Will Selman

Seasonal Variation of Corticosterone Levels in Graptemys flavimaculata, an Imperiled Freshwater Turtle

Currently, little is known about the seasonal variation of corticosterone (CORT) levels, either baseline or stress response, within freshwater turtles. We conducted a seasonal CORT study with a species of freshwater turtle, Graptemys flavimaculata (Yellow-blotched Sawback; family Emydidae), that is endemic to the Pascagoula River system of southeastern Mississippi. Graptemys flavimaculata is commonly observed while basking on deadwood snags, with us using basking traps and dip nets as active capture methods. We caught both male (n  =  60) and female (n  =  49) turtles during the months of April–October during 2007 and 2008. Immediately after capture, we collected an initial blood sample, confined the turtle for 35 minutes, and then took a second blood sample. Competitive binding radioimmunoassays were done to determine CORT levels. Time zero CORT levels for both sexes were generally lower than previously reported levels for other turtle species, likely due to the trapping methods used. By time 35 min, CORT levels were significantly elevated relative to initial levels. We did not detect seasonal differences in time zero CORT levels for males or females. However, seasonal differences in time 35 CORT levels for males were detected, with higher levels observed during summer months (July, August) relative to spring (April) and fall (October) months. Seasonal differences were also detected in time 35 CORT levels of females, with lower levels observed during July (nesting season) relative to September. This study provides novel information and insight into the differences in seasonal physiological demands for this species, and aquatic turtle species in general, while also providing probable connections of physiology to seasonal life history events.

Basking Ecology of the Yellow-Blotched Sawback (Graptemys flavimaculata), an Imperiled Turtle Species of the Pascagoula River System, Mississippi, United States

Abstract Basking is an understudied aspect of turtle biology, especially considering how frequent and observable it is in some species. Researchers have suggested many physiological roles that basking likely fulfills in turtles. We documented seasonal basking behavior of the yellow-blotched sawback (Graptemys flavimaculata) on the Leaf River, a tributary of the Pascagoula River in southeastern Mississippi. We used binoculars and a spotting scope to determine G. flavimaculata individual- and population-level basking patterns throughout the main active months (April–October) and across the daily activity period; we also describe a new method to determine population basking percentage that may be useful for future aquatic turtle surveys. We found distinct differences in individual- and population-level basking behavior across months, sexes, and the daily activity period. We also documented differences in basking structures used between the sexes but found little correlation between population-level basking and several environmental temperature variables.

Habitat-Related Variation in Body Size and Reproductive Output and an Examination of Reproductive Allometry in the Sabine Map Turtle (Graptemys sabinensis) across Three River Drainages

The Sabine Map Turtle (Graptemys sabinensis) inhabits the Sabine-Neches, Calcasieu, and Mermentau river drainages of southwestern Louisiana and east Texas. Sparse data in the literature mark it as having among the smallest body sizes and smallest clutch sizes among the 14 species of the genus Graptemys. All available data on life history originate from the upper Sabine and upper Calcasieu drainages, which are relatively high-gradient rivers with fast currents and numerous sandbars. Downstream segments of these drainages and the entire Mermentau drainage have almost no gradient, with little perceptible current and no sandbars. We sampled G. sabinensis from the Mermentau River and upper and lower portions of both the Sabine and Calcasieu drainages. We collected data on body size and radiographed gravid females in the lower Calcasieu and Mermentau drainages to examine clutch size and egg width and compared our data to literature records and measurements of museum specimens. Both males (to 104 mm in midline plastron length) and females (to 202 mm) were considerably larger in the Mermentau and lower reaches of the Sabine and Calcasieu drainages than in the upper Sabine and upper Calcasieu drainages (to 92 mm and 176 mm, respectively). Clutch sizes were also significantly larger in the Mermentau and lower Calcasieu (mean 5.3 eggs, range 3–7) compared to previously reported clutch sizes for the upper Sabine and upper Calcasieu drainages (mean 2.3 eggs, range 1–4). Comparison with recent findings for other species of Graptemys indicates that it is typical for populations in faster-current habitats to be smaller in body size, although no previous report has shown the magnitude of differences exhibited by G. sabinensis in the present study. Examination of the allometry of reproductive output complemented previous studies of Graptemys in that both egg width and clutch size were hypoallometrically related to female body size, consistent with the hypothesis of anatomical constraints on egg width. The difference between egg width and pelvic aperture width grew larger as females increased in size, suggesting that anatomical constraints may have applied only to smaller females, leaving egg-size optimization possible in larger females. We could not determine the reason for a significant difference in egg width between the Mermentau and lower Calcasieu after correction for female body size, as pelvic aperture width did not vary between the drainages; however, other potential anatomical constraints on egg width were not measured.

High Connectivity Observed in Populations of Ringed Sawbacks, Graptemys oculifera, in the Pearl and Bogue Chitto Rivers Using Six Microsatellite Loci

Graptemys oculifera is endemic to the Pearl River drainage system in Louisiana and Mississippi, and due to this limited range it is vulnerable to environmental changes. Many impacts to this drainage system are due to anthropogenic activities, and alterations may negatively impact the connectivity among populations of G. oculifera. Previous studies show populations below the Ross Barnett Reservoir might be undergoing population declines, suggesting limited movement among populations. In addition to anthropogenic effects, the drainage geomorphology might also play a role in shaping population connectivity, as the sister species of G. oculifera, G. flavimaculata, contains two distinct populations (mainstem Pascagoula and Escatawpa River) and possible subpopulations within the Pascagoula (upper Leaf River, upper Chickasawhay River, and lower sections of the Pascagoula River). We used six polymorphic microsatellite loci to analyze the population genetics of G. oculifera at eight sites in the Pearl River drainage. The STRUCTURE program found support for one genetic group; however, our AMOVA analysis detected small but significant genetic differentiation in our three-group analysis. Both the MIGRATE and Isolation-by-Distance analyses supported a stepping stone model of gene flow, not panmixia. We suggest management agencies should consider these genetic data when developing management plans. Although we did not detect any influence of the reservoir on population connectivity, likely due to the long generation times of turtles, we suggest mark–recapture and/or radio-telemetry studies be performed on populations near the reservoir to determine if cross reservoir movements occur.

Population Structure, Status, and Conservation of Two Graptemys Species from the Pearl River, Mississippi

Abstract Graptemys is one of the least studied turtle genera in North America. Graptemys oculifera (Ringed Sawback) and Graptemys pearlensis (Pearl Map Turtle) are endemic to the Pearl River system of Mississippi and southeastern Louisiana. We studied both species near Columbia, Mississippi, on the Pearl River via a trapping and basking surveys over two years. Additionally, five sites including Columbia were trapped for 27 years to determine long-term trends in capture success and relative abundance (RA). At the Columbia site, body size distribution was bimodal for G. oculifera and atypically unimodal for G. pearlensis; G. pearlensis body lengths were smaller than museum specimens. Population estimates for G. oculifera at the Columbia site indicate a stable population over 25 years. Long-term RA trends indicated that G. pearlensis was less common than G. oculifera in all periods and at all sites from 1988 to 2013. Trends in long-term capture success for G. oculifera and G. pearlensis were negative at all sites, with significant declines at three sites for both G. oculifera and G. pearlensis. Declines occurred both upstream and downstream of a major reservoir. Therefore, a combination of factors (including altered hydrology, human disturbance, lack of recruitment, excessive sedimentation, impaired water quality, and/or the pet trade) appear to be contributing to declines. Additional conservation and protection is warranted for G. pearlensis, and current protections for G. oculifera should be extended. Future studies should continue at our long-term sites to determine whether population declines persist or whether populations stabilize.

Growth in Kyphotic Ringed Sawbacks, Graptemys oculifera (Testudines: Emydidae)

Abstract Kyphosis has not been reported in any Graptemys species (map turtles and sawbacks). We captured four kyphotic individuals of Graptemys oculifera from the Pearl River system, Mississippi, with three individuals recaptured 5 to 12 yrs later; one juvenile female had measurable growth, and two adult females had negligible growth. All kyphotic individuals were females, with an overall occurrence rate of 0.10% (4 of 3830 individuals) at five G. oculifera sample sites.

Spatial, Seasonal, and Sexual Variation in the Diet of Graptemys flavimaculata, a Threatened Turtle of the Pascagoula River System, Mississippi, USA

The conservation of imperiled species often depends upon conserving their prey. Graptemys flavimaculata (Yellow-blotched Sawback) is an imperiled turtle endemic to the Pascagoula River system of Mississippi, USA. We investigated diet variability of G. flavimaculata relative to site geography, sex, seasons, and size. We captured individuals from May to October in 2007 and 2008 at two distant sites. One site is an inland freshwater tributary (Leaf River, LR) and the other site is coastal and tidally influenced (Pascagoula River, PR). Feces from males (n = 68) and females (n = 74) were collected and analyzed. Using the Index of Relative Importance (IRI; 0–100 scale, 100 = only item present in all samples), we found that G. flavimaculata are primarily sponge specialists for both males (IRILR = 85, IRIPR = 91) and females (IRILR = 84, IRIPR = 65). For both sexes, between-site differences were more varied than within-site differences; for the latter, prey items were typically similar for males and females at a single site, but importance varied. Seasonal comparisons suggest that both LR and PR females shifted diets towards mollusks during the spring and fall, possibly associated with increasing energy and calcium for reproduction. Based on the frequency of wood fragments in feces, submerged deadwood appears important for prey species, and therefore, managers should conserve deadwood along riverbanks (i.e., mature riparian corridors). If channel maintenance is needed, deadwood should be moved toward banks rather than removed to conserve structure for prey species colonization.