Inbreeding and outbreeding depression in geographical parthenogensHeterocypris incongruensandEucypris virens(Crustacea: Ostracoda)

Abstract

Heterocypris incongruens and Eucypris virens are geographic parthenogens inhabiting temporary ponds. Several authors proposed that, after the last glaciation, asexual lineages would spread throughout Europe more efficiently than sexual ones. The range expansion, that followed metapopulation dynamics characterized by genetic bottlenecks and subsequent inbreeding/outbreeding depression, had strong negative fitness consequences in sexuals. Using controlled crosses we estimated inbreeding and outbreeding depression in the sexual populations of H. incongruens and E. virens and compared the experimental reproduction rate in sexual and asexual females of both species. Inbreeding depression varied according to species and fitness components but, in general, was not significantly different between inbred and outbred crosses. In H. incongruens, inbred crosses produced a higher percentage of resting eggs and had higher fecundity than intrapopulation outbred crosses. Reproduction rate in asexuals of both species was about twice that in sexuals. Our data does not support the hypothesis that sexual populations exhibit inbreeding depression in geographic parthenogens. However, outbreeding depression and the lower efficiency of sexuals in establishing new populations may account for the role of metapopulation dynamics in geographic parthenogenesis of both species.

Mother's Age and Hatching Phenology Strategy ofHeterocypris incongruens(Crustacea: Ostracoda) in Unpredictable Environment

“…The benefit of producing resting eggs seems obvious for organisms living in temporary ponds, and its adaptive value is suggested by the negligible cost of their production. According to previous (Rossi and Menozzi, ) and present results, the percentage of both resting eggs and nonresting eggs per female was not related to the life span and the number of resting eggs per clutch is positively related to the clutch size. These results suggest that there are not trade‐offs (i.e., costs) between resting eggs production and life span and fecundity.…”

“…In E. virens , we reported the effect of mother presence that is probably linked to behavior (i.e., releasing chemicals in the medium or “handling”) as a possible mechanism for the expression of a risk‐spreading strategy in nonresting eggs (Rossi and Menozzi, ). In both species, we assumed that resting egg investment should have no cost in terms of maternal fecundity because the number of resting eggs did not negatively affected the total number of eggs per female (Rossi and Menozzi, ).…”

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.…”

“…Differences in allele frequencies at PGM and GPI loci were observed in H. barbara from Aria Rossa microcosms inundated at different temperature and photoperiod conditions (Rossi et al, 2004). We cannot rule out that differential responses to trigger stimuli were linked to genetically dependent hatching rates while, a delayed recruitment from resting eggs, allows a generation overlapping reducing the risk of inbreeding depression in small sexual populations (Ellner and Hairston, 1994;Rossi and Menozzi, 2012b). Moreover, having more generations in a given hydroperiod could allow more rapid adaptation, provided selection pressures experienced by the different generations that are sufficiently similar (Rossi et al, 2003;Forrest and MillerRushing, 2010).…”

What does the geography of parthenogenesis teach us about sex?

“…For instance, mating with immigrants can result in the loss of locally adaptive alleles [123]; see [124] for the only evaluation so far of outbreeding depression in a context rstb.royalsocietypublishing.org Phil. Trans.…”