Origin Of Reproductive Isolation Research Articles

Homoploid hybrid speciation and genome evolution via chromosome sorting.

Genomes of numerous diploid plant and animal species possess traces of interspecific crosses, and many researches consider them as support for homoploid hybrid speciation (HHS), a process by which a new reproductively isolated species arises through hybridization and combination of parts of the parental genomes, but without an increase in ploidy. However, convincing evidence for a creative role of hybridization in the origin of reproductive isolation between hybrid and parental forms is extremely limited. Here, through studying Agrodiaetus butterflies, we provide proof of a previously unknown mode of HHS based on the formation of post-zygotic reproductive isolation via hybridization of chromosomally divergent parental species and subsequent fixation of a novel combination of chromosome fusions/fissions in hybrid descendants. We show that meiotic segregation, operating in the hybrid lineage, resulted in the formation of a new diploid genome, drastically rearranged in terms of chromosome number. We also demonstrate that during the heterozygous stage of the hybrid species formation, recombination was limited between rearranged chromosomes of different parental origin, representing evidence that the reproductive isolation was a direct consequence of hybridization.

Ecological speciation along an elevational gradient in a tropical passerine bird?

Local adaptation of populations along elevational gradients is well known, but conclusive evidence that such divergence has resulted in the origin of distinct species in parapatry remains lacking. We integrated morphological, vocal, genetic and behavioural data to test predictions pertaining to the hypothesis of parapatric ecological speciation associated with elevation in populations of a tropical montane songbird, the Grey-breasted Wood-wren (Henicorhina leucophrys: Troglodytidae), from the Sierra Nevada de Santa Marta, Colombia. We confirmed that two distinct populations exist along the elevational gradient. Phylogenetic analyses tentatively indicate that the two populations are not sister taxa, suggesting they did not differentiate from a single ancestor along the gradient, but rather resulted from separate colonization events. The populations showed marked divergence in morphometrics, vocalizations and genetic variation in mitochondrial and nuclear loci, and little to no evidence of hybridization. Individuals of both populations responded more strongly to their own local songs than to songs from another elevation. Although the two forms do not appear to have differentiated locally in parapatry, morphological and vocal divergence along the elevational gradient is consistent with adaptation, suggesting a possible link between adaptive evolution in morphology and songs and the origin of reproductive isolation via a behavioural barrier to gene flow. The adaptive value of phenotypic differences between populations requires additional study.

The chemical‐speciation hypothesis in Liolaemus: a response to Pincheira‐Donoso

The chemical‐speciation hypothesis in <i><scp>L</scp>iolaemus</i>: a response to <scp>P</scp>incheira‐<scp>D</scp>onoso

Developmental plasticity and the origin of species differences.

Speciation is the origin of reproductive isolation and divergence between populations, according to the "biological species concept" of Mayr. Studies of reproductive isolation have dominated research on speciation, leaving the origin of species differences relatively poorly understood. Here, I argue that the origin of species differences, and of novel phenotypes in general, involves the reorganization of ancestral phenotypes (developmental recombination) followed by the genetic accommodation of change. Because selection acts on phenotypes, not directly on genotypes or genes, novel traits can originate by environmental induction as well as mutation, then undergo selection and genetic accommodation fueled by standing genetic variation or by subsequent mutation and genetic recombination. Insofar as phenotypic novelties arise from adaptive developmental plasticity, they are not "random" variants, because their initial form reflects adaptive responses with an evolutionary history, even though they are initiated by mutations or novel environmental factors that are random with respect to (future) adaptation. Change in trait frequency involves genetic accommodation of the threshold or liability for expression of a novel trait, a process that follows rather than directs phenotypic change. Contrary to common belief, environmentally initiated novelties may have greater evolutionary potential than mutationally induced ones. Thus, genes are probably more often followers than leaders in evolutionary change. Species differences can originate before reproductive isolation and contribute to the process of speciation itself. Therefore, the genetics of speciation can profit from studies of changes in gene expression as well as changes in gene frequency and genetic isolation.

The evolutionary genetics of speciation.

The last decade has brought renewed interest in the genetics of speciation, yielding a number of new models and empirical results. Defining speciation as 'the origin of reproductive isolation between two taxa', we review recent theoretical studies and relevant data, emphasizing the regular patterns seen among genetic analyses. Finally, we point out some important and tractable questions about speciation that have been neglected.

Levels of the genealogical hierarchy and the problem of hominoid phylogeny.

Molecular data are widely used to reconstruct phylogenetic relationships among species, and these phylogenies are often used as the basis for inferences about the history of evolutionary change in other nonmolecular characters. This approach is an appropriate and powerful one in many circumstances. But when several lineages diverge over a relatively short period of time, the assumption that a molecular (gene) tree will always be a valid basis for such inferences may not hold. Empirical evidence from humans, nonhuman primates, and other mammals indicates that the relationships among molecular divergence, morphological differentiation, and the origin of reproductive isolation between diverging lineages are complex. The simple dichotomously branching trees that result from molecular systematic studies of Homo, Gorilla, and Pan may be a misleading basis for reconstructions of evolutionary change in nonmolecular characters.

Variation in the Eucalyptus gunnii-archeri Complex. I. Variation in the Adult Phenotype

A study of variation in the E. gunnii-archeri complex indicates continuous variation between the taxa E. gunnii Hook.f. and E. archeri Maiden &amp; Blakely. Populations assigned to either taxon are normally allopatric but intergrade in an area of parapatry in central Tasmania. The E. gunnii-archeri complex is shown to comprise a multidimensional, clinally varying series of highly differentiated populations. In part, population differentiation appears to result from the interaction of multicharacter clines which parallel several major habitat gradients. This variation is summarized by classification of populations into five main phenetic groups. Whilst considerable differentiation occurs between disjunct stands, a large portion of the variation in the complex occurs in the more or less continuous central stands. In this area, major independent clines are associated with increasing exposure to the alpine environment and the north-south transition between subspp. gunnii and archeri. A peak in variability in geographically intermediate populations is apparent along the latter, but not the former, cline. In addition, it is shown that parallel clines in flowering time have the potential to retard gene flow along these clines. It is suggested that parallel clines which incidentally influence gene flow may be of considerable significance in parapatric differentiation and the origin of reproductive isolation.

A computer model of speciation by founder effects

SummaryA computer model of a two-locus genetic system with epistatic selection was used to investigate factors influencing the probability of the origin of reproductive isolation, due to a genetic revolution following a founder event (Mayr, 1954; Carson, 1975). Restricted population size can sometimes cause such a system to drift from one equilibrium to another, which can result in loss of fitness to hybrids with the ancestral population. The chance of such an event was found to be low unless the bottleneck in population size associated with the founder event was preceded by many generations of relaxed selection. It is highest when the bottleneck is not prolonged and when the population size during the bottleneck is not too small. It seems to be difficult to achieve a high degree of reproductive isolation in one step by this method, and it is concluded that it is unlikely to be a major cause of rapid speciation, although it could be a contributory factor.

Immunobiological studies of the jelly-coats of anuran eggs.

A review of some recent experiments in the imrhunobiology of fertilization in frogs is given, with especial emphasis on the role of the jelly-coats of eggs in the initiation of sperm-egg interactions. Data on physical/chemical and antigenic properties of egg-jellies are summarized. Experiments analyzing'the nature of the interaction between sperm and egg-jellies are described. The effects of antibodies against materials of the jelly coat on fertilizability of eggs are presented, as well as an analysis on double-diffusion plates of tissue- and species-specificity of the jelly components. The localization of regional differences between the secretions of different levels of the frog oviduct by means of immunodiffusion patterns, fluorescent-antibody staining and certain histochernical reactions for mucopolysaccharides, is reviewed. A model scheme suggesting the possible operation of various types of jelly antigens in the fertilization process is presented as a working hypothesis for further experimentation. Certain surgical manipulations whereby eggs may be transferred between females of the same or different species are described, and the results of some preliminary experiments made possible by these techniques are evaluated. The role of species-specific and shared jelly antigens in the origin of reproductive isolation among anuran amphibians is discussed.