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)

Life-Cycle Switching and Coexistence of Species with No Niche Differentiation

The increasing evidence of coexistence of cryptic species with no recognized niche differentiation has called attention to mechanisms reducing competition that are not based on niche-differentiation. Only sex-based mechanisms have been shown to create the negative feedback needed for stable coexistence of competitors with completely overlapping niches. Here we show that density-dependent sexual and diapause investment can mediate coexistence of facultative sexual species having identical niches. We modelled the dynamics of two competing cyclical parthenogens with species-specific density-dependent sexual and diapause investment and either equal or different competitive abilities. We show that investment in sexual reproduction creates an opportunity for other species to invade and become established. This may happen even if the invading species is an inferior competitor. Our results suggests a previously unnoticed mechanism for species coexistence and can be extended to other facultative sexual species and species investing in diapause where similar density-dependent life-history switches could act to promote coexistence

Ocorrência de Scapholeberis armata freyi Dumont & Pensaert (Crustácea, Anomopoda, Daphniidae) no estado de São Paulo, Brasil Occurrence of Scapholeberis armata freyi Dumont & Pensaert (Crustácea, Anomopoda, Daphniidae) in São Paulo State, Brazil

<abstract language="eng">For the first time, Scapholeberis armata freyi Dumont & Pensaert, 1983 is registered in São Paulo State. The previously suggested occurrence of this species in Brazil is confirmed

A re-evaluation of the <i>Macrothrix rosea-triserialis</i> group, with the description of two new species (Crustacea Anomopoda: Macrothricidae)

We redescribe Macrothrix rosea (females and males) based on material collected in Belgium. We also compare seven populations of Macrothrix `triserialis' from different parts of the world, including a topotypical population of M. triserialis s. str. from Sri Lanka, and males from South India (here first described), relying heavily on the structure of the trunk limbs, beside classical features of morphology. M. rosea and M. triserialis are extremely closely related: males are easily separated, but the identification of females requires micro-characters such as the relative length of the apical segment of the setae natatoriae and the adornment of the first antenna and of the longest swimming seta of the antenna. M. rosea and triserialis together constitute a sub-group of the rosea-group. Macrothrix triserialis-like animals occur in the tropical–subtropical belts of four continents. We compare populations from Asia, South America and Africa, and find differences in microcharacters of the trunk limbs, but cannot decide whether these represent random variation or sound taxonomical differences.One of the basic characters of the Macrothrix rosea-triserialis subgroup is that the setae natatoriae of the postabdomen are implanted on a prominence, the `heel'. Other characters include the fact that the Fryer' forks are adorned with one or two big teeth only, and that the scrapers of trunk limb two form a row of eight without any doublings. Possibly, scraper five, and scraper four to a lesser degree has an enlarged subapical tooth. The exopodite of trunk limb three has four plumose setae, the back and front row of the endopodite six setae and/or receptors, the exopodite of trunk limb four has two setae, and the back row of the endopodite six setae, plus one on the gnathobase. The pre-epipodite of trunk limb five consists of three lobes, the `endopodite' is small, and the `exopodite' is reduced to a single seta. The male postabdomen has a tubular ending, without true end-claws, although a rudiment of an end-claw is seen in M. triserialis.Two new species are described: M. tabrizensis and M. agsensis. A comparison, including the males of Macrothrix triserialis, M. rosea, M. smirnovi and M. tabrizensis confirms the relationship of all these taxa, but also reveals a morphological series in the shape of the postabdomen, from a complete absence of end-claws, over rudiments of a pair of end-claws, to complete endclaws. Absence of end-claws is here considered to represent an evolved character state. Macrothrix smirnovi Ciros & Elías (1987) is less closely related to the rosea-triserialis group, and is considered to form a sub-group in its own right. It shows a short `heel' on the postabdomen, but carries a supplementary seta behind scraper 4 of the endopodite of trunk limb two, and has a male with a postabdomen that closely resembles that of the female. These are primitive characters, which are also found in Wlassicsia, Bunops and Onchobunops and provide a possible phylogenetic link between Macrothrix and these three genera, although the genetic distance between them is considered to be quite large