To assess the possibility of thermal effects on reproductive function as a range-limiting mechanism in cottonmouths, we investigated the effects of temperature/photoperiod regimes on monthly male testosterone levels in three groups. The first was a field group, the second was a lab control group that received natural temperature/photoperiod conditions, and the third was an experimental lab group that received temperature/photoperiod conditions of a region north of the current range limit. The field and lab control groups exhibited a single testosterone peak in August (34.4 and 14.1 ng ml⁻¹, respectively) that coincided with observed reproductive activities in Northwestern Arkansas. The experimental group also exhibited a single peak (11.7 ng ml⁻¹), but the peak was delayed by one month. We coupled energetic calculations with environmental temperature, the timing of reproductive events, and the time available for foraging to demonstrate how pre- and postcopulation reproductive failure may serve as a sublethal range-limiting mechanism. North of their current range limit, the reduced time for energy acquisition may not allow for sufficient juvenile recruitment into the population to replace losses. Therefore, cottonmouths may be prevented from establishing a more northern range limit due to their reproductive physiology.

To assess the ways in which different selection pressures on male and female spinyhead blennies (Acanthemblemaria spinosa) influence their use of space, we measured a number of features of their shelter sites. Both sexes occurred primarily on dead surfaces of elkhorn coral (Acropora palmata), but significantly more males than females were found on live coral surfaces. Males occurred twice as frequently as females in the vacated constructed tubes of serpulid worms or vermetid molluscs, which provide greater surface for egg deposition than the shorter cavities excavated by other organisms. There was no difference between the sexes in shelter height above the reef surface. Fish size was positively correlated with shelter height above the reef surface for both sexes. Number of eggs being guarded by males was positively correlated with both fish size and shelter height above the reef surface; in concert they account for 44% of the variance in egg number. To assess the effects of competition, we removed spinyheads from corals and documented recolonization along with shelter site parameters. Corals originally harboring larger fish were recolonized at a higher rate, and in all cases the mean size of recolonists was smaller than originals; the original correlation of fish size with height above the reef surface collapsed for recolonists. These observations are consistent with others that indicate that spinyhead blennies compete for quality shelters.

We examined the energetics of calling by male Crinia georgiana because other studies have shown that the costs of attracting a mate for male frogs can limit chorus participation, which in turn can explain significant variation in male mating success. The metabolic cost of producing a single note for C. georgiana (0.0006 ± 0.0001 ml O₂ g⁻¹ min movement⁻¹ note⁻¹) was similar to the cost for other species, but males called at a comparatively low rate (mean = 136.0 ± 21.5 calls per hour). The production of multiple-note calls by C. georgiana is not an energy-saving mechanism because it is not more expensive to produce the same number of notes with single-note calls. Most males were found at the breeding site on one or two nights only during the breeding season, and peak calling activity occurred for approximately nine hours per day. Further, there were only two nights of peak chorus activity during the breeding season (82 days). These data suggest that the overall reproductive effort of male C. georgiana is low. We also show that female mate choice preferences for call rate might allow males to call at a low rate. We discuss the possibility that a positive relationship between male mating success and chorus attendance may not hold for all males in a species because the costs and benefits of attending the chorus can vary considerably among individuals.

We examined fish assemblage structure in three headwater rain-forest streams in the Urubu River Basin, Central Amazonia, as it relates to habitat heterogeneity. Riffles and pools, two types of stream habitat, were defined by current, depth, and substrate parameters, adjusted for Amazonian stream characteristics. We assessed species richness, composition, and abundance as they varied between riffles and pools across three similar streams. Four riffles and four pools were identified in each stream and sampled four times during 1996 and 1997. The samples yielded a total of 856 individuals of 22 species. The most abundant species were in the families Characidae, Lebiasinidae, Helogenidae, and Rivulidae. We found an interactive influence of riffle/pool habitat and stream factors on species richness, composition, and abundance. Rain-forest stream fish assemblages are structured by both habitat and stream locality.

In this paper, we present information on the natural history, reproductive and developmental strategies of the canopy treefrog Phrynohyas resinifictrix. Phrynohyas resinifictrix is a widespread Amazonian species breeding exclusively in water-filled treeholes in terra-firme rain forests. Females laid relatively large, floating egg masses in the treeholes. Gut content analyses indicated that tadpoles are generalists and predominantly macrophageous, basing their diet on detritus and conspecific fertilized eggs of younger cohorts. Tadpole guts were found to contain up to 62 intact eggs. This cannibalistic interaction is presumably of major importance for the completion of the larval stage and may result in depletion of entire egg complements. Strong site fidelity, interference competition for treeholes by territorial males, continuous use of treeholes year after year, repeated oviposition in treeholes, and temporal constancy in density of calling males are consistent with the hypotheses that adequate treeholes are a limiting resource for P. resinifictrix populations, or that location of unoccupied treeholes in the rain-forest canopy involves substantial risk or energetic costs.

Hydrologic variability and connectivity influence stream-fish assemblage structure, but other correlated habitat variables often confound attempts to document such relationships. By their nature, dams decrease stream connectivity, but upstream influences on tributary fish assemblages are infrequently documented and poorly understood. We sampled stream fishes seasonally for one year to compare headwater assemblages of the unimpounded East Fork (nine sites) and the impounded West Fork (12 sites) of the San Jacinto River in Texas. Using multiple regression and canonical ordination, we partitioned variation in species' distributions into that explained by instream structural, hydrologic, and physicochemical factors, drainage features, and season. In addition to effects of temporal variation of connectivity (as related to base flow and season) and other environmental factors, spatial patterns of species distribution between tributaries in the East and West Fork indicated upstream effects of impoundment caused by two probable mechanisms. Lentic habitats of impounded lower reaches in the West Fork apparently reduced movement by fluvial specialists among streams and, thus, reduced their opportunity to recolonize dry reaches compared to populations in East Fork streams. Moreover, West Fork assemblages had more macrohabitat-generalist species, which were abundant in the littoral zone of the impoundment and able to recolonize or tolerate environmental conditions in intermittent reaches. We caution that upstream effects of impoundment could be mistakenly attributed to other factors if they are not explicitly considered in species-environment studies.

We investigated geographical variation in ecological parameters among populations of Cnemidophorus cryptus, Cnemidophorus gramivagus, Cnemidophorus lemniscatus, Cnemidophorus ocellifer, and Cnemidophorus parecis, from three Brazilian biomes (Cerrado, Caatinga, and Amazonian Savannas). Lizards used mainly the open ground, with a high similarity in microhabitat use among populations. Differences in microhabitat use probably resulted from the availability of microhabitats and not from microhabitat preferences. Body temperatures were high and little influenced by environmental temperatures, there being no differences among populations. There were significant differences in diet among populations, with C. ocellifer from Caatinga and Cerrado consuming large quantities of termites, whereas Amazonian Savanna species used primarily ants and insect larvae. The data on reproductive seasonality indicated cyclical reproduction in seasonal biomes and continuous reproduction in unpredictable climate regions. We found significant differences in mean clutch size among populations, independent of body size, with C. lemniscatus having the smallest clutch size (1.50) and C. ocellifer from Cerrado the largest (2.10). There were fewer differences in clutch size among species from Amazonian Savannas, than between populations of C. ocellifer from Caatinga and Cerrado. Apparently, populations under seasonal climates concentrate their reproductive effort during the short reproductive season, producing larger clutches, whereas those under more stable or unpredictable climates reproduce continuously, yielding smaller clutches, corroborating the hypothesis that environmental conditions exert an important influence upon life-history parameters. There were significant differences in body shape among populations, but most of the variation was related to sex. We also observed significant differences in body size among populations, seemingly unrelated to differences in community structure, but the highly conservative morphology of Cnemidophorus species suggests the presence of historical constraints.

The evolution of sexual signaling systems is influenced by natural and sexual selection acting on complex interactions among traits. Natural hybrid zones are excellent systems for assessing fitness effects on sexual phenotypes. Most documented hybrid zones, however, show little variation in sexual signals. A hybrid zone between the swordtails Xiphophorus birchmanni and Xiphophorus malinche is characterized by numerous recombinants for male sexual traits. Analyses of geographic variation in morphological and isozyme traits in the Río Calnali, Hidalgo, Mexico, reveal an upstream-to-downstream gradient from X. malinche- to X. birchmanni-type traits. A second hybrid zone, likely isolated from the R. Calnali, occurs in the nearby Arroyo Pochutla. Although the presumed female preference for swords predicts the introgression of swords from X. malinche-like populations into hybrid populations, the opposite pattern was observed. Swords are reduced in populations otherwise characterized by X. malinche traits. Sexually dimorphic traits were poorly correlated within individuals, indicating that sexual selection does not act against recombinant phenotypes. Hybrid males also exhibit trait values outside the range of parental variation. These patterns are consistent with predictions that females are permissive, preferring generally conspicuous males without attending to specific features.

Based on stomach contents of museum specimens and published records (n = 51 prey items), Lampropeltis zonata eats lizards (37, 72.5%), squamate eggs (6, 11.8%), mammals (6), and birds (2, 3.9%). Juveniles feed on lizards, especially Sceloporus (spiny lizards) and Eumeces (skinks), whereas adults supplement their diet with squamate eggs and endothermic prey. Prey items are located by active foraging, usually swallowed head-first, and average 33% of snake mass. The diet of L. zonata overlaps substantially with that of several other species of sympatric, medium- to large-sized snakes in mesic western North American woodlands; it is narrower than that of the more widely distributed L. getula, and similar to that of allopatric, more closely related L. alterna and L. pyromelana.

Atlantic stingrays, Dasyatis sabina, inhabit shallow bays subject to rapid temperature changes, yet little is known about their thermal tolerance strategies. We quantified critical thermal maxima (CTMaxima) and minima (CTMinima) of Atlantic stingrays from St. Joseph's Bay, Florida. Spiracle contraction cessation for more than one minute was the experimental endpoint. Laboratory-acclimated fish held at 10.8, 20.5, or 35.1 C exhibited CTMaxima of 35.7, 39.3, or 43.2 C, and CTMinima of 0.8, 4.8, or 10.8 C, respectively. Regression analysis revealed that CTMaxima increased by 0.31 C and CTMinima decreased by 0.41 C for every 1.0 C increase in acclimation temperature. Atlantic stingrays exposed to diel thermoperiods of 34.0–37.3 C and 7.0–11.0 C had CTMaxima of 43.1 and 33.4 C and CTMinima of 9.6 and 0.3 C, respectively, suggesting that fish acclimated to low cycle temperatures. A thermal tolerance polygon produced from laboratory data had an area of 978 C², the third largest ever measured in a fish. Seasonally acclimatized fish achieved their lowest respective CTMaxima and CTMinima of 37.3 and 2.5 C in March and highest values of 41.8 and 6.6 C during July. Low extreme temperatures in St. Joseph's Bay came within 0.3 C of the fishes' CTMin; however, extreme high temperatures came no closer than 6.5 C of the fishes' CTMax. Similar to laboratory responses, seasonally acclimatized Atlantic stingrays tuned their physiology to the low cycle temperatures that were most threatening to continued survival.

Reproductive characteristics and the age-body size relationship of female Chrysemys picta marginata were studied at Miller's Marsh on Beaver Island, Michigan. Environmental influences on reproduction were evident in that turtles nested relatively early when the previous spring (April and May) temperatures were relatively warm. Clutch wet mass (CWM), clutch size (CS), and egg wet mass (EWM) were all correlated with maternal carapace length (CL). Over six activity seasons, significant annual variations in EWM and CS occurred, but these variations were not related to temperature or precipitation patterns of the current or previous year. Therefore, it seems unlikely that annual variation in EWM represents proximate variation or adaptive phenotypic plasticity where offspring size might be adjusted to meet predictable temporal changes in offspring growing and survival conditions. Annual variation in CS was mainly caused by slight variations in mean maternal CL. When compared to previously published studies on C. p. marginata populations from southern Michigan, Miller's Marsh turtles were larger in CL, produced large EWM and small CS relative to maternal body size, and apparently delayed sexual maturation, which would have resulted in relatively large maternal CL (and therefore EWM and CS) at primiparity and thereafter.

Apareiodon species from the Rio Tocantins-Araguaia basin, Brazil, were investigated to determine the recognizable species in that basin. Apareiodon machrisi Travassos, 1957, the only previously described species reported for the Rio Tocantins-Araguaia basin, is recognized as valid, and three new species inhabiting primarily headwater streams are described (Apareiodon argenteus, Apareiodon cavalcante, and Apareiodon tigrinus). The species are diagnosed based on aspects of coloration and morphology. Diagnoses and keys to the species are provided.

The effect of predation by large non–gape-limited vertebrates on the survivorship and size distribution of larvae of four anuran species was assessed using two syntopic freshwater turtle species, Emys orbicularis and Mauremys leprosa. Predator species and predator sex within species were used as treatments in replicated, factorial experiments for predation trials on tadpoles of Bufo calamita, Hyla meridionalis, Rana perezi, and Pelobates cultripes. Tadpole consumption rates were significantly higher for the carnivorous E. orbicularis than for M. leprosa. Rana perezi tadpoles were the least consumed, whereas P. cultripes and H. meridionalis had the lowest survivorship rates, being relatively easier to catch than R. perezi. Significant size selection occured for larger tadpoles of P. cultripes, whereas predation upon R. perezi tended to concentrate on the smaller size classes. The results point to an overall tendency of turtles to predate upon large tadpoles, yet the outcome of size selection by large vertebrates may depend on phenotypic traits that enhance the escape potential of tadoles. Mauremys leprosa had a high rejection rate of tadpoles, suggesting a higher sensitivity to unpalatability as compared to E. orbicularis, especially with relation to R. perezi. The results indicate that the effect of unpalatability as a predation deterrent may vary even among taxonomically close predator species.

During the multidiciplinary BIGSET (Biogeochemische Stoff- und Energietransporte in der Tiefsee/Biogeochemical Transport of Matter and Energy in the Deep Sea) programme 1995 and 1998 in the abyssal Arabian Sea, 33 specimens of Pachycara Zugmayer, 1911 were collected. Until then, a single trawl-damaged specimen of Pachycara shcherbachevi Anderson, 1989, caught in 1951 by the Danish research vessel Galathea, represented the only evidence of lycodine eelpouts in the Indian Ocean. One of the newly caught specimens belongs to P. shcherbachevi and provides the basis of a revised description of the species. The rest of the material belong to two different species, which are described here as new.

A recent hypothesis posits that temperature-dependent sex determination (TSD) in reptiles may be maintained if females can assess thermal conditions and lay eggs accordingly to produce the sex benefiting most from maternal investment. Specifically, females should lay large eggs in environments likely to produce the sex benefiting most from larger egg size. This relationship has been demonstrated in diamondback terrapins. To evaluate the generality of this hypothesis, we examined two components of this hypothesis using painted turtles (Chrysemys picta), a reptile with TSD. Vegetation cover around nests at oviposition significantly and negatively influenced nest temperatures during embryonic development, particularly during the period of sexual differentiation. However, no relationship existed between egg mass and either nest temperatures or vegetation cover around nests at oviposition. Therefore, large eggs were not laid in specific thermal microenvironments as a mechanism to match egg size with offspring sex ratio. These results do not support a general relationship between thermally based nest-site choice and maternal investment (egg mass) in reptiles with TSD.

A new species of bagrid catfish in the genus Mystus is described from the Mahakam River drainage in eastern Borneo. Mystus impluviatus closely resembles Mystus nigriceps and Mystus castaneus but differs in having a second posterior fontanel on the supraoccipital. It can be further distinguished from M. nigriceps and M. castaneus a combination of the following characters: maximum height of adipose fin 4.7–6.0% SL, length of adipose fin base 31.6–36.1% SL, long second and third dorsal fin rays, causing the dorsal fin to appear less rounded, maximum height of pectoral spine serrations 3.6–4.8% of spine length, a deeply forked caudal fin with a slender upper lobe, and a brown body with a distinct dark triangular patch on the base of the caudal peduncle.

A new species of hylid frog is described from south of the State of São Paulo, southeastern Brazil in Atlantic rain forest. The new species is a member of the genus Phrynohyas and is characterized by snout rounded in dorsal view and nearly truncate in lateral view, small adhesive disks, fingers slightly webbed, nasal bones widely separated, and frontoparietals without medial articulation.

Eggs and larvae of nurseryfish, Kurtus gulliveri, one of two known species of Kurtidae, are described and illustrated for the first time using material collected in two rivers of Australia's Northern Territory. Nurseryfish are unique among fishes in that males carry a cluster of fertilized eggs on a bony hook projecting from their foreheads. No brooding males were captured during this study, although one partial egg cluster was found adjacent to a male caught in a gill net. Three clusters found attached to gill nets without associated males had approximately 900–1300, slightly elliptical, 2.1–2.5 mm diameter, eggs, each with multiple oil droplets and a single, relatively thick chorionic filamentous strand at opposite poles. Larvae are pelagic and hatch at approximately 5-mm body length (BL) at the flexion stage possessing a large yolk sac, forming dorsal, caudal, and anal fins, and little pigment. Notochord flexion and yolk-sac resorption are complete by 6.9 mm. Post–yolk-sac larvae resemble adults in having a hatchet-shaped body that is almost transparent in life, including a large head with relatively small eyes, preopercular spines and a prominent, inflated gas bladder. Larval length data obtained fortnightly from August to November 2001 suggests that breeding occurs during northern Australia's dry season (May to November) and that larvae leave the pelagic environment at about 25 mm.

Knowledge of the home range of an animal can provide insights for studies of behavioral interactions among individuals, and long-term monitoring of particular animals is necessary to determine whether they exhibit seasonal variation in space-use patterns. I radio-tracked four adult male Pituophis catenifer (gopher snake) in central California for 14 consecutive months to investigate spatial and seasonal movement patterns. Using the fixed kernel density estimator to produce a probability contour, the 95% home ranges of P. catenifer ranged from 0.89–1.78 ha, whereas their core areas (50% polygons), the most heavily used areas of their home ranges, ranged from 0.1–0.29 ha. Movements of male P. catenifer were similar in spring and summer and decreased in autumn and winter. The telemetered snakes were close to marshes and Eucalyptus woodlands but were routinely found in grassland areas, perhaps because this habitat type may provide abundant food resources and partial protection from predators. Despite their proximity, the estimated home ranges of males 2, 3, and 4 did not overlap. These findings, and those of a previous investigation of activity patterns of P. catenifer in eastern Nebraska, suggest that syntopic gopher snakes occupy exclusive home ranges during at least part of their active season.

Behavioral responses of the rocky intertidal mosshead sculpin (Clinocottus globiceps) and woolly sculpin (Clinocottus analis) to increasing environmental hypoxia (low PO₂) were observed in a seawater aquarium with a depth gradient. The experimental design allowed observation of the response of these animals to encroaching environmental hypoxia. We observed three behaviors by which the fish dealt with hypoxia: emergence from substrate (EFS), first avoidance response (FAR), and aquatic surface respiration (ASR). With respect to EFS and FAR, mosshead sculpins were more labile in their responses than woolly sculpins. However, the mean PO₂ at which ASR was initiated was statistically indistinguishable between species. We suggest that the differences we observed represent alternate behaviors by which these related species deal with the trade-off imposed by the simultaneous needs to avoid predation and optimize respiration. We further suggest that these alternate behaviors have evolved around a conserved physiological constraint, the PO₂ at which ASR must be performed.

We tested larval Pacific giant salamanders (Dicamptodon tenebrosus) for chemical and behavioral defenses against cutthroat trout (Oncorhynchus clarki). Young-of-year Dicamptodon were fully palatable to trout during single and repeated offerings. However, larvae increased refuge use in response to chemical cues from trout, although they did not select different microhabitats (shallow or deep) between trout treatments and controls. Our results suggest that, although Dicamptodon larvae are potentially vulnerable to predation by cutthroat trout, increased refuge use by larvae in response to trout chemical cues may reduce the probability of encounters and contribute to the coexistence of these species.

We hypothesized that, through persistent predatory attacks, lizards should increase progressively the magnitude of their escape response. We simulated in the field a continuous attack by a persistent predator on Acanthodactylus erythrurus lizards and examined the characteristics of successive escape responses, microhabitats used for fleeing, and the refuges used. Lizards responded to the persistent attacks by increasing the distances they fled and the degree of cover in microhabitats into which they escaped. Lizards also changed their escape strategy from the first to the successive attacks. Initially, most individuals did not hide but stopped after running and remained vigilant, whereas almost all individuals hid subsequently. In addition, after successive predatory attacks, lizards used more structurally complex refuges (i.e., larger and with more obstructive cover). These refuges were probably safer although they may lower the lizard's capacity to observe the predator's subsequent behavior. These data suggest that lizards interpret persistent predatory attacks as an increase in predation risk and that lizards adjusted the magnitude of their escape and antipredatory responses to predation risk level.