Reproductive behavior of intersexes of an intertidal amphipod Corophium volutator

Abstract

Abstract. Intersexes are common in crustaceans. Typically, these intersexes are sterile or function as females, but prior evidence from laboratory experiments suggests that intersexes of a key species of gammaridean amphipod, Corophium volutator, might function as males. We observed that intersexes of C. volutator behaved as males by crawling (mate‐searching) on a mudflat during ebb tides and pairing in burrows with female amphipods. In the laboratory, intersexes and males did not differ in aspects of crawling such as movement rate and measures of burrow investigation. I`ntersexuality was costly in that intersexes crawled less often than males on a mudflat, formed fewer pairs with females than males, and remained in tandem less often with receptive females than males. The use of PCR‐based identification methods failed to identify the presence of transovarial, feminizing, microsporidian parasites as a major cause of intersexuality in this species in that infected females did not produce broods that contained more intersexes than broods produced by uninfected females. Because intersexes may be mistaken as females, the percentage of functional males in amphipod populations may be underestimated: an important consideration given male limitation in populations of C. volutator. The occurrence of intersexes has significant implications for studies on the evolution and ecology of sex ratios, and the use of crustaceans as indicators of environmental quality.

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

“…Gammarid amphipods mate after a period of mate-guarding and a reduced capacity of intersex males to initiate or maintain this behaviour could also impact reproductive success. The plausibility of such altered behaviours is made more likely given numerous behavioural changes observed in C. volutator intersexes ( McCurdy et al, 2008 ). Investigation of D. haemobaphes reproductive function and behaviour will help determine the extent of dysfunction associated with the intersexuality.…”

“…Male intersexuality is widespread in amphipods; however, our understanding of its reproductive consequences is poorly understood relative to vertebrates ( Harris et al, 2011 ). The extents of morphological and behavioural changes ( McCurdy et al, 2008 ; Yang, Kille & Ford, 2008 ) have led to the suggestion ( Yang, Kille & Ford, 2008 ; Ford, 2012 ) that the impact of crustacean male intersexuality may be similar to that seen in vertebrates ( Harris et al, 2011 ). Despite some evidence of intersexuality in invasive D. haemobaphes ( Bacela, Konopacka & Grabowski, 2009 ), sexual phenotypes in this species have not been studied, even though notable levels of intersexuality in the unambiguously successful invading population would reveal considerable insight into the consequences of intersexuality for wild crustacean populations.…”

Crustacean Intersexuality Is Feminization without Demasculinization: Implications for Environmental Toxicology

“…In this regard, the interpretation of E. marinus male intersexuality as feminization imposed onto a normal male suggests widespread forms of crustacean intersexuality do not necessarily indicate serious sexual dysfunction. This is assuming that male intersexuality is not commonly associated with abnormal mating behaviors that compromise reproductive success …”

“…Although, as E. marinus intersexuality is typical of that found in amphipods and morphologically analogous forms are also described in decapod crustaceans, our findings are likely to be relevant to malacostracans and, more tentatively, copepods. , However, crustacean intersexuality can differ considerably from the typical forms. Extreme intersex phenotypes have been reported in the amphipods Gammarus duebeni and Corophium volutator ,, and it will be of interest to determine if such intersexuality is associated with demasculinzation or represents a more advanced case of feminization without demasculization. The data produced for this study will greatly enhance the capacity of ecotoxicologists to characterize the various forms of crustacean intersexuality and determine the extent to which abnormal sexual phenotypes represent sexual dysfunction.…”

“…The consequences of both parasite and nonparasite associated crustacean intersexuality are the subject of debate . The reproductive deficiencies associated with female intersexuality are statistically significant but relatively subtle ,, and might represent the acceptable cost of adaptive environmental sex determination mechanisms. ,, Furthermore, female intersexuality is not always associated with significant reductions in fecundity, suggesting it may not be maladaptive in some species. − The implications of parasite and nonparasite induced male intersexuality are less well understood. , However, its high frequency, association with lower sperm counts, pronounced morphological changes, ,, altered hormone levels and behavioral changes have led to the suggestion that intersexuality in males is of serious concern . High levels of intersexuality may indicate a population in which a large proportion of all males are to some extent compromised, albeit less conspicuously.…”