THE USE OF DNA DIVERGENCE TO HELP DETERMINE THE CORRELATES OF EVOLUTION OF MORPHOLOGICAL CHARACTERS

Even though, from Darwin onwards, interisland evolution has been a cornerstone of evolutionary theory it has not been possible to determine to what extent this geographic variation reflects the phylogeny (e.g., pattern of island colonization) or ecogenetic adaptation to different ecological conditions on each island. Using the morphology of western Canary Island lacertids (Gallotia galloti) as an example, a procedure is explored that gives a preliminary answer to this problem when there are a limited number of islands. The phylogenetic component (represented by patristic distances derived from 1005 mitochondrial DNA [mtDNA] base pairs) can be separated from two potential ecogenetic factors (environmental richness and climate) by partial Mantel tests. This reveals that, although these components interact, some characters are correlated primarily to biodiversity/paucity (e.g., size), others are correlated to wet and lush environments (e.g., dorsal pattern), and others are correlated primarily to the phylogeny (e.g., sexual leg markings). The former two correlations may be due to ecogenetic adaptation to current ecological conditions, wheras the latter reflects historical processes.     

THE EVOLUTION OF ELONGATE SHAPE IN DIATOMS1

Diatoms have been classified historically as either centric or pennate based on a number of features, cell outline foremost among them. The consensus among nearly every estimate of the diatom phylogeny is that the traditional pennate diatoms (Pennales) constitute a well‐supported clade, whereas centric diatoms do not. The problem with the centric–pennate classification was highlighted by some recent analyses concerning the phylogenetic position of Toxarium, whereby it was concluded that this “centric” diatom independently evolved several pennate‐like characters including an elongate, pennate‐like cell outline. We performed several phylogenetic analyses to test the hypothesis that Toxarium evolved its elongate shape independently from Pennales. First, we reanalyzed the original data set used to infer the phylogenetic position of Toxarium and found that a more thorough heuristic search was necessary to find the optimal tree. Second, we aligned 181 diatom and eight outgroup SSU rDNA sequences to maximize the juxtapositioning of similar primary and secondary structure of the 18S rRNA molecule over a much broader sampling of diatoms. We then performed a number of phylogenetic analyses purposely based on disparate sets of assumptions and found that none of these analyses supported the conclusion that Toxarium acquired its pennate‐like outline independently from Pennales. Our results suggest that elongate outline is congruent with SSU rDNA data and may be synapomorphic for a larger, more inclusive clade than the traditional Pennales.     

USE OF CONTRASTS FOR THE EVALUATION OF PANEL INCONSISTENCY1

The panelist by treatment interaction variation is used to investigate panel inconsistency. The approach tests for panelist outliers with different univariate response patterns to a set of treatments to determine the relative effect(s) of interaction variation sources on the detection of treatment differences. Algorithms and examples are followed by a discussion of the theoretical and practical significance of panel inconsistency and the removal of panelist outliers.     

EVOLUTION OF DEVELOPMENTAL PROGRAMS IN VOLVOX (CHLOROPHYTA)1

The volvocine green algal genus Volvox includes ～20 species with diverse sizes (in terms of both diameter and cell number), morphologies, and developmental programs. Two suites of characters are shared among distantly related lineages within Volvox. The traits characteristic of all species of Volvox—large (>500) numbers of small somatic cells, much smaller numbers of reproductive cells, and oogamy in sexual reproduction—have three or possibly four separate origins. In addition, some species have evolved a suite of developmental characters that differs from the ancestral developmental program. Most multicellular volvocine algae, including some species of Volvox, share an unusual pattern of cell division known as palintomy or multiple fission. Asexual reproductive cells (gonidia) grow up to many times their initial size and then divide several times in rapid succession, with little or no growth between divisions. Three separate Volvox lineages have evolved a reduced form of palintomy in which reproductive cells are small and grow between cell divisions. In each case, these changes are accompanied by a reduction in the rate of cell division and by a requirement of light for cell division to occur. Thus, two suites of characters—those characteristic of all Volvox species and those related to reduced palintomy—have each evolved convergently or in parallel in lineages that diverged at least 175 million years ago (mya).     

THE EVOLUTION OF HOST-PLANT USE AND SEQUESTRATION IN THE LEAF BEETLE GENUS PHRATORA (COLEOPTERA: CHRYSOMELIDAE)

Leaf beetles in the genus Phratora differ in host plant use and in the chemical composition of their larval defensive secretion. Most species specialize on either poplars or willows (family Salicaceae), but two species feed on birch (family Betulaceae). Phratora vitellinae utilizes salicylates from the host plant to produce its larval secretion, which contains salicylaldehyde, while other Phratora species produce an autogenous secretion. To reconstruct the evolutionary history of host plant use and the larval secretion chemistry in this genus, we sequenced 1383 base pairs of the mt cytochrome oxidase I gene for six European and one North American Phratora species and three outgroup taxa. Bootstrap values of the complete nucleotide sequence were 99-100% for six of eight nodes in the maximum parsimony tree. They were 71% and 77% for the two other nodes. The maximum parsimony tree and the maximum likelihood tree based on nucleotide sequence showed the same relationships as a maximum parsimony tree based on the amino acid sequence. Beetle phylogeny overlapped broadly with host plant taxonomy and chemistry, and it revealed historical constraints influencing host plant use. However, there was one host shift from the willow family (Salicaceae) to the birch family (Betulaceae). The use of host plant phenol glycosides for the larval defensive secretion evolved along the lineage that led to P. vitellinae. Phratora vitellinae feeds on the taxonomically widest range of host plants, which are characterized by moderate to high levels of salicylates. The results support the hypothesis that the use of salicylates for the larval secretion evolved twice independently in chrysomeline leaf beetles.     

THE ROLE AND EVOLUTION OF SUPEROXIDE DISMUTASES IN ALGAE1

Superoxide dismutases (SOD) catalyze the disproportionation of the potentially destructive superoxide anion radical (O₂^??, a byproduct of aerobic metabolism) to molecular oxygen and hydrogen peroxide: 2O₂^??+2H⁺→H₂O₂+O₂. Based on metal cofactors, four known metalloforms of SOD enzymes have been identified: they contain either Fe, Mn, Cu and Zn, or Ni. Orthologs of all metalloforms are present in oxygenic photoautotrophs. The expression of SOD is highly regulated, with specific metalloforms playing an inducible protective role for specific cellular compartments. The various metalloforms of SOD are not distributed equally within either cyanobacteria or eukaryotic algae. Typically, cyanobacteria contain either an NiSOD alone or combinations of Mn and Ni or Fe and Mn metalloforms (CuZn is rare among the cyanobacteria). The bacillariophytes and rhodophytes retain an active MnSOD, whereas the chlorophytes, haptophytes, and embryophytes have either FeSOD or multiple combinations of Fe, Mn, and CuZnSODs. The NiSOD is a relatively novel SOD and has been generally excluded from evolutionary analyses. In both cyanobacteria and chlorophyte algae, the FeSOD metalloform appears to be associated with PSI, where its primary role is most likely to deactivate reactive oxygen produced by the Mehler reaction. The CuZnSOD also appears to be associated with the plastid but is phylogenetically more restricted in its distribution. In eukaryotic algae, SODs are all nuclear encoded and, based on nucleotide sequence, protein structures, and phylogenetic distributions, appear to have unique evolutionary histories arising from the lateral gene transfer of three distinct genes to the nucleus after the endosymbiotic acquisition of mitochondria and plastids. The varied phylogenetic histories and subcellular localizations suggest significantly different selection on these SOD metalloforms after the endosymbiont organelle‐to‐host gene transfer.     

THE EVOLUTION OF FITNESS

In every generation, the mean fitness of populations increases because of natural selection and decreases because of mutations and changes in the environment. The magnitudes of these effects can be measured in two ways: either directly, by comparing the fitnesses of selected and unselected populations, or indirectly, by measuring the additive variance of fitness and making use of the fundamental theorem of natural selection. The available data suggest that the amount by which natural selection increases mean fitness each generation (or degradation decreases mean fitness) will usually be between 0.1% and 30%; more tentatively, it is suggested that values will typically fall between 1% and 10%. These values can be used to set an upper limit of 5%–10% on the genetic advantage of mate choice.     

THE EVOLUTION OF BONE

Vertebrates are practically unique among the Metazoa in their possession of a skeleton made from calcium phosphate rather than calcium carbonate. Interpretation of the origin of a phosphatic skeleton in early vertebrates has previously centered primarily on systemic requirements for phosphate and/or calcium storage or excretion. These interpretations afford no anatomical or physiological advantage(s) that would not have been equally valuable to many invertebrates. We suggest the calcium phosphate skeleton is distinctly advantageous to vertebrates because of their relatively unusual and ancient pattern of activity metabolism: intense bursts of activity supported primarily by rapid intramuscular formation of lactic acid. Bursts of intense activity by vertebrates are followed by often protracted periods of marked systemic acidosis. This postactive acidosis apparently generates slight skeletal dissolution, associated with simultaneous vascular hypercalcemia. A variety of apparently unrelated histological features of the skeleton in a number of vertebrates may minimize this postactive hypercalcemia. We present new data that suggest that postactive skeletal dissolution would be significantly exacerbated if bone were composed of calcium carbonate rather than calcium phosphate. The former is far less stable both in vivo and in vitro than is calcium hydroxyapatite, under both resting and postactive physiological conditions.     

生殖内分泌的演化

一切生殖活动都是在内分泌激素的严密调节下进行的。这个调节系统极为复杂,它不仅涉及多科不同类型的激素,而且还涉及激素之间的动态平衡。哺乳动物的生殖内分泌体系和其调控机制已发展到接近高度完善的水平。当前人类面临着一个人口迅速增长的危机,如何对人类自己的生育力加以控制已成为人们共同关心的大事,然而如何才能妥善地解决这一重大问题,对生物医学科学工作者来说,则是一个极大的挑战。毫无疑问,生育力的科学控制,必然要求对生殖活动的内在规律有系统和深入的了解,然后才有可能提