Current Research Activities

 

In the past, my research interests revolved around questions concerning antipredator behavior, communication, and ontogeny.  In particular, I focused on the functional significance of individual differences in how animals signal about and interact with potential predators.  I investigated these issues in ground squirrels (black-tailed prairie dogs and California ground squirrels) and Mexican free-tailed bats.  However, I am now working with my wife (Dr. Colleen McDonough) on what has become a long-term project on the population ecology and behavior of the nine-banded armadillo (Dasypus novemcinctus).

 

Individuals interested in participating in my research as a Master's student should visit the Biology Department home page for information on admission to the Graduate School. Undergraduates interested in directed study opportunities should contact me or Dr. McDonough directly.

 

Nine-banded armadillos are interesting for a variety of reasons:  (1) they are one of the only animals other than humans that contract leprosy; (2) they are undergoing a rapid range expansion in which they have colonized most of the southeastern United States in less than 200 years; (3) they have one of the lowest metabolic rates reported for any placental mammal; (4) after mating, females can apparently delay implantation of the fertilized egg for extremely long periods of time (up to 3 years in one case); and (5) females exhibit obligate polyembryony, whereby a single fertilized egg divides into 4 embryos in the uterus, so that females always give birth to litters of genetically identical quadruplets.  It is this last point we have focused on in our research, attempting to understand what, if any, impact this unusual mode of reproduction has had on armadillo population structure and behavior, particularly with regard to the opportunity for kin selection.  More broadly, this has led recently to an interest in the extent to which other vertebrates that reproduce clonally (i.e., the unisexual/parthenogenetic fishes, reptiles, and amphibians) also do or do not show evidence of kin selection.

 

Possible current research projects include the following:

 

(1)  Population Genetics:  We use DNA fingerprinting to analyze armadillo tissue samples in two ways.  First, we hope to describe the genetic structure of particular populations.  Such information should provide insight into the dispersion of kin and the potential for interactions among kin.  Second, we have collected DNA samples from nine-banded armadillo populations throughout the species’ range (e.g., Brazil, French Guiana, Mexico, and many parts of the U.S.) in order to describe phylogeographic patterns in the genetic structure of these populations.  The colonization of the U.S. by armadillos is well documented, so there is an excellent database on which to map the genetic data we obtain.  Although we have a number of samples at present, we continue to seek more from other parts of the species’ range to make our analyses even better.

 

(2)  Chemical Ecology:  For animals whose primary sense seems to be olfaction, surprisingly little work has been done on the chemical signals produced by armadillos.  In nine-banded armadillos, secretions from the paired anal glands seem a likely source of odors used in chemical communication.  A project here would be to examine what types of information might be available in these secretions (e.g., identity, state of sexual receptivity, etc).  In particular, as D. novemcinctus produces litters of genetically identical quadruplets, it would be exciting to determine whether the composition of odors somehow covaries with genetic relatedness.  Finally, while we have performed laboratory tests showing that juvenile armadillos can discriminate between the odors of siblings and non-siblings, (although this discrimination is not manifested behaviorally in interactions between juveniles), these results need to be extended to examine olfactory and behavioral discrimination among older animals. 

 

(3) Disease Ecology:  Even though nine-banded armadillos are one of the few animal models for leprosy, almost nothing is known about the impact of the disease in wild populations.  In the last 2 years we have begun a project with two main goals. First, we are sampling populations throughout the southeastern U.S. to describe current patterns of infection and evaluate the potential spread of the disease. Second, we have initiated a long-term study of a leprosy-infected population at Yazoo National Wildlife Refuge (near Greenville, MS) in order to examine patterns of infection over time and describe impacts of leprosy on armadillo population biology.

 

(4) Comparative Analyses:  We have found little evidence of any kin selection occurring in D. novemcinctus, but that does not preclude its possible importance in other members of the genus.  What is required are comparative data from the other species in the genus Dasypus (in fact, as a first step, we need genetic data from these other species confirming that littermates are indeed polyembryonic).  At an even broader level, we still have very limited knowledge of basic life-history characteristics for any of the 21 armadillo species living in Latin America.  For example, even published data on something as basic as litter size are often based on very limited observations or rely on information from captive births, which may not be representative of what occurs in the wild.  Such data are critical if we are to ever understand evolutionary patterns within this enigmatic group.  Consequently, another avenue for research is to expand beyond the one species of armadillo found in the U.S. (the nine-banded armadillo) and begin examining all these other species found in Central and South America.  There are virtually no data on any of these species at the moment, so almost any information is valuable and could have important management implications as many of these species are considered threatened or endangered