I recently read two new papers about blue tits in Corsica: Dubuc-Messier et al. (2017 Behav. Ecol.), and Dubuc-Messier et al. (2018 Evol. Biol.).

The 2018 paper was interested in whether the differences between the evergreen and deciduous ecotypes on Corsica were genetic or a plastic response to the different habitat types. They took 7-12 day old nestlings and raised them in a common garden, and they found that evergreen blue tits had slower exploration speed, lower handling aggression, faster heart rate, lower body mass, and shorter tarsus. These differences were consistent with the comparison of wild adults in the 2017 paper. Though they couldn’t rule out epigenetic or early-development effects (e.g. tarsus length may be determined by approx. 15 days old and was subject to a brood-of-rearing effect in a cross-fostering experiment), the high heritability of these traits and their consistency with a pace of life syndrome (below) suggests a genetic and adaptive basis.

The 2017 paper gives the context for why this cluster of personality and physiological traits may differ between ecotypes. The key concept is pace of life syndrome, which is the hypothesis that personality and physiological traits will coevolve with life-history strategies. For example, a species who has low adult survival will invest high in early reproduction, and this is expected to be associated with personality traits like aggression and fast exploration speed. Blue tits in the deciduous habitat have lower survival probability (per year probabilities of 0.39 in deciduous Muro, 0.58 in nearby evergreen Muro, and 0.47 in further-away evergreen Pirio), and so the personality and physiological differences measured between the ecotypes is largely consistent with the hypothesis (one counter-example was nest defensiveness, measured and discussed in the 2017 paper).

I don’t know why survival is lower in the deciduous habitat; the two papers don’t say and I don’t recall an explanation in any of the earlier papers (I will have to go back and double-check). From what I recall, the major difference between habitat types is the caterpillar phenology: that caterpillars peak earlier in the deciduous environment and also higher so that the deciduous environment is richer in food for nestlings. Clutch sizes are also larger in the deciduous habitat. I wonder as well if it’s possible that a feedback between the fast-life syndrome and survival exists, so that e.g. being more aggressive and faster-exploring causes lower survival?

One interesting result was that aggression varied temporally, from year to year, and a preliminary analysis suggests that aggression relates to caterpillar abundance. Perhaps it also suggests another pathway to aggression, that the difference between ecotypes was also driven by the richness of the deciduous habitat? But I wouldn’t have guessed at that relationship between resource availability and aggression; I think I would have expected the opposite. So I hope they will write more about this soon.

One reason that I’m interested in the blue tits system is because of how it might relate to my recent work; in short, I thought that a comparison between the source-sink dynamics of blue tits on the mainland versus the divergence into ecotypes on Corsica might be explained by a combination of carryover effects and relative habitat-type frequencies. I’m not fully certain that that’s true; certainly the patterns match the expectation of my theory, but one of the difficulties with this comparison is that my model represents the process of divergence, whereas the result from Corsica are more like the end-point of the process. In my paper I had speculated that some of the carryover effects that acted as an immigration barrier in the past may have solidified into genetic differences between the ecotypes today. I had focused mainly on the phenological difference between habitats, and the competitive advantage to deciduous types caused by prior residence effects. A pace-of-life effect on personality adds another possibility.

Cited above:

Dubuc-Messier et al. (2017) Gene flow does not prevent personality and morphological differentiation between two blue tit populations Behav Ecol

Dubuc-Messier et al. (2018) Environmental heterogeneity and population differences in blue tits personality traits Evol Biol

My to-read list:

Gabrielle Dubuc Messier’s thesis: Environmental heterogeneity and the evolution of personality traits in blue tits (Cyaniste caeruleus)

Montiglio et al. (2018) The pace-of-life syndrome revisited: the role of ecological conditions and natural history on the slow-fast continuum Behav Ecol Sociobiol

Class and Brommer (2015) A strong genetic correlation underlying a behavioural syndrome disappears during development because of genotype-age interactions Proc R Soc B