Brent M. Graves

AGGREGATION OF SQUAMATE REPTILES ASSOCIATED WITH GESTATION, OVIPOSITION, AND PARTURITION

Prerequisite to the evolution of social behavior is a context in which individuals can interact. Animal aggregations near preferred habitat features can provide such a context. Near times of gestation, oviposition, and parturition, habitat features that facilitate these processes may be specialized and of paramount importance to the fitness of gravid individuals. Additionally, spatial proximity to conspecifics may enhance individual fitness through antipredator, thermoregulatory, or osmoregulatory effects. Such effects could result in selection for attraction to conspecifics, as well as localized habitat features, and more complex mutualistic and manipulative social interactions. Furthermore, philopatry and the proximity of littermates, parents, and offspring at the time of parturition or hatching would enhance inclusive fitness effects of mutualistic interactions. Mutual attraction to preferred habitat features as exhibited by gravid squamates may provide a useful model of early stages in the evolution of more complex social systems. Literature concerning aggregation of gravid squamates, communal nesting and birth, and interactions among neonates and postparturient females is reviewed.

Reproduction, Rookery Use, and Thermoregulation in Free-ranging, Pregnant Crotalus v. viridis

A study of the reproductive biology of pregnant, free-ranging prairie rattlesnakes was conducted in Wyoming from 1982 through 1987. Females reproduced on a flexible superannual cycle. Pregnant females were longer than nonpregnant females, and heavier than nonpregnant females of similar length. Among pregnant snakes, follicle number was positively correlated with increasing body size. Pregnant snakes that had radiotelemetry transmitters surgically implanted early in the active season resorbed follicles, whereas those with transmitters implanted later in the season continued pregnancy through parturition. Movements from hibernacula to rookeries were spatially direct, but often one more or more in duration. Snakes in rookeries were relatively sedentary, frequently shared shelter rocks with pregnant conspecifics, and maintained higher body temperatures than nonpregnant conspecifics that were not in rookeries. Air temperature, date, and microhabitat were important influences on body temperature. Among other potential benefits, residence in rookeries may enhance reproductive success through thermal effects on gestation.

Anuran Population Monitoring: Comparison of the North American Amphibian Monitoring Program's Calling Index with Mark-Recapture Estimates for Rana clamitans

Abstract The North American Amphibian Monitoring Program uses a ranked, categorical calling index to estimate anuran abundance. However, there are few data assessing the assumption that calling index values are accurate indicators of population sizes or to suggest ranges of population sizes associated with specific values of the calling index. This study compared mark-recapture population estimates and call rates to calling index values for Green Frogs (Rana clamitans) in the Upper Peninsula of Michigan. Mean mark-recapture population size estimates and mean calls per minute were greater in ponds with larger calling index values. Similarly, calls per minute increased with increasing population size, although rate of increase declined at high population sizes possibly caused by a higher proportion of noncalling satellite males at high densities. Sex ratios in breeding habitat along the edges of ponds were increasingly male biased as population size increased. These data support the assumption that calling index values are useful indicators of abundance of R. clamitans.

The West Indian manatee (Trichechus manatus) lacks a vomeronasal organ

Completely aquatic marine mammals of the order Cetacea such as whales and dolphins have a reduced or absent olfactory system and neither a vomeronasal organ nor an accessory olfactory bulb. In comparison, seals, which are only partially aquatic, have olfactory and accessory olfactory systems including the vomeronasal organ. Thus, there seems to be a strong relation between the degree of adaptation to an aquatic environment and the degree of reduction in olfactory structures. Sirenians, such as manatees and dugongs, are another family of marine mammals which have secondarily adapted to a fully aquatic existence, yet there is dispute about the status of their olfactory structures. In the present study there was no evidence for a vomeronasal organ in the adult West Indian Manatee, Trichechus manatus. Additionally, the main olfactory system appeared quite rudimentary. These observations support the hypothesis that, in mammals, secondary adaptation to an aquatic environment leads to the reduction or loss of the olfactory senses.

PREY SELECTIVITY AND SIZE-SPECIFIC DIET CHANGES IN BUFO COGNATUS AND B. WOODHOUSII DURING EARLY POSTMETAMORPHIC ONTOGENY

Ontogenetic diet shifts have been documented in many anurans (Smith and Bragg, 1949; Oplinger, 1967; Labanick, 1976; Christian, 1982; Donnelly, 1991; Lima and Moreira, 1993). These studies compared the diets of juveniles as a whole to those of adults (e.g., Livezey, 1961; Clarke, 1974a; Gittins, 1987). Diet patterns among juvenile size classes, however, have yet to be investigated. Bufonids exhibit high postmetamorphic growth rates early in ontogeny, as do other anurans (Clarke, 1974b). These differences in body size may be a means of avoiding overlap in resource use (Schoener, 1974; Toft, 1985). Hence, diet shifts associated with rapid growth during this relatively short period may be important for survival to reproductive age and may affect interactions with heteroand conspecifics (Werner and Gilliam, 1984). Discrete, size-specific diet shifts may result in selectivity for different prey among toad size classes (Werner and Gilliam, 1984). Some authors have suggested that certain Bufo feed indiscriminately (e.g., Smith and Bragg, 1949; Clarke, 1974a; Duellman and Trueb, 1986; Larsen, 1992). However, these conclusions could be an artifact of pooling size classes consisting of selective feeders into a single class for dietary analysis. Indeed, recent studies indicate that toads are selective predators (e.g., Toft, 1980, 1981). We quantified ontogenetic differences in the diets of toads over a range of sizes that occur within the first month after metamorphosis, and compared prey consumption to prey availability for several prey types consumed by juvenile toads during early ontogeny. We collected postmetamorphic, juvenile toads by hand while walking a transect 1 m from the edge of Rose Lake, a prairie-pothole marsh located approximately 5 km NE of Vermillion, Clay Co., South Dakota. We collected 36 Bufo cognatus and 14 B. woodhousii on 15 July 1992, and 20 B. woodhousii on 27 July 1993. During 1992, all breeding occurred on 15-18 May and most tadpoles of Bufo transformed around 15 June (Graves et al., 1993). The average SVL of B. woodhousii at metamorphosis in South Dakota is 10 mm (Underhill, 1960). The largest toad collected had a SVL of

Initial Den Location by Neonatal Prairie Rattlesnakes: Functions, Causes, and Natural History in Chemical Ecology

The concept of adaptation has long been a central idea in the study of the survival and evolution of life on earth (e.g., Williams, 1966). The potential existence of biological adaptation is best thought of as a hypothesis to be tested or an idea to be approached, and not a phenomenon that is automatically inherent in each and every characteristic of a living system1s biology. To be considered an adaptation, sensu stricto, potentially important mechanisms and processes should be rigorously studied to determine if they do in fact figure significantly into an organism’s “fit” with its environment. Once such features of phenotype are determined to be genuinely critical to survival, subsequent analysis of the trait’s mechanisms can lead to much more full explanations of how things actually work, and why they may have evolved into the structural and functional mosaics that we now see.

Spring Emergence Patterns of Wandering Garter Snakes and Prairie Rattlesnakes in Wyoming

Although intraspecific and interspecific variation in dates of spring emergence is known among snakes, factors affecting such variation are not. Dates of spring emergence from hibernation were recorded for individual wandering garter snakes (Thamnophis elegans vagrans) and prairie rattlesnakes (Crotalus viridis) in south-central Wyoming. Due to differing seasons of mating and mating systems of these species, we predicted that male garter snakes, but not male rattlesnakes, would emerge prior to conspecific females. Garter snakes emerged earlier than rattlesnakes, and male garter snakes emerged earlier than conspecific females. Male garter snakes remained near hibernacula where vernal courtship with emerging females was observed frequently. In contrast, spring courtship was never observed among rattlesnakes, and there was no difference between dates of spring emergence of males and females. Thus, predictions concerning associations between emergence patterns and mating systems were supported.

HOME POND DISCRIMINATION USING CHEMICAL CUES IN CHRYSEMYS PICTA

ELINSON, R. P., AND P. PASCERI. 1989. Two UV-sensitive targets in dorsoanterior specification of frog embryos. Development 106:511-518. GRANT, K. P., AND L. E. LICHT. 1995. Effects of ultraviolet radiation on life-history stages of anurans from Ontario, Canada. Can. J. Zool. 73:2292-2301. HIBBARD, B. M. 1993. Folates and fetal development. Br. J. Obstet. Gynaecol. 100:307-309. HIGGINS, G. M., AND C. J. SHEARD. 1926. Effects of ultraviolet radiation on the early larval development of Rana pipiens. J. Exp. Zool. 46:333-343. JABLONSKI, N. G. 1992. Sun, skin colour and spina bifida: An exploration of the relationship between ultraviolet light and neural tube defects Proc. Australas. Soc. Hum. Biol. 5:455-462.

Responses of Resident Male Dendrobates pumilio to Territory Intruders

Abstract Male Dendrobates pumilio are territorial, and vocalize in the presence of intruders. Territory displays are energetically expensive, and residents should modify display behavior according to costs and benefits associated with social contexts of intrusions by conspecifics. Activity censuses found no significant difference in the proportions of male and female D. pumilio found at various times of day, but a higher proportion of animals that were active at 0730 were male. Resident males exhibited a significantly greater mean call group duration when faced with male intruders in the morning than in the afternoon but did not respond differently to male or female intruders. This may reflect greater potential benefits of repelling territorial intruders in the morning than in the afternoon and use of the same territorial displays to defend territory boundaries as well as to attract potential mates. No significant differences were found in responses of resident males to familiar and unfamiliar conspecifics, which suggests that both neighbors and strangers may compete with residents for territory and mates.

Sensory Mediation of Aggregation Among Postmetamorphic Bufo cognatus

Quantification of toad spatial distributions confirmed that postmetamorphic Bufo cognatus form aggregations under natural conditions in southeastern South Dakota. Distributions of toads in sym- metric arenas placed in the field indicated that asymmetrical distribution of habitat features, and resulting mutual attraction to resources, is not required for aggregation formation in postmetamorphic toads. Rather, these data suggest that toadlets are attracted to conspecifics. In a similar laboratory experiment, aggregations occurred under light, but not dark, conditions suggesting a role for vision in mediation of this behavior. Additionally, toads were attracted to areas that had been occupied previously by postmetamorphic con- specifics, suggesting that orientation to chemical cues is involved in the aggregation response. This is the first demonstration of attraction to conspecific chemical cues in nonlarval anurans. Field observations of defensive behavior of grouped and solitary postmetamorphic toads supports the hypothesis that aggre-