The muscle scar in cavellinids and its importance for the phylogeny of platycope ostracodes

The adductor muscle scars of cavellinids from the Visean (in one case from the Upper Devonian) of the European part of the RSFSR have revealed a significant diversity in their morphology. Aggregate, multiserial with up to five series, bi- to triserial and nearly biserial muscle scars existed simultaneously. The verticaliserial muscle scars were initiated by a biserial larval group which in the course of evolution may have passed, due to neoteny, into the adult stage. Together with Cytherella sp. from Syria, the new data show that the genus Cytherella appeared not in Triassic nor Jurassic time, hut originated among cavellinids possibly in the Early Carboniferous. A new genus is Borovitchella , with the type species B. egorovi n. sp.     

Spatial structure leads to ecological breakdown and loss of diversity

Spatial structure has been identified as a major contributor to the maintenance of diversity. Here, we show that the impact of spatial structure on diversity is strongly affected by the ecological mechanisms maintaining diversity. In well-mixed, unstructured environments, microbial populations can diversify by production of metabolites during growth, providing additional resources for novel specialists. By contrast, spatially structured environments potentially limit such facilitation due to reduced metabolite diffusion. Using replicate microcosms containing the bacterium Escherichia coli, we predicted the loss of diversity during an environmental shift from a spatially unstructured environment to spatially structured conditions. Although spatial structure is frequently observed to be a major promoter of diversity, our results indicate that it can also have negative impacts on diversity.     

Systematics of the Dactylorhiza euxina/incarnata/maculata polyploid complex (Orchidaceae) in Turkey: evidence from allozyme data

 Material of Dactylorhiza were sampled from 49 localities in Turkey and investigated for allozyme variation at ten loci (nine enzyme systems). Among diploids, the Anatolian D. osmanica and D. umbrosa were allozymically variable, but not distinct from each other or from D. incarnata. Dactylorhiza saccifera contained the same alleles as the European D. fuchsii. Dactylorhiza iberica and D. euxina were distinct from each other and the other diploids. On basis of allozyme patterns three distinct allotetraploid genotypes were distinguished, and each of them could be treated as a separate species. Dactylorhiza nieschalkiorum is similar to European allotetraploids, and may have arisen from hybridization between D. incarnata s.l. and D. saccifera. Dactylorhiza urvilleana may have arisen from parents related to present-day D. saccifera and D. euxina, but it also contains additional alleles that have not been found in any of the diploids investigated. A third allotetraploid known from four populations in the Ardahan and Kars provinces of north-eastern Turkey combines the allozyme patterns found in material of D. incarnata s.l. from the same area with those from D. euxina. It is here described for the first time as D. armeniaca. Received November 14, 2000 Accepted June 20, 2001     

Dioecious Silene at the X-road: the reasons Y

Among the variety of breeding systems developed by flowering plants, those based on heteromorphic sex chromosomes are the most intellectually challenging in evolutionary terms. This is because, among other things, they enable us to compare sex determination processes between plants and animals. White campion (Silene latifolia, also named Lychnis or Melandrium) is dioecious and, much like us, females are homogametic (XX) and males are heterogametic (XY). Sexual dimorphism in white campion is controlled by two independent developmental pathways operating from the Y chromosome at very early developmental stages and within distinct regions of the flower. In addition, all basic steps in the evolution from the bisexual to the dioecious condition with heteromorphic sex chromosomes are known and available to experimentation in the genus Silene. This group of species has been under scrutiny for more than a century. Such an ideal experimental system enables us to tackle, with novel methodological tools, several classical questions in biology. These include the question of how sexual dimorphism evolved and how dimorphic development is controlled, as well as questions of how sex chromosomes evolve in the absence of meiotic recombination or how male-female genetic conflicts are generated. At the turn of the century, the time is now ripe to have a closer look. Received: 21 September 1999 / Accepted: 11 October 1999     

Interrelationships and evolution of the east Asian grass lizards, Takydromus (Squamata: Lacertidae)

The east Asian lacertid lizard genus, Takydromus , is well-defined but its relationships to other primitive Palaearctic lacertids are still uncertain and, although it has similarities to the lower Miocene Miolacerta, Takydromus does not appear to be identical with this. The 16 or 17 recognizable species are reviewed and a key provided for their identification; the remaining area of uncertainty about species boundaries is the Takydromus sexlineatus group in Assam. A phylogeny for Takydromus is estimated using a data set of 35 morphological characters drawn from external features, skeleton and soft-parts. There are two main constituent clades which may be informally recognized as Takydromus s.s. and Platyplacopus. Platyplacopus is subtropical and perhaps relict, whereas Takydromus ranges from temperate to tropical areas. The two clades have different ranges of eggs per clutch. In both of them, elongate forms that climb extensively in flimsy vegetation have evolved and have independently acquired similar features that confer performance advantages in this situation. Interestingly, the order of assembly of tliese features is markedly different.     

Why there are photodamages to photosystem II at low light intensities

An explanation of photodamages to PS II at low light intensities is proposed. The explanation is based on the two following postulates: 1. Intermediate states of the water-oxidizing complex can undergo parasitic reduction to lower degrees of oxidation. 2. Photosynthetic apparatus can minimize the unfavorable effect of such reduction by changes in the number of active reaction centers of PS II. Some steady-state characteristics were calculated under these assumptions. The results obtained show that the frequency of P680 excitations at low light intensities becomes as high as that at saturating light provided that the rate of parasitic reduction is comparable with the rate of the slowest reaction in the cycle of the water- oxidizing complex conversions.     

Demographic History and Genomic Response to Environmental Changes in a Rapid Radiation of Wild Rats

For organisms to survive and prosper in a harsh environment, particularly under rapid climate change, poses tremendous challenges. Recent studies have highlighted the continued loss of megafauna in terrestrial ecosystems and the subsequent surge of small mammals, such as rodents, bats, lagomorphs, and insectivores. However, the ecological partitioning of these animals will likely lead to large variation in their responses to environmental change. In the present study, we investigated the evolutionary history and genetic adaptations of white-bellied rats (Niviventer Marshall, 1976), which are widespread in the natural terrestrial ecosystems in Asia but also known as important zoonotic pathogen vectors and transmitters. The southeastern Qinghai-Tibet Plateau was inferred as the origin center of this genus, with parallel diversification in temperate and tropical niches. Demographic history analyses from mitochondrial and nuclear sequences of Niviventer demonstrated population size increases and range expansion for species in Southeast Asia, and habitat generalists elsewhere. Unexpectedly, population increases were seen in N. eha, which inhabits the highest elevation among Niviventer species. Genome scans of nuclear exons revealed that among the congeneric species, N. eha has the largest number of positively selected genes. Protein functions of these genes are mainly related to olfaction, taste, and tumor suppression. Extensive genetic modification presents a major strategy in response to global changes in these alpine species.     

Genome structure and evolution in the cruciferous tribe Thlaspideae (Brassicaceae)

Whole-genome duplications (WGDs) and chromosome rearrangements (CRs) play the key role in driving the diversification and evolution of plant lineages. Although the direct link between WGDs and plant diversification is well documented, relatively few studies focus on the evolutionary significance of CRs. The cruciferous tribe Thlaspideae represents an ideal model system to address the role of large-scale chromosome alterations in genome evolution, as most Thlaspideae species share the same diploid chromosome number (2n = 2x = 14). Here we constructed the genome structure in 12 Thlaspideae species, including field pennycress (Thlaspi arvense) and garlic mustard (Alliaria petiolata). We detected and precisely characterized genus- and species-specific CRs, mostly pericentric inversions, as the main genome-diversifying drivers in the tribe. We reconstructed the structure of seven chromosomes of an ancestral Thlaspideae genome, identified evolutionary stable chromosomes versus chromosomes prone to CRs, estimated the rate of CRs, and uncovered an allohexaploid origin of garlic mustard from diploid taxa closely related to A. petiolata and Parlatoria cakiloidea. Furthermore, we performed detailed bioinformatic analysis of the Thlaspideae repeatomes, and identified repetitive elements applicable as unique species- and genus-specific barcodes and chromosome landmarks. This study deepens our general understanding of the evolutionary role of CRs, particularly pericentric inversions, in plant genome diversification, and provides a robust base for follow-up whole-genome sequencing efforts.     

Phylogeny and mechanisms of shared hierarchical patterns in birdsong

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