Browsing by Author "David Tarpy, Committee Member"

Now showing 1 - 3 of 3

Colony genetic structure and effects of inbreeding on body size in three populations of Reticulitermes flavipes in the southeastern U.S.
(2009-02-16) Nino, Bernardo Daniel; David Tarpy, Committee Member; Coby Schal, Committee Member; Edward Vargo, Committee Chair
In this study, I expanded the knowledge base of the eastern subterranean termite R. flavipes by investigating colony and population genetic structure in previously unstudied areas in Florida and Mississippi. I used microsatellite markers to infer colony breeding structure and population genetic structure and genotyped 20 workers in each of 20-30 colonies per population at eight microsatellite loci. I conducted pedigree analysis on the worker genotypes to determine the proportions of colonies that were simple families, extended families or mixed families. I also estimated the coefficient of relatedness and F-statistics and compared these values to those based on computer simulations of different breeding systems to infer levels of inbreeding and numbers of reproductives within colonies. An unexpected finding was the presence of two distinct populations in one collection site in Mississippi (MS). These two populations, MS1 and MS2, differed in the predominant family type. MS1 consisted mainly of simple family colonies whereas MS2 was composed primarily of extended family colonies. The breeding structure in the extended family colonies in both populations was consistent with simulations for colonies with a low number of effective reproductives (2-6) which have been interbreeding for few generations. In Florida I found a high proportion of extended family colonies (~ 63%); the breeding structure in these colonies was consistent with the presence of a higher number of effective reproductives (> 6) which had been interbreeding for many generations. Mixed family colonies were collected in all three populations and composed about 10% of all colonies in each population. In addition, I investigated possible effects of inbreeding and colony family type on worker and soldier body size. Worker and soldier head widths were measured and correlated to colony inbreeding coefficient (FIC). This statistic is highly sensitive to the number of effective reproductives heading colonies. A negative correlation was discovered between worker and soldier body size and the effective number of reproductives heading colonies in two populations. I found a similar trend in the third population (MS1) but it was not significant, most likely due to small sample size. In population MS2 I found a significant effect of colony family type on body size; workers and soldiers in extended family colonies were smaller than individuals in simple family colonies. These finding may indicate a previously little appreciated consequence of inbreeding in termites.
Interactions between the ants Linepithema humile, Tapinoma sessile and aphid mutualists
(2008-12-02) Powell, Bradford E; David Tarpy, Committee Member; Robert Dunn, Committee Member; Edward Vargo, Committee Member; Jules Silverman, Committee Chair
Invasive species have major impacts on the ecosystems they invade. Among the most disruptive groups of invasive species are ants. Invasive ants have caused losses in biodiversity among a wide range of taxa, including birds, mammals, lizards, but especially towards ground nesting arthropods such as native ants. Why native ants are so susceptible to invasion and how invasive ants are able to sustain massive population growth remain unclear. It has been suggested that invasive ants utilize carbohydrate resources from hemipteran exudates to fuel aggressive foraging and colony expansion. Perhaps invasive ants are simply more proficient at usurping these resources, maintaining higher hemipteran populations, etc. Our work uses a model invasive, the Argentine ant, , Linepithema humile, and a native ant Tapinoma sessile to quantify hemipteran tending ability and competition. Through a series of laboratory and field experiments we were able to quantify 1) carbohydrate sequestering performance, 2) the effect either ant species had on hemipteran population growth rates in a predator-free space, 3) the defense ability of either ant against hemipteran predators and parasitoids, and 4) the proportion of invasive ants required to displace a native colony from a hemipteran resource. Neither ant demonstrated a better ability to sequester liquid resources; however recruitment strategies were much different. Hemipteran populations in the presence of L. humile grew larger in a predator free environment and populations exposed to predators were better defended by L. humile than T. sessile. L. humile was able to displace T. sessile from a nest site without having a majority of worker ants. Aggression of either ant species was significantly reduced without hemipterans present. Understanding factors that drive invasive species can give us insight into native areas that may be susceptible for invasion, how potential mutualist populations might respond and possibly provide us with an avenue for secondary control measures given the economic and ecological importance of invasive species.
Population Genetic Structure, Dispersal & Gene Flow in the German Cockroach, Blattella Germanica: A Structural Pest in the Urban Environment
(2008-10-27) Crissman, Jonathan Ross; Coby Schal, Committee Co-Chair; Edward Vargo, Committee Co-Chair; David Tarpy, Committee Member
The goal of the current study was to explore German cockroach population differentiation and dispersal in urban residences at several spatial scales. Little differentiation was expected within buildings due to frequent active dispersal of the German cockroach. However, differentiation was expected between spatially separated buildings because the German cockroach cannot survive beyond human structures and dispersal must be human-mediated. Differentiation was expected to increase with increasing spatial distance as human-mediated dispersal becomes successively less frequent. Cockroaches were collected in a geographical hierarchy, with samples at the scale of single apartments, apartment buildings, and apartment complexes within Raleigh, North Carolina in addition to 16 other cities in the United States and six Eurasian cities. All individuals were genotyped at ten microsatellite loci. Microsatellite diversity was generally high across our samples, with average alleles per locus as high as 9.11, and observed heterozygosity in excess of 0.6 in most populations. However, global differentiation was lower than expected, with a global FST of 0.046 across Raleigh, 0.099 across the U.S. with Raleigh excluded, and 0.158 across global samples with Raleigh excluded. No departure from panmixia was found between German cockroach samples within apartments by pairwise G-tests (P > 0.05). G-tests did detect highly significant departures from panmixia between all but one pair of apartments within Raleigh (all P < 0.001). These tests indicate that each separate apartment represents an individual population. Global FST values suggested that dispersal and gene flow occurred more often within buildings than between them and more within apartment complexes than between them. Similarly, significant Mantel tests of isolation by distance within Raleigh (P < 0.001), across the U.S. (P = 0.029), and across global samples (P < 0.005) indicated a significant positive correlation between genetic distance and geographic distance. These tests suggested that German cockroach dispersal and gene flow occurred less frequently at successively larger spatial scales. However, phylogenetic trees constructed from genetic distances for each spatial scale were unable to cluster apartments according to geographic proximity, except for apartments within a single building. The individual-based clustering program Structure was also unable to detect any informative underlying structure beyond a single building when no a priori population information was used. A similar lack of geographic pattern was shown in B. germanica mitochondrial 16S diversity. Only 10 unique 16S haplotypes were found for 66 individuals across 40 global populations, and haplotypes varied greatly in their frequency and geographic ranges. Beyond the scale of a single building, gene flow by passive dispersal seems to have formed no spatial clustering of genetic similarity, even at the global scale. This may be due to non-equilibrium conditions and non-linear evolution caused by dramatic declines in population size due to insecticides or large fluctuations in temperature, humidity, and food availability. These population bottlenecks are known to rapidly change allele frequencies and affect various evolutionary estimates, including genetic distance. The challenge for future studies will be to find markers conserved enough to be robust to these non-equilibrium conditions but variable enough for fine scale analysis.