The evolutionary dynamics of haplodiploidy: genome architecture and haploid viability

Summary

Ingested 2026-04-21. 3 findings extracted and verified.

Findings worth citing

Finding 1 — Haplodiploid mite species have significantly lower chromosome numbers than diplodiploid mites, with about 2n=5 fewer chromosomes on average.

Both models confirm that haplodiploid species have significantly lower chromosome numbers than diploid species (approximately 2n = 5 fewer chromosomes, PMCMC < 0.001 for both the taxonomic and phylogenetic models, see Fig. 2A, B). — p. 2974

Why this is citable: This quantifies the central empirical result of the paper — the predicted karyotype–ploidy correlation underlying Bull’s haploid-viability hypothesis — and is the specific number downstream papers would cite when invoking this association.

Counter / limitation: The analysis is restricted to mites (Acari), and the authors themselves note that other invertebrate clades with low chromosome numbers and male heterogamety have not evolved haplodiploidy, limiting generalization.

Topics: karyotype_evolution_overview, sex_chromosome_evolution, chromosome_number_evolution

Finding 2 — Low chromosome number in mites evolved prior to the origin of haplodiploidy, with haplodiploid clades arising from nodes with a mean diploid chromosome number of 18.4 versus a null expectation of 20.2.

Using the full dataset stochastic mappings infer an average of 10 origins of haplodiploidy, which arose with a mean diploid chromosome number of 18.4. If chromosome number and ploidy evolved independently we would expect a mean of 20.2 (P = 0.017). — p. 2975

Why this is citable: Establishes directionality — that karyotype reduction precedes haplodiploidy — which is essential for citing Bull’s hypothesis as causal rather than merely correlational.

Counter / limitation: The authors acknowledge that phylogenies provide very little information about the timing of coevolutionary events and that the statistical support is relatively weak; the effect size (~2 chromosomes) is small.

Topics: karyotype_evolution_overview, chromosome_number_evolution

Finding 3 — Haplodiploidy has evolved repeatedly in Acari with an estimated 7.9–12.9 independent origins depending on model, while reversions back to diplodiploidy are not well supported.

Ancestral state reconstruction under a one-rate model in which only transitions from diplodiploidy to haplodiploidy are allowed suggests a mean of 12.9 origins. Using a two-rate model in which reversions from haplodiploidy to diplodiploidy are also allowed, we infer a mean of 7.9 origins of haplodiploidy. However, we find only limited support for the hypothesis that transitions from haplodiploidy to diplodiploidy are possible. — p. 2974

Why this is citable: Mites are uniquely suitable for comparative tests of haplodiploidy evolution because the trait has evolved multiple independent times within the clade. This origin count (7.9–12.9, depending on whether reversions are permitted) is the canonical statistic to cite for the replicated origins of haplodiploidy in Acari and for the near-irreversibility of the transition.

Counter / limitation: The apparent support for reversibility is entirely driven by a single family-level tip (Parasitidae sp.) that is deeply nested among haplodiploid taxa; when this tip is removed, the one-rate irreversible model is preferred. Additionally, origin counts differ substantially between the 109-taxon and 87-species-level datasets, reflecting sensitivity to tip-matching decisions at genus and family levels.

Topics: haplodiploidy_evolution, chromosome_number_evolution, ancestral_state_reconstruction

Read the paper

doi.org/10.1111/evo.12792

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