Reproduction in the amphipod, Echinogammarus marinus: a comparison between normal and intersex specimens

Abstract

The fecundity and occurrence of intersexuality in the amphipod, Echinogammarus marinus, collected from populations on the east coast of Scotland are reported. Intersex specimens have significantly smaller mean brood sizes than normal specimens. Embryo survival, as measured by the ratio of eggs/embryos in early and late stages of development, is lower in intersex specimens than normal specimens. Greater differences in the number of early stage eggs compared with late stage eggs in intersex specimens is suggested to arise by the active ejection of non-viable eggs, or from the passive loss of eggs through malformed brood plates in females. An apparent reduction in brood sizes between early and late stages of development in ‘normal’ specimens, emphasizes the importance of quantifying different egg/embryo stages in amphipod toxicology and fecundity studies.

An investigation into intersex amphipods and a possible association with aquaculture

“…One group contained normal males, the other contained both normal and intersex females and the third intermediate group contained intersex males. The degree to which the intersex males and females were discriminated provides strong evidence for treating these two phenotypes separately, as proposed by Ford et al (2003;2004b). In similarity with this study, Ford et al (2004a) found that the discriminating factor between the groups of normal and intersex specimens from the Firth of Forth (Scotland) was gnathopod size.…”

“…In this study, a higher percentage of intersex individuals was observed at Loch Sunart fish farm than at the site away from the fish farm , unpublished data). This lower incidence of intersexuality found later in the year may be due to the association between size and intersexuality (Ford et al, 2003;Ford et al, 2004b). Both Kelly et al (2004) and Ford et al (2005) found that the incidence of intersexuality in amphipods varied throughout the year, with higher frequencies of intersex observed during warmer months when more, larger, and mature specimens were present within the population.…”

“…The sexual phenotype was recorded and the specimens were weighed. If specimens were intersexed, the phenotype of intersex was recorded as either intersex male or intersex female, as described by Ford et al (2003). Proportions of sexual phenotypes were analysed statistically using chi-square tests (SPSS 11.0).…”

Changes in biomass and elemental composition during early ontogeny of the Antarctic isopod crustacean Ceratoserolis trilobitoides

“…Brood mortality, however, is a common feature in other peracarids (e.g. Johnson et al 2001;Ford et al 2003).…”

Measuring sublethal impacts of pollution on reproductive output of marine Crustacea

“…Whilst investigating fecundity in normal and intersex specimens of the amphipod Echinogammarus marinus (Leach), Ford et al (2003) showed that female intersex specimens produce fewer eggs than normal females. Dick et al (1998) reported that females of the amphipod Crangonyx pseudogracilis would selectively eject non-viable eggs when cycling eggs within the brood chamber.…”