Fifteen species in one: deciphering the Brachionus plicatilis species complex (Rotifera, Monogononta) through DNA taxonomy

Understanding patterns and processes in biological diversity is a critical task given current and rapid environmental change. Such knowledge is even more essential when the taxa under consideration are important ecological and evolutionary models. One of these cases is the monogonont rotifer cryptic species complex Brachionus plicatilis, which is by far the most extensively studied group of rotifers, is widely used in aquaculture, and is known to host a large amount of unresolved diversity. Here we collate a dataset of previously available and newly generated sequences of COI and ITS1 for 1273 isolates of the B. plicatilis complex and apply three approaches in DNA taxonomy (i.e. ABGD, PTP, and GMYC) to identify and provide support for the existence of 15 species within the complex. We used these results to explore phylogenetic signal in morphometric and ecological traits, and to understand correlation among the traits using phylogenetic comparative models. Our results support niche conservatism for some traits (e.g. body length) and phylogenetic plasticity for others (e.g. genome size)

Temporal dynamics of life-history traits of <i>L</i>. <i>garciai</i> in Lake Alchichica.

<p>a) Average reproductive effort, i.e. the absolute quantity of biomass a female invests per clutch; and relative reproductive effort, the proportion of the female biomass invested per clutch. b) Average number of eggs per sac and average size of those eggs. Vertical bars indicate ± one standard deviation.</p

Dispersion plots of the average values of life-history traits of female <i>L</i>. <i>garciai</i> vs. temperature and food availability in Lake Alchichica.

<p>Probability and <i>r</i> coefficient values correspond to Pearson’s correlation tests; a significant correlation between the variability of a trait vs. temperature or phytoplankton is considered evidence of phenotypic plasticity to that factor.</p

Phenotypic plasticity of life-history traits of a calanoid copepod in a tropical lake: Is the magnitude of thermal plasticity related to thermal variability?

<div><p>According to the Climatic Variability Hypothesis [CVH], thermal plasticity should be wider in organisms from temperate environments, but is unlikely to occur in tropical latitudes where temperature fluctuations are narrow. In copepods, food availability has been suggested as the main driver of phenotypic variability in adult size if the range of temperature change is less than 14°C. <i>Leptodiaptomus garciai</i> is a calanoid copepod inhabiting Lake Alchichica, a monomictic, tropical lake in Mexico that experiences regular, narrow temperature fluctuations but wide changes in phytoplankton availability. We investigated whether the seasonal fluctuations of temperature and food produce phenotypic variation in the life-history traits of this tropical species. We sampled <i>L</i>. <i>garciai</i> throughout a year and measured female size, egg size and number, and hatching success, along with temperature and phytoplankton biomass. The amplitude of the plastic responses was estimated with the Phenotypic Plasticity Index. This index was also computed for a published dataset of 84 copepod populations to look if there is a relationship between the amplitude of the phenotypic plasticity of adult size and seasonal change in temperature. The temperature annual range in Lake Alchichica was 3.2°C, whereas phytoplankton abundance varied 17-fold. A strong pattern of thermal plasticity in egg size and adult female size followed the inverse relationship with temperature commonly observed in temperate environments, although its adaptive value was not demonstrated. Egg number, relative reproductive effort and number of nauplii per female were clearly plastic to food availability, allowing organisms to increase their fitness. When comparing copepod species from different latitudes, we found that the magnitude of thermal plasticity of adult size is not related to the range of temperature variation; furthermore, thermal plasticity exists even in environments of limited temperature variation, where the response is more intense compared to temperate populations.</p></div

Correlation coefficients and associated probabilities for the relationship between the index of phenotypic plasticity (PPI) for adult female size and latitude and thermal variables.

<p>Correlation coefficients and associated probabilities for the relationship between the index of phenotypic plasticity (PPI) for adult female size and latitude and thermal variables.</p

Temporal course of life-history traits of <i>L</i>. <i>garciai</i> in Lake Alchichica.

<p>Average proportion of eggs that hatched from a given egg sac and the average number of nauplii produced for each female. Vertical bar show ± one standard deviation.</p

Phylogenetic tree of the 85 copepod species included in the global analysis of phenotypic plasticity of female size.

<p>This phylogeny was assembled using diverse sources and was used to perform phylogenetically informed contrasts.</p

Phenotypic plasticity of female weight across a latitudinal range.

<p>a) Dispersion plot of the Phenotypic Plasticity Index (PPI) for adult female weight of 85 copepod populations (marine and lacustrine species) vs. the absolute latitude of their respective locations. b) Dispersion plot of the PPI for adult female weight of the same copepod populations vs. the TAR of their respective locations. c) Dispersion plot of the intensity of phenotypic expressed as % of change in biomass per °C (PPI/°C) vs. TAR, for the same populations. Open square: <i>L</i>. <i>garciai</i>; open circles: tropical populations; closed circles: temperate populations. Data were obtained from several sources, see details in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0196496#sec002" target="_blank">Methods</a>.</p

Relationships among the life-history traits of <i>L</i>. <i>garciai</i> in Lake Alchichica.

<p>Each point represents the population average at a given month. Probability and <i>r</i> coefficient values correspond to Pearson’s correlation tests; a significant negative correlation between two variables shows a potential functional trade-off. Open circles correspond to the left axis. RE, reproductive effort; RRE, relative reproductive effort (see text for further details).</p