Coleoptera Karyotype
Current understanding
Beetles (Order Coleoptera) display one of the broadest ranges of chromosome number variation among any animal order. A large-scale survey of 4,797 beetle karyotypes reveals that diploid chromosome numbers span an extraordinary range: the minimum recorded is 2n = 4, found in the elaterid Chalcolepidius zonatus, while the maximum reaches 2n = 70 in the adephagan Dixus capito obscuroides (Blackmon & Demuth 2015, Finding 1). This roughly 17-fold spread across a single insect order highlights Coleoptera as a particularly compelling system for studying the mechanisms and tempo of karyotype evolution, including fusion, fission, and polyploidy events that reshape chromosome complements over macroevolutionary time.
Supporting evidence
The empirical bounds on Coleoptera diploid numbers come from a comprehensive database compiled across the order, making it one of the most data-rich karyotype surveys in insects. The contrast between the extreme low (2n = 4 in a polyphagan elaterid) and the extreme high (2n = 70 in an adephagan ground beetle relative) also hints that different beetle suborders may have followed distinct evolutionary trajectories in chromosome number — adephagans and polyphagans differ markedly in their modal and extreme values (Blackmon & Demuth 2015, Finding 1).
Contradictions / open disagreements
The verbatim source quote documenting the upper bound (2n = 70 for Dixus capito obscuroides) is split across two pages of the original paper, meaning the number itself does not appear in the extracted quote and cannot be independently verified from the quote alone. Readers should consult the primary source directly to confirm this value. No contradicting papers are currently indexed on this topic.
Tealc’s citation-neighborhood suggestions
- Comparative studies of chromosome number evolution in other hyperdiverse insect orders (e.g., Lepidoptera, Diptera) would provide useful benchmarks for interpreting the scale of Coleoptera karyotype variation.
- Ancestral-state reconstruction analyses using Bayesian or maximum-likelihood approaches on beetle phylogenies could help disentangle whether the extreme values represent convergent reductions/expansions or lineage-specific events.