The skull of squamates has many functions, with food acquisition and ingestion being paramount. Snakes vary interspecifically in the frequency, size, and types of prey that are consumed. Natural selection should favor phenotypes that minimize the costs of energy acquisition; therefore, trophic morphology should reflect a snake's primary prey type to enhance some aspect of feeding performance. I measured 19 cranial variables for six natricine species that vary in the frequency with which they consume frogs and fish. Both conventional and phylogenetically corrected analyses indicated that fish-eating snakes have relatively longer upper and lower jaw elements than frog-eating snakes, which tended to have broader skull components. I also compared the ratio of the in-lever to the out-lever lengths of the jaw-closing mechanism [jaw mechanical advantage (MA)] among species. Fish-eating snakes had significantly lower MAs in the jaws than did the frog-eating snakes. This result suggests that piscivores have faster closing jaws and that the jaws of frog-eating snakes have higher closing forces. Cranial morphology and the functional demands of prey capture and ingestion appear to be associated with primary prey type in natricine snakes.

Maximum gape is important to the ecology and evolution of many vertebrates, particularly gape-limited predators, because it can restrict the sizes and shapes of prey that can be eaten. Although many cranial elements probably contribute to gape, it is typically estimated from jaw length or jaw width, or occasionally from a combination of these two measures. We measured maximum gape directly for 18 individuals of the western diamond-backed rattlesnake, Crotalus atrox. We measured each individual's body length, several external cranial dimensions, several cranial osteological dimensions from cleaned skeletons, and we calculated gape index values from two published gape indices (GI). Cranial bone lengths and gape circumference showed negative allometry with snout-vent length (SVL), indicating that small individuals have relatively larger heads and gapes than their larger conspecifics. We then used Akaike's Information Criterion to determine which external and osteological measurements were the best predictors of gape. Body size (SVL) was the best predictor of maximum gape overall; however, when SVL was excluded from the analysis, quadrate (QL) and mandible lengths (MdLs) were the best predictors of maximum gape using both external and osteological measurements. Quadrate length probably contributes directly to gape; however, the importance of MdL to gape is less clear and may be due largely to its allometric relationships with head length and SVL. The two published GI did not prove to be better indicators of actual gape than the jaw and QLs in this study, and the gape values they produced differed significantly from our empirically determined gapes. For these reasons, we urge caution with the use and interpretation of computed GI in future studies. The extensive variation in quadrate and mandible morphology among lineages suggest that these bones are more important to variation in gape among species and lineages than within a single species.

Using human spermatozoa stimulated with either progesterone or the Ca2+ ionophore A23187 to undergo acrosomal exocytosis, we have investigated potential pathways for generation of diacylglycerol (DAG) and have examined the possibility that DAG plays an important role in the exocytotic response. Both treatments resulted in rapid and considerable generation of DAG, followed by a limited rise in phosphatidic acid (PA). Further experiments indicated that phospholipase C (PLC) activity is important in this generation of DAG, but phospholipase D activity probably is not. In addition, polyphosphoinositide-specific phosphoinositidase C activation and hydrolysis, of phosphatidylinositol 4,5-bisphosphate appears to be a necessary prerequisite for activation of the PLC pathway. Finally the DAG formed appears to be important in acrosomal exocytosis: (i) blocking DAG metabolism with a DAG kinase inhibitor resulted in both increased endogenous levels of DAG and a significantly increased exocytotic response in stimulated cells and (ii) exogenous DAG induced exocytosis in capacitated spermatozoa whereas PA did not. Taken together, these results suggest that DAG plays a key role in events leading to membrane fusion during human sperm acrosomal exocytosis stimulated by natural agonists.

The use of artificial cover objects, or cover boards, is a common method for collecting and surveying amphibians and reptiles. Cover objects, plywood and corrugated tin, were placed in open and closed canopy sites in an east Texas floodplain. The assemblages captured were compared between tin and wood. The odds of capture were compared between the two types as well as the odds of capture in open and closed canopy sites. The combined amphibian and reptile assemblages differed between tin and plywood. The odds of capturing an amphibian or reptile under corrugated tin were slightly higher (1.2:1) when compared to plywood. Further, the odds of capture were less likely in closed canopy sites (0.89) than open canopy sites.Due to their rather cautious and surreptitious lifestyles, amphibians and reptiles can be difficult to study. Consequently, several methods are used to sample for amphibians and reptiles including drift fence arrays, visual encounter surveys, audible cues, and artificial cover objects (e.g. Fitch, 1987;Lips, 1999;Lewis et al., 2000;Foster and Hampton, 2003), and some studies have compared the accuracy, and efficiency of the different techniques (Ryan et al., 2002;Ford and Hampton, 2005). Sampling artificial cover objects is a popular method for surveying and collecting amphibians and reptiles. Natural ground cover is commonly used by both amphibians and reptiles (Conant and Collins, 1998), and artificial cover objects provide similar refuge for a variety of species. Cover boards are a favorable method for amphibian and reptile studies because they are relatively easy to maintain, effort can be easily analyzed, and many artificial cover objects can be sampled in a short period of time (Grant et al., 1992). Artificial cover objects can be as accurate at detecting activity and abundance of some species as pitfall drift fences (Sutton et al., 1999) but do not

It has been suggested that juveniles have exaggerated morphologies or improved performance to compensate for the disadvantages of being small. As gape-limited predators, juvenile snakes are at a particular disadvantage in terms of prey availability, capture, and ingestion. Prey preference often changes with snake size yet previous studies generally compare only one prey type or relative prey size among age classes. Using Western Ribbon Snakes ( Thamnophis proximus (Say in James, 1823)), I investigated the ontogeny of head dimensions and feeding performance on frogs and fish using a range of relative prey sizes. Comparison among snake sizes indicated that smaller individuals had larger relative head sizes than larger conspecifics; however, larger individuals had larger heads. Initial bite position differed between juveniles and adults fed fish but not frogs. Both frogs and fish were generally consumed headfirst by adults and juveniles. Head length did not influence feeding performance in terms of time or pterygoid protractions for snakes fed either fish or frogs. In general, this study suggests that allometry of trophic morphology does not improve feeding performance.