Obligate mutualism within a host drives the extreme specialization of a fig wasp genome
- Equal contributors
1 Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China
2 BGI-Shenzhen, Shenzhen 518083, China
3 University of Chinese Academy of Sciences, Beijing 100039, China
4 College of Plant Protection, Shandong Agricultural University, Tai’an 271018, China
5 Beijing TransGen Biotech Co. Ltd., Beijing 100192, China
6 Biology Department, University of Rochester, Rochester, NY 14627, USA
7 State Key Laboratory of Genetic Resources and Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming 650223, China
8 Department of Natural History, Royal Ontario Museum, 100 Queen’s Park, Toronto, Ontario M5S 2C6, Canada
9 Environment and Plant Protection Institute, Chinese Academy of Tropical Agricultural Sciences, Danzhou 571737, China
10 College of Life Science, Hebei University, Baoding 071002, China
11 School of Biology, Georgia Institute of Technology, Atlanta, GA 30332, USA
12 Key Laboratory of Plant Resources Conservation and Sustainable Utilization, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou 510650, China
13 College of Life Sciences, Fujian Normal University, Fuzhou 350108, China
14 School of Biological Sciences, University of Reading, Berkshire, Reading RG6 6AH, UK
15 Hawkesbury Institute for the Environment, University of Western Sydney, Locked Bag 1797, Penrith South, DC, NSW 1797, Australia
Genome Biology 2013, 14:R141 doi:10.1186/gb-2013-14-12-r141Published: 20 December 2013
Fig pollinating wasps form obligate symbioses with their fig hosts. This mutualism arose approximately 75 million years ago. Unlike many other intimate symbioses, which involve vertical transmission of symbionts to host offspring, female fig wasps fly great distances to transfer horizontally between hosts. In contrast, male wasps are wingless and cannot disperse. Symbionts that keep intimate contact with their hosts often show genome reduction, but it is not clear if the wide dispersal of female fig wasps will counteract this general tendency. We sequenced the genome of the fig wasp Ceratosolen solmsi to address this question.
The genome size of the fig wasp C. solmsi is typical of insects, but has undergone dramatic reductions of gene families involved in environmental sensing and detoxification. The streamlined chemosensory ability reflects the overwhelming importance of females finding trees of their only host species, Ficus hispida, during their fleeting adult lives. Despite long-distance dispersal, little need exists for detoxification or environmental protection because fig wasps spend nearly all of their lives inside a largely benign host. Analyses of transcriptomes in females and males at four key life stages reveal that the extreme anatomical sexual dimorphism of fig wasps may result from a strong bias in sex-differential gene expression.
Our comparison of the C. solmsi genome with other insects provides new insights into the evolution of obligate mutualism. The draft genome of the fig wasp, and transcriptomic comparisons between both sexes at four different life stages, provide insights into the molecular basis for the extreme anatomical sexual dimorphism of this species.