Abstract: Abstract Ecological specialization to restricted diet niches is driven by obligate, and often maternally inherited, symbionts in many arthropod lineages. These heritable symbionts typically form evolutionarily stable associations with arthropods that can last for millions of years. Ticks were recently found to harbour such an obligate symbiont, Coxiella?LE, that synthesizes B vitamins and cofactors not obtained in sufficient quantities from blood diet. In this study, the examination of 81 tick species shows that some Coxiella?LE symbioses are evolutionarily stable with an ancient acquisition followed by codiversification as observed in ticks belonging to the Rhipicephalus genus. However, many other Coxiella?LE symbioses are characterized by low evolutionary stability with frequent host shifts and extinction events. Further examination revealed the presence of nine other genera of maternally inherited bacteria in ticks. Although these nine symbionts were primarily thought to be facultative, their distribution among tick species rather suggests that at least four may have independently replaced Coxiella?LE and likely represent alternative obligate symbionts. Phylogenetic evidence otherwise indicates that cocladogenesis is globally rare in these symbioses as most originate via horizontal transfer of an existing symbiont between unrelated tick species. As a result, the structure of these symbiont communities is not fixed and stable across the tick phylogeny. Most importantly, the symbiont communities commonly reach high levels of diversity with up to six unrelated maternally inherited bacteria coexisting within host species. We further conjecture that interactions among coexisting symbionts are pivotal drivers of community structure both among and within tick species.

Abstract: 1. The exceptionally long (c. 11 months) growth period of king penguin chicks (Aptenodytes
patagonicus) is interrupted by the Austral winter. As a consequence, penguin chicks born late
in the breeding season have little time to build-up their energy reserves before the drastic
energy bottleneck they experience during winter and face greater risks of mortality than earlyborn
chicks.
2. Whereas it is well known that breeding adults alternate between early- and late-breeding
attempts, little is known on the phenotype of early- and late-chicks, and on the potential
existence of specific adaptive phenotypic responses in late-born individuals.
3. We investigated phenotypic differences between early- and late-chicks and tested their survival
correlates both before the winter and at fledgling. Chicks were sampled 10 days after
hatching to measure body mass, plasma corticosterone levels, oxidative stress parameters and
telomere length.
4. Late-chicks were heavier than early-chicks at day 10. Late-chicks also had higher corticosterone
and oxidative stress levels, shorter telomere lengths and suffered from higher mortality
rates than early-chicks. For both early- and late-chicks, high body mass close to hatching was
a strong predictor of survival up to, and over, the winter period.
5. In late but not early-chicks, high corticosterone levels and long telomeres were significant
predictors of survival up to winter and fledging, respectively.
6. Our study provides evidence that late- and early-king penguin chicks showed marked phenotypic
differences 10 days after hatching. We provide an integrative discussion on whether
these differences may be adaptive or not, and to what extent they may be driven by active
maternal effects, indirectly induced by environmental effects, or stem from individual
differences in parental quality.