Biology subjects

Fuller, R. C.

Publications and source records attributed to Fuller, R. C..

8 recordsLinked to original sources

bioRxiv2026

Transcriptomic differences underlying fin sexual dichromatism and male color polymorphism in bluefin killifish (Lucania goodei)

Color polymorphisms offer a powerful lens for examining how selection shapes genetic and phenotypic variation. Genomic analyses of color variation provide deeper insight into how genetic differences and phenotypic plasticity contribute to trait variation. Here, we use the bluefin killifish (Lucania goodei) to study this relationship. Male fins can display either red or yellow coloration based on pigments (pterins) or blue structural coloration (iridophores) often induced in UV-depauperate environments. Female fins lack pigmentation. To characterize the molecular basis of this variation, we assembled a high-quality genome and examined gene expression in the anal fins of male and female bluefin killifish to identify the molecular mechanisms underlying color variation. Our gene expression analysis found sex differences driven by male-biased upregulation of melanin synthesis and canonical pigment pathway genes. We additionally identified that the progesterone sex receptor was upregulated in females. Among male color morphs, several genes involved in xanthophore and iridophore formation differed between blue and non-blue males, including the transcription factor tfec, and iridophore-patterning genes atic, pnp4a, and sox10. Extraocular opsins, which are involved in non-image-forming light perception, were expressed at low levels across all fins, but showed population- and morph-specific patterns; notably, rgrb (retinal G protein coupled receptor b) was upregulated in blue males. To the best of our knowledge, this is the first report of an extraocular opsin varying as a function of population and color morph. Together, these results identify the pigment pathways underlying male-limited color polymorphisms and reveal candidate genes likely involved in light-sensitive phenotypic plasticity.

evolutionary biology↗

bioRxiv2025

SEXUAL DIMORPHISM IN FIN SIZE AND SHAPE IN BLUEFIN KILLIFISH

Sexual dimorphism provides insight into how trait optima differ between males and females, despite their shared genome. Measuring sexual dimorphism can help identify which traits have been shaped by sexual selection. While fish morphology has been widely described, fewer studies have quantified sexual dimorphism across all fin types--pectoral, pelvic, dorsal, anal, and caudal. Fins are often overlooked due to their small size, tendency to fold against the body, and poor preservation post-collection. In this study, we quantified sexual dimorphism in fin size and shape across all fin types in the bluefin killifish, Lucania goodei. We found striking sexual dimorphism in the dorsal and anal fins, particularly in area, ray length, and base length. In contrast, the pelvic, pectoral, and caudal fins showed moderate, but detectable, levels of dimorphism. In both dorsal and anal fins, males exhibited elongation of the posterior region relative to females. Dorsal and anal fin traits (i.e., area, ray length, base length) were also strongly correlated within both sexes, such that individuals with larger than average dorsal fins also have larger than average anal fins. This correlation is present for both males and females, suggesting shared developmental pathways, pleiotropy, or correlated selection between dorsal and anal fins. Overall, our results indicate that the dorsal and anal fins are key targets of sexual selection in males, likely reflecting their roles in courtship, competition, and/or external fertilization.

zoology↗

bioRxiv2019

Genomic landscape of reproductive isolation in Lucania killifish: The role of sex chromosomes and salinity

Understanding how speciation occurs and how reproductive barriers contribute to population structure at a genomic scale requires elucidating the genetic architecture of reproductive isolating barriers. In particular, it is crucial to determine if loci underlying reproductive isolation are genetically linked or if they are located on sex chromosomes, which have unique inheritance and population genetic properties. Bluefin killifish (Lucania goodei) and rainwater killifish (L. parva) are closely related species that have diverged across a salinity gradient and are reproductively isolated by assortative mating, hybrid male infertility, viability of hybrid offspring at high salinities, as well as reduced overall fitness of F2 offspring and backcrosses to L. goodei. We conducted QTL mapping in backcrosses between L. parva and L. goodei to determine the genetic architecture of sex determination, mate attractiveness, fertility, and salinity tolerance. We find that the sex locus appears to be male determining and located on a chromosome that has undergone a Robertsonian fusion in L. parva relative to L. goodei. We find that the sex locus on the fused chromosome is involved in several genomic incompatibilities, which affect the survival of backcrossed offspring. Among the backcrossed offspring that survived to adulthood, we find that one QTL for male attractiveness to L. goodei females is closely linked to this sex locus on chromosome 1. Males homozygous for L. goodei alleles at the sex locus laid more eggs with L. goodei females. QTL associated with salinity tolerance were spread across the genome but did not tend to co-localize with reproductive isolation. Thus, speciation in this system appears to be driven by reinforcement and indirect selection against hybrids rather than direct natural selection for salinity tolerance. Our work adds to growing evidence that sex chromosome evolution may contribute to speciation.

evolutionary biology↗

bioRxiv2019

Extreme heterogeneity in sex chromosome differentiation and dosage compensation in livebearers

Once recombination is halted between the X and Y chromosome, sex chromosomes begin to differentiate and transition to heteromorphism. While there is a remarkable variation across clades in the degree of sex chromosome divergence, far less is known about variation in sex chromosome differentiation within clades. Here, we combined whole genome and transcriptome sequencing data to characterise the structure and conservation of sex chromosome systems across Poeciliidae, the livebearing clade that includes guppies. We found that the Poecilia reticulata XY system is much older than previously thought, being shared not only with its sister species, Poecilia wingei, but also with Poecilia picta, which diverged 30 mya. Despite the shared ancestry, we uncovered an extreme heterogeneity across these species in the proportion of the sex chromosome with suppressed recombination, and the degree of Y chromosome decay. The sex chromosomes in P. reticulata are largely homomorphic, with recombination persisting over a substantial fraction. However, the sex chromosomes in P. picta are completely non-recombining and strikingly heteromorphic. ln addition to being highly divergent, the sex chromosome system in P. picta includes a neo-sex chromosome, the result of a fusion between the ancestral sex chromosome and part of chromosome 7. Remarkably, the profound degradation of the ancestral Y chromosome in P. picta is counterbalanced by the evolution of complete dosage compensation in this species, the first such documented case in teleost fish. Our results offer important insight into the initial stages of sex chromosome evolution and dosage compensation.

evolutionary biology↗

bioRxiv2018

Agonistic character displacement of genetically based male color patterns across darters

A growing number of studies are demonstrating that interspecific male-male competitive interactions can promote trait evolution and contribute to speciation. Agonistic character displacement (ACD) occurs when selection to avoid maladaptive interspecific aggression leads to the evolution of agonistic signals and/or associated behavioral biases in sympatry. Here we test for a pattern consistent with ACD in male color pattern in darters (Percidae: Etheostoma). Despite the presence of traditional sex roles and sexual dimorphism, male color pattern has been shown to function in male-male competition in several darter species, rather than female mating preferences. A pattern consistent with divergent ACD in male behavioral biases has also been documented in darters. Males bias their aggression towards conspecific over heterospecific males in sympatry but not in allopatry. Here we use a common garden approach to show that differences in male color pattern among four closely related darter species are genetically based. We also demonstrate that male color pattern exhibits enhanced differences in sympatric compared to allopatric populations of two darter species. This study provides evidence that interspecific male-male aggressive interactions alone can promote elaborate male signal evolution both between and within species. We discuss the implications this has for male-driven ACD and cascade ACD.

evolutionary biology↗

bioRxiv2018

Hybridization and postzygotic isolation promote reinforcement of male mating preferences in a diverse group of fishes with traditional sex roles

Behavioral isolation is thought to arise early in speciation due to differential sexual and/or natural selection favoring different preferences and traits in different lineages. Alternatively, behavioral isolation can arise due to reinforcement favoring traits and preferences that prevent maladaptive hybridization. In darters, female preference for male coloration has been hypothesized to drive speciation, because behavioral isolation evolves before F1 inviability. However, as with many long-lived organisms, the fitness of second generation hybrids has not been assessed because raising animals to adulthood in the lab is challenging. Recently, reinforcement of male preferences has been implicated in darters because male preference for conspecific females is high in sympatry but absent in allopatry in multiple species pairs. The hypothesis that reinforcement accounts for behavioral isolation in sympatry assumes that hybridization and postzygotic isolation are present. Here, we used genomic and morphological data to demonstrate that hybridization is ongoing between orangethroat and rainbow darters and used hybrids collected from nature to measure postzygotic barriers across two hybrid generations. We observed sex ratio distortion in adult F1s and a dramatic reduction in backcross survival. Our findings indicate that selection to avoid hybridization promotes the evolution of male-driven behavioral isolation via reinforcement in this system.

evolutionary biology↗

bioRxiv2017

Egg viability decreases rapidly with time since ovulation in the rainbow darter: implications for the costs of choosiness

Egg viability in the rainbow darter Etheostoma caeruleum, a fish apparently lacking female mate choice, was found to decline rapidly after ovulation. We observed that the majority of a females clutch may fail to hatch if she is prevented from mating for as little as six hours. These data suggest that exercising female mate preferences may be selectively disfavoured in E. caeruleum due to the high cost of delaying mating.

animal behavior and cognition↗

bioRxiv2017

Male-driven reinforcement and cascade reinforcement in darters

Reinforcement can act in response to maladaptive hybridization by selecting for increased discrimination against heterospecifics mates in sympatry compared to allopatry (i.e., reproductive character displacement - RCD). Additionally, reinforcement can select for increased discrimination against heterospecifics in a fighting context in sympatry compared to allopatry (i.e., agonistic character displacement - ACD). Because it directly affects conspecific recognition traits (signals and/or preferences), reinforcement between two species in sympatry can incidentally cause behavioral isolation among populations within a species, termed cascade reinforcement. Here we demonstrate that a pattern consistent with male-driven RCD and ACD is present between two groups of darters (orangethroat darter clade Ceasia and rainbow darter Etheostoma caeruleum). Increased male discrimination against heterospecific females as mates and increased male discrimination against heterospecific males as competitors is present in sympatry. Furthermore, there is a pattern consistent with male-driven cascade RCD and cascade ACD within Ceasia. We found low levels of discrimination between two species of Ceasia that occur in allopatry from one another and in allopatry with E. caeruleum. This result contrasts that of a recent study which observed high levels of behavioral isolation between Ceasia species that occurred in sympatry with E. caeruleum. We suggest reinforcement between Ceasia and E. caeruleum in sympatry has led to the evolution of behavioral isolation between lineages within Ceasia that occur in sympatry with E. caeruleum but in allopatry with respect to one another (i.e., cascade reinforcement). This study demonstrates the ability of male behavior to simultaneously drive sympatric and allopatric speciation via reinforcement.

evolutionary biology↗