Flightless brown kiwis of New Zealand possess extremely subdivided population structure and cryptic species like small mammals.

Using allozymes and mtDNA sequences from the cytochrome b gene, we report that the brown kiwi has the highest levels of genetic structuring observed in birds. Moreover, the mtDNA sequences are, with two minor exceptions, diagnostic genetic markers for each population investigated, even though they are among the more slowly evolving coding regions in this genome. A major unexpected finding was the concordant split in molecular phylogenies between brown kiwis in the southern South Island and elsewhere in New Zealand. This basic phylogeographic boundary halfway down the South Island coincides with a fixed allele difference in the Hb nuclear locus and strongly suggests that two morphologically cryptic species are currently merged under one polytypic species. This is another striking example of how molecular genetic assays can detect phylogenetic discontinuities that are not reflected in traditional morphologically based taxonomies. However, reanalysis of the morphological characters by using phylogenetic methods revealed that the reason for this discordance is that most are primitive and thus are phylogenetically uninformative. Shared-derived morphological characters support the same relationships evident in the molecular phylogenies and, in concert with the molecular data, suggest that as brown kiwis colonized northward from the southern South Island, they retained many primitive characters that confounded earlier systematists. Strong subdivided population structure and cryptic species in brown kiwis seem to have evolved relatively recently as a consequence of Pleistocene range disjunctions, low dispersal power, and genetic drift in small populations.

Evolution of single and double Wolbachia symbioses during speciation in the Drosophila simulans complex.

Maternally inherited bacteria of the genus Wolbachia are responsible for the early death of embryos in crosses between uninfected females and infected males in several insect species. This phenomenon, known as cytoplasmic incompatibility, also occurs between strains infected by different symbionts in some species, including Drosophila simulans. Wolbachia was found in two species closely related to D. simulans, Drosophila mauritiana, and Drosophila sechellia, and shown to cause incompatibility in the latter species but not in D. mauritiana. Comparison of bacterial and mtDNA history clarifies the origins of bacterial and incompatibility polymorphisms in D. simulans. Infection in D. mauritiana is probably the result of introgression of an infected D. simulans cytoplasm. Some D. simulans and D. sechellia cytoplasmic lineages harbor two bacteria as a consequence of a double infection which probably occurred in a common ancestor. The descendant symbionts in each species are associated with similar incompatibility relationships, which suggests that little variation of incompatibility types has occurred within maternal lineages beyond that related to the density of symbionts in their hosts.

Founder-effect speciation theory: failure of experimental corroboration.

The theory of founder-effect speciation proposes that colonization by very few individuals of an empty habitat favors rapid genetic changes and the evolution of a new species. We report here the results obtained in a 10-year-long and large-scale experiment with Drosophila pseudoobscura designed to test the theory. In our experimental protocol, populations are established with variable numbers of very few individuals and allowed to expand greatly for several generations until conditions of severe competition for resources are reached and the population crashes. A few random survivors are then taken to start a new population expansion and thus initiate a new cycle of founding events, population flushes, and crashes. Our results provide no support for the theories proposing that new species are very likely to appear as by-products of founder events.

Sexual isolation in Drosophila melanogaster: a possible case of incipient speciation.

It is generally believed that Drosophila melanogaster has no closely related species with which it can produce the viable and fertile hybrids that are essential for the genetic analysis of speciation. Following the recent report of molecular differentiation between a Zimbabwe, Africa, population and two United States populations, we provide evidence that strong sexual isolation exists between the D. melanogaster population in Zimbabwe and populations of other continents. In the presence of males of their own kind, females from most isofemale lines of Zimbabwe would not mate with males from elsewhere; the reciprocal mating is also significantly reduced, but to a lesser degree. The genes for sexual behaviors are apparently polymorphic in Zimbabwe and postmating reproductive isolation between this and other populations has not yet evolved. Whole chromosome substitutions indicate significant genetic contributions to male mating success by both major autosomes, whereas the X chromosome effect is too weak to measure. In addition, the relative mating success between hybrid and pure line males supports the interpretation of strong female choice. These observations suggest that we are seeing the early stages of speciation in this group and that it is driven by sexual selection. The genetic and molecular tractability of D. melanogaster offers great promise for the detailed analysis of this apparent case of incipient speciation.

Description of two cryptic species of Anomala Samouelle (Coleoptera: Scarabaeidae: Rutelinae) from Costa Rica

Two new species of Anomala Samouelle from Costa Rica are described: Anomala moroni new species and A. parvaeucoma new species. Habitus, protibia, distribution map, and male genitalia (aedeagus and endophallus) of each species are illustrated. A key for the dorsally setose species from the Neotropical region is provided.

The status of the beavers of western North America with a consideration of the factors in their speciation ...

Pub. also as University of California publications in zoology, v. 12, no. 15, March 20, 1916.

Arsenic speciation in the urine and hair of individuals exposed to airborne arsenic through coal-burning in Guizhou, PR China

The extent of exposure of residents of Changqing (Guizhou, PR China) to arsenic through coal-burning was investigated. Despite the low coal-arsenic content (56.3 +/- 42.5 mg As kg(-1)) when compared with coals collected at different location and times from the same province, more than 30% of the study subjects have shown symptoms of arsenicosis. Coal, urine, hair, and water samples were collected in mid-September 2001 and analysed for arsenic. The average urinary and hair-arsenic concentrations in the exposed subjects were 71.4 +/- 37.1 mug As g(-1) creatinine (control 41.6 +/- 12.1) and 7.99 +/- 8.16 mg kg(-1), respectively. A positive correlation between the hair and urinary-arsenic concentration (R-2 = 0.601) was found. There was no significant difference between females and males for both urinary and hair-arsenic concentrations. Females were found to have a higher dimethylarsinic acid but lower percentages of inorganic arsenic and monomethylarsonic acid in their urine than males. (C) 2002 Elsevier Science Ireland Ltd. All rights reserved.

Evidence for sympatric speciation by host shift in the sea

The genetic divergence and evolution of new species within the geographic range of a single population (sympatric speciation) contrasts with the well-established doctrine that speciation occurs when populations become geographically isolated (allopatric speciation). Although there is considerable theoretical support for sympatric speciation [1, 2], this mode of diversification remains controversial, at least in part because there are few well-supported examples [3]. We use a combination of molecular, ecological, and biogeographical data to build a case for sympatric speciation by host shift in a new species of coral-dwelling fish (genus Gobiodon). We propose that competition for preferred coral habitats drives host shifts in Gobiodon and that the high diversity of corals provides the source of novel, unoccupied habitats. Disruptive selection in conjunction with strong host fidelity could promote rapid reproductive isolation and ultimately lead to species divergence. Our hypothesis is analogous to sympatric speciation by host shift in phytophagous insects [4, 5] except that we propose a primary role for intraspecific competition in the process of speciation. The fundamental similarity between these fishes and insects is a specialized and intimate relationship with their hosts that makes them ideal candidates for speciation by host shift.

Speciation of Antechinus stuartii and A. subtropicus (Marsupialia : Dasyuridae) in eastern Australia: molecular and morphological evidence

This paper evaluates the systematic status of the Antechinus populations of northern New South Wales and southern Queensland, using a combined morphological and molecular (allozymes and mitochondrial DNA) approach. Analysis of the d-loop section of the mitochondrial DNA control region revealed two highly supported clades within A. stuartii sensu lato that were sympatric in the Border Ranges of northern New South Wales. However, genetic distances between these clades were small ( approximately 3%), indicating that time of divergence was probably relatively recent. Allozyme electrophoresis also showed very small differences between clades/ species. Analyses of cranial and dental characters showed that the members of each of these clades differed morphologically and that the clades corresponded to A. stuartii and the recently described A. subtropicus. The combined results support the species status of A. stuartii and A. subtropicus, and suggest that speciation was likely a result of a recent vicariant event.

Cryptic false spider mites: a new genus, Austrolinus, and a review of the family Linotetranidae (Acari : Prostigmata : Tetranychoidea)

The Linotetranidae (Acari: Tetranychoidea) is a poorly known group of cryptic false spider mites associated with grasses and sedges. We review the family at the world level, provide the first phylogenetic analysis of the family, and describe the first Australian representatives: Austrolinus, gen. nov. and two new species: A. arenulus and A. kinnearae. Linotetranidae is redefined, and keys are provided for the families of the Tetranychoidea, and for all described genera and species of Linotetranidae.

Urinary arsenic speciation and porphyrins in C57B1/6J mice chronically exposed to low doses of sodium arsenate

Arsenic has been classified as a human carcinogen based on epidemiological data however the mechanism of its carcinogenicity is still unclear. Urinary biomarkers for chronic arsenic exposure would be valuable as an early warning indicator for timely interventions. In this study, young female C57BI/6J mice were given drinking water containing 0, 100, 250 and 500 mug As-v/L as sodium arsenate ad libitum for 12 months. Urine was collected bimonthly for urinary arsenic methylation assay and porphyrin analysis. All detectable arsenic species showed strong linear correlation with administered dosage and the arsenic methylation patterns were similar in all three treatment groups. No significant changes of methylation patterns were observed over time for either the control or test groups. Urinary coproporphyrin III was significantly increased in the 8th month in 250 and 500 mug/L groups and remained significantly dose-related after 10 and 12 months. Coproporphyrin I also showed a significant dose-response relationship after 12 months. Our results confirm that urinary arsenic is a useful biomarker for internal dose. The alteration of porphyrin profile suggests that arsenic can affect the heme metabolism and this may occur prior to the onset of arsenic induced carcinogenesis. (C) 2004 Elsevier Ireland Ltd. All rights reserved.

Ecological speciation

Ecological processes are central to the formation of new species when barriers to gene flow (reproductive isolation) evolve between populations as a result of ecologically-based divergent selection. Although laboratory and field studies provide evidence that 'ecological speciation' can occur, our understanding of the details of the process is incomplete. Here we review ecological speciation by considering its constituent components: an ecological source of divergent selection, a form of reproductive isolation, and a genetic mechanism linking the two. Sources of divergent selection include differences in environment or niche, certain forms of sexual selection, and the ecological interaction of populations. We explore the evidence for the contribution of each to ecological speciation. Forms of reproductive isolation are diverse and we discuss the likelihood that each may be involved in ecological speciation. Divergent selection on genes affecting ecological traits can be transmitted directly (via pleiotropy) or indirectly (via linkage disequilibrium) to genes causing reproductive isolation and we explore the consequences of both. Along with these components, we also discuss the geography and the genetic basis of ecological speciation. Throughout, we provide examples from nature, critically evaluate their quality, and highlight areas where more work is required.

Reinforcement drives rapid allopatric speciation

Allopatric speciation results from geographic isolation between populations. In the absence of gene flow, reproductive isolation arises gradually and incidentally as a result of mutation, genetic drift and the indirect effects of natural selection driving local adaptation(1-3). In contrast, speciation by reinforcement is driven directly by natural selection against maladaptive hybridization(1,4). This gives individuals that choose the traits of their own lineage greater fitness, potentially leading to rapid speciation between the lineages(1,4). Reinforcing natural selection on a population of one of the lineages in a mosaic contact zone could also result in divergence of the population from the allopatric range of its own lineage outside the zone(4-6). Here we test this with molecular data, experimental crosses, field measurements and mate choice experiments in a mosaic contact zone between two lineages of a rainforest frog. We show that reinforcing natural selection has resulted in significant premating isolation of a population in the contact zone not only from the other lineage but also, incidentally, from the closely related main range of its own lineage. Thus we show the potential for reinforcement to drive rapid allopatric speciation.