BackgroundThe freshwater calanoid Mastigodiaptomus is a genus with high richness in the Americas and is composed of nine species, seven recorded in Mexico and four that are apparently endemic to small areas. Mastigodiaptomus albuquerquensis is a common, widely distributed species ranging from the southern USA to Central America. This species can be easily identified by a notable butterfly-like sclerotization on the basis of the right fifth leg of males. Nevertheless, morphological differences observed among populations throughout this species distributional range have led to the description of several related species or subspecies, such as M. albuquerquensis patzcuarensis from Lake Pátzcuaro in the Central Plateau of Mexico.MethodsGenetic results based on barcodes, morphology based on scanning electron and light microscopy images, and morphometric analyses were used to describe cryptic species within the M. albuquerquensis complex.ResultsThe morphological analyses coincided partially with the genetic markers, suggesting the existence of at least two sibling species: M. albuquerquensis s. str. and M. patzcuarensis. A third species was genetically separated but was morphologically indistinguishable from the M. patzcuarensis group.ConclusionsHidden diversity has been a major problem in establishing real patterns of species distribution and genetic acquisition from megadiverse hotspots such as Mexico, where the Nearctic and the Neotropical regions of the Americas meet. Barcodes can help taxonomists to reveal and formally name these new species. Here, we describe two of three potential species highlighted by the use of barcodes: M. albuquerquensis s. str. in the northern semi-desert and M. patzcuarensis on the Central Plateau at more than 2000 m above sea level.

Background In Mexico, species of four families of free-living calanoid copepods have been recorded as inhabitants of several freshwater systems. These families are Centropagidae, Temoridae, Pseudodiaptomidae and Diaptomidae. The genera Leptodiaptomus and Mastigodiaptomus are the most speciose diaptomid genera in Mexico, and they inhabit natural and artificial lakes, ephemeral ponds, springs, and caverns. Leptodiaptomus is considered as an endemic Nearctic genus, whereas Mastigodiaptomus is a widely distributed Neotropical genus in the southern USA, Mexico, the Caribbean Islands and Central America. Based on new and recent evidence, Mastigodiaptomus diversity has been underestimated: six species of the genus were known before 2000. In this work three new Mastigodiaptomus species have been described from different regions of Mexico by using integrative taxonomy. We also gave amended diagnosis of M. nesus Bowman (1986) and M. patzcuarensis s. str. (Kiefer, 1938). Methods In this work, the taxonomic status of the species was clarified using modern, integrative method based on the COI gene as a DNA marker, plus micro-structural analysis (based on SEM and ligth microscopy). Results Three new species of Mastigodiaptomus were described based on genetic and morphological analyses: M. alexei sp. n., M. ha sp. n. and M. cihuatlan sp. n. Also amended description of M. nesus, morphological variation of M. patzcuarensis s. str., and a comparison of them with all known sequences within the genus are provided. These new findings show that in Mastigodiaptomus differences in several cuticular microstructures of several appendages (such as the antennules, the fifth legs, or the urosomites of these copepods) agree with the interspecific genetic divergence >3% observed in sequences of the COI gene, and the integration of this information is a powerful tool in species delineation.

The During the annual cycle studied in the meso-eutrophic system, the key environmental parameters related to plankton abundance were pH and temperature whereas in the oligotrophic system, oxygen concentration was important. In both lakes, richness and diversity were related to conductivity, although in the oligotrophic lake the relation was negative whereas in the meso-eutrophic lake it was positive. No relationship was found between the abundance of the studied predator (Chaoborus sp.) and the changes in the abundance, diversity and richness of zooplankton in the systems.

Samples collected from ponds in central Mexico contained male and female specimens of the harpacticoid copepod Elaphoidella grandidieri (Guerne & Richard, 1893). Field-collected ovigerous females were transported to the laboratory where several isofemale lines were established. Cultures were established from a single female and maintained on a mono-algal diet in moderately hard water. Specimens of both sexes, particularly the less known males, were analysed morphologically and compared with records from different geographical regions. Differences among these populations are subtle and not geographically consistent. Variations were found in the relative length of setal elements and ornamentations of swimming legs 1, 2, and 4, the proportions and armature of the exopod of the female leg (P) 5, among other characters. The specimens from Mexico have 1-2 long spines near the posteroventral margin of the anal somite; this character has been described only from a North African population. Our analysis supports the notion that this widespread pantropical species shows a considerable degree of variability in various characters. Since a clonal population of this parthenogenetic species could be established, molecular techniques are recommended to evaluate this variability and determine if E. grandidieri represents a species complex with morphologically similar taxa. The finding of E. grandidieri as an harpacticoid with high reproductive rates suggests that this copepod has an outstanding potential in aquaculture. RÉSUMÉ Des échantillons collectés dans des mares du centre du Mexique contenaient des spécimens mâles et femelles du copépode harpacticoïde Elaphoidella grandidieri

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