International Rotifer Symposia: prospects and retrospects from Rotifera XI

The XI International Rotifer Symposium was held during 11–18 March, 2006 at the National Autonomous University of Mexico Campus Iztacala located at the North Mexico City (Mexico). These triennial international meetings, first organized in Austria by Late Ruttner-Kolisko in September 1976, are gradually becoming the focal point of discussion and collaboration from rotifer workers across the world. The present XI symposium was attended by 125 participants from 20 nations. During this meeting, different themes of rotifer research from morphology to molecular biology were considered. In addition, there were four invited lectures and four workshops covering different themes of the symposium. During the last 30 years, rotifer research has witnessed gradual shift from the conventional morphological taxonomy to molecular and evolutionary systematics. While the basic rotifer ecological studies continue today, applied areas such as ecotoxicology and aquaculture have taken key roles in the recent meetings. The international rotifer meetings provide ample opportunities not only for exchange of ideas and recent research, but also for material and in establishing inter-personal relationships. Over the last 30 years, the number of participants attending the rotifer meetings has increased

Effect of salinity stress on the life history variables of Branchipus schaefferi Fisher, 1834 (Crustacea: Anostraca)

BACKGROUND: Freshwater anostracans inhabit ephemeral water bodies in which as the water level decreases due to evaporation the salt concentration increases. Thus, for most anostracans salinity becomes the major stress factor. RESULTS: We tested five concentrations of NaCl (0 to 8 g/l) on the life table demography of Branchipus schaefferi fed Chlorella (alga). Age-specific survivorship curves of male and female B. schaefferi showed nearly a similar pattern in that increased salt concentration resulted in decreased survivorship. The age-specific reproduction (m(x)) of females showed several peaks of cyst production at 0 and 1 g/l salinity while in treatments containing salt at 4 or 8 g/l, there were fewer peaks. Average lifespan, life expectancy at birth, gross and net reproductive rates, generation time and the rate of population increase were all significantly influenced by the salt concentration in the medium. The highest value of net reproductive rate (970 cysts/female) was in treatments containing 0 g/l of salt, while the lowest was 13 cysts/female at 8 g/l. The rate of population increase (r) varied from 0.52 to 0.32 per day depending on the salt concentration in the medium. CONCLUSION: The low survival and offspring production of B. schaefferi at higher salinity levels suggests that this species is unlikely to colonize inland saline water bodies. Therefore, the temporary ponds in which it is found, proper conservative measures must be taken to protect this species

Effect of cyanobacterium on competition between rotifers: a population growth study

We determined the population growth of Plationus patulus and Brachionus havanaensis grown alone or together (1:1 ratio) on different feeds of solely Chlorella, solely Anabaena, or their mixture at a level of 1 × 106 cells mL-1 for all diets. Our results showed that regardless of diet, population densities of B. havanaensis were higher than those of P. patulus. For both rotifer species, Anabaena caused extinction of populations, regardless whether offered alone or in combination with the green alga. In mixed rotifer cultures, the peak densities of P. patulus or B. havanaensis were much lower than when cultured alone. Rate of population increase (r) of P. patulus fed Chlorella was significantly lower (0.12 d-1; p < 0.001) than for B. havanaensis (0.19 d-1) grown under similar conditions. Growth rates of both rotifers fed Anabaena (alone or together with Chlorella) became significantly lower than when fed solely Chlorella. Thus, our results showed that P. patulus and B. havanaensis have similar sensitivities to Anabaena, with both species failing to grow when this cyanobacterium was included in the diet

Diversity and abundance of rotifers during an annual cycle in the reservoir Valerio Trujano (Tepecoacuilco, Guerrero, Mexico)

We analyzed the diversity and density of monogonont rotifers collected from 10 sites, 5 in the littoral zone and 5 in the pelagic zone, during a 1-year period from March 2010 to April 2011 in the reservoir Valerio Trujano, altitude 820 m a.s.l. (Tepecoacuilco de Trujano, State of Guerrero, Mexico). We also measured physicochemical variables such as temperature, pH, hardness, nitrates, and phosphates. The rotifers were identified to species level and quantified using a Sedgwick-Rafter chamber. We found 62 species belonging to 28 genera and 19 families, representing 22% of total species reported for Mexico. The most abundant species were Brachionus caudatus, B. falcatus, Horaëlla thomassoni, Filinia longiseta, Conochilus dossuarius, and Keratella cochlearis. The highest rotifer densities were those of B. caudatus (around 300 ind. L-1) in June and July. The common phytoplankton genera were Pediastrum, Cosmarium, Closterium, Nitzschia, Suriella, Microcystis, Oscillatoria, and Merismopedia. The species diversity of Rotifera in the reservoir ranged from 1.3 to 3.2 in both the littoral and the pelagic regions. The saprobic index varied from 1.2 to 2 in the pelagic and 1.4 to 2.1 in the littoral region of the reservoir. Nutrient levels and indicator species (Brachionus and Trichocerca) showed that the reservoir, which was nitrogen rather than phosphorus limited, is eutrophic and moderately polluted by organic matter

Effect of food density of Pseudokirchneriella subcapitata and Chlorella vulgaris on the population growth rates of four brachionid rotifers

We conducted population growth experiments for 2–4 weeks using 4 species of brachionid rotifers (Brachionus angularis, B. havanaensis, B. rubens, and Plationus patulus), all isolated from Lake Xochimilco, Mexico City, Mexico. The test rotifers were fed 2 species of green algae (Chlorella vulgaris and Pseudokirchneriella subcapitata) at 3 food concentrations (2.9, 5.8, and 11.6 µg dry weight mL−1) for 24 h. Regardless of algal species, the population density of all 4 rotifer species increased with increasing food density; however, the magnitude of growth rate response of the rotifers differed. At comparable food levels, B. havanaensis had far greater abundances in 3 weeks than the other 3 rotifer species. At a concentration of 2.9 µg mL−1 of C. vulgaris, density of B. angularis was about 50 ind. mL−1, but when the food was enhanced to 11.6 µg mL−1, its population was 3 times higher; similar values were obtained when B. angularis was fed P. subcapitata. In comparison, B. havanaensis fed P. subcapitata at the highest food level had population abundances of about 900 ind. mL−1; at the same food level, when fed C. vulgaris, the density was much lower (250 ind. mL−1). Population abundances of B. rubens fed P. subcapitata were, in general, lower than those fed C. vulgaris. This was also the trend for rotifer P. patulus, which had lower abundances when fed P. subcapitata than when fed C. vulgaris. Regardless of food type and concentration, the rate of population increase per day (r) of the tested rotifer species varied from 0.16 to 0.61 d−1

The Lesser Known Challenge of Climate Change: Thermal Variance and Sex-Reversal in Vertebrates with Temperature-Dependent Sex Determination

Climate change is expected to disrupt biological systems. Particularly susceptible are species with temperature-dependent sex determination (TSD), as in many reptiles. While the potentially devastating effect of rising mean temperatures on sex ratios in TSD species is appreciated, the consequences of increased thermal variance predicted to accompany climate change remain obscure. Surprisingly, no study has tested if the effect of thermal variance around high-temperatures (which are particularly relevant given climate change predictions) has the same or opposite effects as around lower temperatures. Here we show that sex ratios of the painted turtle (Chrysemys picta) were reversed as fluctuations increased around low and high unisexual mean-temperatures. Unexpectedly, the developmental and sexual responses around female-producing temperatures were decoupled in a more complex manner than around male-producing values. Our novel observations are not fully explained by existing ecological models of development and sex determination, and provide strong evidence that thermal fluctuations are critical for shaping the biological outcomes of climate change

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)

Climate change and freshwater zooplankton: what does it boil down to?

Recently, major advances in the climate–zooplankton interface have been made some of which appeared to receive much attention in a broader audience of ecologists as well. In contrast to the marine realm, however, we still lack a more holistic summary of recent knowledge in freshwater. We discuss climate change-related variation in physical and biological attributes of lakes and running waters, high-order ecological functions, and subsequent alteration in zooplankton abundance, phenology, distribution, body size, community structure, life history parameters, and behavior by focusing on community level responses. The adequacy of large-scale climatic indices in ecology has received considerable support and provided a framework for the interpretation of community and species level responses in freshwater zooplankton. Modeling perspectives deserve particular consideration, since this promising stream of ecology is of particular applicability in climate change research owing to the inherently predictive nature of this field. In the future, ecologists should expand their research on species beyond daphnids, should address questions as to how different intrinsic and extrinsic drivers interact, should move beyond correlative approaches toward more mechanistic explanations, and last but not least, should facilitate transfer of biological data both across space and time