John Iverson

Earlham College · Biology

Background The progressive deregulation of the immune system with age, termed immunosenescence, has been well studied in mammalian systems, but studies of immune function in long-lived, wild, non-mammalian populations are scarce. In this study we leverage a 38-year mark-recapture study to quantify the relationships among age, sex, survival, reprodu...

The eruption of Mount Pinatubo in the Philippines in June 1991 reduced global temperatures over the following 2 yrs. The greatest suppression (apart from Antarctica) was centered in the northern Great Plains of North America, directly over my long-term turtle study site. Temperatures at that site in 1992 and 1993 were the coldest in at least 50 yrs...

Within the group of Kinosternids turtles from western Mexico, the Cora mud turtle (Kinosternon cora), known locally as Chacuanita cora, is the most recently described freshwater turtle from Mexico, endemic to the Pacific coastal plain adjacent to the foothills of the Sierra Madre Occidental, distributed in a restricted area of 500 km2, between the...

Comparative studies of mortality in the wild are necessary to understand the evolution of aging; yet, ectothermic tetrapods are underrepresented in this comparative landscape, despite their suitability for testing evolutionary hypotheses. We present a study of aging rates and longevity across wild tetrapod ectotherms, using data from 107 population...

The genus Cyclura includes nine extant species and six subspecies of West Indian Rock Iguanas and is one of the most imperiled genera of squamate reptiles globally. An understanding of species diversity, evolutionary relationships, diversification, and historical biogeography in this group is crucial for implementing sound long-term conservation st...

There is great interspecific variation in the nutritional composition of natural diets, and the varied nutritional content is physiologically tolerated because of evolutionarily based balances between diet composition and processing ability. However, as a result of landscape change and human exposure, unnatural diets are becoming widespread among w...

To promote survival and fitness, organisms use a suite of physiological systems to respond to both predictable and unpredictable changes in the environment. These physiological responses are also influenced by changes in life history state. The continued activation of physiological systems stemming from persistent environmental perturbations enable...

Type specimens are the cornerstones of modern taxonomy and systematics, and should be the starting point of any study of diversity, especially considering the increasing ability to sample them genetically. However, no compilation of type material (beyond holotypes) exists for turtles (Order Testudines). This is the first attempt to locate and compi...

Resumen (Spanish abstract)—Documentamos una nueva localidad para Kinosternon alamosae, este registro representa el segundo para el estado de Sinaloa y el primero para el municipio de Ahome, con una extensión geográfica de 222 km (línea aérea) norte de la localidad más cercana al sur en del municipio de Culiacán y 113 km (línea aérea) sur de la loca...

Assessing community assembly rules has been a prominent task by community ecologists. Using a turtle family (Pelomedusidae) as a study case, we analyze the structure of their communities from the continental scale to the habitat scale, by using a suite of statistical approaches: (i) GIS modeling of the most complete presence sites dataset (from IUC...

This is our 9th edition of an annotated checklist and atlas of all recognized taxa of the world’s modern turtle and tortoise fauna, documenting recent changes and controversies through mid-2021, and including all primary synonyms, updated from eight previous checklists. We provide an updated comprehensive listing of taxonomy and nomenclature, inclu...

We compared patterns of population relatedness in a three-tiered host-parasite system: C. cychlura iguanas, their ticks (genus Amblyomma, preferentially parasitizing these reptiles), and Rickettsia spp. endosymbionts (within tick ectoparasites). Our results indicate that while C. c. cychlura on Andros is consistently supported as a separate clade,...

The Central Chiapas Mud Turtle (Kinosternon abaxillare) is one of the least-studied turtles in Mexico. It is considered a microendemic, with a limited distribution in the Central Depression of Chiapas. In this article, we summarize its population ecology and provide a new assessment of its morphology from Villa Hidalgo, Chiapas, Mexico. We captured...

The Central Chiapas Mud Turtle (Kinosternon abaxillare) is one of the least-studied turtles in Mexico. It is considered a microendemic, with a limited distribution in the Central Depression of Chiapas. In this article, we summarize its population ecology and provide a new assessment of its morphology from Villa Hidalgo, Chiapas, Mexico. We captured...

A frequent response of organisms to climate change is altering the timing of reproduction, and advancement of reproductive timing has been a common reaction to warming temperatures in temperate regions. We tested whether this pattern applied to two common North American turtle species over the past three decades in Nebraska, USA. The timing of nest...

Conservation planners use a variety of decision-making tools, many of which require identifying and prioritizing spatial units based on their biodiversity and levels of imperilment. Turtles are highly imperiled, but present schemes for determining global priority areas are focused mostly on broad regional scales. We conduct the first global evaluat...

We used a 36-yr study of a turtle community in a northern Indiana lake to examine shell anomalies and temporal changes in their frequency in 3 species. The overall frequency of shell anomalies was 17% in painted turtles (Chrysemys picta), 11% in northern map turtles (Graptemys geographica), and 18% in red-eared sliders (Trachemys scripta elegans),...

Turtles and tortoises (chelonians) have been integral components of global ecosystems for about 220 million years and have played important roles in human culture for at least 400,000 years. The chelonian shell is a remarkable evolutionary adaptation, facilitating success in terrestrial, freshwater and marine ecosystems. Today, more than half of th...

Eastern Musk Turtles (Sternotherus odoratus) in a few populations exhibit megacephaly, including those from a population in Arkansas herein described. I initiated a growth experiment in the laboratory with hatchlings from a megacephalic population and those from a nearby normocephalic population in Arkansas, both fed on fish chow for 22 yrs. The ex...

Defaunation in the Anthropocene has created a need to focus limited conservation resources on geographically explicit areas with high conservation significance. Priority conservation areas are often defined as those with high biodiversity – hotspots. While these conservation areas are critical to securing global biodiversity, prevailing approaches...

Body size, growth, and longevity in Northern Map Turtles (Graptemys geographica) from Dewart Lake in northern Indiana were studied from 1979 to 2016. Based on captures of 214 males (72 recaptures) and 99 females (40 recaptures), we generated von Bertalanffy growth equations which corroborated our growth curves based on counts of plastral growth rin...

Measures of reproductive output in turtles are generally positively correlated with female body size. However, a full understanding of reproductive allometry in turtles requires logarithmic transformation of reproductive and body size variables prior to regression analyses. This allows for slope comparisons with expected linear or cubic relationshi...

Population‐scale responses of key ecological traits to local environmental conditions provide insight into their adaptive potential. In species with temperature‐dependent sex determination (TSD), short‐term, individual developmental responses to the incubation environment have long‐term consequences for populations. We took a model‐based approach t...

We utilized natural experiment opportunities presented by differential conditions (presence/absence of seabirds and invasive species) on cays in the Bahamas to study whether interisland variations in food resources contributed to gigantism in Allen Cays Rock Iguanas (Cyclura cychlura inornata). We analyzed the stable carbon (δ¹³C) and nitrogen (δ¹⁵...

Global climate is warming rapidly, threatening vertebrates with temperature-dependent sex determination (TSD) by disrupting sex ratios and other traits. Less understood are the effects of increased thermal fluctuations predicted to accompany climate change. Greater fluctuations could accelerate feminization of species that produce females under war...

Aim This study aims to evaluate phylogenetic structure of turtle communities and their potential correlates on a global scale. More specifically, we tested whether cold temperatures and low precipitation could act as potential environmental filters of turtle communities and whether the dispersal limitation caused by altitudinal range could generate...

Taxa with large geographic distributions generally encompass diverse macroclimatic conditions, potentially requiring local adaptation and/or phenotypic plasticity to match their phenotypes to differing environments. These eco‐evolutionary processes are of particular interest in organisms with traits that are directly affected by temperature, such a...

We present a review and analysis of the conservation status and International Union for Conservation of Nature (IUCN) threat categories of all 360 currently recognized species of extant and recently extinct turtles and tortoises (Order Testudines). Our analysis is based on the 2018 IUCN Red List status of 251 listed species, augmented by provisiona...

1.Oxidative stress is a potential cost of reproduction, but conclusive evidence for this relationship is lacking. The goal of this study was to serially assess across a seasonal gradient the relationship between reproduction, circulating plasma energy metabolites, and oxidative state. 2.Here we examine a study animal ideally suited to test for the...

—Although initially applied to endotherms, Bergmann’s Rule (body size correlated with latitude) has also been demonstrated for a number of ectothermic taxa, including turtles. We examined body size and growth in the Pond Slider (Trachemys scripta) at the northern edge of its range in Indiana. We then compiled body size data from across the range of...

Recreational boating can have significant impacts on freshwater turtle individuals and populations through a variety of mechanisms, including direct injuries due to propeller strikes. We monitored the incidence of propeller wounds in four species of freshwater turtles in Dewart Lake in northern Indiana, USA, nearly annually from 1979-2014. Overall,...

Understanding how the climatic niche of species evolved has been a topic of high interest in current theoretical and applied macroecological studies. However, little is known regarding how species traits might influence climatic niche evolution. Here we evaluated patterns of climatic niche evolution in turtles (tortoises and freshwater turtles) and...

In wide-ranging taxa with historically dynamic ranges, past allopatric isolation and range expansion can both influence the current structure of genetic diversity. Considering alternate historical scenarios involving expansion from either a single refugium or from multiple refugia can be useful in differentiating the effects of isolation and expans...

Globally, populations of diverse taxa have altered phenology in response to climate change. However, most research has focused on a single population of a given taxon, which may be unrepresentative for comparative analyses, and few long‐term studies of phenology in ectothermic amniotes have been published. We test for climate‐altered phenology usin...

Taxonomy is a scientific discipline that has provided the universal naming and classification system of biodiversity for centuries and continues effectively to accommodate new knowledge. A recent publication by Garnett and Christidis [1] expressed concerns regarding the difficulty that taxonomic changes represent for conservation efforts and propos...

This book presents a brief summary of the 25th most endangered tortoise and turtle species. The summary includes a specimen picture, common and scientific names, endangered status, distribution, main causes for population decrease, and on going conservation strategies

This book presents a brief summary of the 25th most endangered tortoise and turtle species. The summary includes both common and scientific names, distribution, causes of population decrease, and conservation strategies.

Aims Geographical gradients in body size have been extensively studied in endotherms, and general rules exist to describe body size variation in these animals. However, the existence of broad‐scale patterns in body size variation in ectotherms remains largely debated. Turtles (tortoises and freshwater turtles) are ectothermic organisms whose geogra...

Laterality has been found in a variety of reptiles. In turtles, one important behaviour is the righting response. Here, we studied laterality of righting response of two species of freshwater turtles, the Painted Turtle (Chrysemys picta) and the Eastern Musk Turtle (Sternotherus odoratus). We found evidence of individual-level laterality in rightin...

Reptiles are highly dependent on climatic patterns to regulate their behavior and physiology, and studies of the effects of climate on the biology of organisms are increasingly important given expected climate change. Our study examined the effects of climate variation over 15 of the 26 years between 1990 and 2015 on the reproductive output of the...

The Eastern Mud Turtle, Kinosternon subrubrum (Family Kinosternidae), is a small (carapace length 85 to 120 mm) polytypic species of the eastern and central United States. All three historically recognized subspecies (K. s. subrubrum, K. s. steindachneri, and K. s. hippocrepis) are semi-aquatic turtles that inhabit much of the U.S. Atlantic and Gul...

This is our 8th edition of an annotated checklist of all recognized and named taxa of the world’s modern chelonian fauna, documenting recent changes and controversies in nomenclature through early 2017, and including all primary synonyms, updated from 7 previous checklists (Turtle Taxonomy Working Group 2007b, 2009, 2010, 2011, 2012, 2014; Rhodin e...

Although general descriptions of nesting in painted turtles (Chrysemys picta) are numerous, few studies have quantified the timing of the components of the nesting process, and no previous study has analyzed the factors influencing those times. The present study was conducted on the Crescent Lake National Wildlife Refuge in Garden County, Nebraska,...

Concentrations of the biomarker pentosidine have been shown to be useful measures of age for a number of avian and mammalian species. However, no study has examined its usefulness as an age marker in a long-lived ectotherm despite the fact that such a marker could prove useful in understanding age distributions of populations subject to conservatio...

Nest-site choice in turtles has a demonstrated impact on their fitness. Previous studies of nest-site choice have focused on environmental factors potentially affecting that choice (e.g., temperature, insolation, soil type, or moisture). Observations of nesting of painted turtles (Chrysemys picta) at the Crescent Lake National Wildlife Refuge in th...

The question whether taxonomic descriptions naming new animal species without type specimen(s) deposited in collections should be accepted for publication by scientific journals and allowed by the Code has already been discussed in Zootaxa (Dubois & Nemésio 2007; Donegan 2008, 2009; Nemésio 2009a–b; Dubois 2009; Gentile & Snell 2009; Minelli 2009;...

This plot is not part of the published stance but derives from it. The plot shows the number of authors by geographic region (courtesy of Dr. Diego Astua).

Life-histories evolve in response to constraints on the time available for growth and development. Nesting date and its plasticity in response to spring temperature may therefore be important components of fitness in oviparous ectotherms near their northern range limit, as reproducing early provides more time for embryos to complete development bef...

Ecological, historical, and evolutionary hypotheses are important to explain geographical diversity gradients in many clades, but few studies have combined them into a single analysis allowing a comparison of their relative importance. This study aimed to evaluate the relative importance of ecological, historical, and evolutionary hypotheses in exp...

Evidence from DNA phylogeny, Plio-Pleis-tocene ocean currents, giant tortoise dispersal , evolution of plant defences, radiocarbon dates and archaeology indicates that the endemic giant tortoises on the Mascarenes and Seychelles colonized naturally and were not translocated there by humans.

Chelonians are expected to be negatively impacted by climate change due to limited vagility and temperature-dependent sex determination. However, few studies have examined how freshwater turtle distributions may shift under different climate change scenarios. We used a maximum entropy approach to model the distribution of five widespread North Amer...

Iguanas are a particularly threatened group of reptiles, with 61% of species at risk of extinction. Primary threats to iguanas include habitat loss, direct and indirect impacts by invasive vertebrates, overexploitation, and human disturbance. As conspicuous, charismatic vertebrates, iguanas also represent excellent flagships for biodiversity conser...

This annotated checklist of the world's iguanas (Iguanidae; Iguaninae) represents an update by the Iguana Taxonomy Working Group (ITWG) of its 2011 list. We recognize 44 extant species (19 subspecies across six species) in eight genera. Ctenosaura (as currently recognized) is the most diverse, with 18 species, and Amblyrhynchus is the least diverse...

We describe the ongoing population recovery of the critically endangered Sandy (or White) Cay Rock Iguanas (Cyclura rileyi cristata), which occur on just one 14.9 hectare island in the southern Exuma Cays, The Bahamas. These large lizards were brought to the brink of extinction in 1997 by a single feral Raccoon (Procyon lotor), which preyed heavily...

The feeding of wildlife by ecotourists has become increasingly popular, but its effects are not well studied. The endangered Allen Cays Iguana is known to occur naturally on only two small cays in the northern Exuma Islands (The Bahamas). One of those cays, Leaf Cay (4 ha) has an easily accessible beach to which up to 150 people converge each day t...

The Endangered Allen Cays Rock Iguana (Cyclura cychlura inornata) is endemic to the Allen Cays, a tiny cluster of islands in the Bahamas. Naturally occurring populations exist on only two cays (<4 ha each). However, populations of unknown origin were recently discovered on four additional cays. To investigate patterns of genetic variation among the...

Cyclura cychlura inornata D-loop, cytochrome b (Cytb), and NADH dehydrogenase subunit 4 (ND4) gene region sequences

The Asiatic Softshell Turtle, Amyda cartilaginea (Family Trionychidae), is a large species (total carapace length up to 850 mm) showing considerable variation in coloration over its wide range in tropical Southeast Asia. A recent genetic analysis suggests A. cartilaginea may be a species complex consisting of three species level clades with several...

Abstract. – We provide a first checklist and review of all recognized taxa of the world's extinct Pleistocene and Holocene (Quaternary) turtles and tortoises that existed during the early rise and global expansion of humanity, and most likely went extinct through a combination of earlier hominin (e.g., Homo erectus, H. neanderthalensis) and later h...