John K. Tucker

Experimental analysis of an early life-history stage: avian predation selects for larger body size of hatchling turtles

One common life‐history pattern involves an elevated rate and nonrandom distribution of neonatal mortality. However, the mechanisms causing this pattern and the specific traits that confer a survival benefit are not always evident. We conducted a manipulative field experiment using red‐eared slider turtles to test the hypothesis that diurnal avian predators are a primary cause of size‐specific neonatal mortality. Body size was a significant predictor of recapturing hatchlings alive and of finding hatchlings dead under natural conditions, but was unimportant when diurnal predators were excluded from the field site. Overall recapture rates also more than doubled when predators were excluded compared to natural conditions (72.4 vs. 34.9%). We conclude that birds are an important cause of size‐specific mortality of recently emerged hatchling turtles and that ‘bigger is better’ in this system, which has important implications for life‐history evolution in organisms that experience size‐specific neonatal mortality.

Lipid Abnormalities and Renal Disease: Is Dyslipidemia a Predictor of Progression of Renal Disease?

&NA; Dyslipidemia is a cardiovascular disease (CVD) risk factor that is associated with enhanced atherosclerosis and plaque instability. Renal insufficiency is associated with abnormalities in lipoprotein metabolism in both the early and the advanced stages of chronic renal failure. These include alterations in apolipoprotein A (apo A)‐ and B‐containing lipoproteins, high‐density lipoproteins, and triglycerides. In animal models, these alterations in lipid metabolism and action lead to macrophage activation and infiltration in the kidney with resultant tubulointerstitial and endothelial cell injury. Limited data in humans suggest that, in addition to contributing to CVD, dyslipidemia may be a risk factor for the progression of renal disease. The effects of dyslipidemia on the kidney are mainly observed in those with other risk factors for renal disease progression such as hypertension, diabetes, and proteinuria. Renal disease is a strong risk factor for CVD and African Americans have high rates of renal disease. Therefore, examining the effects of dyslipidemia on the development or progression or renal disease will be an important question for the Jackson Heart Study and is the topic of this review.

Predation on Zebra Mussels (Dreissena polymorpha) by Common Carp (Cyprinus carpio)

ABSTRACT We examined the gut contents of 31 common carp (Cyprinus carpio) collected at Mississippi River Mile 217 in August 1995 for evidence of predation on zebra mussels (Dreissena polymorpha). We found between 1 and 407 zebra mussel beaks in 83.9% of the fish we examined. For all fish examined, common carp contained 118.2 beaks per fish or about 59 zebra mussels per fish. The survey did not indicate that larger fish consumed more zebra mussels than smaller fish. Estimated valve length for zebra mussels consumed ranged from 1.48 to 42.52 mm with a mean 11.79 mm (SE = 0.10 mm). We found that larger fish tended to prey on larger zebra mussels than did smaller fish. The general size range of zebra mussels consumed by common carp overlapped the upper portion of the size range of young-of-the-year zebra mussels living at the site and the lower portion of the size range of older zebra mussels living at the site.

QUANTITATIVE GENETICS OF PLASTRON SHAPE IN SLIDER TURTLES (TRACHEMYS SCRIPTA)

Abstract Shape variation is widespread in nature and embodies both a response to and a source for evolution and natural selection. To detect patterns of shape evolution, one must assess the quantitative genetic underpinnings of shape variation as well as the selective environment that the organisms have experienced. Here we used geometric morphometrics to assess variation in plastron shell shape in 1314 neonatal slider turtles (Trachemys scripta) from 162 clutches of laboratory‐incubated eggs from two nesting areas. Multivariate analysis of variance indicated that nesting area has a limited role in describing plastron shape variation among clutches, whereas differences between individual clutches were highly significant, suggesting a prominent clutch effect. The covariation between plastron shape and several possible maternal effect variables (yolk hormone levels and egg dimensions) was assessed for a subset of clutches and found to be negligible. We subsequently employed several recently proposed methods for estimating heritability from shape variables, and generalized a univariate approach to accommodate unequal sample sizes. Univariate estimates of shape heritability based on Procrustes distances yielded large values for both nesting populations (h2≅ 0.86), and multivariate estimates of maximal additive heritability were also large for both nesting populations (h2max≅ 0.57). We also estimated the dominant trend in heritable shape change for each nesting population and found that the direction of shape evolution was not the same for the two sites. Therefore, although the magnitude of shape evolution was similar between nesting populations, the manner in which plastron shape is evolving is not. We conclude that the univariate approach for assessing quantitative genetic parameters from geometric morphometric data has limited utility, because it is unable to accurately describe how shape is evolving.

Quantum theory of parametric frequency conversion

Abstract The frequency conversion of electromagnetic fields is treated quantum mechanically through an analysis of a simple theoretical model. Two modes of the field are considered to be coupled by a parameter which oscillates at the difference frequency. The fields are described by means of a time-dependent density operator, which is assumed to have a P representation at t = 0. It is shown that such a system possesses a P representation at all later times, and its time dependence is found to have a particularly simple oscillatory character. The exchange of density operators between the two modes is illustrated explicity for several sets of initial conditions.

Size-biased Mortality Due to Predation in a Nesting Freshwater Turtle, Trachemys scripta

Abstract Differential survivorship within or between stages is an important component of most explanations of turtle reproductive patterns. We tested the null hypothesis that a sample of adult female Trachemys scripta found killed by predators was a random sample of adult females found nesting at a site in W-central Illinois by comparing plastron lengths of the two samples. Mean plastron length of 19 dead female T. scripta was significantly smaller than mean plastron length of 79 females found alive. Apparently smaller females were at greater risk of mortality than were larger ones. Cubic spline analysis indicated that mortality was strongly concentrated among the smallest and perhaps youngest nesting females and was distinctly nonlinear. This finding was consistent with the suggestion that the minimum threshold of maturation size was influenced by the size at which the probability of predation decreases.

Colonization of Unionid Bivalves by the Zebra Mussel, Dreissena polymorpha, in Pool 26 of the Mississippi River

ABSTRACT The relationship between 18 species of native unionid bivalves and the exotic zebra mussel, Dreissena polymorpha, was explored at a monitoring site in Pool 26 of the Mississippi River. From 1992 to 1993, colonization rates increased from 27% to 99.7% of unionids, and the mean number of D. polymorpha per unionid increased from 2.2 to 37.4. The number of D. polymorpha per unionid shell was related to shell length and varied among species. Four types of colonization patterns were found, each differing from the others in the relative number of colonizing D. polymorpha. Shell and ornamentation types were differentially colonized. Thick-shelled, ornamented species were more heavily colonized than were thin-shelled, unornamented species. Habitat alteration of the gravel bar site was profound, with the zebra mussels forming a pavement over the gravel bar. This resulted in adverse effects on the unionids. Once mussels exited the substrate, they were unable to penetrate the entangled mass of zebra mussels ...

The Bighead Carp (Hypophthalmichthys nobilis) in the Mississippi River

ABSTRACT We report collections of the bighead carp, Hypophthalmichthys nobilis (Richardson, 1845) in the Mississippi River in Missouri and Illinois between 1991 and 1994. In all, we collected 48 specimens ranging from 18 to 790 mm total length. Young-of-the-year fish were caught in 1992 and 1994, which suggests that the species is able to reproduce in the Mississippi River and may become established. Because H. nobilis is a low level filter feeder, its presence may affect other filter feeding fishes such as the paddlefish (Polyodon spathula), bigmouth buffalo (Ictiobus cyprinellus), and gizzard shad (Dorosoma cepedianum). Further research is needed to confirm that the species is established and what its biological impact will be.

Initial Occurrences of Zebra Mussels (Dreissena polymorpha) on Freshwater Mussels (Family Unionidae) in the Upper Mississippi River System

ABSTRACT The exotic zebra mussel (Dreissena polymorpha) was found attached to native freshwater mussels (Unionidae) in La Grange, Peoria, and Alton Pools of the Illinois River and Pools 4, 13, and 26 of the Mississippi River. From 1% to 27% of native bivalves collected within these pools in 1992 had one or more zebra mussels attached with the highest densities of zebra mussels found in the Illinois River. At one site in the Alton Pool of the Illinois River, 27% of native mussels had a mean of 2.2 zebra mussels attached. Densities were lower in the Mississippi River sites, ranging from 1% to 12%, with the highest density occurring below the confluence of the Illinois and Mississippi Rivers. Of the 25 native species collected, nine had zebra mussels attached. In the Alton Pool of the Illinois River, Amblema plicata longer than 82 mm had more zebra mussels upon them than A. plicata smaller than 82 mm. The large numbers of young-of-the-year zebra mussels found in the Illinois and Mississippi Rivers indicate D...

TOLERANCE FOR FREEZING IN HATCHLING TURTLES

-Hatchling painted turtles (Chrysemys picta), Blandings turtles (Emydoidea blandingi), slider turtles (Trachemys scripta), and snapping turtles (Chelydra serpentina) were inoculated with ice at temperatures near the equilibrium freezing point for their body fluids (ca. -0.7 C) and then frozen at -2.0 C. All animals survived freezing for up to 30 h, but mortality among sliders and snapping turtles increased rapidly with longer exposures. Despite the fact that neonates of all four species are able to recover from freezing at a high subzero temperature, the adaptive strategy manifested by animals in the field is to avoid freezing altogether via attributes of morphology (painted turtles), behavior (Blandings turtles, snapping turtles), or distribution (slider turtles). The discovery of a tolerance for freezing in hatchlings of species having diverse distributions and natural histories raises the possibility that such tolerance is a trait of general occurrence among neonatal turtles and that it is not an adaptation specifically enabling animals to withstand the rigors of winter. Hatchlings of the North American painted turtle (Emydidae: Chrysemys picta) typically spend their first winter inside the shallow, subterranean nest where they completed embryogenesis the preceding summer (Ernst et al., 1994). This behavior commonly causes neonates in northerly populations to be exposed during winter to ice and cold (Breitenbach et al., 1984; Storey et al., 1988; Packard et al., 1989; Costanzo et al., 1995), with temperatures in nests sometimes going below -10 C (Woolverton, 1963; DePari, 1996; Packard, 1997; Packard et al., 1997a). Hatchling painted turtles are small (3-6 g), ectothermic animals with limited heat capacity, so their deep body temperature presumably tracks the temperature in their nest quite closely (Claussen and Zani, 1991). Nevertheless, some turtles commonly survive exposure to such temperatures and emerge from their nest when the ground thaws the following spring (Woolverton, 1963; DePari, 1996; Packard, 1997; Packard et al., 1997a). We have proposed that neonatal painted turtles in northerly populations withstand exposure to ice and cold by remaining unfrozen and supercooled (Packard and Packard, 1995a). According to this theory, the skin of hatchlings is not easily penetrated by growing crystals of ice (Packard and Packard, 1993b), so turtles are not necessarily caused to freeze by inoculation when they make contact with ice in frozen soil (Packard et al., 1997b, 1999). This protection from inoculation enables the animals to exploit an innate capacity for supercooling (Packard and Packard, 1993a, 1995b, 1997; Packard and Janzen, 1996; Costanzo et al., 1998), so that they remain unfrozen over the usual range of subzero temperatures encountered in nests in the field (Packard et al., 1997b, 1999). However, on those occasions when the integument is not up to the challenge and ice crystals manage to penetrate into body compartments from the environment, the animals freeze and die (Packard et al., 1997b, 1999). Thus, turtles that emerge from nests in the spring presumably are ones that remained unfrozen and supercooled for the entire winter. However, a nagging problem with the concept that hatchling painted turtles exploit a capacity for supercooling to survive winters in the field is the indisputable evidence from experiments in the laboratory that neonates often recover from freezing at relatively high subzero temperatures (Storey et al., 1988; Churchill and Storey, 1992a; Rubinsky et al., 1994; Costanzo et al., 1995; Attaway et al., 1998). The problem that these findings create for proponents of an adaptive strategy based on supercooling can be reduced to a simple question: Why do animals tolerate freezing if such a tolerance is not important to their ecology? We believe that we have obtained a partial answer to the aforementioned question. Results from the first of two experiments reported here indicate that a tolerance for limited freezing is common to hatchling turtles generally, that is, that such tolerance probably was acquired from some common ancestor of turtles and is a shared (plesiomorphic) character in contemporary forms. The evidence was gathered by studying tolerance for freezing in hatchlings of four species of North American turtles-painted turtles, Blandings turtles (Emydoidea blandingi), slider turtles (Trachemys scripta), and snapping This content downloaded from 207.46.13.129 on Sun, 26 Jun 2016 06:51:49 UTC All use subject to http://about.jstor.org/terms FREEZING IN HATCHLING TURTLES turtles (Chelydra serpentina)-that differ in geographic distribution and in the natural history of overwintering neonates. All the hatchlings in this experiment were frozen at -2 C and then held at that temperature for up to 48 h before their condition (i.e., alive or dead) was assessed. We also performed a second experiment, in which hatchling painted turtles were frozen at -2 C for 24 h and then exposed for varying intervals to -2 C, -3 C, or -4 C. Data from this second experiment provide new insights into the possible role of freeze-tolerance in enabling neonates of this species to survive winters in the field. MATERIALS AND METHODS Eggs of painted turtles and snapping turtles were collected in June 1996 from newly constructed nests located on the Valentine National Wildlife Refuge in north-central Nebraska, whereas eggs of Blandings turtles were collected that same month from fresh nests located along the Mississippi River in central Minnesota. Eggs of sliders, on the other hand, were obtained by injecting gravid females from westcentral Illinois with synthetic oxytocin to induce them to oviposit. The eggs of all species were incubated to hatching on damp vermiculite. Hatchling Blandings turtles and sliders later were transported to Colorado State University by air express. Average mass for hatchlings was 3.7 g (SD = 0.6 g) for painted turtles; 7.7 g (SD = 0.4 g) for Blandings turtles; 6.0 g (SD = 1.1 g) for slider turtles; and 7.8 g (SD = 1.1 g) for snapping turtles. The turtles were acclimated to approximately 2 C and held in darkness until they were used to study their tolerance for freezing (Packard and Packard, 1993a). Samples of 8-12 turtles were drawn at random from the pools of available animals. Each hatchling in a sample then was prepared for study by cleaning it thoroughly with a small paint brush, after which the measuring junction of a copper/constantan thermocouple (26 gauge) was affixed to its carapace with epoxy resin. When the resin had hardened, the turtle was dipped in chilled (2 C) tap water to wet its integument-especially the skin in the axillary and inguinal pouches, because this integument in painted turtles may be more susceptible than skin elsewhere on the body to penetration by growing crystals of ice (Packard and Packard, 1995b). Each turtle was placed immediately into a pint-volume canning jar, and the sealed jar was placed in an environmental chamber set at approximately 2 C. After all jars were in the chamber, free ends of the thermocouples were attached via a multiplexor to a Campbell CR-10 datalogger so that temperature on the carapace of the animals could be measured every 30 sec. We next allowed temperature of the turtles to equilibrate with that of the environmental chamber. We then opened the chamber, removed the lid from each jar, placed several pieces of crushed ice against the turtle, and closed the jar. After ice had been added to all the jars, the door to the environmental chamber was closed and the microprocessor controlling the chamber was reset to a nominal temperature of -2 C. Temperature in the chamber declined rapidly, and so too did surface temperature of the turtles (Fig. 1). When temperature reached approximately -0.4 C, ice crystals contacting each turtle caused water on the integument to begin to freeze, as evidenced by a slight decrease in slope of the cooling curve brought about by the release of latent heat of fusion by water changing phase from liquid to solid (Fig. 1). In most cases, the turtle was inoculated shortly thereafter, as evidenced by a pronounced freezing exotherm (i.e., the sudden increase in temperature caused by the release of latent heat of fusion) that lasted for 12-15 h (Fig. 1A, C, D). No freezing exotherm was detected in the temperature profiles for three of the painted turtles (Fig. 1B), so these animals apparently avoided inoculation and remained unfrozen for the duration of their exposure. Timing of each exposure began with the appearance of the freezing exotherm for the turtle itself (Fig. 1A, C, D). Animals in the first experiment comparing hatchlings of all four species were frozen at approximately -2 C for 24-48 h. Some variation occurred in the equilibrium temperatures that actually were measured on the carapace of animals in different jars, owing to the spatial variation in temperature that commonly occurs in environmental chambers (Measures et al., 1973). The average temperature across species and exposures was -2.1 C (range -1.8 C to -2.6 C) and did not vary among species or treatment. Painted turtles in the second experiment were frozen first at -2 C for 24 h. Some of the hatchlings then were allowed to remain at this temperature for another 48 or 72 h whereas animals in other groups were subsequently cooled to minima of -3 (range -2.8 C to -3.2 C) or -4 C (range -3.8 C to -4.2 C). Rates of cooling in the latter tests were 1 C/day or 2 C/day (see Fig. 3). Temperature in the chamber was increased to 2 C at the end of each test and the animals were allowed to thaw overnight. The condition of the turtles (i.e., alive or dead) then was assessed by examining their eyes (which often are only partially open in moribund animals) and by observing their spontaneous activity and respons537 This content downloaded from 207.46.13.129 on Sun, 26 Jun 2016 06:51:49 UTC All use subject to http://about.jstor.org/terms