Changes in selection regime cause loss of phenotypic plasticity in planktonic freshwater copepods.

Rapid phenotypic adaptation is critical for populations facing environmental changes and can be facilitated by phenotypic plasticity in the selected traits. Whereas recurrent environmental fluctuations can favour the maintenance or de novo evolution of plasticity, strong selection is hypothesized to decrease plasticity or even fix the trait (genetic assimilation). Despite advances in the theoretical understanding of the impact of plasticity on diversification processes, comparatively little empirical data of populations undergoing diversification mediated by plasticity are available. Here we use the planktonic freshwater copepod Acanthodiaptomus denticornis from two lakes as model system to study UV stress responses of two phenotypically different populations under laboratory conditions. Our study reveals heritable lake- and sex-specific differences of behaviour, physiological plasticity, and mortality. We discuss specific selective scenarios causing these differences and argue that phenotypic plasticity will be higher when selection pressure is moderate, but will decrease or even be lost under stronger pressure

Lake- and sex-specific distributions of <i>A. denticornis</i> in the water column.

<p>The table provides the posterior probability estimates of the employed predictor variables of a Bayesian logistic analysis of variance (β_i; see text for details). The estimates indicate the deflection of each predictor from the overall central tendency and are the basis for the complex comparisons depicted in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0090010#pone-0090010-g003" target="_blank">Fig. 3</a>. Abbreviations: HDI–high density interval; WH–white light.</p

Study system.

<p>(A) Specimens of <i>Acanthodiaptomus denticornis</i> populations from the neighbouring lakes Lac Pavin (LP) and Lac de Montcineyre (LM). Both sexes in LM as well as LP females are translucent, whereas LP males bright red. (B) The lakes are situated in the French Massif Central. Grey areas around the lakes are woodland, white areas are mainly agricultural or other areas under human use.</p

Bayesian contrasts of posterior probability estimates of the predictor variables in Table 1.

<p>High density intervals (95% HDI) are marked in light grey, values outside the intervals in dark grey. The y-axis represents the density of the probability distribution. Contrasts of distributions of UV versus white light are provided for both sexes of LP (A, B) and LM (D, E). Furthermore, we contrasted the distributions of males versus females under white light in LP (C) and LM (F).</p

Effect of the covariates lake, sex, and treatment on survival.

<p>The first three columns (“Proportional hazards “) provide model diagnostics of the employed Cox proportional-hazards regression, i.e. they test the proportional hazards assumption for the model fit. The non-significant p-values of the statistics indicate that the assumption is not violated. The fourth column (coef [δ]) provides the model estimates for the three coefficients and the fifth column the respective standard errors (SE). All tested covariates had a significant effect (p-values in the sixth column).</p

Contributions of biogeographical functions to species accumulation may change over time in refugial regions

Aim: Elevated biodiversity is the result of the cradle, museum or sink functions. The contributions of these three functions to species accumulation and their changes through time remain unknown for glacial refugia. Additionally, our understanding of the role these functions played during pre-glacial periods is limited. We test for changes in contributions of functions through time leading to the current diversity patterns using a model refugium and taxon. Location: Anatolia, Western Palaearctic. Taxon: Freshwater neritid snails (genus Theodoxus). Methods: Assessments were made to define molecular operational taxonomic units (MOTUs) for Theodoxus and reaffirm the genus as a suitable model taxon with elevated interspecific diversity in noted glacial refugia. Thereafter, we constructed a time-calibrated multilocus Bayesian phylogeny of mtDNA and nDNA by using both fossil data and published substitution rates. Ancestral area estimation was performed on the phylogeny to define the contribution of the functions through time. Results: Accumulation of Theodoxus diversity in Anatolia over the Miocene–Pliocene transition is attributed to the museum function, but its contribution was small as only few divergence events occurred. The cradle function dominated during the Pliocene and Early Pleistocene, when most interspecific diversity built up and extant lineages in Anatolia were established. The sink function acted from the Middle Pleistocene to present-day, but with only a small contribution to the total extant Anatolian interspecific diversity. Main conclusion: Our results do not entirely mitigate the role glacial cycles played in species accumulation, but highlight Ice Ages may have been less effective in forcing temperate aquatic interspecific diversity into more opportune areas. The elevated diversity in refugia may rather be the result of earlier in situ diversification. Elevated interspecific diversity attributed to the legacy of glacially forced retreats may need to be re-evaluated in cases where refugia have long and complex geological histories such as Anatolia. These results highlight the importance of considering species accumulation through a temporal perspective to adequately explain present-day biodiversity patterns

Intraspecific Variation in Cellular and Biochemical Heat Response Strategies of Mediterranean <i>Xeropicta derbentina</i> [Pulmonata, Hygromiidae]

<div><p>Dry and hot environments challenge the survival of terrestrial snails. To minimize overheating and desiccation, physiological and biochemical adaptations are of high importance for these animals. In the present study, seven populations of the Mediterranean land snail species <i>Xeropicta derbentina</i> were sampled from their natural habitat in order to investigate the intraspecific variation of cellular and biochemical mechanisms, which are assigned to contribute to heat resistance. Furthermore, we tested whether genetic parameters are correlated with these physiological heat stress response patterns. Specimens of each population were individually exposed to elevated temperatures (25 to 52°C) for 8 h in the laboratory. After exposure, the health condition of the snails' hepatopancreas was examined by means of qualitative description and semi-quantitative assessment of histopathological effects. In addition, the heat-shock protein 70 level (Hsp70) was determined. Generally, calcium cells of the hepatopancreas were more heat resistant than digestive cells - this phenomenon was associated with elevated Hsp70 levels at 40°C.We observed considerable variation in the snails' heat response strategy: Individuals from three populations invested much energy in producing a highly elevated Hsp70 level, whereas three other populations invested energy in moderate stress protein levels - both strategies were in association with cellular functionality. Furthermore, one population kept cellular condition stable despite a low Hsp70 level until 40°C exposure, whereas prominent cellular reactions were observed above this thermal limit. Genetic diversity (mitochondrial cytochrome c oxidase subunit I gene) within populations was low. Nevertheless, when using genetic indices as explanatory variables in a multivariate regression tree (MRT) analysis, population structure explained mean differences in cellular and biochemical heat stress responses, especially in the group exposed to 40°C. Our study showed that, even in similar habitats within a close range, populations of the same species use different stress response strategies that all rendered survival possible.</p></div

Digestive gland of <i>Xeropicta derbentina</i> in different reaction states.

<p><b>A.</b> Digestive gland of a control animal. a. indicates tight lumina, b. a smooth base of the tubule and c. shows an oval-shaped nucleus and regular vacuolization of the digestive cells. <b>B.</b> Digestive gland of a control animal. a. shows a calcium cell with dense cytoplasm and round nucleus. b. indicates an irregular vacuolization of the digestive cells with partially fused vacuoles. <b>C.</b> Digestive gland in state of reaction. a. indicates dark nuclei and an irregular cytoplasm of the calcium cells. Also hypertrophy of the calcium cells occurs. <b>D.</b> Digestive gland in state of reaction. a. shows enlarged lumina of the tubule and b. shows pronounced and ruptured apices of the digestive cells. <b>E.</b> Digestive gland in state of destruction. a. indicates a very irregular cytoplasm with bright spots in the calcium cells. b. shows cell fragments in the lumen of the tubule. Cell borders are disengaged. <b>F.</b> Digestive gland in state of destruction showing necrosis. The arrow indicates ruptured cell apices. Cell borders are disengaged.</p

Results of the MRT analyses of PCoA transformed physiological heat stress response data (Hsp70 and histology) constrained with population structure information of <i>Xeropicta derbentina</i> under four temperature conditions.

<p>R²: cross-validated proportion of variance explained by the primary grouping (i.e., first split of the tree); P1–P7: populations studied; π: nucleotide diversity; H_MH3: axis 3 of transformed haplotype diversity; F_ST1, F_ST2: axes 1 and 2 of transformed pairwise fixation index; (+): positive correlation; (−): negative correlation; improved histopathology (i); deteriorated histopathology (d).</p