Jacqueline D. Litzgus

I am interested in questions about the adaptive significance of life history variation at geographic extremes, and the application of life history data to the design of conservation plans. My research focuses on geographic variation in the life history, demographics, behavior, and metabolism of the spotted turtle (Clemmys guttata). I also examine questions about the physiological basis, and the adaptive bioenergetic and life history significance of certain behaviors, particularly summer and winter dormancy. Turtles are excellent model organisms for the study of life histories of long-lived, iteroparous species because individuals can be easily permanently marked, many turtles occur in discrete populations at high enough densities to allow a substantial number of individuals to be monitored throughout their lives, reproductive output of females can be repeatedly examined in a nondestructive way using x-rays, and many species are large enough for radio transmitter attachment so that an individual’s location, habitat use, home range and behavior can be monitored over long periods

Study System
I am considered an expert on the natural history and life history of my study system, the spotted turtle (Clemmys guttata). I was competitively awarded a contract from the Canadian government (Committee on the Status of Endangered Wildlife in Canada) to prepare the federal status report on the spotted turtle; the species is currently being considered for up-listing to Endangered status from Special Concern as a result of my report. Over the past 12 years, I have studied spotted turtles from two populations at opposite extremes of the species’ distribution (Ontario and South Carolina), to test hypotheses related to adaptive variation in adult body size, age and size at maturity, and reproductive output. My work has had a conservation focus as the spotted turtle is declining throughout its range as a result of habitat loss and destruction, and collection for the pet trade.
spotted turtle

Program HomePeopleFacilitiesResearchPublicationsCollaboratorsStudent Information
FiW Home

Spotted turtle (Clemmys guttata).
spotted turtle distribution
VT Home
Distribution of the spotted turtle. Note that populations within this distribution are not contiguous, as implied by the range map. The black dots indicate my northern (ON) and southern (SC) study sites.

Field Sites and Techniques
My study site in Ontario has been the focus of a long-term mark-recapture study first begun in 1977, and continued by myself since 1991. This data set is currently the longest-running for the species, and I hope to continue to monitor the Ontario spotted turtle population and make use of this interesting study system with the help of undergraduate and graduate students for many years. I would also like to continue to study the turtles at my South Carolina site; in addition, establishing a population for demographic and life history study in Florida would be extremely informative since little is known about extreme southern populations of the species.

My research uses both lab and field techniques. I have extensive experience with mark-recapture data collection and radio telemetry, and I have recently become proficient with the use of respirometry equipment to measure metabolic rates. In the time between obtaining my Masters and Ph.D. degrees, I worked as a lab coordinator in a physiological-ecology lab that used refrigerated baths and thermocouples interfaced to a multi-channel chart recorder to collect data on the super-cooling and freeze-tolerance capacities of invertebrate and vertebrate ectotherms.

Geographic variation in body size and reproduction
A component of my dissertation focused on a test of Bergmann’s Rule by examining intraspeficic body size patterns in the widely distributed spotted turtle (Litzgus, DuRant and Mousseau, submitted). Bergmann's Rule states that, among conspecific populations, individuals are larger in cooler than in warmer environments as a consequence of selection related to heat conservation. Our analysis of 818 turtles (live animals and preserved museum specimens) collected from across the entire range (45°N to 28°N), indicates that the positive relationship between body size and latitude is driven by a population of large turtles at the northern extreme of the species’ range (Fig.1). When the northern population was removed from the analyses, Bergmann’s rule was not supported, and the smallest turtles occurred near the central part of the species’ distribution. We hypothesized that the observed pattern in body size was related to variation in female size at maturity and reproductive cycles.

The “dip” in body size of spotted turtles at around 39ºN latitude (Fig. 2) may indicate a transition zone at which clutch frequency changes from one or less clutches per season to more than one clutch per season. This north-central latitude may represent the highest latitude at which females can produce more than one clutch of eggs per season without an extreme cost in terms of growth. It may also represent the highest (i.e., coolest) latitude at which a second (or third) clutch could complete incubation before the onset of cool fall temperatures. We hypothesize that turtles in populations above this transition zone produce a maximum of one clutch per year and therefore turtles can allocate more energy into growth and obtain larger body sizes. Populations below the transition zone experience a longer, more predictable growing season that allows turtles to both reach larger body sizes and increase clutch frequency. Published reproductive output data support this hypothesis (Table 1). Spotted turtles from Ontario (45°N, north of the apparent transition zone) are the largest in this study, and produce less than one clutch of eggs per year (Litzgus and Brooks 1998). Spotted turtles from Pennsylvania (41°N, north of the transition zone) produce one clutch per year (Ernst 1970), whereas turtles from South Carolina (33°N, south of the transition zone) produce up to three clutches of eggs per year (Litzgus and Mousseau 2003). Interestingly, average total annual egg production per female is the same among the geographically disparate populations compared (Table 1). Future work will examine clutch frequency in spotted turtle populations around the apparent transition zone as these differences in reproductive ecology influence population persistence in the face of sudden natural environmental changes and deleterious human impacts.

Adaptive variation in behavior and physiology at geographic extremes
A future project will involve an examination of the effects of environmental conditions at geographic extremes on behavior and physiology in the spotted turtle (Fig. 3). The research will involve the use of radio telemetry, thermal models, temperature data logging stations, and laboratory measurements of metabolic rate using respirometry. This study will provide information on behavioral and physiological responses to environmental stresses in populations in northern and southern areas of the species’ distribution, and therefore will be useful for the creation of range-wide management programs for spotted turtles. In collaboration with W.A. Hopkins at the Savannah River Ecology Laboratory, University of Georgia, and R.J. Brooks at the University of Guelph, an NSF proposal has been submitted to support this project.
Figure 1

Figure1. Relationship between body size (carapace length) and latitude in live and preserved Clemmys guttata.
Figure 2

Figure 2. Nonlinear relationship between body size (carapace length) and latitude in live Clemmys guttata.

Figure 3
Table 1. Body size (plastron length in mm) and reproductive output of female spotted turtles (Clemmys guttata) from three populations (location in °N latitude). Values are means ± SE. N = number of gravid females for the body size and mean total annual egg production comparisons, and N = number of clutches for the clutch size comparisons. Means within rows with different superscripts are significantly different.
Figure 3. Seasonal activity patterns of spotted turtles (Clemmys guttata) at the northern (dotted line, italicized font) and southern (solid line, regular font) extremes of the species’ distribution. In the north, the growing season is short, the winter is long and cold, and turtles experience a wider range in temperatures during the annual cycle compared to conspecifics in the south. Hibernation occurs for an extended period (7-8 months) in the north (Litzgus et al. 1999), and turtles do not aestivate during summer (Litzgus and Brooks 2000). In contrast, hibernation does not appear to be a significant component of the annual cycle in the south as turtles became quiescent but did not completely cease activity during winter (Litzgus, unpubl. data). Preliminary field observations indicated that aestivation may occur in the south. As a result of these periods of inactivity at different times in the annual cycle, the length of the period of pronounced activity is approximately the same in northern and southern populations of turtles. We therefore made the null model prediction that annual maintenance metabolism is the same in populations at northern and southern extremes because individuals in each population have evolved strategies (e.g., hibernation and aestivation, respectively) to minimize activity during stressful times of their annual cycle.
 
Ontario (45°N)
Pennsylvania (40°N)
South Carolina (33°N)
Body size (N)
103.4 ± 0.9 (19) a
89.2 ± 1.7 (8) b
90.5 ± 1.4 (10) b
Clutch size (N)
5.3 ± 0.2 (24) a
3.9 ± 0.2 (8) b
2.9 ± 0.2 (19) c
Range of number eggs in clutches
4 – 7
3 – 5
2 – 4
Mean annual clutch frequency
0.7 *
1
1.2 *
Mean total annual egg production for gravid females (N)
5.3 ± 0.2 (24) a
3.9 ± 0.2 (8) b,c
4.6 ± 0.7 (12) a,c
Total annual egg production #
3.7
3.9
3.5
* Calculated using two years (1994-1995 in ON, 2000-2001 in SC) of x-ray data.
# This value accounts for sexually mature females that did not become gravid.
Sources: ON (Litzgus and Brooks, 1998), PA (Ernst, 1970), SC (Litzgus and Mousseau 2003).
Litzgus web page Litzgus CV Litzgus e-mail: litzgus@biol.sc.edu
program home | people | facilities | research | publications | collaborators | student information | FiW Home