251 research outputs found
Sexual signaling pattern correlates with habitat pattern in visually ornamented fishes
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Open Access
Published: 22 May 2020
Sexual signaling pattern correlates with habitat pattern in visually ornamented fishes
Samuel V. Hulse, Julien P. Renoult & Tamra C. Mendelson
Nature Communications volume 11, Article number: 2561 (2020) Cite this article
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Abstract
Sexual signal design is an evolutionary puzzle that has been partially solved by the hypothesis of sensory drive. Framed in signal detection theory, sensory drive posits that the attractiveness of a signal depends on its detectability, measured as contrast with the background. Yet, cognitive scientists have shown that humans prefer images that match the spatial statistics of natural scenes. The explanation is framed in information theory, whereby attractiveness is determined by the efficiency of information processing. Here, we apply this framework to animals, using Fourier analysis to compare the spatial statistics of body patterning in ten species of darters (Etheostoma spp.) with those of their respective habitats. We find a significant correlation between the spatial statistics of darter patterns and those of their habitats for males, but not for females. Our results support a sensory drive hypothesis that recognizes efficient information processing as a driving force in signal evolution.We would like to thank Dr. Thomas Cronin for help with camera calibrations, Matthew Dugas, Natalie Roberts, and Rickesh Patel for assistance with field collections, and the Hancock Biological Station for providing a home base for field work and photography. This work was supported by National Science Foundation grant IOS-1708543 and by the CNRS (PICS project n°08302).https://www.nature.com/articles/s41467-020-16389-
Behavior at the species boundary: the overlooked role of male mate choice in a sexually dimorphic species
No full textBehavioral isolation is a powerful barrier to gene flow and is often considered a major component in the maintenance of species boundaries. Empirical support for mating preferences as an isolating barrier exists across a wide variety of taxa. In monomorphic or unornamented species, such as Lepidoptera (moths and butterflies) and Drosophila, male preferences for conspecific female traits prevent interbreeding between species. However, in sexually dimorphic species, the majority of studies focus on female mate choice for conspecific male signals, and the role of male mate choice in behavioral isolation has not been widely considered. Increasing evidence that males of many species exhibit mate choice, even those in sexually dimorphic species with traditional sex roles, suggests that the process of behavioral isolation via male mate choice should be addressed. Here, I address fundamental questions about the maintenance of species boundaries via male mate choice in a group of diverse freshwater fishes called darters (Percidae: Etheostoma). My results suggest that male mate choice for conspecific females reduces gene flow between the focal species, Etheostoma zonale and Etheostoma barrenense, with male mate choice contributing as much as female mate choice to total behavioral isolation. I also find that male and female preferences appear to be shaped by similar evolutionary mechanisms, with evidence that selection against hybrids strengthens both male and female preferences upon secondary contact. Interestingly, however, I find that the color pattern elements that promote assortative mating differ between males and females, meaning that diversification of male and female traits may follow independent evolutionary paths. Taken together, my results suggest that male behavior is likely to be underappreciated in the maintenance of species boundaries for sexually dimorphic species characterized by elaborate male ornamentation
Using Environmental DNA to Study Brook Trout Populations in the Headwaters of the Chesapeake Bay
No full textBrook Trout (Salvelinus fontinalis), a cold-freshwater species native to eastern North America, are bioindicators of cold, clean water. Recent restoration efforts require improved monitoring methods to assess progress toward conservation goals. Environmental DNA (eDNA) is a potentially rapid, cost-effective method to detect Brook Trout presence from water samples. However, eDNA dynamics in aquatic ecosystems are not well understood for this species. We assessed how water temperature, distance from an eDNA source, and filter pore size affect Brook Trout eDNA concentrations. We found significantly higher Brook Trout eDNA concentration at 20 ? compared to 10 ? in a lab experiment. We were unable to obtain quantifiable eDNA concentration in a natural stream setting, likely due to insufficient water volume collection or filter material. This study highlights the importance of optimized eDNA collection methods for accurate and effective species detection to identify priority restoration streams for Brook Trout conservation
The Evolution of Visual Patterning in North American Freshwater Fishes
No full textVisual patterns make up some of nature's most remarkable traits, which have puzzled biologists for centuries. The evolution of visual patterns can occur through multiple mechanisms, such as natural selection for cryptic camouflage, or sexual selection. In particular, sexual selection has led to some exceptionally flamboyant displays. However, our understanding of how the pressures of sexual selection shape visual patterns lacks a sufficient theoretical and empirical basis. Recent extensions of the sensory drive and sensory bias models of sexual selection have hypothesized that pattern evolution may be related to the visual environments that animals inhabit. According to the processing bias hypothesis, an extension of the efficient coding hypothesis, sexual signals will mimic the visual structure of their habitats so that these visual signals can be efficiently encoded by the receiver's visual systems. Here, I test the predictions of the processing bias hypothesis through both computational and behavioral trials. I use fish called darters (Percidae: Etheostoma) as a model system, given the diversity of male visual patterns and habitat preferences in this genus. First, I collected images of eleven species of darters, as well as underwater photographs of their habitats. To examine the relationship between the spatial statistics of fish and their habitats, I used Fourier analysis and convolutional neural networks. I found that the Fourier slope of male darter nuptial patterns significantly correlates with the Fourier slope of their habitats, while no such correlation exists for females. Using convolutional neural networks, I did not find evidence to reinforce the results of the Fourier analysis, but did find evidence that female darters are more camouflaged with their environments than their male counterparts. Finally, I used behavioral assays to explicitly test preferences in one species, Etheostoma caeruleum, for visual stimuli matching the visual statistics of their preferred habitat. Although my results do not demonstrate clear support for the processing bias hypothesis, this work advances a new theoretical framework for understanding complex visual traits. Furthermore, my results show how convolutional neural networks and Fourier analysis provide tools that can advance our understanding of the evolution of visual patterns
Advancing Technology for Restoration: An investigation of the Solar Oysters Production System
No full textThe Solar Oyster Production System (SOPS) was developed to expand growing capacity while decreasing the area required to grow oysters and reducing labor demands. SOPS is the first system in the world to grow oysters on continuously rotating ladders, however, little is known about the effect of consistent rotation on oyster growth. The goal of this study was to understand (1) the impact of rotation on growth of the Crassostrea virginica and (2) how the performance of oysters on SOPS compares to performance on traditional gardening methods. Oysters were deployed on rotational and static ladders on SOPS as well as oyster gardening cages provided by the Chesapeake Bay Foundation (CBF). The findings from this study reveal how consistent rotation affects shell shape and condition, and they provide baseline metrics for the further development of the technology
Female color preferences, ecological selection, and the evolution of male coloration in darters (Percidae: Etheostomatinae)
No full textSince Charles Darwin's initial observations and hypotheses, the evolution of elaborate male coloration in sexually dichromatic species has been the subject of great interest. Of particular recent interest is how sexual and ecological selection interact to shape variation in male coloration between closely-related species. Using darters (Percidae: Etheostomatinae), a group of fishes that vary in male coloration as a model system, my goal is to determine how sexual and ecological selection interact to shape variation in male coloration between as well as within species lineages. In Chapter 1, I used reflectance spectrophotometry to examine correlations between spectral properties of orange and blue pigmentation in the rainbow darter, Etheostoma caeruleum, with parasite load and observed a correlation between the chroma of orange bars with parasite counts. In Chapter 2, I quantified color preferences in the darter genus Etheostoma to determine if the strengths of attraction to different colors coincided with variation in male coloration between species. The females of most achromatic species exhibited no significant color preferences, while chromatic species varied in preferences, with a positive association between the presence of red or orange on the flanks and preference for red detected across all species. In Chapter 3 I utilized phylogenetic comparative approaches and a laboratory experiment of predator color preferences to quantify the role of ecological variables in shaping variation in male coloration in darters. Compared to achromatic species, chromatic darters tend to inhabit environments where predation risk would be lower; specifically, shallower, faster-flowing upland streams with a lower number of overlapping predatory species. Additionally, a common darter predator, largemouth bass (Micropterus salmoides), exhibited significant preferences for red stimuli in a color choice experiment. Finally, in Chapter 4 I investigated color and size correlations, as well as male and female preferences for different sized and colored mates, in the Roanoke darter, Percina roanoka. Using digital photography I found correlations between size and color, but no preferences for larger or more colorful mates were observed in either sex. The results of this dissertation suggest that sexual and ecological selection do interact to shape color variation between darter species
The role of male color in darter speciation
No full text"This doctoral research examines the role of male nuptial coloration in the maintenance of species boundaries of darters (Percidae: Etheostoma). The two main goals were to identify how conspicuous male colors contribute to pre-mating isolation and to determine the relative importance of such pre-mating isolation in the maintenance of two sympatric species. The focal pair of sympatric species, E. zonale and E. barrenense, allow an examination of conspecific male coloration as a critical factor by which females select mates. According to speciation via sexual selection theory, if species-specific color leads to pre-mating isolation and pre-mating isolation is stronger than other forms of reproductive barriers, then that nuptial coloration plays a key role in maintaining species boundaries. Although conventional wisdom holds that conspicuous male coloration has evolved to attract conspecific female mates and that species-specific colors serve as a prominent cue maintaining species boundaries, this notion has been explicitly tested only rarely. Importantly, nuptial color may not be driven by female choice; alternatively, color cues may function in male-male competition to improve access to female mates. Therefore it is critical to test the precise role of nuptial coloration in speciation. Darters provide an excellent system for examining the role of nuptial coloration in speciation. Darters comprise the most diverse genus of North American freshwater fish, and nearly every species is characterized by unique nuptial coloration. Multiple darter species co-exist in sympatric populations, indicating that reproductive barriers are tantamount to maintaining these extraordinarily diverse color patterns. This doctoral research demonstrates that male coloration plays a role in female choice both within and between the focal species. Additionally, these species exhibit complete behavioral isolation influenced by female preference for conspecific male coloration. I compared the relative strengths of multiple reproductive barriers and found that behavioral isolation is the strongest measured barrier to gene flow between the focal species. These results present empirical evidence for speciation driven by sexual selection and provide insight into the maintenance of diversity among naturally occurring sympatric species."Includes 1 .mov video file
RECONSTRUCTING THE EVOLUTIONARY HISTORY OF DARTERS (PERCIDAE: ETHEOSTOMATINAE): EPIGENETIC DIVERGENCE AS A FIRST STEP IN SPECIATION
No full textThis doctoral research reconstructs the evolutionary history and investigates the possibility of changes in gene expression, rather than nucleotide sequence, being a first step in speciation in the second most speciose group of freshwater fishes in North America. To gain a better understanding of the incredible diversity in this group of fishes known as darters (Percidae: Etheostomatinae), I first determine evolutionary relationships among 69 and then 101 different species representing four genera of darters using a genome-scan approach known as AFLP. Prior to this work, AFLPs had only been used for recent divergences, with the oldest reconstruction dating to approximately 15 million years. In silico studies had predicted that increased homoplasy would weaken the utility of AFLPs in reconstructing ancient evolutionary relationships. We found that dense taxon sampling increased accuracy and resolution in this group of fishes. We were able to resolve problematic nodes and reconstruct the evolutionary history of darters with moderate to strong statistical support at ancient divergences (>25 mya) and thus champion this method for deeper relationships. In addition, we were able to propose a new taxonomic classification of darters based on our and other recent phylogenies. Phylogenetic reconstruction revealed a large amount of interspecific genetic diversity in this group of fishes. This finding led us to question whether fast-evolving changes in gene expression via changes to the methylome, rather than nucleotide sequence, could initiate speciation in this group of fishes. We investigated whether epigenetic divergence acts as a first step in speciation in Etheostoma, a genus of darters. Using Methyl-Sensitive Amplified Polymorphisms (MSAP), we analyzed population structure and differentiation in the methylome and genome across 5 populations of E. olmstedi (the tessellated darter) in the Patuxent River and 6 populations in the Potomac River in Maryland, USA. We predicted that epigenetic variation would be greater than genetic variation both within and between populations, with populations showing greater differentiation in their methylomes compared to their genomes. We also investigated the relationship between genetic divergence, epigenetic divergence, and the strength of various reproductive barriers across more distantly related, geographically isolated species in the subgenera Ulocentra, Etheostoma and Nanostoma. Since previous studies have shown behavioral isolation to be the strongest reproductive barrier between darter species, we predicted that behavioral isolation would be better predicted by epigenetic as compared to genetic differences. Our results indicate that the methylome is indeed changing faster than the nucleotide sequence across all levels of divergence, and that epigenetic divergence better predicts behavioral reproductive isolation than genetic divergence, supporting the hypothesis that epigenetic divergence can act as a first step in speciation in this group
Processing bias: extending sensory drive to include efficacy and efficiency in information processing
No full textInternational audienceCommunication signals often comprise an array of colours, lines, spots, notes or odours that are arranged in complex patterns, melodies or blends. Receiver perception is assumed to influence preference and thus the evolution of signal design, but evolutionary biologists still struggle to understand how perception, preference and signal design are mechanistically linked. In parallel, the field of empirical aesthetics aims to understand why people like some designs more than others. The model of processing bias discussed here is rooted in empirical aesthetics, which posits that preferences are influenced by the emotional system as it monitors the dynamics of information processing and that attractive signals have effective designs that maximize information transmission, efficient designs that allow information processing at low metabolic cost, or both. We refer to the causal link between preference and the emotionally rewarding experience of effective and efficient information processing as the processing bias, and we apply it to the evolutionary model of sensory drive. A sensory drive model that incorporates processing bias hypothesizes a causal chain of relationships between the environment, perception, pleasure, preference and ultimately the evolution of signal design, both simple and complex
Sexual isolation evolves faster than hybrid inviability in a diverse; and sexually dimorphic genus of fish (Percidae: Etheostoma). Evolution 57: 317–327
No full textAbstract. Theory predicts that sexual (or behavioral) isolation will be the first form of reproductive isolation to evolve in lineages characterized by sexual selection. Here I directly compare the rate of evolution of sexual isolation with that of hybrid inviability in a diverse and sexually dimorphic genus of freshwater fish. The magnitude of both sexual isolation and hybrid inviability were quantified for multiple pairs of allopatric species. Rates of evolution were inferred by comparing genetic distances of these species pairs with the magnitude of each form of reproductive isolation: the slope of the regression of genetic distance on the magnitude of reproductive isolation represents the rate of evolution. Of the two forms of isolation, the magnitude of sexual isolation exhibited the steeper slope of regression, indicating that sexual isolation will tend to evolve to completion earlier than hybrid inviability, strictly as a by-product of evolution in geographically isolated populations. Additional evidence from the literature is used to qualitatively compare rates of evolution of sexual isolation with that of other forms of reproductive isolation. Preliminary comparisons support the prediction that sexual isolation will evolve more rapidly than other forms. Because Etheostoma is characterized by striking sexual dimorphism, these results are consistent with the hypothesis that sexual selection for exaggerated mate-recognition characters causes the relatively rapid evolution of sexual isolation
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