Chemistry Between Salamanders: Evolution of the SPF Courtship Pheromone System in Salamandridae

Love bites: male frogs (Plectrohyla, Hylidae) use teeth scratching to deliver sodefrin precursor-like factors to females during amplexus

“…PS = P. sagorum , PM = P. matudai ; **** ≥ 5000, ** ≥ 2500, ** ≥ 1000, * ≥ 500 (in parenthesis = expression level below 50 TPM) Protein homology Extract of known functions in other species Main location of expression in other taxa Expression level References 2D-TFPs (e.g. sodefrin precursor-like factor, phospholipase A2 inhibitor) Sex pheromones, toxins, cholinergic signalling, immune regulation, Phospholipase inhibition Sex glands; various organs PS****, PM**** [ 44 , 45 , 84 ] Kazal-type inhibitors (Ovomucoid-like) Protease inhibitor (e.g. Trypsin), egg protein, possibly secretion protection Oviduct (liver) PS**, PM**** [ 85 – 87 ] Ovostatin Protease inhibitor (e.g.…”

“…The evolution of SPF as a pheromone system has already been well investigated for some amphibians. It is known to have a history of gene duplications of which the derived proteins of two gene lineages (alpha and beta, differing in cysteine patterns, for details see [ 44 ]) were shown to perform a pheromone function in salamanders [ 25 , 45 ]. Furthermore, a recent study showed that multiple families of both terrestrially and aquatically reproducing anurans also independently recruited SPF proteins, most likely for chemical sexual communication.…”

“…SPF increases the female receptivity in one of these species ( Desmognathus ocoee ) after diffusion through the skin [ 51 ]. In other investigated urodelan families (Salamandridae, Ambystomatidae), transdermal delivery does not exist, and SPF was not replaced, but is delivered through the water or directly onto the nares of the female during amplexus [ 44 , 45 ]. The same is the case for anuran species known to express SPF in their breeding glands: they either press their glands onto or next to the female nares before and during amplexus, or they wave them through the water towards the female [ 8 ].…”

“…the wounding of females with specialized male devices (here the teeth) in hylids and suggests the delivery of proteins belonging to an early diverged anuran clade of SPFs as allohormone pheromones during amplexus. Although the exact effects of these molecules in anurans remain unknown [ 8 ] and although SPF has been shown to evoke various effects in urodelan females (such as following behaviour, cloacal gaping or courtship acceleration [ 44 ]), all essentially come down to shortening the courtship duration. Being phylogenetically nested among well-established urodelan SPF pheromones (Fig.…”

Pheromones for amphibian conservation – considering new approaches in conservation breeding programmes

“…The majority of pheromones described in amphibians are proteins directly transferred to the mating partner (over the nose or through the skin) and categorized as courtship pheromones (Arnold & Houck, 1982). In salamanders, it has been shown that such courtship pheromones positively influence female receptivity for reproduction (for reviews see Bossuyt et al, 2019a;Woodley & Staub, 2021). Courtship pheromones are produced by the males in large glandular clusters (i.e.…”