Andrew K. Davis's research while affiliated with University of Georgia and other places
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Publications (145)
Elucidating the adaptations that promote flight in animals can aid the understanding of evolution and species divergence, and/or provide inspiration for aerospace engineering and the design of better aerial vehicles. The famed long-distance migration of monarch butterflies in North America still holds many questions and opportunities for inspiratio...
Some animals react to predation threats or other stressors by adopting a freezing posture in an attempt to avoid detection, and the duration of this behavior usually corresponds with individual personality, such that timid individuals freeze longer. Despite decades of research on this or related behaviors (thanatosis), never has the impact of paras...
An invasive spider (Trichonephila clavata [L. Koch 1878], or jorō spider) is rapidly expanding throughout the southeast of the United States, engendering many questions about how native fauna will be affected. Here, we describe an observation of a northern cardinal (Cardinalis cardinalis, L.) consuming prey items from a jorō web, which serves as an...
Assessing numbers of leukocytes in salamanders and other amphibians can be useful metrics for understanding health or stress levels of individuals in a population. In this chapter we describe the procedures for obtaining blood samples from amphibians, preparing blood films for microscopy, counting, and identifying cells. We also provide reference v...
Monarch butterflies in North America have an exceptionally large breeding distribution, occupying regions west of the Rocky Mountains and throughout the eastern seaboard. An experimental study conducted 17 years ago and published in this journal appeared to show that western monarch larvae tend to have smaller black stripes than those from eastern...
Insect–pathogen dynamics can show seasonal and inter‐annual variations that covary with fluctuations in insect abundance and climate. Long‐term analyses are especially needed to track parasite dynamics in migratory insects, in part because their vast habitat ranges and high mobility might dampen local effects of density and climate on infection pre...
A newly‐invasive spider from east Asia, Trichonephila clavata , or “jorō spider”, is spreading in the southeastern United States. Little is known about the biology or physiology of this species in this new range. Interestingly, a closely‐related species in the same genus, the “golden silk spider,” Trichonephila clavipes , is already successfully es...
A recent study in this journal aimed to understand certain changes in the wintering behavior of monarch butterflies, specifically in the western subpopulation of North America [...]
Neonicotinoids are the most widely used insecticides in North America. Numerous studies document the negative effects of neonicotinoids on bees, and it remains crucial to demonstrate if neonicotinoids affect other non-target insects, such as butterflies. Here we examine how two neonicotinoids (imidacloprid and clothianidin) affect the development,...
Many insects are in clear decline, with monarch butterflies (Danaus plexippus) drawing particular attention as a flagship species. Falling numbers of overwintering monarchs are well documented, but there has been debate regarding population trends of summer breeding populations. Here, we compile a series of long-term monarch monitoring datasets, so...
Ants, like other insects, have a heart that pumps hemolymph rhythmically. We designed an apparatus and procedure to non‐destructively monitor the rate of cardiac contractions in ants, using a modified light microscope and infrared light. This allowed us to obtain the first baseline heart rate data on three ant species in Georgia. We next describe h...
Internal parasites typically are associated with a range of negative effects on their hosts, including reduced energy, which can manifest in behavioral alterations. With this in mind, we examined effects of a naturally-occurring nematode parasite, Chondronema passali, on locomotor activity level in horned passalus beetles, Odontotaenius disjunctus...
Diamond-backed terrapins inhabit coastal salt marshes along the eastern and Gulf coasts of North America. Terrapins are adapted to intermediate salinities yet frequently face saltwater-inundated marsh habitat exceeding 25 ppt (or grams/kilogram). We investigated the effect of salinity on the growth of hatchling terrapins and on their compensatory r...
For many animals and insects that are experiencing dramatic population declines, the only recourse for conservationists is captive rearing. To ensure success, reared individuals should be biologically indistinct from those in the wild. We tested if this is true with monarch butterflies, Danaus plexippus, which are increasingly being reared for rele...
In this project, red-backed salamanders, Plethodon cinereus, were collected from the heart of their range (Mountain Lake, Virginia, USA), in an effort to document the typical, or baseline, leukocyte profile of this species in its natural state. From microscopic examination of thin blood films, we determined relative proportions of all leukocyte typ...
The rigours of the daily lives of insects sometimes lead to minor injuries and wounds, which must be healed to avoid entry of pathogens and to resume normal function. Such healing requires energy, which must be diverted from other bodily reserves. What happens if energy reserves are already low, as would occur in individuals coping with internal pa...
The females of Xyo pseudohystrix Travassos & Kloss, 1958 (Nematoda: Oxyuridomorpha: Hystrignathidae) are redescribed and illustrated with the aid of SEM. New features of the cephalic end, arrangement of the cervical spines and genital tract were observed. The taxonomic status of the species is discussed on the basis of discrepancies with the generi...
How and to what degree an animal deals with potential threats is a fascinating topic that has been well-researched, particularly in insects, though usually not with the impact of parasites in mind. A growing body of work is showing how even benign parasites can affect, positively or negatively, their hosts’ physiological or behavioral reaction to t...
There is growing appreciation for the role that parasites have in ecosystems and food webs, though the possibility that they could improve an ecosystem service has never been considered. In forest ecosystems, fallen trees naturally decay over time and slowly return their nutrients to the soil. Beetles in the family Passalidae play a key role by exc...
Lepidonema magnum Morffe & García, 2010 (Nematoda: Oxyuridomorpha: Hystrignathidae) is redescribed and illustrated with the aid of SEM. New features of the cephalic end and genital tract of the females were observed. New locality records are given. The phylogenetic position of the species is inferred on the basis of the D2-D3 segment of the 28S LSU...
There is mounting evidence that the longterm declines of overwintering monarchs in Mexico are exacerbated by losses during the fall migratory journey. Infection with the protozoan, Ophryocystis elektroscirrha (OE), is known to negatively impact migration success. Here we examine how infections affect specific wing traits of monarchs that are import...
Developed countries around the world are criss-crossed with vast networks of roadways. Conservationists have recently focused attention on roadsides as possible locations for establishing pollinator habitat, with the monarch butterfly (Danaus plexippus) featuring prominently in such discussions. However, roadsides are inherently loud, which could n...
Measuring stress in animals is important in many ecological, zoological and veterinary research settings. A common method is to measure plasma levels of glucocorticoid hormones (cortisol, corticosterone, hereafter CORT ). Over the past decade, an alternative method has become widely popular: assessing leucocyte profiles; in other words, the heterop...
• Pollinator declines have motivated efforts to plant nectar and host plants for butterflies and other pollinators, but whether gardens promote pollinator conservation requires further investigation.
• We established garden plots to determine whether plant type (native vs. exotic) and weed maintenance (low or high) influence adult butterfly abundan...
There are many events in the lives of insects where rapid, effective stress reactions are needed, including fighting conspecifics to defend territories, evading predators, and responding to wounds. A key element of the stress reaction is elevation of heartrate (HR), for enhancing distribution of blood (hemolymph) to body compartments. We conducted...
All animals, whether vertebrate or invertebrate, must be capable of reacting to acute stressors, such as escaping from predators, and most do so with a suite of transient physiological changes that temporarily enhance survival. Some of these changes include mobilization of immune cells and increased cardiac output. A small but growing number of stu...
Amphibians are host to a number of vector-transmitted blood parasites. One parasite for which there is little information is a recently described intracellular bacteria in the order Rickettsiales, found in red-backed salamanders (Plethodon cinereus) in the eastern USA. This parasite was observed in 16.7 % of individuals across three states in the s...
This report describes a series of observations made on 2 parasite species infecting a collection of horned passalus beetles (Odontotaenius disjunctus, n = 135), from Georgia, U.S.A., that were collected as larvae in the wild and were reared to metamorphosis in captivity. Tachinid fly maggots emerged from 15 beetle larvae (11%) and, when they comple...
Heart rates of insects reflect the current level of activity and stress individuals are experiencing, and therefore this information can be useful from a research perspective. In Lepidoptera, as with most insects, the 'heart' consists of a transverse longitudinal tube that runs along the abdomen, just under the abdominal tergites, which pumps or co...
Long-distance migration can lower parasite prevalence if strenuous journeys remove infected animals from wild populations. We examined wild monarch butterflies (Danaus plexippus) to investigate the potential costs of the protozoan Ophryocystis elektroscirrha on migratory success. We collected monarchs from two wintering sites in central Mexico to c...
Parasites are ubiquitous among insects and well-studied, but knowledge of their full range of host effects is not complete, especially concerning their impact on physical performance of hosts. The horned passalus beetle, Odontotaenius disjunctus (Illiger), in the USA is frequently parasitized by Chondronema passali Leidy, a nematode that can number...
Optimal flight in butterflies depends on structural features of the wings and body, including wing size, flight muscle size, and wing loading. Arguably, there is no butterfly for which flight is more important than the monarch (
Danaus plexippus
), which undergoes long-distance migrations in North America. We examined morphological features of mona...
Significance
Amphibians are among the most threatened animal groups. Population declines and extinctions have been linked, in part, to emerging infectious diseases. One such emerging disease has been attributed to Perkinsea-like protists causing mass mortality events in the United States. Using molecular methods, we evaluated the diversity of Perki...
Annual estimates of population size are important for tracking long-term population trajectories. There is concern that monarch butterflies ( Danaus plexippus L.) in eastern North America are declining because the Mexican overwintering colonies have been shrinking over the past 20 yr. We examined a 19-yr data set of fall monarch censuses at a site...
The monarch butterfly, Danaus plexippus (Nymphalidae, Danainae), is one of the most familiar and appreciated insects in North America and is an iconic symbol of insect conservation (Gustafsson et al. 2015); attention on this charismatic species has increased since declines of their Mexican overwintering colonies were reported (Brower et al. 2012)....
Declines in overwintering colonies of monarch butterflies ( Danaus plexxipus ) in Mexico raise questions about other life cycle phases, such as spring migration, where monarchs recolonize their breeding range in the United States and Canada with sequential generations. We used data from a long-term citizen science program, “Journey North” (now with...
World-wide declines of amphibians have heightened the need for information relating to their health status and immune function under natural conditions. Evaluation of differential white blood cell (leukocyte) counts from thin blood smears is one way to gain this information, and this approach is increasingly being used by herpetologists to gauge th...
Parasitic leeches and trypanosomes release chemical signals into their hosts to evade immuno-detection, but it is unknown whether these compounds manipulate host behavior or physiology. We determined whether parasitic infections with leeches and/or trypanosomes affected the immune and stress response of an imperiled giant species of amphibian, the...
The effects of non-lethal parasites may be felt most strongly when hosts engage in intense, energy-demanding behaviors. One such behavior is fighting with conspecifics, which is common among territorial animals, including many beetle species. We examined the effects of parasites on the fighting ability of a saproxylic beetle, the horned passalus (O...
The female of Hystrignathus rigidus Leidy, 1850 (Nematoda: Hystrignathidae) is redescribed on the basis of new material from Odontotaenius disjunctus (Coleoptera: Passalidae) from Athens, Georgia, USA; which also constitutes a new locality record. SEM images are provided for the first time for the species. It is also first shown that H. rigidus pre...
Climate change is altering global patterns of precipitation and temperature variability, with implications for parasitic diseases of humans and wildlife. A recent study confirmed predictions that increased temperature variability could exacerbate disease, because of lags in host acclimation following temperature shifts. However, the generality of t...
Background. Migratory birds are often faced with the challenge of undertaking long-distance journeys while harboring parasites. Objective. I investigated the possibility that Hippoboscid flies (Diptera, Hippoboscidae), blood-feeding ectoparasites, would be associated with reduced body condition or fat reserves of migratory songbirds. Methods. I mis...
Long-distance migrations are energetically expensive for many animals, including migratory songbirds. During these demanding journeys, birds likely face limitations in allocating resources to different physiological functions, including lipid reserves needed to fuel the migration and costly immune defense against pathogens. We sampled three species...
Recent declines in the size of overwintering colonies of monarch butterflies ( Danaus plexippus ) in eastern North America have stimulated calls for greater conservation efforts of the migratory phenomenon. Conservation decisions, however, should be guided by sound science, and the migratory phase of this population is the least‐studied part of its...
The physiological basis for pigment synthesis in lepidopteran wing scales is well-studied, although less is known about the reasons why individuals of the same species vary in pigmentation. Monarch butterflies (Danaus plexippus L.) show subtle variations in the shade of orange on their wings and this is known to predict flight ability and mating su...
Many beetle species engage in territorial behaviors or male-male contests involving lifting or flipping their opponents, although this type of strength has never been empirically quantified. This study examined the lifting capacity of a medium-sized (1–2 g) saprolytic beetle native to the United States (horned passalus beetle, Odontotaenius disjunc...
The migration of monarch butterflies (Danaus plexippus) in North America has a number of parallels with long-distance bird migration, including the fact that migratory populations of monarchs have larger and more elongated forewings than residents. These characteristics likely serve to optimize flight performance in monarchs, as they also do with b...
In animals with complex life cycles, all resources needed to form adult tissues are procured at the larval stage. For butterflies, the proper development of wings involves synthesizing tissue during metamorphosis based on the raw materials obtained by larvae. Similarly, manufacture of pigment for wing scales also requires resources acquired by larv...
Abstract When wild animals become infected, they still must cope with the rigors of daily life, and, thus, they still can be exposed to acute stressors. The suite of physiological responses to acute stress includes modifying the innate immune system, but infections can also cause similar changes. We examined the effects of an acute stressor (captur...
Current evidence suggests that the health effect of avian feather mites is minimal. However, feather mites can still proliferate without effective preening, such as might occur during sickness. House Finches (Haemorhous mexicanus) are prone to infection by Mycoplasma gallisepticum, symptoms of which include conjunctivitis. Impaired vision and letha...
Abstract Over a century ago, a pioneering researcher cleverly devised a means to measure how much weight the horned passalus beetle, Odontotaenius disjunctus (Illiger) (Coleoptera: Passalidae), could pull using a series of springs, pulleys, and careful observation. The technology available in modern times now allows for more rigorous data collectio...
The micronucleus assay is a count of cells containing fragments of nuclear content (micronuclei, MN) that arise during errors in cell division and when animals are exposed to genotoxic agents such as chemicals or radiation. The assay can be performed (via light microscopy) using any nucleated cell type, such as erythrocytes in amphibians, birds, fi...
Monarch butterflies (Danaus plexippus) throughout the world are commonly infected by the specialist pathogen Ophryocystis elektroscirrha (OE). This protozoan is transmitted when larvae ingest infectious stages (spores) scattered onto host plant leaves by infected adults. Parasites replicate internally during larval and pupal stages, and adult monar...
Background/Question/Methods
Feather ornaments and structure play a significant role in avian mate choice, territoriality and molt performance. These characteristics can accurately indicate bird nutritional status and the ability to survive and reproduce. Therefore, given the importance of these feather characteristics during the breeding season,...
The rapid spread of the bacterial disease, Mycoplasma gallisepticum (MG), throughout the introduced range of house finches (Carpodacus mexicanus) in eastern North America, compared to its slower spread through the native western range, has puzzled researchers and highlights the need to understand the relative differences in health state of finches...
The horned passalus, Odontotaenius disjunctus (Illiger), is host to a variety of parasites, including a little-studied nematode, Chondronema passali (Leidy), that can number in the thousands in a single beetle. We attempted to determine the effects of this parasite on two measures of host fitness, physical strength and body size of adult beetles co...
For species at risk of extinction, any parasites they have would be expected to face a similar fate. In such cases, time is running out for efforts to identify and study their parasitic fauna before they are gone. We surveyed the hemoparasite fauna of 50 black-chested, spiny-tailed iguanas (Ctenosaura melanosterna), a critically-endangered species,...
Museum collections have great value for zoological research, but despite careful preservation, over time specimens can show subtle changes in color. We examined the effect of storage time on fur color of two reddish-brown species, golden mice (Ochrotomys nuttalli) and eastern chipmunk (Tamias striatus). Using image analysis, we obtained color data...
Eastern hellbender salamanders (Cryptobranchus alleganiensis alleganiensis) are declining in North America and because of this the health status of individuals in several populations is closely monitored by researchers. During a health survey of hellbenders from a stream in Smyth County, VA, USA, we examined Giemsa-stained blood smears of 71 animal...
The distinctive orange and black wings of monarchs (Danaus plexippus) have long been known to advertise their bitter taste and toxicity to potential predators. Recent work also showed that both the orange and black coloration of this species can vary in response to individual-level and environmental factors. Here we examine the relationship between...
Comparison of digital scan and reflectance spectra methods for quantifying wing color.
(DOC)
Summary tables of additional statistical analyses examining relationships between wing color and flight time and speed.
(DOC)
Video of a monarch attached to the flight mill used in the experiments.
(AVI)
Monarch butterflies (Danaus plexippus) in eastern North America must make frequent stops to rest and refuel during their annual migration. During these stopovers, monarchs form communal roosts, which are often observed by laypersons. Journey North is a citizen science program that compiles roost observations, and we examined these data in an attemp...
Captive-rearing for conservation endeavors is often used as a management tool in response to amphibian declines. The goal of such projects should be to produce organisms that are as functionally equivalent to their wild counterparts as possible. Caudates (salamanders) in the genus Ambystoma represent a challenge for rearing because of their aggress...
1. The status of the eastern North American monarch butterfly population is a highly sensitive issue, given that winter and breeding habitats are being lost at an alarming rate each year, and because of this, most believe the population to be declining, although there has been little empirical data to support this idea. In a recent forum article of...
While the annual fall migration of eastern North American monarch butterflies (Danaus plexippus) to wintering sites in central Mexico is a well-known and frequently-studied phenomenon, one aspect of this behavior that remains poorly understood is the nature of their migratory stopovers. Like migrating birds, monarchs must stop frequently during the...
In polymorphic mammalian species that display multiple color forms, those with dark, or melanic pelage would be prone to overheating, especially if they live in warm climates, because their fur absorbs solar energy at a higher rate. However, experimental studies indicate that certain physical properties of fur of dark individuals appear to prevent,...
We report a host gender bias in haemogregarine infection characteristics in the American alligator (Alligator mississippiensis) at the Savannah River Site, South Carolina, USA. Prevalence and severity in female alligators was higher than it was in males. The reason for this pattern is not clear.
Larval amphibians are increasingly being reared for conservation initiatives to bolster declining populations. Few researchers, however, have asked whether reared individuals are functionally equivalent to their wild counterparts. Compared with those in the wild, amphibians reared in captivity may develop in relatively stress-free environments, bec...
When wild animals are captured for zoological research, researchers must choose a method of capture, and often this can be some form of passive, baited cage trap, or a direct capture with nets or nooses. If information on basal levels of circulating leukocytes is a goal, these two methods may provide different information, since recent evidence ind...
One of the most well-studied avian diseases is the annual outbreak of Mycoplasma gallisepticum (MG) infections in house finches (Carpodacus mexicanus) in North America. This is a bacterial disease that causes conjunctivitis in one or both eyes of the host. While studying this disease in a New York finch population, researchers observed that there w...
The fur of mammals serves many functions, including thermoregulation, camouflage or visual signaling to conspecifics. Fine-scale features of fur, such as hair morphology are often examined by researchers, especially in animals where pelage is of economic importance. Certain studies from this literature body show that males of many species appear to...
Like most migratory species, monarch butterflies (Danaus plexippus) must stop frequently during their long southward migration to rest and refuel, and the places where they stop are important
for the success of the migration. The behavior of monarch butterflies at migratory stopover sites has never been examined
in detail. Here we present results o...
Mammalian pelage color can vary among individuals of many species, although this intraspecific variation is often overlooked by researchers, perhaps because of its sometimes subtle nature and difficulty in assessing it quantitatively. Thus, such variation is rarely studied in mammals, and this is especially true within the order Chiroptera, where t...
Bullfrog tadpoles (Rana catesbeiana) from a wastewater treatment facility were identified with severe lesions consisting of large, up to 1-cm in diameter, mineralized nodules protruding from the tail or gular region. Sectioning of formalin-fixed specimens revealed more extensive mineralization involving the vertebrae or muscles of the head and tail...