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Across 4 African annual killifish species, the paper argues that wild female-biased adult sex ratios arise from extrinsic male mortality linked to predation and maleβmale social interactions, rather than a consistent difference in intrinsic functional aging trajectories (lipofuscin + liver/kidney proliferative biomarkers).
Wild vs captivity, and social vs individual housing, are used to partition sources of sex-biased mortality; actuarial aging is modeled with Bayesian survival trajectory methods, concluding that sex differences in actuarial mortality are driven primarily by baseline mortality (IMR) rather than aging rate (RoA) for at least the key species.
Long Explanation
Paper Review (visual-first): The sources of sex differences in aging in annual fishes
DOI:10.1111/1365-2656.13656Authors (from provided text): Martin Reichard; Radim BlaΕΎek; Jakub Ε½Γ‘k; Alessandro Cellerino; Matej PolaΔik
Figure 1. Male proportion: wild vs captive (estimated at different life stages)
Wild adult sex ratios were recorded throughout adulthood with unknown age at sampling; captive sex ratios were estimated at sexual maturation. Values are the proportion of males.
Interpretation (what the plot supports)
In N. furzeri, N. orthonotus, and N. pienaari, the wild proportion of males is far lower than captive at maturation (e.g., N. furzeri: captive males ~48.9% vs wild adult males ~32.7%), consistent with higher adult male mortality in nature.
For N. kadleci, the paper reports more similar male proportions between wild and captive, aligning with their later finding that sex-biased mortality was not detected for life span in captivity under social housing.
Skeptical note: wild sex ratios were sampled at unknown age within adult life; thus the inference is about cumulative adult mortality patterns, not about when intrinsic aging becomes sex-differential.
Figure 2. Median life span (days): social vs individual housing
Medians with 95% CIs come from the paperβs Table 1 text (social tanks vs individually housed).
Interpretation (core claim vs constraints)
The paper reports male-biased life span under social housing in the more aggressive species N. orthonotus and N. furzeri, but no sex difference under individual housing in any species.
The paperβs mechanistic partition therefore prioritizes extrinsic mortality mechanisms (predation excluded in captive protocols; social interference in group housing) over an intrinsic sex-specific functional aging clock.
Skeptical note (important): βno sex difference in functional aging biomarkersβ depends on biomarker choice/sensitivityβonly three markers are reported (lipofuscin + kidney/liver proliferative changes) and the paper itself acknowledges that other markers (e.g., telomere length) show sex differences in other contexts.
Figure 3. Model-based decomposition: baseline mortality vs aging rate
The paper uses Gompertz-family models inside Bayesian survival trajectory analysis (BaSTA) to interpret sex differences in terms of initial mortality rate (IMR) vs rate of aging (RoA). (We visualize the directional conclusions stated, not the raw posterior density.)
In N. orthonotus, the paper states that male-biased mortality is explained by stronger baseline mortality (IMR) rather than a higher aging rate.
In N. furzeri, Gompertz-logistic modeling better fits than a simple Gompertz model (aging deceleration at old age), and sex differences are described as limited to certain parameters in one population but not the other.
Skeptical note: We cannot see the posterior distributions in the provided excerpt; thus the visualization above is a directional abstraction of the paperβs text (not a reconstruction of the posterior). The authorsβ own criteria include deviance information criterion for model selection and KL discrepancy to compare parameter overlaps.
Figure 4. Functional aging biomarkers: no consistent sex effects
The paper reports non-significant sex effects for lipofuscin (liver) and for proliferative changes (kidney and liver), using young vs old sampling in social housing.
Lipofuscin deposition in liver: sex effect not significant (z=0.17, p=0.862), and no sexΓage interaction (z=0.65, p=0.514).
Proliferative changes: kidney (sex z=1.71, p=0.087; sexΓage z=1.16, p=0.247) and liver (sex z=0.50, p=0.615; sexΓage z=1.45, p=0.147) also not significant.
Wild observational component: 376 wild populations, 4 species, 15,968 fish; sex ratios estimated via GLMM with species fixed and year/site random.
Laboratory partitioning: social vs individual housing to manipulate social contact; temperature fluctuation challenge in one protocol; Cox mixed-effects for survival.
Functional aging biomarkers: lipofuscin quantification in liver; H&E histopathology scoring for proliferative changes in liver/kidney.
Critical appraisal (blind spots & alternative explanations)
Biomarker limitation / measurement coverage: The paper measures only three functional aging readouts and acknowledges that other markers (e.g., telomere length) may reveal sex differences.
Unknown wild sampling age: sex ratios in the wild are estimated at different phases of adult life with unknown age at sampling, which compresses time-resolved aging information into one adult snapshot.
Hormones not measured: The discussion proposes stress/hormonal mediation (e.g., corticosteroids/testosterone) but the experiment reports that hormonal profiles were not measured.
Generalization limits: conclusions are within a discrete lineage/system (four annual killifish species; laboratory husbandry conditions), so extrapolation to other taxa should be cautious.
The paperβs novelty is the explicit triangulation of (i) wild adult sex ratios across many populations with (ii) captivity manipulations that isolate predation/social interference and (iii) actuarial decomposition (IMR vs aging rate) alongside functional aging biomarkers, within closely related annual fish species. This multi-level causal partitioning is strongly emphasized in the text (doi:10.1111/1365-2656.13656).
Scientific Quality
80%
Strong design logic (wild sex ratios + controlled social housing + demographic modeling + biomarker panel) and explicit model choice/interpretation (GLMM, Cox mixed models, BaSTA Gompertz-family). Main quality limitations from the provided text: (a) functional aging is assessed with a limited biomarker set, and the authors themselves note potential insensitivity; (b) wild sex ratios use unknown adult sampling age; (c) hormone/proximate mechanisms are discussed but not measured in the reported work (doi:10.1111/1365-2656.13656).
Study Generality
80%
High generality for the evolutionary-demographic principle that sex differences can be driven by extrinsic mortality and social/ecological contexts, not only intrinsic aging. However, system-specific biology (annual killifish, laboratory husbandry, particular biomarkers) constrains direct cross-taxon extrapolation (doi:10.1111/1365-2656.13656).
Study Usefulness
90%
Useful as a template for dissecting sex-biased longevity into baseline mortality vs aging rate and for designing experiments that remove social contact. Also useful for aging-biomarker selection and the interpretation of βno functional-aging differenceβ findings (doi:10.1111/1365-2656.13656).
Study Reproducibility
80%
Methods are reasonably specified (housing conditions, statistical frameworks, biomarker procedures) and primary data are deposited on Figshare (doi:10.6084/m9.figshare.12752648.v2). Potential reproducibility gaps may remain for exact biomarker scoring and full protocol details not shown in the excerpt, but the data availability supports replication (doi:10.1111/1365-2656.13656).
Explanatory Depth
80%
The paper provides a clear demographic decomposition (baseline vs aging-rate contribution) and a plausible ecological pathway (predation/social interference) consistent with sex-ratio patterns. Depth is somewhat limited by biomarker coverage and lack of measured proximate stress/hormone variables (doi:10.1111/1365-2656.13656).
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Hypothesis Graveyard
The hypothesis that intrinsic functional aging rate (as measured by lipofuscin and liver/kidney proliferative changes) is intrinsically higher in males across all species is weakened because the paper reports no sex differences in these biomarkers under their experimental conditions (doi:10.1111/1365-2656.13656).
The hypothesis that temperature challenge alone reinstates intrinsic sex-biased mortality under individual housing is weakened because the paper reports no significant sex bias in mortality under fluctuating temperature in the tested cohort (doi:10.1111/1365-2656.13656).
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