Initial Divergence (initial + divergence)

Distribution by Scientific Domains

Selected Abstracts


EVOLUTION, Issue 5 2010
Sarah R. Pryke
Assortative mating is a key aspect in the speciation process because it is important for both initial divergence and maintenance of distinct species. However, it remains a challenge to explain how assortative mating evolves when diverging populations are undergoing gene flow (e.g., during hybridization). Here I experimentally test how assortative mating is maintained with frequent gene flow between diverged head-color morphs of the Gouldian finch (Erythrura gouldiae). Contrary to the predominant view on the development of sexual preferences in birds, cross-fostered offspring did not imprint on the phenotype of their conspecific (red or black morphs) or heterospecific (Bengalese finch) foster parents. Instead, the mating preferences of F1 and F2 intermorph-hybrids are consistent with inheritance on the Z chromosomes, which are also the location for genes controlling color expression and the genes causing low fitness of intermorph-hybrids. Genetic associations between color signal and preference loci on the sex chromosomes may prevent recombination from breaking down these associations when the morphs interbreed, helping to maintain assortative mating in the face of gene flow. Although sex linkage of reproductively isolating traits is theoretically expected to promote speciation, social and ecological constraints may enforce frequent interbreeding between the morphs, thus preventing complete reproductive isolation. [source]


EVOLUTION, Issue 7 2003
Lukas Rüber
Abstract., The American seven-spined gobies (Gobiidae, Gobiosomatini) are highly diverse both in morphology and ecology with many endemics in the Caribbean region. We have reconstructed a molecular phylogeny of 54 Gobio-somatini taxa (65 individuals) based on a 1646-bp region that includes the mitochondrial 12S rRNA, tRNA-Val, and 16S rRNA genes. Our results support the monophyly of the seven-spined gobies and are in agreement with the existence of two major groups within the tribe, the Gobiosoma group and the Microgobius group. However, they reject the monophyly of some of the Gobiosomatini genera. We use the molecular phylogeny to study the dynamics of speciation in the Gobiosomatini by testing for departures from the constant speciation rate model. We observe a burst of speciation in the early evolutionary history of the group and a subsequent slowdown. Our results show a split among clades into coastal-estuarian, deep ocean, and tropical reef habitats. Major habitat shifts account for the early significant acceleration in lineage splitting and speciation rate and the initial divergence of the main Gobiosomatini clades. We found that subsequent diversification is triggered by behavior and niche specializations at least in the reef-associated clades. Overall, our results confirm that the diversity of Gobiosomatini has arisen during episodes of adaptive radiation, and emphasize the importance of ecology in marine speciation. [source]

Phylogeographic structuring and volant mammals: the case of the pallid bat (Antrozous pallidus)

Sarah E. Weyandt
Abstract Aim, To examine the phylogeographic pattern of a volant mammal at the continental scale. The pallid bat (Antrozous pallidus) was chosen because it ranges across a zone of well-studied biotic assemblages, namely the warm deserts of North America. Location, The western half of North America, with sites in Mexico, the United States, and Canada. Methods, PCR amplification and sequencing of the mitochondrial control region was performed on 194 pallid bats from 36 localities. Additional sequences at the cytochrome- b locus were generated for representatives of each control-region haplotype. modeltest was used to determine the best set of parameters to describe each data set, which were incorporated into analyses using paup*. Statistical parsimony and measurements of population differentiation (amova, FST) were also used to examine patterns of genetic diversity in pallid bats. Results, We detected three major lineages in the mitochondrial DNA of pallid bats collected across the species range. These three major clades have completely non-overlapping geographic ranges. Only 6 of 80 control-region haplotypes were found at more than a single locality, and sequences at the more conserved cytochrome- b locus revealed 37 haplotypes. Statistical parsimony generated three unlinked networks that correspond exactly to clades defined by the distance-based analysis. On average there was c. 2% divergence for the combined mitochondrial sequences within each of the three major clades and c. 7% divergence between each pair of clades. Molecular clocks date divergence between the major clades at more than one million years, on average, using the faster rates, and at more than three million years using more conservative rates of evolution. Main conclusions, Divergent haplotypic lineages with allopatric distributions suggest that the pallid bat has responded to evolutionary pressures in a manner consistent with other taxa of the American southwest. These results extend the conclusions of earlier studies that found the genetic structuring of populations of some bat species to show that a widespread volant species may comprise a set of geographically replacing monophyletic lineages. Haplotypes were usually restricted to single localities, and the clade showing geographic affinities to the Sonoran Desert contained greater diversity than did clades to the east and west. While faster molecular clocks would allow for glacial cycles of the Pleistocene as plausible agents of diversification of pallid bats, evidence from co-distributed taxa suggests support for older events being responsible for the initial divergence among clades. [source]

Body shape vs. colour associated initial divergence in the Telmatherina radiation in Lake Matano, Sulawesi, Indonesia

Abstract Highly polymorphic colouration patterns are often associated with sexual selection in fish and can be the initial cause of divergence among closely related taxa. Here we use genetic, body colour and geometric morphometric data collected on 118 fish from Lake Matano, Sulawesi, Indonesia to test if colouration is the initial cause of divergence in the radiating Telmatherina genus. Results reveal that all Telmatherina previously described in this system can be categorized into three mitochondrial lineages and that colouration is only weakly associated with early divergence. Clade-specific body shapes, however, likely adapted to microenvironments are key to the initial divergence in this system. Data also show that although colourations were not likely instrumental in seeding divergence in these fish, they appear to have developed in parallel within each clade. Our results are consistent with an emerging pattern repeated in many vertebrate radiations, whereby divergence by colouration or other display traits is preceded by specialization to environmental adaptive peaks. [source]

Impact of ice ages on circumpolar molecular diversity: insights from an ecological key species

Abstract We address the impact of the ice age cycles on intraspecific cpDNA diversity, for the first time on the full circumboreal-circumarctic scale. The bird-dispersed bog bilberry (or arctic blueberry, Vaccinium uliginosum) is a key component of northern ecosystems and is here used to assess diversity in previously glaciated vs. unglaciated areas and the importance of Beringia as a refugium and source for interglacial expansion. Eighteen chloroplast DNA haplotypes were observed in and among 122 populations, grouping into three main lineages which probably diverged before, and thus were affected more or less independently by, all major glaciations. The boreal ,Amphi-Atlantic lineage' included one haplotype occurring throughout northern Europe and one occurring in eastern North America, suggesting expansion from at least two bottlenecked, glacial refugium populations. The boreal ,Beringian lineage' included seven haplotypes restricted to Beringia and the Pacific coast of USA. The ,Arctic-Alpine lineage' included nine haplotypes, one of them fully circumpolar. This lineage was unexpectedly diverse, also in previously glaciated areas, suggesting that it thrived on the vast tundras during the ice ages and recolonized deglaciated terrain over long distances. Its largest area of persistence during glaciations was probably situated in the north, stretching from Beringia and far into Eurasia, and it probably also survived the last glaciation in southern mountain ranges. Although Beringia apparently was important for the initial divergence and expansion of V. uliginosum as well as for continuous survival of both the Beringian and Arctic-Alpine lineages during all ice ages, this region played a minor role as a source for later interglacial expansions. [source]