Extensive studies of vertebrates have shown that brain size scales to body size following power law functions. Most animals are substantially smaller than vertebrates, and extremely small animals face significant challenges relating to nervous system design and function, yet little is known about their brain allometry. Within a well-defined monophyletic taxon, Formicidae (ants), we analyzed how brain size scales to body size. An analysis of brain allometry for individuals of a highly polymorphic leaf-cutter ant, Atta colombica, shows that allometric coefficients differ significantly for small (<1.4 mg body mass) versus large individuals (b = 0.6003 and 0.2919, respectively). Interspecifically, allometric patterns differ for small (<0.9 mg body mass) versus large species (n = 70 species). Using mean values for species, the allometric coefficient for smaller species (b = 0.7961) is significantly greater than that for larger ones (b = 0.669). The smallest ants had brains that constitute ∼15% of their body mass, yet their brains were relatively smaller than predicted by an overall allometric coefficient of brain to body size. Our comparative and intraspecific studies show the extent to which nervous systems can be miniaturized in taxa exhibiting behavior that is apparently comparable to that of larger species or individuals.

Introduction: Although a large part of the population may be exposed to various pressures that can lead to mental or eating problems and increased perceived stress, the transition from adolescence to adulthood has been shown to be a crucial stage. Medical students are particularly vulnerable during the transition period as they must adapt to new circumstances, which may contribute to increased perceived stress. Cortisol plays an important role between stress, weight gain, and the development of obesity. We designed a study to investigate the association between stress, eating behaviour, cortisol, and body weight in a sample of first-year medical students.Methods: We determined 75 first-year medical students' hair and salivary cortisol concentrations by ELISA and related it to self-reported stress, eating behaviour, and anthropometric measurements throughout the academic period. The prevalence of overweight and obesity in females was 25% and 10%, and in males was 35% and 6%, respectively. We report an increase in hair cortisol, higher self-reported stress scores, and BMI mainly in females. Finally, we found evidence of positive associations between hair cortisol and BMI in females (r = 0.348) and males (r = 0.423).Conclusion: There is a low association between short-term single-point cortisol measures and long-term cortisol, mainly in males. Hence, short-term cortisol reactivity is moderately associated with long-term cortisol reactivity when both are evaluated simultaneously. These results support the previous evidence of positive associations between cortisol with body fat percentage and BMI, and finally, that eating behaviours are modified by academic stress perception, mainly in females.

While a great deal of research has been conducted to identify the biotic mechanisms influencing the co-occurrence of aquatic Ae. aegypti and Ae. albopictus mosquitoes, including inter-specific larval competition and mating interference, few studies have been completed to investigate their oviposition behaviors under co-occurrence scenarios. Herein, we performed three experiments to understand the influence of conspecific and heterospecific L4-larvae presence in oviposition by antagonist Aedes spp. mosquitoes. We compared egg counts of Ae. aegypti and Ae. albopictus in cups with water and conspecific or heterospecific larvae (either present or removed), or no larvae as control. In the first experiment, we used small cages; in the second experiment, we used larger cages increasing the number of treatment replicates per cage; and in the third experiment, we removed larvae before allowing gravid females to oviposit. In experiments 1 and 2, Ae. aegypti laid more eggs in conspecific cups, while Ae. albopictus distributed eggs evenly between conspecific and heterospecific cups, and both species laid fewer eggs in controls. In these experiments, more eggs were laid during the first 24 h. In experiment 3, both species laid more eggs in conspecific larvae-conditioned water as compared to controls in the first 24 h; however, in Ae. Aegypti, this inclination was lost with time. Our results suggest that co-occurrence of Ae. aegypti and Ae. albopictus may be explained by Ae. aegypti’s ability to avoid oviposition in habitats colonized by heterospecific L4-larvae. Yet chemical cues in conspecific L4-larvae-conditioned water were insufficient to replicate this behavior, and therefore, additional cues may be involved.

Reversible decreases in synaptic strength, known as short-term depression (STD), are widespread in neural circuits. Various computational roles have been attributed to STD but these tend to focus upon the initial depression rather than the subsequent recovery. We studied the role of STD and recovery at an excitatory synapse between the fast extensor tibiae (FETi) and flexor tibiae (flexor) motor neurons in the desert locust (Schistocerca gregaria) by making paired intracellular recordings in vivo. Over behaviorally relevant pre-synaptic spike frequencies, we found that this synapse undergoes matched frequency-dependent STD and recovery; higher frequency spikes that evoke stronger, faster STD also produce stronger, faster recovery. The precise matching of depression and recovery time constants at this synapse ensures that flexor excitatory post-synaptic potential (EPSP) amplitude encodes the presynaptic FETi interspike interval (ISI). Computational modelling shows that this precise matching enables the FETi-flexor synapse to linearly encode the ISI in the EPSP amplitude, a coding strategy that may be widespread in neural circuits.

Panama has a large number of wild animal species, which could host a highly diverse amount of genetic variants of Toxoplasma gondii (T. gondii). In this context, we highlight the importance of understanding the population structure of T. gondii in Panamanian wildlife and the genetic variants that can be rapidly transferred to domestic environments. This study analyzed the infection frequency and allelic composition of T. gondii in different tissue samples from wild animals. The infection frequency was measured by the PCR technique using the B1 gene as a molecular marker. The results showed a high frequency (65.6%) of infection in tissue samples collected from 221 wild animals. Stratified analyses for bird and mammal samples showed positivity rates of 67.2% and 70.12%, respectively, with no statistically significant differences. Infection frequency was also measured in five types of organs (brain, liver, heart, lung, and skeletal muscle), which showed homogeneous frequencies. The genetic diversity of the T. gondii population contained in the tissues of wild animals was analyzed by the Multilocus Polymerase Chain Reaction-Restriction Fragment Length Polymorphism (PCR-RFLP) technique, using five genes called SAG1, SAG2, SAG3, GRA6, and Apico. This analysis revealed the presence of alleles of these genes corresponding to T. gondii lineages I, II, and III. Allele III was only identified with the Apico gene in a single reptile individual analyzed. Our findings indicated diverse allelic distribution at the analyzed loci, suggesting that the tissues were probably infected by non-archetypal individuals of T. gondii.