Geology topics

Karen E. Mock

Publications and source records attributed to Karen E. Mock.

4 recordsLinked to original sources

USGS2024

Population genetics of museum specimens indicate decreasing genetic resiliency: The case of two bumble bees of conservation concern

Genetic resiliency is the likelihood that populations retain sufficient genetic diversity to respond to environmental change. It is rarely examined through time in conservation genetic studies due to challenges of acquiring and sequencing historical specimens. Focusing on populations of two sibling bumble bee species of conservation concern with different recent patterns of decline, we used museum specimens collected between 1960 and 2020 and 15 microsatellite markers to assess genetic resiliency (allelic richness, expected heterozygosity, and inbreeding) through time and across geographic space. We find evidence of decreasing allelic richness through time, starting at least 30 years before observed abundance declines in one species and at least 20 years before present in a species with apparently stable abundance. We also found increasing expected heterozygosity through time, indicating increased inbreeding, in the putatively stable species. We demonstrate that genetic measurements taken from specimens collected through time can be used to detect population decline in imperiled species before decreases in abundance are detected. We also demonstrate the importance of interpreting population genetic metrics within the context of historical patterns to assess species' conservation statuses. Finally, we discuss the limitations of currently available population genetic methods, including the influence of isolation by distance and sampling density on measurements of genetic structure, and the influence of demographic characteristics and choice of genetic markers on estimates of genetic diversity and structure. We call for further development of individual-based modeling methods to measure genetic structure, as opposed to commonly applied population-based metrics, to overcome these limitations.

Biological Conservation↗

USGS2018

Rare long-distance dispersal of the Island Night Lizard, Xantusia riversiana, maintains high diversity in a fragmented environment

The Island Night Lizard ( Xantusia riversiana ) is endemic to three of the Channel Islands off the coast of California, USA. Introduced species such as goats, sheep, and cats have profoundly affected the fauna and flora of the islands for over 150 years, but most of these non-native species have been recently removed. We measured the distribution of genetic diversity in Island Night Lizards across San Nicolas Island using DNA microsatellites to assess the impacts of historical habitat change on effective population size, gene flow, and population divergence; to provide baseline data for future monitoring of genetic diversity; and to provide recommendations to inform the restoration of degraded habitat. Despite a history of profound anthropogenic habitat disturbance, genetic diversity was high within sites, and there was no evidence of population bottlenecks. Divergence between sites was extraordinarily high, as expected for this sedentary species. Landscape resistance modeling using circuit theory showed that unsuitable habitat is relatively permeable to gene flow compared to suitable habitat, and yet populations separated by very short geographic distances remain genetically distinct. We found no evidence of a need for short-term intervention such as artificial translocations to maintain genetic diversity. Instead, we suggest that management should focus on maintaining, improving, and increasing habitat, especially in creating patches of habitat to link existing sites.

California↗

USGS2016

Cryptic invasion of Northern Leopard Frogs ( Rana pipiens ) across phylogeographic boundaries and a dilemma for conservation of a declining amphibian

Anthropogenic introduction of species is a major contributor to loss of biodiversity. Translocations within the range of a species are less frequently recognized, but have the potential for negative effects as well. Genetic mixing may lead to loss of local adaptations or further decline through outbreeding depression. These cryptic invasions may be quite difficult to recognize, but genetic tools can be used to recognize and monitor such intraspecific introductions. Conversely, translocations within species can be an important conservation tool to reduce inbreeding depression and replace lost genetic diversity. Thus, cryptic invasions can be either an aid or a hindrance to conservation efforts. We tested for the presence of non-native genotypes and assessed the extent and nature of introgression in populations of Northern Leopard Frog ( Rana pipiens ) in the southwestern US, where populations have declined to a few remnant populations. The most abundant and diverse complex of populations in the region contained a mitochondrial haplotype that was not native to the western US, probably resulting from the introduction of released pets, laboratory animals, or release during fish stocking. These non-native haplotypes were well integrated into a large complex of ponds and lakes, contributing to high genetic diversity in this area. Logistically, the geographic extent of non-native genetic influence within this population precludes eliminating or controlling the non-native component of this population. We recommend assessing the progress and fate of the introgression over time—along with population fitness parameters—to determine whether this introduction is beneficial or detrimental to population persistence. Meanwhile, translocations from nearby locations with similar environmental conditions have the best prospects for avoiding problems with outbreeding depression in other declining populations and will also most effectively preserve regional genetic diversity.

Biological Invasions↗

USGS2011

Population status and population genetics of northern leopard frogs in Arizona

Increasing isolation of populations by habitat fragmentation threatens the persistence of many species, both from stochastic loss of small isolated populations, and from inbreeding effects in populations that have become genetically isolated. In the southwestern United States, amphibian habitat is naturally patchy in occurrence because of the prevailing aridity of the region. Streams, rivers, and other wetlands are important both as habitat and as corridors that connect populations. However, populations of some species have become more fragmented and isolated by habitat degradation and loss. Northern leopard frogs (Rana pipiens) have experienced serious declines in the Southwest. We conducted an extensive survey across the known range of northern leopard frogs in Arizona to determine the current distribution and abundance of the species. From a range that once spanned much of the northern and central part of the State, northern leopard frogs have been reduced to three or four widely separated populations, near Lyman Lake in east-central Arizona, in the Stoneman Lake area south of Flagstaff, along Truxton Wash near Peach Springs, and a population of uncertain extent on Navajo Nation lands. The Lyman Lake and Truxton Wash populations are small and extremely isolated. The Stoneman Lake population, however, is an extensive metapopulation spread across several stream drainages, including numerous ponds, wetlands, and artificial tanks. This is the only population in Arizona that is increasing in extent and numbers, but there is concern about the apparent introduction of nonnative genetic stock from eastern North America into this area. We analyzed genetic diversity within and genetic divergence among populations of northern leopard frogs, across both extant and recently extirpated populations in Arizona. We also analyzed mitochondrial DNA to place these populations into a larger phylogenetic framework and to determine whether any populations contained genetic material not native to the region. We found a high level of genetic divergence among the population centers (Lyman Lake, Stoneman Lake, Truxton Wash), and low genetic diversity in the small populations at Lyman Lake and Truxton. The extensive population in the Stoneman Lake area had high genetic diversity and relatively high gene flow among ponds and tanks across the entire extent of the area. However, this population also contained a mitochondrial haplotype from northern leopard frogs from the northeastern United States or southeastern Canada, probably representing the introduction of released pets or laboratory animals. These eastern frogs were extensively distributed through this population, and probably contributed to its high genetic diversity. Genetic diversity in the outlying populations such as Truxton Wash, East Buckskin Tank, and Hess Tank was low and showed signs of recent bottlenecks. However, supplementing genetic diversity in these native populations with artificial gene flow from the Stoneman Lake area may only be advisable in extreme situations for which there are no other alternatives. Until the nature and effects of genetic mixing of eastern and western genetic stocks of northern leopard frogs are better understood, the long-term persistence of the species in the Southwest may be best served by retaining as much genetic integrity of remaining native populations as possible.

Arizona↗