Ontogenetic skull variation in an Amazonian population of lowland tapir, Tapirus terrestris (Mammalia: Perissodactyla) in the department of Loreto, Peru

ABSTRACT The skulls of 54 specimens of the South American tapir, Tapirus terrestris collected in the department of Loreto, Peru were measured, analyzed and compared to investigate skull development of this species. Univariate, multivariate and allometric analyses were performed using 32 skull variables through traditional morphometrics. Significant skull shape variation was detected among ontogenetic classes. Young individuals (class I, n = 22) showed higher variation than subadults and adults (class II, n = 23 and class III, n = 9), without evidence of sexual dimorphism (males = 35, females = 19). Principal component analyses and discriminant function analysis showed almost complete separation of the age classes. Allometric analysis indicated a tendency of unproportioned cranial growth. All our samples come from the same population living under the same ecological condition, which eliminates the effect of confounding variables related to habitat on the pattern of ontogenetic variation of this anatomical structure.

Mapping and Estimation of Above-ground Grass Biomass using Sentinel 2A Satellite Data

Above-Ground Grass Biomass (AGGB) mapping and estimation is one of the important parameters for environmental ecosystem and grazing-lands management, particularly for livestock farming. However, previous models for estimation of AGGB with satellite imagery has some difficulty in choosing a particular satellite and vegetation index that can build a good estimation model at a higher accuracy. This study explores the potentiality of Sentinel 2A data to derive a satellite-based model for AGGB mapping and estimation. The study area was Skudai, Johor in Malaysia Peninsular. Grass parameters of forty grass sample units were measured in the field and their corresponding AGGB was later measured in the laboratory. The samples were used for modelling and assessment. Four indices were tested for their fitness in modelling AGGB from the satellite data. The result from the grass allometric analysis indicates that grass height and volume demonstrate good relationship with the measured AGGB (R² = 0.852 and 0.837 respectively). Vegetation Index Number (VIN) has the best fit for modeling AGGB (R2 = 0.840) compared to other vegetation indices. The derived satellite AGGB estimate was validated with the assessment field and allometry derived AGGB at RMSE = 15.89g and 44.45g, respectively. This study demonstrate that VIN derived from Sentinel 2A MSI satellite data can be used to model AGGB estimation at a good accuracy. Therefore, it will contribute to providing reliable information on AGGB of grazing lands for sustainable livestock farming.

Allometric analysis of brain cell number in Hymenoptera suggests ant brains diverge from general trends

Many comparative neurobiological studies seek to connect sensory or behavioural attributes across taxa with differences in their brain composition. Recent studies in vertebrates suggest cell number and density may be better correlated with behavioural ability than brain mass or volume, but few estimates of such figures exist for insects. Here, we use the isotropic fractionator (IF) method to estimate total brain cell numbers for 32 species of Hymenoptera spanning seven subfamilies. We find estimates from using this method are comparable to traditional, whole-brain cell counts of two species and to published estimates from established stereological methods. We present allometric scaling relationships between body and brain mass, brain mass and nuclei number, and body mass and cell density and find that ants stand out from bees and wasps as having particularly small brains by measures of mass and cell number. We find that Hymenoptera follow the general trend of smaller animals having proportionally larger brains. Smaller Hymenoptera also feature higher brain cell densities than the larger ones, as is the case in most vertebrates, but in contrast with primates, in which neuron density remains rather constant across changes in brain mass. Overall, our findings establish the IF as a useful method for comparative studies of brain size evolution in insects.

Longitudinal allometry of sulcal morphology in health and schizophrenia

Scaling between subcomponents of cortical folding and total brain volume (TBV) in healthy individuals (HI) is allometric, i.e. non-linear. It is unclear whether this is also true in individuals with schizophrenia (SZ) or first-episode psychosis (FEP). The current study first confirmed normative allometric scaling norms in HI using discovery and replication samples. Cross-sectional and longitudinal diagnostic differences in folding subcomponents were then assessed using an allometric analytic framework. Structural imaging from a longitudinal (sample 1: HI and SZ, nHI Baseline = 298, nSZ Baseline = 169, nHI Follow-up = 293, nSZ Follow-up = 168, a total of 1087 images, all individuals ≥ 2 images, age 16-69 years) and a cross-sectional sample (sample 2: nHI = 61 and nFEP = 89, age 10-30 years) is leveraged to calculate global folding and its nested subcomponents: sulcation index (SI, total sulcal/cortical hull area) and determinants of sulcal area; sulcal length and sulcal depth. Scaling of the SI, sulcal area, and sulcal length with TBV in SZ and FEP was allometric and did not differ from HI. Longitudinal age trajectories demonstrated steeper loss of SI and sulcal area through adulthood in SZ. Longitudinal allometric analysis revealed that both annual change in SI and sulcal area was significantly stronger related to change in TBV in SZ compared to HI. Our results detail the first evidence of the disproportionate contribution of changes in SI and sulcal area to TBV changes in SZ. Longitudinal allometric analysis of sulcal morphology provides deeper insight into lifespan trajectories of cortical folding in SZ.

Constant neuropilar ratio in the insect brain

Revealing scaling rules is necessary for understanding the morphology, physiology and evolution of living systems. Studies of animal brains have revealed both general patterns, such as Haller's rule, and patterns specific for certain animal taxa. However, large-scale studies aimed at studying the ratio of the entire neuropil and the cell body rind in the insect brain have never been performed. Here we performed morphometric study of the adult brain in 37 insect species of 26 families and ten orders, ranging in volume from the smallest to the largest by a factor of more than 4,000,000, and show that all studied insects display a similar ratio of the volume of the neuropil to the cell body rind, 3:2. Allometric analysis for all insects shows that the ratio of the volume of the neuropil to the volume of the brain changes strictly isometrically. Analyses within particular taxa, size groups, and metamorphosis types also reveal no significant differences in the relative volume of the neuropil; isometry is observed in all cases. Thus, we establish a new scaling rule, according to which the relative volume of the entire neuropil in insect brain averages 60% and remains constant.

Sensation of the tiniest kind: the antennal sensilla of the smallest free-living insect Scydosella musawasensis (Coleoptera: Ptiliidae)

Miniaturization is a major evolutionary trend prominent in insects, which has resulted in the existence of insects comparable in size to some unicellular protists. The adaptation of the complex antennal multisensory systems to extreme miniaturization is a fascinating problem, which remains almost unexplored. We studied the antennal sensilla of Scydosella musawasensis Hall, 1999 (Coleoptera: Ptiliidae), the smallest free-living insect, using scanning electron microscopy. The antenna of S. musawasensis bears 131 sensilla; no intraspecific variation in the number or position of the sensilla has been revealed. Nine different morphological types of sensilla are described according to their external morphological features and distribution: four types of sensilla trichodea, one type of sensilla chaetica, two types of sensilla styloconica, and two types of sensilla basiconica. Morphometric analysis of the sensilla of S. musawasensis, based on measurements of the lengths and diameters of sensilla and their location and number, showed the absence of significant differences between females and males. Comparative allometric analysis of S. musawasensis and larger Coleoptera showed that the number of sensilla and the size of sensilla chaetica decrease with decreasing body size. However, the number of the types of sensilla and the length and diameter of the multiporous sensilla basiconica revealed no correlation with the body size. Comparison of the acquired data with the results of our earlier study of the antennal sensilla of some of the smallest parasitic wasps is used to put forward hypotheses on the common principles of miniaturization of the antennal sensory systems of insects.