TROC in the Procellariiformes and the pace-of-life
In mammals, shorter telomeres prevailed in large-bodied and long-lived
species (Gomes et al., 2011;
Risques & Promislov, 2018), and short
telomeres are associated with repressed telomerase activity in somatic
cells at adulthood (Tian et al., 2018).
In contrast, we found that bird Adult TL was not related to the
body size PC 1 axis. The variance in body sizes within birds is less
extensive than for mammals, which might partially explain the difference
observed between these two major clades of vertebrates; that is, too low
a range in body size of birds to reveal strong negative selection on
telomere length. Adjustment for the phylogenetic tree reduced the
association to a negligible value (Table 2). Still, our within-orders
regression data suggested negative relationships between Adult TLand body size, and TROC and both body size and the slow-fast
continuum in Procellariiformes, an order with an extensive range of body
sizes of long-lived seabirds. The former relationship suggests that, as
previously found in rodents, the small and long-lived species in theHydrobatidae may have evolved specific mechanisms promoting
long-lifespan while preserving telomerase activity and long telomeres
over life (Tian et al., 2018). The latter
link reveals that the relatively long-living and small-bodied
Procellariiformes exhibit long telomeres in adulthood (Oceanodroma
leucorhoa and Hydrobates pelagicus (both Hydrobatidae ),
and to a lesser extend Fulmarus glacialis )) along with
particularly slow embryonic growth rates (0.104, 0.166 and 1.181vs. a mean procellariform value of 1.938 g/day; note that
variation in clutch size along the slow-fast continuum is negligible for
procellariiform species because they lay only a single egg each breeding
season; ESM1). Thus, long telomeres in this order were not significantly
related to body size (PC1), but were related to the slow end of the
slow-fast continuum (PC2) and thus to species longevity. This
relationship is reversed in the Passeriformes, where long telomeres were
related to the fast (short lifespan) end of the slow-fast continuum of
life history.
One of the pathways that could decelerate the rate of cell division, and
hence the rate of telomere erosion
(Monaghan & Ozanne, 2018), is a
prolonged incubation duration (Vedder et
al., 2018). Prolonged incubation might also be associated with the
maintenance of high telomerase activity throughout life in
procellariiform species (Haussmann et al.,
2004). An alternative explanation could be that theHydrobatidae , which are cavity nesters where chicks grow in a
very contained and stable environment, even after hatching, may exhibit
metabolism that favours the maintenance of the lengths of the telomeres
(Stier, Metcalfe, & Monaghan, 2019).
This pattern supports the antagonistic pleiotropy of telomere length
processes, the main hypothesis proposed to explain why species in
different phylogenetic clades have evolved large differences in telomere
lengths (Hemann & Greider, 2000). This
perspective deserves future exploration, notably on telomerase activity
in the soma among the species of Procellariformes.