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Abstract
In the past two decades, an increasing body of studies has been published on the intersex phenomenon in separate-sexed crustaceans from marine and freshwater ecosystems. Various causes are being considered that could have an influence on the occurrence of intersex. Besides genetic factors, environmental conditions such as photoperiodicity, temperature, salinity and parasitism, but also environmental pollution with endocrine disrupting chemicals (EDCs) are discussed. As part of a long-term monitoring (2012 – 2020) in north-west Brittany, we recorded the occurrence of intersex in the marine amphipod Echinogammarus marinus. We quantified the intersex incidence at marine and estuarine sites and analyzed the incidence in relation to the endocrine potential of the sediments. Intersex occurred with mean frequencies between 0.87% and 12%. It was striking that the incidence of intersex increased with increasing distance from the sea. Since the highest incidence was observed at the range boundary of this stenohaline species, we assume that intersex is triggered by endocrine potential and increasing stress due to increasing freshwater content − and thus an interplay of different environmental factors.
Highlights
The term intersexuality was used for the first time at the beginning of the 20th century and describes in the animal kingdom the atypical expression of both female and male secondary sexual characteristics of an individual of a gonochoristic species [1]
In the present long-term study, we focus on the amphipod species Echinogammarus marinus, which is commonly found in marine and estuarine ecosystems across Europe
The farther the sampling sites were from the coast, the higher the intersex incidence of the E. marinus populations
Summary
The term intersexuality was used for the first time at the beginning of the 20th century and describes in the animal kingdom the atypical expression of both female and male secondary sexual characteristics of an individual of a gonochoristic (separate-sexed) species [1]. About 340 taxa are known to exhibit the intersex phenomenon, most of which belong to the phyla Mollusca and Arthropoda [2]. Intersex in Amphipods - A Longterm Study frequently affected by intersex, with about 256 species. Ford & Fernandez [3] list at least 20 amphipod species from freshwater, estuarine, and marine ecosystems that may exhibit intersex. Several causes are considered for the occurrence of intersex. Environmental pollutants, especially endocrine disruptors (EDC), are discussed as another trigger [8, 9]. Martins et al [10] consider a form of environmental sex determination (ESD) triggered by endocrine disruptors as responsible factor for the occurrence of the intersex phenomenon
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