Aphid Research at NTU Featured Seven Times on Journal Covers and Is the Subject for a Recent Commentary

Aphids are insect pests, belonging to the order Hemiptera. Just as mosquitoes take blood from humans, aphids suck sap from host plants with piercing mouthparts. Viruses vectored by aphids while feeding can be transmitted from one plant to another, causing serious agricultural damage. Apart from the well-known characteristics mentioned above, aphids have another special feature — they experience many cycles of asexual (parthenogenetic) and viviparous reproduction in their life. Aphid embryos form within the ovaries without fertilization, are born live, and the new-born aphids, clones of their mothers, are pregnant when born (Fig. 1). This differs from mosquitoes and most other insects, whose offspring are produced from eggs laid after fertilization by a male. Taking the advantage of asexual viviparity, aphids can propagate very efficiently within a short time window.

To understand how aphids develop asexually and viviparously at the molecular level, Chun-che Chang— Professor in the Department of Entomology in the College of Bio-resources and Agriculture at NTU—has worked on this issue for nearly twenty years since he joined NTU in August of 2003. The Chang Lab has invested its research effort studying “germline specification” and “axis determination”, both of which are important events during early embryogenesis in the asexual pea aphids. Chang, with his former Ph.D. students Gee-way Lin, Cheng-yo Chung plus several other collaborators, had another publication recently. This is an invited review published in Development Genes Evolution (DGE), a journal with long history in the field of Evolution and Development. The paper was highlighted by the journal an editorial article as well as a cover featuring aphids from the Chang Lab (Figs 1, 2, and 3). This cover story in the August issue of DGE is the 7th time aphid development images from the lab have been featured with a journal cover: work at the lab has clearly drawn attention and respect internationally.

According to Prof. Chang, the novelty of asexual and viviparous embryogenesis in pea aphids triggered the invitation by DGE. The lab’s discovery of the “maternal germ plasm” in pea aphids uncovers the possibility of a “germ plasm-driven mode” for germline specification in the Hemimetabola (Fig. 1), a subclass of insects whose metamorphosis lacks pupation and that includes aphids. Prior to this finding by the Chang Lab, germ cells in aphids and other hemimetabolous insects were thought to be derived from somatic cells via signal induction. Now, the evidence suggests that germline specification in the asexual pea aphid depends on germline determinants within the maternal germ plasm. The Chang Lab has additionally found that the hunchback (hb) gene, a conserved neural gene among insects including pea aphids, has unique roles in early embryos. The anterior localization of hb mRNA suggests that it is an anterior determinant and, more strikingly, germline expression of hb mRNA strongly implies that the hb gene in the pea aphid is involved in germline development – this novel role has not been reported in any other insects (Fig. 4). As commentated in the editorial in DGE, these unique findings in the asexual pea aphids will help researchers understand the environmental triggers that cause aphids to switch from reproducing sexually and laying eggs to reproduce through parthenogenesis and bearing live young. Comparison of embryonic development between asexual and sexual aphids will deepen the understanding about ecology-evolution-development (eco-evo-devo) interactions in insects.

In addition to lab members now and before, Chang particularly thank collaborators local and internationally. Notably, the cover will become an iconic cover of DGE.

Links:
https://link.springer.com/article/10.1007/s00427-022-00690-7
https://link.springer.com/article/10.1007/s00427-022-00692-5