Enochrus, THOMSON, 1859

Angus, Robert B, Sadílek, David, Shaarawi, Fatma, Dollimore, Hayley, Liu, Hsing-Che, Seidel, Matthias, Sýkora, Vít & Fikáček, Martin, 2021, Karyotypes of water scavenger beetles (Coleoptera: Hydrophilidae): new data and review of published records, Zoological Journal of the Linnean Society 192 (3), pp. 958-958 : 958-

GENUS ENOCHRUS THOMSON, 1859

( FIGS 8B–J , 9–10 )

Material examined: Enochrus (s.s.) melanocephalus (Olivier, 1792) : 2 spec. ( BMNH): United Kingdom, Surrey, Egham , R. Angus lgt .

Enochrus (Methydrus) affinis (Thunberg, 1794) : 2 spec. ( BMNH): United Kingdom, Hampshire, New Forest , R. Angus lgt .

Enochrus (Methydrus) coarctatus (Gredler, 1863) : 1 spec. ( BMNH): United Kingdom, Dorset, Studland Heath , R. Angus lgt .

Enochrus (Methydrus) nigritus (Sharp, 1872) : 1 spec. ( BMNH): Spain, Peñalara , R. Angus lgt .; 1 spec. ( BMNH): United Kingdom, Norfolk, East Walton , R. Angus lgt .; 1 spec. ( BMNH): Greece, Corfu , R. Angus lgt .

Enochrus (Methydrus) morenae (Heyden, 1870) : 1 spec. ( BMNH): Spain, Plasencia , R. Angus lgt .

Enochrus (Methydrus) sauteri dʼ Orchymont, 1913: 2 spec. (NMPC): Taiwan, 4.8 km SEE of Tonglin, Beikeng Creek Trail , 24.04791°N 120.78434°E, 3.x.2018, Fikáček, Hu, Liang & Liu lgt.

Enochrus (Lumetus) bicolor (Fabricius, 1792) : 1 spec. ( BMNH): United Kingdom, Sussex, Cuckmere , R. Angus lgt .

Enochrus (Lumetus) ochropterus (Marsham, 1802) : 2 spec. ( BMNH): United Kingdom, Dorset, Studland Heath , R. Angus lgt .; 2 spec. ( BMNH): Germany, Niedersachsen, Staatsforest Gohrde , R. Angus lgt .

Enochrus (Lumetus) testaceus (Fabricius, 1801) : 2 spec. ( BMNH): United Kingdom, Norfolk, East Walton , R. Angus lgt .; 2 spec. ( BMNH): Sweden, Öland , R. Angus lgt .

Enochrus (Lumetus) quadripunctatus (Herbst, 1797) : 2 spec. ( BMNH): United Kingdom, Norfolk, East Walton , R. Angus lgt .; 2 spec. ( BMNH): Germany, Schleswig-Holstein, Ratzeburg , R. Angus lgt .

Enochrus (Lumetus) fuscipennis (Thomson, 1884) : 2 spec. ( BMNH): United Kingdom, Cumbria , Drigg, R. Angus lgt .; 2 spec. ( BMNH): United Kingdom, Scotland, Ayrshire, Lochton loch , R. Angus lgt .; 3 spec. ( BMNH): Germany, Schleswig-Holstein , Ratzeburg, R. Angus lgt.; 2 spec. ( BMNH): Spain, Provincia de Santander, Embalse de Ebro , R. Angus lgt.; 2 spec. ( BMNH): Denmark, Rømø Island , R. Angus lgt.; 2 males ( BMNH): Denmark, Rømø Island , R. Angus lgt. Enochrus (Lumetus) halophilus (Bedel, 1878) : 2 spec. ( BMNH): United Kingdom, Sheppey, Kent , R. Angus lgt .; 2 spec. ( BMNH): United Kingdom, Bembridge, Isle of Wight , R. Angus lgt . 2 spec. ( BMNH): Spain, Albacete, Pétrola, P. Arribas lgt .

Karyotypes: 2 n = 16 + Xy p (♂). Enochrus s.s. ( Fig. 8H ) has autosomal pairs 3, 6 and 8 subacrocentric, pair 3 is heterozygous for an extra C-band. The other pairs, and the X chromosome, are metacentric, with well-developed centromeric C-bands. The subgenera Methydrus and Lumetus show no obvious features in their karyotypes, whereas the Taiwanese Enochrus sauteri ( Fig. 8G ) is unusual in having autosome pair 1 clearly twice the lengths of the others, which are all of the similar size.

The karyotypes appear remarkably uniform with some apparent species differences. In European Methydrus, Enochrus coarctatus ( Fig. 8C ) differs from Enochrus affinis ( Fig. 8B ) and Enochrus nigritus ( Fig. 8D–E ) in having autosome pairs 7 and 8, and the X chromosome, subacrocentric, whereas in the others they are metacentric. No differences were found between Spanish (dark brown) and English pale coloured specimens of Enochrus nigritus (compare Fig. 8D and E ). In Lumetus, English Enochrus halophilus ( Fig. 9F–K ) differs from Enochrus quadripunctatus and Enochrus fuscipennis ( Fig. 10 ) in having autosome pairs 7 and 8, and the X chromosome acrocentric, with the centromeric C-bands only about half the size of those of the metacentric autosomes. However, in Spanish Enochrus halophilus , which are inseparable from English material by mitochondrial DNA (P. Arribas, unpubl.), all the chromosomes (apart from the dot-like Y) are metacentric with C-bands of the same size as in Enochrus halophilus ( Fig. 9H–K ). The separation of Enochrus fuscipennis from Enochrus quadripunctatus is also problematic as the mitochondrial DNA reveals Enochrus fuscipennis intermixed with Enochrus quadripunctatus (P. Arribas, unpubl.). The situation is made even more complicated by material from Ratzeburg ( Germany). This material included clear Enochrus quadripunctatus whose karyotype matched that of English specimens (as in Fig. 10A–C ) and also apparent Enochrus fuscipennis whose karyotype differed in the submetacentric autosome 1 and the clearly smaller X chromosome ( Fig. 10D–G ). The material from the Rømø Island ( Denmark) ( Fig. 10H–I ) comprised two males whose karyotypes could only be understood if they were hybrids (but not F1) between western and Ratzeburg-type populations of Enochrus fuscipennis . Both males have small X chromosomes and one has autosome 1 heterozygous for western and Ratzeburg forms, whereas the other has both replicates of the western form. One male has a B-chromosome and both have normal first metaphase of meiosis.

SUBFAMILY ACIDOCERINAE GENUS AGRAPHYDRUS RÉGIMBART, 1903

( FIG. 11A–C, M )

M a t e r i a l e x a m i n e d: A g r a p h y d r u s d e c i p i e n s Minoshima, Komarek & Ohara, 2015: 1 male, 1 female ( BMNH), 1 male ( NMPC): Taiwan, 4.8 km

SEE of Tonglin , Beikeng Creek Trail, 24.04791°N 120.78434°E, 3.x.2018, under leaves on a wet rock, lgt. M. Fikáček, H.-C. Liu, F.-S. Hu & W.- R. Liang .

Agraphydrus variabilis Komarek & Hebauer, 2018: 1 female (BMNH): Taiwan, 4.8 km SEE of Tonglin, Beikeng Creek Trail , 24.04791°N 120.78434°E,

3.x.2018, in gravel at side of a river, lgt. M. Fikáček, H.-C. Liu, F.-S. Hu & W.-R. Liang.

Karyotype: 2 n = 16 + Xy (♂). The autosomes show a gradual decrease in size along the karyotype so that pair 8 is about half the length of pair 1. In Agraphydrus decipiens ( Fig. 11A–B ), pairs 7 and 8, and the X chromosome, are acrocentric, whereas the rest (apart for the dot-like Y chromosome) are metacentric. The sex chromosomes of Agraphydrus variabilis ( Fig. 11C ) cannot be identified as only females are available. The smallest chromosome is acrocentric, the rest metacentric. C-bands are confined to the centromeres and are small, especially in Agraphydrus decipiens .

Figures

Figure 8. Mitotic karyotypes of the Enochrinae. A, Cymbiodyta marginella, embryo. B–D, European usual-looking species of Enochrus (Methydrus) from embryos: (B) Enochrus affinis; (C) Enochrus coarctatus; (D–E) Enochrus nigritus. F–G, unusual species assigned at the moment to Enochrus (Methydrus): (F) Enochrus morenae, midgut; (G) Enochrus sauteri, midgut. H, Enochrus (s.s.) melanocephalus, embryo. A–G, without treatment. H, C-banded. Habitus figures: (I) Cymbiodyta marginella; (J) Enochrus morenae.

Figure 9. Karyotypes of Enochrus (Lumetus), mitosis from embryos. A, Enochrus bicolor. B–C, Enochrus ochropterus. D–E, Enochrus testaceus. F–K, Enochrus halophilus. A, B, D, F, H, I, without treatment. C, E, G, K, C-banded. Habitus figures: (L) Enochrus (Lumetus) testaceus; (M) Enochrus (Lumetus) halophilus.

Figure 10. Karyotypes of Enochrus (Lumetus). A–C, Enochrus quadripunctatus, mitosis, midgut. D–K, Enochrus fuscipennis, mitosis, midgut (H–I, specimens from Denmark, Rømø Island with the karyotypes indicating their hybrid origin). L–N, meiotic metaphase I from testes (L, Enochrus quadripunctatus, UK: East Walton, Norfolk; M–N, Enochrus fuscipennis, Denmark: Rømø Island). O–P, Enochrus fuscipennis, testes, mitotic metaphase from the same specimens as in (H–I). A, B, D, E, H, I, J, M–P, without treatment. C, F, G, K, L, C-banded.

Figure 11. Karyotypes of the Acidocerinae. A–C, Agraphydrus, mitotic metaphase, midgut: (A–B) Agraphydrus decipiens; (C) Agraphydrus variabilis. D–L, Helochares: (D–E) Helochares lividus, mitosis, midgut; (F) Helochares obscurus, mitosis, midgut; (G–H) Helochares punctatus, mitosis, midgut; (I) Helochares punctatus, karyotype of male embryo with multiple y-chromosomes; (J–K) meiotic metaphase I from testes (J, Helochares punctatus; K, Helochares lividus); (L) Helochares sauteri, mitosis, midgut.A, D, F, G, I–L, without treatment. B, C, E, H, C-banded. Habitus figures: (M) Agraphydrus decipiens, from Minoshima, Komarek, & Ȏhara 2015; (N) Helochares obscurus.