Genomics of Mimicry in Neotropical Corydoradinae Catfishes

Phelps, Emily (2024) Genomics of Mimicry in Neotropical Corydoradinae Catfishes. Doctoral thesis, University of East Anglia.

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Abstract

Protective mimicry is a phenomenon that has fascinated evolutionary ecologists since the inception of the field 162 years ago. There are two types of protective mimicry, Batesian and Mullerian. Batesian mimicry is characterised by palatable taxa evolving to resemble unpalatable taxa, whereas Mullerian mimicry occurs when unpalatable taxa evolve a resemblance. Despite the longstanding interest, relatively little is known about the gene1cs underpinning mimetic phenotypes. The Corydoradinae is a species rich and colourful subfamily of Neotropical catfish, with a propensity to form Mullerian mimetic communities. As such, it represents a valuable system through which we can expand our understanding of the evolution of mimetic systems. Among the Corydoradinae, there are 60 species participating in 27 mimicry rings, all defended by venom glands and sharp lockable spines.

In chapter 2, we generate novel genomic resources, including a scaffold level assembly for Corydoras fulleri as well as genome annotations for both C. fulleri and Hoplisoma metae. Utilizing these resources through a comparative genomic approach, we identified substantial differences in genomic composition between the two closely related taxa, including strong evidence for whole genome duplication (WGD) and transposable element proliferation within the introns of Hoplisoma. The origin and timing of the WGD suggest Hoplisoma is a recent autopolyploid occurring only 4.86 mya. This is the youngest autopolyploid event identified within teleosts to date.

In chapter 3, we use the C. fulleri reference genome in conjunction with low coverage resequencing data to explore the nature of polymorphic mimicry. Corydoras fulleri exists in three morphs, which are found in sympatry. The morphs form a probable Mullerian mimicry ring with four additional (non-polymorphic) sympatric Corydoradinae spp, which resemble two of the polymorphic patterns found in C. fulleri. By utilising the variation within C. fulleri, we identify regions characterised by elevated genetic differentiation across the genome associated with the presence or absence of a melanic blotch on the flank, an essential characteristic allowing C. fulleri to share a resemblance with its co-mimics. The regions contain genes associated with melanin dispersion and density, indicating known pigment pathways are being targeted to produce phenotypic variation in this trait. The presence of these genes and associated loci across the genome indicates this trait is underpinned by a more complex architecture than those previously identified in other mimetic systems, highlighting the value of understanding the genetics of mimicry across a diverse spectrum of mimetic taxa.

In chapter 4, we investigated the interaction between mimetic Corydoradinae taxa by exploring the relative toxicity of common co-mimics Hoplisoma and Corydoras species. To do this we quantified the differences in potency between co-mimics using a brine shrimp cytotoxicity assay. Whilst we found a significant increase in mortality associated with crude venom compared to control muscle extract, we identified no significant difference in venom potency between the genera suggesting they are traditional Mullerian mimics. We then used RNA sequencing to identify candidate venom genes and venom housekeeping genes in the Corydoradinae, which allowed a comparison between the Corydoras sp. and Hoplisoma sp. venom gene expression. We did not identify large logfold changes between the two genera in venom gene expression which supports the venom potency assay. This further indicates Corydoradinae co-mimics form mutualistic Mullerian interactions.

In chapter 5, we explored the genetics underpinning a rare case of sex-limited Mullerian mimicry in C. simulatus, where males have a mimetic phenotype, sharing a resemblance with H. metae whilst females have a cryptic phenotype. We used a multi-omics approach, utilising both low coverage whole genome resequencing and RNA sequencing to identify four genes which are differentially expressed in differently pigmented regions within females as well as between males and females, representing novel pigment genes. Additionally, we identify two genes related to sex differentiation representing candidates for sex determination in the Corydoradinae. This study lays the groundwork for the first vertebrate system in which to investigating how sexually antagonistic selection influences contrasting anti-predation strategies at the genetic level.

The work presented in this thesis expands our current understanding of the genetics of mimicry by exploring the molecular basis of both unpalatability and warning colouration in the Corydoradinae. As such, we provide much needed taxonomic breadth to the field.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Biological Sciences
Depositing User:	Chris White
Date Deposited:	24 Mar 2025 11:04
Last Modified:	24 Mar 2025 11:04
URI:	https://ueaeprints.uea.ac.uk/id/eprint/98868
DOI:

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