Facultative Aestivation in a Tropical Freshwater Turtle Chelodina rugosa

Abstract-1. Chelodina rugosa dug from aestivation sites at the end of the dry season were immediately alert and well coordinated. 2. Compared with non-aestivating animals, aestivating turtles had 20% higher plasma osmotic pressure and 7% higher sodium. Coupled with a small, but significant weight gain upon return to the water, this suggested the occurrence of minor dehydration in aestivating animals. 3. Plasma lactate levels of aestivating animals were low, averaging 1.99 mmol/1, consistent with aerobic rather than anaerobic metabolism having sustained their long period under ground. 4. No evidence was seen of dramatic physiological specialization. Aestivation in this species is interpreted as a primarily behavioural adaptation, made possible by typically reptilian abilities to tolerate a wide range in plasma electrolytes and to survive long periods without feeding

Consistent patterns of common species across tropical tree communities

Trees structure the Earth’s most biodiverse ecosystem, tropical forests. The vast number of tree species presents a formidable challenge to understanding these forests, including their response to environmental change, as very little is known about most tropical tree species. A focus on the common species may circumvent this challenge. Here we investigate abundance patterns of common tree species using inventory data on 1,003,805 trees with trunk diameters of at least 10 cm across 1,568 locations1,2,3,4,5,6 in closed-canopy, structurally intact old-growth tropical forests in Africa, Amazonia and Southeast Asia. We estimate that 2.2%, 2.2% and 2.3% of species comprise 50% of the tropical trees in these regions, respectively. Extrapolating across all closed-canopy tropical forests, we estimate that just 1,053 species comprise half of Earth’s 800 billion tropical trees with trunk diameters of at least 10 cm. Despite differing biogeographic, climatic and anthropogenic histories7, we find notably consistent patterns of common species and species abundance distributions across the continents. This suggests that fundamental mechanisms of tree community assembly may apply to all tropical forests. Resampling analyses show that the most common species are likely to belong to a manageable list of known species, enabling targeted efforts to understand their ecology. Although they do not detract from the importance of rare species, our results open new opportunities to understand the world’s most diverse forests, including modelling their response to environmental change, by focusing on the common species that constitute the majority of their trees

Differences in renal-cloacal function between Crocodylus porosus and Alligator mississippiensis have implications for crocodilian evolution

Major electrolytes and nitrogenous excretory products were analysed in the blood plasma, ureteral urine and cloacal urine of juvenile Alligator mississippiensis and Crocodylus porosus in fresh and hypoosmotic salt water (206 mosmol . l). Both species coped well with saline water, showing little (Alligator) or no (Crocodylus) change in plasma composition. Comparisons of renal-cloacal function point to major differences in their osmoregulatory physiology. The cloaca of C. porosus in a very active osmoregulatory organ in salt and fresh water, contributing to water conservation and NaCl excretion through the lingual salt glands. In contrast, the cloaca of Alligator has little impact on the composition of excreted urine. It seems likely that A. mississippiensis is largely constrained to a renal response to osmotic and ionic stress while C. porosus is able to call on a more complex mix of renal response, post-renal modification of urine in the cloaca, and excretion of excess NaCl through the salt glands. The results support the idea that there are deep-seated differences in the osmoregulatory physiology of alligatorids and crocodylids (Eusuchia), an understanding of which should provide valuable insights into their evolution and zoogeography

A gharial from the Oligocene of Puerto Rico: transoceanic dispersal in the history of a non-marine reptile

The Indian gharial (Gavialis gangeticus) is not found in saltwater, but the geographical distribution of fossil relatives suggests a derivation from ancestors that lived in, or were at least able to withstand, saline conditions. Here, we describe a new Oligocene gharial, Aktiogavialis puertoricensis, from deltaic–coastal deposits of northern Puerto Rico. It is related to a clade of Neogene gharials otherwise restricted to South America. Its geological and geographical settings, along with its phylogenetic relationships, are consistent with two scenarios: (i) that a single trans-Atlantic dispersal event during the Tertiary explains the South American Neogene gharial assemblage and (ii) that stem gharials were coastal animals and their current restriction to freshwater settings is a comparatively recent environmental shift for the group. This discovery highlights the importance of including fossil information in a phylogenetic context when assessing the ecological history of modern organisms