John B. Iverson

Reproductive Ecology of the Painted Turtle (Chrysemys picta) in the Nebraska Sandhills and across Its Range

Female painted turtles in western Nebraska matured after 5-6 activity seasons at 160-165 mm carapace length. Annual adult survivorship was at least 91.5%, and some females apparently survive beyond 30 yr of age. Nesting was recorded from 19 May to 17 July, and its onset was inversely related to March-May temperatures. Internesting interval averaged 16.4 days and decreased through the nesting season. Females usually produced two clutches per season, but many produced three clutches, and two may have produced four clutches. Average annual clutch frequency was estimated at 2.78 per female. Egg size was correlated with female size. When standardized for body size, egg size was negatively correlated with body size and clutch size and varied across estimated clutch number (early season clutches having larger, more elongate eggs than later ones) but not among years. Egg size was not constrained by pelvic canal width. Clutch size averaged 13.9, was positively correlated with body size, and varied across estimated clutch number (later clutches being smaller than earlier clutches) as well as across years. Clutch mass increased with body size but remained constant as a proportion of spent female body mass (=RCM). RCM varied across clutch number within years (higher in earlier clutches) and across years (with a trend for higher RCM in years following a warmer Oct.). Actual annual clutch output in triple-nesting females averaged 42 eggs or 30.9% of spent female body mass. Across populations of painted turtles, body size is positively correlated with latitude and elevation and negatively correlated with average frost-free days and mean annual temperature. Clutch frequency remains one of the most elusive traits but seems to be inversely related to latitude and age at maturity and positively related to frost-free days. Both egg size and clutch size tend to vary with body size within and among populations, with clutch size varying the most. Presumably because of its correlation with body size, clutch size also varied with latitude, elevation, the inverse of frost-free days, and the inverse of mean annual temperature. Populations of small turtles (at lower latitudes and/or warmer climates) apparently produce the largest eggs possible within the constraints of their pelvic canal diameter, whereas no such constraint exists for larger-bodied populations at high latitudes. Selection is probably more intense on egg size than clutch size, and clutch size seems to have a much greater environmental component.

Patterns of survival, growth and maturation in turtles

A review of published data suggests that turtles (Order Testudines) resemble other previously studied vertebrate and invertebrate groups in terms of the relationships among growth trajectories, adult survival rates, and ages at maturation. For example, most turtles mature at around 70% of maximum size, as do other reptiles. Adult lifespans are proportional to age at maturity, and the relationship between these two variables is similar in turtles to that documented in other reptiles. Although the ratio of the von Bertalanffy growth constant (k) to the adult instantaneous mortality rate (M) appears to be higher than ratios reported for other animals (including squamate reptiles), the general relationship between these two variables corresponds with that seen in other reptiles. These analyses show that turtles exhibit patterns of growth, survivorship and maturation that are of the same form as those that are present in other types of organisms in which growth continues after maturity

Molecular systematics, phylogeography, and the effects of pleistocene glaciation in the painted turtle (Chrysemys picta) complex

Abstract.— The painted turtle, Chrysemys picta, is currently recognized as a continentally distributed polytypic species, ranging across North America from southern Canada to extreme northern Mexico. We analyzed variation in the rapidly evolving mitochondrial control region (CR) in 241 turtles from 117 localities across this range to examine whether the painted turtle represents a continentally distributed species based on molecular analysis. We found strong support for the novel hypothesis that C. p. dorsalis is the sister group to all remaining Chrysemys, with the remaining Chrysemys falling into a single, extremely wide‐ranging and genetically undifferentiated species. Given our goal of an evolu‐tionarily accurate taxonomy, we propose that two evolutionary lineages be recognized as species within Chrysemys: C. dorsalis (Agassiz 1857) in the southern Mississippi drainage region, and C. picta (Schneider 1783) from the rest of the range of the genus. Neither molecular nor recent morphological analyses argue for the hybrid origin of C. p. marginata as previously proposed. Within C. picta, we find evidence of at least two independent range expansions into previously glaciated regions of North America, one into New England and the other into the upper Midwest. We further find evidence of a massive extinction/recolonization event across the Great Plains/Rocky Mountain region encompassing over half the continental United States. The timing and extent of this colonization is consistent with a recently proposed regional aridification as the Laurentide ice sheets receded approximately 14,000 years ago, and we tentatively propose this paleoclimatological event as a major factor shaping genetic variation in Chrysemys.

The impact of feral cats and dogs on populations of the West Indian rock iguana, Cyclura carinata

Abstract A population of rock iguanas, Cyclura carinata, inhabiting Pine Cay in the Caicos Islands was nearly extirpated during the three years following construction of a hotel and tourist facility. The decline, from an estimated adult lizard population of nearly 5500, was due primarily to predation by domestic dogs and cats introduced to the island simultaneously with hotel construction. Population declines on other nearby islands were also attributed to predation by these feral mammals.

A Global Analysis of Tortoise and Freshwater Turtle Distributions with Identification of Priority Conservation Areas

Abstract There are currently ca. 317 recognized species of turtles and tortoises in the world. Of those that have been assessed on the IUCN Red List, 63% are considered threatened, and 10% are critically endangered, with ca. 42% of all known turtle species threatened. Without directed strategic conservation planning, a significant portion of turtle diversity could be lost over the next century. Toward that conservation effort, we compiled museum and literature occurrence records for all of the worlds tortoises and freshwater turtle species to determine their distributions and identify priority regions for conservation. We constructed projected range maps for each species by selecting geographic information system–defined hydrologic unit compartments (HUCs) with verified locality points, and then added HUCs that connected known point localities in the same watershed or physiographic region and that had similar habitats and elevations as the verified HUCs. We analyzed a total of 305 turtle species and assigned each to 1 of 7 geographic regions of the world. Patterns of global turtle species distributions were determined and regional areas of turtle species richness identified. In only 2 areas of the world did as many as 18 or 19 species occur together in individual HUCs. We then compared species distributions with existing global conservation strategies (GCSs) and established biodiversity priority areas. Presence of a species in a GCS was defined as ≥ 5% its range. Of the 34 biodiversity hotspots, 28 collectively contain the projected ranges of 192 turtle species, with 74 endemic; the 5 high-biodiversity wilderness areas contain 72 species, with 17 endemic; and 16 other wilderness areas contain 52 species, with 1 endemic. However, 116 turtle species have either < 50% of their ranges in existing GCSs (57 species) or do not occur in them at all (59 species, 19.3%), thus potentially leaving many tortoises and freshwater turtles without any regional GCS. For each of these 116 species we identify a priority Ecoregion for further conservation consideration, and we identify 3 new global Turtle Priority Areas for conservation based on aggregated Ecoregions. These are the Southeastern United States, Lower Gangetic Plain, and Coastal Australia Turtle Priority Areas.

Cold Hardiness and Overwintering Strategies of Hatchlings in an Assemblage of Northern Turtles

Field and laboratory studies were conducted during 1989-1994 to investigate the overwintering strategies of hatchling turtles representing four families native to western Nebraska. Whereas hatchling snapping turtles (Chelydra serpentine) and spiny soft-shelled turtles (Apalone spinifera) overwinter in aquatic habitats, yellow mud turtles (Kinosternon flavescens) and ornate box turtles (Terrapene ornata) burrow below the natal nest and hibernate in sandy soil. Painted turtles (Chrysemys picta) overwinter within their shallow natal nests, but this species, and T. ornata, tolerate extensive tissue freezing. Overwintering behaviors of these species are consistent with indices of physiological cold hardiness and patterns of geographic distribution. Frost commonly penetrated and persisted below 10 cm, the soil depth at which hatchling C. picta routinely hibernate. Field and laboratory data suggested that hatchling C. picta survive either by remaining supercooled (unfrozen) or by tolerating tissue freezing, the strategy employed depending on prevailing physiological and microenvironmental conditions. Whereas relatively lower temperatures can be survived in the supercooled state, supercooling capacity may be limited via the inoculation of body fluids by environmental ice. Alternatively, whereas freeze tolerance fortuitously is promoted by ice inoculation, this strategy may be viable only at relatively high subzero temperatures. A cold-hardiness strategy based on both survival mechanisms may promote winter survival in hatchling C. picta by conferring protection under dynamic physiological and microen- vironmental conditions. Physiological cold hardiness and behavior are integrated deter- minants of the northern distributions of temperate region turtles.

Biomass in turtle populations: A neglected subject

SummaryBiomass values for individual turtle species are as high as 586 kg/ha. Typical values are at least an order of magnitude greater than those typical of endotherms, but comparable to ectotherms with aquatic niches. Herbivorous turtle species tend to have higher biomasses than omnivorous or carnivorous species, but the differences are not statistically significant. Semiaquatic species typically have the lowest biomasses. Islands, ponds, and springs harbor species with the highest biomasses. Annual production estimates for two turtle species (three populations) are 1.4 to 14.9 and 6 kg/ha/yr, and are similar to estimates available for most other vertebrate groups except fishes (maximum, 528 kg/ha/yr).

Comparing and combining distance-based and character-based approaches for barcoding turtles.

Molecular barcoding can serve as a powerful tool in wildlife forensics and may prove to be a vital aid in conserving organisms that are threatened by illegal wildlife trade, such as turtles (Order Testudines). We produced cytochrome oxidase subunit one (COI) sequences (650 bp) for 174 turtle species and combined these with publicly available sequences for 50 species to produce a data set representative of the breadth of the order. Variability within the barcode region was assessed, and the utility of both distance‐based and character‐based methods for species identification was evaluated. For species in which genetic material from more than one individual was available (n = 69), intraspecific divergences were 1.3% on average, although divergences greater than the customary 2% barcode threshold occurred within 15 species. High intraspecific divergences could indicate species with a high degree of internal genetic structure or possibly even cryptic species, although introgression is also probable in some of these taxa. Divergences between species of the same genus were 6.4% on average; however, 49 species were <2% divergent from congeners. Low levels of interspecific divergence could be caused by recent evolutionary radiations coupled with the low rates of mtDNA evolution previously observed in turtles. Complementing distance‐based barcoding with character‐based methods for identifying diagnostic sets of nucleotides provided better resolution in several cases where distance‐based methods failed to distinguish species. An online identification engine was created to provide character‐based identifications. This study constitutes the first comprehensive barcoding effort for this seriously threatened order.

Colic modifications in iguanine lizards

All lizard species of the subfamily Iguaninae except Amblyrynchus cristatus possess from one to eleven transverse valves in the proximal colon. Valves are of two kinds: circular (sometimes with a sphincter valve) or semilunar. Circular valves (if present) always occur proximally to semilunar valves. Intraspecific variation in the number and type of valves is small, but increase with modal number of valves. No significant ontogenetic change in number of valves could be demonstrated. Colic valves in iguanine lizards apparently evolved as simple infoldings of the medical colic wall.

Demographics of an ornate box turtle population experiencing minimal human-induced disturbances

Human-induced disturbances may threaten the viability of many turtle pop- ulations, including populations of North American box turtles. Evaluation of the potential impacts of these disturbances can be aided by long-term studies of populations subject to minimal human activity. In such a population of ornate box turtles (Terrapene ornata ornata) in western Nebraska, we examined survival rates and population growth rates from 1981-2000 based on mark-recapture data. The average annual apparent survival rate of adult males was 0.883 (SE = 0.021) and of adult females was 0.932 (SE = 0.014). Minimum winter temperature was the best of five climate variables as a predictor of adult survival. Survival rates were highest in years with low minimum winter temperatures, suggesting that global warming may result in declining survival. We estimated an average adult pop- ulation growth rate (X) of 1.006 (SE = 0.065), with an estimated temporal process variance (6-2) of 0.029 (95% ci = 0.005-0.176). Stochastic simulations suggest that this mean and temporal process variance would result in a 58% probability of a population decrease over a 20-year period. This research provides evidence that, unless unknown density-dependent mechanisms are operating in the adult age class, significant human disturbances, such as commercial harvest or turtle mortality on roads, represent a potential risk to box turtle populations.