Analysis of the transcriptome profile and ovarian morphology of Scaptotrigona bipunctata (Lepeletier) and reproductive strategies of eusocial bees

Author(s)

Danielle Luna Soares Lucena

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Medicina de Ribeirão Preto (PCARP/BC)
• Defense date: 2022-08-30

Examining board members

Zila Luz Paulino Simoes; Fábio Camargo Abdalla; Elza Tiemi Sakamoto Hojo

• Advisor: Zila Luz Paulino Simoes

Abstract

The stingless bees constitute a wide spectrum of eusocial species with considerable diversity of reproductive behaviors. These behaviors have been extensively studied; however, from a molecular perspective, the process of ovary activation and inactivation in these species is still little known. To shed light on the oogenesis process in the stingless bee Scaptotrigona bipunctata, we conducted an integrative study combining RNA-seq data obtained from ovary and fat bodies with morphological analyses of the ovaries of queens and workers sampled at various stages of adult development. First, we examined the reproductive process in S. bipunctata workers. This included ovarian morphology, defining the location of germline stem cells though immunolocalization of Vasa protein, and characterization of the stages of oogenesis along the ovarioles of this caste. Based on the morphology and on molecular markers present in the ovary transcriptomes of S. bipunctata workers, we describe, for the first time for native stingless bees, specific types of cells that are involved in maintenance and differentiation of germline stem cells. These cells have been found to be essential for oogenesis in other organisms. We also examined the expression patterns of genes in S. ezpuuetutu workers that are considered markers of active and inactive states of ovaries in other insect species, based on analyses of ovary and fat body transcriptomes. In the second part of the study, we focused on the transcriptomes as a whole. We compared expression profiles of ovaries and fat bodies at various stages of adult development of queens and workers of S. bipunctata and determined the gene expression profiles during ovary activation and inactivation for these two castes. Our results indicate that in the reproductive process, caste is a secondary factor. The ovarian transcriptional profile exhibited by workers around the seventh day is similar to that of an egg-laying mated queen. Therefore, workers of this species could be considered pseudo-queens, differing from true queens by their roles in tasks other than reproduction. Castes can be separated based on the transcriptional profile of the fat body, which groups together mated and virgin queens. This grouping is characterized by a high level of expression of genes involved in cell and tissue protection against toxins, xenobiotics, and oxidative damage, which may help explain the greater longevity of queens compared to workers. Within the worker caste, the fat body transcriptional profile is affected by ageing, with foraging workers exhibiting the most distinct transcriptional profile. When transcriptional profiles of ovary and fat bodies of foraging workers were compared, we noticed that they converged to similar expression levels. This is apparently due to ovary degeneration in this life stage, with loss of cellular identity of the ovaries as a function of ageing. This study is the first that integrates reproductive organ morphology and transcriptome data in stingless bees. Our results bring new data on the ovarian morphology and reveal molecular mechanisms involved in S. bipunctata queen and worker ovary activation. Furthermore, based on the fat body transcriptional profile we identified genes that are involved in caste differentiation in this species. (AU)

• FAPESP's process: 17/01643-3 - Ovary transcriptome analysis of Scaptotrigona postica and relationship with the reproductive behavior of eusocial species
• Grantee: Danielle Cristina de Luna Lucena
• Support Opportunities: Scholarships in Brazil - Doctorate