Publications

Abstract Variation in pigmentation is common in marine invertebrates, although few studies have shown the existence of genetic differentiation of chromatic forms in these organisms. We studied the genetic structure of a colonial ascidian with populations of different colour morphs in the northwestern Mediterranean. A fragment of the c oxidase subunit 1 (COI) mitochondrial gene was sequenced in seven populations of Pseudodistoma crucigaster belonging to three different colour morphs (orange, yellow and grey). Maximum likelihood analyses showed two well‐supported clades separating the orange morph from the yellow‐grey morphotypes. Genetic divergence between these clades was 2.12%, and γ ST values between populations of the two clades were high (average 0.936), pointing to genetic isolation. Nested clade and coalescence analyses suggest that a past fragmentation event may explain the phylogeographical origin of these two clades. Non‐neutral mtDNA evolution is observed in our data when comparing the two clades, showing a significant excess of nonsynonymous polymorphism within the yellow–grey morphotype using the McDonald–Kreitman test, which is interpreted as further support of reproductive isolation. We conclude that the two clades might represent separate species. We compare the population genetic differentiation found with that estimated for other colonial and solitary ascidian species, and relate it to larval dispersal capabilities and other life‐history traits.

Theory concerning the evolution of sex and recombination and mutation load relies on information on rates and distributions of effects of deleterious mutations. Direct information on the genomic mutation rate in Drosophila implies that an accumulation of mildly deleterious mutations reduces viability of populations by at least 1% per generation. We carried out an experiment to measure the deleterious mutation rate in Caenorhabditis elegans , in which independent sublines were maintained with one hermaphrodite parent per generation, conditions that minimize the opportunity for natural selection and lead to random fixation of deleterious mutations. After 60 generations of mutation accumulation, negligible changes in mean reproductive output and lifespan occurred, but the genetic variance increased at rates typical for life history traits in other species. The estimated deleterious mutation rate per haploid genome for fitness, U , was 0.0026, a figure two orders of magnitude smaller than previously measured for viability in Drosophila .

Abstract In this investigation, we have tested the potential usefulness of variable fluorescence, i.e., the potential photochemical efficiency of photosystem II (Fv/Fm), determined with a fast repetition rate fluorometer (FRRF), as an indicator of the effect of metal pollution on natural phytoplankton assemblages. Phytoplankton populations were collected from an eutrophic embayment and exposed to different copper concentrations within the ppb range for 4 d. Enhanced photosynthesis was found for Cu concentrations of 10 and 20 μg/L, at very short exposure times (1 and 5 h). However, after 72 h even at 10 μg/L of Cu, Fv/Fm-values were significantly lower than those measured in the control. The highest Cu concentration tested (80 μg/L) caused a statistically significant decrease of Fv/Fm after 5 h. This response was contrasted with parallel determinations of chlorophyll a concentration, measurements of photosynthetic O2 production rates, and changes in the taxonomic composition and size structure of the microplankton communities. A reduction in overall particle size was found at Cu concentrations of 80 and 40 μg/L. Enhanced abundance of flagellates and the diatom Pseudonitzschia pungens was observed at 20 μg/L of copper. This study demonstrates the utility of this methodological approach as a rapid, nondestructive way for detecting trace-metal toxicity on natural phytoplankton.