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At least 55 records · Page 3Linked to original sources
USGS2025

Reproductive output of the rare plant Arctomecon californica does not appear to be limited by its floral visitor community

The majority of plants rely on animal-mediated pollination for reproduction. Reductions in pollinator visitations can lead to pollen limitation and declines in seed production. Arctomecon californica, the Las Vegas bearpoppy, is a rare plant native to the northeastern Mojave Desert. It is pollinator dependent for reproduction as it is self-incompatible, but associated pollinator populations can fluctuate greatly year to year. We therefore investigated if the reproductive output of A. californica is reduced in a year with lower pollinator visitation (2022) compared to a year when visitors were more abundant (2023). We documented the visiting bee community across both years and compared rates of A. californica seed fertilization and development across populations and between the two years. We collected and identified bees from 18 genera visiting A. californica flowers over the two years, with significant differences in the bee communities between years. There were significantly fewer overall bee visits to A. californica flowers in 2022 compared to 2023, but we found no impact on reproductive output, with overall high rates of seed production in both years.

Nevada↗
USGS2017

Conservation endocrinology

Endocrinologists can make significant contributions to conservation biology by helping to understand the mechanisms by which organisms cope with changing environments. Field endocrine techniques have advanced rapidly in recent years and can provide substantial information on the growth, stress, and reproductive status of individual animals, thereby providing insight into current and future responses of populations to changes in the environment. Environmental stressors and reproductive status can be detected nonlethally by measuring a number of endocrine-related endpoints, including steroids in plasma, living and nonliving tissue, urine, and feces. Information on the environmental or endocrine requirements of individual species for normal growth, development, and reproduction will provide critical information for species and ecosystem conservation. For many taxa, basic information on endocrinology is lacking, and advances in conservation endocrinology will require approaches that are both “basic” and “applied” and include integration of laboratory and field approaches.

BioScience↗
USGS2017

Evidence for density dependence in foraging and migratory behavior of a subtropical nearshore seabird

Density-dependent competition for food resources influences both foraging ecology and reproduction in a variety of animals. The relationship between colony size, local prey depletion, and reproductive output in colonial central-place foragers has been extensively studied in seabirds; however, most studies have focused on effects of intraspecific competition during the breeding season, while little is known about whether density-dependent resource depletion influences individual migratory behavior outside the breeding season. Using breeding colony size as a surrogate for intraspecific resource competition, we tested for effects of colony size on breeding home range, nestling health, and migratory patterns of a nearshore colonial seabird, the brown pelican ( Pelecanus occidentalis ), originating from seven breeding colonies of varying sizes in the subtropical northern Gulf of Mexico. We found evidence for density-dependent effects on foraging behavior during the breeding season, as individual foraging areas increased linearly with the number of breeding pairs per colony. Contrary to our predictions, however, nestlings from more numerous colonies with larger foraging ranges did not experience either decreased condition or increased stress. During nonbreeding, individuals from larger colonies were more likely to migrate, and traveled longer distances, than individuals from smaller colonies, indicating that the influence of density-dependent effects on distribution persists into the nonbreeding period. We also found significant effects of individual physical condition, particularly body size, on migratory behavior, which in combination with colony size suggesting that dominant individuals remain closer to breeding sites during winter. We conclude that density-dependent competition may be an important driver of both the extent of foraging ranges and the degree of migration exhibited by brown pelicans. However, the effects of density-dependent competition on breeding success and population regulation remain uncertain in this system.

Gulf of Mexico↗
USGS2020

Ambiguities in using telomere length for age determination in two North American bat species

The age of an animal, determined by time (chronological age) as well as genetic and environmental factors (biological age), influences the likelihood of mortality and reproduction and thus the animal’s contribution to population growth. For many long-lived species, such as bats, a lack of external and morphological indicators has made determining age a challenge, leading researchers to examine genetic markers of age for application to demographic studies. One widely studied biomarker of age is telomere length, which has been related both to chronological and biological age across taxa, but only recently has begun to be studied in bats. We assessed telomere length from the DNA of known-age and minimum known-age individuals of two bat species using a quantitative PCR assay. We determined that telomere length was quadratically related to chronological age in big brown bats ( Eptesicus fuscus ), although it had little predictive power for accurate age determination of unknown-age individuals. The relationship was different in little brown bats ( Myotis lucifugus ), where telomere length instead was correlated with biological age, apparently due to infection and wing damage associated with white-nose syndrome. Furthermore, we showed that wing biopsies currently are a better tissue source for studying telomere length in bats than guano and buccal swabs; the results from the latter group were more variable and potentially influenced by storage time. Refinement of collection and assessment methods for different non-lethally collected tissues will be important for longitudinal sampling to better understand telomere dynamics in these long-lived species. Although further work is needed to develop a biomarker capable of determining chronological age in bats, our results suggest that biological age, as reflected in telomere length, may be influenced by extrinsic stressors such as disease.

Journal of Mammalogy↗
USGS1990

Estimation of recruitment from immigration versus in situ reproduction using Pollock's robust design

Recruitment to animal populations can occur through both immigration and in situ reproduction. These two components of recruitment are conceptually distinct and lead to different mechanistic models of population dynamics. We describe a capture—recapture design that can be used to obtain separate estimates of two recruitment components. We then illustrate the use of our method and estimators with capture—recapture data from a population of Microtus pennsylvanicus at the Patuxent Wildlife Research Center in Maryland.

Ecology↗
USGS2010

Biological pathways of exposure and ecotoxicity values for uranium and associated radionuclides: Chapter D in Hydrological, geological, and biological site characterization of breccia pipe uranium deposits in Northern Arizona

This chapter compiles available chemical and radiation toxicity information for plants and animals from the scientific literature on naturally occurring uranium and associated radionuclides. Specifically, chemical and radiation hazards associated with radionuclides in the uranium decay series including uranium, thallium, thorium, bismuth, radium, radon, protactinium, polonium, actinium, and francium were the focus of the literature compilation. In addition, exposure pathways and a food web specific to the segregation areas were developed. Major biological exposure pathways considered were ingestion, inhalation, absorption, and bioaccumulation, and biota categories included microbes, invertebrates, plants, fishes, amphibians, reptiles, birds, and mammals. These data were developed for incorporation into a risk assessment to be conducted as part of an environmental impact statement for the Bureau of Land Management, which would identify representative plants and animals and their relative sensitivities to exposure of uranium and associated radionuclides. This chapter provides pertinent information to aid in the development of such an ecological risk assessment but does not estimate or derive guidance thresholds for radionuclides associated with uranium. Previous studies have not attempted to quantify the risks to biota caused directly by the chemical or radiation releases at uranium mining sites, although some information is available for uranium mill tailings and uranium mine closure activities. Research into the biological impacts of uranium exposure is strongly biased towards human health and exposure related to enriched or depleted uranium associated with the nuclear energy industry rather than naturally occurring uranium associated with uranium mining. Nevertheless, studies have reported that uranium and other radionuclides can affect the survival, growth, and reproduction of plants and animals. Exposure to chemical and radiation hazards is influenced by a plant’s or an animal’s life history and surrounding environment. Various species of plants, invertebrates, fishes, amphibians, reptiles, birds, and mammals found in the segregation areas that are considered species of concern by State and Federal agencies were included in the development of the site-specific food web. The utilization of subterranean habitats (burrows in uranium-rich areas, burrows in waste rock piles or reclaimed mining areas, mine tunnels) in the seasonally variable but consistently hot, arid environment is of particular concern in the segregation areas. Certain species of reptiles, amphibians, birds, and mammals in the segregation areas spend significant amounts of time in burrows where they can inhale or ingest uranium and other radionuclides through digging, eating, preening, and hibernating. Herbivores may also be exposed though the ingestion of radionuclides that have been aerially deposited on vegetation. Measured tissues concentrations of uranium and other radionuclides are not available for any species of concern in the segregation areas. The sensitivity of these animals to uranium exposure is unknown based on the existing scientific literature, and species-specific uranium presumptive effects levels were only available for two endangered fish species known to inhabit the segregation areas. Overall, the chemical toxicity data available for biological receptors of concern were limited, although chemical and radiation toxicity guidance values are available from several sources. However, caution should be used when directly applying these values to northern Arizona given the unique habitat and life history strategies of biological receptors in the segregation areas and the fact that some guidance values are based on models rather than empirical (laboratory or field) data. No chemical toxicity information based on empirical data is available for reptiles, birds, or wild mammals; therefore, the risks associated with uranium and other radionuclides are unknown for these biota.

Arizona↗
USGS2002

Sea otter ( Enhydra lutris ) perspective: Part A. Sea otter population status and the process of recovery from the 1989 Exxon Valdez oil spill

Sea otter ( Enhydra lutris ) populations were severely affected by the 1989 Exxon Valdez oil spill in western Prince William Sound, AK, and had not fully recovered by 2000. Here we present results of population surveys and incorporate findings from related studies to identify current population status and factors affecting recovery. Between 1993 and 2000, the number of sea otters in the spill-area of Prince William Sound increased by about 600 to nearly 2700. However, at Knight Island, where oil exposure and sea otter mortality in 1989 approached 0.90, no increase has been observed. Sea otter reproduction was not impaired and the age and sex structure of animals captured are consistent with both intrinsic reproduction and immigration contributing to recovery. However, low resighting rates of marked animals at Knight Island compared to an unoiled reference area, and a high proportion of young animals in beach cast carcasses through 1998, suggest that the lack of recovery was caused by relatively poor survival or emigration of potential recruits. Significantly higher levels of cytochrome P4501A (CYP1A), a biomarker of hydrocarbons, were found in sea otters at Knight Island in 1996-98 compared to unoiled Montague Island, implicating oil effects in the lack of recovery at Knight Island. Delayed recovery does not appear to be directly related to food limitation. Although food availability was relatively low at both oiled and unoiled areas, we detected significant increases in sea otter abundance only at Montague Island, a finding inconsistent with food as a principal limiting factor. Persistent oil in habitats and prey provides a source of continued oil exposure and, combined with relatively low prey densities, suggests a potential interaction between oil and food. However, sea otters foraged more successfully at Knight Island and young females were in better condition than those at Montague Island. We conclude that progress toward recovery of sea otters in Prince William Sound is evident, but that in areas where initial oil effects were greatest, recovery may be constrained by residual spill effects, resulting in elevated mortality and emigration. It is evident that internal reproduction and immigration of juveniles has been the primary means of population recovery, as opposed to broad scale redistribution of adults from outside affected areas. The result is a recovery period protracted by long-term spill effects on survival and emigration and intrinsic limits to population growth.

Alaska↗
USGS2002

Genetic similarity between mates and extra-pair parentage in three species of shorebirds

Matings between close relatives often reduce the fitness of offspring, probably because homozygosity leads to the expression of recessive deleterious alleles 1 , 2 , 3 , 4 , 5 . Studies of several animals have shown that reproductive success is lower when genetic similarity between parents is high 4 , 5 , 6 , 7 , and that survival and other measures of fitness increase with individual levels of genetic diversity 8 , 9 , 10 , 11 . These studies indicate that natural selection may favour the avoidance of matings with genetically similar individuals. But constraints on social mate choice, such as a lack of alternatives, can lead to pairing with genetically similar mates. In such cases, it has been suggested that females may seek extra-pair copulations with less related males 4 , but the evidence is weak or lacking 4 , 5 . Here we report a strong positive relationship between the genetic similarity of social pair members and the occurrence of extra-pair paternity and maternity (‘quasi-parasitism’) in three species of shorebirds. We propose that extra-pair parentage may represent adaptive behavioural strategies to avoid the negative effects of pairing with a genetically similar mate.

Nature↗
USGS1998

Influence of habitat on behavior of Towndsend's ground squirrels (Spermophilus townsendii)

Trade-offs between foraging and predator avoidance may affect an animal's survival and reproduction. These trade-offs may be influenced by differences in vegetative cover, especially if foraging profitability and predation risk differ among habitats. We examined above-ground activity of Townsend's ground squirrels ( Spermophilus townsendii ) in four habitats in the Snake River Birds of Prey National Conservation Area in southwestern Idaho to determine if behavior of ground squirrels varied among habitats, and we assessed factors that might affect perceived predation risk (i.e. predator detectability, predation pressure, population density). The proportion of time spent in vigilance by ground squirrels in winterfat ( Krascheninnikovia lanata ) and mosaic habitats of winterfat-sagebrush ( Artemisia tridentata ) was more than twice that of ground squirrels in burned and unburned sagebrush habitats. We found no evidence for the “many-eyes” hypothesis as an explanation for differences in vigilance among habitats. Instead, environmental heterogeneity, especially vegetation structure, likely influenced activity budgets of ground squirrels. Differences in vigilance may have been caused by differences in predator detectability and refuge availability, because ground squirrels in the winterfat and mosaic habitats also spent more time in upright vigilant postures than ground squirrels in burned-sagebrush or sagebrush habitats. Such postures may enhance predator detection in low-growing winterfat.

Journal of Mammalogy↗
USGS2006

Investigations of the Effects of Synthetic Chemicals on the Endocrine System of Common Carp in Lake Mead, Nevada and Arizona

Introduction: Lake Mead is the largest reservoir by volume in the United States and was created by the construction of the 221-meter high Hoover Dam in 1935 at Black Canyon on the lower Colorado River between Nevada and Arizona (fig. 1). Inflows of water into the lake include three rivers, Colorado, Virgin, and Muddy; as well as Las Vegas Wash, which is now perennial because of discharges from municipal wastewater treatment plants (Covay and Leiker, 1998) and urban stormwater runoff. As the population within the Las Vegas Valley began to increase in the 1940s, the treated effluent volume also has increased and in 1993 it constituted about 96 percent of the annual discharge of Las Vegas Wash (Bevans and others, 1996). The mean flow of Las Vegas Wash into Las Vegas Bay from 1992 to 1998 was about 490,000 m3/d (Preissler and others, 1999) and in 2001 increased to 606,000 m3/d (U.S. Bureau of Reclamation, 2001). The nutrient concentration in most areas of the lake is low, but wastewater discharged into Las Vegas Bay has caused an increased level of nutrients and primary productivity (aquatic plant and algal production) in this area of the lake (LaBounty and Horn, 1997). A byproduct of this increase in productivity has been the establishment of an important recreational fishery in Las Vegas Bay. However, concentrations of chlorophyll a (a measure of algal biomass) have also increased (LaBounty and Horn, 1997). In the spring of 2001, parts of Lake Mead experienced massive algal blooms. In addition to nutrient loading by wastewater, the presence of numerous synthetic chemicals in water, bottom sediments, and in fish tissue also has been reported (Bevans and others, 1996). Synthetic chemicals discharging into Las Vegas Bay and Lake Mead (fig. 1) originate from several sources that include surplus residential-irrigation water runoff, stormwater runoff, subsurface inflow, and tertiary treated sewage effluent discharging from three sewage-treatment plants. Chemicals detected in Las Vegas Wash and Bay environments include polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), organochlorine pesticides (including DDT and DDE), and 'emerging contaminants' such as fragrances/musks, flame retardants, triclosan and its breakdown products, personal care products, and pharmaceuticals (Bevans and others, 1996; Boyd and Furlong, 2002; Leiker and others, in press). Many of these compounds are able to interact with the endocrine system of animals and potentially cause reproductive impacts. The National Park Service (NPS) manages Lake Mead National Recreation Area (LMNRA) with about 8 million yearly visitors including 500,000 anglers drawn to its world-class recreational fishery. The U.S. Fish and Wildlife Service (FWS) provides management for the federally designated, endangered razorback sucker (Xyrauchen texanus) and for more than 180 species of migratory birds that utilize LMNRA surface waters. These multiple uses of surface water in the area demonstrate their vital importance to the LMNRA as well as the need to maintain the quality of water at levels that are adequate for these uses.

Fact Sheet↗
USGS2005

Exploring individual quality: Basal metabolic rate and reproductive performance in storm-petrels

Despite evidence that some individuals achieve both superior reproductive performance and high survivorship, the factors underlying variation in individual quality are not well understood. The compensation and increased-intake hypotheses predict that basal metabolic rate (BMR) influences reproductive performance; if so, variation in BMR may be related to differences in individual quality. We evaluated whether BMR measured during the incubation period provides a proximate explanation for variation in individual quality by measuring the BMRs and reproductive performance of Leach's storm-petrels (Oceanodroma leucorhoa) breeding on Kent Island, New Brunswick, Canada, during 2000 and 2001. We statistically controlled for internal (body mass, breeding age, sex) and external (year, date, time of day) effects on BMR. We found that males with relatively low BMRs hatched their eggs earlier in the season and that their chicks' wing growth rates were faster compared to males with relatively high BMRs. Conversely, BMR was not related to egg volume, hatching date, or chick growth rate for females or to lifetime (???23 years) hatching success for either sex. Thus, for males but not for females, our results support the compensation hypothesis. This hypothesis predicts that animals with low BMRs will achieve better reproductive performance than animals with high BMRs because they have lower self-maintenance costs and therefore can apportion more energy to reproduction. These results provide evidence that intraspecific variation in reproductive performance is related to BMR and suggest that BMR may influence individual quality in males. ?? The Author 2005. Published by Oxford University Press on behalf of the International Society for Behavioral Ecology. All rights reserved.

Behavioral Ecology↗
USGS1994

Estimating breeding proportions and testing hypotheses about costs of reproduction with capture-recapture data

The proportion of animals in a population that breeds is an important determinant of population growth rate. Usual estimates of this quantity from field sampling data assume that the probability of appearing in the capture or count statistic is the same for animals that do and do not breed. A similar assumption is required by most existing methods used to test ecologically interesting hypotheses about reproductive costs using field sampling data. However, in many field sampling situations breeding and nonbreeding animals are likely to exhibit different probabilities of being seen or caught. In this paper, we propose the use of multistate capture-recapture models for these estimation and testing problems. This methodology permits a formal test of the hypothesis of equal capture/sighting probabilities for breeding and nonbreeding individuals. Two estimators of breeding proportion (and associated standard errors) are presented, one for the case of equal capture probabilities and one for the case of unequal capture probabilities. The multistate modeling framework also yields formal tests of hypotheses about reproductive costs to future reproduction or survival or both fitness components. The general methodology is illustrated using capture-recapture data on female meadow voles, Microtus pennsylvanicus. Resulting estimates of the proportion of reproductively active females showed strong seasonal variation, as expected, with low breeding proportions in midwinter. We found no evidence of reproductive costs extracted in subsequent survival or reproduction. We believe that this methodological framework has wide application to problems in animal ecology concerning breeding proportions and phenotypic reproductive costs.

Ecology↗
USGS2013

WICCI Wildlife Working Group Report

Wisconsin is world-renowned for its diversity of ecological landscapes and wildlife populations. The northern forests, southern prairies, and interior and coastal wetlands of the state are home to more than 500 terrestrial animal species. These animals supply the Wisconsin public with aesthetic, cultural, and economic benefits; our identity and economy are intertwined with these natural resources. Climate change is altering the behavior, distribution, development, reproduction, and survival of these animal populations. In turn, these changes will alter the aesthetic, cultural, and economic benefits we receive from them. The focus of the Wildlife Working Group is to document past and current impacts, anticipate changes in wildlife distribution and abundance, and develop adaptation strategies to maintain the vitality and diversity of Wisconsin's wildlife populations.

Report↗
USGS2016

Effects of seasonal weather on breeding phenology and reproductive success of alpine ptarmigan in Colorado

Animal populations occurring at high elevations are often assumed to be in peril of extinctions or local extirpations due to elevational-dispersal limitations and thermoregulatory constraints as habitats change and warm. However, long-term monitoring of high-elevation populations is uncommon relative to those occurring at lower elevations, and evidence supporting this assumption is limited. We analyzed 45 years of reproductive data for two Colorado populations of white-tailed ptarmigan ( Lagopus leucura ), an alpine-endemic species with restricted distribution in western North America. Seasonal temperatures measured by the number of growing degree days warmed significantly at our study sites for pre-nesting, nesting, and brood-rearing seasonal periods (mean advance of 8 growing degree days per decade), and both populations advanced their reproductive phenology over the study period based on median hatch dates (median advance of 3.7 and 1.9 days per decade for the northern and southern sites, respectively). Reproductive performance measured by the number of chicks per hen declined significantly at one study site but not the other, and differences between sites may have been due to habitat degradation at one study area. Annual variability in chicks per hen was large at both sites but only weakly related to seasonal weather. An index of precipitation and temperature during the brood-rearing period was the best predictor for reproductive success with warm and dry conditions relating positively to number of chicks per hen. Our results provide evidence for two alpine ptarmigan populations that are remarkably invariant to fluctuations in seasonal weather with respect to reproductive success as measured by number of chicks per hen in the breeding population. These results are surprising given the general perception of alpine animal populations as being highly sensitive to warming temperatures.

Colorado↗
USGS2012

Representing the acquisition and use of energy by individuals in agent-based models of animal populations

1. Agent-based models (ABMs) are widely used to predict how populations respond to changing environments. As the availability of food varies in space and time, individuals should have their own energy budgets, but there is no consensus as to how these should be modelled. Here, we use knowledge of physiological ecology to identify major issues confronting the modeller and to make recommendations about how energy budgets for use in ABMs should be constructed. 2. Our proposal is that modelled animals forage as necessary to supply their energy needs for maintenance, growth and reproduction. If there is sufficient energy intake, an animal allocates the energy obtained in the order: maintenance, growth, reproduction, energy storage, until its energy stores reach an optimal level. If there is a shortfall, the priorities for maintenance and growth/reproduction remain the same until reserves fall to a critical threshold below which all are allocated to maintenance. Rates of ingestion and allocation depend on body mass and temperature. We make suggestions for how each of these processes should be modelled mathematically. 3. Mortality rates vary with body mass and temperature according to known relationships, and these can be used to obtain estimates of background mortality rate. 4. If parameter values cannot be obtained directly, then values may provisionally be obtained by parameter borrowing, pattern-oriented modelling, artificial evolution or from allometric equations. 5. The development of ABMs incorporating individual energy budgets is essential for realistic modelling of populations affected by food availability. Such ABMs are already being used to guide conservation planning of nature reserves and shell fisheries, to assess environmental impacts of building proposals including wind farms and highways and to assess the effects on nontarget organisms of chemicals for the control of agricultural pests.

Methods in Ecology and Evolution↗
USGS2017

Temporal constraints on the potential role of fry odors as cues of past reproductive success for spawning lake trout

Deciding where to reproduce is a major challenge for most animals. Many select habitats based upon cues of successful reproduction by conspecifics, such as the presence of offspring from past reproductive events. For example, some fishes select spawning habitat following odors released by juveniles whose rearing habitat overlaps with spawning habitat. However, juveniles may emigrate before adults begin to search for spawning habitat; hence, the efficacy of juvenile cues could be constrained by degradation or dissipation rates. In lake trout ( Salvelinus namaycush ), odors deposited by the previous year's offspring have been hypothesized to guide adults to spawning reefs. However, in most extant populations, lake trout fry emigrate from spawning reefs during the spring and adults spawn during the fall. Therefore, we postulated that the role of fry odors in guiding habitat selection might be constrained by the time between fry emigration and adult spawning. Time course chemical, physiological, and behavioral assays indicated that the odors deposited by fry likely degrade or dissipate before adults select spawning habitats. Furthermore, fry feces did not attract wild lake trout to constructed spawning reefs in Lake Huron. Taken together, our results indicate fry odors are unlikely to act as cues for lake trout searching for spawning reefs in populations whose juveniles emigrate before the spawning season, and underscore the importance of environmental constraints on social cues.

Ecology and Evolution↗
USGS2021

Breeding at higher latitude is associated with higher photoperiodic threshold and delayed reproductive development in a songbird

Many seasonally breeding animals exhibit a threshold day length (critical photoperiod; CPP) for gonadal growth, and populations breeding at higher latitudes typically have a higher CPP. Much less is known about latitudinal variation in CPP in migratory population that winter away from their breeding range and must time their reproduction to match favorable conditions at their destination. To address the relationship between migration, breeding latitude, and CPP, we held two closely related songbird populations in a common environment. One population is resident ( Junco hyemalis carolinensis ), the other winters in sympatry with the residents but migrates north to breed ( Junco hyemalis hyemalis ). We gradually increased photoperiod and measured indices of readiness to migrate (fat score, body mass) and breed (cloacal protuberance volume, baseline testosterone, and gonadotropin releasing hormone challenged testosterone). To estimate breeding latitude, we measured hydrogen isotopes in feathers grown the preceding year. As we predicted, we found a higher CPP in migrants than residents, and a higher CPP among migrants deriving from higher as opposed to lower latitudes. Migrants also terminated breeding earlier than residents, indicating a shorter breeding season. To our knowledge, this is a first demonstration of latitudinal variation in CPP-dependent reproductive timing in bird populations that co-exist in the non-breeding season but breed at different latitudes. We conclude that bird populations appear to exhibit local adaptation in reproductive timing by relying on differential CPP response that is predictive of future conditions on the breeding ground.

Indiana↗
USGS2001

Effects of pre- and postnatal polychlorinated biphenyl exposure on metabolic rate and thyroid hormones of white-footed mice

Energy budgets have proven to be a valuable tool for predicting life history from physiological data in terrestrial vertebrates, yet these concepts have not been applied to the physiological effects of contaminants. Contaminants might affect energy budgets by imposing an additional metabolic cost or by reducing the overall amount of energy taken in; either process will reduce the energy available for production (i.e., growth or reproduction). This study examined whole animal energetic effects of polychlorinated biphenyl (PCB) exposure in white-footed mice ( Peromyscus leucopus ). Exposure to PCBs is known to reduce concentrations of plasma thyroid hormones, and thyroid hormones exert strong control over the rate of energy metabolism in mammals. Peromyscus leucopus that were proven breeders were fed PCBs in their food at 0, 10, and 25 ppm. Through lactation, offspring were exposed to PCB from conception and were maintained on the maternal diet to adulthood. No effects were seen on energy metabolism (O 2 consumption, measured in adulthood) or on growth, but there were large dose-dependent decreases in thyroid hormone concentrations, particularly T 4 . The apparent disparity in our data between unchanged metabolic rates and 50% reductions in T 4 concentrations can be rationalized by noting that free T 3 (the fraction not bound to plasma protein) in treated mice was not significantly different from controls and that metabolism is most strongly influenced by free T 3 . Overall, this study did not demonstrate any energetic consequences of PCB exposure in P. leucopus at dietary concentrations up to 25 ppm.

Environmental Toxicology and Chemistry↗