The Morphology and Behavior of the Endemic Malagasy Whirligig Beetle Heterogyrus milloti Legros, 1953 (Coleoptera: Gyrinidae: Heterogyrinae)

Abstract

The Malagasy endemic whirligig beetle Heterogyrus milloti Legros, 1953 is redescribed. Jumping behavior of H. milloti is reported here for the first time with video recordings provided. Results of a behavioral experiment conducted in the field demonstrate H. milloti jumps in a targeted manner in a downstream direction. The unique habitat of H. milloti is described in detail with both image and video of the habitat included. Morphology of H. milloti is discussed in detail, revealing symplesiomorphies with Spanglerogyrus Folkerts, 1979, characters forming transitional series between Spanglerogyrus and the Gyrininae, and features unique to H. milloti. The potential adaptive significance of these peculiar morphological features in association with the habitat of H. milloti is discussed. Finally, an argument for the necessity of conservation of this species is made, and common names in English, French, Malagasy, and Swedish for H. milloti are proposed to aid conservation efforts.

On the thoracic anatomy of the MadagascanHeterogyrus millotiand the phylogeny of Gyrinidae (Coleoptera)

“…Posteriorly truncated elytra with nine striae and pattern of three broad, partly separated blackish stripes. Stria 1–6 present as canaliculated, narrow, slightly crenulate furrows; striae 7 and 8 less distinct, reduced to separate series of punctures; stria 9 canaliculate and near lateral elytral margin (Brinck, ; see also Gustafson et al ., ). Surface structure reticulated, except on pubescent lateral margin, with meshes in intervals transverse and narrow, mixed with very fine puctures; apical ellipsoid of punctures missing (Brinck, ).…”

“…Elytral epipleura well‐developed, of bright yellow coloration, evenly narrowing posteriorly, reaching anterior region of abdominal sternite VII. Truncated posterior margin of each elytron bisinuate (see also detailed description in Gustafson et al ., ).…”

“…The results of the present study confirm the placement of Heterogyrus as sister group of Gyrininae, a conclusion first documented by Miller & Bergsten (2012) and also confirmed by Gustafson et al . (,b). Modifications of the head of Gyrininae are relatively minor, a broader separation of the ocular subunits, and a shift of the dorsal eye onto the dorsal side of the head, linked with a distinct size reduction.…”

“…The morphology and biology were treated in greater detail by Gustafson et al . (), however, without covering internal structures and anatomical details. Heterogyrus also was recently identified as the oldest dated endemic lineage of animal or plant on Madagascar (Gustafson et al ., ).…”

“…In contrast to the detailed study of Gustafson et al . (), the main emphasis is on the skeletal and mucular elements of the locomotor apparatus (see also Larsén, ). Additionally, features of other body parts are screened and compared with conditons found in other gyrinids.…”