Intersexuality in Crustacea: an environmental issue?

This paper aims to give a historical overview of current understanding about intersexuality in crustaceans, assesses gaps in our knowledge and asks whether it should be an environmental concern. The oldest known cases of intersexuality come from 70 million year old fossil crabs whilst the oldest published case of intersex crustacean stems from a 1730 Royal Society report of a gynandromorph lobster. Many crustacean species are sequential hermaphroditic or simultaneous hermaphrodites. Consequently, there has been confusion as to whether accounts of intersex in the literature are correct. Intersexuality is fairly common throughout the Crustacea and it has been suggested that intersex may arise through different mechanisms. For example, sexual gynandromorphism may arise through disruption in early embryonic development whereas intersexuality may also arise through perturbations of androgenic gland hormone and sexual differentiation in later development. The causes of intersex are multifaceted and can occur through a number of mechanisms including parasitism, environmental sex determination, genetic abnormalities and increasingly pollution is being implicated. Despite many studies on the effects of endocrine disrupters on crustaceans, very few have focussed on wild populations or male related endpoints; rather many laboratory studies have been attempting to assess biomarkers of feminisation. This is surprising as many of the seminal papers on endocrine disruption focussed on effects found in the wild and male specimens. This paper argues that we might have been addressing the right questions (i.e. pollution induced intersex), but in the wrong way (feminisation); and therefore gives recommendations for future directions for research. Biomarker development has been hampered by paucity of genomic and endocrine knowledge of many crustacean model species; however this is rapidly changing with the advent of cheaper affordable genomic techniques and high throughput sequencing.