Relationships between species richness and morphological diversity: insight from a geometric morphometric analysis of scarabs

Abstract

Background Species richness (SR) and morphological diversity (MD) provide insights into biodiversity and have been studied extensively as important indicators in recent years. Most researches have been found a positive correlation between SR and MD in many groups, which reflects the influence of phylogenetic factors. However, if some ecological factors are considered, the relationship of SR and MD is not always consistent. In such cases it is interesting to know how phylogenetic factors and ecological factors affect the relations between SR and MD. Unfortunately, studies that examine both factors quantitatively, in the same group with large dataset are lacking. Results In this study, 5148 scarabs covering 92% families and 70% scarabaeoid subfamilies of Scarabaeoidea were selected as a test group. The taxonomic categories of family and subfamily were selected for phylogenetic representation and four feeding types (omnivory, phytophagy, coprophagy and non-feeding) were selected as ecological factors. A geometric morphometric analysis on the pronotum and elytron, which represent the major aspect of the morphology in dorsal view, were conducted. Correlations between MD and SR among sub-/families were always found to be consistent, except a genus-level test of the pronotum on the subfamily category and a species-level test of elytron on the family category. These phenomena reflected a strong phylogenetic influence. However, morphological diversities were not correlated significantly with species richness for any feeding type (ecological factors). In addition to this hypothesis test, the morphological diversity and known world species richness (~ 32000 species and 2453 genera of Scarabaeoidea) were estimated as well. Our global results were very similar to our sampling results. Conclusions Based on our analyses the hypothesis of ecological factor (represented by feeding habit) correlations was rejected in scarabs. On the contrary, phylogenetic factor correlations were found to be statistically significant. The morphological diversity of scarabs in most sub-/families fitted their species richness. At the same time, the correlation our test parameters revealed variation in both groups and characters, which might be caused by morphological changes under coevolution with different ecological factors.

Comparative analysis of morphospace of Neotropical Sericini (Coleoptera: Scarabaeidae): disparity in the light of species diversity and activity patterns

“…In contrast to that, lineage-specific correlation between disparity and diversity was reported for many other organisms (e.g. Mindel et al, 2016;Neustupa et al, 2009;Gerovasileiou et al, 2015;Zhang et al, 2019;Tong et al, 2020Tong et al, , 2021. In some cases, correlation was evident only at higher systematic level, but not at species level (Tong et al, 2021), or among ecotypes (Tong et al, 2020).…”

“…Mindel et al, 2016;Neustupa et al, 2009;Gerovasileiou et al, 2015;Zhang et al, 2019;Tong et al, 2020Tong et al, , 2021. In some cases, correlation was evident only at higher systematic level, but not at species level (Tong et al, 2021), or among ecotypes (Tong et al, 2020). These results, however, are to be considered with caution since their measure of diversity was often the number of sampled taxa (that was partly very incomplete in respect to the true diversity of the lineage), and no phylogenetic correction was performed (Garland, 1992).…”