Les effets de la sélection sur l'expression des tendances sexuelles et migratoires chez la caille des blés (Coturnix c. coturnix, L.)

A captive population of European quail, descending from migratory wild sample, was submitted to bidirectional selective processes. In one hand, males and females which showed the earliest tendency to develop sexually, together with a low level of fat accumulation, were selected to produce « the precocious sexual and low fat » line (PS-LF). On the other hand, birds which showed the latest sexual development together with the highest fat accumulation tendency were selected as founders of the « long distant migratory » line (LS-HF). We got 54 ofttpring from the « PS-LF » line (24 rnales, 30 females) and 53 from the « LS-HF » line (31 males.22 females). When they were 5 weeks-old, they were exposed to the natural photoperiod of Rennes (48°N). The cloacal vent and the width of the fat band which lies under thoracic skin were measured bimonthly from January to June in order to appreciate their sexual development and the evolution of their migratory tendency.

The mean values of each criteria differ significantly between the two lines at different stages of their first reproductive season ; but we observe a high level of interindividual phenotypic variability in all samples of F1 males and females. We got both « PS-LF » and « LS-HF » birds from the two kinds of parents. Offspring were then classified either as precocious or late sexual birds according to the length of their cloacal vent at each stage of the season. They were also classified either as short- or long-distant migratory birds according to an arbitrary threshold of fat accumulation (11 mm). The data collected over the whole reproductive season show that the frequency of the « sexual » phenotype was higher in the « PS-LF » line : 70-74 %, against 32-23 % in the opposite line. In addition, we found in January less than 8 % of fat birds (males and females F1) in the « PS-LF » line, against more than 62 % in the « LS-HF », one. The tarsus length was significantly greater in the « PS-LF » offspring (27.7 vs 21.1 mm for males ; 28.1 vs 27.5 mm for females). But this difference could be the consequence of environmental factors rather than an indirect effect of selection.

Results indicate that high migratory tendency and sexual precocity are negatively correlated. They demonstrate that both are under endogenous (genetic) control and highly sensitive to selection. They support the idea that microevolutive processes might actually contribute - through the extension of new favorable reproductive areas in maghrebian countries together with the drought of sahelian countries - to change the physiological and behavioural status of the palearctic metapopulation of the common quail towards a higher frequency of short-distant migratory phenotype.