Basis Of Reproductive Isolation Research Articles

Delineating yeast species with genome average nucleotide identity: a calibration of ANI with haplontic, heterothallic Metschnikowia species.

We determined pairwise average nucleotide identity (ANI) values for the genomes of 71 strains assigned to 36 Metschnikowia species, 28 of which were represented by multiple isolates selected to represent the range of genetic diversity of the species, and most of which were defined on the basis of reproductive isolation. Similar to what has been proposed for prokaryote species delineation, an ANI value of 95% emerged as a good guideline for the delineation of yeast species, although some overlap exists, whereby members of a reproductive community could have slightly lower values (e.g., 94.3% for M. kamakouana), and representatives of distinct sister species could give slightly higher values (e.g., 95.2% for the sister species M. drakensbergensis and M. proteae). Unlike what is observed in prokaryotes, a sizeable gap between intraspecific and interspecific ANI values was not encountered. Given the ease with which yeast draft genomes can now be obtained, ANI values are poised to become the new standard upon which yeast species may be delineated on genetic distance. As borderline cases exist, however, the delineation of yeast species will continue to require careful evaluation of all available data. We also explore the often-neglected distinction between phylogenetic relatedness and sequence identity through the analysis of a tree constructed from ANI' (100 - ANI) values.

Captive Hybridization of the Giant ClamsTridacna maxima(Röding, 1798) andTridacna noae(Röding, 1798)

The giant clam Tridacna noae is a recently resurrected taxon distinguished from Tridacna maxima on the basis of reproductive isolation, mitochondrial DNA differences, and mantle morphology and ornamentation; however, the morphological characteristics used to distinguish the two species are not consistent with genetic assignment throughout their zone of overlap. This has led to the suggestion that hybridization occurs and constituted a need to reexamine the reproductive isolation of T. noae and T. maxima. This study provides evidence that sympatric populations of T. maxima and T. noae in the center of their range overlap and can hybridize and produce juveniles. Breeding trials using T. maxima and T. noae for both maternal and paternal hybrid crosses were conducted to compare larval and early juvenile development. The fertilization success and survival of both hybrid crosses suggest potential for T. maxima and T. noae hybrids to exist in nature. On this basis, the previously reported reproductive isolation between T. maxima and T. noae may not be apposite across their zone of overlap. Future genetic, population demographic, and ecological studies should consider the possibility of hybridization between T. maxima and T. noae.

Viral taxonomy: The effect of metagenomics on understanding the diversity and evolution of viruses.

Taxonomy is the attempt to bring some semblance of order to the stunning diversity of life. As a human endeavour, attempts to create a logical and complete classification of all that lives under the sun are not always perfect and have generated much controversy on where and how to put individual species or even whole branches of the tree of life into a greater scheme. This is particularly difficult when it comes to viruses, which are even more challenging to sort and order according to a logical scheme. Not only are viruses technically not cells at all, lacking all the protein machinery, but they can also not be categorized as species on the basis of reproductive isolation since they depend on their host for replication. Moreover, viruses constantly swap genetic material both with their hosts and with each other, which makes it even more challenging to establish evolutionary relationships via phylogenetic trees, as for prokaryotes. > Viral taxonomy has thus become an important source of insight into viral/host co‐evolution and even the origin of life itself However, viral taxonomy is not just a particularly challenging but also rewarding and valuable enterprise because it can contribute to understanding how the first primitive cells evolved, how the eukaryotes emerged and the general role of viruses in evolution, which have been shuttling genetic material between their hosts. Viral taxonomy has thus become an important source of insight into viral/host co‐evolution and even the origin of life itself. It is also of course helping to answer how and when viruses themselves emerged, which is almost one of those chicken and egg questions over which came first: viruses or their host cells. ### A matter of definition The field of virus taxonomy is fairly young and already entering a second phase almost exactly 50 years after the International Committee on Taxonomy …

Pre- and post-mating reproductive barriers drive divergence of five sympatric species of Naryciinae moths (Lepidoptera: Psychidae)

The biological species concept suggests that species can be separated on the basis of reproductive isolation. However, because natural interbreeding capabilities are often unknown, differences in morphology are generally used to separate species. Alternatively, genetic dissimilarity is used to separate morphologically similar species. Many genetic markers, including the maternally inherited mitochondrial cytochrome oxidase I sequence, cannot show interbreeding and therefore species status of groups may remain unresolved. In species of the genera Dahlica and Siederia (Lepidoptera: Psychidae: Naryciinae) the lack of morphological distinction and unknown interbreeding has led to unclear and unresolved taxonomic status. Mitochondrial DNA sequences suggest five sexual species to occur in Finland. However, their species status remains unconfirmed, due to a lack of knowledge on interbreeding, unclear morphological distinction and the limited variation in mitochondrial DNA. We combine three methods, a cross-mating experiment, an analysis of mitochondrial and nuclear DNA, and a detailed male genital morphological examination, to establish the species status of the five suspected species. All suspected species exhibit intraspecies mating preference, although several interspecies pairs readily produce offspring. The genetic analysis, however, fails to show hybrids or introgression, suggesting that both pre- and post-copulation mechanisms isolate the species reproductively. Morphological analysis of the male genitalia confirms that the species have diverged. Our results highlight the need of combining behavioural, morphological and genetic methods to determine species status in challenging taxonomic groups. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 112, 584–605.

An assessment of transgenomics as a tool for identifying genes involved in the evolutionary differentiation of closely related plant species

• Transgenomics is the process of introducing genomic clones from a donor species into a recipient species and then screening the resultant transgenic lines for phenotypes of interest. This method might allow us to find genes involved in the evolution of phenotypic differences between species as well as genes that have the potential to contribute to reproductive isolation: potential speciation genes. • More than 1100 20-kbp genomic clones from Leavenworthia alabamica were moved into Arabidopsis thaliana by transformation. After screening a single primary transformant for each line, clones associated with mutant phenotypes were tested for repeatability and co-segregation. • We found 84 clones with possible phenotypic effects, of which eight were repeatedly associated with the same phenotype. One clone, 11_11B, co-segregated with a short fruit phenotype. Further study showed that 11_11B affects seed development, with as much as one-third of the seeds aborted in some fruit. • Transgenomics is a viable strategy for discovering genes of evolutionary interest. We identify methods to reduce false positives and false negatives in the future. 11_11B can be viewed as a potential speciation gene, illustrating the value of transgenomics for studying the molecular basis of reproductive isolation.

Complex Deleterious Interactions Associated with Malic Enzyme May Contribute to Reproductive Isolation in the Copepod Tigriopus californicus

Dobzhansky-Muller incompatibilities can result from the interactions of more than a single pair of interacting genes and there are several different models of how such complex interactions can be structured. Previous empirical work has identified complex conspecific epistasis as a form of complex interaction that has contributed to postzygotic reproductive isolation between taxa, but other forms of complexity are also possible. Here, I probe the genetic basis of reproductive isolation in crosses of the intertidal copepod Tigriopus californicus by looking at the impact of markers in genes encoding metabolic enzymes in F2 hybrids. The region of the genome associated with the locus ME2 is shown to have strong, repeatable impacts on the fitness of hybrids in crosses and epistatic interactions with another chromosomal region marked by the GOT2 locus in one set of crosses. In a cross between one of these populations and a third population, these two regions do not appear to interact despite the continuation of a large effect of the ME2 region itself in both crosses. The combined results suggest that the ME2 chromosomal region is involved in incompatibilities with several unique partners. If these deleterious interactions all stem from the same factor in this region, that would suggest a different form of complexity from complex conspecific epistasis, namely, multiple independent deleterious interactions stemming from the same factor. Confirmation of this idea will require more fine-scale mapping of the interactions of the ME2 region of the genome.

Variability in Pheromone Communication Among Different Haplotype Populations of Busseola fusca

The relationship between pheromone composition and mitochondrial haplotype clades was investigated by coupling DNA analyses with pheromone identification and male mate searching behavior among different geographic populations of Busseola fusca. The within-population variations in pheromone blend were as great as those observed between geographic populations, suggesting that the female sex pheromone blend was not the basis of reproductive isolation between the geographic clades. Furthermore, while data from wind tunnel experiments demonstrated that most of the tested males were sensitive to small variations in pheromone mixture, there was considerable within-population variability in the observed response. The study identified a new pheromone component, (Z)-11-hexadecen-1-yl acetate, which when added to the currently used three-component synthetic blend resulted in significantly higher traps catches. The new recommended blend for monitoring flight phenology and for timing control measures for optimal efficacy of B. fusca is (Z)-11-tetradecen-1-yl acetate (62%), (E)-11-tetradecen-1-yl acetate (15%), (Z)-9-tetradecen-1-yl acetate (13%), and (Z)-11-hexadecen-1-yl acetate (10%).

Unprecedented chromosomal diversity and behaviour modify linkage patterns and speciation potential: structural heterozygosity in an Australian spider

The Huntsman spider Delena cancerides shows an extraordinary level of chromosomal diversity and meiotic complexity. Some populations form normal bivalents at male meiosis, but 14 populations form chains of chromosomes. Six of these populations form two chains, and so show segregation behaviour which is beyond our current understanding of meiotic processes. Chromosomal variation of this sort is rarely tolerated in other species, because the segregation of long chromosome chains frequently results in gametes with too many or too few chromosomes. The resulting reproductive failure may form the basis for reproductive isolation in many species, and so the mechanisms that allow D. cancerides to segregate long chromosome chains have allowed this species to maintain cohesion despite extensive chromosomal variation over its range. The effect these chromosome chains have on the population genetics of the species is discussed, and a model for the evolution of the system is proposed.

Hidden evolution: progress and limitations in detecting multifarious natural selection.

From illustrative examples of research on the best-studied group of species to date, Drosophila melanogaster and its closest relatives, we argue that selection is multifarious, but often hidden. Selective fixation of new, highly advantageous alleles is the most parsimonious explanation for a typical pattern of molecular variation observed in genomic regions characterized by very low recombination: drastically reduced DNA sequence variation within species and typical levels of sequence divergence among species. At the same time, the identity of the gene (or genes) influenced by selection is not just difficult to discern; it may be impossible. Studies of the genetic basis of reproductive isolation demonstrate that, although the D. melanogaster complex species appear virtually identical, dozens of currently unidentified genes contribute to hybrid sterility. We argue that these findings are best explained by selectively-driven functional divergence and demonstrate the multifarious nature of selection. Although multifarious selection certainly occurs, the exact characters responsible for differences in survival and reproductive success are unknown. We do not see these inherent limits as a cause for despair or a problem for evolutionary biology. Instead, we hope to raise awareness of these complexities of evolution by highlighting both the progress and the limitations of characterizing multifarious natural selection.

The genic view of the process of speciation

Abstract The unit of adaptation is usually thought to be a gene or set of interacting genes, rather than the whole genome, and this may be true of species differentiation. Defining species on the basis of reproductive isolation (RI), on the other hand, is a concept best applied to the entire genome. The biological species concept (BSC; Mayr, 1963) stresses the isolation aspect of speciation on the basis of two fundamental genetic assumptions – the number of loci underlying species differentiation is large and the whole genome behaves as a cohesive, or coadapted genetic unit. Under these tenets, the exchange of any part of the genomes between diverging groups is thought to destroy their integrity. Hence, the maintenance of each species’ genome cohesiveness by isolating mechanisms has become the central concept of species. In contrast, the Darwinian view of speciation is about differential adaptation to different natural or sexual environments. RI is viewed as an important by product of differential adaptation and complete RI across the whole genome need not be considered as the most central criterion of speciation. The emphasis on natural and sexual selection thus makes the Darwinian view compatible with the modern genic concept of evolution. Genetic and molecular analyses of speciation in the last decade have yielded surprisingly strong support for the neo-Darwinian view of extensive genetic differentiation and epistasis during speciation. However, the extent falls short of what BSC requires in order to achieve whole-genome ‘cohesiveness’. Empirical observations suggest that the gene is the unit of species differentiation. Significantly, the genetic architecture underlying RI, the patterns of species hybridization and the molecular signature of speciation genes all appear to support the view that RI is one of the manifestations of differential adaptation, as Darwin (1859, Chap. 8) suggested. The nature of this adaptation may be as much the result of sexual selection as natural selection. In the light of studies since its early days, BSC may now need a major revision by shifting the emphasis from isolation at the level of whole genome to differential adaptation at the genic level. With this revision, BSC would in fact be close to Darwin’s original concept of speciation.

Reproductive isolation in Drosophila: how close are we to untangling the genetics of speciation?

Our understanding of the genetic basis of reproductive isolation in Drosophila has progressed rapidly over the past decade. Details of the genetic structure of hybrid sterility have been revealed and a general consensus has been reached concerning the genetic bases of Haldane's rule. Genetic analyses now reach beyond hybrid sterility and inviability, allowing us to make important comparisons across different traits involved in reproductive isolation. Expansion of genetic studies to include rescue of hybrid incompatibilities has opened the door for more detailed molecular and developmental analyses of reproductive isolation than has ever before been possible.

Interchange chromosomes in Simulium nigricoxum Stone Diptera: Simuliidae

A whole-arm interchange (IS-IIIL/IL-IIIS) is described from a larval population of Simulium nigricoxum Stone in the Yukon Territory. Although unstudied elsewhere, S. nigricoxum appears to differ from its closest presumed relative, Simulium malyschevi, by the whole-arm interchange, a fixed autosomal inversion in the short arm of the second chromosome, and a sex-linked inversion also in the short arm of the second chromosome. It is possible that the interchange provided a chromosomal basis for reproductive isolation of S. nigricoxum from an ancestral form, but because of its apparent localized distribution that hypothesis must remain tentative.Key words: Simulium nigricoxum, Simulium malyschevi, chromosome interchanges, inversions, reproductive isolation.

The Relevance of Ecology to Species Concepts in Bryophytes

Relationships between the ecological niche and species concepts are discussed by developing concepts of the niche and of character and species hypervolumes. Ecological data are best used to evaluate the biological/evolutionary significance of species defined by other criteria. Differences in patterns of ecological variation are as important for delineating species as are differences in the average or typical habitat. Data on both realized and fundamental niches offer useful information. A classification of nine gemmiferous Pohlia species summarizes more ecological than morphological information, although the classification was based on morphology. Combining P. annotina and P. camptotrachela results in a loss of ecological information. Proponents of the biological species concept suggest that species be defined on the basis of reproductive isolation. Although the significance of reproductive barriers to the process of speciation has been questioned, genetic concepts of species are important, especially for investigating evolutionary processes at the population level. Unfortunately, the genetics and reproductive biology of most groups of plants are poorly known. While practicing taxonomists generally agree that species are genetic phenomena, a distinction is usually made between what species are in an evolutionary sense, and how species are delineated in practice. Thus we make systematic judgments on the basis of similarities and differences between organisms. It is axiomatic that all observable characteristics of organisms are to be used in constructing classifications. Morphological characters are traditionally emphasized, but other potentially useful characters come from fields such as cytology, physiology, and chemistry. Ecological data provide additional characters that can often be used in delineating species. Almost all papers that have discussed the relevance of ecology to taxonomy deal with ecological topics in the context of their evolutionary importance in maintaining genetic variation in populations or for promoting reproductive isolation between populations. I will not stress the obvious importance of habitat characteristics as determinants of population genetic structure but will rather focus on the practical aspects of species delineation. RELEVANCE OF THE NICHE CONCEPT TO

A new species of Prosimulium (Diptera: Simuliidae): an interchange as a primary reproductive isolating mechanism?

A previously undescribed species of the IIIL-1 group of Prosimulium differs from Prosimulium mixtum, its nearest relative, principally by a whole-arm interchange. It shares the sex chromosomes of P. mixtum, as well as an X chromosome and autosomal polymorphism. It is apparently a very local species (Centre County, Pennsylvania) that differs from P. mixtum in larval habitat preference and other aspects of its biology. It is argued that the interchange provided a chromosomal basis for reproductive isolation between P. mixtum and the new species, which progressively diverged in biology and mating system.

A Possible Role for Generally Adaptive Features in Mate Selection and Sexual Stimulation

Any trait that is advantageous in the normal business of living will make its possessor a more advantageous mate, thus providing selection pressure favoring the trait of preferring to mate with an individual having such traits. In many cases such a feature will have contributed to radiation into a new niche. It will also distinguish a newly evolved species from its ancestral species, providing a basis for reproductive isolation. Consequently recently evolved generally adaptive features are likely to be sexually stimulating or attended to in mate selection. Therefore, there is a good possibility that there are some biologically based mating preferences and sexual responses in humans that are expressed in most cultures.

Cytogenetic components of reproductive isolation in Trimerotropis thalassica and T. occidentalis.

The grasshopper Trimerotropis thalassica (Bruner) has a diploid count of 2n=23 male (XO), 24 female (XX). The two largest autosomes pairs are regularly metacentric, a consequence of fixed pericentric inversions. The X-chromosome is also a fixed metacentric. The remaining nine pairs of autosmes are polymorphic for floating percentric inversions so that the complement consists of a mixture of telocentric and metacentric members. Trimerotropis occidentalis (Bruner) is polymorphic for comparable inversions in only two of its autosome pairs and has a telocentric X. It is however, unique among the species of the genus Trimerotropis in having only 21 chromosomes in its male diploid set in all the populations so far studied. A single male found in a mixed population of these two species at Jasper Ridge, Stanford University, was characterized by the count 2n=22 male. In both this respect of and in its phenotype it was intermediate in character, representing a natural F1 hybrid between the two species. Cytogenetic analysis of this hybrid male indicated that occidentalis is differentiated from thalassica only is respect of a single tandem translocation. This has involved two of the telocentric elements of thalassica which have fused into a single composite telocentric partly homologous with each of the smaller progenitors. Although potentially capable of forming a multiple of three, one or other of the progenitor chromosomes regularly fails to pair with the tandem product in the hybrid so that one or more univalents invariably occur. These, by lagging, prevent cytokinesis and subsequently lead to the formation of macrospermatids which inevitably produce a measure of sterility. It is argued that this sterility provides a basis of reproductive isolation.

The Genus Riella in North and South America: Distribution, Culture, and Reproductive Isolation

Plants meeting the general description of Riella americana occur in the states of Texas, New Mexico, California, Chihuahua, and Durango, as well as the republic of Argentina. Evidence suggests that the species is more widespread than earlier reported. Experimental crosses between various isolates indicate that all dioecious members of the genus in the Western Hemisphere are part of a single complex. However, in many instances cross-fertilizaation between populations leads not to viable spores but only to initial sporophyte development, followed by disintegration of the contents of the developing capsule. Judged from the basis of reproductive isolation at least three distinct groups exist within the Western Hemisphere. Two of these differ further with respect to habitat and external morphology. Members of the genus Riella have long been considered distinctly uncommon, if not rare; yet as Persson and Imam (1960) suggested, this impression probably stems in large part from the unusual habitat in which the plants are found. Few bryologists appear to spend any appreciable time searching the bottom of muddy desert pools, and, unfortunately, most phycologists are unfamiliar with the genus. I have found Riella to be fairly common throughout western Texas, New Mexico, Chihuahua, and Durango. The same probably holds true in many other arid to semiarid regions of the world as well. The present account summarizes previous information on the distribution of the genus in North and South America, briefly describes means by which new populations have been encountered, and explores the extent of interfertility between spatially isolated populations.

Courtship Behavior and Reproductive Isolation in the Species of Taricha (Amphibia, Caudata)

The basic pattern of courtship is similar in all species of Taricha. The male embraces the female just posterior to her shoulder region with his forelimbs, hooks his chin over her nose, and rubs it with lateral head movements while pressing his cloaca against her dorsum. After about an hour, the male advances obliquely over the left or right shoulder of the female and deposits a spermatophore a few centimeters away from her head. He then orients at a right angle to the axis of her body and makes lateral hip movements; she responds by moving down his side until her cloaca is in position to pick up the spermatophore. The male frequently mounts again for a second period of amplexus. The minor differences detected between the courtship behavior of the species of Taricha do not seem great enough to serve as the basis of reproductive isolation between sympatric forms, and the results of preliminary mating tests under controlled conditions suggest that female sex attractants may be involved in species recognition and the elicitation of a species-specific courtship.