Sex-specific growth is mirrored in feeding rate but not moulting frequency in a sexually dimorphic snake

Sexual dimorphism in Louisiana pine snakes (Pituophis ruthveni)

The Louisiana pine snake, Pituophis ruthveni, is a cryptic, federally threatened snake species with several fragmented populations in Louisiana and Texas, USA. There are currently four captive breeding populations in zoos in the USA; however, little scientific data exists on their life history and anatomy. Accurate sex determination and identification of normal reproductive anatomy are an essential part of a veterinary exam and conservation programs. The authors had encountered various cases of sex misidentification in this species that were attributed to lack of lubrication of the sexing probes and enlarged musk glands. Anecdotal observation led to a hypothesis of sexual dimorphism based on body and tail shape. To test this hypothesis, we measured body length, tail length and width, and body to tail taper angle in 15 P. ruthveni (9 males and 6 females). We also obtained tail radiographs of all animals to document the presence of mineralized hemipenes. Significant dimorphism was identified in relative tail length, width, and taper angle; females consistently exhibited a more acute taper angle. Contrary to previous studies in other Pituophis species, a male-biased sexual size dimorphism was not identified. Mineralized hemipenes were confirmed in all males (a newly described trait in this species), and we found that the lateral view was consistently more reliable for identification of hemipenes compared to the ventrodorsal view. This information contributes to the scientific community's understanding of this species and is of use to biologists and veterinarians working toward conservation of this threatened species.

Energy expenses on prey processing are comparable, but paid at a higher metabolic scope and for a longer time in ambush vs active predators: a multispecies study on snakes

Snakes are characterized by distinct foraging strategies, from ambush to active hunting, which can be predicted to substantially affect the energy budget as a result of differential activity rates and feeding frequencies. Intense foraging activity and continuously upregulated viscera as a result of frequent feeding leads to a higher standard metabolic rate (SMR) in active than in ambush predators. Conversely, the costs of digestion (Specific Dynamic Action—SDA) are expected to be higher in ambush predators following the substantial remodelling of the gut upon ingestion of a meal after a long fasting period. This prediction was tested on an interspecific scale using a large multispecies dataset (> 40 species) obtained from published sources. I found that the metabolic scope and duration of SDA tended to reach higher values in ambush than in active predators, which probably reflects the greater magnitude of postprandial physiological upregulation in the former. In contrast, the SDA energy expenditure appeared to be unrelated to the foraging mode. The costs of visceral activation conceivably are not negligible, but represent a minor part of the total costs of digestion, possibly not large enough to elicit a foraging-mode driven variation in SDA energy expenditure. Non-mutually exclusive is that the higher costs of structural upregulation in ambush predators are balanced by the improved, thus potentially less expensive, functional performance of the more efficient intestines. I finally suggest that ambush predators may be less susceptible than active predators to the metabolic ‘meltdown effect’ driven by climate change.