Centennial Honors College
Western Illinois University
Undergraduate Research Day 2014
Poster Presentation
Does Anatomical Variation in White Grub (Posthodiplostomum minimum
centrarchi) Suggest Unrecognized Species?
Shane Mason
Faculty Mentor: Shawn Meagher
Biology
A major goal in evolutionary biology is to determine whether anatomical differences
between individuals are caused by genetic or environmental differences between them.
This issue raises two problems when trying to identify parasite species. First,
anatomically indistinguishable, but genetically distinct, lineages may exist. Second,
anatomical differences may exist between genetically similar parasites living in different
hosts. White Grub (Posthodiplostomum minimum centrarchi) is a parasitic flatworm
(fluke) that spends the majority of its life cycle encysted within the livers of fish from the
family Centrarchidae. In Spring Lake, there are 3 genetically distinct lineages that infect
4 fish hosts: one infects white crappie (Pomoxis annularis), another, largemouth bass
(Micropterus salmoides), and a third infects 2 species: bluegill (Lepomis macrochirus),
and green sunfish (Lepomis cyanellus). Anatomical similarities and differences between
these worms have not been studied. White grub anatomy will be examined in these four
host species to determine the relative importance of genetic differences (i.e. 3 fluke
lineages), and host environment (i.e. one white grub in 2 Lepomis species) to
anatomical variability. I have collected over 50 flukes per host species, and recorded
several variables that might affect fluke size and shape: fluke counts (per liver) and host
sex, age, and length. Specimens have been manually excised, preserved, stained, and
mounted on slides to be examined and measured under microscopy. Statistical
analyses (principle components) will be performed on several length measurements to
determine the best predictor of anatomical differences. This study could identify
characteristics useful to differentiate between Posthodiplostomum species.