Experimental assessment of the fecundity of Eucypris virens (Ostracoda, Crustacea) under natural sex ratios

Abstract

1. The adaptive significance of the observed variations in sex ratios in non-marine ostracods is unclear. This study quantified the fecundity of females taken from a presumed fully sexual Eucypris virens population that were experimentally combined with different proportions of males (male : female sex ratios: 1 : 1, 1 : 2, 1 : 4, 1 : 8 and 0 : 1). 2. The results yielded no indications that female fecundity is altered by short-term variations in the proportion of males, at least not within the range of sex ratios that are common in natural ostracod populations. Complete removal of males, however, did strongly reduce hatching success of dried eggs. This suggests the need for multiple mating events during the reproductive lifetime of the female. It also emphasizes the need for a minimum number of males, although this minimum number evidently may be rather low, as we found a high number of spermatozoa in the seminal receptacles after a single mating event.3. The sex ratio in the source population was strongly female biased (1 : 3.4; n ¼ 514), whereas in the hatchling assemblages reared in the laboratory, males and females were found in equal proportions (1 : 1.0; n ¼ 1516), irrespective of the prevailing sex ratio. This clear discrepancy is intriguing, and points to the importance of epigenetic factors for the determination of field sex ratios.

Hatching phenology and voltinism of Heterocypris barbara (Crustacea: Ostracoda) from Lampedusa (Sicily, Italy)

“…A similar phenomenon was described in sexual lineages of E. virens and H. incongruens (Vandekerkhove et al, 2007;Rossi and Menozzi, 2012b). We suggest that female biased sex ratio, by reducing mating opportunity may affect egg to adult survival and that a difference in sex ratio between hatchlings from resting and non resting eggs may affect H. barbara voltinism and hence its population growth.…”

Dynamics of sexual and parthenogenetic populations of Eucypris virens (Crustacea: Ostracoda) in three temporary ponds

“…Although the species is typically regarded as univoltine, a second hatching period is possible (Meisch, 2000). Hatching rates are highly variable among populations and lineages, and depend on the prevailing environmental conditions (Otero et al, 1998;Vandekerkhove et al, 2007;Martins et al, 2008). Adult sexual and asexual E. virens can lay two types of eggs: subitaneous (immediate hatching) and diapausing eggs (desiccation-resistant resting eggs).…”

“…This last possibility has been discussed for Ostracoda (Abe, 1990;Cohen & Morin, 1990). Differential mother investment in male or female offspring is also possible (see Fisher, 1930;Godfray & Werren, 1996), but there are no indications for this in E. virens based on laboratory experiments ( Vandekerkhove et al, 2007;Martins et al, 2008). If we assume this population is of mixed reproductive mode, sex ratio changes can be explained by a difference in the hatching response of sexual and asexual resting eggs, or by a differential survival of sexuals and asexuals.…”

Extreme tolerance to environmental stress of sexual and parthenogenetic resting eggs of Eucypris virens (Crustacea, Ostracoda)

“…However, an immediate hatching response may lead to dramatic losses in case the inundation period is too short for reproduction (Martins et al, 2009). Previous studies have shown that inundation of ostracod eggs is sufficient to trigger a hatching response, irrespective of the prevailing temperature and light conditions (Otero et al, 1998;Vandekerkhove et al, 2007;Martins et al, 2008). By relying on a single proximate hatching stimulus, in this case the presence of water, the risk for erratic hatching events is high.…”