Abstract
The striking diversity among herbivorous Scarabaeoidea is still poorly understood. Therefore, we compare in these work linear measurements of body features of Neotropical and Old World linages of Sericini chafers to uncover patterns possibly linked to foraging behavior (day or night activity) or to the success of their diversification in terms of diversity. If diversity in Sericini chafers would be linked to morphological disparity, we would expect in the much less diverse Neotropical lineage a very clear drop of morphological disparity. Comparing the two major sister clades, Old World and Neotropical Sericini, in terms of their disparity and diversity, the here elaborated distance data do not support the hypothesis that morphological disparity could be a driver for the diversity of Sericini in the Old World. The influence of the metacoxal length on morphological disparity appears to represent a possible key for a better understanding of the evolution of Sericini in the Neotropical region (including their lower diversity) and answers the question of why they are so much less diverse than their sister lineage in the Old World. The increasing length of the metacoxal plate appears to be a result of the presence of a secondary metacoxal joint in Old World Sericini, which has a crucial impact on hind leg mobility and digging behavior. General body shape and single morphological characters appear under similar general evolutionary pressure: high morphometric disparity between nocturnal and diurnal Neotropical species was also corroborated by disparity estimated from discrete morphological characters.
Highlights
The enormous diversity of host-specific herbivore insects is well explained by the hypothesis of an arms race between host plant and host (Ehrlich & Raven, 1964; Farrell, 1998; Mitter et al, 1991), the striking diversity among herbivorous Scarabaeoidea is still poorly understood (Ahrens et al, 2014d; Eberle et al, 2014) since they are prevailingly polyphagous herbivorous
Among the here examined traits, the elytral length showed the strongest correlation with the total body size (Fig. 2) (r = 0.94)
We found contrasting results between raw and normalized data for diurnal activity patterns: while diurnal taxa are with raw data well below mean and median values, they are above with normalized data (Table 3)
Summary
The enormous diversity of host-specific herbivore insects is well explained by the hypothesis of an arms race between host plant and host (Ehrlich & Raven, 1964; Farrell, 1998; Mitter et al, 1991), the striking diversity among herbivorous Scarabaeoidea is still poorly understood (Ahrens et al, 2014d; Eberle et al, 2014) since they are prevailingly polyphagous herbivorous. Eberle et al (2014) showed that some lineages with different feeding habits may not be distinguished by morphospace in Pleurostict scarabs, while others and several phylogenetic lineages can; they found that the morphospace coevolved with some morphological key innovations regarding locomotion, in Sericini. Sericini are herbivore pleurostict chafer beetles with more than 4000 described species and a near cosmopolitan distribution (Ahrens, 2006). It is one of the oldest extant chafer lineages (Ahrens et al, 2014d; Eberle et al, 2017a; McKenna et al, 2019) that had its origin in the West Gondwana during mid Cretaceous with repeated subsequent dispersals out of Africa (Eberle et al, 2017a). The oldest split of Sericini is between an Old World and a Neotropical lineage, showing an extreme contrast in species diversity: the Old World lineage is about 20 fold more diverse
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