Biology subjects

Berdan, E. L.

Publications and source records attributed to Berdan, E. L..

6 recordsLinked to original sources

bioRxiv2025

A sensory system for mating in octopus

Sensory systems for mate recognition maintain species boundaries and influence diversification. Therefore, uncovering how molecules and receptors evolve to mediate this critical function is essential to understanding biodiversity. Male octopuses use a specialized arm called the hectocotylus to identify females and navigate their internal organs to reach the oviduct and deliver sperm. Here, we discovered that the hectocotylus is a dual sensory and mating organ that uses contactdependent chemosensation of progesterone, a conserved ovarian hormone. We identify chemotactile receptors for progesterone and resolve the structural basis for their evolution from ancestral neurotransmitter receptors and subsequent expansion and tuning across cephalopods. These findings reveal principles by which sensory innovations shape reproductive behavior and suggest mechanisms for how sensory evolution contributes to the diversification of life.

cell biology↗

bioRxiv2025

Parallel clines of chromosomal inversion in seaweed flies associated with thermal variation

Chromosomal inversion supergenes, which form blocks of linked genes, are increasingly recognized for their role in maintaining intra-specific diversity. They are predicted to be relevant genetic architectures for local adaptation in the face of gene flow. However, pinpointing the underlying traits and functional mechanisms under selection remains challenging. The seaweed fly Coelopa frigida harbors several large polymorphic inversions, of which the Cf-Inv(4.1) inversion displays a latitudinal cline of frequencies along the North American Atlantic Coast, suggesting a putative role in adaptation along the eco-climatic gradient. To investigate this hypothesis, we designed a molecular marker for karyotyping and studied natural and experimental populations from North America and Europe. We confirmed that this inversion is also polymorphic in Europe, and displays parallel latitudinal clines across continents, providing strong indirect support that Cf-Inv(4.1) is under natural selection along similar environmental gradients. We found that Cf-Inv(4.1) had a significant impact on egg-to-adult survival and fecundity under different thermal conditions. However, no effect on cold tolerance could be determined using supercooling point and chill coma recovery time. We speculate that fitness associated with Cf-Inv(4.1) is shaped by subtle life-history differences whose relative advantage depends on climate. While our experimental approaches provided insights into genotype-phenotype associations, it is worth noting that selection acts on the overall fitness, involving complex sets of traits. This is especially relevant for inversions linking hundreds of genes. This multi-gene property also explains why inversions are frequently involved in repeated parallel adaptation to environmental gradients, as demonstrated here in the seaweed fly.

evolutionary biology↗

bioRxiv2022

Genomic analyses of the Linum distyly supergene reveal convergent evolution at the molecular level

Supergenes govern balanced polymorphisms in a wide range of systems. The reciprocal placement of stigmas and anthers in pin and thrum floral morphs of distylous species constitutes an iconic example of a balanced polymorphism governed by a supergene, the distyly S-locus. Recent studies have shown that the Primula and Turnera distyly supergenes are both hemizygous in thrums, but it remains unknown if hemizygosity is pervasive among distyly S-loci. Here we have characterized the genetic architecture and evolution of the distyly supergene in Linum by generating a chromosome-level genome assembly of Linum tenue, followed by the identification of the S-locus using population genomic data. We show that hemizygosity and thrum-specific expression of S-linked genes, including a pistil-expressed candidate gene for style length, are major features of the Linum S-locus. Structural variation is likely instrumental for recombination suppression, and although the non-recombining dominant haplotype has accumulated transposable elements, S-linked genes are not under relaxed purifying selection. Our findings reveal remarkable convergence in the genetic architecture and evolution of independently derived distyly supergenes. The chromosome-level genome assembly and detailed characterization of the distyly S-locus in L. tenue will facilitate elucidation of molecular mechanisms underlying the different forms of flowers described by Darwin.

evolutionary biology↗

bioRxiv2021

A supergene in seaweed flies modulates male traits and female perception

Supergenes, tightly linked allelic combinations that underlie complex adaptive phenotypes represent a critical mechanism protecting intra-specific polymorphism [1, 2]. Supergenes represent some of the best examples of balancing selection in nature and there is increasing evidence that disassortative mating, when individuals preferentially mate with dissimilar phenotypes, is a key force stabilizing supergene polymorphisms. Yet, the underlying biological mechanisms and genetic basis of disassortative mating remain poorly known. Here, we examine a possible mechanism of disassortative mating driven by female mate choice in relation to the overdominant Cf-Inv(1) supergene in the seaweed fly Coelopa frigida by investigating chemical communication and its genomic architecture. We show that Cf-Inv(1) strongly affects chemical signaling; cuticular hydrocarbon (CHC) composition differed between genotypes in males but not females across two continents. In tandem, Cf-Inv(1) affected female perception of these compounds; females are able to sense 36 compounds from the male CHC cocktail but show differential perception between genotypes for almost half of them. This indicates that the genetic underpinnings of male traits and female perceptions are tightly linked within Cf-Inv(1) which likely facilitates disassortative mating [3]. A differential expression approach based on candidate genes for CHC biosynthesis and odorant detection revealed differential expression for CHC biosynthesis in males alone but broad changes in odorant receptors across both sexes. Furthermore, odorant genes clustered together within Cf-Inv(1), with some of them differing between arrangements by 8.3% at the protein level, suggesting evolution via tandem duplication then divergence. We propose that the tight linkage between overdominant loci, male traits, and female perception has helped to maintain the Cf-Inv(1) polymorphism across its range in the face of supergene degeneration.

evolutionary biology↗

bioRxiv2018

Physical linkage and mate preference generate linkage disequilibrium for behavioral isolation in two parapatric crickets

Behavioral isolation is a potent barrier to gene flow and a source of striking diversity in the animal kingdom. However, it remains unclear if the linkage disequilibrium (LD) between sex-specific traits required for behavioral isolation results mostly from physical linkage between signal and preference loci or from directional mate preferences. Here, we test this in the field crickets Gryllus rubens and G. texensis. These closely related species diverged with gene flow and have strongly diverged songs and preference functions for the mate calling song rhythm. We map quantitative trait loci for signal and preference traits (pQTL) as well as for gene expression associated with these traits (eQTL). We find strong, positive genetic covariance between song traits and between song and preference. Our results show that this is in part explained by incomplete physical linkage: although both linked pQTL and eQTL couple male and female traits, major effect loci for different traits were never on the same chromosome. We suggest that the finely-tuned, highly divergent preference functions are likely an additional source of LD between male and female traits in this system. Furthermore, pleiotropy of gene expression presents an underappreciated mechanism to link sexually dimorphic phenotypes.

evolutionary biology↗

bioRxiv2018

Genetic divergence and phenotypic plasticity contribute to variation in cuticular hydrocarbons in the seaweed fly C. frigida

Male sexual signals facilitate female choice and thereby reduce mating costs. The seaweed fly Coelopa frigida is characterized by intense sexual conflict, yet it is unclear which traits are under sexual selection. In this study, we investigated phenotypic and genetic variation in cuticular hydrocarbons (CHCs) in C. frigida for the first time. CHCs are ubiquitous in insects and they act as sex pheromone in many dipterans. We characterized CHCs and found that composition was affected by both genetic (sex and population origin) and environmental (larval diet) factors. We identified general shifts in CHC chemistry as well as individual compounds and found that the methylated compounds, mean chain length, proportion of alkenes, and normalized total CHCs differed between sexes and populations. We combined this data with whole genome resequencing data to examine the genetic underpinnings of these differences. We identified 11 genes related to CHC synthesis and found population level outlier SNPs in 5 that are concordant with phenotypic differences. Together these results reveal that the CHC composition of C. frigida is dynamic, strongly affected by the larval environment, and likely under natural and/or sexual selection.

evolutionary biology↗