Sperm number assessed by flow cytometry in species of Daphnia (Crustacea, Cladocera)

Abstract

Daphnia magna and Daphnia pulex are two important model species in ecotoxicology.In daphniids, studies of the effects of contaminants have mostly focused on female life history traits, yet it would also be important to examine male reproductive traits, particularly in relation to endocrine disruptors. In this study, we developed a protocol that uses flow cytometry to measure sperm number in individual males of different species of Daphnia. We tested our protocol on 114 males from several clones of three common species of Daphnia. Sperm count varied widely among individuals and reached high numbers (up to 1.45 × 10 5 ). Positive relationships between male length and sperm number were observed in D. pulex and Daphnia pulicaria, but not in D. magna. Important inter-clonal differences in sperm production were observed in all species, with some clones producing very little sperm. Duplicated sperm samples showed on average only 6% difference in sperm counts. Sperm counts were stable at least over a 2-hr period and up to 5 hr for most samples. This sperm isolation protocol and flow cytometric enumeration approach will be of major interest to ecotoxicologists. K E Y W O R D SDaphnia magna, Daphnia pulex, ecotoxicology, invertebrates, sperm quality

Genomic evidence of paternal genome elimination in the globular springtailAllacma fusca

“…Germ cells therefore represent $67% of C. elegans cell count. A similar case is found among arthropods: Up to 75% of body cells in Daphnia males are sperm (Dufresne et al 2019). It is important to note we specifically discuss the fraction of cells, not the biomass, as sperm can be substantially smaller compared to other cell types in the body.…”

Sex ratio effects on reproductive success of male and female Daphnia

“…Moreover, at the lowest sex ratio, a substantial fraction of deposited eggs was unviable, that is unfertilized (Figure 4). This supports possible sperm depletion (Winsor & Innes, 2002), despite high sperm production in males (Dufresne et al, 2019). As a result, female RS rapidly increased with increasing male availability at highly female-biased sex ratios as predicted by models that assume that females may experience mate limitation (Kokko et al, 2012).…”

Genital movements are not restricted to spermatozoa transfer in a haplogyne spider

“…The cut‐off line used as a criterion to impute data is the one suggested by Bennett (2001) where the amount of missing data does not exceed 10% of the total data; this way the results would not be biased (reviewed in Dong & Peng, 2013). The body size of individuals was included in the models since it may have some effect on the amount of spermatozoa produced and/or transferred by males and stored by females (Cargnelutti et al, 2018; Dufresne et al, 2019; O'dea et al, 2014; Whitman, 2008; Wiernasz et al, 2001). For each GLM, the model presents the additive effect of all predictive variables and the effect of the interaction between the treatment and the number of pedipalp movements.…”