Inbreeding costs can be high in haplodiploid hymenopterans due to their particular mechanism of sex determination (i.e., single-locus complementary sex-determination system, sl-CSD), as it can lead to the production of sterile males. Therefore, mechanisms contributing to reduced inbred matings can be beneficial. In this sense, asynchronous nest departure of sibling drones and gynes could reduce kin encounters in social hymenopterans. Using six observation colonies, we determined under field conditions the nest departure behaviour of sibling reproductives of the social wasp Vespula germanica (Hymenoptera: Vespidae). We determined that sexuals leave the nests definitively and detected asynchronous departure not fixed to a particular caste at a seasonal scale in some colonies, as gynes or drones delayed their departure as a function of the departure of the opposite sex, depending on the colony. At a higher temporal resolution (i.e., within a day), we discovered that drones consistently began to leave nests 1 h before gynes and this difference was driven by those individuals that left on the same day as did the opposite-sex kin. Even though other mechanisms such as polyandry and differential dispersal could also be important at reducing inbred matings in the species, the observed departure patterns (i.e., in some colonies actually leave together with the opposite caste, while in others temporal segregation seems to occur) from nests could be complementary to the former and be important at reducing the negative effects of inbreeding in this invasive species.

The effects of breeding season and reproductive status on female reproduction were investigated in the common mole-rat, Cryptomys hottentotus hottentotus, a co-operatively breeding rodent that exhibits seasonal breeding and a reproductive division of labour. Body mass, reproductive tract morphometrics, ovarian histology and plasma testosterone concentrations were studied in 80 females from 42 wild-caught colonies. Although the birth of offspring is restricted to the summer, qualitative analysis of ovarian histology revealed that females retained reproductive function during the winter non-breeding period. Seasonal differences were found in ovarian morphometrics and testosterone concentrations and are probably associated with the occurrence of pregnancy in reproductive females during the breeding period. The continuance of reproductive function during the non-breeding period in female common mole-rats parallels the situation in males, and is believed to be important in dispersal in C. h. hottentotus. The non-breeding period coincides with the period of maximal dispersal opportunities in the winter rainfall areas inhabited by the common mole-rat. Reproductive activation in dispersing animals may aid intersexual recognition, assist pair-bond formation and thereby facilitate independent reproduction. Reproductive and non-reproductive females exhibited a similar degree of reproductive function, and as for season, the only clear-cut status-related differences were associated with the occurrence of pregnancy in reproductive females. This absence of a physiologically well-defined suppression of reproduction in female common mole-rats is similar to the situation in males. Incest taboos between philopatric siblings may negate the need for a rigorous suppression of reproduction in subordinate colony members of this obligate outbreeder.

The cestode Schistocephalus solidus is a simultaneous hermaphrodite that grows in 2 intermediate hosts and reproduces rapidly within a few days in the gut of a bird. Reproduction takes place by self- or cross-fertilization. Here, it was tested whether egg production differs between S. solidus that reproduce alone and those that are allowed to reproduce in pairs. Egg production in an in vitro system was found to depend on the cestodes' social situation. When kept alone, larger cestodes produced larger eggs. This was not so when kept in pairs – the difference between these 2 reproductive modes being highly significant in this respect. Further experiments revealed that, within the first 3 days, these hermaphrodites produced a larger total egg mass when kept alone than when kept in pairs. This was also reflected by the energy contents of the cestodes after this time-span: selfers had used up more energy than paired worms. Furthermore, S. solidus appeared to adjust its investment per egg depending on whether the offspring will be the result of self- or cross-fertilization. Selfers produced larger numbers of eggs, but these eggs were smaller and contained even smaller embryos per given egg size than eggs of potentially outbreeding cestodes. Selfed eggs reached lower hatching rates. Although this is to be expected from inbreeding depression it may also be an effect of the reduced maternal investment per egg. The observed phenotypic plasticity in the reproduction of S. solidus is discussed within 4 evolutionary frameworks: local mate competition adjusted for hermaphrodites, the hermaphrodite's dilemma, bet-hedging, and sib-competition.