CENTENNIAL HONORS COLLEGE
Western Illinois University
Undergraduate Research Day 2015
Poster Presentation
Anatomical Variation in White Grub from Four Fish Hosts
Presenter: Shane Mason
Faculty Mentor: Shawn Meagher
Biology
A major problem in evolutionary biology is to determine what factors cause anatomical variation among
closely related populations. White grub (Posthodiplostomum minimum centrarchi) is a parasitic flatworm
(fluke) that spends the majority of its life cycle encysted within the livers of many species of fishes from
the family Centrarchidae. As for many parasites, problems arise when trying to understand species
diversity of white grub in different hosts. First, anatomically similar, but genetically distinct lineages may
exist (cryptic species). Second, anatomical variation may exist in genetically similar parasites living in
different hosts (phenotypic plasticity). Spring Lake, McDonough County, IL, provides a unique
opportunity to study the causes of anatomical variability of parasites from multiple hosts in a single
habitat. I examined the anatomy of white grub collected from four host species: bluegill (Lepomis
macrochirus), green sunfish [L. cyanellus), largemouth bass (Micropterus salmoides), and white crappie
(Pomoxis annularis). Specimens were manually excised using fine forceps, preserved in ethanol, stained,
and mounted on slides. Eighteen linear measurements were made on microscopic digital images of
specimens. Multivariate ANOVA revealed a significant difference in the measurements of worms from
different hosts (Wilks’ Lamda = 0.168, F = 2.45, df = 3, P <0.001). Many measures were significantly
correlated, suggesting that worms from different hosts differ primarily in size, with the rank order of
worms being L.m. > M.s. > P.a. > L. c. Further analyses are required to determine if these anatomical
differences are due to genetic or environmental causes.