ImageJ analysis of morphological changes in mud crabs from the Chesapeake Bay infected with castrating, zombie barnacle parasite

Abstract

Male mud crabs infected with an invasive endoparasite (Loxothylaucus panopaei or loxo) in the Chesapeake Bay are speculated to undergo morphological changes, altering their typical long and narrow aprons to a wider and broader apron seen in female crabs. Here, we analyze these changes in two common mud crabs, Eurypanopeus deressus (e.d.) and Rhithropanopeus harrisii (r.h.), using imageJ, an image processing software. From the data collected, we calculated the relative abdominal width (RAW), a ratio between the widths of apron segments 2 and 5. Low RAW’s are a result of broader aprons, while high RAW’s are a result of a taper being present. Out of 293 crabs, 111 were females and 182 were males. 84% of males were uninfected, while 26% were infected. 62% of females were uninfected, and 48% were infected. An ANOVA test was done comparing the RAW and infection status relationship between genders. The P value between infected males and uninfected males was 1.38e-11, showing there is a significant gap with an average difference of 0.44. The P value between infected females and uninfected females was 0.0108, showing there is a slight difference with an average gap of 0.17. Uninfected males had the highest RAW, followed by infected males, uninfected females, and infected females. These findings show that loxo alters the apron shape drastically in infected males but only slightly in females. While the underlying cause of loxo feminization is still unknown, these results will provide better insight into the morphological changes of this crab-parasite relationship.