Ben Creisler
Some recent non-dino papers that may be of interest:
Free pdf:
High throughput sequencing (HTS) has revolutionized the field of ancient DNA (aDNA) by facilitating recovery of nuclear DNA for greater inference of evolutionary processes in extinct species than is possible from mitochondrial DNA alone. We used HTS to obtain ancient DNA from the little bush moa (Anomalopteryx didiformis), one of the iconic species of large, flightless birds that became extinct following human settlement of New Zealand in the 13 th century. In addition to a complete mitochondrial genome at 249.9X depth of coverage, we recover almost 900 Mb of the moa nuclear genome by mapping reads to a high quality reference genome for the emu (Dromaius novaehollandiae). This first nuclear genome assembly for moa covers approximately 75% of the 1.2 Gb emu reference with sequence contiguity sufficient to identify more than 85% of bird universal single-copy orthologs. From this assembly, we isolate 40 polymorphic microsatellites to serve as a community resource for future population-level studies in moa. We also compile data for a suite of candidate genes associated with vertebrate limb development and show that the wingless moa phenotype is likely not attributable to gene loss or pseudogenization among this candidate set. We also identify potential function-altering coding sequence variants in moa for future experimental assays.
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Free pdf:
As top predators, crocodilians have an acute sense of hearing that is useful for their social life and for probing their environment in hunting situations. Although previous studies suggest that crocodilians are able to localize the position of a sound source, how they do this remains largely unknown. In this study, we measured the potential monaural sound localization cues (head-related transfer functions; HRTFs) on alive animals and skulls in two situations, both mimicking natural positions: basking on the land and cruising at the interface between air and water. Binaural cues were also estimated by measuring the interaural level differences (ILDs) and the interaural time differences (ITDs). In both conditions, HRTF measurements show large spectral variations (greater than 10 dB) for high frequencies, depending on the azimuthal angle. These localization cues are influenced by head size and by the internal coupling of the ears. ITDs give reliable information regarding sound-source position for low frequencies, while ILDs are more suitable for frequencies higher than 1.5 kHz. Our results support the hypothesis that crocodilian head morphology is adapted to acquire reliable localization cues from sound sources when outside the water, but also when only a small part of their head is above the air-water interface.
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Jonathan R. Codd, Kayleigh A. R. Rose, Peter G. Tickle, William I. Sellers, Robert J. Brocklehurst, Ruth M. Elsey and Dane A. Crossley (2019)
A novel accessory respiratory muscle in the American alligator (Alligator mississippiensis).
Biology Letters 15(7): 20190354
doi:
https://doi.org/10.1098/rsbl.2019.0354https://royalsocietypublishing.org/doi/10.1098/rsbl.2019.0354The muscles that effect lung ventilation are key to understanding the evolutionary constraints on animal form and function. Here, through electromyography, we demonstrate a newly discovered respiratory function for the iliocostalis muscle in the American alligator ( Alligator mississippiensis). The iliocostalis is active during expiration when breathing on land at 28ÂC and this activity is mediated through the uncinate processes on the vertebral ribs. There was also an increase in muscle activity during the forced expirations of alarm distress vocalizations. Interestingly, we did not find any respiratory activity in the iliocostalis when the alligators were breathing with their body submerged in water at 18ÂC, which resulted in a reduced breathing frequency. The iliocostalis is an accessory breathing muscle that alligators are able to recruit in to assist expiration under certain conditions.
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Edgar J. GonzÃlez, Marcela MartÃnezâLÃpez, Marco Antonio MoralesâGarduza, Rodrigo GarcÃaâMorales, ÂPierre Charruau & Josà Alberto GallardoâCruz (2019)
The sexâdetermination pattern in crocodilians: A systematic review of three decades of research.
Journal of Animal Ecology (advance online publication)
doi:
https://doi.org/10.1111/1365-2656.13037https://besjournals.onlinelibrary.wiley.com/doi/abs/10.1111/1365-2656.13037Sex in crocodilians is not determined by chromosomes, but by egg incubation temperature, where different temperatures produce different clutch sex ratios. Two patterns have been proposed to describe these changes in sex ratios: a 100% female proportion at low and high temperatures with male predominance at intermediate ones (FMF) or a simpler pattern with a single femaleâtoâmale transition (FM). Over the last three decades, researchers have provided empirical information to support either of these two patterns in different species; however, no consensus has been reached partly because data have not been analysed as a whole.
Here, we aimed at gathering the existing data on these patterns to provide models of temperatureâdependent sex determination in those crocodilians studied so far.
Potentially relevant publications were searched on Web of Knowledge, Scopus, Scielo and Science Direct. Studies that reported results on the sexual identity of crocodilian hatchlings obtained from constant temperature incubation treatments were considered. Using statistical models varying in their underlying assumptions, we evaluated which sexâdetermination pattern was best supported for the studied crocodilians and constructed speciesâspecific and latitudeâspecific models.
Based on the 8,458 sexed hatchlings studied throughout 31 studies, we show that the evidence supports a shared FMF pattern in all the crocodilian species for which enough data are available. We find that such pattern changes between species and at different latitudes.
These results suggest a lability of the FMF crocodilian sexâdetermination pattern, a key feature under the present climate change scenario.