No evidence that the introduced parasite Orthione griffenis Markham, 2004 causes sex change or differential mortality in the native mud shrimp, Upogebia pugettensis (Dana, 1852)

Authors: ASSON, DANIELLE - Oregon State University; CHAPMAN, JOHN - Oregon State University; Dumbauld, Brett

Submitted to: Aquatic Invasions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2017
Publication Date: 4/4/2017
Citation: Asson, D., Chapman, J.W., Dumbauld, B.R. 2017. No evidence that the introduced parasite Orthione griffenis Markham, 2004 causes sex change or differential mortality in the native mud shrimp, Upogebia pugettensis (Dana, 1852). Aquatic Invasions. 12(2):213-224. https://doi.org/10.3391/ai.2017.12.2.09.
DOI: https://doi.org/10.3391/ai.2017.12.2.09

Interpretive Summary: The mud shrimp, Upogebia pugettensis is an important inhabitant of Western North American estuaries and is infected by the recently introduced Asian bopyrid isopod parasite, Orthione griffenis.Infection results in effective castration and the invasion of this isopod is implicated in recent shrimp population declines. The details of how this shrimp causes female shrimp to be effectively castrated and unable to reproduce has remained elusive due largely to the inablility to hold experimental shrimp and parasites over time and the number of observations and large population sample sizes required for in situ analyses. Dramatically greater prevalence of O. griffenis prevalence occurs among female U. pugettensis and this has been attributed to parasite induced sex change, increased male mortality and differential tidal exposure of the two sexes of shrimp to settling larvae of O. griffenis. We examined 508 O. griffenis infestations from all size classes of 2,014 shrimp that we collected from 26 sites in 5 estuaries to test for potential feminization, parasite induced male host mortality and possible estuary or tide level effects on shrimp host vulnerability. The overall male:female ratio in our samples was 1:1.07 and O. griffenis infestations were nearly twice as prevalent among females as among males. Of 4 intersex U. pugettensis, that we found, only one was infested by O. griffenis. The nearly equal sex ratio among the entire U. pugettensis population, and the poor association of O. griffenis with intersex shrimp, indicates that parasite induced feminization and mortality of male shrimp are not significant factors influencing the overall U. pugettensis population. These results indirectly corroborate previous studies which suggest that effective castration occurs due to energetic losses caused by the isopod which feeds on the hosts blood and that this might be driving reduced ability of females to reproduce and the observed declines of U. pugettensis populations.

Technical Abstract: Efforts to resolve the host parasite interactions between native western North American mud shrimp, Upogebia pugettensis and its recently introduced Asian parasite, Orthione griffenis resulting in effective castration and shrimp population declines have remained elusive due largely to the detail of observations and large population sample sizes required for the analyses. Dramatically greater O. griffenis prevalence among female U. pugettensis have been attributed to parasite induced sex change, increased male mortality and differential tidal exposure of sexes to settling O. griffenis larvae. We examined 508 O. griffenis infestations from all size classes of 2,014 shrimp that we collected from 26 sites in 5 estuaries to test for potential feminization, parasite induced male host mortality and possible estuary or tide level effects on host vulnerability. The overall male:female ratio in our samples was 1:1.07 and O. griffenis infestations were nearly twice as prevalent among females as among males. Of 4 intersex U. pugettensis, that we found, only one was infested by O. griffenis. The nearly equal sex ratio among the entire U. pugettensis population, and the poor association of O. griffenis with intersexes, indicate that parasite induced feminization and mortality are not significant among the overall U. pugettensis population. These results indirectly corroborate previous assumptions of effective castration due to energetic losses driving the observed declines of U. pugettensis populations.