Social instability during pregnancy and lactation alters female wild cavy offsprings’ endocrine status and behaviour later in life

The social environment shapes the individual behavioural profile during early phases of life. In guinea pigs the behavioural profile of daughters whose mothers experienced social instability during pregnancy and lactation (UE-daughters) are behaviourally masculinised. Since guinea pigs are domesticated the question arises whether this phenomenon was brought about by domestication or whether it represents an adaptive behavioural mechanism inherited from their wild ancestor, the wild cavy. This study, therefore, investigates the effects of an early unstable social environment on the biobehavioural profile of daughters in wild cavies and compares these effects with the findings in the domestic form. Our results show higher frequencies of aggression and play behaviour in UE-daughters, indicating a comparable behavioural masculinisation as in guinea pigs. Thus, the observed behavioural changes in UE-daughters cannot have been brought about by artificial selection during domestication. Rather they represent maternal effects evolved through natural selection.

Different types of oestrous cycle in two closely related South American rodents (Cavia aperea and Galea musteloides) with different social and mating systems

A comparative approach was used to investigate two closely related South American rodent species: the wild cavy (Cavia aperea) and the yellow-toothed cavy (Galea musteloides). These species of wild guinea-pig inhabit different habitats and show divergent social and mating systems. Cavia have a polygynous mating system, whereas in Galea promiscuous mating occurs. These observations correspond to functional variations in sperm characteristics, which might be interpreted as adaptations to different reproductive patterns in the females of both species. Twenty-two female C. aperea and G. musteloides (11 of each species) were investigated to elucidate differences in the characteristics of the oestrous cycles. The experimental design consisted of three stages, in which the degree of contact between the sexes was successively changed. During these stages, the reproductive cycle of the females was monitored by examining the condition of the vaginal closure membrane, analysing vaginal smears and determining serum concentrations of oestrogens and progesterone. The results revealed different types of oestrous cycle in the two species. Female C. aperea showed periodical cycles with spontaneously occurring oestrous periods, ovulation and corpus luteum activity. In contrast, in female G. musteloides, oestrus was exclusively induced by the presence of a male. However, after the induction of oestrus, ovulation and corpus luteum activity occurred spontaneously without stimuli from copulation. To date this type of oestrous cycle has not been described for any other mammalian species. Thus, these data indicate that differences in the reproductive patterns of the females may have shaped the evolution of different sperm characteristics in the males.