposed by the malaria parasite.

Results: We document varying levels of polymorphism within and divergence between the species, in all four genes. Introgression and the sharing of ancestral polymorphisms, two processes that have been documented in the past, were verified in this study in all four studied genes. These processes appear to affect each gene in different ways and to different degrees. However, there is no evidence of positive selection acting on these genes.

Conclusion: Considering the results presented here in concert with previous studies, genes that interact directly with the Plasmodium parasite, and play little or no role in defense against other microbes, are probably the most likely candidates for a specific adaptive response against P. falciparum. Furthermore, since it is hard to establish direct evidence linking the adaptation of any candidate gene to P. falciparum infection, a comparative framework allowing at least an indirect link should be provided. Such a framework could be achieved, if a similar approach like the one involved here, was applied to all other anopheline complexes that transmit P. falciparum malaria.

Parmakelis, A, M Slotman, JC Marshall, PH Awono-Ambene, C Antonion-Nkondjio, F Simard, A Caccone, JR Powell. 2008.  The molecular evolution of four anti-malarial immune genes in the Anopholes gambiae species complex. BMC Evolutionary Biology 8:79

Wednesday, October 8, 2008

Scientific American 2008

I was interviewed for this article titled 'What is a Species' by Carl Zimmer that appeared in the June issue of Scientific American pages 72-79.  This is a great article, written for a general audience, on some of the scientific issues around identifying species in nature.

Slotman et al. PLoS ONE 2007

Background. Co-evolution between Plasmodium species and its vectors may result in adaptive changes in genes that are crucial components of the vector’s defense against the pathogen. By analyzing which genes show evidence of positive selection in malaria vectors, but not in closely related non-vectors, we can identify genes that are crucial for the mosquito’s resistance against Plasmodium. Methodology/Principle Findings. We investigated genetic variation of three anti-malarial genes; CEC1, GNBP-B1 and LRIM1, in both vector and non-vector species of the Anopheles gambiae complex. Whereas little protein differentiation was observed between species in CEC1 and GNBP-B1, McDonald-Kreitman and maximum likelihood tests of positive selection show that LRIM1 underwent adaptive evolution in a primary malaria vector; An. arabiensis. In particular, two adjacent codons show clear signs of adaptation by having accumulated three out of four replacement substitutions. Furthermore, our data indicate that this LRIM1 allele has introgressed from An. arabiensis into the other main malaria vector An. gambiae. Conclusions/Significance. Although no evidence exists to link the adaptation of LRIM1 to P. falciparum infection, an adaptive response of a known anti-malarial gene in a primary malaria vector is intriguing, and may suggest that this gene could play a role in Plasmodium resistance in An. arabiensis. If so, our data also predicts that LRIM1 alleles in An. gambiae vary in their level of resistance against P. falciparum.

Slotman MA, A Parmakelis, JC Marshall, PH Awono-Ambene, C Antonio-Nkondjo, F Simard, A Caccone, JR Powell. 2007. Patterns of selection in anti-malarial immune genes in malaria vectors: evidence for adaptive evolution in LRIM1 in Anopheles arabiensis.  PLoS ONE 2: e793

Marshall et al. Evolution 2006

Abstract. Species form the fundamental units of analysis in many areas of biology and, therefore, rigorous delimitation of this unit is important to a broad array of researchers. Recently, many new empirical methods have been proposed to delimit species in nature, and a large literature exists on the theoretical merit and superiority of each method. However, few empirical studies actually compare the results of these methods applied in the same study system. We used a large allozyme and chromosome dataset to apply a number of genetic-distance, character-based, and tree-based methods to a well-studied, data-rich system: the Sceloporus grammicus lizard complex of central Mexico. We hypothesized species boundaries under a general lineage or evolutionary species conceptual framework in an a priori fashion using mapped restriction-site data (mitochondrial DNA and nuclear rDNA), allozymes, and morphology. We then compared the ability of different methods to recover the ‘‘hypothesized evolutionary species’’ (HES). Highton’s genetic-distance method and a tree-based method consistently recovered all four HES, although sometimes with weak support. With two exceptions, other methods recovered the same HES, but additional groups were weakly delimited and nested within the HES. Given the apparent recent divergence of some of the chromosome races and distinct populations in this complex, these are encouraging results. We emphasize the value of specifying testable criteria as clearly as possible and testing these with methods that make use of different properties of a single dataset.

Marshall, JC, E Arevalo, E Benavides, JL Sites, JW Sites, Jr. 2006. Delimiting species: Comparing methods for mendelian characters using lizards of the Sceloporus grammicus (Squamata: Phrynosomatidae) complex. Evolution 60: 1050-1065

Tuesday, October 7, 2008

Lee et al. 2006

Abstract- We surveyed Melanoplus femurrubrum populations within the state of Connecticut for genetic diversity at multiple genetic markers, including three mitochondrial [cytochrome oxidase subunit 1 (COI), reduced form of nicotinamide adenine dinucleotide dehydrogenase subunit 2 (ND2), and AT rich] and one nuclear [internal transcribed spacers of the ribosomal DNA cluster (ITS1)] gene regions. All markers were variable, and the AT-rich gene showed the highest sequence divergence. Analysis of molecular variance (AMOVA), fixation index (Fst) analysis, and phylogeographic patterns showed little divergence between northern and southern regions. Estimates of genetic diversity (p) showed higher mitochondrial diversity in the northern region but nearly equal diversity for the ITS1 gene. This study shows for the first time in Melanoplus genetic variation for the ND2, AT rich, and ITS genes within a small geographic area. Our methods and results should be useful for other researchers interested in conducting population-level studies on closely related species.

Lee J, JC Marshall, OJ Schmitz, A Caccone. 2006. Genetic divergence of Connecticut Melanoplus femurrubrum populations. Journal of Heredity 97: 290-293

Crandall & Marshall 2006

KUTV:Researchers Don't Agree If WY Mouse Exists Or Not

May 19, 2006 

Researchers Don't Agree If WY Mouse Exists Or Not

CHEYENNE, Wyo. More research is out on whether the Preble's meadow jumping mouse exists or NOT, and the latest study offers a different view than the last one.This latest review of the Preble's mouse was requested and paid for by the state of Wyoming. Wyoming officials say that two researchers -- Keith Crandall and Jonathan Marshall -- could find NO genetic difference between the Preble's mouse and other mice. Governor Freudenthal said today (Friday) that the latest research shows that the mouse does NOT exist, and thus is NOT entitled to protection as an endangered species. Federal protections for the Preble's mouse stand to hold up development in Preble's mouse habitat in Colorado and Wyoming. Wyoming has asked the federal government to remove the mouse from endangered species protection. A decision is expected sometime before August sixth. A study released in January concluded that the mouse is in fact a distinct subspecies of jumping mouse and therefore is entitled to protection as an endangered species.

Sunday, October 5, 2008

Leyte-Manrique et al. BSHM 2006

Resume- El complejo Sceloporus grammicus ha sido un sistema modelo en diversas areas de investigacion. Aqui proporcionamos un resumen de los estudios sobre la morfologia, ecologia, variacion cromosomica, y limites de especies dentro del complejo.  Concluimos que a pesar de la problematica de las sistematica de complejo, se ha realizado un gran avance en el conocimiento del mismo.  Finalmente, es necesario un conocimiento mas coordinado entre las distinctas areas de investigacion para establecer mejor el estatus taxonomico de las poblaciones de este complejo.

Leyte-Manrique, A, U Hernandez-Salinas, E Chavez-Calzada, M del Carmen Sanchez, JC Marshall, y A Ramirez-Bautista. 2006. El complejo Sceloporus grammicus un grup de largartilla en especiacion. Boletin de la Sociedad Herpetologico de Mexico 14: 18-24.

Thursday, October 2, 2008

Jimenez-Cruz et al. SWN 2005

ABSTRACT Reproductive and fat body cycles were studied in a population of viviparous lizards (Sceloporus grammicus) from the Teotihuaca´n area, state of Mexico between October 1984 and September 1985. Males reached sexual maturity at a snout-vent length (SVL) of 44.5 mm and at an age of 6 to 7 mo; females reached sexual maturity at 44.1 mm SVL and at an age of 8 to 9 mo. Testicular mass of adult males began to increase in size in May and peaked during July, August, and September. Maximum testicular growth was associated with precipitation, but not with temperature and photoperiod. Enlarged vitellogenic follicles appeared during October, and females contained embryos in stages 1 through 8 during November. Females had embryos in later embryonic stages 29 through 40 from January to April. Vitellogenesis and embryonic development were associated with increasing photoperiod, temperature, and precipitation. Mean litter size was 5.09 6 0.24 (2 to 9). Mean RCM was 0.338 6 0.024 (0.015 to 0.80). Litter size and RCM were positively correlated with female SVL.

JImenez-Cruz, E, A Ramirez-Bautista, JC Marshall, M Lizana-Avia, A Nieto-Montes de Oca. 2005. Reproductive cycel of Sceloporus grammicus (Squamata:Phrynosomatidae) from Teotihuacan, Mexico. The Southwestern Naturalist 50: 178-187.