Characters which are closely linked to fitness often have low heritabilities (VA/VP). Low heritabilities could be because of low additive genetic variation (VA), that had been depleted by directional selection. Alternatively, low heritabilities may be caused by large residual variation (VR=VP – VA) compounded at a disproportionately higher rate than VA across integrated characters. Both hypotheses assume that each component of quantitative variation has an independent effect on heritability. However, VA and VR may also covary, in which case differences in heritability cannot be fully explained by the independent effects of elimination‐selection or compounded residual variation. We compared the central tendency of published behavioural heritabilities (mean=0.31, median=0.23) with morphological and life history data collected by Mousseau & Roff (1987). Average behavioural heritability was not significantly different from average life history heritability, but both were smaller than average morphological heritability. We cross‐classified behavioural traits to test whether variation in heritability was related to selection (dominance, domestic/wild) or variance compounding (integration level). There was a significant three‐way interaction between indices of selection and variance compounding, related to the absence of either effect at the highest integration level. At lower integration levels, high dominance variance indicated effects of selection. It was also indicated by the low CVA of domestic species. At the same time CVR increased disproportionately faster than CVA across integration levels, demonstrating variance compounding. However, neither CVR nor CVA had a predominant effect on heritability. The partial regression coefficients of CVR and CVA on heritability were similar and a path analysis indicated that their (positive) correlation was also necessary to explain variation in heritability. These results suggest that relationships between additive genetic and residual components of quantitative genetic variation can constrain their independent direct effects on behavioural heritability.

Behavioral changes have long been hypothesized to be an important driver of evolutionary diversification in animals, as they expose individuals to new environmental pressures and thus favor evolutionary divergence. There have been few empirical tests of this hypothesis, however, and the mechanisms linking behavioral changes and diversification processes remain controversial. We show here that Holarctic passerines with large brain size relative to body size, a character correlated with a high propensity for behavioral changes, generally have experienced more extensive subspecific diversification. This effect appears to be largely independent of other well-known mechanisms thought to promote diversification. As suggested by path analysis, relative brain size seems to affect diversification directly rather than indirectly through its presumed effect on range expansion, which is consistent with the original formulation of the behavioral drive hypothesis. Thus, the results support the long-held, intuitive hypothesis that behavioral changes facilitate evolutionary diversification.

Abstract. Behavioral changes have long been hypothesized to be an important driver of evolutionary diversification in animals, as they expose individuals to new environmental pressures and thus favor evolutionary divergence. There have been few empirical tests of this hypothesis, however, and the mechanisms linking behavioral changes and diversification processes remain controversial. We show here that Holarctic passerines with large brain size relative to body size, a character correlated with a high propensity for behavioral changes, generally have experienced more extensive subspecific diversification. This effect appears to be largely independent of other well-known mechanisms thought to promote diversification. As suggested by path analysis, relative brain size seems to affect diversification directly rather than indirectly through its presumed effect on range expansion, which is consistent with the original formulation of the behavioral drive hypothesis. Thus, the results support the long-held, intuitive hypothesis that behavioral changes facilitate evolutionary diversification. In evolutionary biology, behavior is classically viewed as an important driver of evolutionary change (e.g., Baldwin 1896;Miller 1956;Mayr 1963;Wyles et al. 1983;Bateson 1988;Fitzpatrick 1988;Wcislo 1989;West-Eberhard 1989;Greenberg 1990;Futuyma 1998;Futuyma and Moreno 1998). The idea is that changes in behavior can allow animals to enter new adaptive zones and that this can then favor divergent selection on morphology, physiology, and/or behavior. Mayr (1963, p. 604), for example, argued that ''behavioral changes in habitat and food selection are necessary in the shift to new adaptive zones, with structural changes in morphology acquired secondarily. '' Wyles et al. (1983, p. 4396) expressed a similar view when they wrote that ''As a consequence of adopting a new habit, the species faces a new set of selection pressures favoring those mutations that improve the individual's effectiveness at living in the new way.'' The concept that adaptation to a new niche is initiated by behavioral changes is implicit in influential models of population diversification leading to speciation (e.g

1990. Vertical migration in Daphnia galeata mendotae (Brooks): demographic responses to changes in planktivore abundance. Can. 1. Fish. Aquat. Sci.47: 395400.We tested the hypothesis that changes in vertical migration patterns in Baphnid gsledta rnendstde were correlated with changes in planktivore numbers. A 4-yr data set from bake St. George showed that during 1982, when planktivores numbered approximately 2500-ha-', adult D. galeata mendstag were tsund in the epilimnion at both midday and midnight. During 1984 and 1985, when planktivores were airnsst an order of magnitude more abundant, adult D. galeata mendstae were detected in the epilimnion only at night, and the amplitude sf migration increased by a factor of two. Changes in die1 population densities were associated with these interannual differences in vertical migration patterns. These results suggest that between-year differences in vertical migration patterns were strongly associated with changes in planktivore density whish may have influenced the selective value of increased hypolirnnetic residence time.Nous avons tent6 de verifier l1hiPoth$se selon laquelle les variations des modes de migration verticale de Daphnia galsata mendstae etaient en cortt?lation avec les variations du nornbre de planctonsphages. Une serie de donnees provenant du lac St-George, et $optant sur quatre ans, a montr6 qu'au cours de I'annee 1982, au moment oh les planctonophages se ckifraient a Bnviron 2500 ha-', les adultes 5. g. mendotae s'observaient dans Ir6pifimnion 2 midi et a minuit. En 1984 et 1985, lorsque Bes planctonophages ktaient pr&s d'un ordre de grandeur plus abondants, les adultes D. g. mendatae n'etaient presents dans I'epilimnion que la nuit; de plus, I'ampteur de la migration a double. Les variations des densitks de populations nystkern6rates ktaient associees a ces dif@rences interannuelles des modes de migration verticale. Ces resultats semblent montrer que les diff6rences interannuelles dans les modes cle migration verticale etaient etroiternent associees a des variations de la densit6 des planctonsphages, ce qui aurait pu avoir une influence sur I'importance du facteur (( peaiode de s6jour accrue )) dans I'hypolimnion.