Meeting Abstract
Evolutionary pressures impact both gene sequences and behavioral effects of reproductive hormones differentially. We compared the sequences and functions of egg-laying hormone (ELH) and conopressin (CNP) in Berghia stephanieae, a nudibranch that is amenable to rearing in the laboratory. ELH and CNP differ strongly in the conservation of their amino acid (aa) sequences. The ELH family shows only moderate aa sequence identity (50% or less) across species, and are most similar at the N-terminus and C-terminus. In contrast, the CNP aa sequence is highly conserved among molluscs, even showing strong similarity to vasopressin and oxytocin in mammals. As hormones, ELH and CNP also differ in their breadth of behavioral effects. Whereas species-specific ELH reliably and solely elicits aspects of egg-laying, CNP is responsible for more varied functions. We identified ELH in transcriptomes of several nudibranchs, including Berghia. A gene tree of ELH aa sequences shows that the nudibranch homolog of ELH has undergone changes at the C-terminus compared to other gastropods. We examined the effects of the strongly conserved CNP on mating behavior and the effects of the less well conserved ELH on egg-laying behavior in Berghia. CNP aa sequences are highly conserved even as their role in reproductive behaviors differs, and thus the sequence may be evolutionarily constrained. The aa sequences of ELH show more divergence, but a highly conserved behavioral role. This suggests possible co-evolution with receptors to maintain behavioral outcomes.
