Sexual size dimorphism in stingless bees (Hymenoptera: Apidae; Meliponini)
José Javier G. Quezada-Euán, José Javier G. Quezada-Euán , Salomón Sanabria-Urbán , Corey Smith , Ismael Hinojosa-Díaz , Salvador Medina , Raul Cueva del Castillo
Departamento de Apicultura Tropical, Universidad Autónoma de Yucatán, México; Departamento de Apicultura Tropical, Universidad Autónoma de Yucatán, México ; Laboratorio de Ecología, UBIPRO Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México ; Curatorial Assistant at American Museum of Natural History, USA ; Departamento de Zoología, Instituto de Biología, Universidad Nacional Autónoma de México ; Facultad de Matemáticas, Universidad Autónoma de Yucatán, México ; Laboratorio de Ecología, UBIPRO Facultad de Estudios Superiores Iztacala, Universidad Nacional Autónoma de México
Eusocial insects offer a unique opportunity to analyze the evolution of body size differences between sexes (sexual size dimorphism or SSD) in relation to social environment. The workers, being sterile females, are not subject to selection for reproductive function providing a natural control for parsing the effects of selection on reproductive function (i.e., sexual and fecundity selection) from other natural selection. The most diverse group of corbiculate bees are the stingless bees with contrasting habits in nesting, behavior and morphology among the ca. 500 recognized species. It has been reported that Melipona and non-Melipona stingless bees show differences in the relative size of gynes and males at emergence, but no formal study has compared SSD in this Tribe. Controlling by phylogenetic effects, we used published data and measured the thorax width of ca. 30 species of stingless bees to explore the allometric relationships among queens, males, and workers. We found that despite that selection for fecundity should be similarly influencing the queens of Melipona and non-Melipona species, two patterns of SSD were evident, a male-biased SSD in Melipona, and a female-biased (or no SSD) in non-Melipona species. The rate of divergence from the ancestral size has not differed between the two castes of females and the males. In addition, stingless bees do not seem to follow Rensch’s rule, suggesting that sexual selection has not been the main force driving the evolution of SSD in this taxon. Although empirical data are lacking, factors related to the rate of development of the different sexes (e.g. protogyny) may result in different patterns of SSD in stingless bees. It seems that in Meliponini, the interplay between self and colonial interest could also influence environmentally determined traits such as body size.