Jorge Ciros-Pérez

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

Abstract 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).

Resource competition and patterns of sexual reproduction in sympatric sibling rotifer species

Abstract. We present experimental data on the reproduction patterns of three sympatric sibling rotifer species, belonging to the Brachionus plicatilis complex, as they compete for food. Variation existed in the amount and pattern of sexual reproduction among the three cyclical parthenogenetic species. Competitive exclusion between the three Brachionus species was related to a higher investment in sexual reproduction by the inferior competitor. In general, no correlation was found between sexual reproduction and population density in a given species. However, when pairs of competing species were compared, a negative relationship between sexual investment differences (between species) and average population density differences was frequently found. From the results we conclude that: (1) the characteristic sexual pattern of each species has some implications for the competitive outcome; (2) allocation of resources into sexual reproduction does not mediate coexistence; and (3) the response of sexual reproduction to competitive interaction is unlikely to determine competition outcome. Nevertheless, our results suggest that the competitively inferior species invests more in sexual reproduction, as a response to resource limitation, which would accelerate its exclusion.

Additions to Mexican freshwater copepods with the description of the female Leptodiaptomus mexicanus (Marsh)

A survey on 10 temporary and permanent water-bodies, located at more than 2000 m above the sea level in the central part of Mexico resulted in the presence of 17 cyclopoid and five calanoid copepods. From the total taxa found, seven are new to the country: Leptodiaptomus assiniboiaensis (Anderson), Microcyclops dubitabilis Kiefer, Ectocyclops rubescens Brady, Eucyclops cf. bondi Kiefer, Eucyclops cf. prionophorus Kiefer, Eucyclops pseudoensifer Dussart, and Eucyclops cf. solitarius. The female of Leptodiaptomus mexicanus, a species known only from a single male found near Mexico City in 1929, is here described for the first time. Copepod fauna for each of the systems was highly diverse, with up to 12 species co-occurring in temporary ponds. This study revealed a mixture of north and south American taxa in the area.

A checklist of the littoral cladocerans from Mexico, with descriptions of five taxa recently recorded from the Neovolcanic Province

By 1996 an inventory of Mexican cladocerans hadrecorded 48 species of which 22 belonged toChydoridae, Macrothricidae and Ilyocryptidae.Unfortunately, most of the surveys were made beforeresearchers knew that these crustaceans are notentirely cosmopolitan. For this reason and the lack ofdeposited type material, many of these records aredoubtful and need detailed analyses. In this study,material from 18 water bodies located in theNeovolcanic Province of Mexico is analyzed andcompared with the literature. Also, males of Camptocercus dadayi Stingelin and Leydigialeydigi (Schoedler) and new records Eurycercus longirostris Hann and Biaperturaintermedia (Sars) are described. Half of thetotal number of species recorded are American endemicsand represents a mixture of the North and SouthAmerican fauna, suggesting that Mexico constitutes atransition between Nearctic and Neotropicalzones.

Spinalona anophtalma, n. gen. n. sp. (Anomopoda, Chydoridae) a blind epigean cladoceran from the Neovolcanic Province of Mexico

Spinalona anophtalma n. gen. n. sp. is describedon parthenogenetic and ephippial females andmales from material collected in a temporary lagoonlocated in the Neovolcanic Province from Mexico at analtitude of 2507 m above sea level. It ischaracterized by a strong armature of the antenna,postabdomen and postabdominal claw, no compound eyeor ocellus, the exopod of thoracic limb IIIwith only four setae and that of P5 with only three setae.This new taxon has no relationwith blind Alona from hypogean habitats.

The Structure of the Zooplankton Assemblages from Two Neighboring Tropical High Mountain Lakes

ABSTRACT We studied the zooplankton of two tropical high mountain lakes—Lake El Sol and Lake La Luna—located inside a volcano in central Mexico. A total of 35 taxa was recorded (two copepods, four cladocerans and 29 rotifers). Species richness was higher than that reported in high mountain lakes in temperate regions and even from other tropical systems. Aspelta psitta, Hexarthra bulgarica canadensis, Cephalodella delicata, and Alonella pulchella were recorded for the first time in Mexico. Although there was a high coincidence in species composition, the lakes displayed large differences in dominant taxa, density, and biomass. Seasonal dynamics of zooplankton taxa in both systems were rather comparable to those reported for temperate high mountain lakes. This pattern likely reflected a cold-dry period when abiotic factors (mainly temperature and pH) regulated the assemblage and a warm-rainy period that was regulated by biotic factors. Our results suggest that most important biotic dissimilarities observed between these two neighboring lakes were due to abiotic environmental conditions (mainly pH); however, we suggest that the relatively recent introduction of fish in one of these lakes has magnified the differences between them.

From Local Adaptation to Ecological Speciation in Copepod Populations from Neighboring Lakes

Continental copepods have been derived from several independent invasive events from the sea, but the subsequent evolutionary processes that account for the current diversity in lacustrine environments are virtually unknown. Salinity is highly variable among lakes and constitutes a source of divergent selection driving potential reproductive isolation. We studied four populations of the calanoid copepod Leptodiaptomus cf. sicilis inhabiting four neighboring lakes with a common history (since the Late Pleistocene) located in the Oriental Basin, Mexico; one lake is shallow and varies in salinity periodically (1.4–10 g L-1), while three are deep and permanent, with constant salinity (0.5, 1.1 and 6.5 g L-1, respectively). We hypothesized that (1) these populations belong to a different species than L. sicilis sensu stricto and (2) are experiencing ecologically based divergence due to salinity differences. We assessed morphological and molecular (mtDNA) COI variation, as well as fitness differences and tests of reproductive isolation. Although relationships of the Mexican populations with L. sicilis s.s. could not be elucidated, we identified a clear pattern of divergent selection driven by salinity conditions. The four populations can still be considered a single biological species (sexual recognition and hybridization are still possible in laboratory conditions), but they have diverged into at least three different phenotypes: two locally adapted, specialized in the lakes of constant salinity (saline vs. freshwater), and an intermediate generalist phenotype inhabiting the temporary lake with fluctuating salinity. The specialized phenotypes are poorly suited as migrants, so prezygotic isolation due to immigrant inviability is highly probable. This implication was supported by molecular evidence that showed restricted gene flow, persistence of founder events, and a pattern of allopatric fragmentation. This study showed how ecologically based divergent selection may explain diversification patterns in lacustrine copepods.

Littoral zooplankton–water hyacinth interactions: habitat or refuge?

Abstract Water hyacinth (Eichhornia crassipes) is one of the most problematic invasive macrophyte in the world. Although it has become a key element of the systems where it was introduced several decades ago, there is insufficient information to determine its role on biological interactions. To elucidate water hyacinth–littoral zooplankton–planktivorous fish interactions, we conducted habitat choice experiments in the absence and presence of fish chemical cues (kairomones) for two tropical littoral cladocerans, Chydorus brevilabris and Simocephalus vetulus. We classified habitat selection as a habitat (preference for the plant without predation risk) and/or as a refuge (preference for the plant with predation risk). Our results showed that E. crassipes is used as a habitat by C. brevilabris and as a refuge by S. vetulus against fish predation. Although C. brevilabris did not use the water hyacinth as a refuge in the presence of kairomones, the results suggested that both C. brevilabris and S. vetulus exhibited behavioral responses that further reduced their predation risk. To our knowledge, this study is the first experimental evidence for littoral cladocerans using free-floating macrophytes as a refuge against fish predation in tropical systems. Our results support the assertion that habitat association is not necessarily an evidence of habitat preference.

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

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. Leptodiaptomus garciai 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 L. garciai 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.