Microbe–mineral interactions in naturally radioactive beach sands from Espirito Santo,Brazil: experiments on mutagenicity

Previous studies on naturally radioactive materials suggested that they can have a mutagenic effect on plants (growing in sands in Kerala, South West India), and on bats (dwelling in an abandoned underground mine of primary monazite ore in Namaqualand, Western Cape, South Africa). We hypothesised, based on previous theoretical work, that radioactive sands would not induce mutants in microorganisms over time scales typical of doubling times in the natural environment. The potential of exceptionally monazite (Th)-rich mineral sands collected from the coast of Espirito Santo, Brazil to induce single-point reversion in Escherichia coli cultures (both repair-competent and repair-deficient strains) was tested using the tryptophan reverse mutation assay. The results show that at least on a short-term scale (1–7 days), the monazite-rich sands did not cause an increase in reversion above background.     

Reproductive periodicity of the echinoids Diadema and Echinometra on the two coasts of Panama

Patterns of reproductive periodicity in the regular echinoid species Diadema mexicanum A. Agassiz and Echinometra vanbrunti A. Agassiz from the Bay of Panama, and Diadema antillarum Phillipi, Echinometra lucunter (Linnaeus) and E. viridis A. Agassiz from the Caribbean coast of the Isthmus of Panama exhibit dissimilarities that reflect the differences of the environments they inhabit. Populations of the two species from the seasonal Bay of Panama display synchronous, well-defined, reproductive cycles. Spawning appears to be timed so that newly metamorphosed sea urchins, rather than larvae, can benefit from the increased food production concomitant with dry season upwelling. On the less seasonal Caribbean shore reproductive periodicity is less defined. Populations of Diadema antillarum and Echinometra lucunter from the vicinity of the Panama Canal show indications of periodicity, while those from a locality 20 km to the east display little tendency for synchrony between individuals. The much rarer E. viridis, on the other hand, maintains well-defined, population-wide cycles in both localities. It is suggested that in a constant environment the intensity of selection for synchrony between individual gametogenic cycles may be inversely proportional to population density.     

Effects of In-Feed Inclusion of Clinoptilolite on Blood Serum Concentrations of Aluminium and Inorganic Phosphorus and on Ruminal Ph and Volatile Fatty Acid Concentrations in Dairy Cows

The experiment investigated the effects of the dietary inclusion of 200 g of the natural zeolite, clinoptilolite on the blood serum concentrations of aluminium (Al) and inorganic phosphorus (P) as well as on the ruminal pH and the ruminal concentrations of Al and P and of certain volatile fatty acids. Sixteen Holstein cows with a rumen fistula were randomly assigned to one of two groups. Group A cows (n = 8) were fed the basal ration supplemented with 200 g of clinoptilolite per day, and group B cows (n = 8) were fed the basal ration and served as controls. Blood and rumen fluid samples were collected at the same day of each week and at the same time (5 h after morning feeding) for 12 weeks. Clinoptilolite supplementation had no significant effect on ruminal and blood serum concentrations of Al and P. However, clinoptilolite significantly increased ruminal pH and acetate, and decreased ruminal propionate and valerate.     

Speciation on the coasts of the new world: phylogeography and the evolution of bindin in the sea urchin genus Lytechinus

Abstract Beginning with E. Mayr's study in 1954, tropical sea urchins have played an important role in studies of speciation in the sea, but what are the processes of cladogenesis and divergence that give rise to new species in this group? We attempt to answer this question in the genus Lytechinus. Unlike the majority of other tropical sea urchin genera, which have circumtropical distributions, Lytechinus is mostly confined to the tropics and subtropics of the New World. We sequenced a region of mitochondrial cytochrome oxidase I and the entire molecule of nuclear bindin (a sperm gamete recognition protein) of nearly all species in the genus, and we assayed isozymes of three partially sympatric closely related species and subspecies. We found that in both mitochondrial DNA (mtDNA) and in bindin the genus Lytechinus is paraphyletic, encompassing Sphaerechinus granularis as the sister species of L. euerces. The rest of the species are arranged in an Atlantic clade composed of L. williamsi and L. variegatus, and a Pacific clade containing L. anamesus, L. pictus, L. semituberculatus, and L. panamensis. Divergence between these clades suggests that they were separated no later than the closure of the Isthmus of Panama, and possibly before this time. Our data confirm that L. anamesus and L. pictus from California are a single species, and provide no evidence of differentiation between L. variegatus variegatus from the Caribbean and L. variegatus atlanticus from Bermuda. Lytechinus variegatus variegatus mtDNA is distinct from that of L. variegatus carolinus from the North American seaboard and the Gulf of Mexico, whereas their bindins are very similar. However, there is clear evidence of introgression of mtDNA between the two subspecies and they share alleles in all sampled isozyme loci. Lytechinus williamsi from the Caribbean shares mtDNA haplotypes with L. variegatus variegatus, and they also share isozymes in all assayed loci. Their bindin, however, is distinct and coalesces within each morphospecies. A private clade of mtDNA in L. williamsi may be indicative of former differentiation in the process of being swamped by introgression, or of recent speciation. Recent sudden expansions in effective population size may explain the predominance of a few mitochondrial haplotypes common to the two species. Despite the high divergence of bindin (relative to differentiation of mtDNA) between L. variegatus and L. williamsi, comparison of amino acid replacement to silent substitutions by various methods uncovered no evidence for positive selection on the bindin of any clade of Lytechinus. With the possible exception of L. williamsi and L. variegatus, our results are consistent with a history of allopatric speciation in Lytechinus. The molecular results from Lytechinus, along with those of other similar studies of sea urchins, suggest that the general speciation patterns deduced in the middle of last century by Mayr from morphology and geography have held up, but also have uncovered peculiarities in the evolution of each genus.     

Adaptive evolution of bindin in the genus Heliocidaris is correlated with the shift to direct development

Abstract Sea urchins are widely used to study both fertilization and development. In this study we combine the two fields to examine the evolution of reproductive isolation in the genus Heliocidaris . Heliocidaris tuberculata develops indirectly via a feeding larva, whereas the only other species in the genus, H. erythrogramma , has evolved direct development through a nonfeeding larva. We estimated the time of divergence between H. erythrogramma and H. tuberculata from mitochondrial DNA divergence, quantified levels of gametic compatibility between the two species in cross-fertilization assays, and examined the mode of evolution of the sperm protein bindin by sequencing multiple alleles of the two species. Bindin is the major component of the sea urchin sperm acrosomal vesicle, and is involved in sperm-egg attachment and fusion. Based on our analyses, we conclude that: the two species of Heliocidaris diverged less than five million years ago, indicating that direct development can evolve rapidly in sea urchins; since their divergence, the two species have become gametically incompatible; Heliocidaris bindin has evolved under positive selection; and this positive selection is concentrated on the branch leading to H. erythrogramma . Three hypotheses can explain the observed pattern of selection on bindin: (1) it is a correlated response to the evolution of direct development in H. erythrogramma; (2) it is the result of an intraspecific process acting in H. erythrogramma but not in H. tuberculata; or (3) it is the product of reinforcement on the species that invests more energy into each egg to avoid hybridization.     

Dispersal barriers in tropical oceans and speciation in Atlantic and eastern Pacific sea urchins of the genus Echinometra

Echinometra is a pantropical sea urchin made famous through studies of phylogeny, speciation, and genetic structure of the Indo-West Pacific (IWP) species. We sequenced 630 bp of the cytochrome oxidase I (COI) mitochondrial gene to provide comparable information on the eastern Pacific and Atlantic species, using divergence between those separated by closure of the Isthmus of Panama 3.1 million years ago (Ma) to estimate dates for cladogenic events. Most recently (1.27-1. 62 Ma), the Atlantic species E. lucunter and E. viridis diverged from each other, at a time in the Pleistocene that sea levels fell and Caribbean coral speciation and extinction rates were high. An earlier split, assumed to have been coincident with the completion of the Isthmus of Panama, separated the eastern Pacific E. vanbrunti from the Atlantic common ancestor. Transisthmian COI divergence similar to that in the sea urchin genus Eucidaris supports this assumption. The most ancient split in Echinometra occurred between the IWP and the neotropical clades, due to cessation of larval exchange around South Africa or across the Eastern Pacific Barrier. Gene flow within species is generally high; however, there are restrictions to genetic exchange between E. lucunter populations from the Caribbean and those from the rest of the Atlantic. Correlation between cladogenic and vicariant events supports E. Mayr's contention that marine species, despite their high dispersal potential, form by means of geographical separation. That sympatric, nonhybridizing E. lucunter and E. viridis were split so recently suggests, however, that perfection of reproductive barriers between marine species with large populations can occur in less than 1.6 million years (Myr).     

Evolution and the latitudinal diversity gradient: speciation, extinction and biogeography

A latitudinal gradient in biodiversity has existed since before the time of the dinosaurs, yet how and why this gradient arose remains unresolved. Here we review two major hypotheses for the origin of the latitudinal diversity gradient. The time and area hypothesis holds that tropical climates are older and historically larger, allowing more opportunity for diversification. This hypothesis is supported by observations that temperate taxa are often younger than, and nested within, tropical taxa, and that diversity is positively correlated with the age and area of geographical regions. The diversification rate hypothesis holds that tropical regions diversify faster due to higher rates of speciation (caused by increased opportunities for the evolution of reproductive isolation, or faster molecular evolution, or the increased importance of biotic interactions), or due to lower extinction rates. There is phylogenetic evidence for higher rates of diversification in tropical clades, and palaeontological data demonstrate higher rates of origination for tropical taxa, but mixed evidence for latitudinal differences in extinction rates. Studies of latitudinal variation in incipient speciation also suggest faster speciation in the tropics. Distinguishing the roles of history, speciation and extinction in the origin of the latitudinal gradient represents a major challenge to future research.     

TEMPORAL VARIATION IN POPULATIONS OF THE MARINE ISOPOD EXCIROLANA: HOW STABLE ARE GENE FREQUENCIES AND MORPHOLOGY?

Excirolana braziliensis is a dioecious marine isopod that lives in the high intertidal zone on both sides of tropical America. It lacks a dispersal phase and displays a remarkable degree of genetic divergence even between localities less than 1 km apart. Nine populations of this nominal species from both sides of the Isthmus of Panama and one population of the closely allied species, Excirolana chamensis, from the eastern Pacific were studied for 2 yr for allozymic temporal variation in 13 loci and for 3 to 4 yr for morphological variation in nine characters. The genetic and morphological constitution of 9 out of 10 populations remained stable. Allele frequencies at two loci and overall morphology in a tenth beach occupied by E. braziliensis changed drastically and significantly between 1986 and 1988. The change in gene frequency is too great to explain by genetic drift occurring during a maximum of 14 generations regardless of assumed effective population size; drift is also unlikely to have caused observed changes in morphology. Selective survival of a previously rare genotype is more plausible but still not probable. The most credible explanation is that the resident population at this locality became extinct and that the beach was recolonized by immigrants from another locality. Such infrequent episodes of extinction and recolonization from a single source may account for the large amount of genetic divergence between local populations of E. braziliensis. However, the low probability of large temporal genetic change even in a species such as this, in which gene flow between local demes is limited and generation time is short, suggests that a single sample through time is usually adequate for reconstructing the genetic history of populations.