The Adipokinetic Peptides in Diptera: Structure, Function, and Evolutionary Trends

Abstract

Nineteen species of various families of the order Diptera and one species from the order Mecoptera are investigated with mass spectrometry for the presence and primary structure of putative adipokinetic hormones (AKHs). Additionally, the peptide structure of putative AKHs in other Diptera are deduced from data mining of publicly available genomic or transcriptomic data. The study aims to demonstrate the structural biodiversity of AKHs in this insect order and also possible evolutionary trends. Sequence analysis of AKHs is achieved by liquid chromatography coupled to mass spectrometry. The corpora cardiaca of almost all dipteran species contain AKH octapeptides, a decapeptide is an exception found only in one species. In general, the dipteran AKHs are order-specific-they are not found in any other insect order with two exceptions only. Four novel AKHs are revealed by mass spectrometry: two in the basal infraorder of Tipulomorpha and two in the brachyceran family Syrphidae. Data mining revealed another four novel AKHs: one in various species of the infraorder Culicumorpha, one in the brachyceran superfamily Asiloidea, one in the family Diopsidae and in a Drosophilidae species, and the last of the novel AKHs is found in yet another Drosophila. In general, there is quite a biodiversity in the lower Diptera, whereas the majority of the cyclorraphan Brachycera produce the octapeptide Phote-HrTH. A hypothetical molecular peptide evolution of dipteran AKHs is suggested to start with an ancestral AKH, such as Glomo-AKH, from which all other AKHs in Diptera to date can evolve via point mutation of one of the base triplets, with one exception.

Unique Members of the Adipokinetic Hormone Family in Butterflies and Moths (Insecta, Lepidoptera)

“…In total there are 15 different AKHs in Lepidoptera known to date from biochemical characterization -not counting the incompletely processed, inactive form of Manse-AKH (i.e., Vanca-AKH): six decapeptides, four nonapeptides and five octapeptides; a further two novel decapeptide sequences are predicted. This size distribution is quite different to what is seen in another speciose order, the Diptera, where 14 different AKHs are known to date -all are octapeptides, bar one (Gäde et al, 2020). Most interestingly, nonapeptides are a feature of Lepidoptera: the only other nonapeptide outside the Lepidoptera is found in the Hemiptera (a kissing bug; Marco et al, 2013); this same nonapeptide is identified in the current study in a nymphalid butterfly, A. horta.…”

“…10. As a point of interest, one has to mention that no Val or Ile (normally at position 2) is found in any member of the AKHs of Lepidoptera, unlike in Diptera (Gäde et al, 2020).…”

“…3. As we had previously successfully implemented the use of the primary structure of AKHs in a few insect orders to verify certain phylogenetic trends and ancestral relationships (Gäde, 1989;Marco, 2005, 2017;Gäde et al, 2020), we also wanted to use the structural information of the investigated AKHs to trace the general phylogeny of Lepidoptera and sketch a possible molecular evolution of the AKHs in this order.…”

Biochemically identified neuropeptides in a caddisfly (Trichoptera) and a pygmy mole cricket (Orthoptera: Caelifera: Tridactyloidea)

“…To fill the gap of 113 amu one of the isobaric amino acids, Ile or Leu, can occur at position 2. A peptide with the sequence pGlu‐Leu‐Thr‐Phe‐Thr‐Pro‐Ser‐Trp amide is known to occur, for example, in the yellow fever mosquito, Aedes aegypti , and has the code name Aedae‐AKH (Gäde et al, 2020). Hence, we had the synthetic peptide available and could establish that the peptide from C. villosa indeed contains Aedae‐AKH (Figure ).…”

“…Thus, since nothing is known about AKHs in the most basal superfamily of Caelifera and in the entire order of Trichoptera we have started this investigation to structurally characterize the complement of AKH(s) in these two clades and find out whether this information can be useful to identify relatedness. Previously, we have, for example, shown that speciose orders as the Diptera and the Lepidoptera have mostly order‐specific AKHs (Gäde et al, 2020; Marco et al, 2020).…”