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The myogenic differentiation 1 gene ( MYOD1) has a key role in skeletal muscle differentiation and composition through its regulation of the expression of several muscle-specific genes. We first used a general linear mixed model approach to evaluate the association of MYOD1 expression levels on individual beef tenderness phenotypes. MYOD1 mRNA levels measured by quantitative polymerase chain reactions in 136 Nelore steers were significantly associated ( P ≤ 0.01) with Warner-Bratzler shear force, measured on the longissimus dorsi muscle after 7 and 14 days of beef aging. Transcript abundance for the muscle regulatory gene MYOD1 was lower in animals with more tender beef. We also performed a co-expression network analysis using whole transcriptome sequence data generated from 30 samples of longissimus muscle tissue to identify genes that are potentially regulated by MYOD1. The effect of MYOD1 gene expression on beef tenderness may emerge from its function as an activator of muscle-specific gene transcription such as for the serum response factor (C-fos serum response element-binding transcription factor) gene ( SRF), which determines muscle tissue development, composition, growth and maturation. [ABSTRACT FROM AUTHOR]

The purpose of this study was to correlate the activity and habitat use of a large and ecologically specialized mammal ( Myrmecophaga tridactyla) with the time of day and minimum daily temperature in Brazil's Pantanal wetland. Seven giant anteaters were fitted with very high frequency (VHF) radio transmitters and monitored from March to December 2001. The animal's state of activity or rest, time and ambient temperature were recorded in different patches of the study site, which were covered by a mosaic of vegetation types and several ponds. Whenever a giant anteater was inside a forest patch, the temperature inside and outside of the patch was also recorded. The temperatures throughout the day were recorded by the meteorological station at the study site. The period of greatest activity of giant anteaters started at 18:00 h on hot days, but whenever the daily minimum temperature declined, the species' activity began earlier. Giant anteaters use predominantly forest habitats for rest and open habitats for activity. The forest patches work as a temperature buffer, because they are cooler than the matrix of open habitats during the hot hours of the day and warmer than the matrix during the cold hours. Although the giant anteater is known to be associated with open habitats, this study indicates the need of preserving forest patches for the conservation of this species. [ABSTRACT FROM AUTHOR]