Governance:Governance Frameworks for Wastewater Management

MVZ specimen catalog numbers and views represented. (XLSX 495 kb

Developmental dynamics of Ambystoma tigrinum in a changing landscape

<p>Abstract</p> <p>Background</p> <p>Loss of pond habitat is catastrophic to aquatic larval amphibians, but even reduction in the amount of time a breeding site holds water (hydroperiod) can influence amphibian development and limit reproductive success. Using the landscape variation of a glacial valley in the Greater Yellowstone Ecosystem as the context for a natural experiment, we examined variation in growth pattern and life history of the salamander <it>Ambystoma tigrinum melanostictum </it>and determined how these developmental characteristics varied with hydroperiod over several summers.</p> <p>Results</p> <p>In ponds that dried early in the season, maximum larval size was reduced relative to the sizes achieved in permanent ponds. Ephemeral ponds were associated with early metamorphosis at small body sizes, while permanent ponds facilitated longer larval periods and later metamorphosis. Paedomorphosis resulted from indefinite metamorphic postponement, and was identified only in the most permanent environments. Patterns of growth and allometry were similar between ponds with different hydroperiods, but considerable life history variation was derived from modulating the timing of and size at metamorphosis. Considering maximum rates of growth and inferring the minimum size at metamorphosis across 25 ponds over the course of three years, we calculated that hydroperiods longer than three months are necessary to support these populations through metamorphosis and/or reproductive maturity.</p> <p>Conclusions</p> <p>Landscape heterogeneity fosters life history variation in this natural population. Modulation of the complex ambystomatid life cycle allows this species to survive in unpredictable environments, but current trends towards rapid pond drying will promote metamorphosis at smaller sizes and could eliminate the paedomorphic phenotype from this region. Metamorphosis at small size is has been linked to altered fitness traits, including reduced survival and fecundity. Thus, widespread environmental truncation of larval periods may lead to decreased population persistence. We found that the hydroperiods of many ponds in this region are now shorter than the developmental period required for larvae to reach the minimum size for metamorphosis; these locations serve as reproductive sinks that may be detrimental for persistence of the species in the region.</p

Temporal response of the tiger salamander (Ambystoma tigrinum) to 3,000 years of climatic variation

BACKGROUND: Amphibians are sensitive indicators of environmental conditions and show measurable responses, such as changes in phenology, abundance and range limits to local changes in precipitation and temperature regimes. Amphibians offer unique opportunities to study the important ecological and evolutionary implications of responses in life history characteristics to climatic change. We analyzed a late-Holocene fossil record of the Tiger Salamander (Ambystoma tigrinum) for evidence of population-level changes in body size and paedomorphosis to climatic change over the last 3000 years. RESULTS: We found a significant difference in body size index between paedomorphic and metamorphic individuals during the time interval dominated by the Medieval Warm Period. There is a consistent ratio of paedomorphic to metamorphic specimens through the entire 3000 years, demonstrating that not all life history characteristics of the population were significantly altered by changes in climate on this timescale. CONCLUSION: The fossil record of Ambystoma tigrinum we used spans an ecologically relevant timescale appropriate for understanding population and community response to projected climatic change. The population-level responses we documented are concordant with expectations based on modern environmental studies, and yield insight into population-level patterns across hundreds of generations, especially the independence of different life history characteristics. These conclusions lead us to offer general predictions about the future response of this species based on likely scenarios of climatic warming in the Rocky Mountain region

Getting a head in hard soils: Convergent skull evolution and divergent allometric patterns explain shape variation in a highly diverse genus of pocket gophers (Thomomys)

BACKGROUND: High morphological diversity can occur in closely related animals when selection favors morphologies that are subject to intrinsic biological constraints. A good example is subterranean rodents of the genus Thomomys, one of the most taxonomically and morphologically diverse mammalian genera. Highly procumbent, tooth-digging rodent skull shapes are often geometric consequences of increased body size. Indeed, larger-bodied Thomomys species tend to inhabit harder soils. We used geometric morphometric analyses to investigate the interplay between soil hardness (the main extrinsic selection pressure on fossorial mammals) and allometry (i.e. shape change due to size change; generally considered the main intrinsic factor) on crania and humeri in this fast-evolving mammalian clade. RESULTS: Larger Thomomys species/subspecies tend to have more procumbent cranial shapes with some exceptions, including a small-bodied species inhabiting hard soils. Counter to earlier suggestions, cranial shape within Thomomys does not follow a genus-wide allometric pattern as even regional subpopulations differ in allometric slopes. In contrast, humeral shape varies less with body size and with soil hardness. Soft-soil taxa have larger humeral muscle attachment sites but retain an orthodont (non-procumbent) cranial morphology. In intermediate soils, two pairs of sister taxa diverge through differential modifications on either the humerus or the cranium. In the hardest soils, both humeral and cranial morphology are derived through large muscle attachment sites and a high degree of procumbency. CONCLUSIONS: Our results show that conflict between morphological function and intrinsic allometric patterning can quickly and differentially alter the rodent skeleton, especially the skull. In addition, we found a new case of convergent evolution of incisor procumbency among large-, medium-, and small-sized species inhabiting hard soils. This occurs through different combinations of allometric and non-allometric changes, contributing to shape diversity within the genus. The strong influence of allometry on cranial shape appears to confirm suggestions that developmental change underlies mammalian cranial shape divergences, but this requires confirmation from ontogenetic studies. Our findings illustrate how a variety of intrinsic processes, resulting in species-level convergence, could sustain a genus-level range across a variety of extrinsic environments. This might represent a mechanism for observations of genus-level niche conservation despite species extinctions in mammals. KEYWORDS: Environmental selection pressure; Evolutionary development; Heterochrony; Incisor procumbency; Parallel evolution; Principal component analysis; Repeated evolution; Subterranean nich

Bayesian Estimation of the Timing and Severity of a Population Bottleneck from Ancient DNA

In this first application of the approximate Bayesian computation approach using the serial coalescent, we demonstrated the estimation of historical demographic parameters from ancient DNA. We estimated the timing and severity of a population bottleneck in an endemic subterranean rodent, Ctenomys sociabilis, over the last 10,000 y from two cave sites in northern Patagonia, Argentina. Understanding population bottlenecks is important in both conservation and evolutionary biology. Conservation implications include the maintenance of genetic variation, inbreeding, fixation of mildly deleterious alleles, and loss of adaptive potential. Evolutionary processes are impacted because of the influence of small populations in founder effects and speciation. We found a decrease from a female effective population size of 95,231 to less than 300 females at 2,890 y before present: a 99.7% decline. Our study demonstrates the persistence of a species depauperate in genetic diversity for at least 2,000 y and has implications for modes of speciation in the incredibly diverse rodent genus Ctenomys. Our approach shows promise for determining demographic parameters for other species with ancient and historic samples and demonstrates the power of such an approach using ancient DNA

High levels of gene flow in the California vole (\u3ci\u3eMicrotus californicus\u3c/i\u3e) are consistent across spatial scales

Gene flow links the genetic and demographic structures of species. Despite the fact that similar genetic and demographic patterns shape both local population structure and regional phylogeography, the 2 levels of population connectivity are rarely studied simultaneously. Here, we studied gene flow in the California vole (Microtus californicus), a small-bodied rodent with limited vagility but high local abundance. Within a 4.86-km2 preserve in central California, genetic diversity in 6 microsatellites was high, and Bayesian methods indicated a single genetic cluster. However, individual-based genetic analysis detected a clear signal for isolation-by-distance (IBD) and fine-scale population structure. Mitochondrial cytochrome b sequencing revealed 11 unique haplotypes from the one local area where we sequenced 62 individuals. Phylogeographic analysis of these individuals combined with those sampled from the northern geographic range of the species (the range of the species spans western North America from southern Oregon to northern Mexico and is centered geographically within the state of California) again indicated a lack of structure but a signal for IBD. Patterns of gene flow thus are consistent across spatial scales: while dispersal of the California vole is limited across geographic distance, there is nonetheless considerable movement across the landscape. We conclude that in this species, high local population abundances overcome the potential genetic and demographic effects of limited dispersal

Diet DNA reveals novel African forest elephant ecology on the grasslands of the Congo Basin

Elephants are essential ecological engineers, creating and maintaining landscape structure and ecosystem function. The recently distinguished and critically endangered forest elephant is currently classified as a selective, non-destructive frugivorous browser that maintains forest diversity, while the savanna elephant is a mixed feeder, often pushing over trees while maintaining grasslands. The presence and diets of forest elephants on grasslands and the potential maintenance of these systems remain largely unexplored. In the ecotone between the Guinea-Congolian forest and Sudanian-Guinean savanna ecosystems in Garamba National Park, DRC, we investigated forest elephant diet selection as a function of sex, age, and habitat using diet DNA (dDNA) metabarcoding of non-invasively collected dung. GPS collar data were used to determine annual habitat use. Dietary niche partitioning was assessed among megaherbivores in the grasslands. Fecal samples represented the diet of individuals within each habitat, providing valuable insight into the plant biodiversity. Ecological patterns of diet were also revealed using a taxonomically free exact sequence variance approach, highlighting useability in a poorly characterized region. In the early wet season, these typically frugivorous forest elephants were consuming mostly grasses in both the woodland and grassland habitats and showing no sexual dimorphism in diet selection when in the same habitats. However, males were greater risk-takers, entering the human-altered landscape to forage on fruit. The forest elephants play a distinctive role within this tropical grassland when compared to other megaherbivores and utilize the unique ecosystem throughout the year. This elephant population is exhibiting behavioral plasticity and shifting their gardening efforts to a novel resource in the grasslands as opposed to their standard role in the forests, which is key to understanding their impact as ecosystem drivers within this landscape. This shift in behavior may result in this recovering elephant population playing a functional role in the restoration and maintenance of these grasslands.The Philippe S. Cohen Graduate Fellowship and an African Parks Network grant.http://www.wileyonlinelibrary.com/journal/edn3am2023Mammal Research Institut