Pronounced and prevalent intersexuality does not impede the ‘Demon Shrimp’ invasion

Abstract

Crustacean intersexuality is widespread and often linked to infection by sex-distorting parasites. However, unlike vertebrate intersexuality, its association with sexual dysfunction is unclear and remains a matter of debate. The ‘Demon Shrimp’, Dikerogammarus haemobaphes, an amphipod that has invaded continental waterways, has recently become widespread in Britain. Intersexuality has been noted in D. haemobaphes but not investigated further. We hypothesise that a successful invasive population should not display a high prevalence of intersexuality if this condition represents a truly dysfunctional phenotype. In addition, experiments have indicated that particular parasite burdens in amphipods may facilitate invasions. The rapid and ongoing invasion of British waterways represents an opportunity to determine whether these hypotheses are consistent with field observations. This study investigates the parasites and sexual phenotypes of D. haemobaphes in British waterways, characterising parasite burdens using molecular screening, and make comparisons with the threatened Gammarus pulex natives. We reveal that invasive and native populations have distinct parasitic profiles, suggesting the loss of G. pulex may have parasite-mediated eco-system impacts. Furthermore, the parasite burdens are consistent with those previously proposed to facilitate biological invasions. Our study also indicates that while no intersexuality occurs in the native G. pulex, approximately 50% of D. haemobaphes males present pronounced intersexuality associated with infection by the microsporidian Dictyocoela berillonum. This unambiguously successful invasive population presents, to our knowledge, the highest reported prevalence of male intersexuality. This is the clearest evidence to date that such intersexuality does not represent a form of debilitating sexual dysfunction that negatively impacts amphipod populations.

Hidden diversity: parasites of stream arthropods

“…Most previous studies on local parasite diversity that included more than one group of parasites were focusing either on a single species, or group of hosts [e.g. the amphipods Dikerogammarus villosus (Gammaridae) (Bojko et al, 2013) and D. haemobaphes (Green Etxabe et al, 2015), or mayflies (Arvy & Sowa, 1976)]. To the best of my knowledge, no comprehensive study on the local diversity of parasites in stream arthropods exists to date.…”

Environmental Influences on Crustacean Sex Determination and Reproduction: Environmental Sex Determination, Parasitism, and Pollution

“…; Yang et al (2008) Causes considered multiple although evidence points to infection with microsporidian and/or paramyxean infections in some populations along with speculation on pollution (Short et al 2015) Gammarus chevreuxi…”