A Bacterial Artificial Chromosome-based Genetic Linkage Map of the Nematode Pristionchus Pacificus

Genetics. Sep, 2002  |  Pubmed ID: 12242228

To understand the evolution of developmental processes, nonmodel organisms in the nematodes, insects, and vertebrates are compared with established model systems. Often, these comparisons suffer from the inability to apply sophisticated technologies to these nonmodel species. In the nematode Pristionchus pacificus, cellular and genetic analyses are used to compare vulva development to that of Caenorhabditis elegans. However, substantial changes in gene function between P. pacificus and C. elegans limit the use of candidate gene approaches in studying P. pacificus mutations. To facilitate map-based cloning of mutations in P. pacificus, we constructed a BAC-based genetic linkage map. A BAC library of 13,440 clones was generated and completely end sequenced. By comparing BAC end and EST sequences between the "wild-type" strain P. pacificus var. California and the polymorphic strain P. pacificus var. Washington, 133 single-stranded conformational polymorphisms were identified. These markers were tested on a meiotic mapping panel of 46 randomly picked F(2) animals after a cross of the two strains, providing the first genetic linkage map of P. pacificus. A mapping strategy using two selected markers per chromosome was devised and the efficiency of this approach was illustrated by the mapping of the Ppa-unc-1/Twitchin gene.

The Evolution of Signalling Pathways in Animal Development

Nature Reviews. Genetics. Jan, 2003  |  Pubmed ID: 12509752

Despite the bewildering number of cell types and patterns found in the animal kingdom, only a few signalling pathways are required to generate them. Most cell-cell interactions during embryonic development involve the Hedgehog, Wnt, transforming growth factor-beta, receptor tyrosine kinase, Notch, JAK/STAT and nuclear hormone pathways. Looking at how these pathways evolved might provide insights into how a few signalling pathways can generate so much cellular and morphological diversity during the development of individual organisms and the evolution of animal body plans.

Finally, Worm Polycomb-like Genes Meet Hox Regulation

Developmental Cell. Jun, 2003  |  Pubmed ID: 12791262

Polycomb and Trithorax group proteins have been shown to regulate Hox gene expression in flies and mammals, but not in worms. Two reports in this issue of Developmental Cell establish a first link between Polycomb-like genes and Hox gene regulation in C. elegans. However, sequence comparison indicates that these genes may not be homologous to the fly Polycomb genes, suggesting that independent gene recruitment occurred during nematode evolution.

Conservation of the Global Sex Determination Gene Tra-1 in Distantly Related Nematodes

Genes & Development. May, 2004  |  Pubmed ID: 15155582

Sex determination has long intrigued evolutionists, geneticists, and developmental biologists in a similar way. Substantial evidence indicates that sex determination evolves rapidly and, therefore, can be used to study how molecular patterning processes evolve. In Caenorhabditis elegans, sex determination relies on a signaling pathway that involves a cascade of negatively acting factors, finally triggering the GLI-family zinc-finger transcription factor TRA-1. We have started to investigate sex determination in the nematode satellite species Pristionchus pacificus that is separated from C. elegans for 200-300 million years. In P. pacificus, animals with two X chromosomes develop as hermaphrodites, whereas XO animals develop as males. We used an unbiased forward genetic approach and isolated several mutants with a hermaphrodite to male transformation of the XX karyotype. We identified one complementation group as representing the P. pacificus ortholog of tra-1, providing the first evidence for the conservation of a global sex determination gene over a time period of at least 200 million years. A Ppa-tra-1 morpholino phenocopies Ppa-tra-1 mutants and establishes the morpholino technology as a reverse genetic approach in P. pacificus.

The World of a Worm: a Framework for Caenorhabditis Evolution. Workshop on the Study of Evolutionary Biology with Caenorhabditis Elegans and Closely Related Species

EMBO Reports. Oct, 2006  |  Pubmed ID: 16977337

Evolution of the Control of Sexual Identity in Nematodes

Seminars in Cell & Developmental Biology. Jun, 2007  |  Pubmed ID: 17306573

Most animals are male/female species and reproduce sexually. Variation in this pattern of reproduction has arisen many times during animal evolution, particularly in nematodes. Little is known about the evolutionary forces and constraints that influenced the origin of self-fertilization, for instance, a type of reproduction that seems to have evolved many times in the phylum Nematoda. Caenorhabditis elegans, a very well known nematode, provides the framework for comparative studies of sex determination. The relative ease with which nematodes can be studied in the laboratory and the fact that many recently developed techniques can be applied to many species make them attractive for comparative research. It is relatively poorly understood how the evolution of new types of sex determination and mode of reproduction results in changes in genome structure, ecology and population genetics. Here, I review the evolution of sex determination and mating types in the phylum Nematoda with the objective of providing a framework for future research.

Evolutionary Morphology of the Rattlesnake Style

BMC Evolutionary Biology. 2009  |  Pubmed ID: 19208237

The rattlesnake rattling system is an evolutionary novelty that includes anatomical, behavioral, and physiological modifications of the generalized pitviper tail. One such modification, the formation of a bony clublike style at the terminal region of the caudal vertebrae, has not previously been examined in a phylogenetic context. Here we used skeletal material, cleared and stained preparations, and radiographs of whole preserved specimens to examine interspecific variation in style morphology among 34 rattlesnake species.

Natural Variation of Outcrossing in the Hermaphroditic Nematode Pristionchus Pacificus

BMC Evolutionary Biology. 2009  |  Pubmed ID: 19379507

Evolution of selfing can be associated with an increase in fixation of deleterious mutations, which in certain conditions can lead to species extinction. In nematodes, a few species evolved self-fertilization independently, making them excellent model systems to study the evolutionary consequences of this type of mating system.

Body Size Evolution in Insular Speckled Rattlesnakes (Viperidae: Crotalus Mitchellii)

PloS One. 2010  |  Pubmed ID: 20209105

Speckled rattlesnakes (Crotalus mitchellii) inhabit multiple islands off the coast of Baja California, Mexico. Two of the 14 known insular populations have been recognized as subspecies based primarily on body size divergence from putative mainland ancestral populations; however, a survey of body size variation from other islands occupied by these snakes has not been previously reported. We examined body size variation between island and mainland speckled rattlesnakes, and the relationship between body size and various island physical variables among 12 island populations. We also examined relative head size among giant, dwarfed, and mainland speckled rattlesnakes to determine whether allometric differences conformed to predictions of gape size (and indirectly body size) evolving in response to shifts in prey size.

Asymmetric Spermatocyte Division As a Mechanism for Controlling Sex Ratios

Nature Communications. Jan, 2011  |  Pubmed ID: 21245838

Although Mendel's first law predicts that crosses between XY (or XO) males and XX females should yield equal numbers of males and females, individuals in a wide variety of metazoans transmit their sex chromosomes unequally and produce broods with highly skewed sex ratios. Here, we report two modifications to the cellular programme of spermatogenesis, which, in combination, help to explain why males of the free-living nematode species Rhabditis sp. SB347 sire <5% male progeny. First, the spermatogenesis programme involves a modified meiosis in which chromatids of the unpaired X chromosome separate prematurely, in meiosis I. Second, during anaphase II, cellular components essential for sperm motility are partitioned almost exclusively to the X-bearing sperm. Our studies reveal a novel cellular mechanism for the differential transmission of X-bearing sperm and suggest Rhabditis sp. SB347 as a useful model for studying sex chromosome drive and the evolution of new mating systems.

Regulation of Sexual Plasticity in a Nematode That Produces Males, Females, and Hermaphrodites

Current Biology : CB. Sep, 2011  |  Pubmed ID: 21906947

The mechanisms by which new modes of reproduction evolve remain important unsolved puzzles in evolutionary biology. Nematode worms are ideal for studying the evolution of mating systems because the phylum includes both a large range of reproductive modes and large numbers of evolutionarily independent switches [1, 2]. Rhabditis sp. SB347, a nematode with sexual polymorphism, produces males, females, and hermaphrodites [3]. To understand how the transition between mating systems occurs, we characterized the mechanisms that regulate female versus hermaphrodite fate in Rhabditis sp. SB347. Hermaphrodites develop through an obligatory nonfeeding juvenile stage, the dauer larva. Here we show that by suppressing dauer formation, Rhabditis sp. SB347 develops into females. Conversely, larvae that under optimal growth conditions develop into females can be respecified toward hermaphroditic development if submitted to dauer-inducing conditions. These results are of significance to understanding the evolution of complex mating systems present in parasitic nematodes.

The Genome of Tetranychus Urticae Reveals Herbivorous Pest Adaptations

Nature. Nov, 2011  |  Pubmed ID: 22113690

The spider mite Tetranychus urticae is a cosmopolitan agricultural pest with an extensive host plant range and an extreme record of pesticide resistance. Here we present the completely sequenced and annotated spider mite genome, representing the first complete chelicerate genome. At 90 megabases T. urticae has the smallest sequenced arthropod genome. Compared with other arthropods, the spider mite genome shows unique changes in the hormonal environment and organization of the Hox complex, and also reveals evolutionary innovation of silk production. We find strong signatures of polyphagy and detoxification in gene families associated with feeding on different hosts and in new gene families acquired by lateral gene transfer. Deep transcriptome analysis of mites feeding on different plants shows how this pest responds to a changing host environment. The T. urticae genome thus offers new insights into arthropod evolution and plant-herbivore interactions, and provides unique opportunities for developing novel plant protection strategies.