Energetic and reproductive costs of coral recovery in divergent bleaching responses

Mass thermal bleaching events are a primary threat to coral reefs, yet the sublethal impacts, particularly on energetics and reproduction, are poorly characterized. Given that the persistence of coral populations is contingent upon the reproduction of individuals that survive disturbances, there is an urgent need to understand the sublethal effects of bleaching on reproductive output to accurately predict coral recovery rates. In 2019, the French Polynesian island of Mo’orea experienced a severe mass bleaching event accompanied by widespread coral mortality. At the most heavily impacted sites, we observed Acropora hyacinthus individuals that were resistant to bleaching, alongside colonies that bleached but showed signs of symbiont recovery shortly after the bleaching event. We collected fragments from A. hyacinthus colonies five months post-bleaching and, using energetic assays and histological measurements, examined the physiological and reproductive consequences of these two distinct heat stress responses. Despite healthy appearances in both resistant and recovered corals, we found that recovered colonies had significantly reduced energy reserves compared to resistant colonies. In addition, we detected compound effects of stress on reproduction: recovered colonies displayed both a lower probability of containing gametes and lower fecundity per polyp. Our results indicate that bleaching inflicts an energetic constraint on the concurrent re-accumulation of energy reserves and development of reproductive material, with decreased reproductive potential of survivors possibly hampering overall reef resilience. These findings highlight the presence of intraspecific responses to bleaching and the importance of considering multiple trajectories for individual species when predicting population recovery following disturbance.

Calibration Invariance of the MaxEnt Distribution in the Maximum Entropy Principle

The maximum entropy principle consists of two steps: The first step is to find the distribution which maximizes entropy under given constraints. The second step is to calculate the corresponding thermodynamic quantities. The second part is determined by Lagrange multipliers’ relation to the measurable physical quantities as temperature or Helmholtz free energy/free entropy. We show that for a given MaxEnt distribution, the whole class of entropies and constraints leads to the same distribution but generally different thermodynamics. Two simple classes of transformations that preserve the MaxEnt distributions are studied: The first case is a transform of the entropy to an arbitrary increasing function of that entropy. The second case is the transform of the energetic constraint to a combination of the normalization and energetic constraints. We derive group transformations of the Lagrange multipliers corresponding to these transformations and determine their connections to thermodynamic quantities. For each case, we provide a simple example of this transformation.

Visual cues of predation risk outweigh acoustic cues: a field experiment in black-capped chickadees

Foragers rely on various cues to assess predation risk. Information theory predicts that high certainty cues should be valued more than low certainty cues. We measured the latency of black-capped chickadees ( Poecile atricapillus ) to resume feeding during winter in response to cues that conferred different degrees of certainty about current predation risk: a high certainty visual cue (predator mount) and a lower certainty acoustic cue (conspecific mobbing calls), presented either alone or in combination. As predicted, chickadees took longer to resume feeding after the visual than the acoustic cue, and this effect was greatest under conditions of high starvation risk (i.e. low temperatures). Presenting both cues together produced the same foraging delay as the visual cue alone under low starvation risk, but surprisingly, resulted in lower responses under high starvation risk compared to the visual cue alone. We suggest that this may be due to prey using a form of information updating, whereby differences in the timing of perception of acoustic versus visual cues interacts with energetic constraint to shape perceived risk. Although the sequential perception of cues is likely in a range of decision-making contexts, studies manipulating the order in which cues are perceived are needed to test existing models of multimodal cue integration.

Infanticide and reproductive restraint in a polygynous social mammal

Alpha male chacma baboons experience uncontested access to individual estrus females. Consequently, alpha male paternity certainty is high and underpins significant levels of infanticide by immigrant males that, in turn, has selected for male defense of infants. There is also, however, a high probability that alpha males will be absent during the period when their own offspring are vulnerable, suggesting selection for additional countermeasures. We use data from a long-term study to test the prediction that alpha male chacma baboons cede reproductive opportunities to subordinate males and that this leads to the presence of other fathers that can serve as a buffer against infanticidal attack. We found that subordinate males obtained significantly more conceptive opportunities than predicted by priority of access alone, and that this occurred because alpha males did not consort all receptive periods. There was no evidence that this was due to energetic constraint, large male cohorts, alpha male inexperience, or the competitive strength of queuing subordinates. The number of males who benefited from concession and the length of time that they were resident relative to those who did not benefit in this way greatly reduced the probability that infants of alpha males would face immigrant males without a surrogate father whose own offspring were vulnerable. The absence of such males was associated with observed infanticide as well as, unexpectedly, an increased likelihood of takeover when alpha males with vulnerable infants were present.

Time budgets of Tibetan eared pheasants during the non-breeding season in an alpine scrub habitat

Time allocations of the group-living Tibetan eared pheasants Crossoptilon harmani with and without supplementary food were investigated by full-day sampling from winter through spring in an alpine scrub zone, south Tibet. At a flock scale, both the different food-supply flocks displayed similar daily patterns of activity, foraging in the morning and evening, and resting around midday. In terms of individual activity, either foraging or resting was highly synchronous with the flock’s. Non-provisioned birds spent more time feeding and less resting in midwinter than in late autumn. In early spring as climates became warmer and day longer, however, non-provisioned birds did not decrease their feeding efforts significantly but the provisioned birds did. Across the non-breeding seasons, the provisioned birds (relying on nutrition-rich artificial food) devoted less time to feeding and more to resting than did the non-provisioned ones (relying on nutrition-poor plant roots). Multivariate analysis showed increased food supply and ambient temperature resulted in a reduced foraging effort. However, the fact that the non-provisioned birds can save daily time for resting even in the cold short-day length mid-winter indicated that they faced no energetic constraint. Thus, protecting shelter vegetation rather than providing extra food is suggested to be important for long-term survival of the endangered galliform birds.