Assessment of cardiotoxicity and effects of malathion on the early development of zebrafish (Danio rerio) using computer vision for heart rate quantification.

Malathion, a common organophosphate insecticide, is a proven acetylcholinesterase inhibitor and is the most applied organophosphate insecticide in the United States. The use of zebrafish as a model to study the effects of pesticides on development is an innovative approach yielding relevant implications for determining the potential toxic effects of these pesticides on humans. In this study, a simple noninvasive technique was developed to investigate the cardiotoxicity of malathion on Danio rerio embryos, and to detect and quantify its effect on heart rate. Videos were recorded under a stereomicroscope and examined with our custom-made software (FishBeat) to determine the heart rate of the embryos. The pixel average intensity frequency (PI) of the videos was computed at its maximum probability to indicate the average number of heartbeats per second. Experimental observations successfully demonstrated that this method was able to detect the heart rate of zebrafish embryos as compared with manual stopwatch counting, with no significant difference. Embryos were treated acutely with increasing malathion concentrations (33.3 and 50 µg/mL malathion) at 52, 76, and 96 hpf. Embryos treated with 33.3 µg/mL malathion had significant bradycardia at 52 and 76 hpf, whereas embryos treated with 50 µg/mL malathion presented bradycardia at all hpf. These novel observations confirmed that malathion, acting as an acetylcholinesterase inhibitor, induced heartbeat irregularity in zebrafish embryos.

Qualitative comparison of the cranio-dental osteology of the extant elephants, Elephas Maximus (Asian elephant) and Loxodonta africana (African elephant).

Few osteological descriptions of the extant elephants and no detailed morphological comparison of the two genera, Elephas and Loxodonta, have been done in recent years. In this study, 786 specimens of extant elephants (crania, mandibles, and molars) were examined for characters unique to each species. Differences between sexes in each species were described, as well as differences between subspecies of each species. Striking differences in morphology were noted between sexes of both elephants and between subspecies, which may complement current genetic studies, the focus of which is to determine division at the subspecies or species level, particularly differences between the savanna elephant (Loxodonta africana africana) and the forest elephant (Loxodonta africana cyclotis). In addition, examination of the two living elephants provides an excellent dataset for identifying phylogenetic characters for use in examining evolutionary relationships within and between fossil lineages of elephantids.

New phylogenetic analysis of the family elephantidae based on cranial-dental morphology.

In 1973, Vincent Maglio published a seminal monograph on the evolution of the Elephantidae, in which he revised and condensed the 100+ species named by Henry Fairfield Osborn in 1931. Michel Beden further revised the African Elephantidae in 1979, but little systematic work has been done on the family since this publication. With addition of new specimens and species and revisions of chronology, a new analysis of the phylogeny and systematics of this family is warranted. A new, descriptive character dataset was generated from studies of modern elephants for use with fossil species. Parallel evolution in cranial and dental characters in all three lineages of elephants creates homoplastic noise in cladistic analysis, but new inferences about evolutionary relationships are possible. In this analysis, early Loxodonta and early African Mammuthus are virtually indistinguishable in dental morphology. The Elephas lineage is not monophyletic, and results from this analysis suggest multiple migration events out of Africa into Eurasia, and possibly back into Africa. New insight into the origin of the three lineages is also proposed, with Stegotetrabelodon leading to the Mammuthus lineage, and Primelephas as the ancestor of Loxodonta and Elephas. These new results suggest a much more complex picture of elephantid origins, evolution, and paleogeography.

Effects of Sevin (carbaryl insecticide) on early life stages of zebrafish (Danio rerio).

Sevin brand carbaryl insecticide is one of the most commonly used insecticides in the United States, with great potential for leaching into ground- and surface water reserves. Its possible teratogenic effects were tested on zebrafish eggs in four dilutions of decreasing concentration. The average mortality rate was low, indicating that Sevin does not directly kill embryos at these concentrations. Eggs and embryos were consistently smaller than the control starting at 24 h after spawning until hatching. Embryos in the highest concentration took up to twice as long to hatch as the control. This delayed hatching time increases vulnerability to predation. In addition, as minnows are lower on the food chain, bioaccumulation of Sevin in tissues may increase in larger predators, affecting their metabolism and reproduction.