The mechanisms underlying colour polymorphisms in trumpetfish

Supervisor: Dr James Herbert-Read

Co-Supervisors: Dr Josefin Stiller, Dr Martin How & Dr Sam Matchette

Some populations contain individuals with two or more distinct colour morphs, providing opportunities to study how and why colour variation within species is maintained by evolutionary and ecological processes. At a functional level, polymorphisms can be maintained by natural or sexual selection, environmental variation, or frequency-dependent selection. At a mechanistic level, the underlying drivers of colouration result from pigmentation and structural elements whose distribution and activity are under both genetic and physiological control. Understanding how different colour morphs are maintained, and whether they represent discrete genetic units or variations in phenotypic plasticity, provides opportunities to understand the adaptive value of colour variation within populations.

Trumpetfish (Aulostomus maculatus) have three putative colour morphs; yellow, brown, and blue individuals. This project will investigate trumpetfish colouration at multiple biological levels. The project will quantify variation in colour and pattern among morphs, characterise pigment composition and chromatophores using histology and reflectance spectrophotometry, assess gene flow between putative morphs, and compare gene expression profiles using RNA-seq or qPCR. By integrating morphological, biochemical, and genetic data, this study will reveal whether these morphs represent distinct genetic lineages or flexible phenotypic states, advancing our understanding of how colour diversity is generated and maintained within populations.

Type of work:

The student will investigate trumpetfish colouration through a combination of field, laboratory, and data analysis. The project will begin with field surveys and specimen imaging to document and quantify colour and pattern variation across the putative yellow, brown, and blue morphs. This will involve diving under SCUBA, standardised photography, image analysis, and statistical comparisons to define morphs.

In the laboratory, the student will conduct histological examinations and chromatophore identification to map the types and distributions of pigment cells in trumpetfish skin. They will use reflectance spectrophotometry to measure the spectral properties of intact skin, generating objective profiles of each morph’s colouration. There is further scope to explore properties of the morphs’ visual capabilities and relate this to their ecology and colouration.

The student will also perform molecular analyses to explore genetic and transcriptomic differences between morphs. This may include extracting DNA and RNA, preparing and processing samples for RNA-seq, conducting qPCR assays on candidate pigmentation genes, and analysing sequence or expression data to identify potential genetic drivers of colouration. Finally, the student will quantify gene flow between morphs using population genetic analyses, integrating these results with phenotypic and pigment data to assess whether morphs are genetically distinct or not.

The project will be supported by four supervisors with different expertises; Dr Herbert-Read & Dr Sam Matchette (behavioural ecology), Dr Josefin Stiller (genetics of colouration) and Dr Martin How (visual ecology). By the end of the project, the student will have developed skills in marine fieldwork, microscopy, spectrophotometry, molecular biology, bioinformatics, and statistical analysis, while contributing to a novel, multidisciplinary investigation of colour polymorphisms.

Importance of the area of research

Colour polymorphisms within species offer useful systems to test fundamental questions about adaptation, selection, and the origins of diversity. Understanding how morphs arise and persist helps clarify the processes driving speciation, the balance between genetic determination and environmental influence, and the role of polymorphisms in evolutionary stability.

References

Matchette, S. R., Schneider, J., Drerup, C., Winters, S., Radford, A. N., & Herbert-Read, J. E. (2025). Antagonistic effects of predator color morph abundance and saliency on prey anti-predator responses. Behavioral Ecology, 36(4).

Lochmann, S. E. (1989). Mechanisms of coloration of the Atlantic trumpetfish, Aulostomus maculatus. Copeia, 4, 1072-1074.