Processes at the origin of similarities in dispersal behaviour among siblings

Processes which generate natal dispersal are largely unknown. This is parti cularly the case for the sources of differences among families. Three types of processes can generate the variability among families: genetic, prenata l and postnatal. We first tested the family resemblance of dispersal behavi our in the common lizard (Lacerta vivipara). We then experimentally investi gated the role of pre- and postnatal factors in the variability of dispersa l among families. From 1989 to 1992, we studied dispersal of juveniles from pregnant females captured in the field and maintained in laboratory until parturition. We manipulated the conditions of gestation to test for prenata l effects on juvenile dispersal. We tested postnatal effects by releasing s iblings of the same family in contrasted environments. We also examined cov ariances of natal dispersal with maternal and offspring traits. The results showed that: (1) dispersal behaviour was similar among siblings, (2) deter minants of offspring dispersal differed between sexes and years, (3) offspr ing dispersal was related to litter sex-ratio and offspring corpulence at b irth, (4) postnatal conditions influenced male dispersal, (5) short-term pr enatal conditions (i.e. maternal conditions during gestation) influenced ju venile dispersal, varying per year, (6) long-term prenatal conditions (i.e. maternal conditions during gestation in the previous year) could also infl uence juvenile dispersal (marginally significant). Thus, several types of processes determine natal dispersal in the common li zard. Resemblance among siblings can partly be explained by both pre- and p ostnatal effects. The environment seems to be the major factor influencing juvenile dispersal in this species, i.e. dispersal essentially appears cond ition-dependent. The genetic basis of dispersal in vertebrates remains to b e demonstrated by studies controlling for both prenatal and postnatal condi tions.