Cassidinae

Simões, M. V. P., Baca, S. M., Toussaint, E. F. A., Windsor, D. M. & Short, A. E. Z., 2018, Solving a thorny situation: DNA and morphology illuminate the evolution of the leaf beetle tribe Dorynotini (Coleoptera: Chrysomelidae: Cassidinae), Zoological Journal of the Linnean Society 185, pp. 1123-1136 : 1123-1125

Cassidinae s.l., commonly known as tortoise beetles, is the second largest subfamily of leaf beetles, with ~6300 described species worldwide ( Borowiec & Świętojańska, 2018). The tribe Dorynotini Monrós & Viana, 1949 is an exclusively Neotropical clade of cassidines ( Chaboo, 2007) distributed from central Mexico to northern Argentina, including the Greater Antilles ( Borowiec & Świętojańska, 2018). The tribe currently contains 56 species distributed in five genera: Dorynota Chevrolat, 1836 , Heteronychocassis Spaeth, 1915 (one species), Omoteina Chevrolat, 1836 (one species), Paranota Monrós & Viana, 1949 (five species) and Paratrikona Spaeth, 1923 (seven species). The most diverse genus, Dorynota , is further split into two subgenera: Dorynota s.s. (18 species) and Akantaka Maulik, 1916 (24 species) ( Bouchard et al., 2011; Simões, 2014; Simões & Sekerka, 2014; Simões & Sekerka, 2015; Borowiec & Świętojańska, 2018).

Chevrolat (in Dejean, 1836) first proposed the genus Dorynota for Neotropical cassidines with a post-scutellar spiniform projection. Later, Maulik (1916) erected two additional genera, Akantaka and Trikona , based on the presence and shape of the post-scutellar projection on the elytra and provided an identification key, where the shape of the scutellum was also proposed to distinguish the three genera. Monrós & Viana (1949) considered the classification proposed by Chapuis (1835) as better supported by morphological characters, and revalidated the tribe (= group; Chapuis, 1835) ‘Batonotites’, changing its name to Dorynotini , characterized by: (1) the presence of insertion pockets (for the posterior margin of the pronotum) on the anterior margin of the elytra; (2) the presence and shape of a vertical post-scutellar spine/ tubercle on the elytral suture; and (3) the symmetry and angle between pretarsal claws. The genera in this tribe were grouped mostly based on the presence or absence and shape of the elytral spine/tubercle, forming five conspicuous, recognizable morphotypes ( Figs 1, 2). Moreover, Monrós & Viana (1949) described the genus Paranota and recognized six other genera in the tribe: Akantaka , Dorynota , Heteronychocassis , Omoteina , Paratrikona and Eremionycha Spaeth, 1911 .

Hincks (1952) downgraded Akantaka to a subgenus of Dorynota and synonymized the genus Trikona with Omoteina for sharing the type species ( Cassida humeralis Olivier, 1808 ), a classification that was accepted in later works ( Borowiec, 1999; Borowiec & Świętojańska, 2018). In 1999, Borowiec transferred Eremionycha to the tribe Cassidini Gyllenhal , resulting in the current composition of Dorynotini .

Multiple cladistic analyses based on adult morphology ( Borowiec, 1995; Chaboo, 2007; López-Pérez et al., 2017) and molecular data (12S mitochondrial DNA; Hsiao & Windsor, 1999) have supported the monophyly of the Dorynotini . However, phylogenetic relationships among genera remain unresolved, and insights about the homology and function of the elytral spine/tubercle are still lacking.

Spaeth (1923) observed that members of the tribe lacking the post-scutellar projection or with a tubercle-shaped projection are restricted to the Greater Antilles ( Omoteina and Paratrikona ) and the Amazon Basin region ( Akantaka ), whereas species with a spiniform post-scutellar projection occur throughout the Neotropics, with their diversity concentrated in the southern part of the tribal range. Based on this distribution pattern, he suggested that the presence and prominence of the post-scutellar projection would be correlated with environmental gradients across the distribution of the clade, allowing the species with the spine to invade cooler areas of the Neotropics. Simões et al. (2017) rejected the hypothesis posed by Spaeth (1923), concluding that morphological divergence occurs with high levels of environmental overlap, and suggested that the presence of the post-scutellar projection could be related to biotic interactions, perhaps as camouflage to guard against predation.

The tribe Dorynotini was last reviewed by Monrós & Viana (1949), and no systematic work has been conducted at the tribal level since. Here, we combine morphological and molecular data to (1) test the monophyly of the tribe; (2) test the monophyly and relationships among the genera within the tribe; (3) elucidate biogeographical patterns; and (4) investigate the homology and evolution of the post-scutellar projection and other key characters using ancestral character state reconstruction (ACSR). This is the first systematic attempt to resolve relationships among dorynotine lineages, allowing further insight into their intriguing evolution and morphology.