Fredric J. Janzen's research while affiliated with Michigan State University and other places

Publications (202)

Article
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Synchronous hatching and emergence of turtles from nests may be adaptive in predator avoidance during dispersal. However, little is known about the phenotypic consequences of such synchrony or the generality of predator avoidance in driving the evolution of this trait. Colbert et al. (2010) found that less advanced embryos hatched early in the pres...
Article
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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...
Article
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In contrast to genotypic sex determination (GSD), temperature-dependent sex determination (TSD) in amniotic vertebrates eludes intuitive connections to Fisherian sex-ratio theory. Attempts to draw such connections have driven over 50 years of research on the evolution of sex-determining mechanisms (SDM), perhaps most prominently among species in th...
Article
We are grateful for Keevil’s (2020) identification of a mistakenly limited prior in the code we supplied as a supplement to Reinke et al. 2020, describing a new model. Within our paper, we demonstrated use of a hierarchical model using mark‐recapture datasets which were also published as supplementary material. The introduction of the model was the...
Article
The unprecedented advancement of global climate change is affecting thermal conditions across spatial and temporal scales. Reptiles with temperature-dependent sex determination (TSD) are uniquely vulnerable to even fine-scale variation in incubation conditions and are a model system for investigating the impacts of shifting temperatures on key phys...
Article
Nesting is an essential, yet variable, reproductive behavior in most oviparous organisms. Although many factors conceivably influence nesting behaviors, it is unclear which factors strongly influence terrestrial nest timing in aquatic nonavian reptiles. As climate is changing rapidly, understanding the relative influences of biotic and abiotic fact...
Article
Life-history theory predicts that investment into reproduction should increase as future reproductive opportunities (i.e., residual reproductive value, RRV) decrease. Researchers have thus intuitively used age as a proxy for RRV and assume RRV decreases with age when interpreting age-specific investment. Yet, age is an imperfect proxy for RRV and m...
Preprint
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Sexual selection is often assumed to elicit sexually dimorphic traits. However, most work on this assumption in tetrapod vertebrates has focused on birds. In this field experiment, we assessed relationships between both sexually dimorphic (body size, claw length) and non-dimorphic traits (forelimb stripe color, baseline corticosterone concentration...
Article
The quantification of repeatability has enabled behavioral and evolutionary ecologists to assess the heritable potential of traits. For behavioral traits that vary across life, age-related variation should be accounted for to prevent biasing the microevolutionary estimate of interest. Moreover, to gain a mechanistic understanding of ontogenetic var...
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Biological control—the use of organisms (e.g., nematodes, arthropods, bacteria, fungi, viruses) for the suppression of insect pest species—is a well-established, ecologically sound and economically profitable tactic for crop protection. This approach has served as a sustainable solution for many insect pest problems for over a century in North Amer...
Article
Environmental conditions during embryonic development affect morphology, behavior, and survival in turtles. Nest temperature also could affect posthatching traits of offspring, such as emergence behaviors. We monitored thermal conditions in painted turtle (Chrysemys picta) nests along the Mississippi River in Illinois to examine their influence on...
Article
Parents increase their fitness by investing resources to offspring. However, such investment is costly for parents, leading to tradeoffs, which should shift towards heavier investment to reproduction as females age and future reproductive opportunities decrease. Nests of aquatic turtles laid farther from water have higher survival than those laid c...
Article
Oxygen deprivation swiftly damages tissues in most animals, yet some species show remarkable abilities to tolerate little or even no oxygen. Painted turtles exhibit a development-dependent tolerance that allows adults to survive anoxia ∼4x longer than hatchlings: adults survive ∼170 days and hatchlings survive ∼40 days at 3°C. We hypothesized this...
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Long-term studies have been crucial to the advancement of population biology, especially our understanding of population dynamics. We argue that this progress arises from three key characteristics of long-term research. First, long-term data are necessary to observe the heterogeneity that drives most population processes. Second, long-term studies...
Article
Developmental environments can have lasting effects on an individual's phenotype. In many reptiles, for example, egg incubation temperature permanently determines offspring sex (temperature-dependent sex determination, TSD) and also influences a suite of morphological, physiological, and behavioral traits. Thus, the contributions of sex and incubat...
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Understanding age‐dependent patterns of survival is fundamental to predicting population dynamics, understanding selective pressures, and estimating rates of senescence. However, quantifying age‐specific survival in wild populations poses significant logistical and statistical challenges. Recent work has helped to alleviate these constraints by dem...
Article
A key trend in the 210-million-year-old history of modern turtles was the evolution of shell kinesis, that is, shell movement during neck and limb retraction. Kinesis is hypothesized to enhance predator defense in small terrestrial and semiaquatic turtles and has evolved multiple times since the early Cretaceous. This complex phenotype is nonfuncti...
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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...
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Biological responses to climate change have been widely documented across taxa and regions, but it remains unclear whether species are maintaining a good match between phenotype and environment, i.e. whether observed trait changes are adaptive. Here we reviewed 10,090 abstracts and extracted data from 71 studies reported in 58 relevant publications...
Article
Fisherian sex-ratio theory predicts sexual species should have a balanced primary sex ratio. However, organisms with environmental sex determination (ESD) are particularly vulnerable to experiencing skewed sex ratios when environmental conditions vary. Theoretical work has modeled sex-ratio dynamics for animals with ESD with regard to 2 traits pred...
Article
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Environmental DNA (eDNA) is an increasingly used non-invasive molecular tool for detecting species presence and monitoring populations. In this article, we review the current state of non-avian reptile eDNA work in aquatic systems, and present a field experiment on detecting the presence of painted turtle (Chrysemys picta) eDNA. Thus far, turtle an...
Article
Temperature-dependent sex determination, where egg incubation temperature irreversibly determines offspring sex, is a common sex-determining mechanism in reptiles. Weather is the primary determinant of temperature in reptile nests, yet the effects of weather are mediated through the nest microhabitat selected by the mother (e.g., overstory canopy c...
Article
Temperature-dependent sex determination, where egg incubation temperature irreversibly determines offspring sex, is a common sex-determining mechanism in reptiles. Weather is the primary determinant of temperature in reptile nests, yet the effects of weather are mediated through the nest microhabitat selected by the mother (e.g., overstory canopy c...
Article
Optimal maternal investment is often a tradeoff between conflicting pressures and varies depending upon environmental context and intrinsic female traits. Yet, offspring phenotype might also interact with such factors to influence investment. In aquatic turtles, terrestrial nests constructed farther from shore often have higher survival because nes...
Preprint
Full-text available
Environmental DNA (eDNA) is an increasingly used non-invasive molecular tool for detecting species presence and monitoring populations. In this article, we review the current state of non-avian reptile eDNA work in aquatic systems, as well as present a field experiment on detecting the presence of painted turtle (Chrysemys picta) eDNA. Thus far, tu...
Article
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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...
Article
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Understanding developmental processes is foundational to clarifying the mechanisms by which convergent evolution occurs. Here, we show how a key convergently evolving trait is slowly ‘acquired’ in growing turtles. Many functionally relevant traits emerge late in turtle ontogeny, owing to design constraints imposed by the shell. We investigated this...
Article
Environmentally cued hatching allows embryos to alter the time of hatching in relation to environment through phenotypic plasticity. Spatially variable temperatures within shallow nests of many freshwater turtles cause asynchronous development of embryos within clutches, yet neonates still hatch synchronously either by hatching early or via metabol...
Article
Diversification of the turtle's shell comprises remarkable phenotypic transformations. For instance, two divergent species convergently evolved shell‐closing systems with shoulder blade (scapula) segments that enable coordinated movements with the shell. We expected these unusual structures to originate via similar changes in underlying gene networ...
Article
Studies of reptiles have contributed greatly to understanding the impacts of developmental environments on offspring phenotypes. A major challenge for these studies, however, is quantifying the effects of embryonic environments on adult phenotypes and reproductive success. Such measurements may be necessary to gain full insight into the evolution o...
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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...
Article
Background: Individual growth rates both comprise and determine life-history phenotypes. Despite decades of interest in understanding the relationship between individual growth and life history, chelonian longevity has limited our ability to robustly estimate individual growth curves that span the life of both sexes. Questions: (1) Do patterns o...
Article
Maternal stressors can play an integral role in offspring development and ultimate behaviors in many vertebrates. Increased circulating stress avoidance hormones can be reflected in elevated concentrations in ova, thus providing a potential mechanism for maternal stress to be transmitted to offspring even in taxa without parental care. In this stud...
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1. The fitness consequence of maternal nest-site choice has attracted increasing scientific attention, but field studies identifying the long-term effects of nest-site choice on offspring survival and reproductive success are still rare in vertebrates. 2. To investigate the consequences of nest-site choice in lizards, we quantified the thermal and...
Article
Exogenous application of steroids and related substances to eggs affects offspring sex ratios in species with temperature-dependent sex determination (TSD). Laboratory studies demonstrate that this effect is most pronounced near the constant temperature that produces 1:1 sex ratios (i.e., pivotal temperature). However, the impact of such chemicals...
Article
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The mechanisms that mediate the interaction between the thermal environment and species' ranges are generally uncertain. Thermal environments may directly restrict species when environments exceed tolerance limits (i.e. the fundamental niche). However, thermal environments might also differentially affect relative performance among species prior to...
Article
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Theory predicts prey should flee to safety when the fitness benefits of flight meet or exceed the costs. Empirical work has shown the importance of predation risk (e.g., predator behavior, distance to refuge) to prey flight behavior. However, less is known about the influence of flight costs. We monitored nesting painted turtles (Chrysemys picta (S...
Article
Predatory lady beetles (Coccinellidae) contribute to biological control of agricultural pests, however, multiple species frequently compete for similar resources in the same environment. Numerous studies have examined ecological interactions among the native North American convergent lady beetle (Hippodamia convergens) and two introduced species, t...
Article
Background: Many reptiles have temperature-dependent sex determination (TSD), and thus are potentially directly influenced by climate change. Where and when a reptile nests can influence nest temperature and offspring characteristics (including sex). Understanding how nesting behaviours are affected by climate is important, particularly in these te...
Article
Habitat destruction and modification may be the most prominent anthropogenic forces affecting extant biological systems. Growing evidence suggests that turtles are especially vulnerable to many anthropogenic stressors. We evaluated the effects of habitat modification on survival rates of the threatened ornate box turtle (Terrapene ornata) in northw...
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Group formation is a common behaviour among prey species. In egg-laying animals, despite the various factors that promote intra-clutch variation leading to asynchronous hatching and emergence from nests, synchronous hatching and emergence occurs in many taxa. This synchrony may be adaptive by reducing predation risk, but few data are available in a...
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Egg and nest crypsis is a strategy to reduce detection by predators, thereby minimizing offspring mortality. While this strategy has been well studied in birds, it has received little attention in other taxa. Turtles are plausibly able to camouflage their subterranean nests by reducing the level of soil surface disturbance. To test the hypothesis t...
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Lifespan and aging rates vary considerably across taxa; thus, understanding the factors that lead to this variation is a primary goal in biology and has ramifications for understanding constraints and flexibility in human aging. Theory predicts that senescence-declining reproduction and increasing mortality with advancing age-evolves when selection...
Article
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Historically, egg-bound reptile embryos were thought to passively thermoconform to the nest environment. However, recent observations of thermal taxis by embryos of multiple reptile species have led to the widely-discussed hypothesis that embryos behaviorally thermoregulate. Because temperature affects development, such thermoregulation could allow...
Article
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Four decades ago, it was proposed that environmental sex determination (ESD) evolves when individual fitness depends on the environment in a sex-specific fashion - a form of condition-dependent sex allocation. Many biological processes have been hypothesized to drive this sex asymmetry, yet a general explanation for the evolution of sex-determining...
Article
Predation strongly influences reproductive behaviours because reproducing individuals must balance mortality risks to themselves and to their offspring. In many freshwater turtles, the nest predation risk decreases with nest distance from water, whereas the predation risk to females increases farther from water. To determine whether predation press...
Article
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Organisms become adapted to their environment by evolving through natural selection, a process that generally transpires over many generations. Currently, anthropogenically driven environmental changes are occurring orders of magnitude faster than they did prior to human influence, which could potentially outpace the ability of some organisms to ad...
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The insulin/insulin-like signaling and target of rapamycin (IIS/TOR) network regulates lifespan and reproduction, as well as metabolic diseases, cancer, and aging. Despite its vital role in health, comparative analyses of IIS/TOR have been limited to invertebrates and mammals. We conducted an extensive evolutionary analysis of the IIS/TOR network a...
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Phenotypic variation is strongly impacted by environmental conditions experienced during development. Substantial laboratory research has shown that reptiles with flexible-shelled eggs are particularly sensitive to hydric conditions, yet research on nests in the wild is sparse.In this two-year field experiment, we explore the influence of hydric co...
Conference Paper
Quantifying non-target effects of augmentative releases on populations of conspecifics is key to understanding the long-term impacts of augmentation biological control. Potential deleterious (and advantageous) allelic variation carried over to augmented populations from ‘source’ populations could shape adaptive evolutionary trajectories. Variation...
Article
Temperature-dependent sex determination (TSD) is widespread in reptiles, yet its adaptive significance and mechanisms for its maintenance remain obscure and controversial. Comparative analyses identify an ancient origin of TSD in turtles, crocodiles and tuatara, suggesting that this trait should be advantageous in order to persist. Based on this as...
Article
Offspring phenotypic variation can be substantially influenced by non-genetic factors such as maternal effects, which ultimately can influence organismal fitness. For oviparous organisms that lack parental care, oviposition-site choice and egg size are maternal effects that can greatly affect offspring traits. Yet, few studies examine the consequen...
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Normal developmental staging tables often undergo expansion and enhancement in response to advancing research paradigms and technologies. The Painted Turtle, Chrysemys picta, has long been a preferred reference taxon for comparative embryology and recently became the first turtle species to feature a sequenced genome. However, modern descriptive st...
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Extreme environmental events (EEEs) are likely to exert deleterious effects on populations. From 1996 to 2012 we studied the nesting dynamics of a riverine population of painted turtles (Chrysemys picta) that experienced seven years with significantly definable spring floods. We used capture-mark-recapture methods to estimate the relationships betw...
Article
Evolutionary theory predicts that dioecious species should produce a balanced primary sex ratio maintained by frequency-dependent selection. Organisms with environmental sex determination, however, are vulnerable to maladaptive sex ratios, because environmental conditions vary spatio-temporally. For reptiles with temperature-dependent sex determina...
Article
Maternal ability to match nest characteristics with environmental conditions can influence offspring survival and quality, and may provide a mechanism by which animals can keep pace with climate change. In species with temperature-dependent sex determination that construct subterranean nests, the depth of the nest may affect incubation temperatures...
Article
Read the Feature Paper: Nest depth may not compensate for sex ratio skews caused by climate change in turtlesCommentaries on this Feature Paper: Chelonians in a changing climate: can nest site selection prevent sex ratio skews?; For reptiles with temperature‐dependent sex determination, thermal variability may be as important as thermal averages; R...
Conference Paper
Background/Question/Methods We present an overview of six years (2006-2012) of student-coordinated efforts centered on ecological outreach, education, and research. This work was conducted by the Iowa State University (ISU) chapter of Strategies for Ecology Education, Diversity, and Sustainability (SEEDS), a program of the Ecological Society of A...
Conference Paper
Background/Question/Methods Novel phenotypes are usually a response to selective pressures in the environment. Thus, these traits may allow for organisms to occupy new ecological niches. In turtles, a key innovation that likely promoted the invasion of terrestrial environments is their shell closing systems. Shell closing systems are an adaptatio...
Article
Increases in extreme environmental events are predicted to be major results of ongoing global climate change and may impact the persistence of species. We examined the effects of heat and cold waves during embryonic development of painted turtles (Chrysemys picta) in natural nests on the occurrence of abnormal shell morphologies in hatchlings. We f...
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Abstract By altering phenology, organisms have the potential to match life-history events with suitable environmental conditions. Because of this, phenological plasticity has been proposed as a mechanism whereby populations might buffer themselves from climate change. We examine the potential buffering power of advancing one aspect of phenology, ne...
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Does life history affect molecular evolutionary rates? The molecular evolutionary rate measures the frequency with which DNA or protein sequence mutations are fixed (i.e., shared by most individuals) in a population. On the other hand, the mutation rate refers to the amount of change in a DNA or protein sequence for a given unit of time. These two...
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Background: We describe the genome of the western painted turtle, Chrysemys picta bellii, one of the most widespread, abundant, and well-studied turtles. We place the genome into a comparative evolutionary context, and focus on genomic features associated with tooth loss, immune function, longevity, sex differentiation and determination, and the s...
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Blanding’s turtle (Emys blandingii) has declined substantially in North America due to anthropogenic activities, leaving populations smaller and increasingly fragmented spatially. We sampled 212 turtles to evaluate variation at eight microsatellite loci within and among 18 populations of E. blandingii across its primary range in the midwestern Unit...