Salinity tolerances of two Australian freshwater turtles, Chelodina expansa and Emydura macquarii (Testudinata: Chelidae).

Freshwater biota experience physiological challenges in regions affected by salinization, but often the effects on particular species are poorly understood. Freshwater turtles are of particular concern as they appear to have limited ability to cope with environmental conditions that are hyperosmotic to their body fluids. Here, we determined the physiological responses of two Australian freshwater chelid turtles, Emydura macquarii and Chelodina expansa, exposed to freshwater (0‰) and brackish water (15‰, representing a hyperosmotic environment). Brackish water is common in the Murray-Darling River Basin within the natural range of these species in Australia during periods of drought, yet it is unknown how well these species tolerate saline conditions. We hypothesized that these turtles would be unable to maintain homeostasis in the 15‰ water treatment and would suffer osmotic loss of water, increased ionic concentrations and a decrease in body mass. Results revealed that these turtles had elevated plasma concentrations of sodium, chloride, urea and uric acid in the plasma. Plasma ionic concentrations increased proportionally more in E. macquarii than in C. expansa. Individuals of both species reduced feeding in 15‰ water, indicating that behaviour may provide an additional means for freshwater turtles to limit ion/solute influx when in hyperosmotic environments. This osmoregulatory behaviour may allow for persistence of turtles in regions affected by salinization; however, growth rates and body condition may be affected in the long term. Although we demonstrate that these turtles have mechanisms to survive temporarily in saline waters, it is likely that sustained salinization of waterways will exceed their short- to medium-term capacity to survive increased salt levels, making salinization a potentially key threatening process for these freshwater reptiles.

Ultrastructure of the mature spermatozoa of caecilians (Amphibia: Gymnophiona).

The spermatozoa of Gymnophiona show the following autapomorphies: 1) penetration of the distal centriole by the axial fiber; 2) presence of an acrosomal baseplate; 3) presence of an acrosome seat (flattened apical end of nucleus); and 4) absence of juxta-axonemal fibers. The wide separation of the plasma membrane bounding the undulating membrane is here also considered to be apomorphic. Three plesiomorphic spermatozoal characters are recognized that are not seen in other Amphibia but occur in basal amniotes: 1) presence of mitochondria with a delicate array of concentric cristae (concentric cristae of salamander spermatozoa differ in lacking the delicate array); 2) presence of peripheral dense fibers associated with the triplets of the distal centriole; and 3) presence of a simple annulus (a highly modified, elongate annulus is present in salamander sperm). The presence of an endonuclear canal containing a perforatorium is a plesiomorphic feature of caecilian spermatozoa that is shared with urodeles, some basal anurans, sarcopterygian fish, and some amniotes. Spermatozoal synapomorphies are identified for 1) the Uraeotyphlidae and Ichthyophiidae, and 2) the Caeciliidae and Typhlonectidae, suggesting that the members of each pair of families are more closely related to each other than to other caecilians. Although caecilian spermatozoa exhibit the clear amphibian synapomorphy of the unilateral location of the undulating membrane and its axial fiber, they have no apomorphic characters that suggest a closer relationship to either the Urodela or Anura.

Spermatozoal ultrastructure in the spiny lobster Jasus novaehollandiae Holthuis, 1963 (Palinuridae, Palinura, Decapoda).

The spermatozoal ultrastructure of the spiny lobster Jasus novaehollandiae is most similar to that in other investigated palinurans and, in particular, to the spermatozoa of Panulirus species. Shared characters include the globular nucleus penetrated by the bases of three or more microtubular arms; an anteriorly situated cytoplasmic zone with mitochondria and conspicuous lamellar bodies; a complex, four-zoned acrosomal vesicle (however, lacking the crystalline region present in Panulirus) with a homogeneous region; a scroll region; a flocculent region; and a region of periacrosomal material that forms finger-like involutions into the flocculent region. The related scyllarid slipper lobsters (Scyllarus and Thenus) possess spermatozoa with acrosome morphology similar to that of Jasus, but the sperm is generally more flattened, numerous radiating acrosome fins are present, and the microtubular arms (in Scyllarus) are cytoplasmic in origin and not nuclear. Sperm morphology provides preliminary evidence in support of the hypothesis of two independent lines of evolution in the Palinuridae but investigation into additional taxa within this group is required. J. Morphol. 236:117-126, 1998. © 1998 Wiley-Liss, Inc.